A low voltage ride through control method and device of a virtual synchronous generator

Abstract

The application discloses a low-voltage ride-through control method and device of a virtual synchronous generator, and the method comprises the following steps: acquiring a grid voltage; judging whether a low-voltage fault occurs according to the grid voltage, if the low-voltage fault occurs, adopting model predictive control; and if the low-voltage fault does not occur, adopting balanced current control; the overcurrent problem caused by grid-side voltage drop is inhibited through switching of the model predictive control and the balanced current control, the power quality of the microgrid is improved, and the microgrid can realize grid connection friendly.

Description

Technical Field

[0001] This invention relates to a low-voltage ride-through control method and device for a virtual synchronous generator, belonging to the field of microgrid fault control technology. Background Technology

[0002] With the increasing penetration rate of distributed power sources, more and more distributed power sources with inverters as their main interface are being connected to the power grid. Among them, the virtual synchronous generator (VSG) provides inertial and damping support to the power grid by simulating the operating characteristics of a synchronous generator, meeting the grid's requirements for frequency and voltage regulation, and enabling distributed power sources to be connected to the grid in a friendly manner.

[0003] While the virtual inertia introduced by VSG can suppress high-frequency oscillations and enhance the inverter's disturbance rejection capability in steady state, it also makes it difficult to provide reactive power support under transient conditions, such as grid voltage dips, and easily leads to current surges. Currently, domestic and international scholars have conducted research on VSG low-voltage fault ride-through from different perspectives. For example, using energy storage devices, this control method has two modes: using the voltage drop depth as the switching signal, PI excitation control is used to restore voltage when the voltage drop is shallow, and when the voltage drops to a certain depth, the power system stabilizer is activated for strong excitation to quickly restore the generator terminal voltage. This method has good ride-through performance, but requires energy storage equipment, and the additional hardware increases costs and reduces the flexibility of the control system. Another approach is to switch the inverter's control strategy during grid-side faults, using traditional low-voltage fault ride-through control methods and VSG control to smoothly switch and suppress overcurrent, but the instantaneous fault response speed is slow and the internal parameter design is complex. Using hysteresis control to suppress current has a fast response speed and provides good suppression of inrush current. However, although hysteresis control has good dynamic performance, its sampling frequency is too high and the switching frequency is prone to be unstable, which leads to an increase in harmonic content and affects power quality. Summary of the Invention

[0004] The purpose of this invention is to overcome the shortcomings of the prior art and provide a low-voltage ride-through control method and device for a virtual synchronous generator. By switching between model predictive control and balanced current control, the overcurrent problem caused by grid-side voltage drop is suppressed, the power quality of the microgrid is improved, and the grid-friendly operation is achieved.

[0005] To achieve the above objectives, the present invention is implemented using the following technical solution:

[0006] In a first aspect, the present invention provides a low-voltage ride-through control method for a virtual synchronous generator, comprising:

[0007] Obtain the grid voltage;

[0008] The system determines whether a low-voltage fault has occurred based on the grid voltage. If a low-voltage fault occurs, model predictive control is employed. The model predictive control includes:

[0009] Obtain the rated current and rated voltage of the power grid to calculate the reference current;

[0010] Determine the inverter's operating state, obtain the grid voltage for the current cycle, the filter inductor current output by the inverter in each operating state, and the line equivalent inductor voltage, and perform abc / dq conversion;

[0011] Obtain the DC voltage input to the inverter, and calculate the predicted value of the filter inductor current output by the inverter in each operating state of the next cycle based on the abc / dq transformation result.

[0012] The absolute value of the error for each operating state is calculated based on the reference current and the predicted value of the filter inductor current output by the inverter in each operating state of the next cycle.

[0013] An objective function is constructed with the goal of minimizing the absolute value of the error, and the optimal working state for the next cycle is obtained by solving the objective function.

[0014] The inverter is switched on and off for the next cycle based on the optimal operating state for the next cycle.

[0015] Optionally, determining whether a low-voltage fault has occurred based on the grid voltage includes:

[0016] The grid voltage is transformed using an abc / dq converter to generate voltage e. d e q ;

[0017] If e d ≥0.9U N If so, no low-voltage fault occurred;

[0018] If e d <0.9U N If so, a low-voltage fault will occur;

[0019] Among them, U N This is the rated voltage of the power grid.

[0020] Optionally, the expression for obtaining the grid rated current and grid rated voltage to calculate the reference current is as follows:

[0021]

[0022]

[0023] In the formula, i′ dref 、i′qref The reference currents for the dq components are I and I, respectively. N U N These are the grid rated current and grid rated voltage, respectively, and e is the effective value after the grid voltage drops.

[0024] Optionally, the expression for calculating the predicted value of the filter inductor current output by the inverter in each operating state of the next cycle is as follows:

[0025]

[0026] In the formula, i di(k+1) i qi(k+1) These are the predicted values ​​of the inverter output filter inductor current in the (k+1)th cycle and the i-th state, respectively, representing the dq components; T is the cycle length, and L... f For filter inductance; e d(k) e q(k) These are the abc / dq transformation results of the grid voltage in the k-th cycle, U 1di(k) U 1qi(k) Let a, b, c, and dq be the abc / dq transformation results of the line equivalent inductance voltage of the inverter output in the i-th state of the k-th cycle, respectively. di(k) i qi(k) These are the abc / dq transformation results of the filter inductor current output by the inverter in the i-th state of the k-th cycle; u di(k+1) u qi(k+1) The predicted value of the filter inductor voltage at the inverter output in the (k+1)th cycle and the i-th state of the dq component.

[0027] Optionally, the predicted value u di(k+1) u qi(k+1) The acquisition includes:

[0028] Based on the DC voltage U input to the inverter dc Calculate the inverter output voltage for each operating state in the next cycle:

[0029]

[0030] In the formula, (S a S b S c ) indicates the working status, U aN(k+1) U bN(k+1) U cN(k+1) The working state for the next cycle (S) a S b S c Inverter output voltage;

[0031] For inverter output voltage U aN(k+1) U bN(k+1) UcN(k+1) Perform an abc / dq transformation to generate the predicted value u. di(k+1) u qi(k+1) .

[0032] Optionally, there are 8 working states, namely (0 0 0), (0 0 1), (0 1 0), (0 1 1), (1 00), (1 0 1), (1 1 0), and (1 1 1).

[0033] Optionally, the expression for calculating the absolute value of the error for each operating state based on the reference current and the predicted value of the filter inductor current output by the inverter in each operating state of the next cycle is as follows:

[0034] g i =|i′ dref -i di(k+1) |+|i′ qref -i qi(k+1) |

[0035] In the formula, i′ dref 、i′ qref The reference currents for the dq components are i and i', respectively. di(k+1) i qi(k+1) These are the predicted values ​​of the filter inductor current output by the inverter in the (k+1)th cycle and the ith state of the dq component.

[0036] Optionally, if no low-voltage fault occurs, balanced current control is employed; the employed balanced current control includes:

[0037] Obtain the voltage of the filter capacitor and the current of the filter inductor at the inverter output and perform an abc / αβ transformation to generate voltage U. α U β and current i α i β ;

[0038] According to voltage U α U β and current i α i β Calculate the active power P output by the VSG. e and reactive power Q e :

[0039] P e =U α *i α +U β *i β

[0040] Q e =U β *i α -U α*i β

[0041] Get active power command P * and reactive power command Q * And combined with active power P e and reactive power Q e Calculate the amplitude U of the voltage reference command * and phase angle θ * :

[0042]

[0043]

[0044] In the formula, E o E * For the mains voltage and its reference value, D q D p These are the voltage droop coefficient and damping coefficient, respectively; k is the inertia coefficient of excitation regulation; ω0 is the reference value of synchronous angular velocity; and j is the virtual moment of inertia.

[0045] According to the amplitude U of the voltage reference command * and phase angle θ * The reference voltage u of the synthesized VSG * :

[0046]

[0047] Reference voltage u * Perform an abc / dq transformation to generate a voltage. According to voltage Calculate the reference current i dref i qref :

[0048]

[0049]

[0050] In the formula, For grid voltage E o The positive-order dq components, R, L s Both are the line equivalent resistance and line equivalent inductance, and ω is the angular frequency of the grid voltage;

[0051] Obtain the grid-side current and perform an abc / dq transformation to generate voltage i. d i q Combined with the reference current i dref i qref Calculate the reference voltage

[0052]

[0053]

[0054] In the formula, K p T i All are PI parameters;

[0055] For reference voltage Perform dq / abc transformation to generate the reference voltage for current inner loop control.

[0056] According to the reference voltage Generate an SWPM wave and control the inverter's on / off state based on the SWPM wave.

[0057] Optionally, the control method further includes, during model predictive control, controlling the output reference current i based on the balanced current. dref i qref The predicted value i of the model predictive control output di(k+1) i qi(k+1) Calculate the active power tracking power P of the system f and system reactive power Q f :

[0058]

[0059]

[0060] The system active power follower P f and system reactive power Q f As the input to the balanced current control, it ensures the reference current i of the balanced current control output. dref i qref The predicted value i of the model predictive control output di(k+1) i qi(k+1) .

[0061] In a second aspect, the present invention provides a low-voltage ride-through control device for a virtual synchronous generator, comprising a judgment module, a model prediction control module, a balanced current control module, a current inner loop control module, an SPWM module, a power calculation module, a value function module, and switches K1, K2, K3, and K4.

[0062] The balancing circuit control module is connected to the signal terminal via switch K1, and the signal terminal includes the active power command P. * Reactive power command Q * The active power P output by VSG e and reactive power Q e The balancing circuit control module controls the power output according to the active power command P.* Reactive power command Q * The active power P output by VSG e and reactive power Q e Calculate the reference current i dref i qref ;

[0063] The inner current control module is connected to the output of the balance circuit control module via switch K2. The inner current control module is based on the reference current i. dref i qref Calculate the reference voltage u2* for the inner loop current control;

[0064] The SWPM module is connected to the output of the current inner loop control module, and the SWPM module is based on the reference voltage. Generate an SWPM wave and send it to the control terminal of the inverter;

[0065] The model prediction control module is used to calculate the predicted value i of the filter inductor current output by the inverter in each operating state of the next cycle. di(k+1) i qi(k+1) ;

[0066] The value function module is connected to the output of the model prediction control module via switch K4. The value function module is based on the predicted value i. di(k+1) i qi(k+1) Calculate the optimal operating state of the inverter for the next cycle and send it to the inverter's control terminal.

[0067] The power calculation module is connected to the output terminals of the predictive control module and the balancing current control module, and is also connected to the input terminal of the balancing current control module via switch K3. During model predictive control, the power calculation module calculates the reference current i output by the balancing current control module. dref i qref The predicted value i of the model predictive control output di(k+1) i qi(k+1) Calculate the active power tracking power P of the system f and system reactive power Q f And send it to the balanced current control module;

[0068] The judgment module is connected to the control terminals of switches K1, K2, K3, and K4 respectively. The judgment module determines whether a low-voltage fault has occurred based on the grid voltage. If no low-voltage fault has occurred, it controls switches K1 and K2 to close and switches K3 and K4 to open. If a low-voltage fault has occurred, it controls switches K1 and K2 to open and switches K3 and K4 to close.

[0069] Compared with the prior art, the beneficial effects achieved by the present invention are as follows:

[0070] This invention provides a low-voltage ride-through control method and device for a virtual synchronous generator. When a low-voltage ride-through fault occurs on the grid side, overcurrent is suppressed through smooth mode switching. Specifically, model predictive control is used when the fault occurs, and switching back to balanced current control is performed after the fault ends. This method requires no additional hardware and, compared with traditional low-voltage fault ride-through control methods, model predictive control has good adaptability and robustness, and does not require inner-loop current control and PWM modulation, making the control scheme easier to implement. Furthermore, compared with hysteresis control, model predictive control does not cause resonance problems due to changing switching frequencies. Therefore, this technology, utilizing model predictive control combined with the requirements of low-voltage ride-through, enables the inverter to have good tracking performance, faster response speed, and reduced peak and harmonic content of output current during grid-side faults, thus meeting grid connection requirements. Attached Figure Description

[0071] Figure 1 This is a schematic diagram of a low-voltage ride-through control method for a virtual synchronous generator provided in Embodiment 1 of the present invention;

[0072] Figure 2 This is a schematic diagram of the topology of the virtual synchronous generator (VSG) provided in Embodiment 1 of the present invention;

[0073] Figure 3 This is a schematic diagram of the model predictive control process provided in Embodiment 1 of the present invention;

[0074] Figure 4 This is a schematic diagram of the virtual synchronization control algorithm provided in Embodiment 1 of the present invention;

[0075] Figure 5 This is a schematic diagram of the balanced current control process provided in Embodiment 1 of the present invention;

[0076] Figure 6 This is a schematic diagram of a low-voltage ride-through control device for a virtual synchronous generator provided in Embodiment 2 of the present invention. Detailed Implementation

[0077] The present invention will be further described below with reference to the accompanying drawings. The following embodiments are only used to more clearly illustrate the technical solution of the present invention, and should not be used to limit the scope of protection of the present invention.

[0078] Example 1:

[0079] like Figure 1 As shown, this invention provides a low-voltage ride-through control method for a virtual synchronous generator, comprising the following steps:

[0080] Obtain the grid voltage;

[0081] Determine if a low-voltage fault has occurred based on the grid voltage.

[0082] If a low-voltage fault occurs, model predictive control will be used.

[0083] If no low-voltage fault occurs, balanced current control is used.

[0084] like Figure 2 As shown, the topology of the virtual synchronous generator (VSG) sampled in this embodiment includes (inverters S1, S2, S3, S4, S5, S6) and an LCL filter (filter inductor L). f Line equivalent inductance L s Filter capacitor C f DC voltage U dc The equivalent resistance of the line is R.

[0085] Based on the above topology, determining whether a low-voltage fault has occurred based on the grid voltage includes:

[0086] The grid voltage (e) a e b e c And perform an abc / dq transformation to generate voltage e. d e q ;

[0087] If e d ≥0.9U N If so, no low-voltage fault occurred;

[0088] If e d <0.9U N If so, a low-voltage fault will occur;

[0089] Among them, U N This is the rated voltage of the power grid.

[0090] like Figure 3 As shown, ignoring the equivalent line resistance R, the PLL is a phase-locked loop used to obtain the parameter θ of the abc / dq transformation;

[0091] Model predictive control includes:

[0092] S101. Obtain the rated current and rated voltage of the power grid and calculate the reference current.

[0093]

[0094]

[0095] In the formula, i′ dref 、i′ qref The reference currents for the dq components are I and I, respectively. N U NThese are the grid rated current and grid rated voltage, respectively, and e is the effective value after the grid voltage drops.

[0096] S102. Determine the operating state of the inverter. Since the upper and lower bridge arms of the converter are prohibited from being turned on or off simultaneously, the operating states of the inverter S1-S6 are represented by (S... a S b S c )express:

[0097]

[0098]

[0099]

[0100] There are a total of 8 operating states for the 6 inverters, namely (0 0 0), (0 0 1), (0 1 0), (0 1 1), (1 00), (1 0 1), (1 1 0), and (1 1 1). The 8 different operating states are numbered i = 1, 2, 3, 4, 5, 6, 7, 8.

[0101] Get the grid voltage for the current period (e a e b e c ) k The current of the filter inductor output of the inverter in each operating state (i a i b i c ) k and the line equivalent inductance voltage (U) 1a U 1b U 1c ) k And perform the abc / dq transformation.

[0102] S103. Obtain the DC voltage U input to the inverter. dc(k+1) The predicted values ​​of the filter inductor current output by the inverter in each operating state of the next cycle are calculated by combining the abc / dq transformation results.

[0103]

[0104] In the formula, i di(k+1) i qi(k+1) These are the predicted values ​​of the inverter output filter inductor current in the (k+1)th cycle and the i-th state, respectively, representing the dq components; T is the cycle length, and L... f For filter inductance; e d(k) e q(k) These are the abc / dq transformation results of the grid voltage in the k-th cycle, U 1di(k) U1qi(k) Let a, b, c, and dq be the abc / dq transformation results of the line equivalent inductance voltage of the inverter output in the i-th state of the k-th cycle, respectively. di(k) i qi(k) These are the abc / dq transformation results of the filter inductor current output by the inverter in the i-th state of the k-th cycle; u di(k+1) u qi(k+1) The predicted value of the filter inductor voltage at the inverter output in the (k+1)th cycle and the i-th state of the dq component.

[0105] Among them, the predicted value u di(k+1) u qi(k+1) The acquisition includes:

[0106] Based on the DC voltage U input to the inverter dc Calculate the inverter output voltage for each operating state in the next cycle:

[0107]

[0108] In the formula, (S a S b S c ) indicates the working status, U aN(k+1) U bN(k+1) U cN(k+1) The working state for the next cycle (S) a S b S c Inverter output voltage;

[0109] For inverter output voltage U aN(k+1) U bN(k+1) U cN(k+1) Perform an abc / dq transformation to generate the predicted value u. di(k+1) u qi(k+1) .

[0110] S104. Calculate the absolute value of the error for each operating state based on the reference current and the predicted value of the filter inductor current output by the inverter in each operating state of the next cycle.

[0111] g i =|i′ dref -i di(k+1) |+|i′ qref -i qi(k+1) |

[0112] In the formula, i′ dref 、i′ qref The reference currents for the dq components are i and i', respectively. di(k+1) i qi(k+1) These are the predicted values ​​of the filter inductor current output by the inverter in the (k+1)th cycle and the ith state of the dq component.

[0113] S105. Construct an objective function with the goal of minimizing the absolute value of the error, and solve the objective function to obtain the optimal working state for the next cycle;

[0114] S106. Control the inverter's on / off state for the next cycle based on the optimal operating state for the next cycle.

[0115] Balanced current control includes:

[0116] like Figure 4 As shown:

[0117] S201. Obtain the output voltage of the filter capacitor and the current of the filter inductor from the inverter and perform an abc / αβ transformation to generate voltage U. α U β and current i α i β ;

[0118] S202, according to voltage U α U β and current i α i β Calculate the active power P output by the VSG. e and reactive power Q e :

[0119] P e =U α *i α +U β *i β

[0120] Q e =U β *i α -U α *i β

[0121] S203, Obtain active power command P * and reactive power command Q * And combined with active power P e and reactive power Q e Calculate the amplitude U of the voltage reference command * and phase angle θ * :

[0122]

[0123]

[0124] In the formula, E o E * For the mains voltage and its reference value, D q Dp These are the voltage droop coefficient and damping coefficient, respectively; k is the inertia coefficient of excitation regulation; ω0 is the reference value of synchronous angular velocity; and j is the virtual moment of inertia.

[0125] S204, According to the amplitude U of the voltage reference command * and phase angle θ * The reference voltage u of the synthesized VSG * :

[0126]

[0127] like Figure 5 As shown:

[0128] S205, Set the reference voltage u * Perform an abc / dq transformation to generate a voltage. According to voltage Calculate the reference current i dref i qref :

[0129]

[0130]

[0131] In the formula, For grid voltage E o The positive-order dq components, R, L s Both are the line equivalent resistance and line equivalent inductance, and ω is the angular frequency of the grid voltage;

[0132] S206. Obtain the grid-side current and perform an abc / dq transformation to generate voltage i. d i q Combined with the reference current i dref i qref Calculate the reference voltage

[0133]

[0134]

[0135] In the formula, K p T i All are PI parameters;

[0136] S207, Reference Voltage Perform dq / abc transformation to generate the reference voltage for current inner loop control.

[0137] S208, Based on reference voltage Generate an SWPM wave and control the inverter's on / off state based on the SWPM wave.

[0138] The control method in this embodiment also includes, during model predictive control, controlling the output reference current i based on the balanced current. dref i qref The predicted value i of the model predictive control output di(k+1) i qi(k+1) Calculate the active power tracking power P of the system f and system reactive power Q f :

[0139]

[0140]

[0141] The system active power follower P f and system reactive power Q f As the input for balanced current control, i.e., Q * -Q e P * -P e To ensure the reference current i of the balanced current control output dref i qref The predicted value i of the model predictive control output di(k+1) i qi(k+1) By tracking the current value, it can be ensured that the reverse switching process will not cause overcurrent.

[0142] Example 2:

[0143] like Figure 6 As shown, the present invention provides a low-voltage ride-through control device for a virtual synchronous generator, including a judgment module, a model prediction control module, a balanced current control module, a current inner loop control module, an SPWM module, a power calculation module, a value function module, and switches K1, K2, K3, and K4.

[0144] The balance circuit control module is connected to the signal terminal via switch K1. The signal terminal includes the active power command P. * Reactive power command Q * The active power P output by VSG e and reactive power Q e The balancing circuit control module controls the power output according to the active power command P. * Reactive power command Q * The active power P output by VSG e and reactive power Q e Calculate the reference current i dref i qref ;

[0145] The current inner loop control module is connected to the output of the balance circuit control module via switch K2. The current inner loop control module controls the current based on the reference current i. dref i qref Calculate the reference voltage for the inner loop control of the current.

[0146] The SPWM module is connected to the output of the current inner loop control module. The SPWM module adjusts the voltage based on the reference voltage. Generate an SWPM wave and send it to the control terminal of the inverter;

[0147] The model predictive control module is used to calculate the predicted value i of the filter inductor current output by the inverter in each operating state of the next cycle. di(k+1) i qi(k+1) ;

[0148] The value function module is connected to the output of the model prediction control module via switch K4. The value function module calculates the value based on the predicted value i. di(k+1) i qi(k+1) Calculate the optimal operating state of the inverter for the next cycle and send it to the inverter's control terminal.

[0149] The power calculation module is connected to the outputs of the predictive control module and the balancing current control module, and is also connected to the input of the balancing current control module via switch K3. During model predictive control, the power calculation module calculates the reference current i output by the balancing current control module. dref i qref The predicted value i of the model predictive control output di(k+1) i qi(k+1) Calculate the active power tracking power P of the system f and system reactive power Q f And send it to the balanced current control module; ensure the reference current i of the balanced current control output dref i qref The predicted value i of the model predictive control output di(k+1) i qi(k+1) By tracking the current value, it can be ensured that the reverse switching process will not cause overcurrent;

[0150] The judgment module is connected to the control terminals of switches K1, K2, K3, and K4 respectively. The judgment module determines whether a low-voltage fault has occurred based on the grid voltage. If no low-voltage fault has occurred, it controls switches K1 and K2 to close and switches K3 and K4 to open. If a low-voltage fault has occurred, it controls switches K1 and K2 to open and switches K3 and K4 to close.

[0151] Those skilled in the art will understand that embodiments of this application can be provided as methods, systems, or computer program products. Therefore, this application can take the form of a completely hardware embodiment, a completely software embodiment, or an embodiment combining software and hardware aspects. Furthermore, this application can take the form of a computer program product embodied on one or more computer-usable storage media (including but not limited to disk storage, CD-ROM, optical storage, etc.) containing computer-usable program code.

[0152] This application is described with reference to flowchart illustrations and / or block diagrams of methods, apparatus (systems), and computer program products according to embodiments of this application. It will be understood that each block of the flowchart illustrations and / or block diagrams, and combinations of blocks in the flowchart illustrations and / or block diagrams, can be implemented by computer program instructions. These computer program instructions can be provided to a processor of a general-purpose computer, special-purpose computer, embedded processor, or other programmable data processing apparatus to produce a machine, such that the instructions, which execute via the processor of the computer or other programmable data processing apparatus, generate instructions for implementing the flowchart... Figure 1 One or more processes and / or boxes Figure 1 A device that provides the functions specified in one or more boxes.

[0153] These computer program instructions may also be stored in a computer-readable storage medium that can direct a computer or other programmable data processing device to function in a particular manner, such that the instructions stored in the computer-readable storage medium produce an article of manufacture including instruction means, which are implemented in a process Figure 1 One or more processes and / or boxes Figure 1 The function specified in one or more boxes.

[0154] These computer program instructions may also be loaded onto a computer or other programmable data processing equipment to cause a series of operational steps to be performed on the computer or other programmable equipment to produce a computer-implemented process, thereby providing instructions that execute on the computer or other programmable equipment for implementing the process. Figure 1 One or more processes and / or boxes Figure 1 The steps of the function specified in one or more boxes.

[0155] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the technical principles of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A low-voltage ride-through control method for a virtual synchronous generator, characterized in that, include: Obtain the grid voltage; The system determines whether a low-voltage fault has occurred based on the grid voltage. If a low-voltage fault occurs, model predictive control is used. If no low-voltage fault occurs, balanced current control is used; The model predictive control includes: Obtain the rated current and rated voltage of the power grid to calculate the reference current; Determine the inverter's operating state, obtain the grid voltage for the current cycle, the filter inductor current output by the inverter for each operating state, and the line equivalent inductor voltage, and then perform... Transformation; Obtain the DC voltage input to the inverter, combined with The transformation results are used to calculate the predicted values ​​of the filter inductor current output by the inverter in each operating state of the next cycle; The absolute value of the error for each operating state is calculated based on the reference current and the predicted value of the filter inductor current output by the inverter in each operating state of the next cycle. An objective function is constructed with the goal of minimizing the absolute value of the error, and the optimal working state for the next cycle is obtained by solving the objective function. The inverter is switched on and off for the next cycle based on the optimal operating state for the next cycle. The control method further includes calculating the system active power and system reactive power during model predictive control based on the reference current output by the balanced current control and the predicted value output by the model predictive control. The system's active power and reactive power are used as inputs to the balanced current control, ensuring that the reference current following model predicts the output value of the balanced current control.

2. The low-voltage ride-through control method for a virtual synchronous generator according to claim 1, characterized in that, The method of determining whether a low-voltage fault has occurred based on the grid voltage includes: Combine the grid voltage with Transformation, generating voltage ; like If so, no low-voltage fault occurred; like If so, a low-voltage fault will occur; in, This is the rated voltage of the power grid.

3. The low-voltage ride-through control method for a virtual synchronous generator according to claim 1, characterized in that, The expressions for obtaining the grid rated current and grid rated voltage and calculating the reference current are as follows: In the formula, , They are respectively The reference current of the component, These are the grid rated current and grid rated voltage, respectively. This is the effective value after the grid voltage drops.

4. The low-voltage ride-through control method for a virtual synchronous generator according to claim 1, characterized in that, The expression for calculating the predicted value of the filter inductor current output by the inverter in each operating state of the next cycle is as follows: In the formula, They are respectively The first component The first cycle The predicted value of the filter inductor current at the inverter output in this state; For the duration of the cycle, For filtering inductors; The first The grid voltage in each cycle Transformation result The first The first cycle The line equivalent inductance voltage of the inverter output in this state Transformation result The first The first cycle The current of the filter inductor output from the inverter in this state Transformation result; for The first component The first cycle The predicted value of the filter inductor voltage at the inverter output in this state.

5. The low-voltage ride-through control method for a virtual synchronous generator according to claim 4, characterized in that, The predicted value The acquisition includes: Based on the DC voltage input to the inverter Calculate the inverter output voltage for each operating state in the next cycle: In the formula, In working state, For the next cycle of work status Inverter output voltage; Inverter output voltage conduct Transformation to generate predicted values .

6. The low-voltage ride-through control method for a virtual synchronous generator according to claim 1, characterized in that, There are 8 working states, namely: , , , , , , , .

7. The low-voltage ride-through control method for a virtual synchronous generator according to claim 1, characterized in that, The expression for calculating the absolute value of the error for each operating state based on the reference current and the predicted value of the filter inductor current output by the inverter in each operating state of the next cycle is as follows: In the formula, They are respectively The reference current of the component, They are respectively The first component The first cycle The predicted value of the filter inductor current at the inverter output in this state.

8. The low-voltage ride-through control method for a virtual synchronous generator according to claim 1, characterized in that, The use of balanced current control includes: Obtain the voltage of the filter capacitor and the current of the filter inductor at the inverter output and perform... Transformation, generating voltage and current ; According to voltage and current Calculate the active power output of the VSG. and reactive power : Get active power command and reactive power command and combined with active power and reactive power Calculate the amplitude of the voltage reference command and phase angle : In the formula, The mains voltage and its reference value. These are the voltage droop coefficient and the damping coefficient, respectively. The inertia coefficient for excitation regulation. This is a reference value for the synchronous angular velocity. This is a virtual moment of inertia; According to the amplitude of the voltage reference command and phase angle Reference voltage of synthesized VSG : Reference voltage conduct Transformation, generating voltage According to voltage Calculate the reference current , : In the formula, , For grid voltage orthogonal order Quantity, These are the equivalent resistance and equivalent inductance of the line. The angular frequency of the grid voltage; Obtain grid-side current and perform Transformation, generating voltage Combined with reference current , Calculate the reference voltage : In the formula, All are PI parameters; For grid voltage The transformed voltage; For reference voltage conduct Transformation to generate the reference voltage for the inner current loop control. : According to the reference voltage Generate an SWPM wave and control the inverter's on / off state based on the SWPM wave.

9. The low-voltage ride-through control method for a virtual synchronous generator according to claim 8, characterized in that, During model predictive control, the reference current output is controlled based on the balanced current. , The predicted value of the model predictive control output Computing system active power tracking and system reactive power following : The system's active power follows the power and system reactive power following As the input to the balanced current control, it ensures the reference current of the balanced current control output. , Predicted values ​​of the model predictive control output .

10. A low-voltage ride-through control device for a virtual synchronous generator, characterized in that, It includes a judgment module, a model predictive control module, a balanced current control module, a current inner loop control module, an SPWM module, a power calculation module, a value function module, and a switch. ,switch ,switch ,switch ; The balanced current control module is controlled via a switch. Connected to a signal terminal, the signal terminal including an active power command Reactive power command Active power output by VSG and reactive power The balanced current control module controls the current according to the active power command. Reactive power command Active power output by VSG and reactive power Calculate the reference current , ; The current inner loop control module is controlled via a switch. Connected to the output of the balanced current control module, the inner current loop control module controls the current based on the reference current. , Calculate the reference voltage for the inner loop control of the current. ; The SWPM module is connected to the output terminal of the current inner loop control module, and the SWPM module is based on the reference voltage. Generate an SWPM wave and send it to the control terminal of the inverter; The model prediction control module is used to calculate the predicted values ​​of the filter inductor current output by the inverter in each operating state of the next cycle. ; The value function module is controlled by a switch. Connected to the output of the model prediction control module, the value function module calculates the predicted value. Calculate the optimal operating state of the inverter for the next cycle and send it to the inverter's control terminal. The power calculation module is connected to the output terminals of the predictive control module and the balanced current control module, and is also connected via a switch. Connected to the input of the balanced current control module, the power calculation module calculates the reference current output by the balanced current control during model predictive control. , The predicted value of the model predictive control output Computing system active power tracking and system reactive power following And send it to the balanced current control module; The judgment module is connected to the switch respectively. ,switch ,switch ,switch The control terminal of the circuit breaker determines whether a low-voltage fault has occurred based on the mains voltage. If no low-voltage fault has occurred, the control switch is activated. ,switch Close, switch ,switch Disconnect; if a low-voltage fault occurs, control switch ,switch Disconnect, switch ,switch closure.

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