KR100847654B1 - Engine-generator provided with super capacitor - Google Patents

Abstract

An engine-generator system having a super capacitor is provided to improve a response speed of a generator for variation of a load size by discharging an electric energy charged at the super capacitor to the load when the load is increased instantaneously. An engine-generator system includes an engine(110), a generator(120), a rectifier(302), an inverter(400), and a super capacitor(500). The generator is driven by an output of the engine and generates an electric power. The rectifier converts an electric power outputted from the generator into a direct current. The inverter is coupled between a positive terminal and a negative terminal of an output terminal of the rectifier. The inverter converts the direct current power outputted from the rectifier into an alternative current power and supplies an electric power to a load. The super capacitor charges and discharges an electric energy. The super capacitor is coupled between a neutral point of the generator and the positive terminal or the negative terminal of the output terminal of the rectifier.

Description

Engine-Generator Provided with Super Capacitor

1 is a block diagram of a conventional constant speed engine-generator system.

2 is a block diagram of a conventional variable speed engine-generator system.

3 is a block diagram of an inverter used in an engine-generator system.

4 is a block diagram of a variable speed engine-generator system without a separate starter.

5 is a block diagram of a pulse width modulation (PWM) boost type rectifier used in a variable speed engine-generator system.

6 is a configuration diagram of an engine-generator system according to a first embodiment of the present invention.

7 is a block diagram of an engine-generator system according to a second embodiment of the present invention.

8 is a block diagram of a DC / DC converter used in the engine-generator system according to the second embodiment of the present invention.

9 is a configuration diagram of an engine-generator system according to a third embodiment of the present invention.

10 is a configuration diagram of an engine-generator system according to a fourth embodiment of the present invention.

11 shows an example of using the engine-generator system according to the present invention as an uninterruptible power supply.

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an engine-generator system that generates power by driving an engine, including an engine, a generator, a rectifier, an inverter, and a supercapacitor, wherein the supercapacitor includes a positive terminal or a (-) terminal of an output of the rectifier. ) Is connected between the terminal and the neutral point of the generator. When the magnitude of the load supplied with power from the engine generator increases momentarily, electrical energy charged in the supercapacitor is discharged and supplied to the load. Therefore, it is possible to improve the response speed of the generator system to the variation of the load size.

Engine-generators are now widely used in many industrial sites. Engine-generators deliver constant voltage / constant frequency power at construction sites where terrain is difficult to supply commercially, on topographically isolated sites, or on transport equipment (eg heavy trucks, port container cranes, etc.). It is widely used to supply.

1 illustrates a conventional conventional engine-generator system. The engine-generator system includes an engine-generator (100) comprising an engine (110) and a winding-type synchronous generator (122) driven by the output of the engine to generate power, the output from the generator (122). The power to be supplied is supplied to the electrical load 200.

The electrical load 200, which is the load of the engine-generator system, is an electrical system, so its response characteristics are very fast, and the load size fluctuates. On the other hand, since the engine-generator 100 using the engine 110 is a mechanical drive system and thus has a relatively slow response speed, the output voltage and frequency variation of the engine-generator 100 are inevitable.

To mitigate this, a conventional engine-generator system controls the throttle valve 114 in response to an engine rotational speed (ω _rpm ) value as shown in FIG. 1 to adjust the amount of fuel entering the engine. And a speed governor 112 which constantly adjusts the speed (output frequency). In addition, a voltage regulator 122 is used to control the excitation current of the generator using the field winding 124 in response to the output voltage value of the generator, and to constantly adjust the output voltage.

However, in spite of such a control device, fluctuations in output voltage and frequency are inevitable due to the slow response characteristics of the mechanical system in the case of sudden changes in the electrical load.

In general, in order to suppress such fluctuations, an engine-generator with a capacity greater than the maximum rating of the load is installed, so that the system is designed to make the engine-generator less sensitive to rapidly changing electrical loads. However, this lowers the operating efficiency at normal load or light load, thereby increasing the operating cost of the power generation system and increasing the initial installation cost since an engine-generator having a larger capacity than the load must be installed.

Since most generators have much more time to operate at light load or no load than at near nominal speed, improvement of power generation efficiency at light load is a very important problem for improving the overall operating efficiency of the engine-generator. If the cost of fuel continues to rise, the improvement of power generation efficiency at light loads becomes more important.

Existing engine-generators must continue to rotate at a constant speed where rated power is available to keep the generator's output frequency constant, even at no or light loads. However, in this case, the fuel consumption is very large compared to the output due to the engine characteristics.

In a vehicle that obtains mechanical power through the engine, by operating the transmission in response to the engine's mechanical power, the engine speed is improved by moving the operating speed of the engine to an operating point at which fuel efficiency is optimized. However, such an operation is not possible with an engine generator that must always rotate at a constant speed so that the engine-generator efficiency at no load or light load is less than a few minutes of the rated engine-generator efficiency.

In addition, since the engine-generator system must control the field current to suppress the variation of the terminal voltage due to the internal impedance drop that occurs when the output fluctuates even under a constant speed, the winding type synchronization having the field winding 124 is provided. Generator 122 should be used. This engine-generator system is complicated in structure due to the field winding and the mechanical system for supplying the winding thereof, and the generator itself is less efficient than the synchronous generator using permanent magnets.

In order to solve this problem, a variable speed engine-generator has been developed. A typical variable speed engine-generator is connected to the diode rectifier 300 to the output of the permanent magnet alternator 120, as shown in Figure 2 to obtain a direct current power, using an inverter 400 to drive the direct current power It is converted into alternating current of a constant voltage / constant frequency and supplied to the electric load 200. In addition, by placing the capacitor 310 between the output stage in the rectifier, it is possible to control the throttle valve 114 in response to the voltage value between the output stage to control the engine speed. Therefore, the engine speed can be adjusted according to the electrical load, thereby significantly improving fuel efficiency at no load and light load.

3 illustrates the configuration of a three phase constant voltage / constant frequency (CVCF) inverter 400 used in the engine-generator system.

However, since the output voltage of the variable speed engine-generator system is proportional to the rotational speed, the DC voltage, which is the output of the diode rectifier 300, is also lowered when the engine speed is lowered to optimize the fuel efficiency of the engine 110 at light load. do. Therefore, the engine-generator should be designed such that the inverter 400 outputs the rated voltage even for the minimum operating speed of the engine 110. To this end, the voltage rating of the inverter 400 and the diode element 300 is excessively increased compared to the AC output voltage during the rated speed operation for the rated output, the capacity of the inverter 400 and the diode rectifier 300 is increased And the price rises.

In this case, a winding type alternator (122 of FIG. 1) having a field winding as the generator 120 may be used to mitigate the output voltage variation of the diode rectifier 300 according to the engine rotational speed variation to some extent. However, in the case of the wound alternator (122 of FIG. 1), there is a problem in that the structure is complicated, the efficiency is low, and the price of the generator is increased.

Meanwhile, the constant speed engine generator shown in FIG. 1 and the variable speed engine generator shown in FIG. 2 should each include a separate starting motor (not shown) for starting the engine 110. This causes cost burden and mechanical complexity.

As power electronic technology has become more common in recent years and the price of power semiconductors has decreased, the diode rectifier (300 in FIG. 2) of a variable speed engine-generator system is shown in FIG. A system has emerged that has been replaced with a PWM Boost Rectifier (302). 5 illustrates a configuration of a three-phase pulse width modulation type boosting rectifier used in the engine-generator system.

In the engine-generator system, when the voltage is secured to the DC stage 310 at the initial startup, the generator 120 is driven by an electric motor using the pulse width modulation rectifier 302 as an inverter without a separate starter. 100 can be activated. Even if the engine speed changes from 0 (stopped) to the rated speed, the DC stage 310 voltage can be kept constant. Therefore, it is possible to optimize the voltage rating of the constant voltage / constant frequency inverter outputting the AC voltage.

Conventional engine-generator systems as described above all derive electrical output from the mechanical engine 110. Thus, there is still a fundamental problem that the AC output voltage fluctuates due to the response delay of the mechanical drive system (ie, the output of the engine-generator) when the electrical load 200 changes suddenly.

In particular, in the case of a variable speed engine-generator, in order to improve the fuel efficiency of the engine at light loads, the engine is operated at a speed significantly lower than the engine operating speed at the rated output point. At this time, if the electrical load increases rapidly, the engine speed does not increase rapidly. As a result, the AC output voltage of the inverter drops sharply, causing the load to be cut off or malfunction. Therefore, the variable speed engine-generator system can dramatically improve the fuel economy of the engine when the fluctuation of the electrical load is slow or when the fluctuation can be predicted in advance, but the load, such as a generator used in general emergency generators or construction equipment If it is unpredictable or the load fluctuation cannot be controlled, the use thereof is limited despite the excellent fuel efficiency improvement due to the fact that the output voltage fluctuation is large in reality.

The present invention has been made to solve the problems described above, the engine-generator system according to the present invention includes an engine, a generator, a boosted rectifier, an inverter, and a supercapacitor, wherein the supercapacitor is the output stage of the rectifier It is connected between the positive (+) terminal or the (-) terminal and the neutral point of the generator. When the magnitude of the load supplied with power from the engine generator increases momentarily, electrical energy charged in the supercapacitor is discharged and supplied to the load.

Therefore, according to the present invention, the response speed of the generator system to the change in the load size can be improved, and the mechanical response (that is, the control of the engine speed) to the change in the load size in the conventional engine-generator system is slow. Solved.

Accordingly, it is an object of the present invention to provide an engine-generator system which improves the response speed to a change in load size.

The present invention relates to an engine-generator system that generates power by driving an engine. More specifically, the present invention, the engine; A generator driven by the output of the engine to generate power; A rectifier for converting the power output from the generator into direct current; An inverter electrically connected to an output terminal of the rectifier and converting DC power output from the rectifier into AC power to supply power to a load; And a supercapacitor capable of charging and discharging electrical energy.

Here, the supercapacitor is connected between the positive or negative terminal of the output terminal of the rectifier and the neutral point of the generator. When the magnitude of the load supplied with power from the engine generator increases momentarily, electrical energy charged in the supercapacitor is discharged and supplied to the load.

Therefore, according to the present invention, the response speed of the generator system to the change in the load size can be improved, and the mechanical response to the change in the load size (that is, the adjustment of the engine speed) is slow in the conventional engine-generator system. Solved.

Alternatively, the supercapacitor may be connected between the positive and negative terminals of the output of the rectifier. In this case, the supercapacitor is electrically connected in parallel with the inverter.

Hereinafter, an engine-generator system according to the present invention will be described in detail with reference to the drawings. However, the present invention is not limited by the following examples. For convenience of description, the same or similar reference numerals are given to the same or similar elements in each embodiment, and the description is not repeated for the same or similar elements.

6 shows the configuration of an engine-generator system according to the first embodiment of the present invention.

Engine-generator system according to the first embodiment of the present invention is driven by the output of the engine 110, the engine 110, the generator 120 for generating power, the power output from the generator 120 direct current Step-up rectifier 302 of the pulse width modulation method, and electrically connected to the output terminals (1, 2) of the rectifier 302, converts the DC power output from the rectifier 302 to AC power to load An inverter 400 for supplying power to the 200; And a supercapacitor 500 capable of charging and discharging electrical energy.

The supercapacitor 500 is connected between the positive terminal (1) and the negative terminal (2) of the output terminal of the rectifier, and the inverter 400 is electrically connected in parallel. The supercapacitor 500 may charge from the DC stage 1 and 2 voltages of the boost type rectifier 302 when there is a margin in the output of the engine generator 100.

When the size of the electric load 200 is rapidly increased, and the mechanical response of the engine-generator 100 is delayed and a power shortage occurs momentarily, the energy charged in the supercapacitor 500 is loaded into the load 200. ) Can solve the power shortage problem.

In addition, by supplying additional power to the instantaneous load by utilizing supercapacitor energy for the instantaneously applied electrical load even at the rated speed / rated output operation, the capacity of the engine generator is not limited to the instantaneous maximum load but rather to the normal maximum load. Can be set correspondingly. Thus, the capacity of the engine generator can be greatly reduced.

In the system as shown in FIG. 6, the energy of the supercapacitor 500 is proportional to the square of the DC link voltage (Ecap = 1/2 × CV ² ). Therefore, in order to use the energy of the supercapacitor 500 up to 3/4 of the total energy in the fully charged state (that is, to discharge 3/4 of the maximum capacity of the supercapacitor 500), the DC link voltage At this maximum charge, it should fluctuate to half of the voltage. Even in such a case, in order to output the AC power of a constant voltage, as in the case of the variable speed engine-generator system using the diode rectifier (300 in FIG. 2) described above, the inverter element 400 is operated at the rated speed for the rated output. The rated voltage is excessively large compared to the AC output voltage, thereby increasing the capacity and price of the inverter 400.

7 is a configuration diagram of an engine-generator system according to a second embodiment of the present invention.

In this embodiment, in order to be able to use the inverter 400 having a small capacity, the supercapacitor 500 and the DC terminal 1 may include a DC / DC converter 510 capable of transferring power in both directions by converting the magnitude of the DC voltage. , Between 2).

In this configuration, since the DC / DC converter 510 can properly maintain the voltage difference between the input and the output, the DC terminals 1 and 2 regardless of the charge and discharge of the supercapacitor 500. The voltage can be kept in an optimal state. In addition, the charging and discharging of the supercapacitor 500 may be independently controlled by the DC / DC converter 510 regardless of the DC terminal voltage.

FIG. 8 illustrates a configuration of the bidirectional DC / DC converter 510 used in the engine-generator system, and as shown in FIG. 8, one end of the DC / DC converter 510 is connected to a DC terminal 1, 2), and the other end is connected to the supercapacitor 500 through the smoothing inductor 512. Therefore, even if the voltage of the supercapacitor 500 varies depending on the energy charging and discharging, the desired amount of energy may be supplied to the DC terminal of a constant voltage, and energy may also be supplied.

The engine-generator system may solve various disadvantages of the variable speed engine-generator system using the supercapacitor 500, and may improve the fuel efficiency of the engine-generator at no load or light load. However, the additional cost of the system increases because of the additional DC / DC converter 510.

9 is a configuration diagram of an engine-generator system according to a third embodiment of the present invention.

In this embodiment, in order to improve the engine-generator fuel efficiency at no load or light load without using a DC / DC converter (510 in FIG. 7), the neutral point 3 of the stator winding of the generator 120 and the DC terminal ( +) Connect the supercapacitor 500 between the terminal 1 or the (-) terminal 2 (connected between the neutral point 3 and the (-) terminal 2 in FIG. 6 for convenience).

By configuring in this way, it is possible to efficiently control the charging and discharging of the energy stored in the supercapacitor 500 even without providing a separate DC / DC converter.

The supercapacitor 500 may be charged when the size of the load 200 is smaller than the output of the engine generator 100 so that the output of the engine generator 100 is sufficient. The supercapacitor 500 may control charge / discharge of the supercapacitor 500 by controlling the image voltage of each phase of the boost type rectifier 302.

By controlling the voltage of each phase of the boosted rectifier 302 by a controller (not shown) that controls the operation of the boosted rectifier 302, the image current (i.e., 1/3 of the sum of the currents flowing in each phase) is controlled. In this case, three times the image current may flow in the supercapacitor 500. Therefore, it is possible to control the charge and discharge of the supercapacitor 500 by controlling the video voltage of each phase and controlling the current flowing through the supercapacitor.

When the size of the load 200 increases or decreases, the voltage of each phase of the boosted rectifier 302 can be controlled by adjusting the PWM pattern of the boosted rectifier 302 through a controller (not shown) of the boosted rectifier. And ultimately, it is possible to control the charge and discharge of the supercapacitor 500.

When the size of the electric load 200 is rapidly increased and the mechanical response of the engine-generator 100 is delayed and a power shortage occurs momentarily, the energy charged in the supercapacitor 500 is loaded into the load 200. The problem of power shortage can be solved.

In the engine-generator system according to the present embodiment, the engine speed is controlled by controlling the throttle valve 114 so that the engine-generator 100 operates in that fuel efficiency is optimized according to the electrical output.

If the electrical load rapidly increases while the engine speed is lowered at light load or no load, the image voltage of the boost type rectifier 302 is controlled to control the image current of the generator (that is, the current flowing through the supercapacitor). Electrical energy is supplied to the load 200 through the discharge of the supercapacitor 500. Then, when the rotational speed of the engine reaches the speed at which the engine-generator output corresponding to the increased load at the optimum fuel economy by adjusting the throttle valve 114, the image voltage is adjusted again to supercapacitor 500 To stop the discharge of, if necessary, the output of the engine-generator 100 is greater than the load to make extra power and can be used to charge the supercapacitor 500.

If the size of the load 200 is drastically reduced while the engine generator 100 is supplying the rated power to the load 200 at the rated load, between the output of the engine generator 100 and the load 200. The surplus power of the supercapacitor 500 absorbs. In addition, the speed of the engine 110 is reduced to a speed having an optimal fuel economy with respect to the reduced load, so that the direct current stage for the excess phenomenon of the output of the engine-generator 100 even in a transient state in which the size of the load 200 changes rapidly. Do not allow voltage to fluctuate.

When the permanent magnet generator 120 is connected to a conventional boost type rectifier 302, since the neutral point of the generator is not connected anywhere, so that each phase of the generator is in equilibrium (i.e., the impedance of each phase is the same), No matter what voltage the boosted rectifier 302 creates, there is no image voltage and current on each generator. That is, the sum of the currents flowing in each phase is always zero instantaneously according to Kirchhoff's current law.

However, when the generator neutral point 3 is connected to the DC terminal ((-) terminal 2 in the above embodiment) through the supercapacitor 500 as in the above embodiment, the boost type rectifier 302 is connected to the image. A voltage is generated, and an image current is generated through the supercapacitor 500 by the image voltage. Therefore, by appropriately controlling the image voltage of the boost type rectifier 302, the magnitude and direction of the current flowing through the supercapacitor 500 can be controlled.

In addition, the image inductance (leakage inductance) of the winding of the generator 120 is used as an inductance between the supercapacitor 500 and the boost type rectifier 302. Therefore, the pulsation component of the supercapacitor 500 current can be reduced, and the loss of the supercapacitor 500 itself can be reduced.

10 is a configuration diagram of an engine-generator system according to a fourth embodiment of the present invention.

In the present embodiment, in order to reduce the operating state loss caused by the pulsation component of the image current flowing through the windings of the supercapacitor 500 and the generator 120, the smooth inductor 530 or the inductor in series with the supercapacitor 500. And it was configured by connecting a smoothing filter (not shown) consisting of a capacitor.

In addition, in order to suppress the loss of the generator 120 and the supercapacitor 500 due to the image split current itself in a state where the supercapacitor 500 is not charged or discharged and is in standby, in series with the supercapacitor 500. A magnetic contactor 520 or a solid state relay (not shown) composed of a power semiconductor may be connected.

11 shows an example of using the engine-generator system according to the present invention as an uninterruptible power supply.

In this embodiment, the engine-generator system according to the fourth embodiment is configured to be used as an uninterruptible power supply (UPS).

That is, the electric load 200 is driven by connecting to the commercial power source 330 through the inverter 400 and the diode rectifier 320, the electric load 200 in case the commercial power source 330 is out of power. An engine-generator system according to the present invention is connected to the electrical load 200 in parallel with respect to the commercial power source 330 to supply power to the commercial power source 330.

In such a configuration, the supercapacitor 500 is charged from the spare power of the commercial power source 330 through the PWM boost type rectifier 302 to prepare for the case where the commercial power supply is out of power. If the commercial power source 330 is out of power (most of the instantaneous power outages are short power failures within 1 to 2 seconds), the energy stored in the supercapacitor 500 is discharged through the boost type rectifier 302. By supplying the DC terminal, it is possible to supply power to the load 200 for a short time when the commercial power source 330 is not supplied.

When the blackout time is long, the energy stored in the supercapacitor 500 is discharged using the PWM boost type rectifier 302 to operate the generator 120 in an electric motor mode to start the engine 110. The mechanical output of 110 may be converted through a generator 120, a boosted rectifier 302, and an inverter 400 to produce a constant voltage / constant frequency to supply power to the load 200. At the same time, until the engine-generator 100 is started to produce the output required by the load 200, the PWM boosted rectifier 302 is used to supply the energy stored in the supercapacitor 500 to the DC stage 310. Can supply power without interruption.

The supercapacitor 500 may be charged through the boost type rectifier 310 after the commercial power 330 is normalized again, and the extra generator may be charged when the electrical load is less than or equal to the output of the engine generator 100 even during a power failure. You can also charge through the output.

Even when the engine-generator 100 supplies power to the load 200 during a power failure, a part of the instantaneous maximum power of the load 200 may be charged by the supercapacitor 500, and the electricity charged in the supercapacitor Energy is supplied to the electrical load 200 at the time of power failure. Therefore, it is possible to reduce the capacity of the emergency engine-generator 110 that operates during power outages.

In the above embodiment, the three-phase, two-level engine-generator 100 is used, but various types of engine-generators such as two-phase, four-phase, five-phase, and six-phase may be used as necessary. In addition, a multi-level engine-generator of three or more levels can be used as necessary. Accordingly, it is apparent to those skilled in the art that suitable types of rectifiers, inverters, and the like can be used.

As described above, in the present invention, when the magnitude of the load increases instantaneously, electrical energy charged in the supercapacitor is discharged and supplied to the load. Therefore, it is possible to improve the response speed of the generator system to the variation in load size, and solve the problem that the mechanical response (ie control of the engine speed) to the variation in load size is slow in the conventional engine-generator system.

The embodiment according to the present invention is not limited to the above-described embodiments, and various alternatives, modifications, and changes can be made without departing from the scope of the present invention.

Claims (10)

engine; A generator driven by the output of the engine to generate power; A rectifier for converting the power output from the generator into direct current; An inverter connected between the (+) terminal and the (-) terminal of the output terminal of the rectifier and converting the DC power output from the rectifier into AC power to supply power to the load; And Includes a supercapacitor capable of charging and discharging electrical energy, The supercapacitor is connected between a positive or negative terminal of the output of the rectifier and a neutral point of the generator. The engine-generator system according to claim 1, wherein when the magnitude of the load increases, electric energy charged in the supercapacitor is discharged from the supercapacitor and supplied to the load. 3. The engine-generator system according to claim 2, wherein the control of the charging and discharging of the supercapacitor is performed by controlling the image current of the generator. 2. An engine-generator system according to claim 1, wherein a smoothing inductor or a smoothing filter is connected in series with the supercapacitor to remove pulsation components of the video capacitor current of the supercapacitor and the generator. The method of claim 1, wherein a magnetic contactor or a stationary circuit breaker is connected in series with the supercapacitor to remove the image current of the generator during the period during which the supercapacitor is not charged and discharged. Engine-generator system. 2. The engine-generator system according to claim 1, wherein the rectifier is a pulse width modulation (PWM) rectifier. According to claim 1, The output voltage of the rectifier and the rotation speed of the engine receives the input, by controlling a throttle valve for adjusting the amount of fuel supplied to the engine to control the rotation speed of the engine to optimize the fuel economy An engine-generator system, further comprising an engine speed regulator. 7. An engine-generator system according to claim 6, wherein said generator operates as an electric motor by said pulse width modulation rectifier for starting said engine when said engine is stopped. engine; A generator driven by the output of the engine to generate power; A rectifier for converting the power output from the generator into direct current; An inverter connected between the (+) terminal and the (-) terminal of the output terminal of the rectifier and converting the DC power output from the rectifier into AC power to supply power to the load; And Includes a supercapacitor capable of charging and discharging electrical energy, And said supercapacitor is connected between the (+) and (-) terminals of the output of said rectifier and is electrically connected in parallel with said inverter. 10. An engine-generator system according to claim 9, wherein a DC / DC converter for converting the magnitude of the DC voltage is interposed between the output terminal of the rectifier and the supercapacitor.

Images