Grid-forming converter control method and system

Abstract

This invention discloses a control method and system for a grid-connected converter. The method includes: acquiring the grid-connected point voltage of the converter; determining the negative-sequence current setpoint of the converter based on the negative-sequence component of the grid-connected point voltage; acquiring the negative-sequence component in the current grid-connected current command of the converter; generating a negative-sequence voltage regulation amount based on the deviation between the negative-sequence component in the current grid-connected current command and the negative-sequence current setpoint; using the negative-sequence voltage regulation amount to compensate for the current virtual internal potential of the converter, generating an AC voltage command, and controlling the converter according to the AC voltage command. This invention's control method can maintain the positive-sequence voltage support capability of the grid-connected converter while performing precise quantitative control of the negative-sequence current, thereby reducing the overcurrent risk under asymmetrical grid conditions and improving the stability and adaptability of the converter's grid-connected operation.

Description

Technical Field

[0001] This invention relates to the field of new energy power generation technology, and in particular to a grid-type converter control method and system. Background Technology

[0002] As the proportion of renewable energy generation continues to increase, renewable energy grid-connected systems, mainly based on grid-connected converters, are showing signs of declining voltage and frequency stability. Grid-connected converters, because they can simulate the operating characteristics of synchronous generators and autonomously establish voltage and frequency, are considered a key technology for solving the stability problems of weak power grids.

[0003] However, when an asymmetrical fault occurs in the power grid (such as single-phase grounding, two-phase short circuit, etc.), a negative sequence component will appear in the grid connection point voltage. If the grid-connected converter still operates in a symmetrical manner, its output negative sequence current cannot be effectively controlled. This may not only lead to the inability to provide effective negative sequence support to the power grid, but may also cause problems such as converter overcurrent, increased power module losses, and aggravated DC side voltage fluctuations due to excessive negative sequence current. Summary of the Invention

[0004] The technical problem to be solved by the present invention is to provide a grid-type converter control method that can achieve precise quantitative control of negative sequence current while retaining the positive sequence voltage support capability of the grid-type converter.

[0005] To address the aforementioned technical problems, firstly, a grid-type converter control method is provided, comprising: Collect the grid connection point voltage of the converter; The negative sequence current setting value of the converter is determined based on the negative sequence component of the grid connection point voltage; Obtain the negative sequence component in the current grid current command of the converter; Based on the deviation between the negative sequence component in the current grid current command and the negative sequence current set value, a negative sequence voltage adjustment amount is generated; The negative sequence voltage regulation is used to compensate for the current virtual internal potential of the converter, an AC voltage command is generated, and the converter is controlled according to the AC voltage command.

[0006] Secondly, a grid-type converter control system is provided, including a converter and a controller, wherein the controller is used to execute the steps of the above-described grid-type converter control method to control the converter.

[0007] In the aforementioned grid-connected converter control method and system, the grid-connected point voltage is collected and the negative-sequence component of the converter is extracted to determine the negative-sequence current setpoint of the converter. Based on this, the quantitative demand of the grid for negative-sequence support from the converter is determined. Furthermore, the negative-sequence component of the current grid-connected current command, reflecting the negative-sequence current that the converter will output under the current control strategy, is obtained and compared with the negative-sequence current setpoint. The deviation between the negative-sequence component in the current grid-connected current command and the negative-sequence current setpoint is determined, thereby generating a negative-sequence voltage regulation quantity to compensate for the current virtual internal potential of the converter. It can be seen that the compensation effect occurs within the converter's internal electromotive force, thus enabling the converter to output the desired negative-sequence current without disrupting the original grid-connected voltage support characteristics. Finally, an AC voltage command is generated based on the compensated virtual internal potential, achieving closed-loop precise quantitative control of the converter. Therefore, this method can maintain the positive sequence voltage support capability of the grid-connected converter while accurately quantifying and controlling the negative sequence current, reducing the overcurrent risk under asymmetrical grid conditions, and improving the stability and adaptability of the converter in grid-connected operation. Attached Figure Description

[0008] Figure 1 This is a schematic diagram of the converter topology; Figure 2 This is a flowchart illustrating the grid-type converter control method provided in the first embodiment of the present invention; Figure 3 yes Figure 2 A schematic diagram of the specific flow of S120 in the control method of the grid-type converter shown; Figure 4 This is a schematic diagram illustrating the principle of generating the negative sequence current setpoint of the converter in the first embodiment of the present invention; Figure 5 yes Figure 4 The diagram shows the specific implementation principle of the amplitude limiting step in the instruction. Figure 6 yes Figure 2 A schematic diagram of the specific flow of S140 in the control method of the grid-type converter shown. Figure 7 This is a schematic diagram illustrating the principle of generating the negative sequence voltage regulation of the converter in the first embodiment of the present invention; Figure 8 yes Figure 2 A schematic diagram of the specific flow of S150 in the control method of the grid-type converter shown. Figure 9 This is a schematic diagram illustrating the generation principle of the converter's drive signal in the first embodiment of the present invention; Figure 10 This is a flowchart illustrating the grid-type converter control method provided in the second embodiment of the present invention; Figure 11 yes Figure 10 A schematic diagram of the specific flow of S250 in the control method of the grid-type converter shown. Figure 12 This is a schematic diagram illustrating the principle of generating AC voltage command compensation for the converter in the first embodiment of the present invention. Figure 13 yes Figure 10 A schematic diagram of the specific flow of S260 in the control method of the grid-type converter shown. Figure 14 This is a schematic diagram illustrating the generation principle of the converter's drive signal in the second embodiment of the present invention; Figure 15 This is a simulation diagram of the grid-type converter control method provided in the second embodiment of the present invention when a grid asymmetric fault occurs. Figure 16 The simulation results are shown when a power grid asymmetric fault occurs, but the control method of this invention is not used in the general network control method. Figure 17 The simulation results are shown in the figure after adopting the conventional negative sequence current control scheme when a power grid asymmetric fault occurs. Figure 18 This is a schematic diagram of the structure of a grid-type converter control system provided in an embodiment of the present invention. Detailed Implementation

[0009] To better understand the technical content of this invention, the technical solution of this invention will be further introduced and explained below with reference to the schematic diagram, but it is not limited thereto.

[0010] The control method provided in this invention can be applied to grid-connected converters. During operation, the grid-connected converter simulates the inertia and voltage source characteristics of a synchronous generator by controlling the phase and amplitude of its virtual internal potential, and uses this as a reference to establish and maintain the grid connection point voltage. For example... Figure 1 As shown, the power module of the converter (mainly consisting of a PWM rectifier bridge composed of power devices and DC capacitors) is connected to an AC filter inductor. AC filter capacitor Connected to the grid connection point, the grid connection point is connected to the grid impedance. Connected to the power grid. The AC side voltage of the converter is filtered to form the grid connection point voltage. The output current of the converter It is injected into the power grid, and its DC side collects electrical energy through the DC bus. The DC bus capacitor is connected to the DC bus capacitor, and the DC side voltage is... It is indicated that, in the figure This is the drive signal for the converter power module. The grid-connected converter control method of this invention generates a negative-sequence voltage regulation quantity based on the deviation between the negative-sequence current setpoint (reflecting the negative-sequence support target of the converter) and the negative-sequence component (reflecting the negative-sequence current to be output by the converter under the current control strategy). This regulation quantity is used to compensate for the current virtual internal potential of the converter. Since the compensation occurs at the virtual internal potential level, the grid-connected voltage support characteristics of the positive-sequence component are fully preserved, while the negative-sequence component is actively reshaped to a level compatible with the grid's negative-sequence voltage. The compensated virtual internal potential is used to generate AC voltage commands and control the converter accordingly. This allows the grid-connected converter to achieve closed-loop precise quantitative control of the negative-sequence current without changing its inherent control architecture. That is, while maintaining the positive-sequence voltage support capability of the grid-connected converter, precise quantitative control of the negative-sequence current can be achieved, effectively improving the controllability of the negative-sequence current, thereby reducing the overcurrent risk under asymmetrical grid conditions, and further improving the stability and adaptability of the converter's grid-connected operation. The following is a related analysis. Figure 2 The specific workflow of the grid-type converter control method provided in the first embodiment of the present invention will be described in detail.

[0011] Please see Figure 2 As shown, Figure 2 This is a flowchart illustrating the grid-type converter control method provided in the first embodiment of the present invention. In the embodiment shown in the figures, the grid-type converter control method includes the following steps: S110: Collects the grid connection point voltage and output current of the converter.

[0012] In this invention, grid-side parameters such as the grid connection point voltage and output current of the converter connected to the power grid are collected.

[0013] S120. Determine the negative sequence current setting value of the converter based on the negative sequence component of the grid connection point voltage.

[0014] In this invention, when an asymmetrical fault occurs at the grid connection point, the grid connection point voltage is extracted. Negative order components in the stationary coordinate system And perform coordinate system transformation to obtain the grid connection point voltage. Negative-order components; such as Figure 4 As shown, the negative order component includes the negative order d-axis component. and negative q-axis components , The phase angle for network operation, i.e., the phase of the current virtual internal potential, is shown in the figure. Specifically, the phase of the virtual internal potential can be used to adjust the negative sequence component. Perform coordinate transformation to obtain the grid connection point voltage. The corresponding d-axis components in the dq coordinate system and q-axis components .

[0015] Specifically, such as Figure 3 As shown, step S120 specifically includes the following steps S121-S122: S121. Generate an initial value for the negative sequence current based on the negative sequence component of the grid connection point voltage and the preset negative sequence current support coefficient.

[0016] In this invention, the negative sequence current setting value represents the negative sequence current that the grid-connected converter is expected to inject into the grid. In this embodiment, the initial negative sequence current setting value, including the initial negative sequence active current value and the initial negative sequence reactive current value, can be generated based on the negative sequence component of the grid connection point voltage, the preset negative sequence active current support coefficient, and the negative sequence reactive current support coefficient.

[0017] Specifically, this step may include: obtaining the d-axis and q-axis components of the negative sequence component of the grid connection point voltage in the negative sequence coordinate system; and calculating the initial value of the negative sequence current of the converter based on the d-axis and q-axis components of the negative sequence component of the grid connection point voltage using the following formula: ;in, and These are the initial settings for the negative sequence active current and the negative sequence reactive current of the converter, respectively. and These are the d-axis and q-axis components of the negative sequence voltage at the grid connection point, respectively. and These are the rated current and rated voltage of the converter, respectively. and These are the preset negative-sequence active current support coefficient and negative-sequence reactive current support coefficient for the converter. These coefficients characterize the preset parameters of the converter's support for the grid's negative-sequence current under asymmetrical grid conditions. Understandably, the magnitude of these support coefficients can be set according to grid connection guidelines or upper-level dispatch instructions to determine the proportional relationship between the required output negative-sequence active and reactive currents of the converter and the negative-sequence component of the grid connection point voltage. Specifically, this is achieved by adjusting... and The magnitude of the current can be used to quantify and control the negative-sequence active and reactive current components injected into the grid by the converter, so as to support the voltage at the grid connection point and assist in the active power balance of the power system during asymmetrical faults.

[0018] S122. Limit the initial value of the negative sequence current based on the current limiting condition to obtain the set value of the negative sequence current.

[0019] Specifically, in this step, such as Figure 4 and Figure 5 As shown, the formula can be used based on the collected output current of the converter and the preset current limit value. The limiting coefficient is calculated; then based on the limiting coefficient... The initial value of the negative sequence current is limited to obtain the set value of the negative sequence current, which is obtained according to the formula. The negative sequence current setting value is calculated, whereby the negative sequence current setting value includes the negative sequence active current setting value. and negative sequence reactive current setpoint ; This is the amplitude limiting factor. The preset current limit value, and This represents the positive-sequence component of the converter's output current in the positive-sequence dq coordinate system.

[0020] S130. Obtain the negative sequence component in the current grid current command of the converter.

[0021] In this step, when an asymmetrical fault occurs in the power grid, the current grid connection current command of the converter is obtained, and the d-axis component of the current grid connection current command is analyzed. and q-axis components Using the current network operating phase angle, i.e., the phase of the virtual internal potential Perform coordinate transformation to obtain the α-axis and β-axis components of the current grid current command in the αβ coordinate system, then separate the positive and negative sequences and extract the negative sequence component. and (like Figure 7 As shown), then according to Perform a coordinate system transformation to obtain the d-axis component of the negative sequence current command in the negative sequence dq coordinate system. and q-axis components .

[0022] Understandably, the current grid current command is the target current that the grid-type converter should output in order to achieve the desired voltage support characteristics. This current grid current command is different from the actual output current of the converter and is a control command generated internally by the grid-type converter.

[0023] In some other embodiments, the grid-type converter control method may further include: acquiring the The converter's active power value, active power setpoint, reactive power value, and reactive power setpoint are used to determine the current virtual internal potential (EVP). Specifically, the active power setpoint and reactive power setpoint of the converter before the occurrence of a grid asymmetry fault are obtained. Real-time active power and reactive power values ​​can be calculated based on the positive-sequence components of the grid connection point voltage and output current in the stationary coordinate system from the grid-side parameters. The phase of the current virtual EMP is determined by adjusting the generator's rotor motion equation based on the deviation between the active power value and the active power setpoint. The amplitude of the virtual EMP is determined by adjusting the generator's reactive power setpoint and reactive power value using a PI controller (Proportional-Integral Controller).

[0024] S140. Generate a negative sequence voltage adjustment amount based on the deviation between the negative sequence component in the current grid current command and the negative sequence current setting value.

[0025] In this invention, when a grid asymmetric fault occurs, a negative sequence voltage regulation amount is generated based on the deviation between the negative sequence component in the current grid current command and the negative sequence current setting value, so that the negative sequence current of the converter tracks the negative sequence current setting value. This allows for quantitative control of the negative sequence current without changing the original control architecture of the grid-type converter.

[0026] like Figure 6 As shown, this step specifically includes the following steps S141-S142: S141. Calculate the negative sequence current deviation between the negative sequence component in the current network current command and the negative sequence current setting value.

[0027] S142. Using a PI controller, the negative sequence current deviation is adjusted to obtain the negative sequence voltage adjustment.

[0028] In this embodiment, a negative sequence current deviation regulator employing a PI control algorithm can be used. (i.e., the PI controller used to regulate negative sequence current) generates negative sequence voltage regulation based on the negative sequence component in the current grid current command and the negative sequence current deviation of the negative sequence current setting value.

[0029] Specifically, the generation of the negative sequence voltage regulation is mainly shown in the following formula: ; obtained and Then, a coordinate transformation is performed to obtain the final negative sequence voltage regulation; the coordinate transformation is shown in the following equation: Combining Figure 7Using two negative sequence current deviation regulators Based on the d-axis components of the negative sequence components in the current grid current command, respectively and negative sequence active current setpoint The deviation value and the q-axis component of the negative sequence component in the current grid current command. and negative sequence reactive current setpoint The deviation value is used to obtain the initial negative sequence voltage d-axis adjustment component. and the initial negative sequence voltage q-axis adjustment component Then utilize phase The final negative sequence voltage d-axis adjustment component is obtained by performing coordinate transformation. and negative sequence voltage q-axis adjustment component Together, they constitute the negative sequence voltage regulation amount.

[0030] S150. The current virtual internal potential of the converter is compensated by the negative sequence voltage regulation, an AC voltage command is generated, and the converter is controlled according to the AC voltage command.

[0031] In this step, the negative sequence voltage regulation is used to compensate for the current virtual internal potential of the converter. Specifically, as follows: Figure 8 As shown, this step may include the following steps S151-S155: S151. Obtain the d-axis and q-axis components of the negative sequence voltage regulation in the positive sequence coordinate system; S152. Based on the d-axis and q-axis components of the negative-sequence voltage regulation in the positive-sequence coordinate system and the current virtual internal potential, the AC voltage command is calculated using the following formula: in, and These are the d-axis and q-axis components of the AC voltage command, respectively. The magnitude of the current virtual internal potential. and These are the d-axis and q-axis components of the negative-sequence voltage regulation in the positive-sequence coordinate system, respectively.

[0032] S153. Generate a grid current adjustment command based on the deviation between the AC voltage command and the grid connection point voltage.

[0033] In this step, the d-axis component difference and the q-axis component difference between the AC voltage command and the grid connection point voltage are calculated respectively, that is, the calculations are performed respectively. and The difference and and In this embodiment, the difference between the d-axis component and the q-axis component is used to calculate the grid current adjustment command based on the virtual admittance model.

[0034] Specifically, in combination Figure 9 The calculation of the grid current adjustment command using the virtual admittance model based on the difference between the d-axis and q-axis components may specifically include: calculating the difference between the d-axis components (... - ) and q-axis component difference ( - ), using formula The d-axis component of the grid current regulation was calculated. And the current adjustment of the q-axis component of the network Together, they constitute the grid current regulation command; where s is the Laplace operator, representing the differential operation in the time domain. and These are virtual inductance and virtual resistance, respectively. The overall representation represents the impedance of the virtual inductive branch. Using a virtual admittance model allows the calculated network current regulation command to not only reflect the steady-state amplitude of the voltage difference, but also, through differential terms... By introducing a dynamic rate of change constraint for the current, the unique current inertia and damping characteristics of a physical inductor are simulated, enabling the power module of the converter to smoothly transition the current when responding to grid disturbances, avoiding impacts and improving operational stability.

[0035] Understandably, in some other embodiments, a PI controller may also be used to adjust the deviation between the AC voltage command and the grid connection point voltage to obtain the grid current regulation command.

[0036] S154. Generate a modulation voltage command based on the deviation between the grid current adjustment command and the converter output current.

[0037] In this embodiment, the modulation voltage command is generated as shown in the following formula: ; combination Figure 9 In this step, the d-axis component is adjusted according to the grid current. and the d-axis component of the converter output current The difference and the q-axis component of the grid current adjustment and the q-axis component of the converter output current The difference is determined using a current regulator. (Such as a PI controller) generates the d-axis component and q-axis component of the initial modulation voltage, and then superimposes the d-axis component and q-axis component of the initial modulation voltage onto the d-axis component of the grid connection point voltage, respectively. and q-axis components The final modulation voltage d-axis component is obtained. and the q-axis component of the modulation voltage Together, they constitute the modulation voltage command.

[0038] S155. The modulation voltage command is pulse-width modulated to generate a drive signal to control the converter.

[0039] In this embodiment, the phase angle of the network operation is utilized. Perform a coordinate transformation on the modulation voltage command in the dq coordinate system to obtain the α-axis component of the modulation voltage command in the αβ coordinate system. and β-axis components And modulate it with PWM, that is and The input is fed to the space vector modulation module (SVM) to generate drive signals for driving the power devices in the converter's power module. This enables control of the converter.

[0040] It should be noted that although the steps in the above embodiments are described using a grid asymmetry fault as an example, the application scenarios of the method of the present invention are not limited to this. Under non-fault conditions such as grid load asymmetry or line parameter asymmetry that cause negative sequence components in the grid voltage, the control method of the present invention can also suppress unfavorable negative sequence current components through closed-loop precise control of negative sequence current, thereby improving the operational adaptability and stability of the converter under asymmetrical grid conditions.

[0041] As can be seen, the grid-connected converter control method provided in the first embodiment of the present invention generates a negative-sequence voltage regulation amount based on the difference between the negative-sequence current setpoint of the converter and the negative-sequence component in the current grid-connected current command. That is, it generates the negative-sequence voltage regulation amount based on the difference between the current negative-sequence current output capability and the grid's target requirement for the converter's negative-sequence support, and uses this to compensate for the converter's current virtual internal potential. Based on the compensated virtual internal potential, a drive signal for controlling the converter is generated. During the control process, the compensation effect occurs within the converter's internal electromotive force. The grid-connected voltage support characteristics of the positive-sequence component are fully preserved, while the negative-sequence component is actively reshaped to a level compatible with the grid's negative-sequence voltage. In other words, the control method of the present invention, while maintaining the positive-sequence voltage support capability of the grid-connected converter, can achieve precise quantitative control of the negative-sequence current, reducing the overcurrent risk under asymmetrical grid conditions, ensuring stable operation during faults, and improving the stability and adaptability of the converter's grid-connected operation.

[0042] It should be understood that the above method embodiments are described as a series of actions for the sake of simplicity. However, those skilled in the art should know that the present invention is not limited by the described order of actions. The execution order of each process should be determined by its function and internal logic, and should not constitute any limitation on the implementation process of the embodiments of the present invention.

[0043] Reference Figure 10 , Figure 10 This is a flowchart illustrating the grid-type converter control method provided in the second embodiment of the present invention. In the embodiment shown in the figures, the grid-type converter control method includes the following steps: S210: Collects the grid connection point voltage and output current of the converter.

[0044] This step is similar to step S110, and will not be described again here.

[0045] S220. Determine the negative sequence current setting value of the converter based on the negative sequence component of the grid connection point voltage.

[0046] This step is similar to step S120, and will not be described again here.

[0047] S230. Obtain the negative sequence component in the current grid current command of the converter.

[0048] This step is similar to step S130, and will not be described again here.

[0049] S240. Generate a negative sequence voltage adjustment amount based on the deviation between the negative sequence component in the current grid current command and the negative sequence current setting value.

[0050] This step is similar to step S140, and will not be described again here.

[0051] S250. Obtain the DC-side voltage of the converter and generate an AC voltage command compensation amount based on the DC-side voltage.

[0052] Specifically, such as Figure 11 As shown, this step may include the following steps S251-S252: S251. Obtain the DC side voltage of the converter.

[0053] In this embodiment, the DC-side voltage is the voltage across the DC bus capacitor of the converter. .

[0054] S252. Extract the second harmonic component from the DC side voltage and generate an AC voltage command compensation amount based on the second harmonic component.

[0055] like Figure 12 As shown, a bandpass filter (BPF) can be used to extract... Second harmonic component Using a PI controller Obtain the d-axis component of the AC voltage command compensation. ; The d-axis component of the AC voltage command compensation amount Invert the signal and pass it through an orthogonal signal generator. The q-axis component of the AC voltage command compensation is obtained. .

[0056] S260. The current virtual internal potential of the converter is compensated using the negative sequence voltage regulation amount and the AC voltage compensation amount, an AC voltage command is generated, and the converter is controlled according to the AC voltage command.

[0057] In this step, the negative sequence voltage regulation and AC voltage compensation are used together to compensate for the current virtual internal potential of the converter. The AC voltage command compensation can effectively suppress the coupling effect of the DC side voltage second harmonic ripple on the AC side output voltage, further improving the steady-state accuracy and dynamic response performance of the negative sequence current control.

[0058] Specifically, such as Figure 13 As shown, step S260 may include the following steps S261-S265: S261. Obtain the d-axis and q-axis components of the negative sequence voltage regulation and the AC voltage compensation in the positive sequence coordinate system, respectively.

[0059] S262. Based on the d-axis and q-axis components of the negative-sequence voltage adjustment and the AC voltage compensation in the positive-sequence coordinate system, and the current virtual internal potential, the AC voltage command is calculated using the following formula: Combination Figure 14 This embodiment combines negative sequence voltage regulation and AC voltage command compensation based on DC-side voltage to compensate for the current virtual internal potential of the converter. and These are the d-axis and q-axis components of the AC voltage command, respectively. The magnitude of the current virtual internal potential. and These represent the d-axis and q-axis components of the negative-sequence voltage regulation in the positive-sequence coordinate system, respectively. and These are the d-axis and q-axis components of the AC voltage compensation, respectively.

[0060] S263. Generate a grid current adjustment command based on the deviation between the AC voltage command and the grid connection point voltage.

[0061] This step is similar to step S153, and will not be described again here.

[0062] S264. Generate a modulation voltage command based on the deviation between the grid current adjustment command and the converter output current.

[0063] This step is similar to step S154, and will not be described again here.

[0064] S265. The modulation voltage command is pulse-width modulated to generate a drive signal to control the converter.

[0065] This step is similar to step S155, and will not be described again here.

[0066] Figure 15 The grid-type converter control method described in the above embodiments of the present invention is applied to, for example, Figure 1 The simulation results for a grid asymmetry fault are shown in the converter topology diagram. Figure 16 This demonstrates the application of a general network control scheme without quantitative negative sequence current control in applications such as... Figure 1 The figure shows simulation results of the same degree of grid asymmetry fault when the converter topology is shown. Figure 17 This demonstrates the application of a conventional negative sequence current control scheme in applications such as... Figure 1The simulation results for a grid asymmetry fault of the same degree are shown in the converter topology diagram. The specific implementation of the general grid control scheme without quantitative negative sequence current control can be as follows: In the positive sequence dq coordinate system, the deviation between the grid connection point voltage and the current grid voltage command is directly generated into a current command to control the actual current after passing through a voltage regulator. The specific implementation of the conventional negative sequence current control scheme can be as follows: The grid connection point voltage is collected, and the voltage components of the grid connection point voltage in the αβ coordinate system are obtained through a positive-negative sequence separation module. Based on the grid operation phase angle, a coordinate transformation is performed to obtain the positive-sequence and negative-sequence components of the grid connection point voltage in the positive sequence dq coordinate system. Subsequently, the positive-sequence voltage component of the grid connection point in the positive sequence dq coordinate system is subtracted from a preset output voltage reference value. The deviation is processed by a voltage regulator to generate the d-axis and q-axis components of the positive-sequence command value of the grid-side current. Simultaneously, in the positive sequence dq coordinate system, the extracted negative-sequence voltage component is directly used in conjunction with the preset negative sequence current command value. The reactive current support coefficient and the negative-sequence active current support coefficient are algebraically calculated to obtain the d-axis and q-axis components of the negative-sequence current setpoint required by the converter. Finally, the d-axis components of the positive-sequence command value and the negative-sequence current setpoint are added together, and the q-axis components of the positive-sequence command value and the negative-sequence current setpoint are added together to obtain the d-axis and q-axis components of the current command, respectively, which constitute the current command value. The deviation between the current command value and the actual current is input to the current regulator. After adjustment, the voltage feedforward term is superimposed to obtain the modulated voltage command in the dq coordinate system, and the drive signal is generated by inverse coordinate transformation and PWM modulation.

[0067] As can be seen from the figure, Figure 15 , Figure 16 and Figure 17 Each sub-plot contains four sets of sub-plots: The first set of sub-plots, eabc, is a three-phase AC voltage curve, where the red, black, and blue curves represent the AB line voltage, BC line voltage, and CA line voltage at the grid connection point, respectively; the second set of sub-plots, igabc, is a three-phase AC current curve, where the red, black, and blue curves represent the A, B, and C phases of the converter's three-phase output current, respectively; the third set of sub-plots, with the black curve (Vg_pos) and the red curve (Vg_neg) representing the positive-sequence and negative-sequence component amplitudes of the grid connection point voltage, respectively; and the fourth set of sub-plots, with the black curve (Ip_neg) and the red curve (Iq_neg) representing the negative-sequence active current and negative-sequence reactive current, respectively.

[0068] from Figure 15 The waveform shows that during the fault, the lowest positive-sequence voltage was approximately 0.85 pu, the negative-sequence voltage had no overshoot, and the negative-sequence reactive current reached approximately 0.35 pu 10 ms after the fault occurred. Furthermore, the negative-sequence active current remained stable at -0.015 pu during the fault. Figure 16The waveform shows that the lowest positive-sequence voltage during the fault was 0.84 pu, and the negative-sequence reactive current reached 0.36 pu 10 ms after the fault occurred. The negative-sequence active current during the fault was -0.619 pu. Without the strategy proposed in this invention, it is impossible to effectively and quantitatively control the negative-sequence active / reactive current when dealing with asymmetrical faults in the power grid. A large negative-sequence active current will lower the negative-sequence voltage, and indirectly lower the positive-sequence voltage through the boundary conditions of the composite sequence network. The positive-sequence reactive power support has a fast response, but the voltage support effect is relatively inferior. Figure 17 The waveform shows that during the fault, the lowest positive-sequence voltage was 0.84 pu, and the negative-sequence voltage overshooted. The negative-sequence reactive current only reached 0.23 pu 10 ms after the fault. The reactive current response speed of conventional negative-sequence current control for grid asymmetry faults is similar to the strategy proposed in this invention, but the voltage support effect is not as good. It can be seen that when a grid asymmetry fault occurs, the scheme of this invention rapidly raises the negative-sequence current to 0.35 pu within 10 ms after the fault occurs. Its response speed and amplitude of the negative-sequence current are superior to the conventional negative-sequence current control scheme. Figure 17 The 0.23 pu indicates that the present invention can provide negative sequence reactive power support more quickly and fully, which is beneficial to grid fault recovery; at the same time, the present invention maintains the minimum positive sequence voltage at 0.85 pu during the fault period, which is higher than the negative sequence current control scheme and the conventional negative sequence current control scheme. Figure 17 The 0.84 pu indicates that the present invention maintains the grid support capability for positive sequence voltage during the fault period. Moreover, the negative sequence active current of the present invention is only -0.015 pu, which is much lower than the uncontrollable negative sequence active current of -0.619 pu in the non-negative sequence control scheme. This shows that the present invention effectively suppresses the unfavorable negative sequence active component and avoids the problems of increased power module loss and aggravated DC side voltage fluctuation caused by excessive negative sequence active current. It can be seen that the present invention achieves precise quantitative control of negative sequence current without sacrificing the positive sequence voltage support performance, and can effectively eliminate the overcurrent risk and operational stability hazards caused by uncontrolled negative sequence current under asymmetrical faults.

[0069] As described above, the grid-connected converter control method provided in the second embodiment of the present invention generates a negative-sequence voltage regulation amount based on the difference between the negative-sequence current setpoint of the converter and the negative-sequence component in the current grid-connected current command. Specifically, it generates the negative-sequence voltage regulation amount based on the difference between the current negative-sequence current output capability and the grid's target requirement for the converter's negative-sequence support. This is combined with an AC voltage command compensation amount generated based on the DC-side voltage to compensate the converter's virtual internal potential, thereby generating a drive signal to control the converter based on the compensated virtual internal potential. During the control process, the compensation effect occurs within the converter's internal electromotive force. The grid-connected voltage support characteristics of the positive-sequence component are fully preserved, while the negative-sequence component is actively reshaped to a level compatible with the grid's negative-sequence voltage. Therefore, the control method of the present invention, while maintaining the positive-sequence voltage support capability of the grid-connected converter, can achieve precise quantitative control of the negative-sequence current, reducing the overcurrent risk under asymmetrical grid conditions, ensuring stable operation during fault periods, and effectively suppressing the second harmonic fluctuation of the DC-side voltage, thus improving the stability and adaptability of the converter's grid-connected operation.

[0070] Reference Figure 18 , Figure 18 This is a block diagram of a grid-type converter control system provided in an embodiment of the present invention. Figure 18 As shown, the grid-type converter control system includes a converter 101 and a controller 102. The controller 102 includes an acquisition module 1021, a power regulation module 1022, a voltage and current control module 1023, and a regulation control module 1024. The acquisition module 1021 is used to acquire the grid connection point voltage of the converter 101 and acquire the negative sequence component in the current grid current command of the converter 101. The power regulation module 1022 is used to determine the negative sequence current setting value of the converter 101 based on the negative sequence component of the grid connection point voltage. The voltage and current control module 1023 is used to generate a negative sequence voltage adjustment amount based on the deviation between the negative sequence component in the current grid current command and the negative sequence current set value. The adjustment and control module 1024 is used to compensate the current virtual internal potential of the converter 101 using the negative sequence voltage adjustment amount, generate an AC voltage command, and control the converter 101 according to the AC voltage command.

[0071] In one embodiment, the power regulation module 1022 is specifically used for: Based on the negative sequence component of the grid connection point voltage and the preset negative sequence current support coefficient, an initial value for the negative sequence current is generated. The initial value of the negative sequence current is limited based on the current limiting condition to obtain the set value of the negative sequence current.

[0072] In one embodiment, the power regulation module 1022 is further specifically used for: Obtain the negative sequence components of the grid connection point voltage in the negative sequence coordinate system along the d-axis and q-axis. Based on the d-axis and q-axis components of the negative sequence voltage at the grid connection point, the initial value of the negative sequence current of the converter 101 is calculated using the following formula: in, and These represent the d-axis and q-axis components of the initial negative sequence current of the converter, respectively. and These are the d-axis and q-axis components of the negative sequence voltage at the grid connection point, respectively. and These are the negative-sequence active current support coefficient and the negative-sequence reactive current support coefficient of the converter, respectively. and These are the rated current and rated voltage of the converter, respectively.

[0073] In one embodiment, the acquisition module 1021 is further configured to acquire the output current of the converter 101; the power regulation module 1022 is further configured to: Based on the output current of the converter 101 and the preset current limit value, the formula is used. The amplitude limiting coefficient is calculated; where, This is the limiting factor. The preset current limit value, and This represents the positive-sequence component of the converter's output current in the positive-sequence dq coordinate system. The initial value of the negative sequence current is limited based on the limiting coefficient to obtain the set value of the negative sequence current.

[0074] In one embodiment, the voltage and current control module 1023 is specifically used for: Calculate the negative sequence current deviation between the negative sequence component in the current grid current command and the negative sequence current setting value; The negative sequence current deviation is adjusted using a PI controller to obtain the negative sequence voltage adjustment.

[0075] In one embodiment, the adjustment control module 1024 is specifically used for: Obtain the d-axis and q-axis components of the negative sequence voltage regulation in the positive sequence coordinate system; Based on the d-axis and q-axis components of the negative-sequence voltage regulation in the positive-sequence coordinate system and the current virtual internal potential, the AC voltage command is calculated using the following formula: in, and These are the d-axis and q-axis components of the AC voltage command, respectively. The magnitude of the current virtual internal potential. and These are the d-axis and q-axis components of the negative-sequence voltage regulation in the positive-sequence coordinate system, respectively.

[0076] In one embodiment, the acquisition module 1021 is further configured to acquire the DC side voltage of the converter 101 and generate an AC voltage command compensation amount based on the DC side voltage; The adjustment and control module 1024 can also be used to adjust the compensated virtual internal potential using the AC voltage command compensation amount, thereby generating the AC voltage command. Based on the above design, in this embodiment, the virtual internal potential can also be compensated using the AC voltage command compensation amount, that is, the virtual internal potential can be compensated by using the AC voltage command compensation amount and the negative sequence voltage adjustment amount together, so as to further improve the steady-state accuracy and dynamic response performance of the negative sequence current control.

[0077] In one embodiment, the adjustment control module 1024 is specifically used for: Based on the deviation between the AC voltage command and the grid connection point voltage, a grid current adjustment command is generated; Based on the deviation between the grid current regulation command and the converter output current, a modulation voltage command is generated; The modulation voltage command is pulse-width modulated to generate a drive signal to control the converter 101.

[0078] This invention provides a grid-connected converter control system. By acquiring the grid connection point voltage and extracting the negative-sequence component, the negative-sequence current setpoint of the converter is determined. Based on this, the quantitative demand of the grid for negative-sequence support from the converter is obtained. Furthermore, the negative-sequence component of the current grid-connected current command, reflecting the negative-sequence current that the converter will output under the current control strategy, is obtained and compared with the negative-sequence current setpoint. The deviation between the negative-sequence component in the current grid-connected current command and the negative-sequence current setpoint is determined, thereby generating a negative-sequence voltage regulation quantity to compensate for the current virtual internal potential of the converter. It is understood that the compensation effect occurs within the converter's internal electromotive force, thus enabling the converter to output the desired negative-sequence current without disrupting the original grid-connected voltage support characteristics. Finally, an AC voltage command is generated based on the compensated virtual internal potential, achieving closed-loop precise quantitative control of the converter. Therefore, this method can maintain the positive sequence voltage support capability of the grid-connected converter while accurately quantifying and controlling the negative sequence current, reducing the overcurrent risk under asymmetrical grid conditions, and improving the stability and adaptability of the converter in grid-connected operation.

[0079] For specific limitations regarding the grid-type converter control system, please refer to the limitations on the grid-type converter control method mentioned above, which will not be repeated here. Each module in the aforementioned grid-type converter control system can be implemented entirely or partially through software, hardware, or a combination thereof. These modules can be embedded in or independent of the processor in a computer device in hardware form, or stored in the memory of a computer device in software form, so that the processor can call and execute the corresponding operations of each module.

[0080] Those skilled in the art will clearly understand that, for the sake of convenience and brevity, the above-described division of functional units and modules is used as an example. In practical applications, the above functions can be assigned to different functional units and modules as needed, that is, the internal structure of the device can be divided into different functional units or modules to complete all or part of the functions described above.

[0081] The above embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit it. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention, and should all be included within the protection scope of the present invention.

Claims

1. A control method for a grid-type converter, characterized in that, include: Collect the grid connection point voltage of the converter; The negative sequence current setting value of the converter is determined based on the negative sequence component of the grid connection point voltage; Obtain the negative sequence component in the current grid current command of the converter; Based on the deviation between the negative sequence component in the current grid current command and the negative sequence current set value, a negative sequence voltage adjustment amount is generated; The negative sequence voltage regulation is used to compensate for the current virtual internal potential of the converter, an AC voltage command is generated, and the converter is controlled according to the AC voltage command. Specifically, determining the negative sequence current setting value of the converter based on the negative sequence component of the grid connection point voltage includes: Based on the negative sequence component of the grid connection point voltage and the preset negative sequence current support coefficient, an initial value for the negative sequence current is generated. The initial value of the negative sequence current is limited based on the current limiting condition to obtain the set value of the negative sequence current. The step of using the negative sequence voltage regulation to compensate the current virtual internal potential of the converter and generate an AC voltage command specifically includes: Obtain the d-axis and q-axis components of the negative sequence voltage regulation in the positive sequence coordinate system; Based on the d-axis and q-axis components of the negative-sequence voltage regulation in the positive-sequence coordinate system and the current virtual internal potential, the AC voltage command is calculated using the following formula: in, and These are the d-axis and q-axis components of the AC voltage command, respectively. The magnitude of the current virtual internal potential. and These are the d-axis and q-axis components of the negative-sequence voltage regulation in the positive-sequence coordinate system, respectively.

2. The grid-type converter control method as described in claim 1, characterized in that, The preset negative sequence current support coefficient includes a negative sequence active current support coefficient and a negative sequence reactive current support coefficient; wherein, the step of generating an initial negative sequence current value based on the negative sequence component of the grid connection point voltage and the preset negative sequence current support coefficient specifically includes: Obtain the negative sequence components of the grid connection point voltage in the negative sequence coordinate system along the d-axis and q-axis. Based on the d-axis and q-axis components of the negative sequence voltage at the grid connection point, the initial value of the negative sequence current of the converter is calculated using the following formula: in, and These represent the d-axis and q-axis components of the initial negative sequence current of the converter, respectively. and These are the d-axis and q-axis components of the negative sequence voltage at the grid connection point, respectively. and These are the negative-sequence active current support coefficient and the negative-sequence reactive current support coefficient of the converter, respectively. and These are the rated current and rated voltage of the converter, respectively.

3. The grid-type converter control method as described in claim 1, characterized in that, The step of limiting the initial value of the negative sequence current based on the current limiting condition to obtain the set value of the negative sequence current specifically includes: Obtain the output current of the converter; Based on the output current of the converter and the preset current limit value, the formula is used. The amplitude limiting coefficient is calculated; where, This is the amplitude limiting factor. The preset current limit value, and This represents the positive-sequence component of the converter's output current in the positive-sequence dq coordinate system. The initial value of the negative sequence current is limited based on the limiting coefficient to obtain the set value of the negative sequence current.

4. The grid-type converter control method as described in claim 1, characterized in that, The step of generating a negative-sequence voltage regulation amount based on the deviation between the negative-sequence component in the current grid current command and the negative-sequence current set value specifically includes: Calculate the negative sequence current deviation between the negative sequence component in the current grid current command and the negative sequence current setting value; The negative sequence current deviation is adjusted using a PI controller to obtain the negative sequence voltage adjustment.

5. The grid-type converter control method as described in claim 1, characterized in that, The grid-type converter control method further includes: Obtain the DC-side voltage of the converter and generate an AC voltage command compensation amount based on the DC-side voltage; The method of compensating the current virtual internal potential of the converter using the negative sequence voltage regulation further includes: The compensated virtual internal potential is adjusted using the AC voltage command compensation amount, thereby generating the AC voltage command.

6. The grid-type converter control method as described in claim 1, characterized in that, The step of controlling the converter according to the AC voltage command specifically includes: Obtain the output current of the converter; Based on the deviation between the AC voltage command and the grid connection point voltage, a grid current adjustment command is generated; Based on the deviation between the grid current regulation command and the converter output current, a modulation voltage command is generated; The modulation voltage command is pulse-width modulated to generate a drive signal to control the converter.

7. A grid-type converter control system, characterized in that, The device includes a converter and a controller, wherein the controller is configured to perform the steps of the grid-type converter control method as described in any one of claims 1-6 to control the converter.

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