Control method, device and equipment of network-following type converter and medium

Abstract

The invention discloses a control method, device and equipment of a grid-following converter and a medium, and relates to the technical field of converter control, an alternating current side impedance model of the grid-following converter is determined in advance, and a link of performing current prediction based on the alternating current side impedance model is added when a current loop of the grid-following converter works; feedforward compensation can be carried out on a current loop according to the predicted current variable quantity; meanwhile, the voltage feed-forward quantity subjected to phase lead compensation is adopted to carry out feed-forward compensation on the modulation wave control voltage finally output by the current loop; possible disturbance of a power grid or a direct current side is actively compensated through setting of voltage feed-forward compensation and current feed-forward compensation, and the control precision of a voltage loop and a current loop is improved, so that the dynamic performance and the steady-state performance of a whole control system of the grid-following type converter are improved, current impact caused by power grid fluctuation or sudden loading and unloading of the direct current side is reduced, and the service life of the grid-following type converter is prolonged. And the reliability and the safety of the whole grid-connected system are improved.

Description

Technical Field

[0001] The present invention relates to the technical field of converter control, and particularly to a control method, device, equipment and medium for a grid-following converter. Background Art

[0002] With the continuous development of energy storage systems, various types of energy storage systems achieve energy grid connection through grid-following converters. The AC side of the grid-following converter is connected to the power grid, and the DC side is connected to the energy storage system, which can realize the energy conversion between the energy storage system and the power grid, thereby using the energy storage system to improve the stability of the power grid and ensure the output power quality of the power grid. The grid-following converter can obtain the phase information of the grid voltage through a phase-locked loop, and then adopt a double closed-loop structure of a voltage loop and a current loop to control the grid voltage or grid current, so as to realize the energy interaction between the energy storage system and the power grid under different application scenarios. However, in the prior art, the dynamic and steady-state performances of the control system of the grid-following converter are relatively poor. Once there are energy fluctuations in the power grid or the DC side, such as voltage fluctuations in the power grid, sudden loading or sudden unloading on the DC side, this kind of fluctuation will cause disturbances to the control system, resulting in control errors and being unable to accurately and quickly follow the fluctuation. The grid-following converter may also have abnormal current overshoot due to this kind of fluctuation, and in severe cases, it may cause the device to shut down. Summary of the Invention

[0003] The purpose of the present invention is to provide a control method, device, equipment and medium for a grid-following converter, aiming to improve the dynamic performance and steady-state performance of the entire control system of the grid-following converter and reduce the current impact caused by power grid fluctuations or sudden loading and unloading on the DC side.

[0004] To solve the above technical problems, the present invention provides a control method for a grid-following converter, including:

[0005] Performing phase lead compensation on the obtained grid voltage to obtain a voltage feedforward quantity;

[0006] Estimating the current change amount of the AC side of the grid-following converter before and after a preset delay time according to the AC side impedance model of the grid-following converter and the current modulation wave control voltage;

[0007] Performing feedforward compensation on the current reference value based on the current change amount, and performing feedforward compensation on the modulation wave control voltage based on the voltage feedforward quantity to obtain a compensated modulation wave control voltage;

[0008] Wherein, the current reference value is the current value output from the voltage loop of the grid-connected converter to the current loop of the grid-connected converter; the modulation wave control voltage is the control voltage output from the current loop of the grid-connected converter; the current change amount is negatively correlated with the modulation wave control voltage; the voltage feedforward amount is positively correlated with the modulation wave control voltage;

[0009] Generate the modulation wave of the grid-connected converter based on the compensated modulation wave control voltage.

[0010] Optionally, the phase lead compensation of the obtained grid voltage to obtain the voltage feedforward amount includes:

[0011] Obtain the three-phase grid voltages of the grid connected to the grid-connected converter;

[0012] Convert the three-phase grid voltages into two-phase orthogonal components in the stationary coordinate system to obtain the α-axis voltage and β-axis voltage of the three-phase grid voltages;

[0013] Extract the positive sequence components of the α-axis voltage and the positive sequence components of the β-axis voltage;

[0014] Input the positive sequence component of the α-axis voltage into the phase lead compensator to obtain the first compensation amount, and input the positive sequence component of the β-axis voltage into the phase lead compensator to obtain the second compensation amount;

[0015] Convert the first compensation amount and the second compensation amount into two-phase orthogonal components in the dq rotating coordinate system to obtain the voltage feedforward amount.

[0016] Optionally, the transfer function of the phase lead compensator is:

[0017] ;

[0018] Wherein, is the calculation frequency of the control system, is the preset phase compensation coefficient, is the preset gain compensation coefficient.

[0019] Optionally, the feedforward compensation of the current reference value based on the current change amount and the feedforward compensation of the modulation wave control voltage based on the voltage feedforward amount include:

[0020] Perform reverse superposition of the current change amount and the current reference value to perform feedforward compensation on the current reference value;

[0021] Perform positive superposition of the voltage feedforward amount and the modulation wave control voltage to perform feedforward compensation on the modulation wave control voltage.

[0022] Optionally, before performing feedforward compensation on the current reference value based on the current change amount, it further includes:

[0023] Input the current change amount into a low-pass filter to obtain a filtered current change amount;

[0024] In the case where the filtered current change amount is greater than a preset limit value, adjust the current change amount to the preset limit value.

[0025] Optionally, it further includes:

[0026] Obtain the grid current of the grid connected to the grid-connected converter;

[0027] Judge whether the grid current is greater than a current threshold;

[0028] If so, stop outputting the modulation wave of the grid-connected converter to the grid-connected converter.

[0029] Optionally, the predicting the current change amount of the AC side of the grid-connected converter before and after a preset delay time according to the AC side impedance model of the grid-connected converter and the current modulation wave control voltage includes:

[0030] Convert the AC side impedance model of the grid-connected converter into a current prediction model by using discretization processing;

[0031] Based on the current prediction model, determine the predicted current value of the AC side of the grid-connected converter at the current moment;

[0032] Obtain the predicted current value of the AC side of the grid-connected converter before the preset delay time;

[0033] Subtract the predicted current value before the preset delay time from the predicted current value at the current moment to obtain a current change amount.

[0034] To solve the above technical problems, the present invention further provides a control device for a grid-connected converter, including:

[0035] A voltage compensation amount determination unit, configured to perform phase lead compensation on the obtained grid voltage to obtain a voltage feedforward amount;

[0036] A current compensation amount determination unit, configured to predict the current change amount of the AC side of the grid-connected converter before and after a preset delay time according to the AC side impedance model of the grid-connected converter and the current modulation wave control voltage;

[0037] A compensation unit, configured to perform feedforward compensation on the current reference value based on the current change amount, and perform feedforward compensation on the modulation wave control voltage based on the voltage feedforward amount to obtain a compensated modulation wave control voltage;

[0038] Wherein, the current reference value is the current value output by the voltage loop of the grid-following converter to the current loop of the grid-following converter; the modulation wave control voltage is the control voltage output by the current loop of the grid-following converter; the current variation is negatively correlated with the modulation wave control voltage; the voltage feedforward amount is positively correlated with the modulation wave control voltage;

[0039] A control unit, configured to generate a modulation wave of the grid-following converter based on the compensated modulation wave control voltage.

[0040] To solve the above technical problems, the present invention also provides an electronic device, including:

[0041] A memory, configured to store a computer program;

[0042] A processor, configured to implement the steps of the control method of the grid-following converter as described above.

[0043] To solve the above technical problems, the present invention also provides a computer-readable storage medium, on which a computer program is stored, and when the computer program is executed by a processor, the steps of the control method of the grid-following converter as described above are implemented.

[0044] The present invention provides a control method for a grid-following converter. First, an AC-side impedance model of the grid-following converter is determined in advance. When the current loop of the grid-following converter works, a current prediction link based on the AC-side impedance model is added, and the current loop can be feedforward compensated according to the predicted current variation; at the same time, a voltage feedforward amount with phase lead compensation is used to feedforward compensate the modulation wave control voltage finally output by the current loop; through the settings of voltage feedforward compensation and current feedforward compensation, the possible disturbances in the power grid or DC side can be actively compensated, the control precision of the voltage loop and the current loop can be improved, so as to enhance the dynamic performance and steady-state performance of the entire control system of the grid-following converter, reduce the current impact caused by power grid fluctuations or sudden load addition and subtraction on the DC side, and improve the reliability and safety of the entire grid-connected system.

[0045] The present invention also provides an electronic device and a computer-readable storage medium, which have the same beneficial effects as the above control method of the grid-following converter. BRIEF DESCRIPTION OF THE DRAWINGS

[0046] To more clearly illustrate the technical solutions in the embodiments of the present invention, the following will briefly introduce the drawings required for the prior art and the embodiments. Obviously, the drawings in the following description are only some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can be obtained based on these drawings.

[0047] Figure 1 Flow schematic diagram of a control method for a grid-following converter provided by the present invention;

[0048] Figure 2 Control loop schematic diagram of a control system for a grid-following converter provided by the present invention;

[0049] Figure 3 Schematic diagram of a method for obtaining a voltage feedforward quantity provided by the present invention;

[0050] Figure 4 Schematic diagram of a grid current waveform after current limiting protection is adopted according to the present invention;

[0051] Figure 5 Schematic diagram of a method for obtaining a current feedforward quantity provided by the present invention;

[0052] Figure 6a Schematic diagram of a waveform of the d-axis component of current in a control system before compensation is adopted according to the present invention;

[0053] Figure 6b Schematic diagram of a waveform of the d-axis component of current in a control system after compensation is adopted according to the present invention;

[0054] Figure 7a Schematic diagram of a waveform of the alternating current on the AC side of a grid-following converter before compensation is adopted according to the present invention;

[0055] Figure 7b Schematic diagram of a waveform of the alternating current on the AC side of a grid-following converter after compensation is adopted according to the present invention. Detailed implementation manners

[0056] The core of the present invention is to provide a control method, device, equipment and medium for a grid-following converter. By setting voltage feedforward compensation and current feedforward compensation, the possible disturbances in the power grid or the DC side are actively compensated, the control accuracy of the voltage loop and the current loop is improved, so as to enhance the dynamic performance and steady-state performance of the entire control system of the grid-following converter, reduce the current impact caused by power grid fluctuations or sudden loading and unloading on the DC side, and improve the reliability and safety of the entire grid-connected system.

[0057] To make the objectives, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are some, but not all, of the embodiments of the present invention. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0058] SeeFigure 1 As shown Figure 1 is a schematic flow chart of a control method for a grid-following converter provided by the present invention; see Figure 2 As shown Figure 2 is a schematic diagram of the control loop of a control system for a grid-following converter provided by the present invention; to solve the above technical problems, the present invention provides a control method for a grid-following converter, including:

[0059] S11: Perform phase lead compensation on the obtained grid voltage to obtain a voltage feedforward quantity.

[0060] It can be understood that, in order to improve the dynamic performance of the control system of the grid-following converter, a feedforward compensation method is adopted in this application to actively resist interference. Considering that when the grid voltage suddenly changes, the control system of the grid-following converter cannot quickly respond to the voltage fluctuation, a voltage feedforward link is set for the control system in this application. The voltage feedforward link will directly detect the voltage disturbance by obtaining the real-time grid voltage, and then perform phase lead compensation on the detected grid voltage to obtain a voltage feedforward quantity. The voltage feedforward quantity is injected into the control system as a compensation signal, so that the control system can respond to the influence of this voltage disturbance in advance in terms of phase and offset the dynamic lag. The grid voltage refers to the voltage of the grid to which the grid-following converter is connected. The specific acquisition method of the grid voltage and the like are not particularly limited in this application, and the specific method of phase lead compensation can be designed according to the compensation requirements in actual application.

[0061] S12: Estimate the current change amount of the AC side of the grid-following converter before and after a preset delay time according to the AC side impedance model of the grid-following converter and the current modulation wave control voltage.

[0062] Considering that it is also difficult for the control system of the grid-following converter to quickly respond to the change of the AC current on the AC side, a current feedforward link is also set for the control system in this application. When the current feedforward link is applied, it will first determine the AC side impedance model of the grid-following converter according to the actual circuit topology of the grid-following converter, and then predict the current AC current on the AC side according to the current modulation wave control voltage output by the control system. At the same time, each predicted current will be saved and recorded in a specific position. When the control system predicts the current AC current, it can obtain the AC current before the preset delay time from the specific position, and determine the current change amount by taking the difference between the two, so that after the current change amount is injected into the control system as a feedforward compensation amount, the control system can determine the current disturbance through the current change amount, thereby offsetting the influence of the current change on the control system.

[0063] It should be noted that the AC-side impedance model of the grid-connected converter refers to the mathematical model obtained by equivalently representing the AC side of the grid-connected converter, which can characterize the impedance characteristics of the AC side. The modulation wave control voltage refers to the control voltage output by the control system of the grid-connected converter for controlling the modulation wave. As the control command for the modulation wave of the grid-connected converter, the modulation wave control voltage adjusts the working parameters such as the AC voltage on the AC side, the AC current, and the DC voltage on the DC side of the grid-connected converter by adjusting parameters such as the duty cycle of the modulation wave. The specific method for obtaining the AC-side impedance model and the like are not particularly limited in this application. Currently, the modulation wave control voltage can be directly obtained from the output signal of the control system. The specific value and determination method of the preset delay time are not particularly limited in this application and can be selected and designed according to the actual application situation of the converter. The specific prediction method of the current change amount and the like are not particularly limited in this application. Specifically, a prediction model of the AC current can be constructed based on the AC-side impedance model, and the predicted current value can be calculated using the discretized prediction model.

[0064] S13: Perform feedforward compensation on the current reference value based on the current change amount, and perform feedforward compensation on the modulation wave control voltage based on the voltage feedforward amount to obtain the compensated modulation wave control voltage.

[0065] Among them, the current reference value is the current value output from the voltage loop of the grid-connected converter to the current loop of the grid-connected converter; the modulation wave control voltage is the control voltage output from the current loop of the grid-connected converter; the current change amount is negatively correlated with the modulation wave control voltage; the voltage feedforward amount is positively correlated with the modulation wave control voltage.

[0066] It is not difficult to understand that the control system is implemented using a double closed-loop structure of a voltage loop and a current loop. The predicted current change amount can be directly compensated to the current reference value, thereby realizing the feedforward compensation of the current loop of the control system. The voltage feedforward amount is directly compensated to the modulation wave control voltage to complete the voltage feedforward compensation before the modulation wave control voltage is used for modulation wave control. As Figure 2 shown, the DC bus voltage given value of the converter is input into the voltage loop, and after subtracting from the DC bus voltage feedback value of the converter , it generates a current reference value through a PI link. The current reference value includes a d-axis component and a q-axis component . For the d-axis component or the q-axis component , current loops are set in the control system. A cross-coupling compensation link is constructed between the two current loops to eliminate the coupling effect between the d-axis current and the q-axis current. After the current reference value is input into the current loop, it is subtracted from the corresponding AC current feedback value. The AC current feedback value includes the corresponding d-axis component d-axis and q-axis components Meanwhile, the current change amount is used as a negative compensation amount and compensated into the current reference value. After passing through the PI link, the compensated signal generates a modulation wave control voltage. The generated modulation wave control voltage is used to predict the current change amount on the one hand, and on the other hand, after being compensated by the voltage feedforward amount, it is output as the final modulation wave control voltage. The modulation wave control voltage also includes the corresponding d-axis component and q-axis component . The voltage feedforward amount also includes the corresponding first voltage feedforward component and the second voltage feedforward component . After the modulation wave control voltage finally output by the current loop undergoes overmodulation, coordinate transformation, and dead zone compensation processing in sequence, it is used to generate the modulation wave of the grid-connected converter

[0067] Furthermore, in order to improve the accuracy and reliability of the voltage feedforward link and avoid the impact on the control system when the voltage feedforward value is too large, the voltage feedforward value can be further filtered and / or limited before being output to the control loop for voltage feedforward compensation. The specific implementation methods of the filtering and limiting processes are not particularly limited in this application. The filtering process can be specifically implemented by means such as low-pass filtering, and the limiting process can be implemented by means of a limiter, etc

[0068] S14: Generate the modulation wave of the grid-connected converter based on the compensated modulation wave control voltage

[0069] It can be understood that the control system generates the modulation wave of the grid-connected converter according to the modulation wave control voltage finally output by the compensated current loop to control the operation of the grid-connected converter. It should be noted that the specific type and implementation method of the grid-connected converter are not particularly limited in this application. It can be implemented by a rectifier and a grid-connected inverter. There are also various choices for the specific implementation method of its modulation wave, which are not particularly limited in this application. Specifically, it can be implemented by means of a PWM (Pulse Width Modulation) wave, etc. The control method provided by this application can be applied to a PWM rectifier to improve the dynamic and steady-state performance of the entire grid-connected converter, and is applicable to various types of grid-connected conversion devices or other types of grid-connected equipment

[0070] The control method of the grid-following converter provided by the present invention adds a phase-advance compensation link to the control system of the grid-following converter, and can obtain the voltage feedforward value after phase-advance compensation to improve the dynamic performance of the control system and the converter. At the same time, a predictive current loop based on a model is added, and the predicted current change can be used as a feedforward compensation amount to be compensated to the front of the current loop, which can effectively improve the dynamic and steady-state performance of the entire grid-following converter and reduce the current impact caused by grid fluctuations or sudden load addition or subtraction on the DC side. Under normal grid, weak grid or abnormal grid conditions, the voltage feedforward value can be obtained in time through phase-advance compensation calculation to compensate for the abnormal conditions caused by the feedforward delay of the control system. Through the cooperation of voltage feedforward compensation and current feedforward compensation, the dynamic performance and steady-state performance of grid-following equipment, especially large-scale grid-following equipment, are effectively improved, and the reliability of grid-following equipment and its control system during sudden load addition or subtraction or light grid faults is improved.

[0071] Based on the above embodiments:

[0072] See Figure 3 as shown Figure 3 which is a schematic diagram of a method for obtaining a voltage feedforward amount provided by the present invention. As an optional embodiment, phase-advance compensation is performed on the obtained grid voltage to obtain the voltage feedforward amount, including:

[0073] Obtain the three-phase grid voltages of the grid connected to the grid-following converter;

[0074] Convert the three-phase grid voltages into two-phase orthogonal components in the stationary coordinate system to obtain the α-axis voltage and β-axis voltage of the three-phase grid voltages;

[0075] Extract the positive-sequence component of the α-axis voltage and the positive-sequence component of the β-axis voltage;

[0076] Input the positive-sequence component of the α-axis voltage into the phase-advance compensator to obtain a first compensation amount, and input the positive-sequence component of the β-axis voltage into the phase-advance compensator to obtain a second compensation amount;

[0077] Convert the first compensation amount and the second compensation amount into two-phase orthogonal components in the dq rotating coordinate system to obtain the voltage feedforward amount.

[0078] It is not difficult to understand that after sampling the power grid, the three-phase power grid voltages Ua, Ub, and Uc can be obtained. After sampling the three-phase power grid voltages, they are first transformed through a 3s2s coordinate transformation into two-phase orthogonal components in the stationary coordinate system to obtain Uα and Uβ. Then, the positive-sequence components of the power grid voltage are obtained through positive-sequence separation. The positive-sequence components of the power grid voltage include the positive-sequence component of the α-axis voltage and the positive-sequence component of the β-axis voltage. After that, the compensated power grid voltage is obtained through phase-advance compensation. For the positive-sequence component of the α-axis voltage and the positive-sequence component of the β-axis voltage, phase-advance compensation needs to be carried out separately. The Uα is input into the phase-advance compensator to obtain the first compensation amount Uα', and the Uβ is input into the phase-advance compensator to obtain the second compensation amount Uβ'. Finally, through a 2s2r coordinate transformation, the first compensation amount and the second compensation amount are transformed into two-phase orthogonal components in the dq rotating coordinate system to obtain the first voltage feedforward component for the d-axis component in the modulation wave control voltage and the second voltage feedforward component for the q-axis component in the modulation wave control voltage. The first voltage feedforward component and / or the second voltage feedforward component can further be processed by a first-order low-pass filter and a limiter and then input into the current loop for voltage feedforward compensation. The extraction of the positive-sequence components of the power grid voltage can be specifically implemented by means of a double second-order generalized integrator, etc. This application does not make special limitations here. This application does not make special limitations on the sampling method of the three-phase power grid voltage, etc.

[0079] Specifically, to ensure the effect of phase-advance compensation, after obtaining the three-phase power grid voltages, they are first transformed to the stationary coordinate system for phase-advance compensation. The stationary coordinate system retains the phase attributes of the alternating quantities and supports phase analysis and compensation. After that, to be consistent with the modulation wave control voltage in the current loop, after phase-advance compensation, they are then transformed to the dq rotating coordinate system to obtain the voltage feedforward components corresponding to the d-axis component and the q-axis component in the modulation wave control voltage respectively, so as to achieve an accurate and effective voltage feedforward link.

[0080] As an optional embodiment, the transfer function of the phase-advance compensator is:

[0081] ;

[0082] Wherein, is the calculation frequency of the control system, is the preset phase compensation coefficient, is the preset gain compensation coefficient.

[0083] It should be noted that in the case of a weak or faulty power grid, the control system cannot respond to voltage or current fluctuations on the grid side in a timely manner, and there is a delay in the sampled grid voltage or grid current. Therefore, a phase lead compensator for the grid voltage can be designed to implement the phase compensation link. The phase lead compensator is used to quickly detect the amplitude and / or phase change of the grid voltage, compensate for the phase lag caused by sampling and control system delays, etc., and improve the phase margin of the control system. The calculation frequency refers to the calculation frequency of the control system of the grid-connected converter, and the preset phase compensation coefficient can be set according to actual application requirements. Moreover, the closer its value is to 1, the smaller the compensation effect. Considering that there will be a certain amplitude attenuation when the grid voltage passes through the phase lead compensator, a gain compensation coefficient is also set in the phase lead compensator to compensate the amplitude of the grid voltage to a certain extent. Both the phase compensation coefficient and the gain compensation coefficient are selected according to the actual topology of the converter, and no special limitation is made in this application.

[0084] Specifically, the phase lead compensation of the grid voltage can be achieved by designing a phase lead compensator, different compensation effects can be achieved by adjusting the phase compensation coefficient, and at the same time, the gain compensation coefficient is used to avoid the amplitude attenuation of the grid voltage and ensure the compensation effect of the final voltage feedforward quantity.

[0085] As an alternative embodiment, feedforward compensation is performed on the current reference value based on the current change amount, and feedforward compensation is performed on the modulation wave control voltage based on the voltage feedforward quantity, including:

[0086] Reversely superimpose the current change amount and the current reference value to perform feedforward compensation on the current reference value;

[0087] Forwardly superimpose the voltage feedforward quantity and the modulation wave control voltage to perform feedforward compensation on the modulation wave control voltage.

[0088] It is not difficult to understand that the current feedforward compensation can be specifically achieved by directly reversely superimposing the current change amount and the current reference value, and the voltage feedforward compensation can be specifically achieved by directly forwardly superimposing the voltage feedforward quantity and the modulation wave control voltage. The feedforward compensation value is directly superimposed into the control link to ensure the compensation effect.

[0089] Specifically, by directly using the current change amount or the voltage feedforward quantity as the compensation value and superimposing it into the corresponding control link, the accurate cancellation of current or voltage interference is ensured, the control design is simplified, and the design cost is saved.

[0090] As an alternative embodiment, before performing feedforward compensation on the current reference value based on the current change amount, it further includes:

[0091] Input the current change amount into a low-pass filter to obtain the filtered current change amount;

[0092] In the case where the filtered current change amount is greater than a preset limit value, adjust the current change amount to the preset limit value.

[0093] It can be understood that, in order to improve the accuracy of current feedforward compensation and ensure the safety of the control loop, the current change amount as the current feedforward compensation amount can also be further subjected to filtering processing and / or limiting processing before being superimposed into the control loop. The current change amount is first input into a low-pass filter for filtering, and at the same time, a preset limit value is set for the current change amount to limit the current change amount, so as to avoid the current feedforward compensation amount exceeding the preset limit value. After the filtering processing and limiting processing, the processed current change amount is then superimposed into the control loop as the current feedforward compensation amount. The specific value of the preset limit value and the like are not particularly limited in this application and can be set and adjusted according to the actual application situation.

[0094] Specifically, by further performing filtering processing and / or limiting processing on the current change amount, the accuracy and reliability of the current feedforward compensation amount compensated into the control loop can be effectively ensured, the impact of the current feedforward compensation amount on the control loop can be avoided, and the stable operation of the control loop can be guaranteed.

[0095] See Figure 4 as shown Figure 4 is a schematic diagram of the grid current waveform after current limiting protection provided by the present invention; the abscissa is time, and the ordinate represents the grid current; as an optional embodiment, it further includes:

[0096] Obtain the grid current of the grid connected to the grid-connected converter;

[0097] Judge whether the grid current is greater than the current threshold;

[0098] If so, stop outputting the modulation wave of the grid-connected converter to the grid-connected converter.

[0099] It is not difficult to understand that, considering that current spikes are likely to occur in grid current during normal operation, abnormal current spikes may cause faults in the grid-connected converter or the grid, leading to the collapse of the grid-connected system. Therefore, an operation of current limiting protection can also be added to the control system. When an abnormal situation of current spikes occurs in the grid current, the grid-connected converter is subjected to wave blocking processing. The comparison between the grid current and the current threshold refers to the comparison of the current magnitudes. The specific implementation methods of current limiting protection and current threshold are not particularly limited in this application. Specifically, it can be implemented by additionally setting hysteresis control in the control system. Two current limiting points are set to form a hysteresis region. The current value of the first current limiting point I1 is less than the current value of the second current limiting point I2. The current value of the second current limiting point I2 is used as the current threshold. When the current value of the grid current is not greater than the current threshold, the control system normally sends waves. When the current value of the grid current is greater than the current threshold, wave blocking processing is performed, and the control system no longer sends modulation waves to the grid-connected converter, so that the grid current decreases. When the grid current decreases to between the second current limiting point and the first current limiting point, that is, within the hysteresis region, wave blocking processing is still maintained until the grid current decreases to less than the first current limiting point, and then the control system normally sends waves.

[0100] Specifically, current limiting protection is used to avoid the influence of current spikes on the equipment in the grid-connected converter, protect the equipment, and ensure the safety and reliability of the grid-connected converter. Specifically, hysteresis control can be used to implement current limiting protection, and the control logic of the previous state is maintained in the hysteresis region, so as to reduce frequent wave blocking processing, and avoid large power consumption caused by frequent wave blocking while realizing fault current limiting.

[0101] See Figure 5 as shown in Figure 5 FIG. is a schematic diagram of a method for obtaining the current feedforward quantity provided by the present invention. As an optional embodiment, according to the AC side impedance model of the grid-connected converter and the current modulation wave control voltage, the current change amount of the AC side of the grid-connected converter before and after a preset delay time is estimated, including:

[0102] The AC side impedance model of the grid-connected converter is converted into a current prediction model by discretization processing;

[0103] Based on the current prediction model, the predicted current value of the AC side of the grid-connected converter at the current moment is determined;

[0104] The predicted current value of the AC side of the grid-connected converter before the preset delay time is obtained;

[0105] The predicted current value at the current moment is subtracted from the predicted current value before the preset delay time to obtain the current change amount.

[0106] It is not difficult to understand that by discretizing the AC-side impedance model of the grid-following converter, a corresponding current prediction model can be obtained, so as to directly calculate the predicted current value after passing through the AC-side impedance model using the current prediction model; at the same time, the delay time of the control system is pre-estimated to calculate the predicted current value of the AC side of the grid-following converter before the preset delay time, that is, the predicted current value after passing through the AC-side impedance model and the preset delay time. After taking the difference between the two, the current change amount is obtained. For different converter topologies, their AC-side impedance models are different, and the corresponding current prediction models are also different. Therefore, the current prediction model needs to be determined according to the actual circuit topology of the converter. There are multiple choices for the specific method of discretization processing, and this application does not make special limitations here. Methods such as zero-pole cancellation method, backward Euler method, and bilinear discretization method can be used. Through discretization processing, the impedance model in space can be converted into a discrete-time model, so as to calculate the predicted current value at the corresponding moment.

[0107] It should be noted that this application does not make special limitations on the specific value and determination method of the preset delay time. Generally speaking, the preset delay time will be realized in units of the control rhythm of the control system. The control rhythm of the control system refers to the control period of the control system, which is the reciprocal of the calculation frequency of the control system and the time interval for the control system to execute a complete control algorithm. Therefore, the preset delay time mainly depends on the entire control loop delay compensation time of the control system. Specifically, the algorithm execution time, sampling delay time, and loop delay time in the actual control system can be estimated through experiments or simulations, and then the three are added together to estimate the loop compensation delay time, such as 1 beat or 2 beats, etc. After clarifying the preset delay time, the predicted current value of the AC side of the grid-following converter before the preset delay time can be obtained from the historical calculation results of the current prediction model, and the predicted current value of the AC side of the grid-following converter at the current moment is . For example, when the preset delay time is 1 beat, the predicted current value of the AC side of the grid-following converter before the preset delay time is , and the calculation formula for the corresponding current change amount is ; when the preset delay time is 1 beat, the predicted current value of the AC side of the grid-following converter before the preset delay time is , and the calculation formula for the corresponding current change amount is .

[0108] Specifically, through discretization processing, the AC-side impedance model of the grid-connected converter can be converted into a current prediction model based on discrete time, so as to calculate the predicted current value at a certain moment. The predicted current value at the current moment can be directly obtained by substituting it into the current prediction model, and the calculated predicted current value is recorded at a specific position during each calculation, establishing the corresponding relationship between the predicted current value and the corresponding moment, which is convenient for determining the predicted current value before the preset delay time, and thus obtaining the final current change amount.

[0109] It can be understood that the AC side of the grid-connected converter is connected to the power grid through a filter. Therefore, the AC-side impedance model of the grid-connected converter mainly depends on the specific topology of the filter. The filter topologies include: single-L filter, LC filter, LCL filter. For the single-L filter, its equivalent AC-side impedance model is , where is the complex frequency variable, is the equivalent resistance in the single-L filter, is the equivalent inductance in the single-L filter; for the LC filter, its equivalent AC-side impedance model is , where is the equivalent resistance in the LC filter, is the equivalent inductance in the LC filter, is the equivalent capacitance in the LC filter; for the LCL filter, its equivalent AC-side impedance model is , where is the grid-side equivalent inductance in the LCL filter, is the machine-side equivalent inductance in the LCL filter, is the equivalent capacitance in the LCL filter. The grid-side equivalent inductance refers to the reactor close to the power grid side, and the machine-side equivalent inductance refers to the reactor close to the converter side.

[0110] Further, taking the discretization of the backward Euler method ( ) as an example, when the filter is a single-L filter, discretizing the above mathematical model, the obtained current prediction model is: , where is the predicted current value estimated at moment, is the calculation frequency, is the voltage component of the modulation wave control voltage output by the current loop of the grid-connected converter at moment, is the predicted current value estimated at is the d-axis component of the modulation wave control voltage output by the current loop. In the current loop where the q-axis component of the current reference value is located, is the q-axis component of the modulation wave control voltage output by the current loop; when the filter is an LC filter, the above mathematical model is discretized to obtain the current prediction model as: , is the predicted current value estimated at time ; when the filter is an LCL filter, the discretized current prediction model is where is the predicted current value estimated at time

[0111] Furthermore, experiments are respectively conducted on the control system before adding the voltage feedforward link and the current feedforward link without using the control method provided in this application and the control system after adding the voltage feedforward link and the current feedforward link using the control method provided in this application. Refer to Figure 6a as shown in Figure 6a which is a waveform diagram of the d-axis component of the current in a control system without compensation provided by the present invention; refer to Figure 6b as shown in Figure 6b which is a waveform diagram of the d-axis component of the current in a control system with compensation provided by the present invention; Figure 6a and Figure 6b the abscissa of which is time (hour:minute:second), and the ordinate is the current value in Q14 format, where purple represents the d-axis component of the current reference value in the current loop, and orange represents the d-axis component of the AC current feedback value in the current loop. Refer to Figure 7a as shown in Figure 7a which is a waveform diagram of the AC current on the AC side of a grid-connected converter without compensation provided by the present invention; refer to Figure 7b as shown in Figure 7b which is a waveform diagram of the AC current on the AC side of a grid-connected converter with compensation provided by the present invention; Figure 7a and Figure 7b the abscissa of which is time, and the ordinate is the current value of the AC current on the AC side of the grid-connected converter.

[0112] To solve the above technical problems, the present invention also provides a control device for a grid-connected converter, including:

[0113] a voltage compensation amount determination unit for performing phase lead compensation on the obtained grid voltage to obtain a voltage feedforward amount;

[0114] a current compensation amount determination unit for estimating the current change amount on the AC side of the grid-connected converter before and after a preset delay time according to the AC side impedance model of the grid-connected converter and the current modulation wave control voltage;

[0115] A compensation unit, configured to perform feed-forward compensation on a current reference value based on the current change amount, and perform feed-forward compensation on a modulation wave control voltage based on the voltage feed-forward amount, so as to obtain a compensated modulation wave control voltage;

[0116] Wherein, the current reference value is the current value output from the voltage loop of the grid-following converter to the current loop of the grid-following converter; the modulation wave control voltage is the control voltage output from the current loop of the grid-following converter; the current change amount is negatively correlated with the modulation wave control voltage; the voltage feed-forward amount is positively correlated with the modulation wave control voltage;

[0117] A control unit, configured to generate a modulation wave of the grid-following converter based on the compensated modulation wave control voltage.

[0118] For the introduction of a control device for a grid-following converter provided by the present invention, please refer to the embodiments of the control method of the grid-following converter described above, and the present invention will not be elaborated herein.

[0119] To solve the above technical problems, the present invention further provides an electronic device, including:

[0120] A memory, configured to store a computer program;

[0121] A processor, configured to implement the steps of the control method of the grid-following converter as described above.

[0122] Wherein, the processor may include one or more processing cores, such as a 4-core processor, an 8-core processor, etc. The processor may be implemented in at least one hardware form of DSP (Digital Signal Processor), FPGA (Field-Programmable Gate Array), and PLA (Programmable Logic Array). The processor may also include a main processor and a coprocessor. The main processor is a processor for processing data in the wake state, also known as a central processor; the coprocessor is a low-power processor for processing data in the standby state. In some embodiments, the processor may integrate a GPU (graphics processing unit), and the GPU is responsible for rendering and drawing the content to be displayed on the display screen. In some embodiments, the processor may further include an AI (Artificial Intelligence) processor, and the AI processor is used to process computational operations related to machine learning.

[0123] The memory may include one or more computer-readable storage media, which may be non-transitory. The memory may also include high-speed random access memory and non-volatile memory, such as one or more disk storage devices and flash storage devices. In this embodiment, the memory is at least used to store the following computer programs. After the computer programs are loaded and executed by the processor, the relevant steps of the control method of the grid-connected converter disclosed in any of the foregoing embodiments can be implemented. In addition, the resources stored in the memory may also include an operating system and data, etc., and the storage method may be temporary storage or permanent storage. Among them, the operating system may include Windows, Unix, Linux, etc. The data may include, but is not limited to, the data of the control method of the grid-connected converter, etc.

[0124] In some embodiments, the electronic device may further include a display screen, an input / output interface, a communication interface, a power supply, and a communication bus. Those skilled in the art can understand that the above description does not constitute a limitation on the electronic device, and it may include more or fewer components than the above.

[0125] For the introduction of an electronic device provided by the present invention, please refer to the embodiments of the control method of the grid-connected converter described above, and the present invention will not be elaborated herein.

[0126] To solve the above technical problems, the present invention also provides a computer-readable storage medium, on which a computer program is stored. When the computer program is executed by a processor, the steps of the control method of the grid-connected converter as described above are implemented.

[0127] It can be understood that if the method in the above embodiments is implemented in the form of a software functional unit and sold or used as an independent product, it can be stored in a computer-readable storage medium. Based on this understanding, the technical solution of the present application, in essence, or the part that makes a contribution to the prior art, or all or part of this technical solution, can be embodied in the form of a software product. This computer software product is stored in a storage medium and executes all or part of the steps of the methods described in various embodiments of the present application. Specifically, the computer-readable storage medium may include, but is not limited to, any type of disk, including floppy disks, optical discs, mobile hard disks, etc., or any type of medium or device suitable for storing instructions and data, etc. The present application does not make a special limitation herein.

[0128] For the introduction of a computer-readable storage medium provided by the present invention, please refer to the embodiments of the control method of the grid-connected converter described above, and the present invention will not be elaborated herein.

[0129] In this specification, the various embodiments are described in a progressive manner. Each embodiment focuses on the differences from other embodiments. For the similarities and common parts among the embodiments, reference can be made to each other. For the devices disclosed in the embodiments, since they correspond to the methods disclosed in the embodiments, the description is relatively simple. For the relevant parts, reference can be made to the description in the method section. It should also be noted that in this specification, relational terms such as "first" and "second" are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any actual relationship or order between these entities or operations. Moreover, the term "comprising", "including" or any other variant thereof is intended to cover non-exclusive inclusion, so that a process, method, article or device comprising a series of elements not only includes those elements, but also includes other elements not expressly listed, or further includes elements inherent to such process, method, article or device. Without further limitation, an element defined by the statement "comprising an..." does not exclude the existence of additional identical elements in the process, method, article or device comprising the said element.

[0130] Those skilled in the art can further realize that the units and algorithm steps of the examples described in combination with the embodiments disclosed herein can be implemented by electronic hardware, computer software, or a combination of both. To clearly illustrate the interchangeability of hardware and software, the composition and steps of the examples have been generally described according to functions in the above description. Whether these functions are executed in a hardware or software manner depends on the specific application and design constraints of the technical solution. Those skilled in the art can use different methods to implement the described functions for each specific application, but such implementation should not be considered to exceed the scope of the present invention. The above description of the disclosed embodiments enables those skilled in the art to implement or use the present invention. Various modifications to these embodiments will be obvious to those skilled in the art. The general principles defined herein can be implemented in other embodiments without departing from the spirit or scope of the present invention. Therefore, the present invention will not be limited to the embodiments shown herein, but will conform to the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A control method for a grid-following converter, characterized in that, Including: Performing phase-advance compensation on the acquired grid voltage to obtain a voltage feedforward quantity; Predicting the current variation of the AC side of the grid-connected converter before and after a preset delay time according to the AC side impedance model of the grid-connected converter and the current modulation wave control voltage; Performing feedforward compensation on the current reference value based on the current variation, and performing feedforward compensation on the modulation wave control voltage based on the voltage feedforward quantity to obtain a compensated modulation wave control voltage; Wherein, the current reference value is the current value output from the voltage loop of the grid-connected converter to the current loop of the grid-connected converter; the modulation wave control voltage is the control voltage output from the current loop of the grid-connected converter; the current variation is negatively correlated with the modulation wave control voltage; the voltage feedforward quantity is positively correlated with the modulation wave control voltage; Generating the modulation wave of the grid-connected converter based on the compensated modulation wave control voltage.

2. The control method of the network-following type converter according to claim 1, wherein The performing phase-advance compensation on the acquired grid voltage to obtain a voltage feedforward quantity includes: Acquiring the three-phase grid voltage of the grid connected to the grid-connected converter; Converting the three-phase grid voltage into two-phase orthogonal components in a stationary coordinate system to obtain the α-axis voltage and β-axis voltage of the three-phase grid voltage; Extracting the positive sequence component of the α-axis voltage and the positive sequence component of the β-axis voltage; Inputting the positive sequence component of the α-axis voltage into a phase-advance compensator to obtain a first compensation quantity, and inputting the positive sequence component of the β-axis voltage into a phase-advance compensator to obtain a second compensation quantity; Converting the first compensation quantity and the second compensation quantity into two-phase orthogonal components in a dq rotating coordinate system to obtain a voltage feedforward quantity.

3. The control method of the network-following type converter according to claim 2, characterized in that The transfer function of the phase-advance compensator is: ； Among them, is the calculation frequency of the control system, is the preset phase compensation coefficient, is the preset gain compensation coefficient.

4. The control method of the network-following type converter according to claim 1, characterized in that The performing feedforward compensation on the current reference value based on the current variation, and performing feedforward compensation on the modulation wave control voltage based on the voltage feedforward quantity includes: Performing reverse superposition on the current variation and the current reference value to perform feedforward compensation on the current reference value; Performing forward superposition on the voltage feedforward quantity and the modulation wave control voltage to perform feedforward compensation on the modulation wave control voltage.

5. The control method of the grid-following converter according to claim 1, wherein Before performing feedforward compensation on the current reference value based on the current variation, it further includes: Inputting the current variation into a low-pass filter to obtain a filtered current variation; In the case where the filtered current variation is greater than a preset limit value, adjusting the current variation to the preset limit value.

6. The control method of the network-following type converter according to claim 1, characterized in that It further includes: Acquiring the grid current of the grid connected to the grid-connected converter; Judging whether the grid current is greater than a current threshold; If so, stopping outputting the modulation wave of the grid-connected converter to the grid-connected converter.

7. The control method of the network-following type converter according to any one of claims 1 to 6, characterized in that, The predicting the current variation of the AC side of the grid-connected converter before and after a preset delay time according to the AC side impedance model of the grid-connected converter and the current modulation wave control voltage includes: Converting the AC side impedance model of the grid-connected converter into a current prediction model by using discretization processing; Determining the predicted current value of the AC side of the grid-connected converter at the current moment based on the current prediction model; Acquiring the predicted current value of the AC side of the grid-connected converter before the preset delay time; The predicted current value at the current moment is subtracted from the predicted current value before the preset delay time to obtain the current change amount.

8. A control device for a grid-following converter, characterized in that, It includes: A voltage compensation amount determination unit for performing phase lead compensation on the obtained grid voltage to obtain a voltage feedforward amount; A current compensation amount determination unit for estimating the current change amount of the AC side of the grid-connected converter before and after the preset delay time according to the AC side impedance model of the grid-connected converter and the current modulation wave control voltage; A compensation unit for performing feedforward compensation on the current reference value based on the current change amount and performing feedforward compensation on the modulation wave control voltage based on the voltage feedforward amount to obtain a compensated modulation wave control voltage; Wherein, the current reference value is the current value output from the voltage loop of the grid-connected converter to the current loop of the grid-connected converter; the modulation wave control voltage is the control voltage output from the current loop of the grid-connected converter; the current change amount is negatively correlated with the modulation wave control voltage; the voltage feedforward amount is positively correlated with the modulation wave control voltage; A control unit for generating the modulation wave of the grid-connected converter based on the compensated modulation wave control voltage.

9. An electronic device, characterized in that, It includes: A memory for storing computer programs; A processor for implementing the steps of the control method of the grid-connected converter according to any one of claims 1 to 7.

10. A computer-readable storage medium, characterized in that, A computer program is stored on the computer-readable storage medium, and when the computer program is executed by the processor, the steps of the control method of the grid-connected converter according to any one of claims 1 to 7 are implemented.

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