A high-voltage DC cascaded energy storage system and its control and protection method

Abstract

The present invention discloses a high-voltage DC cascaded energy storage system and its control and protection method. The energy storage system includes a power valve body, a high-voltage DC access circuit, and a controller. Among them, the power valve body is composed of n DCDC power modules based on a full-bridge topology. One DC port of the DCDC power module is connected in series to the high-voltage DC, and the other DC ports are respectively connected to the battery clusters to realize the conversion from low-voltage batteries to high-voltage DC. The high-voltage DC access circuit includes a DC voltage and current sampling, a current-limiting inductor, an isolation contactor, and a pre-charge circuit to realize the access of the high-voltage DC bus and the soft start of the power valve body. The controller communicates with each power module through optical fibers, collects the electrical information of the power modules and issues modulation commands to realize the control and protection of the energy storage system. The control method includes non-linear filtering DC voltage control and direct DC current control, and has the fault blocking ability during high-voltage DC short circuit.

Description

Technical Field

[0001] The present invention belongs to the technical fields of power electronics and energy storage, and particularly relates to a high-voltage DC cascaded energy storage system and a control and protection method therefor. Background Art

[0002] Currently, the high-voltage energy storage system mainly adopts the AC-type high-voltage cascaded energy storage technology based on the SVG (Static Var Generator) topology. Compared with the traditional low-voltage energy storage system, its main advantages are that the batteries are connected in clusters without parallel connection, the single-machine capacity is large, and the direct grid connection efficiency is high, making it the main technical route of the current high-voltage energy storage system. For example, the prior art 1 (CN108011379 A) discloses a new type of static var compensator based on a single-stage conversion module cascaded converter, which includes a variety of single-phase and three-phase main power circuits cascaded by a number of module units, and a number of branches composed of inductors and capacitors connected in series and parallel to the main power circuit. However, this solution has some disadvantages. For example, there is a large second-harmonic frequency fluctuation when the power module is connected to the DC side of the battery, and a large LC filter or DCDC conversion circuit needs to be added, increasing the volume and cost of the system.

[0003] The DC-type high-voltage cascaded energy storage system based on the series connection of DCDC power modules, with its characteristics such as simple system topology, small proportion of filtering links, and easy capacity expansion that the AC-type high-voltage cascaded energy storage does not have, is being studied and applied. For example, the prior art 2 (CN105897018A) discloses a topology structure of a high-voltage large-capacity energy storage converter, which includes a modular cascaded structure with each phase circuit connected in parallel. Each phase consists of a symmetrically arranged upper bridge arm and a lower bridge arm. The upper bridge arm is composed of a sub-module string, an inductor, and a resistor connected in series, and the lower bridge arm is composed of a resistor, an inductor, and a sub-module string connected in series. Its control method includes controlling the DC / DC converter to charge and discharge the super capacitor to smooth the input and output currents on the AC side to stabilize the DC bus voltage. However, currently, most of the studied high-voltage DC cascaded energy storage systems are mainly based on half-bridge DCDC modules, which do not have the ability to quickly block overcurrent and short-circuit faults on the high-voltage DC side. When a fault occurs on the high-voltage side, it is easy to involve the battery side and cause serious faults, with a relatively high safety risk.

[0004] The prior art 3 (CN114465316A) discloses a cascaded high-voltage direct-connected DC-DC battery energy storage system and its parameter design method. The cascaded high-voltage direct-connected DC-DC battery energy storage system includes a DC bus and a DC link, and the DC bus and the DC link are connected through a DC reactor. The DC link includes two or more cascaded H-bridge sub-modules. Any one of the H-bridge sub-modules includes a full-bridge unit, a battery unit, and a low-pass filter. The full-bridge unit includes an IGBT module and an anti-parallel diode. The improvement of this solution compared to D1 is that modulation instructions can be issued by collecting the electrical information of the power module, and the non-linear filtering DC voltage and direct DC current control method are used to control the current and voltage. The beneficial technical effect generated is that the control and protection of the energy storage system can be realized, and the fault blocking ability during high-voltage DC short circuit is possessed.

[0005] Therefore, the DC-type high-voltage cascaded energy storage system has an urgent need for safe, efficient, and reliable circuit topologies and control protection technologies. Summary of the Invention

[0006] Based on the above problems, the present invention proposes a high-voltage DC cascaded energy storage system and its control protection method to solve the problems of low safety and incomplete control protection existing in the current DC-type high-voltage cascaded energy storage system.

[0007] In the first aspect, the present invention proposes a high-voltage DC cascaded energy storage system, including a power valve body, a high-voltage DC access circuit, and a main controller, characterized in that

[0008] The power valve body includes a plurality of DCDC power modules based on a full-bridge topology. One DC port of the DCDC power module is connected in series to high-voltage DC, and one DC port of each is connected to a battery cluster respectively, for the transformation from low-voltage batteries to high-voltage DC.

[0009] Preferably, the calculation method of the number of DCDC power modules is:

[0010]

[0011] Wherein, U dc_bus is the DC voltage between the positive and negative poles on the high-voltage side, U c is the voltage on the series side of the module, k is the DC bus voltage fluctuation margin, and N dcmin is the minimum value of the output voltage range of the battery cluster.

[0012] Preferably, the DCDC power module includes: a module bypass switch (Km1), a full-bridge circuit, a support capacitor (Cm1), and a filter inductor (Lm1). The full-bridge circuit includes four switching devices (Q1 to Q4) and their anti-parallel diodes (D1 to D4). The switching devices, through high-frequency switching operations, form a DCDC conversion circuit with the support capacitor (Cm1) and the filter inductor (Lm1) for voltage conversion from the DC on the battery side to the DC on the series side.

[0013] Preferably, the fourth switching device (Q4) conducts continuously, forming a buck circuit from the battery side to the series side and a boost circuit from the series side to the battery side. When a short-circuit fault occurs on the DC side, all the switching devices are blocked, and the battery-side current is blocked by the switching devices, enabling rapid removal of the fault current and preventing the expansion of the fault feedback.

[0014] Preferably, the DCDC power module includes: a battery-side contactor (Km2), a battery-side pre-charge contactor (Km3), a pre-charge resistor (Rm1), and a DC fuse (Fu1);

[0015] The battery-side contactor is used to connect and disconnect the power module from the battery cluster;

[0016] The combination of the battery-side pre-charge contactor and the pre-charge resistor is used for soft-start charging of the support capacitor inside the module when the system starts from the battery side;

[0017] The DC fuse is used to cut off the fault current when a DC short circuit occurs on the battery side.

[0018] Preferably, the high-voltage DC access circuit includes: positive and negative current-limiting inductors (L1, L2), positive and negative DC voltage samplings (T1, T2), positive and negative current samplings (LA1, LA2), positive and negative high-voltage vacuum contactors (QC1, QC2), positive and negative pre-charge contactors (QC3, QC4), and positive and negative pre-charge resistors (CR1, CR2), which are used for the access of the high-voltage DC bus and soft-start charging when the power valve body starts from the high-voltage DC side;

[0019] Among them, the current-limiting inductor is used for current filtering;

[0020] The DC voltage and current samplings are used to collect the voltage and signals on the high-voltage DC side for power control and fault protection on the high-voltage side;

[0021] The high-voltage contactor is used to connect and disconnect the valve body from the high-voltage DC side;

[0022] The pre-charge circuit consists of a pre-charge high-voltage vacuum contactor and a pre-charge resistor, which is used for charging the capacitor inside the valve body power module when the system starts from the high-voltage DC side of the system;

[0023] The main controller communicates with each power module through optical fibers, collects the electrical information of the power module and issues modulation instructions for the control and protection of the energy storage system.

[0024] Preferably, the valve body adopts a modular multilevel structure, which is composed of six bridge arms and reactors. Each bridge arm is composed of N power modules connected in series. The power module includes two types: full-bridge module and half-bridge module. At least N / 2 of the N modules in each bridge arm are full-bridge modules.

[0025] Second, the present invention also proposes a control and protection method for a high-voltage DC cascaded energy storage system, including non-linear compensation DC voltage control and direct DC current control, characterized in that:

[0026] The non-linear compensation DC voltage control includes an instruction feed-forward voltage and a non-linear filtered voltage feedback link. The voltage feed-forward link is used to improve the rapid response of the voltage loop, and the non-linear voltage feedback link is used to compensate for the voltage deviation and ensure the stability of the system at the same time;

[0027] The direct current control includes a current outer loop and a current inner loop. The current outer loop ensures the accuracy of the output current through the output current feedback link, and the current inner loop uses a DC deadbeat current loop to improve the current dynamic response speed of the device.

[0028] Preferably, the non-linear compensation DC voltage control includes:

[0029] Step A: Obtain the DC voltage value U through DC voltage sampling dc , and the external instruction is U dcset ;

[0030] Step B: Filter U dc to remove high-frequency components and obtain U dcavr ;

[0031] Step C: Calculate the DC voltage deviation U dcsub , and there is:

[0032] U dces = U dcset - U dcavr

[0033] Step D: Perform control dead zone limitation on U dcsub to obtain the input U of the non-linear integrator dcintin , and there is:

[0034]

[0035] Among them, k int is the integral coefficient, U submax and U submin are the upper and lower limits of the control dead zone;

[0036] Step E: For U dcintin Obtain the voltage feedback compensation output U through non-linear accumulation dcintout , the non-linear accumulator calculates once every Ts, for U dcintin Perform decimation and accumulation once to obtain the output result; where Ts is the accumulation execution period;

[0037] Step F: Add U dcset and U dcintout to obtain the modulated output voltage U mod .

[0038] Preferably, the direct current control includes:

[0039] Step a: Obtain the DC current value I through DC current sampling dc , obtain the DC voltage value U through DC voltage sampling dc , and accept the external current command as I dcset ;

[0040] Step b: Use I dc and I dcset as inputs to perform PI control to obtain the current outer loop output I dcPI ;

[0041] Step c: Add I dcset and I dcPI to obtain the current inner loop command input I dcref ;

[0042] Step d: Execute the DC deadbeat current algorithm to obtain the modulated output voltage U mod ; The control algorithm is:

[0043]

[0044] where k dead is the deadbeat coefficient, L is the DC reactance, and T c is the calculation period.

[0045] The beneficial technical effects of this solution are as follows: On one side of the DCDC power module, a high-voltage DC is connected in series to the DC port, and on the other side, the DC ports are respectively connected to the battery clusters, realizing the conversion from low-voltage batteries to high-voltage DC; through the high-voltage DC access circuit composed of DC voltage and current sampling, current-limiting inductors, isolation contactors, and pre-charge circuits, the access of the high-voltage DC bus and the soft start of the power valve body are realized; the modulation command can be issued by collecting the electrical information of the power module, and the non-linear filtering DC voltage and direct DC current control methods are used to control the current and voltage, thereby realizing the control and protection of the energy storage system, and having the fault blocking ability during high-voltage DC short circuits. Description of the Drawings

[0046] Figure 1 Topological schematic diagram of a high - voltage DC cascaded energy storage converter

[0047] Figure 2 Non - linear compensation DC voltage control loop

[0048] Figure 3 Direct current control loop Detailed Implementation Modes

[0049] The following combines the drawings to make a detailed description of the principle and implementation scheme of a high - voltage DC cascaded energy storage system and its control and protection method involved in the present invention.

[0050] A primary schematic diagram of a high - voltage DC cascaded energy storage system involved in the present invention is as Figure 1 shown. The energy storage system includes:

[0051] The energy storage system includes a power valve body, which is composed of a total of n DCDC power modules from SM1 to SMn. One DC port of the DCDC power module is connected in series to the high - voltage DC, and one DC port of each is connected to the battery cluster respectively, realizing the transformation from low - voltage batteries to high - voltage DC. The method for determining the number of modules is as follows:

[0052] The number of modules mainly depends on the DC voltage of the battery cluster. Assume that the output voltage range of the battery cluster is U dcmin ~U dcmax . According to the principle that the module steps down from the battery side to the series side, that is, the battery voltage U c on the series side should not be higher than U dcmin .

[0053] Set the voltage U c on the series side of the module, and the DC bus voltage fluctuation margin is k. Then the number of modules required for the bridge arm is:

[0054]

[0055] Among them, U dc_bus is the DC voltage between the positive and negative poles on the high - voltage side.

[0056] The DCDC power module consists of a module bypass switch (Km1), a full-bridge circuit, a support capacitor (Cm1), a filter inductor (Lm1), a battery-side main contactor (Km2), a battery-side pre-charge contactor (Km3), a pre-charge resistor (Rm1), and a DC fuse (Fu1). Among them: The module bypass switch is used for bypass removal after a module failure; the full-bridge circuit consists of 4 switching devices (Q1~Q4) and their anti-parallel diodes (D1~D4). The switching tubes form a DCDC conversion circuit with the support capacitor and the filter inductor through high-frequency switching actions to achieve voltage conversion from DC on the battery side to DC on the series side; the battery-side contactor is used to connect and disconnect the power module from the battery cluster; the combination of the battery-side pre-charge contactor and the pre-charge resistor is used to softly charge the support capacitor inside the module when the system starts from the battery side; the DC fuse is used to cut off the fault current when there is a DC short circuit on the battery side.

[0057] Regarding the working principle of the DCDC power module, keep Q4 continuously conducting. The bridge arm where Q1 and Q2 are located, together with the DC pole inductors L1 and L2, forms a Buck / boost circuit (step-up / step-down conversion circuit). A step-down circuit is formed from the battery side to the series side (Q1 switches, Q2 locks), and a step-up circuit is formed from the series side to the battery side (Q2 switches, Q1 locks). When a short-circuit fault occurs on the DC side, each switching tube locks, and the battery-side current is blocked by the switching tubes, so that the fault current can be quickly cut off to avoid the expansion of the fault feedback.

[0058] The energy storage system includes a high-voltage DC access circuit, which consists of positive and negative current-limiting inductors (L1, L2), positive and negative DC voltage samplings (T1, T2), positive and negative current samplings (LA1, LA2), positive and negative high-voltage vacuum contactors (QC1, QC2), positive and negative pre-charge contactors (QC3, QC4), and positive and negative pre-charge resistors (CR1, CR2), to achieve the access of the high-voltage DC bus and the soft start of charging when the power valve body starts from the high-voltage DC side. Among them, the current-limiting inductor is mainly used for current filtering, that is, to reduce the current fluctuation on the high-voltage DC side and suppress the current change rate during over-current or short-circuit faults on the DC side. This inductor can be placed separately on the positive and negative poles, or evenly distributed to the series side of each module, as long as the total sum of the series inductors on the positive and negative poles remains unchanged; the DC voltage and current samplings are used to collect the voltage and signals on the high-voltage DC side for power control and fault protection on the high-voltage side; the high-voltage contactor is used to connect and disconnect the valve body from the high-voltage DC side; the pre-charge circuit consists of a pre-charge high-voltage vacuum contactor and a pre-charge resistor, which is used to charge the capacitor inside the power module of the valve body when the system starts on the high-voltage DC side.

[0059] The energy storage system includes a main controller. The main controller communicates with each power module through optical fibers, collects the electrical information of the power module and issues modulation instructions to achieve the control and protection of the energy storage system.

[0060] The present invention also provides a control and protection method for a high-voltage DC cascaded energy storage system. The control and protection method adopts the following technical solutions, including non-linear compensation DC voltage control and direct DC current control.

[0061] As Figure 2 shown, the non-linear compensation DC voltage control loop includes an instruction feed-forward voltage and a non-linear filtering voltage feedback link. The voltage loop response rapidity is improved through the voltage feed-forward link, and while compensating for the voltage deviation caused by factors such as impedance through the non-linear voltage feedback link, the stability of the system is ensured. The specific implementation scheme is as follows:

[0062] Step 1: Obtain the DC voltage value U dc , and accept the external instruction as U dcset , and execute Step 2.

[0063] Step 2: Perform digital sliding filtering on U dc to filter out high-frequency components and obtain U dcavr .

[0064] Step 3: Calculate the DC voltage deviation U dcsub , and there is:

[0065] U dcsub = U dcset - U dcavr (1)

[0066] Execute Step 4:

[0067] Step 4: Perform control dead zone limitation on U dcsub to obtain the non-linear integrator input U dcintin , and there is:

[0068]

[0069] where k int is the integration coefficient, U dcsubmax and U dcsubmin are the upper and lower limits of the control dead zone. Execute Step 5.

[0070] Step 5: Obtain U dcintin through non-linear accumulation to obtain U dcintout as the voltage feedback compensation output. The non-linear accumulator calculates once every Ts, samples U dcintin once and accumulates it to obtain the output result. Where Ts is the accumulation execution period. Execute Step 6.

[0071] Step 6: Sum U dcset and U dcintout to obtain the modulation output voltage U mod。

[0072] By controlling the combination of the dead zone and the non - linear accumulator, the stability of the DC voltage output of the DC chain energy storage system can be ensured, and the unstable oscillation caused by the weak damping frequency band with the external system can be avoided. This voltage control algorithm has extremely high stability while ensuring the accuracy of the voltage output.

[0073] As Figure 3 shown, the direct current control includes two parts: an outer current loop and an inner current loop. The outer current loop ensures the accuracy of the output current through the output current feedback link, and the inner current loop adopts a DC deadbeat current loop to improve the current dynamic response speed under normal and fault - handling conditions of the equipment. The specific implementation scheme is as follows:

[0074] Step 1: Obtain the DC current value I through DC current sampling dc , and obtain the DC voltage value U through DC voltage sampling dc . Receive the external current command as I dcset , and execute Step 2.

[0075] Step 2: Use I dc and I dcset as inputs to execute PI control, and obtain the output I of the outer current loop dcPI . Execute Step 3.

[0076] Step 3: Sum I dcset and I dcPI to obtain the input I of the inner current loop command dcref , and execute Step 4.

[0077] Step 4: Execute the DC deadbeat current algorithm to obtain the modulated output voltage U mod . The control algorithm is:

[0078]

[0079] where k dead is the deadbeat coefficient, L is the DC reactance, and T c is the calculation period.

[0080] The flexible DC converter valve adopts a modular multi - level structure, which consists of six bridge arms and reactors. Each bridge arm is composed of N power modules connected in series. The power modules include two types: full - bridge modules and half - bridge modules. At least N / 2 full - bridge modules are included in the N modules of each bridge arm;

[0081] The positive and negative poles of the DC port of the power module (such as SMA1) of the device under test are connected to the positive and negative poles of the DC 1 port of the DCDC power module, and the positive and negative poles of the DC port of the power module (such as SMU 1) of the accompanying test device are connected to the positive and negative poles of the DC2 port of the DCDC power module. In this way, the 3n modules of the device under test are sequentially connected to the 3n DCDC modules.

[0082] The beneficial technical effects of this solution are as follows: A high-voltage DC is connected in series to one DC port of the DCDC power module, and each DC port is connected to a battery cluster on the other side, realizing the conversion from low-voltage batteries to high-voltage DC; Through the high-voltage DC access circuit composed of DC voltage and current sampling, current-limiting inductors, isolation contactors, and pre-charge circuits, the access of the high-voltage DC bus and the soft start of the power valve body are realized; The control of current and voltage can be achieved by collecting the electrical information of the power module and issuing modulation commands, and adopting the non-linear filtering DC voltage and direct DC current control methods to realize the control and protection of the energy storage system, and it has the ability to block faults during high-voltage DC short circuits.

[0083] The above implementation example is a specific circuit schematic diagram of the present invention, and does not limit the protection scope of the present invention.

Claims

1. A high-voltage DC cascaded energy storage system, comprising a power valve body, a high-voltage DC access circuit, and a main controller, characterized in that, the power valve body includes a plurality of DCDC power modules based on a full-bridge topology. One DC port of each DCDC power module is connected in series to the high-voltage DC, and the other DC port of each DCDC power module is connected to a battery cluster respectively, for converting low-voltage batteries to high-voltage DC; The DCDC power module includes: a module bypass switch Km1, a full-bridge circuit, a support capacitor Cm1, and a filter inductor Lm1. The full-bridge circuit includes 4 switching devices Q1 to Q4 and their anti-parallel diodes D1 to D4. The switching devices form a DCDC conversion circuit with the support capacitor Cm1 and the filter inductor Lm1 through high-frequency switching actions, for converting the DC voltage on the battery side to the DC voltage on the series side; The high-voltage DC access circuit includes: positive and negative current-limiting inductors L1, L2, positive and negative DC voltage samplers T1, T2, positive and negative current samplers LA1, LA2, positive and negative high-voltage vacuum contactors QC1, QC2, positive and negative pre-charge contactors QC3, QC4, positive and negative pre-charge resistors CR1, CR2, for accessing the high-voltage DC bus and soft-starting the charging when the power valve body starts from the high-voltage DC side; Among them, the current-limiting inductor is used for current filtering; The DC voltage and current samplers are used to collect the voltage and signals on the high-voltage DC side, for power control and fault protection on the high-voltage side; The high-voltage contactor is used to connect and disconnect the valve body from the high-voltage DC side; The pre-charge circuit consists of a pre-charge high-voltage vacuum contactor and a pre-charge resistor, for charging the capacitors in the power modules of the valve body when the system starts on the high-voltage DC side of the system; The main controller communicates with each power module through optical fibers, collects the electrical information of the power module and issues modulation instructions, for controlling and protecting the energy storage system.

2. A high-voltage DC cascaded energy storage system according to claim 1, characterized in that, the calculation method of the number of DCDC power modules is: Among them, U dc_bus is the DC voltage between the positive and negative poles of the high-voltage side, U c is the voltage of the module series side, k is the DC bus voltage fluctuation margin, U dcmin is the minimum value of the battery cluster output voltage range.

3. A high-voltage DC cascaded energy storage system according to claim 1, characterized in that, The fourth switching device Q4 conducts continuously, forming a buck circuit from the battery side to the series side and a boost circuit from the series side to the battery side; when a short-circuit fault occurs on the DC side, each switching device is blocked, and the battery-side current is blocked by the switching device, and the fault current can be quickly cut off to avoid the expansion of the fault feedback.

4. A high-voltage DC cascaded energy storage system according to claim 1, characterized in that, The DCDC power module includes: a battery-side contactor Km2, a battery-side pre-charge contactor Km3, a pre-charge resistor Rm1, and a DC fuse Fu1; The battery-side contactor is used to connect and disconnect the power module from the battery cluster; The combination of the battery-side pre-charge contactor and the pre-charge resistor is used for soft-starting the charging of the support capacitor in the module when the system starts from the battery side; The DC fuse is used to cut off the fault current when a DC short circuit occurs on the battery side.

5. A high-voltage DC cascaded energy storage system according to claim 1, characterized in that, The valve body adopts a modular multi-level structure, which is composed of six bridge arms and reactors. Each bridge arm is composed of N power modules connected in series. The power modules include two types: full-bridge modules and half-bridge modules. At least N / 2 of the N modules in each bridge arm are full-bridge modules.

6. A control and protection method for a high-voltage DC cascaded energy storage system according to any one of claims 1-5, including non-linear compensation DC voltage control and direct DC current control. Characterized in that: The non-linear compensation DC voltage control includes an instruction feed-forward voltage and a non-linear filtered voltage feedback link. The voltage feed-forward link is used to improve the rapid response of the voltage loop, and the non-linear voltage feedback link is used to compensate for voltage deviation and ensure the stability of the system at the same time. The direct current control includes a current outer loop and a current inner loop. The current outer loop ensures the accuracy of the output current through an output current feedback link, and the current inner loop uses a DC deadbeat current loop to improve the current dynamic response speed of the device.

7. A control and protection method for a high-voltage DC cascaded energy storage system according to claim 6. Characterized in that The non-linear compensation DC voltage control includes: Step A: Obtain the DC voltage value U through DC voltage sampling dc , and accept the external instruction as U dcset ; Step B: Filter U dc to remove high-frequency components and obtain U dcavr ; Step C: Calculate the DC voltage deviation U dcsub , there is: U dcsub = U dcset - U dcavr Step D: Perform control dead zone limitation on U dcsub to obtain the input U of the non-linear integrator dcintin , and we have: where k int is the integral coefficient, and U submax and U submin are the upper and lower limits of the control dead zone; Step E: For U dcintin Obtain the voltage feedback compensation output U through non - linear accumulation dcintout , and the non - linear accumulation is calculated every Ts. For U dcintin A decimation is performed once and the accumulations are carried out to obtain the output result; where Ts is the accumulation execution period; Step F: Add U dcset and U dcintout to obtain the modulated output voltage U mod .

8. A control and protection method for a high-voltage DC cascaded energy storage system according to claim 6. Characterized in that The direct current control includes: Step a: Obtain the DC current value I through DC current sampling dc , obtain the DC voltage value U through DC voltage sampling dc , and receive the external current command as I dcset ; Step b: Take I dc and I dcset as inputs to perform PI control, obtaining the output I dcPI ; Step c: Add I dcset and I dcPI to obtain the input I dcref of the inner current loop command; Step d: Execute the DC deadbeat current algorithm to obtain the modulated output voltage U mod ; The control algorithm is as follows: Among them, k dead is the deadbeat coefficient, L is the DC reactance, and T c is the calculation period.

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