Improved virtual synchronous inverter secondary frequency modulation control method and related device

Abstract

The invention discloses an improved secondary frequency modulation control method for a virtual synchronous inverter and a related device, and belongs to the technical field of converter control, and the method comprises the steps: obtaining the actual instantaneous active power and the actual instantaneous reactive power of a micro-grid; obtaining an angular frequency difference value between the angular frequency rated value and the virtual angular frequency, and compensating the actual angular frequency based on a PI proportional-integral control algorithm according to the angular frequency difference value to obtain a control signal of an active power-frequency control structure; constructing a function of an active power given value changing along with the angular frequency based on a translation method, and substituting the function into the control signal to obtain an active power control signal; in the active-frequency control structure, based on the actual instantaneous active power, the actual instantaneous reactive power and the active power control signal, obtaining the virtual back electromotive force of the micro-grid; secondary frequency modulation control is carried out on a switch tube of the virtual synchronous inverter based on the virtual back electromotive force, and the problem caused by the uncertainty of load power change can be effectively solved.

Description

Technical Field

[0001] The present invention belongs to the technical field of converter control, and in particular relates to an improved virtual synchronous inverter secondary frequency modulation control method and a related device. Background Art

[0002] Grid-connected systems are the main form of photovoltaic power generation popularization in urban areas. In the rapid evolution of grid-connected inverter systems, energy storage converters are the key technology for achieving efficient flow and conversion of electric energy. The importance of grid-connected control strategies for energy storage converters has gradually increased, which is directly related to grid stability, reliability and optimal energy configuration. Synchronous inverters are a special type of VSG (Virtual Synchronous Generator) that can suppress frequency fluctuations in the medium and high frequency range. Compared with other VSGs, synchronous inverters use simpler control structures to achieve the mathematical equivalence of SG (Synchronous Generator). The output impedance characteristics of synchronous inverters are closer to SG because the actual inductance in synchronous inverters is used to simulate the internal impedance of SG. In particular, synchronous inverters can maintain relatively stable reactance characteristics and ensure system stability. With the application of distributed power grid connection and microgrids, synchronous inverter technology has been deeply studied in the control method of grid-connected inverters.

[0003] With the development of distributed power sources, more and more applications are providing energy for local loads. Synchronous inverters can provide frequency support for microgrids through primary frequency modulation, but primary frequency modulation is differential regulation, which may cause frequency crossing due to sudden changes in load. This requires improvements to synchronous inverters to enable them to have secondary frequency modulation capabilities. At the same time, for applications with higher requirements for frequency fluctuations, it is hoped that the frequency modulation time will be short and the frequency fluctuation range will be small. For this reason, it is necessary to further improve the secondary frequency modulation control strategy. Summary of the invention

[0004] The purpose of the present invention is to overcome the deficiencies in the prior art and to provide an improved virtual synchronous inverter secondary frequency modulation control method and related devices. On the basis of a voltage-controlled virtual synchronous inverter algorithm, the output of a given active power value is predicted by detecting the module angular frequency, so that the frequency fluctuation range is smaller, which can effectively improve the problems caused by the uncertainty of load power changes.

[0005] To achieve the above object, the present invention is implemented by adopting the following technical solutions:

[0006] In a first aspect, the present invention provides an improved virtual synchronous inverter secondary frequency modulation control method, comprising:

[0007] Obtain the actual instantaneous active power and actual instantaneous reactive power of the microgrid;

[0008] Obtaining an angular frequency difference between an angular frequency rated value and a virtual angular frequency, and compensating the actual angular frequency based on a PI proportional-integral control algorithm according to the angular frequency difference to obtain a control signal of an active-frequency control structure;

[0009] Constructing a function of the active power given value varying with the angular frequency based on the translation method, and substituting the function into the control signal to obtain an active power control signal;

[0010] In the active-frequency control structure, a virtual back-EMF of the microgrid is obtained based on the actual instantaneous active power, the actual instantaneous reactive power and the active power control signal;

[0011] Secondary frequency modulation control is performed on the switch tube of the virtual synchronous inverter based on the virtual back electromotive force.

[0012] Optionally, the obtaining of the actual instantaneous active power and the actual instantaneous reactive power of the microgrid includes:

[0013] Collect the three-phase voltage and three-phase current of the microgrid;

[0014] The three-phase voltage and three-phase current are transformed into the d-axis voltage by coordinate transformation , d-axis current , q-axis voltage and q-axis current ;

[0015] According to the d-axis voltage , d-axis current , q-axis voltage and q-axis current Calculate the actual instantaneous active power and actual instantaneous reactive power of the microgrid. The calculation formula is as follows:

[0016] ,

[0017] in, is the actual instantaneous active power, is the actual instantaneous reactive power, is the line impedance, is the load impedance, is the voltage amplitude of the AC output terminal at the midpoint of the bridge arm, For phase.

[0018] Optionally, the acquiring an angular frequency difference between the angular frequency rated value and the virtual angular frequency, and compensating the actual angular frequency based on a PI proportional-integral control algorithm according to the angular frequency difference to obtain a control signal of an active-frequency control structure, comprises:

[0019] The angular frequency difference is obtained by subtracting the angular frequency rated value from the virtual angular frequency;

[0020] The product of the angular frequency difference and the frequency droop coefficient is added to the output of the angular frequency difference after passing through the integrator, and the sum is used as the new virtual damping. The calculation formula is as follows:

[0021] ,

[0022] in, For the new virtual damping, is the frequency droop coefficient, is the integration coefficient, is the angular frequency rating, is the virtual angular frequency, Indicates time;

[0023] The new virtual damping is added to the swing equation, so that the frequency droop coefficient and the integral coefficient constitute a PI controller to control the virtual angular frequency. The swing equation calculation formula is as follows:

[0024] ,

[0025] in, is the virtual inertia, is the active power given value input to the secondary frequency regulation system, is the actual instantaneous active power.

[0026] Optionally, constructing a function of active power given value varying with angular frequency based on the translation method comprises:

[0027] According to the secondary frequency modulation process of the microgrid, the corresponding translation of the curve between active power and angular frequency under load change state is obtained;

[0028] According to the translation situation, the range of the inverter output power and the range of the angular frequency in the microgrid, the function of the active power set value with the angular frequency is constructed as follows:

[0029] ,

[0030] in, is the angular frequency setting value, is the maximum value of the angular frequency setting, is the minimum value of the angular frequency setting, is the maximum difference in active power, is the given value of active power.

[0031] Optionally, obtaining a virtual back electromotive force of the microgrid based on the actual instantaneous active power, the actual instantaneous reactive power and the active power control signal includes:

[0032] Calculating a phase angle of a virtual potential based on the actual instantaneous active power and the active power control signal;

[0033] Based on the actual instantaneous reactive power, calculating the virtual excitation of the microgrid;

[0034] Based on the phase angle and virtual excitation, a virtual back electromotive force of the microgrid is calculated.

[0035] Optionally, the calculating the phase angle of the virtual potential based on the actual instantaneous active power and the active power control signal comprises:

[0036] The actual instantaneous active power calculation formula, the swing equation and the active power given value as a function of the angular frequency are combined to calculate the virtual angular frequency;

[0037] The calculation formula for the phase angle based on the virtual angular frequency is:

[0038] ,

[0039] in, is the phase angle.

[0040] Optionally, the calculating the virtual excitation of the microgrid based on the actual instantaneous reactive power includes:

[0041] The virtual excitation calculation formula of the microgrid is as follows:

[0042] ,

[0043] in, is virtual excitation, is the reactive power reference value, is the actual instantaneous reactive power, is the reactive power regulation coefficient.

[0044] Optionally, the calculating the virtual back electromotive force of the microgrid based on the phase angle and the virtual excitation includes:

[0045] The calculation formula of the virtual back electromotive force of the microgrid is as follows:

[0046] ,

[0047] in, is the virtual back EMF, is virtual excitation, is the phase angle.

[0048] Optionally, the secondary frequency modulation control of the switch tube of the virtual synchronous inverter based on the virtual back EMF includes: using SPWM sinusoidal pulse width modulation method, inputting the virtual back EMF into the PWM pulse width modulation loop and intersecting the triangular carrier to obtain a high-frequency PWM pulse width modulation pulse, and performing secondary frequency modulation control on the switch tube.

[0049] In a second aspect, the present invention provides an improved virtual synchronous inverter secondary frequency modulation control system, comprising:

[0050] Actual power acquisition module: used to obtain the actual instantaneous active power and actual instantaneous reactive power of the microgrid;

[0051] A control signal acquisition module based on angular frequency: used to obtain the angular frequency difference between the rated angular frequency and the virtual angular frequency, and compensate the actual angular frequency based on the PI proportional-integral control algorithm according to the angular frequency difference to obtain a control signal of the active-frequency control structure;

[0052] Active power-based control signal acquisition module: used to construct a function of active power given value varying with angular frequency based on translation method, and substitute the function into the control signal to obtain active power control signal;

[0053] A virtual back-EMF acquisition module is used to obtain the virtual back-EMF of the microgrid based on the actual instantaneous active power, the actual instantaneous reactive power and the active power control signal in the active-frequency control structure;

[0054] Secondary frequency modulation control module: used for performing secondary frequency modulation control on the switch tube of the virtual synchronous inverter based on the virtual back electromotive force.

[0055] In a third aspect, the present invention provides a computer storage medium having a computer program stored thereon, and when the computer program is executed by a processor, the improved virtual synchronous inverter secondary frequency modulation control method as described in any step of the first aspect is implemented.

[0056] Compared with the prior art, the beneficial effects achieved by the present invention are as follows: in order to solve the problems of frequency fluctuation exceeding the limit and power quality deterioration caused by the uncertainty of load power changes in the island mode of distributed power sources, the improved synchronous inverter control strategy in the present application collects angular frequency signals and constructs a function of the corresponding active power set value and angular frequency change, and outputs the set value of active power through angular frequency changes, thereby accelerating the stabilization of frequency, quickly adjusting the frequency to meet the needs of the microgrid, improving the performance of the synchronous inverter in frequency support performance, and can effectively improve the problems caused by the uncertainty of load power changes. BRIEF DESCRIPTION OF THE DRAWINGS

[0057] Figure 1Shown is a flow chart of an improved virtual synchronous inverter secondary frequency modulation control method in an embodiment of the present invention;

[0058] Figure 2 Shown is a schematic diagram of a synchronous inverter circuit for performing secondary frequency modulation control in an embodiment of the present invention;

[0059] Figure 3 Shown is a block diagram of secondary frequency modulation control of a synchronous inverter under load changes in one embodiment of the present invention;

[0060] Figure 4 It is a schematic diagram showing the translation change of the curve of active power and angular frequency when the load suddenly increases in one embodiment of the present invention;

[0061] Figure 5 It is a schematic diagram showing the translation change of the curve of active power and angular frequency when the load is suddenly reduced in one embodiment of the present invention;

[0062] Figure 6 The figure shows a block diagram of a synchronous inverter secondary frequency modulation control under load change in which a translation method is introduced in an embodiment of the present invention;

[0063] Figure 7 An embodiment of the present invention is shown in FIG. Figure 2 The schematic diagram of the simulation of the frequency when the synchronous inverter performs a frequency modulation is shown;

[0064] Figure 8 An embodiment of the present invention is shown in FIG. Figure 2 The schematic diagram of frequency simulation when the synchronous inverter performs secondary frequency modulation is shown;

[0065] Fig. 9 An embodiment of the present invention is shown in FIG. Figure 2 The schematic diagram of frequency simulation when the synchronous inverter is subjected to secondary frequency modulation by introducing the translation method is shown;

[0066] Fig.10 An embodiment of the present invention is shown in FIG. Figure 2 The experimental waveform diagram of the frequency when the synchronous inverter performs a frequency modulation is shown;

[0067] Fig.11 An embodiment of the present invention is shown in FIG. Figure 2 The experimental waveform diagram of the frequency when the synchronous inverter performs secondary frequency modulation is shown;

[0068] Fig.12 An embodiment of the present invention is shown in FIG. Figure 2 The experimental waveform diagram of the frequency when the synchronous inverter is subjected to secondary frequency modulation by introducing the translation method is shown. DETAILED DESCRIPTION

[0069] The present invention will be further described below in conjunction with the accompanying drawings. The following embodiments are only used to more clearly illustrate the technical solution of the present invention, and cannot be used to limit the protection scope of the present invention.

[0070] Example 1

[0071] like Figure 1 As shown, this embodiment provides an improved virtual synchronous inverter secondary frequency modulation control method, including:

[0072] Obtain the actual instantaneous active power and actual instantaneous reactive power of the microgrid;

[0073] Obtaining an angular frequency difference between an angular frequency rated value and a virtual angular frequency, and compensating the actual angular frequency based on a PI proportional-integral control algorithm according to the angular frequency difference to obtain a control signal of an active-frequency control structure;

[0074] Constructing a function of the active power given value varying with the angular frequency based on the translation method, and substituting the function into the control signal to obtain an active power control signal;

[0075] In the active-frequency control structure, a virtual back-EMF of the microgrid is obtained based on the actual instantaneous active power, the actual instantaneous reactive power and the active power control signal;

[0076] Secondary frequency modulation control is performed on the switch tube of the virtual synchronous inverter based on the virtual back electromotive force.

[0077] By introducing the synchronous inverter secondary frequency modulation control strategy of the translation method and giving the function of the active power set value and the system angular frequency, the performance of the synchronous inverter in frequency support is improved, which can effectively improve the problems caused by the uncertainty of load power changes.

[0078] Example 2

[0079] Based on Example 1, this example also makes the following design.

[0080] The three-phase PWM (Pulse Width Modulation) inverter three-level circuit topology diagram provided in this embodiment is as follows: Figure 2 As shown, a three-level topology with diode clamping is used. - There are 12 IGBTs (Insulated Gate Bipolar Transistor) with anti-parallel diodes. - There are 6 clamping diodes. , are the converter side filter inductor and its internal resistance, , are the grid-side filter inductor and its internal resistance, is the AC side filter capacitor, is the damping resistor. , , They are the three-phase grid voltages, and the voltage sensors are used to sample the values. , , They are the three-phase grid current, and the current sensors are used to sample the values. , , are the fundamental wave of the output voltage at the midpoint of the three-phase bridge arm, , , are the AC voltages of the three-phase filter capacitors, is the DC voltage source output current, For the DC voltage source voltage or energy storage battery voltage, use a voltage sensor to sample the value. , They are the upper and lower split capacitors on the DC side respectively.

[0081] The three-phase voltage , , and three-phase current , , The d-axis voltage is obtained by coordinate transformation , d-axis current , q-axis voltage and q-axis current , according to the d-axis voltage , d-axis current , q-axis voltage and q-axis current Calculate the actual instantaneous active power of the microgrid and actual instantaneous reactive power , the calculation formula is as follows:

[0082] .

[0083] In island mode, assuming the load exhibits a resistive-inductive characteristic, the sum of the line and load impedance for , let the AC output voltage amplitude at the midpoint of the bridge arm be , the phase is , the apparent power output of the AC output voltage at the midpoint of the three-phase bridge arm for:

[0084] ,

[0085] Among them, the actual instantaneous active power , actual instantaneous reactive power It is expressed as:

[0086] .

[0087] Figure 3 The figure shows the secondary frequency regulation control block diagram of the microgrid under load changes, including PLL (Phase Locked Loop), synchronous machine core link, secondary frequency regulation link, direct power loop, reactive loop, process quantity calculation loop and PWM modulation loop. In the secondary frequency regulation link, It is the switch that switches the synchronous inverter from primary frequency regulation to secondary frequency regulation. is the integration coefficient of the integrator, is a complex variable in the frequency domain, in the reactive loop, It is the voltage at the PCC (Programmable Computer Controller). The programmable computer controller PCC is used for reactive power compensation.

[0088] Set the angular frequency to the rated value With virtual angular frequency Make a difference to get the angular frequency difference, and multiply the angular frequency difference by the frequency droop coefficient The sum of the difference between the angular frequency and the angular frequency is taken as the new damping part through the integrator, and the new damping part is added to the swing equation, so that the frequency droop coefficient and the integral coefficient It can be compared to a PI (Proportional-Integral) controller to achieve zero static error control of the angular frequency. At this time, the new damping part is: , so that the synchronous inverter has the ability of secondary frequency modulation, where Indicates time.

[0089] When the virtual synchronous inverter outputs current, the synchronous generator is used as the simulation object, otherwise, the motor is used as the simulation object. The swing equations of the two cases when droop control is adopted are:

[0090] ,

[0091] in, is the virtual inertia, is the virtual electromagnetic torque, is the virtual mechanical torque, is the angular frequency difference.

[0092] The core loop of the synchronous machine refers to the mechanical motion equation of the synchronous motor and introduces virtual inertia in the control of the three-phase PWM rectifier. , virtual speed , virtual electromagnetic torque , virtual mechanical torque and virtual damping , the specific expression is as follows:

[0093] ,

[0094] ,

[0095] ,

[0096] Among them, in the control of the virtual synchronous inverter, the Simulating virtual mechanical torque , Simulating virtual electromagnetic torque , It is the given value of active power input to the secondary frequency regulation system.

[0097] Virtual corner frequency Integrate to get the rectifier phase angle , the calculation formula is as follows:

[0098] .

[0099] The actual angular frequency of the power grid is obtained by the PLL phase-locked loop , when connected to the grid .

[0100] The reactive loop refers to the excitation equation of the synchronous motor:

[0101] ,

[0102] in, is virtual excitation, is the reactive power regulation coefficient, is a complex variable in the frequency domain, is the voltage droop coefficient, is the reference voltage, is the excitation voltage of the synchronous motor, Is the reactive power reference value. Introducing virtual excitation in the control of three-phase PWM rectifier and reactive power regulation factor , virtual excitation Calculated by the following formula:

[0103] .

[0104] Calculation of virtual electromagnetic torque in process quantity calculation link , Instantaneous reactive power and virtual back EMF .

[0105] Virtual electromagnetic torque It is obtained from the electromagnetic transient relationship of the synchronous motor and calculated by the following formula:

[0106] ,

[0107] in, is the grid current, , , Represents the transpose of a vector.

[0108] Instantaneous reactive power Calculated by the following formula:

[0109] ,

[0110] Virtual Back EMF Calculated by the following formula:

[0111] ,

[0112] In the formula .

[0113] The virtual back EMF is modulated by SPWM The high-frequency PWM pulse is sent to the PWM modulation loop for intersection with the triangular carrier to control the switch tube, thus achieving Figure 2 Virtual synchronous control of the energy storage converter is shown.

[0114] like Figure 4 In the secondary frequency regulation process of the microgrid shown in the figure, when the load suddenly increases, the angular frequency will decrease from the rated angular frequency Reduce to , from the original stable point A to point B, if the given value of active power is changed at this time, it means that the curve of active power and angular frequency will shift to the right. Then, under this given active power, point B will shift to the right to point C, and the angular frequency corresponding to point C is Distance from the original rated angular frequency The distance is less than the initial From rated angular frequency distance.

[0115] like Figure 5 In the secondary frequency regulation process of the microgrid shown in the figure, when the load suddenly decreases, the angular frequency will increase from the rated angular frequency Increase to , from the original stable point A to point B, if the given value of active power is changed at this time, it means that the curve of active power and angular frequency will shift to the left. Then, under this given active power, point B will move right to point C, and the angular frequency corresponding to point C is Distance from the original rated angular frequency The distance is less than the initial From rated angular frequency distance.

[0116] like Figure 6 The figure shows the block diagram of the secondary frequency modulation control of the synchronous inverter with the translation method. According to the above two situations, the range of the inverter output power and the range of the angular frequency in the microgrid are combined to construct the function of the active power set value with the angular frequency. The maximum value of The maximum output power of the inverter Limitation, the maximum value of the angular frequency setting value At this moment the system angular frequency , Rated angular frequency , frequency droop coefficient And the maximum difference in active power Decision means following The curve of active power given value and angular frequency is shifted in the increasing direction until the most suitable curve is selected. When the angular frequency of the system runs to the minimum value, the inverter should output the maximum power. Corresponding is the maximum angular frequency setting selected by the system, so that The following is the function of the active power given value with the angular frequency:

[0117] .

[0118] The angular frequency change caused by load change is used to predict the output of the active power given value, reduce the upper and lower limits of the angular frequency, speed up the stabilization of the angular frequency, and make the frequency fluctuation range smaller.

[0119] The swing equation and excitation equation of the synchronous engine are combined to derive the power frequency small signal model of the synchronous inverter and calculate the virtual moment of inertia. , excitation coefficient , voltage droop coefficient , frequency droop coefficient Then, the open-loop and closed-loop transfer functions of the angular frequency are analyzed to determine the appropriate integral coefficients , which makes the angular frequency of the synchronous inverter have better dynamic characteristics.

[0120] right Figure 2The energy storage converter shown is simulated using the control method of this embodiment, with a DC voltage source voltage setting value of 750V, an active power reference value of 0kW, a reactive power reference value of 0kVar, a rated voltage effective value of 220V, and a rated angular frequency of 314rad / s. The system is running at no load from 0 to 1s, a three-phase resistance load is suddenly added at t=1s, and a three-phase resistance load is suddenly reduced at t=2.5s.

[0121] from Figure 7 The simulation results of the primary frequency modulation shown in the figure show that when the load is applied at t=1s, the frequency drops by 0.101Hz, and when the load is reduced at t=2.5s, the frequency rises to the original 50Hz. Figure 8 The simulation results of the secondary frequency modulation shown in the figure show that when the load is applied at t=1s, the frequency drops by a difference of 0.082Hz, and after about 0.5s, the frequency recovers to 50Hz. When the load is reduced at t=2.5s, the frequency rises by a difference of 0.082Hz from the stable 50Hz, and then after about 0.5s, the frequency recovers to 50Hz. Fig. 9 The simulation results of the secondary frequency modulation with the shift method shown in the figure show that when the load is applied at t=1s, the frequency decreases by a difference of 0.076Hz, and after about 0.5s, the frequency recovers to 50Hz. When the load is reduced at t=2.5s, the frequency increases by a difference of 0.076Hz from the stable 50Hz, and then after about 0.5s, the frequency recovers to 50Hz. From the comparison of the frequency decrease, it can be seen that the secondary frequency modulation with the shift method can reduce the frequency variation range caused by load disturbances compared to the secondary frequency modulation algorithm, and better meet the stable operation of the microgrid system.

[0122] right Figure 2 The energy storage converter shown uses the control method of this embodiment to experimentally verify the primary frequency modulation, secondary frequency modulation, and secondary frequency modulation control algorithm with the translation method at a power level of 10kW. The system initially runs in a no-load state, and a 10kW resistive load is suddenly added at a certain moment to compare and observe the changes in the key parameter frequency under the three control strategies.

[0123] Fig.10 The frequency for the primary frequency modulation algorithm The experimental waveform of a sudden addition of 10kW load when the initial active power setting is 0kW and the reactive power setting is 0kVar. It can be seen that the frequency drops by about 0.107Hz at the moment of loading, and then the frequency remains stable. The frequency change amplitude is about 10.7%, which is in line with the damping parameter design principle, and the frequency transition time is about 80ms.

[0124] Fig.11 Frequency for the secondary frequency modulation algorithm When the initial active power setting value is 0kW and the reactive power setting value is 0kVar, the experimental waveform of a sudden addition of a 10kW load is shown. It can be seen that the frequency drops by about 0.085Hz when loading, and the frequency recovers to 50Hz after 720ms, with a frequency change of about 8.5%.

[0125] Fig.12 The frequency of the secondary frequency modulation algorithm when the translation method is introduced When the initial active power setting is 0kW and the reactive power setting is 0kVar, the experimental waveform of a sudden 10kW load is shown. It can be seen that the frequency drops by about 0.048Hz when loading, and the frequency recovers to 50Hz after 800ms, with a frequency change of about 4.8%.

[0126] Compared with primary frequency modulation, secondary frequency modulation can achieve frequency zero-difference control. Compared with the simple secondary frequency modulation control algorithm, secondary frequency modulation with the translation method can achieve a smaller frequency change range under the same load mutation. Under a 10kW load mutation, the change range is reduced by 43.53%, making it less likely to exceed the frequency limit. The control algorithm is effective because the sudden change in load will cause the given value of active power to change, which in turn causes the frequency to move.

[0127] Example 3

[0128] This embodiment provides an improved virtual synchronous inverter secondary frequency modulation control system, including:

[0129] Actual power acquisition module: used to obtain the actual instantaneous active power and actual instantaneous reactive power of the microgrid;

[0130] A control signal acquisition module based on angular frequency: used to obtain the angular frequency difference between the rated angular frequency and the virtual angular frequency, and compensate the actual angular frequency based on the PI proportional-integral control algorithm according to the angular frequency difference to obtain a control signal of the active-frequency control structure;

[0131] Active power-based control signal acquisition module: used to construct a function of active power given value varying with angular frequency based on translation method, and substitute the function into the control signal to obtain active power control signal;

[0132] A virtual back-EMF acquisition module is used to obtain the virtual back-EMF of the microgrid based on the actual instantaneous active power, the actual instantaneous reactive power and the active power control signal in the active-frequency control structure;

[0133] Secondary frequency modulation control module: used for performing secondary frequency modulation control on the switch tube of the virtual synchronous inverter based on the virtual back electromotive force.

[0134] Example 4

[0135] This embodiment provides a computer storage medium on which a computer program is stored. When the computer program is executed by a processor, the improved virtual synchronous inverter secondary frequency modulation control method as described in any step of Embodiment 2 is implemented.

[0136] Those skilled in the art will appreciate that the embodiments of the present application may be provided as methods, systems, or computer program products. Therefore, the present application may adopt the form of a complete hardware embodiment, a complete software embodiment, or an embodiment combining software and hardware. Moreover, the present application may adopt the form of a computer program product implemented on one or more computer-usable storage media (including but not limited to disk storage, CD-ROM, optical storage, etc.) containing computer-usable program codes.

[0137] The present application is described 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 application. It should be understood that each process and / or box in the flowchart and / or block diagram, as well as the combination of the processes and / or boxes in the flowchart and / or block diagram, can be implemented by computer program instructions. These computer program instructions can be provided to a processor of a general-purpose computer, a special-purpose computer, an embedded processor, or other programmable data processing device to generate a machine, so that the instructions executed by the processor of the computer or other programmable data processing device generate instructions for implementing the processes in the flowchart and / or block diagram. Figure 1 A process or multiple processes and / or boxes Figure 1 A device that provides the functions specified in a block or multiple blocks.

[0138] These computer program instructions may also be stored in a computer-readable memory capable of directing a computer or other programmable data processing device to operate in a specific manner, so that the instructions stored in the computer-readable memory produce an article of manufacture including an instruction device, which implements the process Figure 1 A process or multiple processes and / or boxes Figure 1 A function specified in one or more boxes.

[0139] These computer program instructions can also be loaded onto a computer or other programmable data processing device so that a series of operating steps are executed on the computer or other programmable device to produce a computer-implemented process, thereby providing instructions for implementing the process. Figure 1 A process or multiple processes and / or boxes Figure 1 The steps for the functions specified in one or more boxes.

[0140] The embodiments of the present invention are described above in conjunction with the accompanying drawings, but the present invention is not limited to the above-mentioned specific implementation methods. The above-mentioned specific implementation methods are merely illustrative and not restrictive. Under the enlightenment of the present invention, ordinary technicians in this field can also make many forms without departing from the scope of protection of the purpose of the present invention and the claims, which all fall within the protection of the present invention.

Claims

1. An improved virtual synchronous inverter secondary frequency modulation control method, characterized in that: include: Obtain the actual instantaneous active power and actual instantaneous reactive power of the microgrid; Obtaining an angular frequency difference between an angular frequency rated value and a virtual angular frequency, and compensating the actual angular frequency based on a PI proportional-integral control algorithm according to the angular frequency difference to obtain a control signal of an active-frequency control structure; Constructing a function of the active power given value varying with the angular frequency based on the translation method, and substituting the function into the control signal to obtain an active power control signal; In the active-frequency control structure, a virtual back-EMF of the microgrid is obtained based on the actual instantaneous active power, the actual instantaneous reactive power and the active power control signal; Secondary frequency modulation control is performed on the switch tube of the virtual synchronous inverter based on the virtual back electromotive force.

2. The improved virtual synchronous inverter secondary frequency modulation control method according to claim 1, characterized in that: The obtaining of the actual instantaneous active power and the actual instantaneous reactive power of the microgrid includes: Collect the three-phase voltage and three-phase current of the microgrid; The three-phase voltage and three-phase current are transformed into the d-axis voltage by coordinate transformation , d-axis current , q-axis voltage and q-axis current ; According to the d-axis voltage , d-axis current , q-axis voltage and q-axis current Calculate the actual instantaneous active power and actual instantaneous reactive power of the microgrid. The calculation formula is as follows: ， in, is the actual instantaneous active power, is the actual instantaneous reactive power, is the line impedance, is the load impedance, is the voltage amplitude of the AC output terminal at the midpoint of the bridge arm, For phase.

3. The improved virtual synchronous inverter secondary frequency modulation control method according to claim 1, characterized in that: The step of obtaining an angular frequency difference between the angular frequency rated value and the virtual angular frequency, and compensating the actual angular frequency based on the PI proportional-integral control algorithm according to the angular frequency difference to obtain a control signal of the active-frequency control structure includes: The angular frequency difference is obtained by subtracting the angular frequency rated value from the virtual angular frequency; The product of the angular frequency difference and the frequency droop coefficient is added to the output of the angular frequency difference after passing through the integrator, and the sum is used as the new virtual damping. The calculation formula is as follows: ， in, For the new virtual damping, is the frequency droop coefficient, is the integration coefficient, is the angular frequency rating, is the virtual angular frequency, Indicates time; The new virtual damping is added to the swing equation, so that the frequency droop coefficient and the integral coefficient constitute a PI controller to control the virtual angular frequency. The swing equation calculation formula is as follows: ， in, is the virtual inertia, is the active power given value input to the secondary frequency regulation system, is the actual instantaneous active power.

4. The improved virtual synchronous inverter secondary frequency modulation control method according to claim 3, characterized in that: The method of constructing a function of active power given value varying with angular frequency based on the translation method includes: According to the secondary frequency modulation process of the microgrid, the corresponding translation of the curve between active power and angular frequency under load change state is obtained; According to the translation situation, the range of the inverter output power and the range of the angular frequency in the microgrid, the function of the active power set value with the angular frequency is constructed as follows: ， in, is the angular frequency setting value, is the maximum value of the angular frequency setting, is the minimum value of the angular frequency setting, is the maximum difference in active power, is the given value of active power.

5. The improved virtual synchronous inverter secondary frequency modulation control method according to claim 4, characterized in that: The step of obtaining a virtual back electromotive force of the microgrid based on the actual instantaneous active power, the actual instantaneous reactive power and the active power control signal comprises: Calculating a phase angle of a virtual potential based on the actual instantaneous active power and the active power control signal; Based on the actual instantaneous reactive power, calculating the virtual excitation of the microgrid; Based on the phase angle and virtual excitation, a virtual back electromotive force of the microgrid is calculated.

6. The improved virtual synchronous inverter secondary frequency modulation control method according to claim 5, characterized in that: The step of calculating the phase angle of the virtual potential based on the actual instantaneous active power and the active power control signal comprises: The actual instantaneous active power calculation formula, the swing equation and the active power given value as a function of the angular frequency are combined to calculate the virtual angular frequency; The calculation formula for the phase angle based on the virtual angular frequency is: ， in, is the phase angle.

7. The improved virtual synchronous inverter secondary frequency modulation control method according to claim 5, characterized in that: The calculating of the virtual excitation of the microgrid based on the actual instantaneous reactive power includes: The virtual excitation calculation formula of the microgrid is as follows: ， in, is virtual excitation, is the reactive power reference value, is the actual instantaneous reactive power, is the reactive power regulation coefficient.

8. The improved virtual synchronous inverter secondary frequency modulation control method according to claim 5, characterized in that: The step of calculating the virtual back electromotive force of the microgrid based on the phase angle and the virtual excitation includes: The calculation formula of the virtual back electromotive force of the microgrid is as follows: ， in, is the virtual back EMF, is virtual excitation, is the phase angle.

9. The improved virtual synchronous inverter secondary frequency modulation control method according to claim 1, characterized in that: The secondary frequency modulation control of the switch tube of the virtual synchronous inverter based on the virtual back electromotive force includes: using SPWM sinusoidal pulse width modulation method, inputting the virtual back electromotive force into a PWM pulse width modulation loop and intersecting it with a triangular carrier to obtain a high-frequency PWM pulse width modulation pulse, and performing secondary frequency modulation control on the switch tube.

10. An improved virtual synchronous inverter secondary frequency modulation control system, characterized in that: include: Actual power acquisition module: used to obtain the actual instantaneous active power and actual instantaneous reactive power of the microgrid; A control signal acquisition module based on angular frequency: used to obtain the angular frequency difference between the rated angular frequency and the virtual angular frequency, and compensate the actual angular frequency based on the PI proportional-integral control algorithm according to the angular frequency difference to obtain a control signal of the active-frequency control structure; Active power-based control signal acquisition module: used to construct a function of active power given value varying with angular frequency based on translation method, and substitute the function into the control signal to obtain active power control signal; A virtual back-EMF acquisition module is used to obtain the virtual back-EMF of the microgrid based on the actual instantaneous active power, the actual instantaneous reactive power and the active power control signal in the active-frequency control structure; Secondary frequency modulation control module: used for performing secondary frequency modulation control on the switch tube of the virtual synchronous inverter based on the virtual back electromotive force.

11. A computer storage medium having a computer program stored thereon, characterized in that: When the computer program is executed by a processor, the improved virtual synchronous inverter secondary frequency modulation control method as claimed in any one of claims 1 to 9 is implemented.

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