CN107769247B - RLC load simulation system for anti-islanding detection and control method thereof - Google Patents
RLC load simulation system for anti-islanding detection and control method thereof Download PDFInfo
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- H02J3/00—Circuit arrangements for ac mains or ac distribution networks
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- H—ELECTRICITY
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Abstract
The invention provides an RLC load simulation system for anti-islanding detection and a control method thereof, wherein the RLC load simulation system comprises an energy feedback unit, a load characteristic simulation unit, a control module and a control platform; the alternating current end of the energy feedback unit is connected to an alternating current power grid, the direct current end of the energy feedback unit and the load characteristic simulation unit share a direct current bus, and the alternating current end of the load characteristic simulation unit is connected to a grid-connected inverter and then connected to the alternating current power grid; the control module receives an instruction of a control platform and sends the instruction to the energy feedback unit and the load characteristic simulation unit; the energy feedback unit performs pulse width modulation rectification on the power grid voltage according to the instruction of the control platform; and the load characteristic simulation unit selects a working mode according to an instruction of the control platform. According to the technical scheme provided by the invention, the energy is fed into the power grid from the EUT to the load characteristic simulation unit and then fed into the power grid through the energy feedback unit, so that the energy consumption resistor in the conventional RLC anti-islanding load device is saved, a large amount of electric energy is saved, and the method is green and environment-friendly.
Description
Technical Field
The invention belongs to the technical field of variable flow control, and particularly relates to an RLC load simulation system for anti-islanding detection and a control method thereof.
Background
Smart grids and distributed power generation technologies including renewable energy have been rapidly developed and popularized in the last decade, and since a grid-connected system directly inverts electric energy generated by renewable energy and then feeds the inverted electric energy to a grid, technical requirements for grid connection must be met during operation to ensure safety of system installers and reliable operation of the grid. For fault states such as power device overcurrent, power device overheating, power grid overvoltage/undervoltage and the like which may occur during normal system operation, detection, identification and processing are easy to perform through the cooperation of a hardware circuit and software. However, for renewable grid-connected systems, a solution for coping with a special fault condition, namely, prevention of islanding, should be considered.
According to reports provided by the International Energy Agency (IEA): the islanding phenomenon is a phenomenon in which when a power grid connected to a distributed power generation system fails or power is cut off due to maintenance of power workers, a grid-connected power generation system installed at each user side cannot detect disconnection of the power grid in time and stops operating, but continues to supply power alone to a local load, thereby generating an isolated power generation system that supplies power without control and by itself as shown in fig. 1.
The study of islanding can be divided into two cases, anti-islanding and the use of islanding. The anti-islanding (which may be referred to as anti-islanding) refers to prohibiting the occurrence of the unplanned islanding, because the power supply state is unknown, which causes a series of adverse effects, and as the number of distributed power generation devices in the power grid increases, the possibility of causing danger increases, and the conventional over/under voltage and over/under frequency protection no longer meets the requirement of safe power supply, so the power generation devices must adopt an anti-islanding scheme to prohibit the occurrence of the unplanned islanding in UL1741 and ieee std.929. The islanding is used for planned occurrence of the islanding according to a pre-configured control strategy, specifically, when power supply is interrupted due to grid failure or maintenance, the distributed power generation device continues to supply power to surrounding loads, so that loss caused by power failure is reduced, and power supply quality and reliability are improved.
The anti-islanding detection is a function which is required to be detected in a factory test of the grid-connected inverter, and the acceptance of the photovoltaic power station also lists the anti-islanding test as a detection item which is required to be detected. The device of the present anti-islanding test is an RLC load, the requirement on the selection of resistance components of the RLC load is very high, and in order to avoid resistance value thermal drift caused by heating of a resistor R in long-time testing, products on the market all adopt components with positive drift and negative drift in each branch so as to offset resistance change caused by the thermal drift. In addition, parasitic inductance on the resistor R can cause resonant frequency deviation and influence an island test result, and products in the market need to adopt a parasitic quantity compensation function to avoid over-under-frequency protection of a tested device (EUT) caused by overlarge parasitic quantity instead of island protection. Moreover, the configuration of the RLC load device values is realized by combining a large number of components through contactors, and belongs to step switching, and the precision and the reliability are poor.
Therefore, it is desirable to provide an RLC load simulation system for anti-islanding detection and a control method thereof to solve the above-mentioned disadvantages.
Disclosure of Invention
Aiming at the defects of the prior art, the invention provides an RLC load simulation system for anti-islanding detection and a control method thereof, which are used for solving the problems of high requirements on component selection, large parasitic influence, poor precision and reliability and the like of the existing anti-islanding test device, and can conveniently and flexibly realize simulation of various load characteristics to adapt to the anti-islanding detection requirements of a grid-connected inverter.
An RLC load simulation system for anti-islanding detection, comprising: the system comprises an energy feedback unit, a load characteristic simulation unit, a control module and a control platform;
the alternating current end of the energy feedback unit is connected to an alternating current power grid, the direct current end of the energy feedback unit and the load characteristic simulation unit share a direct current bus, and the alternating current end of the load characteristic simulation unit is connected to a grid-connected inverter and then connected to the alternating current power grid; the control module receives an instruction of a control platform and sends the instruction to the energy feedback unit and the load characteristic simulation unit;
the energy feedback unit performs pulse width modulation rectification on the power grid voltage according to the instruction of the control platform;
and the load characteristic simulation unit selects a working mode according to an instruction of the control platform.
Furthermore, the control module comprises an energy feedback control unit and a load characteristic simulation control unit;
the energy feedback control unit adopts double closed-loop control of a direct-current voltage outer loop and an inversion current inner loop;
the load characteristic simulation control unit adopts single current closed-loop control.
Further, the energy feedback control unit includes: the first comparator, the first PI controller, the second comparator and the first current repetition controller; the instruction of the control platform and the capacitor voltage on the direct current bus are respectively connected with the input end of a first comparator, the output end of the first comparator is connected with the input end of a first PI controller, the grid-connected current instruction output by the output end of the first PI controller and the output current of the energy feedback unit are respectively connected with the input end of a second comparator, the output end of the second comparator is connected with the input end of a first current repetitive controller, and the output end of the first current repetitive controller outputs the voltage modulation wave of a converter in the energy feedback unit.
Further, the load characteristic simulation control unit includes: a third comparator, a second PI controller, a fourth comparator and a second current repetition controller; the instruction of the control platform and the capacitor voltage on the direct current bus are respectively connected with the input end of a third comparator, the output end of the third comparator is connected with the input end of a second PI controller, the output end of the second PI controller and the instruction of the control platform are respectively connected with the input end of an amplitude limiter, the current instruction after amplitude limiting output by the output end of the amplitude limiter and the output current of the load characteristic simulation unit are respectively connected with the input end of a fourth comparator, the output end of the fourth comparator is connected with the input end of a second current repetitive controller, and the output end of the second current repetitive controller outputs the voltage modulation wave of a converter in the load characteristic simulation unit.
Further, the energy feedback unit comprises a first capacitor C1, a first reactor L1 and a first three-phase current transformer;
the first capacitor C1 and the first reactor L1 form an LC filter; the other end of the first reactor L1 is connected to a three-phase arm of the first three-phase converter; the first three-phase current transformer is connected with the direct current end of the load characteristic simulation unit.
Further, the number of the first capacitors C1 and the first reactors L1 is 3.
Further, the load characteristic simulation unit comprises a second capacitor C2, a second reactor L2 and a second three-phase current transformer;
the second capacitor C2 and a second reactor L2 form an LC filter; the other end of the second reactor L2 is connected to a three-phase arm of the second three-phase converter; the second three-phase current transformer is connected with the direct current end of the energy feedback unit.
Further, the number of the second capacitors C2 and the second reactors L2 is 3.
Further, the operation mode of the load characteristic simulation unit includes: a resistive load characteristic simulation mode, a capacitive load characteristic simulation mode, an inductive load characteristic simulation mode, a resistive-capacitive load characteristic simulation mode, and a resistive-inductive load characteristic simulation mode.
A control method of an RLC load simulation system for anti-islanding detection comprises the following steps:
the control module receives an instruction issued by the control platform and transmits the instruction to the energy feedback unit and the load characteristic simulation unit;
the energy feedback unit compares the direct current bus capacitor voltage with the instruction to perform pulse width modulation rectification on the power grid voltage;
and the load characteristic simulation unit compares the instruction with the direct current bus capacitor voltage and then selects a working mode, so as to provide conditions for anti-islanding detection of the grid-connected inverter.
Furthermore, the control module comprises an energy feedback control unit and a load characteristic simulation control unit;
the energy feedback control unit adopts double closed-loop control of a direct-current voltage outer loop and an inversion current inner loop;
the load characteristic simulation control unit adopts single current closed-loop control.
Further, the step of comparing the power grid voltage with the dc bus capacitor voltage according to the command by the energy feedback unit to perform pwm rectification on the power grid voltage includes:
the instruction received by the energy feedback unit and the capacitor voltage on the direct current bus are both sent to a first comparator of the energy feedback control unit for comparison, and the difference value of the instruction and the capacitor voltage on the direct current bus is output as a grid-connected current instruction through a first PI controller of the energy feedback control unit;
and the output current of the energy feedback unit and the grid-connected current instruction are both sent to a second comparator of the energy feedback control unit for comparison, and the difference value of the output current and the grid-connected current instruction is output to a voltage modulation wave of a converter in the energy feedback unit through a first current repetition controller of the energy feedback control unit so as to perform pulse width modulation rectification on the voltage of the power grid.
Further, the selecting of the working mode after the load characteristic simulation unit compares the instruction with the voltage of the dc bus capacitor according to the instruction includes:
the instruction received by the load characteristic simulation unit and the capacitor voltage on the direct current bus are both sent to a third comparator of the load characteristic simulation control unit for comparison, the difference value is output through a second PI controller of the load characteristic simulation control unit, and the output value carries out amplitude limiting on the instruction of the control platform;
and the output current of the load characteristic simulation unit and the current command obtained after amplitude limiting are both sent to a fourth comparator of the load characteristic simulation control unit for comparison, and the difference value is output to a voltage modulation wave of a converter in the load characteristic simulation unit through a second current repetitive controller of the load characteristic simulation control unit and is used for selecting a working mode by the load characteristic simulation unit.
Further, the selection of the working mode by the load characteristic simulation unit includes:
the load characteristic simulation unit calculates an equivalent R, L, C parallel admittance angle according to the current instruction;
and the load characteristic simulation unit selects a working mode according to the admittance angle.
Further, the selecting, by the load characteristic simulation unit, the operating mode according to the admittance angle includes:
when phi isYWhen the temperature is equal to 0 ℃, the working mode of the load characteristic simulation unit is a resistive load characteristic simulation mode, and the load characteristic simulation unit is equivalent to a pure resistive load;
when phi isYWhen the angle is 90 degrees, the working mode of the load characteristic simulation unit is a capacitive load characteristic simulation mode, and the load characteristic simulation unit is equivalent to a pure capacitive load;
when phi isYWhen the angle is minus 90 degrees, the working mode of the load characteristic simulation unit is an inductive load characteristic simulation mode, and the load characteristic simulation unit is equivalent to a pure inductive load;
when 0 DEG < phiYWhen the temperature is less than 90 degrees, the working mode of the load characteristic simulation unit is a resistance-capacitance load characteristic simulation mode, and the load characteristic simulation unit is equivalent to a resistance-capacitance load;
when-90 DEG < phiYWhen the temperature is less than 0 ℃, the working mode of the load characteristic simulation unit is a resistance-inductance load characteristic simulation mode, and the load characteristic simulation unit is equivalent to a resistance-inductance load;
wherein phi isYR, L, C parallel admittance angle equivalent to an RLC load simulation system for anti-islanding detection.
Compared with the closest prior art, the technical scheme provided by the invention has the following beneficial effects:
according to the technical scheme provided by the invention, energy is fed into a power grid from the EUT to the load characteristic simulation unit and then fed back to the power grid through the energy feedback unit, so that an energy consumption resistor in the conventional RLC anti-islanding load device is saved, a large amount of electric energy is saved, and the method is green and environment-friendly.
The technical scheme provided by the invention is based on a three-phase VSR topology, adopts a flexible current control technology, simulates the RLC load characteristics, and solves the problems of resonant frequency deviation caused by overlarge parasitic inductance of the resistor R in the traditional RLC anti-islanding load device and resistance value thermal drift caused by heating of the resistor R during long-time testing.
The technical scheme provided by the invention solves the problem of the stepped change of R, L, C value obtained by switching the contactors in the traditional RLC anti-islanding load device, realizes high-precision stepless regulation of load power, and can better meet the requirement of anti-islanding characteristic test research of a grid-connected inverter.
Drawings
FIG. 1 is a schematic diagram of distributed power generation system island operation;
FIG. 2 is a grid-connected inverter anti-islanding detection scheme;
FIG. 3 is an anti-islanding RLC load simulator topology;
FIG. 4 is a control block diagram of an energy feedback control unit;
fig. 5 is a control block diagram of a load characteristic simulation control unit;
FIG. 6 is a schematic diagram illustrating an obtaining of a current reference command of a load characteristic simulation unit according to an embodiment of the present invention;
fig. 7 is an alternating voltage and alternating current vector diagram of the anti-islanding RLC electronic simulator.
Detailed Description
The present invention will be described in further detail with reference to the accompanying drawings. In order to make the objects, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are some, but not all, embodiments of the present invention. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.
The grid-connected inverter anti-islanding detection scheme is shown in fig. 2, the grid-connected inverter is a device under test (EUT), the EUT is incorporated into a power grid at nodes U, V and W, anti-islanding RLC loads are also connected to points U, V and W, and power grid voltage sources a, B and C can be separated from the points U, V and W through an air switch K1. Firstly, an air switch K1 is closed, and the EUT and the power grid supply power to the load at the same time; then adjusting power P of anti-islanding RLC load simulatorld、QldMake the output power P of EUTo、QoAre respectively connected with Pld、QldAnd (4) disconnecting the air switch K1, separating the EUT from the power grid, and testing the anti-islanding protection time of the EUT by using a wave recorder.
The topology of the anti-islanding RLC load simulator in fig. 2 is shown in fig. 3, and a three-phase voltage type PWM rectifier (VSR) connected to the grid side is referred to as an energy feedback unit; a three-phase voltage type PWM converter (VSR) connected to a device under test (EUT) is called a load characteristic simulation unit. The energy feedback unit and the load characteristic simulation unit share a direct current bus.
1. Energy feedback unit
The energy feedback unit in this embodiment includes a three-phase VSR converter and a controller thereof.
(1) Three-phase VSR converter
In this embodiment, the main circuit of the energy feedback unit adopts a three-phase VSR topology, as shown in fig. 3, a primary winding of the isolation transformer is connected to a power grid, a secondary winding of the isolation transformer is connected to a first capacitor C1, the first capacitor C1 and a first reactor L1 form an LC filter, and the first reactor L1 is connected to a three-phase bridge arm of a three-phase inverter bridge. The number of the first transformers and the first capacitors is 3. And the direct current end of the three-phase VSR converter is connected with a direct current bus of the load characteristic simulation unit and is provided with direct current power supply.
In the embodiment, the power switch device in the inverter bridge module adopts the IGBT, so that the requirements of high voltage and high power are met.
(2) Energy feedback unit controller
And the energy feedback unit controller performs PWM rectification on the power grid voltage according to the direct-current bus voltage command. The energy feedback unit mainly plays a role in stabilizing the direct current bus voltage and controlling the grid-connected power factor, and ensures that the output stable direct current voltage is used as the post-stage input. As shown in fig. 4, the energy feedback unit controller adopts double closed-loop control of a dc voltage outer loop and an inverter current inner loop, wherein the current inner loop adopts a repetitive control strategy to improve steady-state performance and improve waveform quality of grid-connected current so as to meet performance requirements of grid-connected control. DC bus voltage command udc1 *Is related to the voltage u on the DC bus capacitordcComparing, and outputting a grid-connected current instruction i by the difference value through a voltage PI controller1 *The current command and the output current i1And comparing, outputting the difference value through a current repetitive controller (RP) and outputting a voltage modulation wave of the VSR converter.
2. Load characteristic simulation unit
The load characteristic simulation unit in this embodiment includes a three-phase VSR converter and a control portion thereof.
(1) Three-phase VSR converter
The direct current end of the three-phase VSR converter is connected to the direct current end of the three-phase VSR converter of the energy feedback unit; the output end of the inverter bridge is connected to a second capacitor C2 after passing through a second reactor L2; the second reactor and the second capacitor form a second LC filter. The number of the second reactors and the number of the second capacitors are both 3.
In the embodiment, the power switch device in the inverter bridge module adopts the IGBT, so that the requirements of high voltage and high power are met.
(2) Load characteristic simulation unit controller
The load characteristic simulation unit controller is communicated with the control platform, receives a current instruction issued by the control platform, performs feedback control on the current on the second reactor according to the current instruction, and works in a load characteristic simulation mode. The load characteristic simulation unit mainly plays a role in simulating the RLC load and provides necessary test conditions for EUT.
As shown in fig. 5, the load characteristic simulation unit controller adopts single-current closed-loop control, and in order to prevent the dc bus voltage from being uncontrolled when the energy feedback unit suddenly stops (disconnects, or halts in a fault, or is damaged), and the capacitor voltage is charged to cause the dc bus overvoltage, a dc voltage protection ring is added in the load characteristic simulation unit control structure to participate in the adaptive control of the dc bus voltage, so as to prevent the dc bus overvoltage. Setting a DC bus voltage command udc2 *Is related to the voltage u on the DC bus capacitordcComparing, outputting the difference value through a voltage PI controller, and using the difference value to receive a current command irefLimiting the amplitude to obtain an AC current instruction i after amplitude limiting2 *The current command and the output current i2And comparing, and outputting a modulation wave by the difference value through the current repetitive controller.
3. Control platform
The control platform is an upper computer, and the upper computer can realize a human-computer interaction function. The characteristics of resistive load, capacitive load, inductive load, resistive load and inductive load which are required to be simulated by the detection device are set in the upper computer, and corresponding current amplitude and phase commands are issued to the controller.
4. Operating mode of load characteristic simulation unit
In this embodiment, the operation mode includes resistive, capacitive, inductive, resistive, and resistive-inductive load characteristic simulation modes.
As shown in fig. 2, the anti-islanding RLC electronic simulator can be equivalently R, L, C parallel, and its admittance Y is:
the admittance angle is:
the angular frequency of the LC parallel resonance is:
by setting different admittance angles, different load characteristics can be obtained.
Setting the angular frequency of the power grid as omega, and the instantaneous value of the three-phase power grid voltage as:
uA＝Umcos(ωt)
setting R, L, C values in the upper computer control platform, obtaining a schematic diagram according to the current reference instruction of the load characteristic simulation unit in the figure 6, and calculating the current reference instruction value in the load characteristic simulation unit controller:
irefU＝uAY＝uA|Y|∠φY
irefV＝uBY＝uB|Y|∠φY
irefW＝uCY＝uC|Y|∠φY
where | Y | is the modulus of admittance Y.
(1) Resistive load characteristic simulation mode
When phi isYAt 0 °, i.e. angular frequency ω of LC parallel resonancerWhen the angular frequency of the power grid is equal to ω, the load characteristic simulation unit can be equivalent to a pure resistive load R, and at this time, the alternating voltage and the alternating current vector of the anti-islanding RLC electronic simulator are shown in fig. 7 (a).
(2) Capacitive load characteristic simulation mode
When phi isYWhen the angle is 90 °, the load characteristic simulation unit may be equivalent to a pure capacitive load C, and the ac voltage and ac current vectors of the anti-islanding RLC electronic simulator are as shown in fig. 7 (b).
(3) Perceptual load characteristic simulation model
When phi isYWhen the load characteristic simulation unit is equal to-90 °, the load characteristic simulation unit can be equivalent to a pure inductive load L, and the alternating voltage and alternating current vectors of the anti-islanding RLC electronic simulator are shown in fig. 7 (c).
(4) Resistance-capacitance load characteristic simulation mode
When 0 DEG < phiYWhen the angle is less than 90 degrees, the load characteristic simulation unit can be equivalent to a resistance-capacitance load, and the alternating voltage and alternating current vectors of the anti-islanding RLC electronic simulator are shown in FIG. 7 (d).
(5) Resistive load characteristic simulation mode
When-90 DEG < phiYWhen the angle is less than 0 degrees, the load characteristic simulation unit can be equivalent to a resistance-inductance load, and the alternating voltage and alternating current vectors of the anti-islanding RLC electronic simulator are shown in FIG. 7 (e).
As will be appreciated by one skilled in the art, embodiments of the present application may be provided as a method, system, or computer program product. Accordingly, the present application may take the form of an entirely hardware embodiment, an entirely software embodiment or an embodiment combining software and hardware aspects. Furthermore, the present application may take the form of a computer program product embodied on one or more computer-usable storage media (including, but not limited to, disk storage, CD-ROM, optical storage, and the like) having computer-usable program code embodied therein.
The present application is described with reference to flowchart illustrations and/or block diagrams of methods, apparatus (systems), and computer program products according to embodiments of the application. It will be understood that each flow and/or block of the flow diagrams and/or block diagrams, and combinations of flows and/or blocks in the flow diagrams and/or block diagrams, can be implemented by computer program instructions. These computer program instructions may be provided to a processor of a general purpose computer, special purpose computer, embedded processor, or other programmable data processing apparatus to produce a machine, such that the instructions, which execute via the processor of the computer or other programmable data processing apparatus, create means for implementing the functions specified in the flowchart flow or flows and/or block diagram block or blocks.
These computer program instructions may also be stored in a computer-readable memory that can direct a computer or other programmable data processing apparatus to function in a particular manner, such that the instructions stored in the computer-readable memory produce an article of manufacture including instruction means which implement the function specified in the flowchart flow or flows and/or block diagram block or blocks.
These computer program instructions may also be loaded onto a computer or other programmable data processing apparatus to cause a series of operational steps to be performed on the computer or other programmable apparatus to produce a computer implemented process such that the instructions which execute on the computer or other programmable apparatus provide steps for implementing the functions specified in the flowchart flow or flows and/or block diagram block or blocks.
Finally, it should be noted that: the above embodiments are only for illustrating the technical solutions of the present invention and not for limiting the same, and although the present invention is described in detail with reference to the above embodiments, those of ordinary skill in the art should understand that: modifications and equivalents may be made to the embodiments of the invention without departing from the spirit and scope of the invention, which is to be covered by the claims.
Claims (10)
1. An RLC load simulation system for anti-islanding detection, comprising: the system comprises an energy feedback unit, a load characteristic simulation unit, a control module and a control platform;
the alternating current end of the energy feedback unit is connected to an alternating current power grid, the direct current end of the energy feedback unit and the load characteristic simulation unit share a direct current bus, and the alternating current end of the load characteristic simulation unit is connected to a grid-connected inverter and then connected to the alternating current power grid; the control module receives an instruction of a control platform and sends the instruction to the energy feedback unit and the load characteristic simulation unit;
the energy feedback unit performs pulse width modulation rectification on the power grid voltage according to the instruction of the control platform;
the load characteristic simulation unit selects a working mode according to an instruction of the control platform;
the control module comprises an energy feedback control unit and a load characteristic simulation control unit;
the energy feedback control unit adopts double closed-loop control of a direct-current voltage outer loop and an inversion current inner loop;
the load characteristic simulation control unit adopts single current closed-loop control;
the energy feedback control unit includes: the first comparator, the first PI controller, the second comparator and the first current repetition controller; the instruction of the control platform and the capacitor voltage on the direct current bus are respectively connected with the input end of a first comparator, the output end of the first comparator is connected with the input end of a first PI controller, the grid-connected current instruction output by the output end of the first PI controller and the output current of the energy feedback unit are respectively connected with the input end of a second comparator, the output end of the second comparator is connected with the input end of a first current repetitive controller, and the output end of the first current repetitive controller outputs the voltage modulation wave of a converter in the energy feedback unit;
the load characteristic simulation control unit includes: a third comparator, a second PI controller, a fourth comparator and a second current repetition controller; the instruction of the control platform and the capacitor voltage on the direct current bus are respectively connected with the input end of a third comparator, the output end of the third comparator is connected with the input end of a second PI controller, the output end of the second PI controller and the instruction of the control platform are respectively connected with the input end of an amplitude limiter, the current instruction after amplitude limiting output by the output end of the amplitude limiter and the output current of the load characteristic simulation unit are respectively connected with the input end of a fourth comparator, the output end of the fourth comparator is connected with the input end of a second current repetitive controller, and the output end of the second current repetitive controller outputs the voltage modulation wave of a converter in the load characteristic simulation unit.
2. The RLC load simulation system for anti-islanding detection of claim 1, wherein the energy feedback unit comprises a first capacitor C1, a first reactor L1 and a first three-phase current transformer;
the first capacitor C1 and the first reactor L1 form an LC filter; the other end of the first reactor L1 is connected with a three-phase bridge arm of the first three-phase converter; and the first three-phase current transformer is connected with the direct current end of the load characteristic simulation unit.
3. The RLC load simulation system for anti-islanding detection of claim 2, wherein the number of the first capacitors C1 and the first reactors L1 is 3.
4. The RLC load simulation system for anti-islanding detection of claim 1, wherein the load characteristic simulation unit comprises a second capacitor C2, a second reactor L2 and a second three-phase current transformer;
the second capacitor C2 and a second reactor L2 form an LC filter; the other end of the second reactor L2 is connected with a three-phase bridge arm of the second three-phase converter; the second three-phase current transformer is connected with the direct current end of the energy feedback unit.
5. The RLC load simulation system for anti-islanding detection of claim 4, wherein the number of the second capacitors C2 and the second reactors L2 is 3.
6. The RLC load simulation system for anti-islanding detection according to claim 1, wherein the operation mode of the load characteristic simulation unit includes: a resistive load characteristic simulation mode, a capacitive load characteristic simulation mode, an inductive load characteristic simulation mode, a resistive-capacitive load characteristic simulation mode, and a resistive-inductive load characteristic simulation mode.
7. A control method of an RLC load simulation system for anti-islanding detection is characterized by comprising the following steps:
the control module receives an instruction issued by the control platform and transmits the instruction to the energy feedback unit and the load characteristic simulation unit;
the energy feedback unit compares the direct current bus capacitor voltage with the instruction to perform pulse width modulation rectification on the power grid voltage;
the load characteristic simulation unit compares the instruction with the direct current bus capacitor voltage and then selects a working mode to provide conditions for anti-islanding detection of the grid-connected inverter;
the control module comprises an energy feedback control unit and a load characteristic simulation control unit;
the energy feedback control unit adopts double closed-loop control of a direct-current voltage outer loop and an inversion current inner loop;
the load characteristic simulation control unit adopts single current closed-loop control;
the selection of the working mode after the load characteristic simulation unit compares the instruction with the voltage of the direct current bus capacitor comprises the following steps:
the instruction received by the load characteristic simulation unit and the capacitor voltage on the direct current bus are both sent to a third comparator of the load characteristic simulation control unit for comparison, the difference value is output through a second PI controller of the load characteristic simulation control unit, and the output value carries out amplitude limiting on the instruction of the control platform;
and the output current of the load characteristic simulation unit and the current command obtained after amplitude limiting are both sent to a fourth comparator of the load characteristic simulation control unit for comparison, and the difference value is output to a voltage modulation wave of a converter in the load characteristic simulation unit through a second current repetitive controller of the load characteristic simulation control unit and is used for selecting a working mode by the load characteristic simulation unit.
8. The method as claimed in claim 7, wherein the step of comparing the energy feedback unit with the dc bus capacitor voltage to perform pwm rectification on the grid voltage according to the command comprises:
the instruction received by the energy feedback unit and the capacitor voltage on the direct current bus are both sent to a first comparator of the energy feedback control unit for comparison, and the difference value of the instruction and the capacitor voltage on the direct current bus is output as a grid-connected current instruction through a first PI controller of the energy feedback control unit;
and the output current of the energy feedback unit and the grid-connected current instruction are both sent to a second comparator of the energy feedback control unit for comparison, and the difference value of the output current and the grid-connected current instruction is output to a voltage modulation wave of a converter in the energy feedback unit through a first current repetition controller of the energy feedback control unit so as to perform pulse width modulation rectification on the voltage of the power grid.
9. The method as claimed in claim 7, wherein the selecting of the operation mode by the load characteristic simulation unit comprises:
the load characteristic simulation unit calculates an equivalent R, L, C parallel admittance angle according to the current instruction;
and the load characteristic simulation unit selects a working mode according to the admittance angle.
10. The method as claimed in claim 9, wherein the selecting of the operation mode by the load characteristic simulation unit according to the admittance angle comprises:
when phi isYWhen the temperature is equal to 0 ℃, the working mode of the load characteristic simulation unit is a resistive load characteristic simulation mode, and the load characteristic simulation unit is equivalent to a pure resistive load;
when phi isYWhen the angle is 90 degrees, the working mode of the load characteristic simulation unit is a capacitive load characteristic simulation mode, and the load characteristic simulation unit is equivalent to a pure capacitive load;
when phi isYWhen the angle is minus 90 degrees, the working mode of the load characteristic simulation unit is an inductive load characteristic simulation mode, and the load characteristic simulation unit is equivalent to a pure inductive load;
when 0 DEG < phiYWhen the temperature is less than 90 degrees, the working mode of the load characteristic simulation unit is a resistance-capacitance load characteristic simulation mode, and the load characteristic simulation unit is equivalent to a resistance-capacitance load;
when-90 DEG < phiYWhen the temperature is less than 0 ℃, the working mode of the load characteristic simulation unit is a resistance-inductance load characteristic simulation mode, and the load characteristic simulation unit is equivalent to a resistance-inductance load;
wherein phi isYR, L, C parallel admittance angle equivalent to an RLC load simulation system for anti-islanding detection.
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| CN112152469A (en) * | 2020-10-14 | 2020-12-29 | 浙江省机电产品质量检测所有限公司 | Repetitive control method for three-phase AC electronic load |
| CN114256872A (en) * | 2021-12-03 | 2022-03-29 | 合肥科威尔电源系统股份有限公司 | Alternating current source control method, device, equipment and medium with island test function |
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