A method and system for testing primary frequency regulation function of virtual synchronous machine in microgrid

Abstract

The present invention proposes a method and system for testing the primary frequency regulation function of a virtual synchronous machine in a microgrid, the method comprising: setting the main controller to adopt constant voltage and constant frequency control; setting the charging and discharging state of the main controller, the voltage and frequency of the constant voltage and constant frequency control according to different test conditions; switching the microgrid system from the grid-connected mode to the off-grid mode, and switching the main controller from the constant power control to the constant voltage and constant frequency control; testing the bus voltage and the line current of the virtual synchronous machine to be tested; and analyzing the primary frequency regulation function index of the virtual synchronous machine using the test results. The present invention makes full use of the PQ control and VF control mode conversion functions during the on-grid and off-grid switching of the microgrid system to achieve frequency steps, and has the advantages of no power outage, no impact on the normal operation of the virtual synchronous machine, and simple wiring.

Description

Technical Field

[0001] The present invention belongs to the technical field of renewable energy power generation, and in particular, relates to a method and system for testing the primary frequency regulation function of a microgrid virtual synchronous machine. Background Art

[0002] Since photovoltaic and wind power generation are intermittent and volatile, directly connecting them to the main grid in large quantities will inevitably affect the power quality and stability of the power system. Therefore, connecting these distributed power sources to the main grid through microgrids can realize the local consumption of part of the distributed energy, eliminating the loss in power transmission, and the remaining power after local consumption can also be transmitted to the main grid. At the same time, the microgrid system contains various power electronic devices, which can flexibly and quickly control various devices in the system, reflecting the speed and flexibility of the microgrid. The various forms of energy in the microgrid, reasonable planning can optimize energy management and improve the efficiency of multi-energy complementarity.

[0003] At the same time, with the large-scale distributed power generation connected to the grid, the stability of the power grid cannot be maintained by synchronous generators alone. By applying virtual synchronous machine control technology to the control of distributed power grid-connected inverters, the distributed power source can also have the same inertia and damping characteristics as the synchronous machine. While providing power to the grid, the distributed power source can participate in maintaining the stability of the grid system and solve the problem that large-scale distributed power generation cannot be connected to the grid due to stability.

[0004] The primary frequency regulation function is the basic function of the distributed power supply virtual synchronous machine. It means that when the power system frequency deviates from the target frequency, the generator set adjusts the active output to reduce the frequency deviation through the automatic response of the control system. The primary frequency regulation capability of the generator set is the first important barrier to maintain the power balance and safety and stability of the power grid. Its regulation performance plays a very important role in the dynamic stability of the power grid, and its performance needs to be verified through testing.

[0005] In the prior art, there are two methods for detecting primary frequency regulation of a microgrid virtual synchronous machine:

[0006] (1) Rapid load switching generates power shortage, resulting in frequency deviation, recording the frequency response curve of the virtual synchronous machine, and then analyzing indicators such as lag time, response time, adjustment time, and adjustment accuracy. This method generates frequency deviation by rapidly switching loads, and there is a problem that the frequency deviation value is uncontrollable, and it will cause fluctuations in the microgrid system, or even power outages, reducing power supply reliability. In the prior art, the primary frequency modulation instructions between the active primary frequency modulation master station and the active primary frequency modulation substation are forwarded by the PMU phase data concentrator, and the primary frequency modulation phasor, analog quantity, and switch quantity are sent to the active primary frequency modulation substation at regular intervals. It can quickly implement the test of the primary frequency modulation performance without affecting the normal operation of the existing real-time dynamic monitoring system. However, the virtual signal sent by the primary frequency modulation master station can only be used to determine whether the logic strategy of the primary frequency modulation system is correct and monitor the primary frequency modulation system of the substation, and cannot detect the real response characteristics of the system, such as adjustment time, control accuracy, etc.

[0007] (2) The frequency acquisition module of the virtual synchronous machine needs to collect the frequency of the grid connection point, disconnect its acquisition loop, inject the frequency disturbance signal through the frequency modulation and voltage regulation signal source, generate the frequency deviation, and then analyze the indicators such as lag time, response time, adjustment time, and adjustment accuracy. This method needs to disconnect the frequency acquisition loop, which makes it difficult to implement the virtual synchronous machine. In addition, the frequency acquisition and synchronous phase locking of some virtual synchronous machines are in the same loop. After disconnection, the virtual synchronous machine cannot work. In the prior art, the frequency generating device is connected between the wind farm step-up transformer and the wind turbine step-up transformer, and the frequency generating device is adjusted according to the frequency change test point. The wind turbine under test is tested, and the test data of each acquisition point in the wind turbine under test is collected. The results of all the test data are comprehensively analyzed to determine the primary frequency regulation capability of the wind turbine under test. However, connecting the frequency generating device between the wind farm step-up transformer and the wind turbine step-up transformer has problems such as difficult wiring, endangering personal safety, and affecting the normal operation of the wind turbine. Summary of the invention

[0008] In order to solve the deficiencies in the prior art, the present invention provides a method and system for testing the primary frequency regulation function of a microgrid virtual synchronous machine. During the seamless switching process between the grid-connected operation and the off-grid operation of the microgrid system, the constant power (PQ) control of the microgrid system main controller is changed to the constant voltage and frequency (VF) control, so that the frequency of the microgrid system produces a step, thereby detecting the primary frequency regulation function of the virtual synchronous machine.

[0009] The present invention adopts the following technical solution.

[0010] On one hand, the present invention proposes a method for testing the primary frequency regulation function of a microgrid virtual synchronous machine, comprising:

[0011] Step 1, setting the main controller to adopt constant voltage and constant frequency control;

[0012] Step 2, according to different test conditions, the charge and discharge state of the main controller, the voltage and frequency of the constant voltage and constant frequency control are set; wherein the test conditions include: the main controller charging state frequency disturbance, the main controller discharging state frequency disturbance, the main controller charging state frequency disturbance, the main controller discharging state frequency disturbance;

[0013] Step 3: the microgrid system switches from the grid-connected mode to the off-grid mode, and the main controller switches from the constant power control to the constant voltage and frequency control; the bus voltage and the line current of the virtual synchronous machine to be tested are tested;

[0014] Step 4, using the test results of step 3, analyze the primary frequency regulation function indicators of the virtual synchronous machine; the indicators include: lag time, response time, regulation time, and regulation accuracy.

[0015] Preferably, step 1 comprises:

[0016] When the microgrid is connected to the grid, the main controller is set to operate in constant power control, and the frequency of the microgrid is consistent with the grid frequency, both of which are 50Hz;

[0017] When the microgrid is off-grid, the main controller is set to operate in constant voltage and constant frequency control, and the control frequency is set not equal to 50Hz.

[0018] Preferably, in step 2, the frequency disturbance test method of the main controller in the charging state includes: setting the main controller to the charging state, setting the voltage of the main controller under constant voltage and constant frequency control to the rated voltage of the grid, and setting the frequency value range to be greater than or equal to 50.05 Hz and less than or equal to 50.15 Hz.

[0019] Preferably, in step 2, the frequency disturbance test method of the main controller in the discharge state includes: setting the main controller to the discharge state, setting the voltage of the main controller under constant voltage and constant frequency control to the rated voltage of the grid, and setting the frequency value range to be greater than or equal to 50.05 Hz and less than or equal to 50.15 Hz.

[0020] Preferably, in step 2, the frequency disturbance test method of the main controller in the charging state includes: setting the main controller to the charging state, setting the voltage of the main controller under constant voltage and constant frequency control to the rated voltage of the grid, and setting the frequency value range to be less than or equal to 49.95 Hz and greater than or equal to 49.85 Hz.

[0021] Preferably, in step 2, the frequency disturbance test method of the main controller in the discharge state includes: setting the main controller to the discharge state, setting the main controller VF control voltage to the rated voltage of the grid, and setting the frequency value range to be less than or equal to 49.95 Hz and greater than or equal to 49.85 Hz.

[0022] Preferably, the microgrid system switches from the grid-connected mode to the off-grid mode, and uses an electric quantity recording and analyzing instrument to record the bus voltage and the line current of the virtual synchronous machine to be tested.

[0023] Preferably, step 3 comprises:

[0024] Step 3.1, the primary frequency modulation control system sets the frequency deviation dead zone constant;

[0025] Step 3.2, when the microgrid frequency deviates from the target frequency, the generator set adjusts the active output through the control system;

[0026] Step 3.3, when the frequency deviation exceeds the dead zone, the primary frequency modulation system is implemented based on the active power-frequency droop characteristic curve function, and the function satisfies the following relationship:

[0027]

[0028] In the formula,

[0029] f is the frequency of the virtual synchronous machine,

[0030] f d is the primary frequency modulation response dead zone,

[0031] f n is the system rated frequency,

[0032] P n is the rated power of the virtual synchronous machine,

[0033] δ% is the frequency modulation response error rate of the virtual synchronous machine.

[0034] P0 is the initial value of the active power of the virtual synchronous machine;

[0035] Step 3.4, the electric quantity record analyzer records data of at least 30 seconds before and at least 30 seconds after the frequency deviation crosses the dead zone; the data includes voltage, current, active power and reactive power data;

[0036] Step 3.5, calculate the lag time, response time, adjustment time and adjustment accuracy of the frequency modulation system through the above data.

[0037] Preferably, in step 3.5, the lag time is the time required for the microgrid to switch from the grid-connected mode to the off-grid mode to the time when the power change of the virtual synchronous machine reaches 10%;

[0038] The response time is the time required from the moment the microgrid switches from the grid-connected mode to the off-grid mode to the moment the power change of the virtual synchronous machine reaches 90%;

[0039] The adjustment time is the shortest time from the moment when the microgrid switches from the grid-connected mode to the off-grid mode until the absolute value of the virtual synchronous machine power does not exceed 5% of the final steady-state value;

[0040] The regulation accuracy is the deviation between the power of the virtual synchronous machine and the target value when it reaches stability.

[0041] Preferably, the primary frequency modulation response upper power limit coefficient k1, the primary frequency modulation response lower power limit coefficient k2 and the primary frequency modulation response total power lower limit coefficient k1 are determined according to the active power-frequency droop characteristic curve function. min .

[0042] On the other hand, the present invention also proposes a microgrid virtual synchronous machine primary frequency regulation function test system, the system includes: an acquisition module, a working condition test module, and a primary frequency regulation function analysis module;

[0043] A collection module, used for collecting bus voltage and line current of the virtual synchronous machine to be tested when the microgrid system switches from the grid-connected mode to the off-grid mode;

[0044] The working condition test module includes: a working condition setting unit and an on-grid and off-grid switching unit; the working condition setting unit is used to set the charge and discharge state of the main controller, the voltage and frequency of the constant voltage and constant frequency control according to different test conditions; the on-grid and off-grid switching unit is used to switch the microgrid system from the on-grid mode to the off-grid mode;

[0045] The primary frequency modulation function analysis module is used to analyze the primary frequency modulation function indicators of the virtual synchronous machine using the test results collected by the acquisition module; the indicators include: lag time, response time, adjustment time, and adjustment accuracy.

[0046] The acquisition module includes: a voltage transformer connected to the bus, a current transformer connected to the virtual synchronous machine line, and an electric quantity recording and analyzing instrument; the voltage transformer is used to collect the voltage signal of the bus when the microgrid system switches from the grid-connected mode to the off-grid mode, and the current transformer is used to collect the current signal of the virtual synchronous machine line to be tested when the microgrid system switches from the grid-connected mode to the off-grid mode; the voltage signal and the current signal are transmitted together to the electric quantity recording and analyzing instrument.

[0047] The working condition setting unit includes: a main controller state setting unit, a main controller voltage and frequency setting unit;

[0048] When the main controller state setting unit sets the main controller to the charging state, and the main controller voltage and frequency setting unit sets the voltage of the main controller constant voltage and frequency control to the rated voltage of the grid and the frequency to 50.05Hz-50.15Hz, the main controller is in the charging state frequency disturbance test mode;

[0049] When the main controller state setting unit sets the main controller to the discharge state, and the main controller voltage and frequency setting unit sets the voltage of the main controller constant voltage and frequency control to the rated voltage of the grid and the frequency to 50.05Hz-50.15Hz, the main controller is in the discharge state frequency disturbance test mode;

[0050] When the main controller state setting unit sets the main controller to the charging state, and the main controller voltage and frequency setting unit sets the voltage of the main controller constant voltage and frequency control to the rated voltage of the grid and the frequency to 49.95Hz-49.85Hz, the main controller is in the charging state frequency disturbance test mode;

[0051] The main controller state setting unit sets the main controller to the discharge state. When the main controller voltage and frequency setting unit sets the voltage of the main controller constant voltage and frequency control to the rated voltage of the grid and the frequency to 49.95Hz-49.85Hz, the main controller is in the discharge state frequency disturbance test mode.

[0052] The beneficial effect of the present invention is that, compared with the prior art, the present invention proposes a method for testing the primary frequency regulation function of a microgrid virtual synchronous machine. When the microgrid system is connected to the grid, each power electronic device (including the main controller) operates in the PQ control mode, and the system frequency is consistent with the grid frequency, which is 50Hz. The main controller of the microgrid system is used to perform seamless switching between the grid and the off-grid mode, and the microgrid system is converted from the grid-connected mode to the off-grid mode. The main controller is switched from the PQ control to the VF control. During the switching, the frequency of the VF control mode of the main controller is set to be slightly greater than or less than 50Hz, so that the frequency of the microgrid system is stepped from 50Hz to a new frequency, thereby detecting the primary frequency regulation function of the virtual synchronous machine and analyzing its lag time, response time, adjustment time, adjustment accuracy and other indicators.

[0053] The present invention solves the problems of uncontrollable deviation, system fluctuation, reduced power supply reliability, etc. in testing the primary frequency modulation function by using a fast load shedding method, and overcomes the problems of wiring difficulties and influence on the operation of the virtual synchronous machine in testing the primary frequency modulation function by using a frequency acquisition module to inject a disturbance signal.

[0054] The present invention makes full use of the PQ control and VF control mode conversion functions during the on-grid and off-grid switching of the microgrid system to achieve frequency stepping, and has the advantages of no power outage, no influence on the normal operation of the virtual synchronous machine, simple wiring, etc.

[0055] The primary frequency regulation function detection of the virtual synchronous machine is crucial to verifying its grid-connected performance. Reasonable standardization and monitoring of the primary frequency regulation parameters and performance of the unit are of great significance to the safe and stable operation of the power grid and the optimal scheduling in the future smart grid environment. BRIEF DESCRIPTION OF THE DRAWINGS

[0056] Figure 1It is a flow chart of a method for testing the primary frequency regulation function of a microgrid virtual synchronous machine proposed by the present invention;

[0057] Figure 2 It is a wiring diagram for detecting the primary frequency regulation function of a virtual synchronous machine in a typical microgrid system in an embodiment of the present invention;

[0058] Figure 3 Schematic diagram of active power-frequency droop characteristic curve of primary frequency modulation function in an embodiment of the present invention;

[0059] Figure 4 is a result diagram of a frequency disturbance test of a main controller in a charging state according to an embodiment of the present invention;

[0060] Figure 5 Result diagram of the frequency disturbance test of the main controller in the discharge state according to the embodiment of the present invention;

[0061] Figure 6 : is a result diagram of a frequency disturbance test of a main controller in a charging state in an embodiment of the present invention;

[0062] Figure 7 1 is a result diagram of a frequency disturbance test of a main controller in a discharge state in an embodiment of the present invention. DETAILED DESCRIPTION

[0063] In order to make the purpose, technical scheme and advantages of the present invention clearer, the technical scheme of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. The embodiments described in this application are only embodiments of a part of the present invention, rather than all embodiments. Based on the spirit of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work belong to the protection scope of the present invention.

[0064] Example 1.

[0065] On the one hand, the present invention proposes a method for testing the primary frequency regulation function of a microgrid virtual synchronous machine. Figure 1 As shown, including:

[0066] Step 1: Set the main controller to use constant voltage and constant frequency control.

[0067] In the microgrid system, there are mainly grid-connected operation mode and off-grid operation mode.

[0068] (1) In normal operation, the AC bus of the microgrid is connected to the distribution network through the point of common coupling (PCC), the system works in the grid-connected mode, and the power dispatch is carried out according to the system instructions. The power electronic equipment works in the constant power control (PQ control) mode. At this time, the output voltage is consistent with the grid voltage, the system voltage and frequency are provided by the grid, and the power electronic equipment works at a constant power output. In this control mode, only the output power value needs to be set, and the equipment operates according to the power set value;

[0069] (2) When a system failure occurs in the distribution network, the controller will quickly disconnect the PCC node between the microgrid and the distribution network and change the control mode. At this time, the microgrid system works in off-grid mode and in constant voltage and frequency control (VF control) mode. Generally, when master-slave control is adopted in an isolated microgrid, the master power supply adopting the VF control strategy is required to provide voltage and frequency reference for the isolated microgrid, and the remaining distributed power supplies as slave controllers generally adopt PQ control. The master controller adopting VF control needs to be able to track the changes in load in a timely manner. All power surpluses in the microgrid need to be borne by the master power supply. Therefore, a stable and controllable energy storage unit or a large-capacity distributed power supply with energy storage is usually used as the master controller.

[0070] Typical microgrid system structure is as follows: Figure 2 shown. Figure 2 In the example, line 1 is connected to the main controller (usually energy storage), lines 2 and 3 are connected to the distributed power virtual synchronous machine, and other lines are connected to the load.

[0071] Figure 2 The microgrid system in the system is connected to the grid and operates, and electric energy is dispatched according to system instructions. All power electronic equipment (including the main controller) works in PQ control mode. At this time, the frequency of the microgrid system is consistent with the grid frequency of 50Hz, the output voltage is consistent with the grid voltage, the system voltage and frequency are provided by the grid, and the power electronic equipment works at a constant power output. In this control mode, you only need to set the output power value, and the equipment operates according to the power set value.

[0072] Figure 2 The medium-sized microgrid system operates off-grid and works in VF control mode. The main power supply adopting VF control strategy is required to provide voltage and frequency reference for the off-grid island microgrid. The voltage and frequency can be preset manually. The VF control mode frequency of the main controller is preset to be slightly greater than or less than 50Hz. The remaining distributed power sources as slave controllers generally adopt PQ control, and usually use a storage unit with stable and controllable power or a large-capacity distributed power supply with energy storage as the main controller.

[0073] Step 2: According to different test conditions, the charge and discharge state of the main controller, the voltage and frequency of the constant voltage and constant frequency control are set.

[0074] The primary frequency modulation function test of the virtual synchronous machine includes four working condition tests: (1) frequency up-disturbance in the main controller charging state, (2) frequency up-disturbance in the main controller discharging state, (3) frequency down-disturbance in the main controller charging state, and (4) frequency down-disturbance in the main controller discharging state.

[0075] The method for testing the frequency disturbance in the charging state of the main controller is as follows: set the main controller to the charging state, set the VF control voltage of the main controller to the rated voltage of the grid, and the frequency to 50.05Hz-50.15Hz;

[0076] The method for testing the frequency disturbance in the discharge state of the main controller is as follows: set the main controller to the discharge state, set the VF control voltage of the main controller to the rated voltage of the grid, and the frequency to 50.05Hz-50.15Hz;

[0077] The frequency disturbance test method of the main controller in the charging state is as follows: set the main controller to the charging state, set the main controller VF control voltage to the rated voltage of the grid, and the frequency to 49.95Hz-49.85Hz;

[0078] The frequency disturbance test method of the main controller in the discharge state is as follows: set the main controller to the discharge state, set the main controller VF control voltage to the rated voltage of the grid, and the frequency to 49.95Hz-49.85Hz.

[0079] The present invention makes full use of the PQ control and VF control mode conversion functions during the switching process of the microgrid system on and off the grid to achieve frequency step, and has the advantages of no power outage, no impact on the normal operation of the virtual synchronous machine, and simple wiring. The present invention solves the problems of uncontrollable deviation, system fluctuation, and reduced power supply reliability when testing the primary frequency modulation function using the rapid load shedding method, and overcomes the problems of wiring difficulties and impact on the operation of the virtual synchronous machine when testing the primary frequency modulation function using the frequency acquisition module to inject disturbance signals.

[0080] Step 3: The microgrid system switches from the grid-connected mode to the off-grid mode, and the bus voltage and the line current of the virtual synchronous machine to be tested are tested.

[0081] In Example 1, the microgrid system is switched from the grid-connected mode to the off-grid mode, and the bus voltage and the line current of the virtual synchronous machine to be tested are recorded using an electric quantity recording and analyzing instrument. Figure 2 As shown, the voltage transformer PT connected to the bus collects the voltage signal of the bus, and the current transformer CT connected to the bus side of line 2 collects the current signal of the virtual synchronous machine line to be tested; the voltage signal and the current signal are transmitted together to the power recording analyzer.

[0082] By seamlessly switching between grid-connected and off-grid modes, the microgrid system is converted from grid-connected mode to off-grid mode, and the main controller is switched from PQ control to VF control, so that the frequency of the microgrid system can be stepped from 50Hz to a new frequency, and the primary frequency regulation function of the virtual synchronous machine can be detected. Figure 2 Seamless switching between grid-connected and off-grid means that when the operating state of the microgrid system is switched, the control strategy of the main controller converter also switches between constant voltage and frequency control and constant power control. When PQ control is adopted, the main controller converter adopts the current inner loop control mode. When VF control is adopted, the current loop reference current of the main controller converter is calculated by the voltage outer loop according to the voltage reference signal.

[0083] Figure 3 The primary frequency regulation function of the virtual synchronous generator is realized as follows: when the power system frequency deviates from the target frequency, the generator set adjusts the active output to reduce the frequency deviation through the automatic response of the control system. The primary frequency regulation control system sets the frequency deviation dead zone constant. When the frequency deviation exceeds the dead zone, the primary frequency regulation function is realized by setting the frequency and active power broken line function (active power-frequency droop characteristic curve function), that is:

[0084]

[0085] In the formula,

[0086] f is the virtual synchronous machine frequency, unit: 50Hz,

[0087] f d is the primary frequency modulation response dead zone, unit: Hz,

[0088] f n is the system rated frequency, unit: 50Hz,

[0089] P n is the rated power of the virtual synchronous machine, unit: MW,

[0090] δ% is the frequency modulation response error rate of the virtual synchronous machine.

[0091] P0 is the initial value of the virtual synchronous machine active power, unit: MW.

[0092] Active power-frequency droop characteristic curve of primary frequency modulation function Figure 2 As shown, Figure 2 In the above equation, k1 is the power limit coefficient of the primary frequency modulation response, k2 is the power limit coefficient of the primary frequency modulation response, and k min Adjust the total power lower limit coefficient for the primary frequency modulation response.

[0093] Step 4, using the test results of step 3, analyze the primary frequency regulation function indicators of the virtual synchronous machine; the indicators include: lag time, response time, regulation time, and regulation accuracy.

[0094] The lag time is the time required for the microgrid to switch from the grid-connected mode to the off-grid mode to the time when the power change of the virtual synchronous machine reaches 10%.

[0095] The response time is the time required for the microgrid to switch from the grid-connected mode to the off-grid mode to the time when the power change of the virtual synchronous machine reaches 90%.

[0096] The adjustment time is the shortest time from the moment when the microgrid switches from the grid-connected mode to the off-grid mode to the moment when the absolute value of the virtual synchronous machine power and the final steady-state value does not exceed 5% change.

[0097] The regulation accuracy is the deviation between the power of the virtual synchronous machine and the target value when it reaches stability.

[0098] Example 2.

[0099] Taking a 10kV microgrid system as an example, the structure of the 10kV microgrid system is as follows: Figure 2 The rated capacity of the distributed power virtual synchronous machine of line 2 is 10MW, the primary frequency regulation dead zone is 0.05Hz, the primary frequency regulation difference rate is 2%, the primary frequency regulation power regulation limit coefficient is 10%, and the primary frequency regulation total power lower limit coefficient is 20%; the main controller VF control mode setting voltage is 10.5kV, and the primary frequency regulation function upper and lower interference test frequencies are set to 50.15Hz and 49.85Hz respectively.

[0100] (1) Main controller charging state frequency disturbance test:

[0101] When the microgrid system is connected to the grid, each power electronic device (including the main controller) operates in the PQ control mode, and the system frequency is consistent with the grid frequency of 50Hz. The main controller of the microgrid system is used to perform seamless switching between the grid and the grid, switching the main controller of the microgrid system from PQ control to VF control, and the frequency changes to 50.15Hz. The test results are as follows: Figure 4 shown.

[0102] The main controller charging state frequency disturbance test results show that the lag time, response time, adjustment time, and adjustment accuracy are shown in Table 1:

[0103] Table 1 Main controller charging state frequency disturbance test results

[0104]

[0105] (2) Frequency disturbance test of main controller in discharge state:

[0106] When the microgrid system is connected to the grid, each power electronic device (including the main controller) operates in the PQ control mode, and the system frequency is consistent with the grid frequency of 50Hz. The main controller of the microgrid system is used to perform seamless switching between the grid and the grid, switching the main controller of the microgrid system from PQ control to VF control, and the frequency changes to 50.15Hz. The test results are as follows: Figure 5 shown.

[0107] The results of the main controller's discharge state frequency disturbance test show that the lag time, response time, adjustment time, and adjustment accuracy are shown in Table 2:

[0108] Table 2 Main controller discharge state frequency disturbance test results

[0109]

[0110] (3) Frequency disturbance test of main controller charging state:

[0111] When the microgrid system is connected to the grid, each power electronic device (including the main controller) operates in the PQ control mode, and the system frequency is consistent with the grid frequency of 50Hz. The main controller of the microgrid system is used to perform seamless switching between the grid and the grid, switching the main controller of the microgrid system from PQ control to VF control, and the frequency changes to 49.85Hz. The test results are as follows: Figure 6 shown.

[0112] The results of the main controller charging state frequency disturbance test show that the lag time, response time, adjustment time and adjustment accuracy are shown in Table 3:

[0113] Table 3 Main controller charging state frequency disturbance test results

[0114]

[0115] (4) Frequency disturbance test of main controller in discharge state:

[0116] When the microgrid system is connected to the grid, each power electronic device (including the main controller) operates in the PQ control mode, and the system frequency is consistent with the grid frequency of 50Hz. The main controller of the microgrid system is used to perform seamless switching between the grid and the grid, switching the main controller of the microgrid system from PQ control to VF control, and the frequency changes to 49.85Hz. The test results are as follows: Figure 7 shown.

[0117] The results of the main controller's discharge state frequency disturbance test show that the lag time, response time, adjustment time, and adjustment accuracy are shown in Table 4:

[0118] Table 4 Main controller discharge state frequency disturbance test results

[0119]

[0120] The test results of the four operating conditions of the primary frequency regulation function of the virtual synchronous machine meet the standard requirements, and the primary frequency regulation function test of the virtual synchronous machine of the microgrid is completed.

[0121] On the other hand, the present invention also proposes a primary frequency regulation function test of a microgrid virtual synchronous machine, comprising: an acquisition module, a working condition test module, and a primary frequency regulation function analysis module.

[0122] The acquisition module includes: a voltage transformer connected to the bus, a current transformer connected to the virtual synchronous machine line, and an electric quantity recorder and analyzer; the voltage transformer is used to collect the voltage signal of the bus when the microgrid system switches from the grid-connected mode to the off-grid mode, and the current transformer is used to collect the current signal of the virtual synchronous machine line to be tested when the microgrid system switches from the grid-connected mode to the off-grid mode; the voltage signal and the current signal are transmitted to the electric quantity recorder and analyzer together. Through the transformation ratio setting, the primary values ​​of the voltage signal and the current signal are restored, and the voltage frequency and the power of the virtual synchronous machine are calculated through the electric quantity recorder and analyzer.

[0123] The working condition test module includes: a working condition setting unit and an on-grid and off-grid switching unit; the working condition setting unit is used to set the charging and discharging state of the main controller, the voltage and frequency of the constant voltage and constant frequency control according to different test working conditions; wherein the test working conditions include: the main controller charging state frequency up-disturbance, the main controller discharging state frequency up-disturbance, the main controller charging state frequency down-disturbance, and the main controller discharging state frequency down-disturbance; the on-grid and off-grid switching unit is used to switch the microgrid system from the on-grid mode to the off-grid mode;

[0124] The primary frequency modulation function analysis module is used to analyze the primary frequency modulation function indicators of the virtual synchronous machine using the test results collected by the acquisition module; the indicators include: lag time, response time, adjustment time, and adjustment accuracy. The function analysis module calculates the time required for the output active power change to reach 10% of the difference between the active power target value and the initial value from the time the frequency exceeds the primary frequency modulation dead zone, which is the lag time; the function analysis module calculates the time required for the output active power change to reach 90% of the difference between the active power target value and the initial value from the time the frequency exceeds the primary frequency modulation dead zone, which is the response time; the function analysis module calculates the shortest time for the absolute value of the difference between the output active power and the active power target value to always not exceed the allowable deviation from the time the frequency exceeds the primary frequency modulation dead zone, which is the adjustment time; the function analysis module calculates the percentage of the deviation between the actual active power and the target active power when the primary frequency modulation reaches stability as a percentage of the rated active power, which is the adjustment accuracy.

[0125] The present disclosure may be a system, a method and / or a computer program product. The computer program product may include a computer-readable storage medium carrying computer-readable program instructions for causing a processor to implement various aspects of the present disclosure.

[0126] A computer-readable storage medium may be a tangible device that can hold and store instructions used by an instruction execution device. A computer-readable storage medium may be, for example, but not limited to, an electrical storage device, a magnetic storage device, an optical storage device, an electromagnetic storage device, a semiconductor storage device, or any suitable combination of the foregoing. More specific examples of computer-readable storage media (a non-exhaustive list) include: a portable computer disk, a hard disk, a random access memory (RAM), a read-only memory (ROM), an erasable programmable read-only memory (EPROM or flash memory), a static random access memory (SRAM), a portable compact disk read-only memory (CD-ROM), a digital versatile disk (DVD), a memory stick, a floppy disk, a mechanical encoding device, such as a punch card or a raised structure in a groove on which instructions are stored, and any suitable combination of the foregoing. As used herein, a computer-readable storage medium is not to be interpreted as a transient signal per se, such as a radio wave or other freely propagating electromagnetic wave, an electromagnetic wave propagating through a waveguide or other transmission medium (e.g., a light pulse through a fiber optic cable), or an electrical signal transmitted through a wire.

[0127] The computer-readable program instructions described herein can be downloaded from a computer-readable storage medium to each computing / processing device, or downloaded to an external computer or external storage device via a network, such as the Internet, a local area network, a wide area network, and / or a wireless network. The network can include copper transmission cables, optical fiber transmissions, wireless transmissions, routers, firewalls, switches, gateway computers, and / or edge servers. The network adapter card or network interface in each computing / processing device receives the computer-readable program instructions from the network and forwards the computer-readable program instructions for storage in the computer-readable storage medium in each computing / processing device.

[0128] The computer program instructions for performing the operation of the present disclosure may be assembly instructions, instruction set architecture (ISA) instructions, machine instructions, machine-related instructions, microcode, firmware instructions, state setting data, or source code or object code written in any combination of one or more programming languages, including object-oriented programming languages, such as Smalltalk, C++, etc., and conventional procedural programming languages, such as "C" language or similar programming languages. Computer-readable program instructions may be executed completely on a user's computer, partially on a user's computer, as an independent software package, partially on a user's computer, partially on a remote computer, or completely on a remote computer or server. In the case of a remote computer, the remote computer may be connected to the user's computer via any type of network, including a local area network (LAN) or a wide area network (WAN), or may be connected to an external computer (e.g., using an Internet service provider to connect via the Internet). In some embodiments, an electronic circuit, such as a programmable logic circuit, a field programmable gate array (FPGA), or a programmable logic array (PLA), may be customized by utilizing the state information of the computer-readable program instructions, and the electronic circuit may execute the computer-readable program instructions, thereby realizing various aspects of the present disclosure.

[0129] Various aspects of the present disclosure are described herein with reference to the flowcharts and / or block diagrams of the methods, devices (systems) and computer program products according to the embodiments of the present disclosure. It should be understood that each box in the flowchart and / or block diagram and the combination of each box in the flowchart and / or block diagram can be implemented by computer-readable program instructions.

[0130] These computer-readable program instructions can be provided to a processor of a general-purpose computer, a special-purpose computer, or other programmable data processing device, thereby producing a machine, so that when these instructions are executed by the processor of the computer or other programmable data processing device, a device that implements the functions / actions specified in one or more boxes in the flowchart and / or block diagram is generated. These computer-readable program instructions can also be stored in a computer-readable storage medium, and these instructions cause the computer, programmable data processing device, and / or other equipment to work in a specific manner, so that the computer-readable medium storing the instructions includes a manufactured product, which includes instructions for implementing various aspects of the functions / actions specified in one or more boxes in the flowchart and / or block diagram.

[0131] Computer-readable program instructions may also be loaded onto a computer, other programmable data processing apparatus, or other device so that a series of operating steps are performed on the computer, other programmable data processing apparatus, or other device to produce a computer-implemented process, thereby causing the instructions executed on the computer, other programmable data processing apparatus, or other device to implement the functions / actions specified in one or more boxes in the flowchart and / or block diagram.

[0132] The flow chart and block diagram in the accompanying drawings show the possible architecture, function and operation of the system, method and computer program product according to multiple embodiments of the present disclosure. In this regard, each square box in the flow chart or block diagram can represent a part of a module, program segment or instruction, and a part of the module, program segment or instruction includes one or more executable instructions for realizing the specified logical function. In some alternative implementations, the function marked in the square box can also occur in a sequence different from that marked in the accompanying drawings. For example, two continuous square boxes can actually be executed substantially in parallel, and they can sometimes be executed in reverse order, depending on the functions involved. It should also be noted that each square box in the block diagram and / or flow chart, and the combination of the square boxes in the block diagram and / or flow chart can be implemented with a dedicated hardware-based system that performs the specified function or action, or can be implemented with a combination of special hardware and computer instructions.

[0133] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention rather than to limit it. Although the present invention has been described in detail with reference to the above embodiments, ordinary technicians in the relevant field should understand that the specific implementation methods of the present invention can still be modified or replaced by equivalents, and any modifications or equivalent replacements that do not depart from the spirit and scope of the present invention should be covered within the scope of protection of the claims of the present invention.

Claims

1. A method for testing the primary frequency modulation function of a microgrid virtual synchronous machine, characterized in that: include: Step 1, setting the main controller to adopt constant voltage and constant frequency control; Step 2, according to different test conditions, set the charge and discharge state, constant voltage and frequency control voltage and frequency of the main controller; wherein the test conditions include: the main controller charging state frequency disturbance, the main controller discharge state frequency disturbance, the main controller charging state frequency disturbance, the main controller discharge state frequency disturbance; the main controller charging state frequency disturbance test method is as follows: set the main controller to the charging state, set the voltage of the main controller constant voltage and frequency control to the rated voltage of the grid, and the frequency to 50.05Hz-50.15Hz; the main controller discharge state frequency disturbance test method is as follows: set Set the main controller to the discharge state, set the voltage of the main controller's constant voltage and constant frequency control to the rated voltage of the grid, and the frequency to 50.05Hz-50.15Hz; the frequency disturbance test method of the main controller in the charging state is as follows: set the main controller to the charging state, set the voltage of the main controller's constant voltage and constant frequency control to the rated voltage of the grid, and the frequency to 49.95Hz-49.85Hz; the frequency disturbance test method of the main controller in the discharge state is as follows: set the main controller to the discharge state, set the voltage of the main controller's constant voltage and constant frequency control to the rated voltage of the grid, and the frequency to 49.95Hz-49.85Hz; Step 3: the microgrid system switches from the grid-connected mode to the off-grid mode, and the main controller switches from the constant power control to the constant voltage and frequency control; the bus voltage and the line current of the virtual synchronous machine to be tested are tested; Step 4, using the test results of step 3, analyze the primary frequency regulation function indicators of the virtual synchronous machine; the indicators include: lag time, response time, regulation time, and regulation accuracy.

2. The method for testing the primary frequency modulation function of a microgrid virtual synchronous machine according to claim 1, characterized in that: Step 1 includes: When the microgrid is connected to the grid, the main controller is set to run in constant power control, and the frequency of the microgrid is consistent with the grid frequency, both of which are 50Hz; When the microgrid is off-grid, the main controller is set to operate in constant voltage and constant frequency control, and the control frequency is set not equal to 50Hz.

3. The method for testing the primary frequency modulation function of a microgrid virtual synchronous machine according to claim 1, characterized in that: The microgrid system switches from the grid-connected mode to the off-grid mode, and uses the power recording and analyzing instrument to record the bus voltage and the line current of the virtual synchronous machine to be tested.

4. The method for testing the primary frequency modulation function of a microgrid virtual synchronous machine according to claim 1, characterized in that: Step 3 includes: Step 3.1, the primary frequency modulation control system sets the frequency deviation dead zone constant; Step 3.2, when the microgrid frequency deviates from the target frequency, the generator set adjusts the active output through the primary frequency regulation control system; Step 3.3, when the frequency deviation exceeds the dead zone, the primary frequency control system is implemented based on the active power-frequency droop characteristic curve function, and the function satisfies the following relationship: In the formula, f is the frequency of the virtual synchronous machine, f d is the primary frequency modulation response dead zone, f n is the system rated frequency, P n is the rated power of the virtual synchronous machine, δ% is the frequency modulation response error rate of the virtual synchronous machine. P0 is the initial value of the active power of the virtual synchronous machine. Step 3.4, the electric quantity record analyzer records data of at least 30 seconds before and at least 30 seconds after the frequency deviation crosses the dead zone; the data includes voltage, current, active power and reactive power data; Step 3.5, calculate the lag time, response time, adjustment time and adjustment accuracy of the primary frequency modulation control system through the above data.

5. The method for testing the primary frequency regulation function of a microgrid virtual synchronous machine according to claim 4, characterized in that: In step 3.5, the lag time is the time required from the moment the microgrid switches from the grid-connected mode to the off-grid mode to the moment the power change of the virtual synchronous machine reaches 10%; The response time is the time required from the moment the microgrid switches from the grid-connected mode to the off-grid mode to the moment the power change of the virtual synchronous machine reaches 90%; The adjustment time is the shortest time from the moment when the microgrid switches from the grid-connected mode to the off-grid mode until the absolute value of the virtual synchronous machine power does not exceed 5% of the final steady-state value; The regulation accuracy is the deviation between the power of the virtual synchronous machine and the target value when it reaches stability.

6. The method for testing the primary frequency regulation function of a microgrid virtual synchronous machine according to claim 4, characterized in that: According to the active power-frequency droop characteristic curve function, the primary frequency modulation response upward power limit coefficient k1, the primary frequency modulation response downward power limit coefficient k2 and the primary frequency modulation response total power lower limit coefficient k min .

7. A microgrid virtual synchronous machine primary frequency regulation function test system using the method described in any one of claims 1 to 6, characterized in that: The system includes: an acquisition module, a working condition test module, and a primary frequency modulation function analysis module; A collection module, used for collecting bus voltage and line current of the virtual synchronous machine to be tested when the microgrid system switches from the grid-connected mode to the off-grid mode; The working condition test module includes: a working condition setting unit and an on-grid and off-grid switching unit; the working condition setting unit is used to set the charging and discharging state of the main controller, the voltage and frequency of the constant voltage and constant frequency control according to different test working conditions; the on-grid and off-grid switching unit is used to switch the microgrid system from the on-grid mode to the off-grid mode; Among them, the test conditions include: frequency disturbance in the charging state of the main controller, frequency disturbance in the discharging state of the main controller, frequency disturbance in the charging state of the main controller, and frequency disturbance in the discharging state of the main controller; the frequency disturbance test method of the charging state of the main controller is as follows: set the main controller to the charging state, set the voltage of the constant voltage and constant frequency control of the main controller to the rated voltage of the power grid, and the frequency to 50.05Hz-50.15Hz; the frequency disturbance test method of the discharge state of the main controller is as follows: set the main controller to the discharge state, set the voltage of the constant voltage and constant frequency control of the main controller to the rated voltage of the power grid, and the frequency to 50.05Hz-50.15Hz; the frequency disturbance test method of the charging state of the main controller is as follows: set the main controller to the charging state, set the voltage of the constant voltage and constant frequency control of the main controller to the rated voltage of the power grid, and the frequency to 49.95Hz-49.85Hz; the frequency disturbance test method of the discharge state of the main controller is as follows: set the main controller to the discharge state, set the voltage of the constant voltage and constant frequency control of the main controller to the rated voltage of the power grid, and the frequency to 49.95Hz-49.85Hz; The primary frequency modulation function analysis module is used to analyze the primary frequency modulation function indicators of the virtual synchronous machine using the test results collected by the acquisition module; the indicators include: lag time, response time, adjustment time, and adjustment accuracy.

8. The microgrid virtual synchronous machine primary frequency regulation function test system according to claim 7 is characterized in that: The acquisition module includes: a voltage transformer connected to the bus, a current transformer connected to the virtual synchronous machine line, and an electric quantity recording and analyzing instrument; the voltage transformer is used to collect the voltage signal of the bus when the microgrid system switches from the grid-connected mode to the off-grid mode, and the current transformer is used to collect the current signal of the virtual synchronous machine line to be tested when the microgrid system switches from the grid-connected mode to the off-grid mode; the voltage signal and the current signal are transmitted together to the electric quantity recording and analyzing instrument.

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