A control method for a modular alternating support converter

Abstract

The application provides a control method of a modular alternating support converter, and relates to the technical field of power electronics. The method comprises the following steps: collecting three-phase currents to perform alternating current inner loop control, so as to obtain modulation waveforms of three-phase bridge arm submodules; performing three-phase energy balance control on the three-phase bridge arm, so as to obtain direct current reference currents; performing direct current inner loop control based on the direct current reference currents, so as to obtain port voltage reference values; inputting the modulation waveforms and the port voltage reference values into a modulator to perform NLM modulation and capacitor voltage sequencing, and then combining bridge arm currents and enable signals to control submodule input. Through the precise cooperation between the decoupled energy balance control and the alternating support timing, the energy balance between the upper and lower bridge arms of each phase is realized, and through the generation of the port voltage reference values and the modulation waveforms, the control requirements of the MASC in the capacitor voltage balance and the alternating support timing coordination can be met, and the stable and reliable operation requirements of the MASC in the high-voltage and high-power scene can be ensured.

Description

Technical Field

[0001] This invention relates to the field of power electronics technology, and in particular to a control method for a modular alternating support converter. Background Technology

[0002] With the continued growth of global energy demand, the Modular Multilevel Converter (MMC), as a core component for achieving flexible grid interconnection, has become the mainstream solution for medium- and high-voltage flexible DC transmission due to its modular structure, excellent output waveform quality, and good scalability. However, three major bottlenecks severely restrict the application of MMC in space- and cost-constrained scenarios: first, high-voltage applications require a large number of sub-modules to be connected in series, increasing system complexity and cost; second, suppressing circulating current requires large arm reactors; and third, the large-capacity DC capacitors required to smooth power ripple occupy more than 50% of the sub-module volume. To address these issues, the Modular Alternate Supporting Converter (MASC) topology has been proposed. By reconstructing the operating mode of the traditional MMC, this topology eliminates the need for arm reactors and significantly reduces the demand for sub-module capacitors. Therefore, compared to the traditional MMC, it has significant advantages in construction cost and size.

[0003] Unlike traditional MMCs where the upper and lower bridge arms are connected in parallel with the DC side, in steady-state operation, MASCs have only one bridge arm connected in parallel with the DC side at any given time. The upper and lower bridge arms of the remaining two phases are complementary and alternately turned on and off. Only one bridge arm of each phase participates in the synthesis of AC voltage, eliminating the existence of circulating current. Its energy balance mode is completely different from that of traditional MMCs, which means that the traditional MMC submodule capacitor voltage equalization control method is no longer applicable to MASCs.

[0004] Currently, research on control methods for modular multilevel converters and their derived topologies (such as hybrid multilevel converters and alternating support converters) is relatively mature. In terms of capacitor voltage equalization control, circulating current suppression, and energy balance strategies, various methods based on submodule voltage sequencing, directional switch on-pulse width, predictive control, and hybrid control are available. Specifically, these include the following:

[0005] 1) By configuring a closed-loop controller based on capacitor voltage for each submodule, the modulation wave magnitude of different submodules is modified in real time to balance the capacitor voltage of the submodules.

[0006] 2) By defining a prediction function in each submodule control system and using this function to predict the fluctuation trend of the submodule capacitor voltage and adjust the submodule's activation time, the capacitor voltage balance can be achieved.

[0007] 3) Equalization control method based on CD-PWM (Carrier Disposition Pulse Width Modulation) strategy. This method assumes that different triangular carriers will cause different trends in the submodule capacitor voltage. Therefore, the triangular carriers of different submodules can be rotated according to the magnitude of the submodule capacitor voltage and the positive or negative sign of the bridge arm current, thereby achieving capacitor voltage equalization.

[0008] 4) The CPS-PWM (Carrier Pulse Shift Pulse Width Modulation) strategy is used to inject high-frequency harmonics into the modulation wave, thereby changing the high-frequency components in the bridge arm current and the charging time of the submodule capacitor, thus achieving capacitor voltage balance.

[0009] However, the aforementioned control methods are all based on the energy flow path and bridge arm structure design of traditional MMC or its derivative topologies, which differs fundamentally from the operating mechanism of modular alternating support converters. Existing control methods struggle to meet the control requirements of modular alternating support converters in terms of capacitor voltage balancing and alternating support timing coordination, and cannot guarantee their stable and reliable operation under high-voltage, high-power scenarios. Summary of the Invention

[0010] To address the aforementioned technical problems in the prior art, this invention aims to provide a control method for a modular alternating support converter, thereby meeting the control requirements of the modular alternating support converter in terms of capacitor voltage balancing and alternating support timing coordination, and ensuring its stable and reliable operation in high-voltage and high-power scenarios.

[0011] Specifically, the technical solution is as follows: A control method for a modular alternating support converter, comprising:

[0012] The three-phase current is collected for AC current inner loop control to obtain the modulation waveform of the three-phase bridge arm neutron module;

[0013] Three-phase energy balance control is performed on the three-phase bridge arm to obtain the DC reference current;

[0014] DC current inner loop control is performed based on DC reference current to obtain port voltage reference value;

[0015] The modulation waveform and port voltage reference value are input into the modulator, and the modulation voltage of the upper and lower bridge arms of the corresponding phase is obtained after NLM modulation.

[0016] For each phase's upper and lower arms:

[0017] The number of sub-modules to be put into operation is calculated based on the corresponding modulation voltage; then, based on the bridge arm current, the number of sub-modules to be put into operation, and the capacitor voltage of each sub-module, the sub-modules to be put into operation are determined; the bridge arm current and the corresponding enable signal are ANDed to control the input of the sub-modules to be put into operation.

[0018] Preferably, the three-phase current is collected for AC current inner-loop control to obtain the modulation waveform of the three-phase bridge arm submodule, including:

[0019] Collect three-phase currents and transform them to the dq coordinate system to obtain the d-axis component current. and q-axis component current ;

[0020] Calculate the d-axis reference current Subtract the d-axis component current The first difference is used to calculate the q-axis reference current. Subtract the q-axis component current The second difference;

[0021] The first and second differences are subjected to current inner-loop control, and the output is converted to a three-phase stationary coordinate system to obtain the modulation waveforms of each sub-module in the three-phase bridge arm. , .

[0022] Preferably, three-phase energy balance control is performed on the three-phase bridge arms to obtain a DC reference current, including:

[0023] right Phase bridge arm, calculate the first DC component current. Second DC component current The formula is as follows:

[0024] ;

[0025] ;

[0026] In the formula, This is the first proportional control coefficient. This is the second proportional control coefficient. This is the second integral control coefficient. For the Laplace operator, for Upper bridge arm reference voltage, for Lower bridge arm reference voltage, for Phase upper arm voltage, for Lower bridge arm voltage; This means that after sampling multiple times through a sliding window, the mean of the differences between the two samples is calculated. This indicates that the average of the two samples is calculated after multiple samplings through a sliding window.

[0027] right Calculate the corresponding DC current for each phase bridge arm. The formula is as follows:

[0028] ;

[0029] ;

[0030] In the formula, The DC reference current is calculated based on the active power on the AC side. For symbolic functions, Active power on the AC side;

[0031] when When the upper and lower bridge arms output voltage simultaneously, the selector selects the voltage. Corresponding DC current As DC reference current .

[0032] Preferably, DC current inner-loop control is performed based on the DC reference current to obtain the port voltage reference value, as shown in the following formula:

[0033] ;

[0034] In the formula, This is the port voltage reference value. This is the DC port voltage. It is direct current. This is the third proportional control coefficient. This is the third integral control coefficient.

[0035] Compared to existing technologies, the technical solution provided by this invention achieves energy balance between the upper and lower bridge arms in each phase through three-phase energy balance control, generates port voltage reference values ​​through DC current inner loop control, and generates modulation waveforms for each phase through AC inner loop current control. This can meet the control requirements of modular alternating support converters in terms of capacitor voltage balancing and alternating support timing coordination, ensuring their stable and reliable operation in high-voltage and high-power scenarios. Attached Figure Description

[0036] Figure 1 This is a schematic diagram of the topology of MASC in this invention.

[0037] Figure 2 This is a schematic diagram of the state of the MASC bridge arm in this invention.

[0038] Figure 3 This is a key operating waveform diagram of MASC in this invention.

[0039] Figure 4 This is the overall control structure diagram of MASC in this invention.

[0040] Figure 5 This is a block diagram of the DC inner loop control in this invention.

[0041] Figure 6 This is a waveform diagram of the steady-state operation of MASC in this invention. Detailed Implementation

[0042] The technical solution provided by the present invention will be further described in detail below with reference to the accompanying drawings.

[0043] 1. Description of MASC Topology Operation Status

[0044] like Figure 1 As shown in the topology diagram of MASC, each phase unit is divided into an upper arm and a lower arm, for a total of 6 arms. Each arm consists of N submodules (SMs) connected in series. Submodules can be composed of half-bridge submodules, full-bridge submodules, or full-half-bridge submodules, etc. Figure 1 middle, This is the DC port voltage. It is direct current. for AC phase voltage on the output side of the phase bridge arm, for Voltage of the upper bridge arm, for Current in the upper arm of the bridge, for Voltage of the lower bridge arm, for Current in the lower bridge arm, For smoothing reactors, For AC side filter inductance, For DC-side filter inductance, For the communication side Phase voltage, For the communication side Phase current. Among them, .

[0045] Define the communication side Phase voltage and Phase current, the formula is as follows:

[0046] ;

[0047] ;

[0048] ;

[0049] In the formula, The amplitude of the AC voltage. The amplitude of the alternating current. for The initial phase of the phase voltage, It is the power frequency angular frequency. The power factor angle.

[0050] Each phase of the MASC bridge has both an enable output and a latching mode in its upper and lower arms. The upper arm enable signal logic is set as follows:

[0051] ;

[0052] In the formula, for The enable signal for the upper bridge arm, For synchronization signal, for The initial phase of the phase voltage.

[0053] when When the upper bridge arm is enabled, the submodule switching signal is either enabled or bypassed according to the modulation logic; when At that time, all switch signals of the upper bridge arm are locked.

[0054] Similarly, the lower arm enable signal logic is set as follows:

[0055]

[0056] In the formula, for The enable signal for the lower bridge arm,

[0057] when When the lower bridge arm is enabled, the submodule switching signal is either enabled or bypassed according to the modulation logic; when At that time, all switch signals of the lower bridge arm are locked.

[0058] by Taking one phase as an example, we will analyze the key voltages and currents of the bridge arm. Figure 2 The diagram shows three operating states of the upper and lower bridge arms within one power frequency cycle: simultaneous output voltage from both arms, upper arm lockout, and lower arm lockout. Analysis yields the following expressions for the bridge arm voltages in each state:

[0059] ;

[0060] In the formula, for Phase voltage of alternating current.

[0061] The current expressions for the upper and lower bridge arms are as follows:

[0062] ;

[0063] .

[0064] like Figure 3 As shown, to further illustrate the timing coordination and switching logic of the above three topology states within the actual power frequency cycle, key waveforms of the modular alternating support converter during steady-state operation are presented. Corresponding to... Figure 2 The defined state, Figure 3 The middle section displays items sequentially from top to bottom. Phase upper and lower bridge arm voltages, Phase upper arm enable signal, Lower bridge arm enable signal and The waveforms of the current in the upper and lower bridge arms as a function of time. A complete power frequency cycle is divided into three states of time-series distribution. For example, the shaded period... When the phase bridge arm is in state 1, that is, the upper bridge arm and the lower bridge arm output voltage simultaneously.

[0065] 2. MASC's energy balance control strategy

[0066] Under ideal conditions, the energy of the upper and lower arms of each phase in a MASC is naturally balanced. However, this conclusion does not consider practical factors such as system losses, parameter deviations, and dynamic adjustments (changes in the steady-state point). Therefore, in practical systems, a closed-loop control mechanism is still needed to achieve dynamic energy balance for each phase arm. During steady-state operation, in a traditional MMC, each phase upper and lower arm is equivalent to a voltage source on the DC side. Fluctuations in capacitor voltage can cause a slight voltage deviation in the voltage source during parallel operation, resulting in circulating current. In a MASC, only one phase voltage source is connected in parallel with the DC side, eliminating the aforementioned circulating current problem. This is fundamentally different from a traditional MMC, and therefore, the relevant control components also need to be modified.

[0067] The overall control structure of MASC mainly consists of two parts. The first part is the AC current inner loop control, which generates the modulation waveform required by the bridge arm submodule control system. The second part is the DC current inner loop control. Through the energy balance link between the bridge arms, each phase can generate a corresponding DC current reference. Then, according to the enabling status of the upper and lower bridge arms of each phase, the corresponding DC current reference value is selected as the actual DC current reference. Then, it is tracked by the current inner loop to obtain the reference common-mode voltage. Finally, the references from both parts are sent to the modulator, and after NLM (Nearest Level Modulation) modulation and capacitor voltage sorting algorithm, the PWM (Pulse-Width Modulation) signal is obtained.

[0068] Specifically, when When the upper and lower bridge arms are enabled, the overall control structure of MASC is as follows: Figure 4 As shown. express The output reference voltage of the phase, i.e. Modulation waveform of the neutron module in the phase bridge arm. DC current reference, synchronization signal The AC voltage is calculated by the phase-locked loop (PLL). During normal operation, MASC uses an inner-loop control of the AC current in the dq coordinate system to generate the modulation waveform required by the arm submodule control system. Specifically, the calculated d-axis and q-axis AC current reference values ​​are compared with the actual acquired and coordinate-transformed d-axis and q-axis currents. Subsequently, the current error signal enters the PI controller for zero steady-state error adjustment, thereby obtaining the converter output voltage reference value in the dq coordinate system. Finally, this voltage reference value is transformed inversely to restore the AC voltage reference waveform in the abc three-phase stationary coordinate system. This waveform serves as the modulation waveform required for pulse width modulation by the arm submodule control system.

[0069] A. Acquire three-phase current for AC current inner-loop control to obtain the modulation waveform of the three-phase bridge arm neutron module:

[0070] Collect three-phase currents and transform them to the dq coordinate system to obtain the d-axis component current. and q-axis component current ; Calculate the d-axis reference current Subtract the d-axis component current The first difference is used to calculate the q-axis reference current. Subtract the q-axis component current The second difference; current inner loop control is applied to the first and second differences, and the output is converted to a three-phase stationary coordinate system to obtain the modulation waveforms of each submodule in the three-phase bridge arm. , .

[0071] B. Perform three-phase energy balance control on the three-phase bridge arms to obtain the DC reference current:

[0072] The average value of the total capacitor voltage of the submodule and the voltage between the upper and lower bridge arms. DC current The amplitude of AC voltage and the amplitude of alternating current Related. Theoretically, the total energy balance of the upper and lower arms of each phase can be achieved by adjusting any one of the four variables mentioned above: for example, by adjusting the zero-sequence voltage injection amount to change the equivalent amplitude. Alternatively, the amplitude can be dynamically adjusted by adding a new control element. This, in turn, regulates the accumulated energy of the bridge arm. However, due to the amplitude... and amplitude The adjustment will act synchronously on all cascaded submodules, requiring a complex partitioned control strategy to ensure system convergence. Considering voltage... and DC current and voltage right The energy accumulation in the phase bridge arms has a similar mechanism, but due to the equivalent internal resistance voltage of the power supply... Smaller, slight voltage adjustment It will significantly change the direct current. The value of . Therefore, to ensure control stability, energy balance control of the bridge arms can be achieved by injecting a new DC current component. Since each phase contains two sets of sub-modules, upper and lower, a decoupled control structure needs to be designed to achieve energy balance between the upper and lower bridge arms. Assuming that the DC current after injecting the DC current component is . Can be re-represented as The formula is as follows:

[0073] ;

[0074] ;

[0075] In the formula, The DC reference current is calculated based on the active power on the AC side. For symbolic functions, This represents the first DC component current injected to control the voltage difference between the upper and lower bridge arms' capacitors. This represents the second DC component current injected to achieve the sum of the capacitor voltages of the upper and lower bridge arms. This refers to the active power on the AC side. Therefore, decoupling of energy balance between the upper and lower bridge arms can be achieved. Energy balance control of the submodule can be converted into control of the sum and difference of the average values ​​of the total capacitor voltage of the submodule.

[0076] Specifically, the formula is as follows:

[0077] ;

[0078] ;

[0079] In the formula, This is the first proportional control coefficient. This is the second proportional control coefficient. This is the second integral control coefficient. For the Laplace operator, for Upper bridge arm reference voltage, for Lower bridge arm reference voltage, for Phase upper arm voltage, for Lower bridge arm voltage; This means that after sampling multiple times through a sliding window, the mean of the differences between the two samples is calculated. This indicates that the average of the two samples is calculated after multiple samplings through a sliding window.

[0080] right Calculate the corresponding DC current for each phase bridge arm. .when When the upper and lower bridge arms output voltage simultaneously, the selector selects the voltage. Corresponding DC current As DC reference current .

[0081] Depend on Figure 4 It can be seen that the DC current reference consists of the following parts:

[0082] Energy compensation circuit for the upper and lower axle arms: The compensation component consists of two parts: a balance circuit for the sum of the energy of the upper and lower axle arms and a balance circuit for the energy difference between the upper and lower axle arms. The output of the total energy balance control of the upper and lower axle arms is... The output of the differential energy balance control between the upper and lower bridge arms, i.e. The energy regulation of the upper and lower arms can be achieved using the components included in this section. Phase fundamental frequency information.

[0083] DC current feedforward: Based on power conservation, it can be determined from the active power on the AC side. Divide by rated voltage Calculated DC current reference value Power is conserved on both the AC and DC sides, i.e., in steady state. .

[0084] Based on the enable signals of each phase upper and lower bridge arm, when When the upper and lower bridge arms output voltage simultaneously, the selector selects the input. The phase output reference value is used as the DC reference current. .

[0085] C. Perform DC current inner loop control based on the DC reference current to obtain the port voltage reference value:

[0086] In a traditional HB-MMC (Half-Bridge Modular Multilevel Converter), each of the three bridge arms is equivalent to a DC voltage source on the DC side. When the three voltage sources operate in parallel, small common-mode voltage deviations caused by factors such as voltage fluctuations in the capacitors of each phase submodule will directly affect the bridge arm reactors, thus generating interphase circulating currents. These circulating currents not only increase system losses but also further exacerbate voltage fluctuations in the submodule capacitors, severely impacting system stability. Therefore, HB-MMCs must be equipped with an additional circulating current suppression controller to fine-tune the common-mode voltage, forcing a balance in the DC current flowing through each phase (all values ​​are DC current reference values). In contrast, the MASC proposed in this invention, although symmetrical in hardware structure, adopts an alternating support operation mode. At any given moment, only the upper and lower arms of one phase (the supporting phase) are simultaneously conducting, which is equivalent to a DC voltage source on the DC side, directly clamping and establishing the DC bus voltage; while the other two phases are in an unsupported state, exhibiting current source characteristics on the DC side. This control mechanism reconstructs the DC-side network into a structure of a single voltage source and multiple current sources in parallel, eliminating the circulating current path caused by the inconsistency of multiple voltage sources in parallel from a physical mechanism perspective. Therefore, complex circulating current suppression control is not required, and the DC voltage stability is directly determined by the supporting phase.

[0087] DC current control block diagram as follows Figure 5 As shown, the difference between the DC current reference value and the actual value is calculated, and the error is then processed by a PI controller and multiplied by the DC port voltage. Summing yields the port voltage reference value. Finally, set the port voltage reference value. Input modulator. Specifically, the formula is as follows:

[0088] ;

[0089] In the formula, It is direct current. This is the third proportional control coefficient. This is the third integral control coefficient.

[0090] D. PWM signal generation: Specifically, the modulation waveform and port voltage reference value are input to the modulator, and after NLM modulation, the modulation voltages of the corresponding upper and lower bridge arms are obtained.

[0091] The modulation waveform of the AC current inner loop control output and the port voltage reference value of the DC current inner loop control output. The input modulator, through NLM modulation and capacitor voltage sorting algorithm, produces a PWM signal.

[0092] Specifically, it includes the following steps:

[0093] Step S1: NLM modulation;

[0094] The modulation voltages of the upper and lower bridge arms are calculated using the following formulas:

[0095] ;

[0096] In the formula, for Modulation voltage of the upper bridge arm, for The modulation voltage of the lower bridge arm.

[0097] Calculate the number of sub-modules required for each of the corresponding modulation voltages, i.e., calculate the number of sub-modules required for the upper bridge arm. The number of sub-modules required for the lower bridge arm The formula is as follows:

[0098] ;

[0099] ;

[0100] In the formula, The rated capacitor voltage of the submodule. This indicates the integer division operation.

[0101] Step S2: Determine the switching sequence of submodules in each bridge arm; Based on the bridge arm current, the number of submodules to be connected, and the capacitor voltage of each submodule, determine the submodules that need to be connected for each segment:

[0102] right Phase upper arm, if the arm current Then choose the capacitor with the lowest voltage. Each submodule is put into operation; if the bridge arm current... Then choose the capacitor with the highest voltage. Each sub-module has been deployed. For If the current in the lower bridge arm is... Then choose the capacitor with the lowest voltage. Each submodule is put into operation; if the bridge arm current... Then choose the capacitor with the highest voltage. Each sub-module has been deployed. Among them, , ;

[0103] Step S3: For each upper and lower bridge arm, perform an AND operation between the bridge arm current and the corresponding enable signal, and obtain the corresponding PWM signal through modulation. Control the corresponding sub-module to be put into operation, so as to realize the state alternation of the three phase units.

[0104] Simulation results verification:

[0105] Table 1. Basic Simulation Parameters

[0106]

[0107] Based on the basic simulation parameters shown in Table 1, the steady-state operating waveform of MASC is as follows: Figure 6 As shown, the simulation results are based on MATLAB / Simulink. Figure 6 As can be seen in (a) and (b), the DC current is stably regulated to around 0.55kA with small ripple; the three-phase current on the AC side exhibits a balanced and smooth sinusoidal waveform, indicating that the system has good grid-connected power quality. Figure 6 (c) further confirms the effectiveness of the energy balance control; the total capacitor voltage of each bridge arm submodule stably converges to the rated value of 220kV, with a maximum voltage fluctuation of only 5.8kV (approximately 2.6% of the rated value). Furthermore, Figure 6 In (d) and (e), The phase bridge arm voltage and current waveforms strictly follow the preset alternating support logic. The simulation results verify the correctness of the bridge arm energy balance and capacitor voltage equalization control proposed in this invention.

[0108] As can be seen from the above figures and simulation results, the technical solution provided by this invention achieves energy balance between the upper and lower bridge arms in each phase through three-phase energy balance control, generates port voltage reference values ​​through DC current inner loop control, and generates modulation waveforms for each phase through AC inner loop current control. This can meet the control requirements of modular alternating support converters in terms of capacitor voltage balancing and alternating support timing coordination, and ensure their stable and reliable operation in high-voltage and high-power scenarios.

Claims

1. A control method for a modular alternating support converter, characterized in that, include: The three-phase current is collected for AC current inner loop control to obtain the modulation waveform of the three-phase bridge arm neutron module; Three-phase energy balance control is performed on the three-phase bridge arm to obtain the DC reference current; DC current inner loop control is performed based on DC reference current to obtain port voltage reference value; The modulation waveform and port voltage reference value are input into the modulator, and the modulation voltage of the upper and lower bridge arms of the corresponding phase is obtained after NLM modulation. For each phase's upper and lower arms: The number of sub-modules to be put into operation is calculated based on the corresponding modulation voltage; then, based on the bridge arm current, the number of sub-modules to be put into operation, and the capacitor voltage of each sub-module, the sub-modules to be put into operation are determined; the bridge arm current and the corresponding enable signal are ANDed to control the input of the sub-modules to be put into operation.

2. The control method for a modular alternating support converter according to claim 1, characterized in that, The acquisition of three-phase current and the application of AC current inner-loop control yield the modulation waveform of the three-phase bridge arm submodule, including: Collect three-phase currents and transform them to the dq coordinate system to obtain the d-axis component current. and q-axis component current ; Calculate the d-axis reference current Subtract the d-axis component current The first difference is used to calculate the q-axis reference current. Subtract the q-axis component current The second difference; The first and second differences are subjected to current inner-loop control, and the output is converted to a three-phase stationary coordinate system to obtain the modulation waveforms of each sub-module in the three-phase bridge arm. , .

3. The control method for a modular alternating support converter according to claim 2, characterized in that, The three-phase energy balance control of the three-phase bridge arms to obtain the DC reference current includes: right Phase bridge arm, calculate the first DC component current. Second DC component current The formula is as follows: ； ； In the formula, This is the first proportional control coefficient. This is the second proportional control coefficient. This is the second integral control coefficient. For the Laplace operator, for Upper bridge arm reference voltage, for Lower bridge arm reference voltage, for Phase upper arm voltage, for Lower bridge arm voltage; This means that after sampling multiple times through a sliding window, the mean of the differences between the two samples is calculated. This indicates that the average of the two samples is calculated after multiple samplings through a sliding window. right Calculate the corresponding DC current for each phase bridge arm. The formula is as follows: ； ； In the formula, The DC reference current is calculated based on the active power on the AC side. For symbolic functions, Active power on the AC side; when When the upper and lower bridge arms output voltage simultaneously, the selector selects the voltage. Corresponding DC current As DC reference current .

4. The control method for a modular alternating support converter according to claim 3, characterized in that, The DC current inner-loop control based on the DC reference current obtains the port voltage reference value, as shown in the following formula: ； In the formula, This is the port voltage reference value. This is the DC port voltage. It is direct current. This is the third proportional control coefficient. This is the third integral control coefficient.

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