Cascade converter control method and device, power supply system, medium and program product

Abstract

The invention discloses a cascade converter control method and device, a power supply system, a medium and a program product, and relates to the technical field of power electronics, and the disclosed cascade converter control method comprises the steps: obtaining a preset negative sequence voltage suppression demand of the power supply system where a cascade converter is located under the condition that the cascade converter enters a low voltage ride through state; if the preset negative sequence voltage suppression demand is negative sequence voltage suppression, controlling the cascade converter by using a zero sequence voltage injection strategy so as to enable the cascade converter to maintain power balance; and if the preset negative-sequence voltage suppression demand is that negative-sequence voltage suppression is not carried out, controlling the cascade converter by using a negative-sequence current injection strategy so as to enable the cascade converter to maintain power balance. According to the invention, the control strategy of the cascade converter during the low-voltage ride-through period is more consistent with the actual condition of the power supply system of the cascade converter, and the universality of the cascade converter control method is improved.

Description

Technical Field

[0001] The present application relates to the field of power electronics technology, and in particular to a cascade converter control method, device, power supply system, medium and program product. Background Art

[0002] In the new power supply system based on renewable energy power generation technology, the access to energy storage equipment through cascade converters can smooth out the fluctuations of renewable energy and provide peak-shaving capability and stable power support for the power supply system.

[0003] In the related art, during the low voltage ride-through of the power supply system, the system voltage imbalance will cause the DC side power imbalance of the cascade converter, and the SOC difference will increase. At this time, the cascade converter can be controlled by injecting zero-sequence voltage to maintain the power balance between the phases of the cascade converter grid connection point. However, this cascade converter control method does not take into account the actual negative sequence voltage suppression requirements of the power supply system, and its versatility is low. Summary of the invention

[0004] The main purpose of this application is to provide a cascade converter control method, device, power supply system, medium and program product, aiming to solve the technical problem of how to improve the versatility of the cascade converter control method during low voltage ride-through.

[0005] To achieve the above object, the present application proposes a cascade converter control method, the cascade converter control method comprising:

[0006] When the cascade converter enters a low voltage ride-through state, obtaining a preset negative sequence voltage suppression requirement of a power supply system where the cascade converter is located;

[0007] If the preset negative sequence voltage suppression requirement is to perform negative sequence voltage suppression, a zero sequence voltage injection strategy is used to control the cascade converter so that the cascade converter maintains power balance;

[0008] If the preset negative sequence voltage suppression requirement is not to perform negative sequence voltage suppression, the negative sequence current injection strategy is used to control the cascade converter so that the cascade converter maintains power balance.

[0009] In one embodiment, before the step of controlling the cascade converter by using the zero-sequence voltage injection strategy, the cascade converter control method further includes:

[0010] Obtaining the positive sequence active current of the cascade converter before it enters the low voltage ride-through state and the three-phase system voltage of the grid connection point where the cascade converter is located;

[0011] Perform positive and negative sequence separation on the three-phase system voltage to obtain positive sequence voltage and negative sequence voltage;

[0012] The steps of controlling the cascade converter by using the zero-sequence voltage injection strategy include:

[0013] Determine a first d-axis current, a first q-axis current, a second d-axis current, and a second q-axis current in the two-phase rotating coordinate system according to the positive-sequence voltage, the positive-sequence active current, the rated current of the cascade converter, and the d-axis voltage and the q-axis voltage of the negative-sequence voltage in the two-phase rotating coordinate system;

[0014] determining a first positive-sequence reference current according to the first d-axis current and the first q-axis current;

[0015] determining a first negative-sequence reference current according to the second d-axis current and the second q-axis current;

[0016] Reconstructing a three-phase first reference current according to a first positive-sequence reference current and a first negative-sequence reference current;

[0017] Determining a three-phase first reference voltage according to the three-phase first reference current and the impedance characteristics of the grid connection point;

[0018] Determine a zero-sequence voltage phase and a first zero-sequence voltage amplitude according to selected reference currents of any two phases in the three-phase first reference current and a selected system voltage corresponding to the selected reference currents of any two phases in the three-phase system voltage;

[0019] Determining a first zero-sequence voltage according to a zero-sequence voltage phase and a first zero-sequence voltage amplitude;

[0020] Superimposing the first zero-sequence voltage with the three-phase first reference voltages respectively to obtain the three-phase first target voltages;

[0021] The cascade converter is controlled according to the first three-phase target voltage.

[0022] In one embodiment, the step of determining a first d-axis current, a first q-axis current, a second d-axis current, and a second q-axis current in a two-phase rotating coordinate system according to the positive-sequence voltage, the positive-sequence active current, the rated current of the cascade converter, and the d-axis voltage and the q-axis voltage of the negative-sequence voltage in a two-phase rotating coordinate system comprises:

[0023] Obtain the voltage drop amplitude of the grid connection point;

[0024] Determine the negative sequence current coefficient corresponding to the voltage drop amplitude according to the mapping relationship between the preset voltage drop amplitude and the preset negative sequence current coefficient;

[0025] According to the negative-sequence current coefficient, the positive-sequence voltage, the positive-sequence active current, the rated current of the cascade converter, the d-axis voltage and the q-axis voltage of the negative-sequence voltage in the two-phase rotating coordinate system, the first d-axis current, the first q-axis current, the second d-axis current and the second q-axis current in the two-phase rotating coordinate system are determined.

[0026] In one embodiment, the step of superimposing the first zero-sequence voltage with the three-phase first reference voltages to obtain the three-phase first target voltages includes:

[0027] Superimposing the first zero-sequence voltage with the three-phase first reference voltages respectively to obtain the three-phase intermediate reference voltage;

[0028] If the amplitude of any intermediate reference voltage among the three-phase intermediate reference voltages is greater than the amplitude of the rated voltage of the cascade converter, the second zero-sequence voltage amplitude is determined according to the amplitude of the rated voltage, the amplitude of the positive-sequence voltage component and the amplitude of the negative-sequence voltage component;

[0029] Determine the second zero-sequence voltage according to the zero-sequence voltage phase and the second zero-sequence voltage amplitude;

[0030] The second zero-sequence voltage is superimposed on the three-phase first reference voltages respectively to obtain the three-phase first target voltages.

[0031] In one embodiment, the steps of controlling the cascade converter using the negative sequence current injection strategy include:

[0032] Determine the third d-axis current, the third q-axis current, the fourth d-axis current and the fourth q-axis current in the two-phase rotating coordinate system according to the positive-sequence voltage, the positive-sequence active current, the rated current and the negative-sequence voltage;

[0033] determining a second positive-sequence reference current according to the third d-axis current and the third q-axis current;

[0034] determining a second negative-sequence reference current according to the fourth d-axis current and the fourth q-axis current;

[0035] Reconstructing a three-phase second reference current according to the second positive-sequence reference current and the second negative-sequence reference current;

[0036] Determining a three-phase second target voltage according to a three-phase second reference current and an impedance characteristic of a grid connection point;

[0037] The cascade converter is controlled according to the second three-phase target voltage.

[0038] In one embodiment, before the step of determining the three-phase second target voltage according to the three-phase second reference current and the impedance characteristics of the grid connection point, the cascade converter control method further includes:

[0039] If the amplitude of any reference current among the three-phase second reference currents is greater than the amplitude of the rated current of the cascade converter, the current adjustment ratio is determined according to the amplitude of the rated current and the amplitude of the maximum reference current, and the maximum reference current is the reference current with the largest amplitude among the three-phase second reference currents;

[0040] According to the current adjustment ratio, the three-phase second reference currents are adjusted respectively to obtain the three-phase target currents;

[0041] The step of determining the three-phase second target voltage according to the three-phase second reference current and the impedance characteristics of the grid connection point includes:

[0042] According to the impedance characteristics of the three-phase second reference target and the grid connection point, the three-phase second target voltage is determined.

[0043] In addition, to achieve the above-mentioned purpose, the present application also proposes a cascade converter control device, which includes: a memory, a processor, and a computer program stored in the memory and executable on the processor, wherein the computer program is configured to implement the steps of the cascade converter control method as described above.

[0044] In addition, to achieve the above purpose, the present application also proposes a power supply system, the power supply system comprising:

[0045] at least one cascade converter;

[0046] As the above-mentioned cascade converter control device, the cascade converter control device is connected to at least one cascade converter.

[0047] In addition, to achieve the above objectives, the present application also proposes a storage medium, which is a computer-readable storage medium. A computer program is stored on the storage medium. When the computer program is executed by a processor, the steps of the cascade converter control method as described above are implemented.

[0048] In addition, to achieve the above-mentioned purpose, the present application also provides a computer program product, which includes a computer program. When the computer program is executed by a processor, the steps of the cascade converter control method as described above are implemented.

[0049] One or more technical solutions proposed in this application have at least the following technical effects:

[0050] The present application provides a cascade converter control method, equipment, power supply system, medium and program product. When the cascade converter enters a low voltage ride-through state, the preset negative sequence voltage suppression requirement of the power supply system is used to determine whether negative sequence voltage suppression is required. When negative sequence voltage suppression is required, the cascade converter is controlled by a zero sequence voltage injection strategy. When negative sequence voltage suppression is not required, the cascade converter is controlled by a negative sequence current injection strategy, so that the cascade converter maintains power balance. Therefore, when the cascade converter enters a low voltage ride-through state, different control strategies are selected to control the cascade converter according to the actual requirements of the power supply system where the cascade converter is located, so that the control strategy of the cascade converter during the low voltage ride-through period is more in line with the actual situation of the cascade converter power supply system, thereby improving the versatility of the cascade converter control method. BRIEF DESCRIPTION OF THE DRAWINGS

[0051] The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments consistent with the present application and, together with the description, serve to explain the principles of the present application.

[0052] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the related technologies, the drawings required for use in the embodiments or the related technical descriptions are briefly introduced below. Obviously, for ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0053] Figure 1 This is a partial structural diagram of the power supply system of this application;

[0054] Figure 2 This is a flow chart of the first embodiment of the cascade converter control method of the present application;

[0055] Figure 3 An exemplary current and voltage phasor diagram provided for the cascade converter control method of the present application;

[0056] Figure 4 A simulation waveform diagram of voltage and current in an exemplary power supply system provided by the cascade converter control method of the present application;

[0057] Figure 5 An exemplary simulation waveform diagram of the inter-phase power difference and three-phase SOC average value of a cascade converter provided for the cascade converter control method of the present application;

[0058] Figure 6 An exemplary waveform diagram of zero-sequence voltage amplitude provided for the cascade converter control method of the present application;

[0059] Figure 7 An exemplary maximum value waveform diagram of the three-phase first target voltage provided for the cascade converter control method of the present application;

[0060] Figure 8 Another exemplary current-voltage phasor diagram provided for the cascade converter control method of the present application;

[0061] Fig. 9 Another exemplary simulation waveform diagram of voltage and current in a power supply system provided by the cascade converter control method of the present application;

[0062] Fig.10 Another exemplary simulation waveform diagram of the inter-phase power difference and three-phase SOC average value of the cascade converter provided for the cascade converter control method of the present application;

[0063] Fig.11 An exemplary maximum value waveform diagram of the second target voltage of three phases provided for the cascade converter control method of the present application;

[0064] Fig.12 Schematic diagram of the device structure of the hardware operating environment involved in the cascade converter control method in the embodiment of the present application.

[0065] The realization of the purpose, functional features and advantages of this application will be further explained in conjunction with embodiments and with reference to the accompanying drawings. DETAILED DESCRIPTION

[0066] It should be understood that the specific embodiments described herein are only used to explain the technical solutions of the present application and are not used to limit the present application.

[0067] In order to better understand the technical solution of the present application, a detailed description will be given below in conjunction with the accompanying drawings and specific implementation methods.

[0068] The main solution of the embodiment of the present application is: when the cascade converter enters the low voltage ride-through state, the preset negative-sequence voltage suppression requirement of the power supply system where the cascade converter is located is obtained; if the preset negative-sequence voltage suppression requirement is to perform negative-sequence voltage suppression, the zero-sequence voltage injection strategy is used to control the cascade converter so that the cascade converter maintains power balance; if the preset negative-sequence voltage suppression requirement is not to perform negative-sequence voltage suppression, the negative-sequence current injection strategy is used to control the cascade converter so that the cascade converter maintains power balance.

[0069] Therefore, the present application provides a solution. When the cascade converter enters a low voltage ride-through state, the preset negative-sequence voltage suppression requirement of the power supply system is used to determine whether negative-sequence voltage suppression is needed. When negative-sequence voltage suppression is needed, the cascade converter is controlled by a zero-sequence voltage injection strategy. When negative-sequence voltage suppression is not needed, the cascade converter is controlled by a negative-sequence current injection strategy to keep the power balance of the cascade converter. Therefore, when the cascade converter enters a low voltage ride-through state, different control strategies are selected to control the cascade converter according to the actual requirements of the power supply system where the cascade converter is located, so that the control strategy of the cascade converter during the low voltage ride-through period is more in line with the actual situation of the cascade converter power supply system, thereby improving the versatility of the cascade converter control method.

[0070] First, the present application embodiment provides a power supply system, referring to Figure 1 , the power supply system may include:

[0071] at least one cascade converter;

[0072] As the above-mentioned cascade converter control device, the cascade converter control device is connected to at least one cascade converter.

[0073] It should be noted that the power supply system is a three-phase power supply system, and the power supply system may include one or more cascade converters.

[0074] The present application embodiment is described by taking the energy storage cascade converter as an example. Figure 1 As shown, the energy storage cascade converter may include a three-phase commutation bridge arm, the commutation bridge arm includes a plurality of cascaded power modules, connected to the power grid through a reactor, and the power module includes an H bridge, a DC capacitor, a DC filter reactor and a battery.

[0075] It can be understood that the cascade converter control device can control the output power of the cascade converter by using the cascade converter control method of the following embodiment when the cascade converter enters the low voltage ride-through state.

[0076] Based on this, the embodiment of the present application provides a cascade converter control method, referring to Figure 2 , Figure 2 This is a flow chart of the first embodiment of the cascade converter control method of the present application.

[0077] In this embodiment, the cascade converter control method may include steps S100 to S500:

[0078] Step S100, when the cascade converter enters a low voltage ride-through state, obtaining a preset negative sequence voltage suppression requirement of a power supply system where the cascade converter is located.

[0079] Step S200: If the preset negative sequence voltage suppression requirement is to perform negative sequence voltage suppression, a zero sequence voltage injection strategy is used to control the cascade converter so that the cascade converter maintains power balance.

[0080] Step S300: If the preset negative sequence voltage suppression requirement is not to perform negative sequence voltage suppression, a negative sequence current injection strategy is used to control the cascade converter so that the cascade converter maintains power balance.

[0081] It should be noted that when an asymmetric grid fault occurs in the power supply system where the cascade converter is located, a voltage drop will occur at the grid connection point where the cascade converter is located, and the cascade converter can enter a low voltage ride-through state. At this time, the three-phase system voltage at the grid connection point where the cascade converter is located can be collected to determine the target voltage, and the cascade converter can be controlled to ensure power balance between the three phases of the cascade converter, thereby maintaining the consistency of the three-phase SOC of the cascade converter.

[0082] It is understandable that different power supply systems have different preset negative-sequence voltage suppression requirements, and the preset negative-sequence voltage suppression requirements can be preset according to actual usage requirements of the power supply system.

[0083] Therefore, this embodiment provides a cascade converter control method. When the cascade converter enters a low voltage ride-through state, the preset negative sequence voltage suppression requirement of the power supply system is used to determine whether negative sequence voltage suppression is needed. When negative sequence voltage suppression is needed, the cascade converter is controlled by a zero sequence voltage injection strategy. When negative sequence voltage suppression is not needed, the cascade converter is controlled by a negative sequence current injection strategy to keep the power balance of the cascade converter. Therefore, when the cascade converter enters a low voltage ride-through state, different control strategies are selected to control the cascade converter according to the actual requirements of the power supply system where the cascade converter is located, so that the control strategy of the cascade converter during the low voltage ride-through period is more in line with the actual situation of the cascade converter power supply system, thereby improving the versatility of the cascade converter control method.

[0084] In a feasible implementation manner, before step S200, the cascade converter control method may further include steps S400 to S500; correspondingly, step S200 may include steps A210 to A290:

[0085] Step S400, obtaining the positive sequence active current of the cascade converter before it enters the low voltage ride through state and the three-phase system voltage of the grid connection point where the cascade converter is located.

[0086] Step S500, performing positive-sequence and negative-sequence separation processing on the three-phase system voltage to obtain a positive-sequence voltage and a negative-sequence voltage.

[0087] Step A210, determines the first d-axis current, the first q-axis current, the second d-axis current and the second q-axis current in the two-phase rotating coordinate system based on the positive-sequence voltage, the positive-sequence active current, the rated current of the cascade converter, the d-axis voltage and the q-axis voltage of the negative-sequence voltage in the two-phase rotating coordinate system.

[0088] Step A220: determining a first positive-sequence reference current according to the first d-axis current and the first q-axis current.

[0089] Step A230: determining a first negative-sequence reference current according to the second d-axis current and the second q-axis current.

[0090] Step A240: reconstruct a three-phase first reference current according to the first positive-sequence reference current and the first negative-sequence reference current.

[0091] Step A250, determining a three-phase first reference voltage according to the three-phase first reference current and the impedance characteristics of the grid connection point.

[0092] Step A260, determining the zero-sequence voltage phase and the first zero-sequence voltage amplitude according to the selected reference currents of any two phases in the three-phase first reference current and the selected system voltage corresponding to the selected reference currents of any two phases in the three-phase system voltage.

[0093] Step A270, determining a first zero-sequence voltage according to the zero-sequence voltage phase and the first zero-sequence voltage amplitude;

[0094] Step A280, superimposing the first zero-sequence voltage with the three-phase first reference voltages respectively to obtain the three-phase first target voltages.

[0095] Step A290: Control the cascade converter according to the first three-phase target voltage.

[0096] It should be noted that the system voltage is the grid voltage at the grid connection point where the cascade converter is located. The positive-sequence voltage and negative-sequence voltage can be obtained by performing positive-sequence and negative-sequence separation processing on the three-phase system voltage. The positive-sequence active current can be obtained based on the current and / or voltage data before the cascade converter enters the low voltage ride-through state. In the case where negative-sequence voltage suppression is required, a zero-sequence voltage injection strategy of injecting zero-sequence voltage into the reference voltage can be used to determine the first target voltage and control the cascade converter. In the case where negative-sequence voltage suppression is not required, a negative-sequence current injection strategy of injecting negative-sequence current into the reference current corresponding to the reference voltage can be used to determine the second target voltage and control the cascade converter.

[0097] It can be understood that the d-axis voltage and the q-axis voltage can be obtained by performing coordinate transformation on the negative-sequence voltage. The first d-axis current and the first q-axis current can be the d-axis current and the q-axis current corresponding to the positive-sequence reference current of the first reference current required for subsequent control of the cascade converter. The second d-axis current and the second q-axis current can be the d-axis current and the q-axis current corresponding to the negative-sequence reference current of the first reference current. When determining the first d-axis current, the first q-axis current, the second d-axis current and the second q-axis current in this embodiment, the rated current of the cascade converter is combined, and the actual output capacity of the cascade converter is taken into account, which can further improve the reliability of the cascade converter control method.

[0098] In this embodiment, the first d-axis current, the first q-axis current, the second d-axis current and the second q-axis current may be calculated using the following formula 1. Formula 1 is:

[0099] I pd1 =K pd *V p *I pd

[0100] I pq1 =K pq *(0.9-V p )*I R

[0101] I nd1 =K n *V nq

[0102] Inq1 =-K n *V nd

[0103] Among them, I pd1 is the first d-axis current; K pd V is the active current retention coefficient, which indicates the amplitude of active current maintained when the voltage drops, ranging from 0 to 1.0; p is the amplitude of the positive sequence voltage; I pd is the positive sequence active current; I pq1 is the first q-axis current; K pq I is the reactive power support coefficient, which indicates the amplitude of reactive current support provided when the voltage drops, ranging from 0 to 1.5; R is the rated current of the cascade converter; I nd1 is the second d-axis current; K n is the negative sequence current coefficient, which indicates the suppression amplitude of negative sequence voltage during drop, ranging from 0 to 1.0; V nq is the amplitude of the q-axis voltage of the negative sequence voltage; I nq1 is the second q-axis current; V nd is the amplitude of the d-axis voltage of the negative sequence voltage. pd , K pq and K n It can be determined based on the actual voltage drop at the grid connection point.

[0104] In formula 1, the positive-sequence d-axis reference current is proportional to the positive-sequence voltage and the positive-sequence active current, and is adjusted by the active power retention coefficient during voltage drop; the positive-sequence q-axis reference current is proportional to the difference between the positive-sequence voltage and the low-through threshold voltage and the rated current of the cascade converter, and is adjusted by the reactive amplitude system during voltage drop; the negative-sequence d-axis reference current component is proportional to the negative-sequence voltage q-axis component, and is modulated by the negative-sequence voltage suppression coefficient; the negative-sequence q-axis reference current component is proportional to the reverse value of the negative-sequence voltage d-axis component, and is adjusted by the negative-sequence voltage suppression coefficient. Among them, the phase of the negative-sequence reference current is 90° different from the phase of the negative-sequence voltage, which can ensure that the negative-sequence reference current reduces the amplitude of the negative-sequence voltage to the greatest extent without affecting the phase of the negative-sequence voltage.

[0105] It can be understood that the first positive-sequence reference current can be obtained by performing an inverse coordinate transformation on the first d-axis current and the first q-axis current. The first negative-sequence reference current can be obtained by performing an inverse coordinate transformation on the second d-axis current and the second q-axis current. After obtaining the first positive-sequence reference current and the first negative-sequence reference current, the three-phase first reference current can be reconstructed, and then combined with the impedance characteristics of the grid connection point, the three-phase first reference voltage can be determined as the reference voltage for subsequent control of the cascade converter.

[0106] In the zero-sequence voltage injection strategy, it is necessary to inject the first zero-sequence voltage into the three-phase first reference voltage.

[0107] The phase and amplitude of the first zero-sequence voltage can be determined using the following formula 2:

[0108]

[0109] Among them, θ0 is the zero-sequence voltage phase, τ is the calculation factor, P0 is the sum of the three-phase power, U a is the amplitude of the A phase system voltage, I a is the amplitude of the first reference current of phase A, θ a is the phase of the A-phase system voltage, is the phase of the first reference current of phase A, U b is the amplitude of the B-phase system voltage, I b is the amplitude of the first reference current of phase B, θ b is the phase of the B-phase system voltage, is the phase of the first reference current of phase B, and U0 is the first zero-sequence voltage amplitude.

[0110] It should be noted that the selected reference current in Formula 2 is taken as an example of the first reference current of phase A and the first reference current of phase B, and the corresponding selected system voltage is taken as an example of the system voltage of phase A and the system voltage of phase B. In actual use, any two-phase first reference currents can be selected from the three-phase first reference currents as the selected reference currents, and the two-phase system voltages with the same phase as the two-phase selected reference currents can be determined from the three-phase system voltages as the selected system voltages.

[0111] Therefore, after obtaining the three-phase first reference voltage and the first zero-sequence voltage, the first zero-sequence voltage is superimposed on the three-phase first reference voltages respectively using the following formula 3 to obtain the three-phase first target voltage. Formula 3 is:

[0112]

[0113] Among them, u a is the first target voltage of phase A, u aref is the first reference voltage of phase A, u0 is the first zero-sequence voltage, u b is the first target voltage of phase B, u bref is the first reference voltage of phase B, u c is the first target voltage of phase C, u cref It is the first reference voltage of phase C.

[0114] In one example, taking a 35kV / 25MW cascaded energy storage converter as an example, a two-phase short circuit fault occurs at the grid connection point of the cascaded converter, and the voltage drops to 0.2pu. The first positive sequence reference current I p1, the first negative sequence reference current I n1 , positive sequence voltage V p , negative sequence voltage V n The phasor diagram of the zero-sequence voltage u0 is shown in Figure 3. Based on Formula 1, in order to suppress the negative-sequence voltage to the greatest extent, the phase difference between the negative-sequence reference current and the negative-sequence voltage is set to 90 degrees, the amplitude of the negative-sequence reference current is proportional to the amplitude of the negative-sequence voltage, and the negative-sequence compensation coefficient is 1.0. When the zero-sequence voltage is added to ensure the power balance between phases, the power generated by the zero-sequence voltage and the positive and negative-sequence current is calculated, and the power and the power of the positive-sequence voltage, the negative-sequence current, and the negative-sequence voltage and the positive-sequence current are offset. In this low-voltage ride-through state, the simulated waveforms of the voltages and currents in the power supply system are as follows: Figure 4 As shown in the figure, a two-phase short-circuit fault occurs in the grid voltage, and the fault phase voltage drops to 0.2pu. The output current of the cascade converter (such as Figure 4 The device current includes positive sequence current and negative sequence current, and the zero sequence voltage is added at 1.6s to balance the phase power. Figure 5 As shown in the simulation waveforms of the interphase power difference and the three-phase SOC average value of the cascade converter, when the cascade converter only outputs positive and negative sequence currents before 1.6s, there is a constant power difference between the three phases, and the three-phase SOC difference continues to increase; after the zero-sequence voltage is added at 1.6s, the interphase power difference of each phase is 0, and the difference in the three-phase SOC values ​​remains constant.

[0115] Therefore, this embodiment provides a cascade converter control method. During the low voltage ride-through period of the cascade converter, when it is determined that negative-sequence voltage suppression is required, a negative-sequence reference current perpendicular to the negative-sequence voltage is added for suppression, and zero-sequence voltage injection is used to perform phase-to-phase power balancing, thereby achieving negative-sequence voltage suppression of the cascade converter during the low voltage ride-through period and maintaining power balance among the three phases of the cascade converter, thereby maintaining the SOC of the cascade converter constant during the low voltage ride-through period.

[0116] In a feasible implementation, step A210 may include: obtaining the voltage drop amplitude of the grid-connected point; determining the negative-sequence current coefficient corresponding to the voltage drop amplitude according to the mapping relationship between the preset voltage drop amplitude and the preset negative-sequence current coefficient; determining the first d-axis current, the first q-axis current, the second d-axis current and the second q-axis current in the two-phase rotating coordinate system according to the negative-sequence current coefficient, the positive-sequence voltage, the positive-sequence active current, the rated current of the cascade converter, and the d-axis voltage and q-axis voltage of the negative-sequence voltage in the two-phase rotating coordinate system.

[0117] It should be noted that the voltage drop amplitudes at the grid-connected points of the cascaded converters are different, and different negative-sequence current coefficients can be used to suppress the negative-sequence voltage.

[0118] In actual use, the mapping relationship between different preset voltage drop amplitudes and preset negative-sequence current coefficients can be pre-set to obtain a mapping relationship table between the preset voltage drop amplitudes and the preset negative-sequence current coefficients. Therefore, after collecting the voltage drop amplitude of the grid-connected point, the corresponding negative-sequence current coefficient can be obtained by looking up the table to perform the first reference current calculation.

[0119] It can be understood that the voltage drop amplitude can be determined according to the voltage difference between the system voltage where the grid fault occurs and the original system voltage.

[0120] In a feasible implementation, step A280 may include: superimposing the first zero-sequence voltage with the three-phase first reference voltages respectively to obtain a three-phase intermediate reference voltage; if the amplitude of any intermediate reference voltage in the three-phase intermediate reference voltages is greater than the amplitude of the rated voltage of the cascade converter, determining the second zero-sequence voltage amplitude according to the amplitude of the rated voltage, the amplitude of the positive-sequence voltage component and the amplitude of the negative-sequence voltage component; determining the second zero-sequence voltage according to the zero-sequence voltage phase and the second zero-sequence voltage amplitude; superimposing the second zero-sequence voltage with the three-phase first reference voltages respectively to obtain the three-phase first target voltage.

[0121] It should be noted that after the first zero-sequence voltage is superimposed with the three-phase first reference voltages respectively, it may happen that the superimposed intermediate reference voltage exceeds the output capacity of the cascade converter, that is, the amplitude of the intermediate reference voltage is greater than the amplitude of the rated voltage of the cascade converter. At this time, the zero-sequence voltage can be limited to avoid the situation where the amplitude of the final first target voltage is greater than the amplitude of the rated voltage of the cascade converter, thereby avoiding the situation where the first target voltage exceeds the output capacity of the cascade converter.

[0122] The second zero-sequence voltage amplitude can be determined using the following formula 4:

[0123] U 0lim =V max -V p -V n

[0124] U 0lim is the second zero-sequence voltage amplitude, V max is the rated voltage amplitude of the cascade converter, V p is the amplitude of the positive sequence voltage, V n is the magnitude of the negative sequence voltage.

[0125] In one example, the zero-sequence voltage is calculated at different voltage drop amplitudes (0.2-0.9 pu) and different negative-sequence current coefficients (0.0-1.0), and the waveform of the zero-sequence voltage amplitude can be obtained as follows: Figure 6As shown in the figure, it can be seen that when the voltage drop is small and the negative sequence current coefficient is high, the zero sequence voltage has a large amplitude, and some even exceed 1.0pu. At this time, the maximum value waveform of the three-phase first target voltage superimposed with the zero sequence voltage is as follows Figure 7 As shown, the amplitude of the first target voltage exceeds 1.0 pu, which exceeds the output capacity of the cascade converter, so it is necessary to take the above-mentioned zero-sequence voltage limiting measure.

[0126] Therefore, this embodiment provides a cascade converter control method. In the zero-sequence voltage injection strategy, the zero-sequence voltage is limited based on the actual output capacity of the cascade converter, ensuring that the obtained three-phase first target voltage does not exceed the actual output capacity of the cascade converter, thereby further improving the reliability of the cascade converter control method.

[0127] In a feasible implementation manner, step A300 may include steps A310 to A360:

[0128] Step A310, determining a third d-axis current, a third q-axis current, a fourth d-axis current and a fourth q-axis current in a two-phase rotating coordinate system according to the positive-sequence voltage, the positive-sequence active current, the rated current and the negative-sequence voltage.

[0129] Step A320: determining a second positive-sequence reference current according to the third d-axis current and the third q-axis current.

[0130] Step A330: determining a second negative-sequence reference current according to the fourth d-axis current and the fourth q-axis current.

[0131] Step A340: reconstruct a three-phase second reference current according to the second positive-sequence reference current and the second negative-sequence reference current.

[0132] Step A350, determining a three-phase second target voltage according to a three-phase second reference current and an impedance characteristic of the grid connection point.

[0133] Step A360: Control the cascade converter according to the second three-phase target voltage.

[0134] It should be noted that the third d-axis current and the third q-axis current may be the d-axis current and the q-axis current corresponding to the positive sequence reference current of the second reference current required for the subsequent control of the cascade converter. The fourth d-axis current and the fourth q-axis current may be the d-axis current and the q-axis current corresponding to the negative sequence reference current of the second reference current. According to the impedance characteristics of the three-phase second reference current and the grid connection point, the three-phase second target voltage may be obtained as the reference voltage for the subsequent control of the cascade converter.

[0135] In this embodiment, the third d-axis current, the third q-axis current, the fourth d-axis current and the fourth q-axis current can be obtained by using the following formula 5. Formula 5 is:

[0136] I pd2 =K pd *V p *I pd

[0137] I pq2 =K pq *(0.9-V p )*I R

[0138]

[0139] Where, Ipd2 is the third d-axis current, I pd is the positive sequence active current, I R is the rated current of the cascade converter, I pq2 is the third q-axis current, I nd2 is the fourth d-axis current, I p is the second positive sequence reference current, I nq2 is the fourth q-axis current, V n is the negative sequence voltage, is the phase of the second negative sequence reference current, is the phase of the negative sequence voltage, is the phase of the positive sequence voltage, is the phase of the second positive sequence reference current.

[0140] In formula 5, the power generated by the negative-sequence current and positive-sequence voltage can offset the power generated by the positive-sequence current and negative-sequence voltage, so there is no need to add zero-sequence voltage to ensure three-phase power balance.

[0141] In one example, continuing with the 35kV / 25MW cascade energy storage converter as an example, a two-phase short circuit fault occurs at the grid connection point of the cascade converter, and the voltage drops to 0.2pu. The second positive sequence reference current I p2 , the second negative sequence reference current I n2 , positive sequence voltage V p and negative sequence voltage V n The phasor diagram is shown in Figure 8. At this time, the power generated by the injected negative-sequence reference current and the positive-sequence voltage cancels out the power generated by the positive-sequence reference current and the negative-sequence voltage. The amplitude of the negative-sequence reference current is proportional to the ratio of the positive-sequence reference current, the negative-sequence voltage, and the positive-sequence voltage. In this low voltage ride-through state, the simulated waveforms of voltage and current are as follows: Fig. 9 As shown in the figure, a two-phase short-circuit fault occurred in the grid voltage, and the fault phase voltage dropped to 0.2pu. The output current of the cascade converter includes positive sequence current, and negative sequence current is added at 1.6s to balance the phase power. At this time, the phase power difference and the three-phase SOC average simulation waveform are as follows: Fig.10As shown in the figure, when only positive sequence current is output, there is a constant power difference among the three phases, and the SOC difference among the three phases continues to increase; after adding negative sequence current, the power difference among the phases is 0, and the difference of the SOC values ​​among the three phases remains constant.

[0142] In a feasible implementation, before step A550, the cascade converter control method may further include: if the amplitude of any reference current among the three-phase second reference currents is greater than the amplitude of the rated current of the cascade converter, then determining the current adjustment ratio according to the amplitude of the rated current and the amplitude of the maximum reference current, the maximum reference current being the reference current with the largest amplitude among the three-phase second reference currents; according to the current adjustment ratio, adjusting the three-phase second reference currents respectively to obtain the three-phase target current.

[0143] Correspondingly, step A550 may include: determining a three-phase second target voltage according to the three-phase second reference target and the impedance characteristics of the grid connection point.

[0144] It should be noted that if the amplitude of any reference current in the three-phase second reference current is greater than the amplitude of the rated current of the cascade converter, it means that any reference current exceeds the output capacity of the cascade converter, and the three-phase second reference current can be limited to obtain the target current.

[0145] In a specific implementation, the current adjustment ratio can be determined by using Formula 6 according to the amplitude of the rated current and the amplitude of the maximum reference current. Formula 6 is:

[0146]

[0147] Among them, K ix is the current adjustment ratio, I x is the magnitude of the rated current of the cascade converter, I a1 is the amplitude of the second reference current of phase A, I b1 is the amplitude of the second reference current of phase B, I c1 is the amplitude of the second reference current of phase C.

[0148] It can be understood that after obtaining the current adjustment ratio, the three-phase second reference currents are multiplied by the current adjustment ratio respectively to obtain the three-phase target currents, thereby realizing the limiting process.

[0149] In one example, at different drop levels (0.2-0.9 pu) and different negative sequence compensation degrees (0.0-1.0), the three-phase reference current is calculated using the above formulas 5 and 6, and the waveform of the three-phase reference current amplitude is obtained as follows: Fig.11 As shown, it can be seen that the amplitude of the reference current does not exceed the amplitude of the rated current of the cascade converter.

[0150] Therefore, this embodiment provides a cascade converter control method, during the low voltage ride-through of the cascade converter, when it is determined that negative sequence voltage suppression is not required, the negative sequence current injection method is used to perform phase-to-phase power balancing, thereby maintaining the SOC of the cascade converter constant during the low voltage ride-through period. In addition, the reference current is limited by adopting a three-phase proportional limiting method, ensuring that the target current does not exceed the current output capacity of the cascade converter, further improving the reliability of the cascade converter control method.

[0151] The present application provides a cascade converter control device, which includes: at least one processor; and a memory communicatively connected to the at least one processor; wherein the memory stores instructions executable by the at least one processor, and the instructions are executed by the at least one processor so that the at least one processor can execute the cascade converter control method in the above-mentioned embodiment one.

[0152] Reference below Fig.12 , which shows a schematic diagram of the structure of a cascade converter control device suitable for implementing the embodiment of the present application. The cascade converter control device in the embodiment of the present application may include but is not limited to mobile terminals such as controllers, notebook computers, PDAs (Personal Digital Assistants), PADs (Portable Application Descriptions), etc., and fixed terminals such as desktop computers, etc. Fig.12 The cascade converter control device shown is merely an example and should not bring any limitation to the functions and scope of use of the embodiments of the present application.

[0153] like Fig.12As shown, the cascade converter control device may include a processing device 1001 (e.g., a central processing unit, a graphics processor, etc.), which can perform various appropriate actions and processes according to a program stored in a read-only memory (ROM: Read Only Memory) 1002 or a program loaded from a storage device 1003 to a random access memory (RAM: Random Access Memory) 1004. In RAM1004, various programs and data required for the operation of the cascade converter control device are also stored. The processing device 1001, ROM1002, and RAM1004 are connected to each other through a bus 1005. An input / output (I / O) interface 1006 is also connected to the bus. Generally, the following systems can be connected to the I / O interface 1006: an input device 1007 including, for example, a touch screen, a touch pad, a keyboard, a mouse, an image sensor, a microphone, etc.; an output device 1008 including, for example, a liquid crystal display (LCD: Liquid Crystal Display), a speaker, etc.; a storage device 1003 including, for example, a magnetic tape, a hard disk, etc.; and a communication device 1009. The communication device 1009 can allow the cascade converter control device to communicate with other devices wirelessly or by wire to exchange data. Although the cascade converter control device with various systems is shown in the figure, it should be understood that it is not required to implement or have all the systems shown. More or fewer systems can be implemented or have alternatively.

[0154] In particular, according to the embodiments disclosed in the present application, the process described above with reference to the flowchart can be implemented as a computer software program. For example, the embodiments disclosed in the present application include a computer program product, which includes a computer program carried on a computer-readable medium, and the computer program includes a program code for executing the method shown in the flowchart. In such an embodiment, the computer program can be downloaded and installed from a network through a communication device, or installed from a storage device 1003, or installed from a ROM 1002. When the computer program is executed by the processing device 1001, the above-mentioned functions defined in the method of the embodiment disclosed in the present application are executed.

[0155] The cascade converter control device provided by the present application adopts the cascade converter control method in the above embodiment, which can solve the technical problem of how to improve the versatility of the cascade converter control method during low voltage ride-through. Compared with the related art, the beneficial effects of the cascade converter control device provided by the present application are the same as the beneficial effects of the cascade converter control method provided by the above embodiment, and the other technical features in the cascade converter control device are the same as the features disclosed in the method of the previous embodiment, which will not be repeated here.

[0156] It should be understood that the various parts disclosed in this application can be implemented by hardware, software, firmware or a combination thereof. In the description of the above embodiments, specific features, structures, materials or characteristics can be combined in any one or more embodiments or examples in a suitable manner.

[0157] The above is only a specific implementation of the present application, but the protection scope of the present application is not limited thereto. Any person skilled in the art who is familiar with the present technical field can easily think of changes or substitutions within the technical scope disclosed in the present application, which should be included in the protection scope of the present application. Therefore, the protection scope of the present application should be based on the protection scope of the claims.

[0158] The present application provides a computer-readable storage medium having computer-readable program instructions (ie, computer programs) stored thereon, and the computer-readable program instructions are used to execute the cascade converter control method in the above-mentioned embodiment.

[0159] The computer-readable storage medium provided in the present application may be, for example, a USB flash drive, but is not limited to electrical, magnetic, optical, electromagnetic, infrared, or semiconductor systems, systems or devices, or any combination of the above. More specific examples of computer-readable storage media may include, but are not limited to: an electrical connection with one or more wires, a portable computer disk, a hard disk, a random access memory (RAM), a read-only memory (ROM), an erasable programmable read-only memory (EPROM or flash memory), an optical fiber, a portable compact disk read-only memory (CD-ROM), an optical storage device, a magnetic storage device, or any suitable combination of the above. In this embodiment, the computer-readable storage medium may be any tangible medium containing or storing a program that can be used by or in combination with an instruction execution system, system or device. The program code contained on the computer-readable storage medium may be transmitted using any appropriate medium, including but not limited to: wires, optical cables, RF (Radio Frequency), etc., or any suitable combination of the above.

[0160] The computer-readable storage medium may be included in the cascade converter control device; or may exist independently without being assembled into the cascade converter control device.

[0161] The above-mentioned computer-readable storage medium carries one or more programs. When the above-mentioned one or more programs are executed by the cascade converter control device, the cascade converter control device: when the cascade converter enters the low voltage ride-through state, obtains the preset negative-sequence voltage suppression requirement of the power supply system where the cascade converter is located; if the preset negative-sequence voltage suppression requirement is to perform negative-sequence voltage suppression, then the zero-sequence voltage injection strategy is used to control the cascade converter so that the cascade converter maintains power balance; if the preset negative-sequence voltage suppression requirement is not to perform negative-sequence voltage suppression, then the negative-sequence current injection strategy is used to control the cascade converter so that the cascade converter maintains power balance.

[0162] Computer program code for performing the operations of the present application may be written in one or more programming languages ​​or a combination thereof, including object-oriented programming languages ​​such as Java, Smalltalk, C++, and conventional procedural programming languages ​​such as "C" or similar programming languages. The program code may be executed entirely on the user's computer, partially on the user's computer, as a separate software package, partially on the user's computer and partially on a remote computer, or entirely on a remote computer or server. In the case of a remote computer, the remote computer may be connected to the user's computer through any type of network, including a local area network (LAN) or a wide area network (WAN), or may be connected to an external computer (e.g., via the Internet using an Internet service provider).

[0163] The flow chart and block diagram in the accompanying drawings illustrate the possible architecture, function and operation of the system, method and computer program product according to various embodiments of the present application. In this regard, each square box in the flow chart or block diagram can represent a module, a program segment or a part of a code, and the module, the program segment or a part of the code contains one or more executable instructions for realizing the specified logical function. It should also be noted that in some alternative implementations, the functions marked in the square box can also occur in a sequence different from that marked in the accompanying drawings. For example, two square boxes represented in succession can actually be executed substantially in parallel, and they can sometimes be executed in the opposite order, depending on the functions involved. It should also be noted that each square box in the block diagram and / or flow chart, and the combination of the square boxes in the block diagram and / or flow chart can be implemented with a dedicated hardware-based system that performs a specified function or operation, or can be implemented with a combination of dedicated hardware and computer instructions.

[0164] The modules involved in the embodiments described in this application may be implemented by software or hardware, wherein the name of the module does not constitute a limitation on the unit itself in some cases.

[0165] The readable storage medium provided in the present application is a computer-readable storage medium, which stores computer-readable program instructions (i.e., computer programs) for executing the above-mentioned cascade converter control method, and can solve the technical problem of how to improve the versatility of the cascade converter control method during low voltage ride-through. Compared with the related art, the beneficial effects of the computer-readable storage medium provided in the present application are the same as the beneficial effects of the cascade converter control method provided in the above-mentioned embodiment, and will not be repeated here.

[0166] The present application also provides a computer program product, comprising a computer program, wherein when the computer program is executed by a processor, the steps of the cascade converter control method as described above are implemented.

[0167] The computer program product provided by the present application can solve the technical problem of how to improve the versatility of the cascade converter control method during low voltage ride-through. Compared with the related art, the beneficial effects of the computer program product provided by the present application are the same as the beneficial effects of the cascade converter control method provided by the above embodiment, which will not be repeated here.

[0168] The above descriptions are only some embodiments of the present application, and are not intended to limit the patent scope of the present application. All equivalent structural changes made using the contents of the present application specification and drawings under the technical concept of the present application, or direct / indirect applications in other related technical fields are included in the patent protection scope of the present application.

Claims

1. A cascade converter control method, characterized in that: The cascade converter control method comprises: When the cascade converter enters a low voltage ride-through state, obtaining a preset negative sequence voltage suppression requirement of a power supply system where the cascade converter is located; If the preset negative sequence voltage suppression requirement is to perform negative sequence voltage suppression, a zero sequence voltage injection strategy is used to control the cascade converter so that the cascade converter maintains power balance; If the preset negative sequence voltage suppression requirement is not to perform negative sequence voltage suppression, a negative sequence current injection strategy is used to control the cascade converter so that the cascade converter maintains power balance.

2. The cascade converter control method according to claim 1, characterized in that: Before the step of controlling the cascade converter by using the zero-sequence voltage injection strategy, the cascade converter control method further includes: Obtaining the positive-sequence active current of the cascade converter before it enters the low voltage ride-through state and the three-phase system voltage of the grid connection point where the cascade converter is located; Performing positive-sequence and negative-sequence separation processing on the three-phase system voltage to obtain a positive-sequence voltage and a negative-sequence voltage; The step of controlling the cascade converter by using a zero-sequence voltage injection strategy comprises: Determine a first d-axis current, a first q-axis current, a second d-axis current, and a second q-axis current in the two-phase rotating coordinate system according to the positive-sequence voltage, the positive-sequence active current, the rated current of the cascade converter, and the d-axis voltage and the q-axis voltage of the negative-sequence voltage in the two-phase rotating coordinate system; determining a first positive-sequence reference current according to the first d-axis current and the first q-axis current; determining a first negative-sequence reference current according to the second d-axis current and the second q-axis current; Reconstructing a three-phase first reference current according to the first positive-sequence reference current and the first negative-sequence reference current; Determining a three-phase first reference voltage according to the three-phase first reference current and the impedance characteristics of the grid connection point; Determine a zero-sequence voltage phase and a first zero-sequence voltage amplitude according to selected reference currents of any two phases among the three-phase first reference currents and selected system voltages corresponding to the selected reference currents of any two phases among the three-phase system voltages; Determining a first zero-sequence voltage according to the zero-sequence voltage phase and the first zero-sequence voltage amplitude; Superimposing the first zero-sequence voltage with the first reference voltages of the three phases respectively to obtain the first target voltages of the three phases; The cascade converter is controlled according to the first target voltage of three phases.

3. The cascade converter control method according to claim 2, characterized in that: The step of determining a first d-axis current, a first q-axis current, a second d-axis current, and a second q-axis current in the two-phase rotating coordinate system according to the positive-sequence voltage, the positive-sequence active current, the rated current of the cascade converter, and the d-axis voltage and the q-axis voltage of the negative-sequence voltage in the two-phase rotating coordinate system comprises: Obtaining a voltage drop amplitude of the grid connection point; Determine the negative sequence current coefficient corresponding to the voltage drop amplitude according to the mapping relationship between the preset voltage drop amplitude and the preset negative sequence current coefficient; According to the negative-sequence current coefficient, the positive-sequence voltage, the positive-sequence active current, the rated current of the cascade converter, and the d-axis voltage and q-axis voltage of the negative-sequence voltage in the two-phase rotating coordinate system, the first d-axis current, the first q-axis current, the second d-axis current and the second q-axis current in the two-phase rotating coordinate system are determined.

4. The cascade converter control method according to claim 2, characterized in that: The step of superimposing the first zero-sequence voltage with the first reference voltages of the three phases to obtain the first target voltages of the three phases comprises: Superimposing the first zero-sequence voltage with the first reference voltages of the three phases respectively to obtain a three-phase intermediate reference voltage; If the amplitude of any of the intermediate reference voltages of the three phases is greater than the amplitude of the rated voltage of the cascade converter, determining the second zero-sequence voltage amplitude according to the amplitude of the rated voltage, the amplitude of the positive-sequence voltage component and the amplitude of the negative-sequence voltage component; Determining a second zero-sequence voltage according to the zero-sequence voltage phase and the second zero-sequence voltage amplitude; The second zero-sequence voltage is superimposed on the first reference voltages of the three phases respectively to obtain the first target voltages of the three phases.

5. The cascade converter control method according to claim 2, characterized in that: The step of controlling the cascade converter by using a negative sequence current injection strategy comprises: Determine a third d-axis current, a third q-axis current, a fourth d-axis current, and a fourth q-axis current in a two-phase rotating coordinate system according to the positive-sequence voltage, the positive-sequence active current, the rated current, and the negative-sequence voltage; determining a second positive-sequence reference current according to the third d-axis current and the third q-axis current; determining a second negative-sequence reference current according to the fourth d-axis current and the fourth q-axis current; Reconstructing a three-phase second reference current according to the second positive-sequence reference current and the second negative-sequence reference current; Determining a three-phase second target voltage according to the three-phase second reference current and the impedance characteristics of the grid connection point; The cascade converter is controlled according to the second target voltage of the three phases.

6. The cascade converter control method according to claim 5, characterized in that: Before the step of determining the three-phase second target voltage according to the three-phase second reference current and the impedance characteristics of the grid connection point, the cascade converter control method further includes: If the amplitude of any reference current among the three-phase second reference currents is greater than the amplitude of the rated current of the cascade converter, the current adjustment ratio is determined according to the amplitude of the rated current and the amplitude of the maximum reference current, and the maximum reference current is the reference current with the largest amplitude among the three-phase second reference currents; According to the current adjustment ratio, respectively adjust the second reference current of the three phases to obtain the three-phase target current; The step of determining the three-phase second target voltage according to the three-phase second reference current and the impedance characteristics of the grid connection point comprises: A three-phase second target voltage is determined according to the three-phase second reference target and the impedance characteristics of the grid connection point.

7. A cascade converter control device, characterized in that: The cascade converter control device comprises: a memory, a processor, and a computer program stored in the memory and executable on the processor, wherein the computer program is configured to implement the steps of the cascade converter control method according to any one of claims 1 to 6.

8. A power supply system, characterized in that: The power supply system comprises: at least one cascade converter; The cascade converter control device according to claim 7, wherein the cascade converter control device is connected to at least one of the cascade converters.

9. A storage medium, characterized in that: The storage medium is a computer-readable storage medium, and a computer program is stored on the storage medium. When the computer program is executed by a processor, the steps of the cascade converter control method according to any one of claims 1 to 6 are implemented.

10. A computer program product, characterized in that The computer program product comprises a computer program, and when the computer program is executed by a processor, the steps of the cascade converter control method according to any one of claims 1 to 6 are implemented.

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