CN110086396B

CN110086396B - Power generation equipment running off grid and vector control method thereof

Info

Publication number: CN110086396B
Application number: CN201810496833.XA
Authority: CN
Inventors: 廖勇; 唐华平; 张维佳; 谢美长
Original assignee: Chongqing Heya Technology Co ltd
Current assignee: Chongqing Heya Technology Co ltd
Priority date: 2018-01-25
Filing date: 2018-05-22
Publication date: 2023-03-17
Anticipated expiration: 2038-05-22
Also published as: CN110086396A

Abstract

The invention provides an off-grid operating power generation device and a vector control method thereof. The power generation apparatus includes a rotor having a multi-phase symmetrical winding, a stator having a single-phase winding, a sensor, and an excitation control device. A voltage sensor detects an amplitude of an output voltage, a current sensor detects amplitudes of a load current and a rotor phase current, and a position sensor detects a position angle of a rotor. The excitation control device is provided with: calculating load power according to the output voltage and the amplitude of the load current and determining the required engine speed according to the load power; calculating the actual rotating speed of the rotor according to the rotor position angle; adjusting the rotation speed of the engine according to the required rotation speed of the engine and the actual rotation speed of the rotor; determining a target vector value of the rotor phase current according to the output voltage amplitude; determining a target vector value of the rotor voltage according to the rotor phase current vector value and the target vector value rate of the rotor phase current; and generating an adjusting signal according to the target vector value of the rotor voltage and the slip angle to adjust the exciting current.

Description

Power generation equipment running off grid and vector control method thereof

Technical Field

The present invention relates to a power generating apparatus and a control method thereof, and more particularly to a variable speed constant frequency power generating apparatus driven by an engine and a control method thereof.

Background

One way to generate ac power and supply the electrical load is to use an off-grid running power generation system. The power generation system which is not connected with the power grid temporarily or for a long time is called a power generation system which runs off the power grid. Today, off-grid operating power generation systems are widely used in people's lives and works. For example, when people camp, eat, or work outdoors, off-grid operated power generation systems have been widely used to electrically connect to electrical consumers to provide energy to the electrical consumers. Power generation systems like this are also used to provide backup power in emergency situations (e.g., during a power outage).

Off-grid operating power generation systems typically use an engine to provide motive power, with the engine and generator being coupled together by a common shaft. The engine, upon starting, drives the shaft to rotate, thereby driving the generator to generate electrical energy. As is known, most electrical appliances are designed to use fixed frequency power, for example 60 hz in north america and 50 hz in china. The frequency of the power generation system output power is mainly determined by the operating speed of the engine. Thus, the operating speed of some power plant engines is fixed to maintain the frequency of the output power constant. However, when the load driven by the power generation system is smaller than the rated load of the unit, if the engine is still operated at the rated rotation speed, the fuel efficiency of the engine is less than the optimum value, and the operation noise is very large.

In addition, since many loads are designed to use electrical energy having a certain level of voltage, power generation systems that are typically operated off-grid need to produce a known level of output voltage. For example, most north american appliances (e.g., stoves, ovens, audio and video equipment) use voltages on the order of 120/240 volts, while most chinese appliances use voltages on the order of 220 volts.

Therefore, the market needs an off-grid generator set with an adjustable engine speed but constant output voltage frequency and amplitude.

Disclosure of Invention

Next, a power plant operating off grid and a method for controlling the same according to the present invention will be described. In order to reduce the weight of the product and the cost of production, the power generation equipment adopts a structure that the stator is provided with a single-phase winding and the rotor is provided with a multi-phase symmetrical winding. However, power plants of this configuration present challenges to the control strategy of existing power plants. The invention provides a power generation device with a simple and economical control mode and a vector control method thereof. The power generation equipment adjusts the rotating speed of the engine according to the load power, so that the oil consumption of the engine is the lowest. At the same time, the control system controls the amplitude and frequency of the field current in the generator rotor windings to maintain the amplitude and frequency of the stator generating device output voltage constant (i.e., to achieve constant voltage and constant frequency). Here, the power generation facility operating off-grid refers to a power generation facility that is not connected to the grid temporarily or for a long time. The single-phase winding refers to a winding with a coil having only one axial direction, and the single-phase winding can be formed by a plurality of coils, but the axial directions of the coils need to be overlapped. A symmetrical winding refers to a winding arranged in a form capable of generating a rotating magnetic field. The rotating magnetic field is the air gap magnetic field of the motor with the constant size and the axis position changing at a fixed frequency in space. The "phases" in a multi-phase symmetrical winding may be two or more phases.

Some embodiments provide an off-grid operated power plant. The power generation device includes an engine, a generator, and an excitation control device. The generator includes a rotor, a stator, a voltage sensor, a stator-side current sensor, a rotor-side current sensor, and a position sensor. The rotor and the engine are coaxially connected and comprise multi-phase symmetrical windings. The stator has a single phase winding capable of generating an induced voltage, the single phase winding being connected to an electrical load to provide an output voltage to the load and to the rotor winding to provide an excitation voltage to the rotor winding. The voltage sensor detects the magnitude of the output voltage. The stator-side current sensor detects the magnitude of the load current. The rotor-side current sensor detects an amplitude of a rotor-side current. The position sensor detects a position angle of the rotor. The excitation control device is electrically connected with the engine and the generator, controls the change of a magnetic field to enable the stator single-phase winding to generate induction voltage with preset frequency, and comprises: the device comprises a first calculating unit, a second calculating unit, an engine rotating speed adjusting unit, a third calculating unit, a fourth calculating unit, a fifth calculating unit, a sixth calculating unit and an exciting current adjusting unit. The first calculation unit is arranged to calculate a load power from at least the output voltage and the magnitude of the load current and to determine a required engine speed from the calculated load power. The second calculation unit is arranged for calculating the actual rotational speed of the rotor from the rotor position angle. The engine speed adjusting unit adjusts the engine speed according to the required engine speed and the actual speed of the rotor. The third calculation unit is arranged to determine a target vector value for the rotor phase current at least based on the magnitude of the output voltage. The fourth calculation unit is arranged to determine the slip angle and the slip ratio at least from the actual rotational speed of the rotor. The fifth calculation unit is arranged for extracting vector values of the rotor phase current based on the magnitude and the slip angle of the rotor phase current. The sixth calculation unit is arranged for determining a target vector value for the rotor voltage based on the vector value for the rotor phase current, the target vector value for the rotor phase current and the slip ratio. The field current adjusting unit is arranged to generate an adjusting signal for adjusting the amplitude and frequency of the field current in the rotor winding in dependence on the target vector value of the rotor voltage and the slip angle. Here, the magnitudes of the output voltage and the load current and the magnitude of the rotor-side phase current may be instantaneous values detected by the sensor, for example, instantaneous values detected every 1 millisecond or 1 second, or may be an average value or an integrated value detected by the sensor over a certain period of time, for example, once per second, and the magnitudes of the output voltage and the load current and the magnitude of the rotor-side phase current may be an average value or an integrated value every 10 consecutive seconds. The position angle may be a measurement of the position sensor at intervals, such as rotor position detected every 1 millisecond or 5 milliseconds.

According to some embodiments, the frequency conversion device further comprises an inverter for supplying an ac excitation voltage to the rotor winding, the inverter comprises a switching device, and the adjustment signal is a pulse signal having a duty cycle, and the pulse signal is used for controlling the switching device of the inverter, thereby adjusting the amplitude and frequency of the excitation current in the rotor winding.

According to some embodiments, the output voltage includes a high-level output voltage and a low-level output voltage. The power plant further includes a switch, the stator single phase winding including first and second segments, each of the first and second segments including at least one coil, the first and second segments being connected to the switch, respectively, the switch being selectively switchable by a user to connect the first and second segments in series or in parallel to provide a high level of output voltage and a low level of output voltage to the load. The voltage sensor detects magnitudes of first and second output voltages supplied to the load from the first and second segments, respectively. The stator-side current sensor detects magnitudes of a first load current and a second load current supplied to the load from the first segment and the second segment, respectively. The first calculating unit calculates the load power of the first section according to the first output voltage and the amplitude of the first load current, calculates the load power of the second section according to the second output voltage and the amplitude of the second load current of the second section, calculates the sum of the load power of the first section and the load power of the second section as the total load power, and determines the required engine speed according to the total load power. The fourth computing unit determines a target vector value of the rotor phase current based on at least the magnitude of the first output voltage or the magnitude of the second output voltage.

According to some embodiments, the fourth calculation unit determines the target vector value of the rotor phase current at least based on the magnitude of the output voltage using a closed-loop control circuit. The generator further includes a circuit connecting the stator single phase winding to the load, the circuit causing the induced voltage generated in the stator single phase winding to be at the same frequency as the output voltage provided to the load.

Some embodiments also disclose a method of controlling an off-grid operated power plant. The above power generation equipment includes an engine and a generator, and the generator includes: the motor comprises a stator with a single-phase winding and a rotor with a multi-phase symmetrical winding, wherein the rotor is coaxially connected with the motor, induced voltage can be generated in the single-phase winding of the stator, the single-phase winding is connected with an electric load to provide output voltage for the load, and the single-phase winding is also connected with the rotor winding to provide excitation voltage for the rotor winding. The control method includes detecting an amplitude of an output voltage supplied from a stator to a load; detecting a magnitude of a load current supplied by the stator to the load; detecting the amplitude of the phase current of the rotor; detecting a position angle of the rotor; calculating load power according to the output voltage and the amplitude of the load current; determining a required engine speed from the calculated load power; calculating the actual rotating speed of the rotor according to the rotor position angle; adjusting the rotation speed of the engine according to the required rotation speed of the engine and the calculated actual rotation speed of the rotor; determining a slip angle and a slip ratio at least according to the actual rotation speed of the rotor; determining a target vector value of the rotor phase current at least according to the amplitude of the output voltage; extracting a vector value of the rotor phase current according to the amplitude and the slip angle of the rotor phase current; determining a target vector value of the rotor voltage according to the vector value of the rotor phase current, the target vector value of the rotor phase current and the slip ratio; and generating an adjusting signal according to the target vector value and the slip angle of the rotor voltage, and adjusting the amplitude and the frequency of the exciting current in the rotor winding by using the adjusting signal.

According to some embodiments, the output voltage includes a high-level output voltage and a low-level output voltage. The power plant further includes a switch, the stator single phase winding including first and second segments, the first and second segments each including at least one coil, the first and second segments each being connected to the switch, the user selectively switching the switch to connect the first and second segments in series or in parallel to provide a high level of output voltage and a low level of output voltage to the load. The detecting the magnitude of the output voltage provided by the stator to the load includes detecting the magnitudes of a first output voltage and a second output voltage provided by the first segment and the second segment, respectively, to the load. The detecting the magnitude of the load current provided by the stator to the load may include detecting the magnitudes of a first load current and a second load current provided by the first segment and the second segment, respectively, to the load. The calculating the load power according to the output voltage and the magnitude of the load current includes: and calculating the load power of the first section according to the first output voltage and the amplitude of the first load current, calculating the load power of the second section according to the second output voltage and the amplitude of the second load current, and calculating the sum of the load power of the first section and the load power of the second section as the total load power. The determining a desired engine speed based on the calculated load power as described above includes determining a desired engine speed based on the total load power. The determining a target vector value for the rotor phase current based on at least the magnitude of the output voltage comprises determining the target vector value for the rotor phase current based on at least the magnitude of the first output voltage or the magnitude of the second output voltage.

According to some embodiments, the determining the target vector value for the rotor phase current at least based on the magnitude of the output voltage may be embodied by determining the target vector value for the rotor phase current at least based on the magnitude of the output voltage using a closed-loop control.

The above-mentioned off-grid-operated power generation apparatus includes a stator having a single-phase winding and a rotor having a multi-phase symmetrical winding, and the symmetrical winding of the rotor can generate a rotating magnetic field. The combination of a stator with single-phase windings and a rotor with multi-phase symmetrical windings in a power plant makes it possible to supply low-power single-phase consumers, such as household appliances. The control method adjusts the rotating speed of the engine according to the load power, so that the oil consumption of the engine is the lowest. And simultaneously controlling the amplitude and the frequency of the exciting current in the rotor winding of the generator so as to maintain the amplitude and the frequency of the output voltage of the stator unchanged.

Brief description of the drawings

FIG. 1 is a schematic diagram of an off-grid operated power plant in some embodiments.

FIG. 2A illustrates one arrangement of rotors in some embodiments.

Fig. 2B shows another arrangement of rotors in other embodiments.

Fig. 2C shows another arrangement of rotors in other embodiments.

Fig. 3 is a schematic structural diagram of an excitation control device in some specific embodiments.

FIG. 4 is a schematic diagram of an off-grid operated power plant in accordance with further embodiments.

FIG. 5 is a schematic diagram of an off-grid operated power plant in accordance with further embodiments.

Fig. 6A illustrates a schematic diagram of a dc bus voltage providing apparatus in some embodiments.

Fig. 6B shows a schematic diagram of another dc bus voltage providing apparatus in some other embodiments.

Fig. 7 shows another way of providing the excitation voltage to the rotor windings.

FIG. 8 is a schematic diagram of a power plant operating off-grid in some embodiments.

FIG. 9 is a schematic diagram of an off-grid operated power plant in some embodiments.

FIG. 10 illustrates a schematic diagram of a control system for operating a power plant off-grid in some embodiments.

Fig. 11 is a flowchart of a control method corresponding to the control system shown in fig. 10.

FIG. 12 is a control logic diagram of stator voltage in some embodiments.

FIG. 13 illustrates a schematic representation of rotor current coordinate transformation in some embodiments.

Fig. 14 is a control logic diagram of rotor current.

FIG. 15 is a schematic diagram of a control system for operating a power plant off-grid in some embodiments.

Fig. 16 is a flowchart of a control method corresponding to the control system shown in fig. 15.

FIG. 17 is a control logic diagram for stator voltage in some embodiments.

FIG. 18 illustrates a schematic representation of rotor current coordinate transformation in some embodiments.

Fig. 19 is a control logic diagram of rotor current.

Fig. 20 illustrates a waveform of rotor excitation current in some embodiments.

Fig. 21 shows waveforms of current and voltage output from the stator side of the power generating apparatus in some embodiments.

DETAILED DESCRIPTION OF EMBODIMENT (S) OF INVENTION

Some embodiments of the invention will now be described with reference to the drawings. Like reference symbols in the various drawings indicate like elements. It is to be understood that the terminology used herein is for the purpose of describing particular embodiments and is not intended to limit the scope of the present application.

FIG. 1 is a schematic diagram of an off-grid operated power plant in some embodiments. The load 140 driven by the power generating device may be a load that is not connected to the power grid, such as an oven and a sound device, used by people during camping, or an electrical device used during a power outage, etc. The off-grid operated power plant includes an engine 110, a generator, and a field control device 170. Engine 110 may receive a fuel such as gasoline, diesel, natural gas, or liquid propane through an inlet. The fuel entering the engine 110 is compressed and ignited, thereby causing the pistons of the engine 110 to reciprocate. The reciprocating motion of the pistons is converted to rotary motion by the crankshaft of the engine 110. The crankshaft may be coupled to a generator. The generator may be a variable speed constant frequency, induction generator with rotor voltage provided by a frequency conversion device (i.e. converter). Specifically, the generator mainly includes a rotor 120 and a stator 130. The rotor 120 may be a cylindrical rotor with multiple phase symmetric windings. The rotor is rotatably disposed within the stator 130 and is coaxially coupled to the crankshaft of the engine 110 via a common shaft 121. When the motor 110 rotates, the shaft 121 drives the rotor 120 to rotate, and a rotating magnetic field is generated in the windings of the rotor 120.

The field control device 170 is used to monitor the operation of the generator and motor 110. The excitation control device 170 may be electrically connected to the generator and the engine 110, for example, the excitation control device 170 may be fixed to the generator and connected to the engine 110 by a wire or wireless connection. In this way, the excitation control device 170 can collect the operation data of the power generation equipment detected by the voltage sensor and the stator-side current sensor, calculate the load power in real time using the operation data of the power generation equipment detected by the sensors, and adjust the rotation speed of the engine 110 in real time according to the load power. In addition to directly controlling ENGINE 110 using field CONTROL device 170, operation of ENGINE 110 may be directly controlled by an ENGINE CONTROL MODULE (ECM, not shown), with field CONTROL device 170 controlling the ENGINE CONTROL MODULE. The excitation control device 170 and the engine control module may be connected by one communication line. The engine control module may be secured to the engine 110. The engine control module may regulate engine speed, and thus output power of the generator, and may also monitor various characteristics of the engine, such as fuel consumption, engine start information, and oil pressure. The excitation control device 170 may also adjust the amplitude and frequency of the generator excitation voltage such that the output voltage of the generator output has a constant frequency and amplitude. The excitation control means will be described in more detail below.

The stator 130 of the generator comprises a single phase winding. The rotation of the rotating magnetic field established in the multi-phase symmetrical winding of the rotor 120 induces a single-phase induced voltage in the stator single-phase winding. The single phase winding may be connected to a load 140 through a circuit to provide an output voltage to the load. The circuit may include the conductors L120, N120, L240, N240 shown in fig. 1, and may also include some electrical components, such as the switch 150 shown in fig. 1. The electrical components may also include sockets to plug loads, etc. These electrical components connect the stator single-phase winding and the load, and supply the induced voltage generated in the stator single-phase winding as an output voltage to the load. In addition, an electrical component such as a circuit breaker may also be provided on the circuit between the single-phase winding and the load to break the circuit in the event of an overload. The electrical component may also be an automatic SWITCH (AUTO TRANSFERS SYSTEM OR SWITCH) for switching between multiple output voltages. However, the electrical component is not a converter such as a rectifier or an inverter that changes the frequency of the voltage or current, i.e., the circuit needs to ensure that the induced voltage generated by the single-phase winding of the stator is the same as the frequency of the output voltage provided by the circuit to the load.

Since the nominal voltage frequency applicable to most electrical appliances in various countries is fixed, for example, 60 hz in north america and 50 hz in china. Therefore, in order to supply electric energy to most household appliances and other electric devices, the excitation control device 170 controls the frequency of the induced voltage generated in the stator single-phase winding to be within a predetermined range, for example, about 60 hz in north america and about 50 hz in china. Since the frequency of the induced voltage is the same as the frequency of the output voltage, the frequency of the output voltage of the power generation device is within a predetermined range.

The single-phase windings of the stator 130 are also connected to the symmetrical windings of the rotor 120 to provide an excitation voltage to the rotor windings to energize the rotating magnetic field in the rotor windings to compensate for variations in the magnitude and frequency of the induced voltage generated in the single-phase windings of the stator 130 caused by variations in the speed of rotation of the motor. Such a mode of operation allows the amplitude of the output voltage of the power plant to remain stable while the frequency of the output voltage remains constant.

In some embodiments, the single-phase winding of the stator 130 may include an output portion 130A and an excitation portion 130B (shown in fig. 1). The output portion 130A and the excitation portion 130B each include one or more coils. In some particular embodiments, output portion 130A and excitation portion 130B provide an output voltage to a load and an excitation voltage to a rotor winding, respectively.

The rotor 120 may include a multi-phase symmetrical winding. FIG. 2A illustrates one arrangement of a rotor 220A in some embodiments. Rotor 220A has three-phase windings U, V, W connected in a star. The axes of the three-phase windings U, V, W are spatially 120 degrees apart. Each phase of the three-phase winding U, V, W includes a coil having an equal number of turns. As shown in fig. 2A, the leads of the coil may be connected by terminals 220U, 220V, 220W. Other symmetrical arrangements of the three-phase windings, for example a delta arrangement, are also suitable for the above-described power plant. FIG. 2B illustrates another arrangement of rotors in some embodiments. Rotor 220B includes a symmetrically arranged five-phase winding M, N, O, P, Q. The axes of the five-phase windings M, N, O, P, Q are spatially separated by 72 degrees. As shown in fig. 2B, the leads of the coil may be connected by posts 220O, 220P, 220Q, 220M, 220N. FIG. 2C illustrates another arrangement of the rotor 220C in some embodiments. The rotor comprises two symmetrical windings R and S spaced 90 degrees apart. Each phase of the two-phase symmetrical winding R, S includes a coil having an equal number of turns. As shown in fig. 2C, the leads of the coil may be connected by posts 220R, 220S, 220J. When an excitation voltage is applied to such a rotor winding, a rotating magnetic field is generated in the rotor winding.

The generator also comprises a detection stator single-phase winding output voltage amplitude U _{S LOAD} Voltage sensor of (2), detecting negativeAmplitude of current I _{S LOAD} Stator-side current sensor, rotor-side current sensor for detecting rotor phase current amplitudes Ira, irb, irc, and rotor position angle θ _r Not shown in fig. 1, shown in fig. 10 and 15. The operation data of the power generating equipment detected by the voltage sensor, the stator-side current sensor, the rotor-side current sensor, and the position sensor may be transmitted to the excitation control device 170. A microprocessor-based or other computer-driven system may be used as the excitation control means 170, for example the excitation control means 170 may comprise a processor and a memory. The memory may have stored therein program instructions that implement the control functions of the excitation control device 170, with the processor operating under the control of the program instructions in the memory. The excitation control device 170 may include logic CIRCUITs such as CMOS (COMPLEMENTARY METAL OXIDE SEMICONDUCTOR), ASIC (APPLICATION specific integrated CIRCUIT) SPECIFIC INTEGRATED CIRCUIT, PGA (PROGRAMMABLE gate array), FPGA (FIELD PROGRAMMABLE gate array GATE ARRAY), etc., and the control function thereof is realized by these logic CIRCUITs.

Fig. 3 is a schematic structural diagram of an excitation control device in some specific embodiments. The excitation control device 170 includes a first calculation unit 171, a second calculation unit 172, an engine speed adjustment unit 173, a third calculation unit 175, a fourth calculation unit 174, a fifth calculation unit 176, a sixth calculation unit 177, and an excitation current adjustment unit 178. The first calculating unit 171 is used for calculating the amplitude U of the output voltage detected by the voltage sensor _{S LOAD} And the amplitude I of the load current detected by the stator side current sensor _{S LOAD} Calculating the load power P _LOAD And based on the calculated load power P _LOAD A desired engine speed is determined. The second calculation unit calculates the rotor position angle theta based on the rotor position detected by the position sensor _r Calculating the actual rotational speed omega of the rotor _r . The engine speed adjusting unit 173 adjusts the actual speed ω of the rotor according to the required engine speed and the required engine speed _r The rotational speed of the engine 110 is adjusted. Specifically, the engine speed adjustment unit 173 may correct the rotor position using the desired engine speed using closed loop controlInterstation speed omega _r . The third calculation unit 175 is based on the actual rotational speed ω of the rotor _r Determining a slip angle theta _slip And slip S. The fourth calculation unit 174 calculates the magnitude U of the output voltage detected by the voltage sensor _{S LOAD} Determining a target vector value I for a rotor phase current _rq ^* And I _rd ^* . The fifth calculation unit 176 converts the detected amplitudes Ira, irb, irc of the rotor phase currents from the three-phase stationary coordinate system to the two-phase coordinate system to obtain a conversion result I _rα 、I _rβ Then mix I _rα 、I _rβ Sum and slip angle theta _slip As input to the park transformation, the vector value I of the phase current is extracted _rq And I _rd . The sixth calculating unit 177 calculates a vector value I according to at least the rotor phase current _rq And I _rd Target vector value I of rotor phase current _rq ^* And I _rd ^* Determining target vector value U of rotor voltage by using sum-slip ratio S _rq ^* And U _rd ^* . The exciting current adjusting unit 178 adjusts the target vector value U according to the rotor voltage _rq ^* 、U _rd ^* Sum and slip angle theta _slip An adjustment signal is generated and used to adjust the amplitude and frequency of the field current in the windings of the rotor 120.

FIG. 4 is a schematic diagram of an off-grid operated power plant in accordance with further embodiments. The output 430A of the stator single phase winding of the power plant has only one independent coil, in which only one level of output voltage, such as 120 volts or 240 volts, is generated. The one level output voltage is applied directly to the load 440 through circuitry (specifically consisting of the hot, neutral, UAN lines UAL, UAN in figure 4).

Turning now to fig. 1. In the particular embodiment shown in fig. 1, the output has more than one coil to provide a two-level output voltage. The output portion 130A shown in fig. 1 includes a first segment 130A1 and a second segment 130A2. The first segment 130A1 may include a coil having a first lead UAL (which may be hot) and a second lead UAN (which may be neutral). The first segment 130A2 may include another coil having a third lead UBL and a fourth lead UBN (which may be hot and neutral, respectively). In some embodiments, the first segment 130A1 and the second segment 130A2 also each include a plurality of coils connected in series.

In some embodiments, as shown in FIG. 1, the generator may include a switch 150. Switch 150 may be a manual transfer switch or other similar switch. Leads UAN, UAL, UBL, UBN of the first segment 130A1 and the second segment 130A2, respectively, are connected to a switch 150. The switch may be a combination switch, and the user may manipulate the switch 150 to selectively connect the first segment 130A1 and the second segment 130A2 in parallel or in series. In this manner, a bi-level output voltage, such as 120 volts and 240 volts (i.e., the most common nominal voltages in north america), may be generated that is provided from switch 150 to load 140.

The exciting portion 130B may include one coil. The lead wires of the coil may be connected to the rotor winding U, V, W to supply the induced voltage generated in the exciting portion 130B to the rotor winding to supply energy to the rotating magnetic field. In the above-described embodiment, the exciting portion 130B is independent of the output portion 130A, so that a dc bus voltage greater than the output voltage can be easily generated by the exciting portion 130B, thus facilitating adjustment of the exciting voltage. For example, the exciting portion 130B may generate an exciting voltage of 320 volts when the coil of the exciting portion 130B has a required number of turns.

FIG. 5 is a schematic diagram of an off-grid operated power plant in some embodiments. Like reference numerals are used to indicate like components in fig. 1, 4 and 5. In some embodiments, the stator 530 includes a first portion 530A1 and a second portion 530A2. The first portion 530A1 may include one coil with leads UAL and UAN, and the second portion 530A2 may include another coil with leads UBL and UBN. Leads UAL, UAN, UBL, UBN are each connected to switch 550. The user can switch the switch 550 to selectively connect the first section 530A1 and the second section 530A2 in parallel and in series to obtain different levels of output voltage. Unlike the power generating apparatus having independent exciting portions shown in fig. 1 and 4, one of the first and second portions 530A1 and 530A2 of the power generating apparatus is also used to supply an exciting voltage. For example, in fig. 5, the second portion 530A2 is further connected to a pair of lead wires EXN and EXL, which are connected to an electric circuit of the rotor winding (not shown in fig. 5) to supply the excitation voltage to the rotor winding.

In other embodiments, the second portion 530A2 connected to the rotor winding may include a first coil and a second coil (not shown in fig. 5) connected in series, the leads UBL and UBN of the first coil are connected to the switch 550 for providing the output voltage to the load 540, and the lead UBL (hot wire) of the first coil and the lead EXL (hot wire) of the second coil are connected to the rotor winding, i.e., the first coil and the second coil are excited by the induced voltage generated in series. This scheme can reduce the number of turns of the exciting coil as compared with a scheme in which a separate exciting coil is provided.

In some embodiments, a frequency conversion device 560 may be disposed between the second portion 530A2 and the rotor windings. The frequency conversion device 560 is a converter, as is commonly known in the motor art, that modulates the induced voltage generated by the second portion 530A2 to produce a voltage having a desired frequency and amplitude that is supplied to the rotor windings to energize the rotating magnetic field. The frequency conversion means 560 may include a dc BUS voltage supply means for receiving the excitation voltage (which is an ac voltage) from the stator single phase winding and supplying a dc BUS voltage to the buses BUS +, BUS-. The dc bus voltage providing means may be a rectifier. Fig. 6A illustrates a schematic diagram of a dc bus voltage providing device 661A in some embodiments. The dc bus voltage providing device 661A includes an uncontrolled rectifier bridge circuit 661A1 that is comprised of four rectifier diodes arranged in a "bridge" configuration. A bus capacitor 662A2 may also be provided to smooth the output voltage of the uncontrolled rectifier bridge circuit 661A1. Fig. 6B is a schematic diagram of a dc bus voltage supply apparatus in some other embodiments. The dc bus voltage providing device 661B mainly includes a POWER FACTOR CORRECTION (POWER FACTOR CORRECTION) circuit that performs rectification and boosting. In addition, a bus capacitor 661B2 may be provided to store energy and filter out high frequency ac voltage components.

Fig. 7 shows another way of providing the excitation voltage to the rotor windings. According to some embodiments, the single phase winding of the stator may also not provide an excitation voltage to the rotor winding. A dc power source, such as a battery 710, may be used to provide the dc bus voltage. A dc-dc converter 720 connected to the battery 710 may also be provided, the dc-dc converter 720 being arranged to increase the magnitude of the dc voltage before supplying it to the BUS bars BUS +, BUS-connected to the rotor windings to energize the rotating magnetic field in the rotor windings. A bus capacitor 730 may also be provided to store energy and filter out high frequency ac voltage components.

FIG. 8 is a schematic diagram of an off-grid operated power plant in some embodiments. The power plant is similar to that described above with reference to figures 1, 4 and 5 and so the description of the same and similar components will not be repeated here. The power plant comprises a frequency conversion device 860. The frequency conversion device 860 mainly includes a dc bus voltage supply device 861 and an inverter 862. The dc bus voltage supply device 861 for supplying dc voltage to the inverter via the bus is similar to the dc bus voltage supply device described above with reference to fig. 6A and 6B, and therefore, the dc bus voltage supply device 861 will not be further described here.

The number of phases of the inverter 862 corresponding to the rotor windings may be two-phase, three-phase, four-phase, and five-phase dc-ac inverters. As shown in fig. 8, inverter 862 is a three-phase six-switch dc-ac inverter that receives a pulse control signal (e.g., SPWM wave or SVPWM wave) from field control device 870, the pulse control signal being substantially a constant duty cycle, field control device 870 having a program that generates the pulse control signal that generates an SPWM or SVPWM field signal having a desired frequency and amplitude that adjusts the amplitude and frequency of the field current in the rotor windings, the field current having an appropriate amplitude and frequency that energizes the rotating magnetic field to compensate for the tendency of amplitude and frequency variations of the induced voltage generated in the stator single phase windings caused by the change in speed of the engine, the tendency of the stator single phase windings induced voltage amplitude and frequency variations being mainly caused by the change in engine speed that is adjusted with the change in load. The excitation control device 870 applies a pulse control signal to the rotor winding to adjust the strength of the rotating magnetic field induced in the rotor winding and the rotational speed relative to the rotor. Therefore, the amplitude of the output voltage of the stator can be kept stable, and the frequency of the output voltage is kept constant. The PWM or SVPWM wave may be a square wave, modified sine wave, etc., and what waveform is used depends mainly on the circuit design of the inverter 862. Each leg of the inverter 862 is connected to one phase winding of the rotor by a wire. One or more switching devices are provided on each leg of the inverter 862. The switching device may be a semiconductor switching device. As shown in fig. 8, in some specific embodiments, a pair of IGBTs (INSULATED GATE bipolar transfer) are provided on each leg of inverter 862. The pulse signal from the excitation control device 870 continuously controls the on and off times of the switching devices of the inverter 862 by a certain duty ratio. The dc bus voltage supply 861 supplies a relatively stable dc bus voltage to the inverter 862. The dc bus voltage required by the inverter 862 depends on the system design, including, for example, stator voltage magnitude, generator speed variation range, generator rotor winding design, IGBT device voltage-current parameters, and system cost. The inverter 862 generates an SPWM or SVPWM excitation signal having an amplitude and frequency and uses the excitation signal to adjust the amplitude and frequency of the current in the rotor windings, thereby generating a rotating magnetic field in the rotor windings having a desired strength and relative speed (relative to the speed of the rotor). For example, the inverter 862 used in the above power plant having a power rating of 7000 watts may have a power rating of less than 1500 watts, typically 700-800 watts. In contrast, if an inverter is used to regulate the full power produced by a generator, the power of the inverter used in a generator rated at 7000 watts will also be 7000 watts. In the invention, the current output by the stator end is directly supplied to the load through the electric element without any frequency change, namely the frequency of the current output by the stator end is already a target value, and the adjustment by the inverter is not needed. Since the inverter 862 in the power plant of the above-described embodiment only regulates the field power, which is only a small fraction of the full power generated by the single-phase windings of the stator, the power of the inverter 862 can be much smaller. The weight of the inverter 862 can be greatly reduced and the cost thereof can be greatly reduced. It is estimated that the inverter cost can account for 20% -60% of the generator cost, and therefore a mobile power generating unit having the above features has a great cost advantage.

The excitation control device 870 calculates the real-time load power using the real-time operation data of the power generating equipment detected by the voltage sensor and the stator-side current sensor (not shown in fig. 8), and adjusts the rotational speed of the engine in response to the calculated real-time load power. The excitation control device 870 tracks the lowest oil consumption point of the engine by adopting a predefined engine lowest oil consumption curve to determine and adjust the power of the engine. The predefined engine minimum fuel consumption curve may be stored in the excitation control device 870.

In some embodiments, the generator may also include a battery 880. For safety, the battery 880 may be electrically isolated from the BUS BUS +, BUS-. For example, the DC voltage of the battery 880 may be applied to the buses BUS +, BUS-via an excitation voltage supply 890 to provide an excitation voltage to the rotor windings to generate a rotating magnetic field in the rotor windings upon start-up of the power plant. The structure of the excitation voltage supply device 890 may be similar to that of a transformer. The magnitude of the excitation voltage may be relatively small, and may be, for example, 1-20 volts.

In some specific embodiments, the power plant is configured to operate at a rotational speed less than or equal to the synchronous rotational speed. For example, a gasoline engine may operate at 3000-3600 revolutions per minute with a synchronous speed of 3600 revolutions per minute. The higher the engine speed is, the larger the output power is, so that when the generator set drives a load from no load to rated power, the engine speed will reach the maximum speed of 3600 r/min, at this time, the frequency of the rotor excitation voltage will be reduced, and when the engine speed is 3600 r/min, the rotor excitation voltage will be direct current. Thus, in the case where the synchronous rotational speed of the power plant is set at 3600 revolutions per minute, the power plant driven by the gasoline engine is always operated in a sub-synchronous or synchronous state. This means that the electrical energy in the power plant always flows from the stator side to the rotor side without a reverse flow of energy. This feature allows the power plant to use low cost devices or components (e.g., the uncontrolled rectifier bridge of FIG. 6A) with unidirectional characteristics. It should be appreciated, however, that the operating speed of the power plant may be greater than the synchronous speed under some undesirable operating conditions. A protection mechanism, such as a circuit breaker, may be provided in the power plant to shut down the power plant when it is rotating at excessive speeds.

FIG. 9 is a schematic diagram of an off-grid operated power plant in some embodiments. The main difference between the power generating apparatus in fig. 8 and the power generating apparatus in fig. 9 is that the latter has no separate field section (similar to the power generating apparatus shown in fig. 5). In view of the foregoing description, those skilled in the art will readily understand the power generation apparatus shown in fig. 9, and will not be described in detail herein.

An off-grid operated power plant is described above with reference to fig. 1-9. The stator of the power plant has a single phase winding and the rotor has a multi-phase symmetrical winding, which presents challenges to the control strategy of existing power plants. In particular, it is difficult to achieve a satisfactory control effect using a simple and economical control system in a power generating apparatus in which a stator single-phase winding directly outputs a voltage (i.e., a voltage applied to a load) without passing through a frequency conversion device. The control system of the power plant of the present invention will be described in detail with reference to fig. 10 to 19.

In the control system, the amplitude and frequency of the excitation current in the rotor windings are adjusted by an excitation signal (a target vector value and slip angle characterizing the rotor voltage) having a desired frequency and amplitude, thereby controlling the strength of the rotating magnetic field and the relative rotational speed with respect to the rotor. It is ensured that the amplitude of the output voltage of the power generating equipment is kept stable, the frequency of the output voltage is kept constant, and the rotation speed of the engine is changed corresponding to the change of the load, so that the optimization of the fuel efficiency can be realized. This control system enables the power plant to operate over a wide range of engine speeds depending on load requirements to optimize fuel efficiency with the output voltage held constant.

FIG. 10 illustrates control of a power plant in some embodimentsAnd (5) manufacturing a system. Fig. 11 is a flowchart of a control method corresponding to the control system shown in fig. 10. The stator single phase windings in these embodiments only output one level of output voltage. For example, a pure high voltage U applied to a load of 240 volts through a live lead A, B _SAB (as shown in fig. 10). And a pure low voltage of 120 volts (not shown) is output to the load, for example, through the leads A, N for the line and neutral conductors. In addition, the level of the output voltage output by the stator single-phase winding can be adjusted by adjusting the strength of the rotating magnetic field in the rotor winding. For example, a pure low voltage of 120 volts can be output to a pure high voltage of 240 volts by increasing the strength of the rotating magnetic field. The following describes a control system of a power plant by taking only the power plant outputting 240 v as an example. It should be understood that the control circuit shown in fig. 10 and the control method shown in fig. 11 can also be used for a power generating device that outputs 120 volts on the stator side.

The rotor has three-phase windings U, V, W arranged in a symmetrical manner, which are connected to the three legs of inverter 1062, respectively. As described above, the dc link voltage U outputted from the dc bus voltage supply device (not shown in fig. 10) _dc Is supplied to the inverter 1062. The voltage sensor 10V and the stator side current sensor 10AS are connected to a lead A, B, respectively, to detect the amplitude U of the output voltage output from the stator single-phase winding _SAB And the amplitude I of the load current _SAB . The rotor-side current sensor 10AR is connected to the three-phase symmetrical winding of the rotor, and detects the amplitudes Ira, irb, and Irc of the rotor-side currents. The position sensor 10P is connected to the rotor to detect the position angle theta of the rotor _r . Since the rotor and the shaft of the engine are coaxially connected, the position sensor 11P may be connected to the shaft of the engine to detect the position angle of the shaft. The operation data of the power generating equipment detected by the voltage sensor 10V, the stator-side current sensor 10AS, the rotor-side current sensor 10AR, and the position sensor 10P may be filtered and then supplied to the excitation control device 1070.

After the excitation control device 1070 collects the detected operation data of the power generation equipment, the load power P can be calculated using the following equation 1 _load ：

P _load＝ U _SAB* I _SAB Equation 1

Wherein, U _SAB For the amplitude of the detected output voltage, I _SAB The magnitude of the detected load current. The desired engine speed can thus be determined using a predefined engine characteristic curve. A characteristic curve of an engine is a curve that characterizes the relationship between the operating parameters of the engine (e.g., engine power, torque, and speed). The curve can be summarized from experimental data. The characteristic curve may be stored in advance in the excitation control device. The rotor position angle θ detected from the position sensor can be detected using the following equation 2 _r Calculating the actual rotational speed omega of the rotor _r 。

Then, the excitation control means 1070 may calculate the actual rotor rotation speed ω from the required engine rotation speed and the calculated rotor rotation speed ω _r The rotational speed of the engine 110 is adjusted. Specifically, the excitation control means may use closed loop control to adjust the rotational speed of the engine, i.e. at the actual rotational speed ω of the engine _r For negative feedback, the magnitude of the engine speed is corrected with the required engine speed to optimize fuel consumption corresponding to changes in load.

The excitation control unit 1070 may calculate the actual rotor speed ω based on the calculated actual rotor speed ω _r Determining a slip angle theta _slip And slip S. The formula used is as follows:

ω _slip ＝ω ₁ -ω _r equation 3

θ _slip ＝∫ω _slip Equation 4

Wherein ω is _r Is the actual rotational speed of the rotor, ω ₁ Is the synchronous speed of the generator.

Fig. 12 is a stator voltage control logic diagram in some embodiments. Excitation controlThe device 1070 is based on the amplitude U of the output voltage detected by the voltage sensor _SAB Determining a target vector value I for rotor phase current _rq ^* And I _rd ^* . In the particular embodiment shown in fig. 12, the target vector magnitude I of the rotor phase current is for a convenient period _rd ^* Is set to zero and is not shown in fig. 12. The control loop uses closed-loop control, and can automatically correct the output voltage in real time, so that the amplitude of the output voltage at the stator side is kept constant. The control loop is provided with a target vector value I for reducing the phase current of the rotor _rq ^* And I _rd ^* Proportional-integral (PI) regulator of error. Amplitude U of output voltage _SAB (as negative feedback) and reference voltage value U of stator _s * As an input value to the PI regulator. The reference voltage value U of the stator may be determined in accordance with characteristics of the power generation equipment (including, for example, rotor resistance, inductance, and an operation target of the power generation equipment) _s * . The output value of the PI regulator is the target vector value I of the rotor phase current _rq *。

FIG. 13 illustrates a schematic representation of rotor current coordinate transformation in some embodiments. The excitation control unit 1070 depends on the rotor phase current amplitudes Ira, irb, irc and the slip angle θ _slip Extracting vector value I of rotor phase current _rq And I _rd . Specifically, the excitation control device 1070 converts the detected amplitudes Ira, irb, irc of the rotor phase currents from the three-phase stationary coordinate system to the two-phase coordinate system to obtain a conversion result I _rα 、I _rβ Then mix I _rα 、I _rβ Sum and slip angle θ _slip As input to the park transformation, the vector value I of the phase current is extracted _rq And I _rd 。

Fig. 14 is a control logic diagram of rotor current. Excitation control unit 1070 adjusts vector value I according to rotor phase current _rq And I _rd Target vector value I of rotor phase current _rq ^* And I _rd ^* (set to zero as described above), slip S and resistance R of the rotor winding _r Reference voltage value U of stator _s * Determining a target vector value U of a rotor voltage _rq ^* And U _rd ^* . The control loop of the rotor current uses a PI regulator to regulate the vector value I of the rotor phase current _rq And I _rd As negative feedback, the target vector value I of the rotor phase current is used _rq ^* Correcting vector value I of rotor phase current _rq And I _rd Thereby reducing the target vector value U of the rotor voltage _rq ^* And U _rd ^* The error of (2).

Finally, the excitation control device 1070 controls the target vector value U according to the rotor voltage _rq ^* 、U _rd ^* Sum and slip angle theta _slip A pulse signal having a certain duty ratio is generated and inputted into the inverter 1062 as shown in fig. 10 to control the switching time of the inverter switching devices. The inverter adjusts the amplitude and frequency of the current flowing through the rotor windings, thereby adjusting the strength of the rotating magnetic field in the rotor windings and the rotational speed of the rotating magnetic field relative to the rotor, thereby ensuring that the amplitude and frequency of the induced voltage (i.e., the output voltage) generated in the stator single-phase windings are maintained constant.

In the control strategy shown in FIG. 11, the stator side voltage sensor, current sensor and lead A, B are electrically connected to measure the output voltage U of the stator single phase winding output _SAB And a load current I _SAB . The current sensor on the rotor side is electrically connected with the rotor winding and is used for measuring the amplitudes Ira, irb and Irc of the rotor phase current. The position sensor is connected to the rotor to detect the position angle theta of the rotor _r . The excitation control device (or engine control module) uses the formula P _load ＝U _SAB *I _SAB Calculating the load power P _load According to P _load A desired engine speed is determined. The excitation control means being dependent on the position angle theta of the rotor _r Calculating the actual rotational speed omega of the rotor _r And according to the required engine speed and the actual speed omega of the rotor _r The rotational speed of the engine 110 is adjusted. The excitation control device calculates the actual rotation speed omega of the rotor _r Determining a slip angle theta _slip And slip S and is based at least on the measured output voltage U _SAB Calculating a target vector value I of the rotor phase current _rq ^* And I _rd ^* . The excitation control means is responsive to at least the rotor phase current amplitudes Ira, irb, irc and the slip angle θ _slip Extracting the vector value of the rotor phase current, and then at least according to the vector value I of the rotor phase current _rq And I _rd Target vector value I of rotor phase current _rq ^* And I _rd ^* Determining target vector value U of rotor voltage by using sum-slip ratio S _rq ^* And U _rd ^* . The excitation control device is based on the target vector value U of the rotor voltage _rq ^* And U _rd ^* Sum and slip angle theta _slip An adjustment signal is generated and used to adjust the amplitude and frequency of the field current in the rotor windings.

FIG. 15 is a schematic diagram of a control system for operating a power plant off-grid in some embodiments. Fig. 16 is a flowchart of a control method corresponding to the control system shown in fig. 15. FIG. 17 is a control logic diagram for stator voltage in some embodiments. FIG. 18 illustrates a schematic representation of rotor current coordinate transformation in some embodiments. Fig. 19 is a control logic diagram of rotor current. The power generating equipment and the control method thereof shown in fig. 15 to 19 are mainly different from the power generating equipment and the control method thereof shown in fig. 10 to 14 as follows.

As shown in fig. 15, the stator single-phase winding outputs a two-level output voltage, i.e., a high-level voltage and a low-level voltage, to the load through the live line A, B and the neutral line N. The high-grade voltage is the voltage U between the live wire and the live wire _SAB The low-level voltage is the voltage U between the live wire and the zero wire _AN 、U _BN (also called stator winding single side voltage). The user can operate the switch to switch between the high-level voltage mode and the low-level voltage mode. The stator-side first current sensor 15AS1 and the second current sensor 15AS2 can be arranged to detect the amplitude I of the first current between the first live wire and the neutral wire _BN And the amplitude I of a second current between the second live wire and the neutral wire _AN . The rotor-side current sensor 15AR detects the amplitudes Ira, irb, irc of the rotor phase currents. The position sensor 15P is connected to the rotor to detect the position angle theta of the rotor _r . Similarly, a first may be providedA voltage sensor 15V1 and a second voltage sensor 15V2 to detect a first voltage amplitude U between the first live wire and the neutral wire _BN And a second voltage amplitude U between the second live line and neutral line _AN (i.e., one-sided low voltage). These embodiments do not require sensing the output voltage between the hot and live wires (i.e., a high level voltage), but rather only a low level voltage between the hot and neutral wires.

Fig. 16 is a flowchart of a control method corresponding to the control system shown in fig. 15. In this control method, the excitation control device 1570 adopts the same control method regardless of whether the power generation equipment is operating in the high-level voltage mode or the low-level voltage mode, and monitoring of the power generation equipment can be realized without a mode switching signal from a switch. The total load power P of the power generating equipment is calculated using the following equation 6 regardless of whether the power generating equipment is operated in the low level voltage mode or the high level voltage mode _{load total} ：

P _{load total＝＝} U _AN* I _AN +U _BN* I _BN Equation 6

Wherein, I _BN 、I _AN Is the amplitude of a first current at the stator side between the first live wire and the zero wire and the amplitude of a second current between the second live wire and the zero wire, U _BN 、U _AN Is the amplitude of a first output voltage between the first live wire and the neutral wire and the amplitude of a second output voltage between the second live wire and the neutral wire. The excitation control device uses the obtained total load power P _{load total} To determine the desired engine speed.

Specifically, the control strategy shown in fig. 16 includes the following steps. Arranging a first stator side current sensor and a second stator side current sensor to detect the amplitude I of a first current and a second current between a live wire and a zero wire _AN And I _BN . Similarly, the first and second voltage sensors are arranged to detect the magnitude U of the first and second voltages between the live and neutral conductors _BN And U _AN . The rotor side current sensor is connected to the polyphase winding of the rotor for detecting the amplitudes Ira, irb, irc of the rotor phase currents. The position sensor is connected to the rotor to detect the position angle theta of the rotor _r . Excitation control device(or engine control module) using the formula P _{load total} ＝U _AN* I _AN +U _BN* I _BN Calculating the load power P _{load total} According to the load power P _{load total} A desired engine speed is determined. The excitation control means being dependent on the position angle theta of the rotor _r Calculating the actual rotational speed omega of the rotor _r And according to the required engine speed and the actual speed omega of the rotor _r The rotational speed of the engine 110 is adjusted. The excitation control device calculates the actual rotation speed omega of the rotor _r Determining a slip angle theta _slip And a slip ratio S and is dependent on at least the amplitude U of the first or second voltage between the live and neutral lines _BN 、U _AN Calculating a target vector value I of the rotor phase current _rq ^* And I _rd ^* . The excitation control means is responsive to at least the rotor phase current amplitudes Ira, irb, irc and the slip angle θ _slip Extracting vector value I of rotor phase current _rq And I _rd Then at least according to the vector value I of the rotor phase current _rq And I _rd Target vector value I of rotor phase current _rq ^* And I _rd ^* Determining target vector value U of rotor voltage by using sum-slip ratio S _rq ^* And U _rd ^* . The excitation control device is based on the target vector value U of the rotor voltage _rq ^* And U _rd ^* Sum and slip angle theta _slip An adjustment signal is generated and used to adjust the amplitude and frequency of the field current in the rotor windings.

FIG. 17 is a control logic diagram for stator voltage in some embodiments. In these particular embodiments, the control loop for the stator voltage does not switch between a high level voltage mode and a low level voltage mode. Corresponding to the control system shown in fig. 15, the stator voltage control loop uses only a single-sided output voltage U of the stator winding _AN Or U _BN As negative feedback, reference voltage value U of stator _s * As another input value to the PI regulator. The output value of the PI regulator is a reference vector value I of the rotor phase current _rq * . Rotor current coordinate transformation shown in fig. 18 and rotor current coordinate transformation shown in fig. 19The control logic of the flow is the same as in fig. 13 and 14, and a description thereof will not be repeated.

It should be noted that in some specific embodiments, the operations illustrated in the figures may be performed in a different order than illustrated in fig. 11, 16. Indeed, operations shown in the figures as occurring in succession may be executed substantially concurrently or may be executed in the reverse order. Whether operations may be performed concurrently or in reverse order of that shown in the figures depends upon the functionality implemented by the operations. For example, the operation of adjusting the engine speed in accordance with the desired engine speed and the calculated actual speed of the rotor may be performed simultaneously with or after the operation of determining the slip angle and slip ratio in accordance with at least the actual speed of the rotor.

In the control systems described above, the excitation control device can easily implement these control systems in a simple manner. Therefore, the control equipment with lower performance can be used as an excitation control device, and the cost of the motor is reduced. Fig. 20 illustrates a waveform of rotor excitation current in some embodiments. The waveform is generated by a power plant having a stator single phase winding and a rotor three phase winding, the power plant operating at 3000 rpm with a stator side output voltage of 240 volts and a resistive load of 5 Kilowatts (KW). Fig. 21 shows waveforms of current and voltage output from the stator side of the power generating apparatus in some embodiments. The waveform is generated by a power plant with a stator single phase winding, the operating speed of the plant is 3000 rpm, the output voltage at the stator side is 240 volts, and the resistive load it drives is 5 kw. Figures 20 and 21 clearly show that the control system described above can produce satisfactory waveforms.

The specific embodiments disclosed above may provide numerous benefits. The power generating apparatus includes a stator having a single-phase winding and a rotor having a multi-phase symmetrical winding, the symmetrical winding of the rotor may generate a rotating magnetic field. The combination of a stator with single-phase windings and a rotor with multi-phase symmetrical windings in a power plant enables the power plant to supply low-power single-phase consumers, such as household appliances, while the control method of the power plant is relatively simple and easy.

An off-grid operated power plant that supplies energy to a load outputs electrical energy directly from the stator side without any frequency conversion. Compared to a conventional generator that regulates full power using a stator-side ac-dc-ac converter, the above power generation apparatus regulates only a small portion of full power using an inverter provided on the rotor side (not the stator side that outputs load power). The inverter adjusts the amplitude and frequency of the excitation voltage applied to the rotor winding to provide energy for the rotating magnetic field to compensate for the change in the amplitude and frequency of the induced voltage generated in the stator single-phase winding caused by the change in the speed of the motor, so that the amplitude and frequency of the induced voltage are maintained constant at different motor speeds. In this way, the amplitude of the stator induced voltage (i.e. the output voltage of the power plant) is kept stable, while the frequency of the output voltage of the power plant is kept constant. It is estimated that the maximum power rating of the inverter in the power plant is only about 10% of the inverter used in conventional power plants. Therefore, the power generation equipment can use an inverter with lower rated power.

In some embodiments, the inverter provides an alternating voltage to the rotor windings. The alternating voltage is used as an excitation voltage, and the amplitude and frequency of the alternating voltage can be controlled. The method using a dc voltage as the excitation voltage can control only the amplitude of the excitation voltage, and therefore the above-described method using an ac voltage as the excitation voltage is more advantageous.

The rotational speed of the engine in the power plant is adjustable to maximize fuel efficiency and thereby reduce carbon dioxide emissions. Optimizing the rotation speed of the engine corresponding to the load may also reduce noise generated by the operation of the power generating equipment and extend the life of the engine. The frequency of the stator side output voltage remains constant. The use of a closed voltage loop for determining a target value for the rotor voltage for adjusting the strength of the rotating magnetic field allows the amplitude of the stator-side output voltage to also be kept stable. This feature enables the use of the above-described power generation apparatus to power audio and video players and some instruments for scientific research that are sensitive to voltage and frequency variations. In addition, the generating equipment can generate double-level voltage by utilizing a single-phase winding of the stator, so that a user can use the generating equipment to supply power for electrical equipment with different calibration voltages.

The power plant is set to run at synchronous or sub-synchronous rotational speeds. This means that the electric power in the power plant always flows in one direction, i.e. from the stator side to the rotor side, without the electric power flowing in the opposite direction. This feature allows the power plant to use some low cost means such as an uncontrolled rectifier bridge. This feature also makes it possible to control the power plant using a simple, easy control strategy. Devices with relatively low power can also be used in the power plant.

It should be understood that the above description is only illustrative of some specific embodiments of the present invention, and is not intended to limit the scope of the present invention. The details of the above-described embodiments may be suitably modified without departing from the scope of the invention. The scope and nature of the invention is defined in the claims.

Claims

1. An off-grid operated power plant, the power plant comprising:

an engine;

a generator, the generator comprising:

the rotor is coaxially connected with the engine and comprises a multiphase symmetrical winding;

a stator having a single phase winding capable of generating an induced voltage, the single phase winding being connected to an electrical load to provide an output voltage to the load and to the rotor winding to provide an excitation voltage to the rotor winding; and

a voltage sensor arranged to detect a magnitude of a power plant output voltage; and

a stator-side current sensor configured to detect a magnitude of a power plant load current;

a rotor-side current sensor configured to detect a magnitude of a rotor-phase current; and

a position sensor configured to detect a position angle of the rotor; and

an excitation control device electrically connected to the engine and the generator, and controlling a change in a magnetic field such that the stator single-phase winding generates an induced voltage having a preset frequency, the excitation control device comprising:

a first calculation unit configured to calculate a load power from at least the output voltage and the magnitude of the load current, and to determine a required engine speed from the calculated load power;

a second calculation unit configured to calculate an actual rotation speed of the rotor from the rotor position angle;

an engine speed adjusting unit configured to adjust a speed of the engine according to a desired engine speed and an actual speed of the rotor;

a third calculation unit arranged to determine a target vector value for the rotor phase current at least in dependence on the magnitude of the output voltage;

a fourth calculation unit arranged to determine a slip angle and a slip ratio at least from an actual rotational speed of the rotor;

a fifth calculation unit arranged to extract vector values of the rotor phase current from the magnitude and the slip angle of the rotor phase current;

a sixth calculation unit arranged to determine a target vector value for the rotor voltage based on at least the vector value for the rotor phase current, the target vector value for the rotor phase current, and the slip ratio; and

an excitation current adjusting unit arranged to generate an adjustment signal to adjust the amplitude and frequency of the excitation current in the rotor winding in dependence on a target vector value of the rotor voltage and the slip angle.

2. The power generation apparatus of claim 1, comprising a frequency conversion device, the frequency conversion device further comprising an inverter for providing an ac excitation voltage to the rotor winding, the inverter comprising switching devices, wherein the adjustment signal is a pulse signal having a duty cycle, the pulse signal being used to control the switching devices of the inverter to thereby achieve adjustment of the amplitude and frequency of the excitation current in the rotor winding.

3. The power generation apparatus of claim 1, the output voltage comprising a high level output voltage and a low level output voltage, the power generation apparatus further comprising a switch, the stator single phase winding comprising first and second segments, each of the first and second segments comprising at least one coil, each of the first and second segments being connected to the switch, the switch being selectively switchable by a user to connect the first and second segments in series or in parallel to provide the high level output voltage and the low level output voltage to a load, wherein:

the voltage sensor detects the amplitudes of a first output voltage and a second output voltage which are respectively provided to a load by the first section and the second section;

the stator side current sensor detects the amplitudes of a first load current and a second load current which are respectively provided to a load by the first section and the second section;

the first calculating unit calculates the load power of a first section according to the first output voltage and the amplitude of the first load current, calculates the load power of a second section according to the second output voltage of the second section and the amplitude of the second load current, calculates the sum of the load power of the first section and the load power of the second section as the total load power, and determines the required engine speed according to the total load power; and

the fourth calculation unit determines a target vector value of the rotor phase current at least based on the magnitude of the first output voltage or the magnitude of the second output voltage.

4. The power generation apparatus according to claim 1, wherein the fourth calculation unit determines a target vector value of the rotor phase current at least according to the magnitude of the output voltage using a closed-loop control circuit.

5. The power generation apparatus of claim 1, the generator further comprising a circuit connecting the stator single phase winding and the load, the circuit causing the induced voltage generated in the stator single phase winding to be at the same frequency as the output voltage provided to the load.

6. A method of controlling an off-grid operated power plant, the power plant comprising an engine and a generator, the generator comprising: a stator having a single phase winding and a rotor having a multi-phase symmetrical winding, the rotor being coaxially connected to the motor, an induced voltage being able to be generated in the single phase winding of the stator, the single phase winding being connected to an electrical load for providing an output voltage to the load, and the single phase winding being further connected to the rotor winding for providing an excitation voltage to the rotor winding, the method comprising:

detecting the amplitude of an output voltage provided by the stator to a load;

detecting a magnitude of a load current supplied by the stator to the load;

detecting the amplitude of the phase current of the rotor;

detecting a position angle of the rotor;

calculating load power according to the output voltage and the amplitude of the load current;

determining a required engine speed according to the calculated load power;

calculating the actual rotating speed of the rotor according to the rotor position angle;

adjusting the rotational speed of the engine according to the desired engine rotational speed and the actual rotational speed of the rotor;

determining a slip angle and a slip ratio at least according to the actual rotational speed of the rotor;

determining a target vector value of the rotor phase current at least according to the amplitude of the output voltage;

extracting a vector value of the rotor phase current according to the amplitude and the slip angle of the rotor phase current;

determining a target vector value of the rotor voltage according to the vector value of the rotor phase current, the target vector value of the rotor phase current and the slip ratio; and

and generating an adjusting signal according to the target vector value and the slip angle of the rotor voltage to adjust the amplitude and the frequency of the exciting current in the rotor winding.

7. The control method of claim 6, wherein the generator further comprises a frequency conversion device comprising an inverter for providing an ac excitation voltage to the rotor winding, and wherein the adjustment signal is a pulse signal having a duty cycle, the pulse signal being used to control switching devices in the inverter to achieve adjustment of the amplitude and frequency of the excitation current in the rotor winding.

8. The control method of claim 6, the output voltage comprising a high level output voltage and a low level output voltage, the power plant further comprising a switch, the stator single phase winding comprising first and second segments, each comprising at least one coil, the first and second segments each being connected to the switch, the switch being selectively switchable by a user to connect the first and second segments in series or in parallel to provide the high level output voltage and the low level output voltage to a load, wherein:

the detecting the amplitude of the output voltage provided by the stator to the load comprises detecting the amplitudes of a first output voltage and a second output voltage provided by the first section and the second section to the load respectively;

the detecting the amplitude of the load current provided by the stator to the load comprises detecting the amplitudes of a first load current and a second load current provided by the first section and the second section to the load respectively;

the calculating the load power according to the output voltage and the amplitude of the load current comprises: calculating the load power of a first section according to the first output voltage and the amplitude of the first load current, calculating the load power of a second section according to the second output voltage and the amplitude of the second load current, and calculating the sum of the load power of the first section and the load power of the second section as the total load power;

determining a desired engine speed based on the calculated load power comprises determining a desired engine speed based on the total load power; and

the determining the target vector value for the rotor phase current based on at least the magnitude of the output voltage includes determining the target vector value for the rotor phase current based on at least the magnitude of the first output voltage or the magnitude of the second output voltage.

9. The control method of claim 6, wherein the determining a target vector value for a rotor phase current based at least on the magnitude of the output voltage comprises: and determining a target vector value of the rotor phase current at least according to the amplitude of the output voltage by using a closed-loop control mode.