Medium-voltage flexible interconnection device based on cooperation of SiC and Si heterogeneous units and regulation and control method of medium-voltage flexible interconnection device

Abstract

The invention discloses a medium-voltage flexible interconnection device based on SiC and Si heterogeneous unit cooperation and a regulation and control method thereof, and the device comprises a first heterogeneous unit cooperation converter and a second heterogeneous unit cooperation converter, the first heterogeneous unit cooperation converter comprises a three-phase bridge arm, the three-phase bridge arm comprises a first ANPC unit and a first CCM unit, the second heterogeneous unit cooperation converter comprises a three-phase bridge arm, and the three-phase bridge arm comprises a second ANPC unit and a second CCM unit. The three-phase bridge arm comprises a second ANPC unit and a second CCM unit. The invention further discloses a medium-voltage flexible interconnection device regulation and control method based on cooperation of the SiC and Si heterogeneous units, and the method comprises the steps: controlling the overall DC side voltage of the flexible interconnection device to be stabilized at a given value, and generating an initial three-phase modulation wave for reactive compensation; the neutral point potential balance of the ANPC unit is controlled, and a corresponding ANPC unit switching signal is output; and meanwhile, the capacitor voltage of the CCM unit is controlled to be balanced, and a corresponding switching signal of the CCM unit is output. According to the invention, the number requirements of power devices and sub-module capacitors are reduced, and economy and power density are improved.

Description

Technical Field

[0001] The present invention relates to the technical field of flexible interconnection of distribution networks, and in particular to a medium voltage flexible interconnection device based on the collaboration of SiC and Si heterogeneous units and a control method thereof. Background Art

[0002] With the access of a high proportion of renewable energy and power electronic devices, problems such as overload and bidirectional power flow in distribution networks are becoming increasingly severe. The difficulty in absorbing renewable energy and the power quality problems of new distribution networks need to be solved urgently. In order to cope with the challenges of bidirectional power flow, voltage balance and reactive power control in distribution networks, interconnected devices that support the complementary spatiotemporal characteristics of multiple distribution networks have been widely studied by relevant scholars.

[0003] According to whether the device contains power electronic devices, the existing interconnection devices are mainly divided into traditional interconnection devices and flexible interconnection devices. Traditional distribution networks are mostly radial grid structures, and traditional interconnection devices are often set at the end of the feeder, generally tie switches. In order to limit the short-circuit capacity and avoid electromagnetic loop network problems, the tie switches between feeders are usually disconnected during normal operation, so that the distribution network is in an open-loop operation state, and the flow is naturally distributed according to the circuit parameters and load demand. Although the network can be reconstructed and the flow direction can be changed by operating the tie switch, the regulation capacity is limited. In recent years, the concept of flexible interaction device (FID) has gradually emerged and has received widespread attention from academia and engineering circles. Its basic idea is to use advanced power electronics technology to upgrade and transform the key branches and nodes of the distribution network, so that the distribution network can operate in a closed loop and have the ability to actively regulate the flow.

[0004] The difficulty in realizing flexible interconnection devices lies mainly in the topology design. The existing flexible interconnection device topologies are mainly half-bridge modular multilevel FID (HBMM-FID) and full-bridge modular multilevel FID (FBMM-FID). However, limited by the modular multilevel topology, both HBMM-FID and FBMM-FID have a large number of power devices and sub-module capacitors, which leads to low device power density and high device cost. In order to improve the power density and economy of FID, Zhejiang University proposed a hybrid cascaded multilevel FID (HCM-FID), which significantly reduces the number of power devices and sub-module capacitors through the coordination of high-voltage units and cascaded H-bridge modules. However, the withstand voltage of the high-voltage unit switch device of HCM-FID is the same as the DC bus voltage, which increases the number of power devices in series in the high-voltage unit, thereby reducing the reliability of the device operation. Summary of the invention

[0005] The technical problem to be solved by the present invention is to overcome the shortcomings of the above-mentioned background technology and provide a medium-voltage flexible interconnection device and a control method thereof based on the collaboration of SiC and Si heterogeneous units, which effectively reduces the demand for the number of power devices and sub-module capacitors and significantly improves the economy and power density of the flexible interconnection device.

[0006] The technical solution adopted by the present invention to solve its technical problems is a medium-voltage flexible interconnection device based on the cooperation of SiC and Si heterogeneous units, including a first heterogeneous unit cooperative converter and a second heterogeneous unit cooperative converter, the first heterogeneous unit cooperative converter includes a three-phase bridge arm, the three-phase bridge arm includes a first ANPC unit and a first CCM unit, and the first ANPC unit is connected in series with the first CCM unit; the second heterogeneous unit cooperative converter includes a three-phase bridge arm, the three-phase bridge arm includes a second ANPC unit and a second CCM unit, and the second ANPC unit is connected in series with the second CCM unit.

[0007] Furthermore, the first ANPC unit comprises a three-phase ANPC unit, each phase ANPC unit comprises a Si IGBT switch , Si IGBT switch Series, Si IGBT switch Series, Si IGBT switch Series structure and Si IGBT switch The second ANPC unit includes a three-phase ANPC unit, each phase ANPC unit includes a Si IGBT switch , Si IGBT switch Series, Si IGBT switch Series, Si IGBT switch Series structure and Si IGBT switch The series structure is connected in parallel; and also includes a first capacitor , the second capacitor , the first capacitor With the second capacitor Series connection, first ANPC unit, second ANPC unit, first capacitor With the second capacitor Series structure in parallel.

[0008] Furthermore, the first CCM unit includes a three-phase CCM unit, each phase CCM unit includes N submodules connected in series; each submodule includes a SiC MOSFET switch and capacitor , SiC MOSFET switch Switching with SiC MOSFET After connecting in series with capacitor Parallel, SiC MOSFET switches Switching with SiC MOSFET After connecting in series with capacitor Parallel, capacitor The input is switched by SiC MOSFET With capacitor Output connection, capacitor The output is switched by SiC MOSFET With capacitor The second CCM unit includes a three-phase CCM unit, each phase CCM unit includes N The second CCM unit submodule includes a SiC MOSFET switch and capacitor , SiC MOSFET switch Switching with SiC MOSFET After connecting in series with capacitor Parallel, SiC MOSFET switches Switching with SiC MOSFET After connecting in series with capacitor Parallel, capacitor The input is switched by SiC MOSFET With capacitor Output connection, capacitor The output is switched by SiC MOSFET With capacitor Input connection.

[0009] Further, the , indicating three phases.

[0010] A control method for a medium voltage flexible interconnection device based on the cooperation of SiC and Si heterogeneous units comprises the following steps: Step S1: upper control: controlling the overall DC side voltage of the flexible interconnection device to be stable at a given value, and generating an initial three-phase modulation wave for reactive power compensation; Step S2: Lower-level regulation: control the ANPC unit midpoint potential balance and output the corresponding ANPC unit switch signal; at the same time, control the CCM unit capacitor voltage balance and output the corresponding CCM unit switch signal.

[0011] Furthermore, for the first heterogeneous unit cooperative converter, the control method is as follows: Step S-A1: Input the active power set by the first heterogeneous unit cooperative converter and reactive power , through active power Calculate the reference active current , through reactive power Calculate the reference reactive current , the actual active current , Reference active current and actual reactive current , Reference reactive current After the proportional integral controller, the active modulation wave is obtained respectively. , reactive modulation wave , the active modulation wave , reactive modulation wave After dq-abc transformation, the initial three-phase modulation wave is obtained , and ; Step S-A2: Input the first capacitor of the ANPC unit DC side Voltage and the second capacitor on the DC side Voltage The difference between the two is passed through the proportional integral controller to output the modulated wave voltage stabilization component , the modulation wave voltage stabilization component The initial three-phase modulation wave and Add them together to get the modulation wave of each phase of the first ANPC unit. Through the ANPC nearest level approximation modulation strategy, the switch of the first ANPC unit is obtained. , , Signal; Step S-A 3: Input Actual voltage on the DC side of each submodule of the first CCM unit of the phase and the DC side reference voltage of each submodule of the first CCM unit , each reference voltage The actual voltage After passing through the proportional controller, the output current of the first heterogeneous unit coordinated with the normalized converter Multiply them to get the modulation wave voltage-balanced component of the current submodule , the modulation wave voltage component With modulation wave The total modulation wave of the front submodule is formed by superposition , the total modulation wave of the front submodule The current submodule switch of the first CCM unit is obtained by CCM carrier superposition modulation signal; modulated wave is the initial modulation wave With the first ANPC unit output voltage The difference, for or or .

[0012] Further, in step S-A3: the specific calculation formula is: (1) (2) (3) In the formula, is the proportionality coefficient, is the integration coefficient, is a complex variable; the normalized output current of the first heterogeneous unit cooperative converter Expressed as , is the normalized reference value, that is The amplitude of .

[0013] Furthermore, for the second heterogeneous unit cooperative converter, the control method is as follows: Step S-B1: Input the DC side reference voltage of the second ANPC unit and the actual voltage on the DC side The difference between the DC side reference voltage of the second CCM unit and the actual voltage on the DC side The difference is passed through the proportional integral controller to obtain the regulated active current ; Step S-B2: Input the reactive power Q set by the second heterogeneous unit cooperative converter 2 , calculate the reference reactive current , the actual active current , Stabilized active current and actual reactive current , Reference reactive current After the proportional integral controller, the active modulation wave is obtained respectively. , reactive modulation wave , the active modulation wave , reactive modulation wave After dq-abc transformation, the initial three-phase modulation wave is obtained and ; Step S-B3: Input the first capacitor of the ANPC unit DC side Voltage and the second capacitor on the DC side Voltage The difference between the two is passed through the proportional integral controller to output the modulated wave voltage stabilization component , the modulation wave voltage stabilization component The initial three-phase modulation wave and Add them together to get the modulation wave of each phase of the second ANPC unit. Through the ANPC nearest level approximation modulation strategy, the switch of the second ANPC unit is obtained. , Signal; Step S-B4: Input Actual voltage on the DC side of each submodule of the second CCM unit and the DC side reference voltage of each submodule of the second CCM unit , each reference voltage The actual voltage After passing through the proportional controller, the output current of the converter is coordinated with the second heterogeneous unit in the unitized state. Multiply them to get the modulation wave voltage-balanced component of the current submodule , the modulation wave voltage component With modulation wave The total modulation wave of the front submodule is formed by superposition , the total modulation wave of the front submodule The current submodule switch of the second CCM unit is obtained through CCM carrier superposition modulation signal; modulated wave is the initial modulation wave The second ANPC unit output voltage The difference, for or or .

[0014] Further, in step S-B4: the specific calculation formula is: (4) (5) (6) In the formula, is the proportionality coefficient, is the integration coefficient, is a complex variable; the normalized output current of the second heterogeneous unit cooperative converter Expressed as , is the normalized reference value, that is The amplitude of .

[0015] Compared with the prior art, the advantages of the present invention are as follows: In view of the problem of large number of devices and low power density in existing flexible interconnection devices, the present invention proposes a medium-voltage flexible interconnection device based on the cooperation of SiC and Si heterogeneous units and a control method thereof, which realizes the coordinated cooperation between the low-frequency square wave of the three-level active neutral point clamped (ANPC) unit and the high-frequency shaped pulse modulation wave (PWM, Pulse Width Modulation) of the crossconnected module (CCM) unit. Through the coordinated cooperation of the ANPC unit and the CCM unit, the demand for the number of power devices and sub-module capacitors is effectively reduced, and the economy and power density of the flexible interconnection device are significantly improved. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 It is a topological structure diagram of the flexible interconnection device according to an embodiment of the present invention.

[0017] Figure 2 yes Figure 1 A structural diagram of the CCM unit submodule of the illustrated embodiment.

[0018] Figure 3 yes Figure 1 A block diagram of the ANPC unit of the illustrated embodiment.

[0019] Figure 4 yes Figure 1 Schematic diagram of the hierarchical control principle of the embodiment shown.

[0020] Figure 5 yes Figure 1 The power transfer waveform of the first heterogeneous unit cooperative converter in the illustrated embodiment.

[0021] Figure 6 yes Figure 1 The power transfer waveform of the second heterogeneous unit cooperative converter of the illustrated embodiment. DETAILED DESCRIPTION

[0022] The present invention is further described in detail below with reference to the accompanying drawings and specific embodiments.

[0023] Reference Figure 1-3 In this embodiment, the flexible interconnection device includes a first heterogeneous unit cooperative converter (HUCC) and a second heterogeneous unit cooperative converter.

[0024] The first heterogeneous unit cooperative converter includes a three-phase bridge arm, the three-phase bridge arm includes a first ANPC (active neutral point clamped) unit and a first CCM (cross connected module) unit, and the first ANPC unit is connected in series with the first CCM unit.

[0025] The first CCM unit includes three-phase CCM units, each phase CCM unit includes N Each submodule consists of a SiC MOSFET switch. and capacitor , SiC MOSFET switch Switching with SiC MOSFET After connecting in series with capacitor Parallel, SiC MOSFET switches Switching with SiC MOSFET After connecting in series with capacitor Parallel, capacitor The input is switched by SiC MOSFET With capacitor Output connection, capacitor The output is switched by SiC MOSFET With capacitor Input connection.

[0026] The first ANPC unit includes a three-phase ANPC unit, each phase ANPC unit includes a Si IGBT switch , Si IGBT switch Series, Si IGBT switch Series, Si IGBT switch Series structure and SiIGBT switch Series structure in parallel.

[0027] The second heterogeneous unit cooperative converter includes a three-phase bridge arm, which includes a second ANPC (active neutral point clamped) unit and a second CCM (cross connected module) unit. The second ANPC unit is connected in series with the second CCM unit.

[0028] The second CCM unit includes three-phase CCM units, each phase CCM unit includes N The second CCM unit submodule has the same structure as the first CCM unit submodule. The second CCM unit submodule includes a SiC MOSFET switch and capacitor , SiC MOSFET switch Switching with SiC MOSFET After connecting in series with capacitor Parallel, SiC MOSFET switches Switching with SiC MOSFET After connecting in series with capacitor Parallel, capacitor The input is switched by SiC MOSFET With capacitor Output connection, capacitor The output is switched by SiC MOSFET With capacitor Input connection.

[0029] The second ANPC unit includes a three-phase ANPC unit, each phase ANPC unit includes a Si IGBT switch , Si IGBT switch Series, Si IGBT switch Series, Si IGBT switch Series structure and SiIGBT switch Series structure in parallel.

[0030] Also includes a first capacitor With the second capacitor , the first capacitor With the second capacitor Series connection, first ANPC unit, second ANPC unit, first capacitor With the second capacitor Series structure in parallel.

[0031] The first heterogeneous unit cooperative converter is connected to the first distribution network, and the second heterogeneous unit cooperative converter is connected to the second distribution network.

[0032] is the grid phase voltage of the first distribution network; is the grid phase voltage of the second distribution network; is the grid connection point voltage of the first heterogeneous unit cooperative converter, It is the grid connection point voltage of the second heterogeneous unit cooperative converter. is the filter inductance of each bridge arm.

[0033] , indicating three phases. It is the switch of the first ANPC unit. is the first capacitor, is the second capacitor, is the voltage of the first capacitor, is the second capacitor voltage, is the output voltage of the first ANPC unit, is the output voltage of the first CCM unit, is the output current of the first heterogeneous unit cooperative converter, x is a or b or c, is the first CCM unit submodule switch, is the first CCM unit submodule capacitance.

[0034] For the second ANPC unit, is the output voltage of the second ANPC unit, is the output voltage of the second CCM unit, is the output current of the second heterogeneous unit cooperative converter, is the second CCM unit submodule switch, is the second CCM unit submodule capacitance.

[0035] The flexible interconnection device control method of this embodiment includes the following steps: Step S1: upper control: controlling the overall DC side voltage of the flexible interconnection device to be stable at a given value, and generating an initial three-phase modulation wave for reactive power compensation; Step S2: Lower-level regulation: control the ANPC unit midpoint potential balance and output the corresponding ANPC unit switch signal; at the same time, control the CCM unit capacitor voltage balance and output the corresponding CCM unit switch signal.

[0036] Reference Figure 4 , for the first heterogeneous unit cooperative converter, the control method is as follows: Step S-A1: Input the active power P set by the first heterogeneous unit cooperative converter 1 and reactive power Q 1 , through the active power P 1 Calculate the reference active current , through the reactive power Q 1 Calculate the reference reactive current , the actual active current , Reference active current and actual reactive current , Reference reactive current After the proportional integral (PI) controller, the active modulation wave is obtained respectively. , reactive modulation wave , the active modulation wave , reactive modulation wave After dq-abc transformation, the initial three-phase modulation wave is obtained and .

[0037] Step S-A2: Input the first capacitor of the ANPC unit DC side Voltage and the second capacitor on the DC side Voltage The difference between the two is passed through the proportional integral (PI) controller to output the modulated wave voltage stabilization component , the modulation wave voltage stabilization component The initial three-phase modulation wave and Add them together to get the modulation wave of each phase of the first ANPC unit. Through the ANPC nearest level approximation modulation strategy, the switch of the first ANPC unit is obtained. , , Signal.

[0038] Step S-A 3: Input x ( x The actual DC side voltage of each submodule of the first CCM unit of phase a, b or c (That is, the capacitance of each submodule of the first CCM unit Voltage or capacitance voltage) and the DC side reference voltage of each submodule of the first CCM unit , each reference voltage The actual voltage After passing through the proportional controller (P), the output current of the first heterogeneous unit coordinated with the normalized converter is Multiply them to get the modulation wave voltage-balanced component of the current submodule , the modulation wave voltage component With modulation wave The total modulation wave of the front submodule is formed by superposition , the total modulation wave of the front submodule The current submodule switch of the first CCM unit is obtained by CCM carrier superposition modulation , , Signal. The specific calculation formula is: (1) (2) (3) Modulation Wave is the initial modulation wave With the first ANPC unit output voltage The difference, for or or . is the proportionality coefficient, is the integration coefficient, is a complex variable. The normalized output current of the first heterogeneous unit cooperative converter is Expressed as , is the normalized reference value, that is The amplitude of .

[0039] For the second heterogeneous unit cooperative converter, the control method is as follows: Step S-B1: Input the DC side reference voltage of the second ANPC unit and the actual voltage on the DC side The difference between the DC side reference voltage of the second CCM unit and the actual voltage on the DC side The difference is passed through the proportional integral (PI) controller to obtain the regulated active current ; Step S-B2: Input the reactive power Q set by the second heterogeneous unit cooperative converter 2 , calculate the reference reactive current , the actual active current , Stabilized active current and actual reactive current , Reference reactive current After the proportional integral (PI) controller, the active modulation wave is obtained respectively. , reactive modulation wave , the active modulation wave , reactive modulation wave After dq-abc transformation, the initial three-phase modulation wave is obtained and ; Step S-B3: Input the first capacitor of the ANPC unit DC side Voltage and the second capacitor on the DC side Voltage The difference between the two is passed through the proportional integral (PI) controller to output the modulated wave voltage stabilization component , the modulation wave voltage stabilization component The initial three-phase modulation wave and Add them together to get the modulation wave of each phase of the second ANPC unit. Through the ANPC nearest level approximation modulation strategy, the switch of the second ANPC unit is obtained. , , Signal.

[0040] Step S-B4: Input x ( x The actual DC side voltage of each submodule of the second CCM unit of phase a, b or c (That is, the capacitance of each submodule of the second CCM unit Voltage or capacitance Voltage) and the DC side reference voltage of each submodule of the second CCM unit , each reference voltage The actual voltage After passing through the proportional controller (P), the output current of the converter is coordinated with the second heterogeneous unit in the normalization mode. Multiply them to get the modulation wave voltage-balanced component of the current submodule , the modulation wave voltage component With modulation wave The total modulation wave of the front submodule is formed by superposition , the total modulation wave of the front submodule The current submodule switch of the second CCM unit is obtained through CCM carrier superposition modulation , , Signal. The specific calculation formula is: (4) (5) (6) Modulation Wave is the initial modulation wave The second ANPC unit output voltage The difference, for or or . is the proportionality coefficient, is the integration coefficient, is a complex variable. The normalized output current of the second heterogeneous unit cooperative converter is Expressed as , is the normalized reference value, that is The amplitude of .

[0041] In view of the problem that the existing flexible interconnection devices have a large number of devices and low power density, the present invention proposes a medium-voltage flexible interconnection device based on the cooperation of SiC and Si heterogeneous units and a control method thereof, which realizes the cooperation between the low-frequency square wave of the three-level active neutral point clamped (ANPC) unit and the high-frequency shaped pulse modulation wave (PWM, Pulse Width Modulation) of the crossconnected module (CCM) unit. Through the cooperation of the ANPC unit and the CCM unit, the power devices (SiC MOSFET switch, Si IGBT) are effectively reduced. The number of switches and sub-module capacitors required significantly improves the economy and power density of flexible interconnect devices.

[0042] The present invention is based on the idea of ​​hierarchical regulation. The upper-level regulation strategy includes an overall voltage stabilization outer loop and a three-phase bridge arm current inner loop; the lower-level regulation strategy includes ANPC unit midpoint potential balance control, ANPC unit modulation, CCM unit submodule capacitor voltage balancing outer loop and CCM unit modulation. On the modulation wave obtained by the upper-level regulation, an active power vector parallel to the output current direction is superimposed. When the voltage of the CCM unit submodule is low, a vector with the same current direction is superimposed, and when the voltage of the CCM unit submodule is high, a vector with the opposite current direction is superimposed, so as to achieve a reasonable distribution of active power among each unit submodule. The normalized output current amplitude is close to 1, and when the load fluctuates or suddenly changes, it is not easy to cause a large proportional controller output change and limiter saturation. Compared with the existing flexible interconnection device, the present invention effectively improves the output waveform quality and power density, and significantly reduces the device cost.

[0043] Simulation waveform In order to verify the feasibility and effectiveness of the proposed HUC-FID, a simulation model of HUC-FID and 10kV distribution network was built based on Matlab / Simulink. The specific simulation parameters are shown in Table 1: Table 1 Main simulation parameters , In order to verify the effectiveness of the proposed HUC-FID under the condition of transmission power variation, the following two simulation conditions are set: (1) Condition 1: During 0.40s~0.48s, HUCC 1 (The first heterogeneous unit cooperative converter) outputs 1MW of active power and 1.4MVar of reactive power; HUCC 2 (The second heterogeneous unit cooperative converter) absorbs 1MW of active power and outputs 0.4MVar reactive power.

[0044] (2) Condition 2: During 0.48s~0.60s, HUCC 1 The side outputs 1.4MW active power and 1MVar reactive power; HUCC 2 The side absorbs 1.4MW active power and outputs 1.0MVar reactive power.

[0045] like Figure 5 , 6 As shown, during the period of 0.48s~0.60s, HUCC 1 The output active power increased from 1MW to 1.4MW, and the output reactive power decreased from 1.4MVar to 0.4MVar. 2 The absorbed active power increased from 1MW to 1.4MW, and the output reactive power increased from 0.4MVar to 1.0MVar. Analysis of the simulation results shows that HUC-FID has the ability to quickly respond to changes in the power transfer of the interconnected feeder.

[0046] Those skilled in the art may make various modifications and variations to the present invention. If these modifications and variations are within the scope of the claims of the present invention and their equivalents, then these modifications and variations are also within the protection scope of the present invention.

[0047] The contents not described in detail in the specification are prior art known to those skilled in the art.

Claims

1. A medium voltage flexible interconnection device based on the collaboration of SiC and Si heterogeneous units, characterized in that: It includes a first heterogeneous unit cooperative converter and a second heterogeneous unit cooperative converter. The first heterogeneous unit cooperative converter includes a three-phase bridge arm, the three-phase bridge arm includes a first ANPC unit and a first CCM unit, and the first ANPC unit is connected in series with the first CCM unit; the second heterogeneous unit cooperative converter includes a three-phase bridge arm, the three-phase bridge arm includes a second ANPC unit and a second CCM unit, and the second ANPC unit is connected in series with the second CCM unit.

2. The medium voltage flexible interconnection device based on the cooperation of SiC and Si heterogeneous units according to claim 1, characterized in that: The first ANPC unit includes a three-phase ANPC unit, each phase ANPC unit includes a Si IGBT switch , Si IGBT switch Series, Si IGBT switch Series, Si IGBT switch Series structure and Si IGBT switch The second ANPC unit includes a three-phase ANPC unit, each phase ANPC unit includes a Si IGBT switch , Si IGBT switch Series, Si IGBT switch Series, Si IGBT switch Series structure and Si IGBT switch The series structure is connected in parallel; and also includes a first capacitor , the second capacitor , the first capacitor With the second capacitor Series connection, first ANPC unit, second ANPC unit, first capacitor With the second capacitor Series structure in parallel.

3. The medium voltage flexible interconnection device based on the cooperation of SiC and Si heterogeneous units according to claim 2, characterized in that: The first CCM unit includes a three-phase CCM unit, each phase CCM unit includes N submodules connected in series; each submodule includes a SiC MOSFET switch and capacitor , SiC MOSFET switch Switching with SiC MOSFET After connecting in series with capacitor Parallel, SiC MOSFET switches Switching with SiC MOSFET After connecting in series with capacitor Parallel, capacitor The input is switched by SiC MOSFET With capacitor Output connection, capacitor The output is switched by SiC MOSFET With capacitor The second CCM unit includes a three-phase CCM unit, each phase CCM unit includes N The second CCM unit submodule includes a SiC MOSFET switch and capacitor , SiC MOSFET switch With SiC MOSFET switch After connecting in series with capacitor Parallel, SiC MOSFET switches Switching with SiC MOSFET After connecting in series with capacitor Parallel, capacitor The input is switched by SiC MOSFET With capacitor Output connection, capacitor The output is switched by SiC MOSFET With capacitor Input connection.

4. The medium voltage flexible interconnection device based on the cooperation of SiC and Si heterogeneous units according to claim 3, characterized in that: Said , indicating three phases.

5. A control method for a medium voltage flexible interconnection device based on the cooperation of SiC and Si heterogeneous units, applied to the medium voltage flexible interconnection device based on the cooperation of SiC and Si heterogeneous units according to any one of claims 1 to 4, characterized in that: The following steps are involved: Step S1: upper control: controlling the overall DC side voltage of the flexible interconnection device to be stable at a given value, and generating an initial three-phase modulation wave for reactive power compensation; Step S2: Lower-level regulation: control the ANPC unit midpoint potential balance and output the corresponding ANPC unit switch signal; at the same time, control the CCM unit capacitor voltage balance and output the corresponding CCM unit switch signal.

6. The control method of the medium voltage flexible interconnection device based on the cooperation of SiC and Si heterogeneous units according to claim 5 is characterized in that: For the first heterogeneous unit cooperative converter, the control method is as follows: Step S-A1: Input the active power set by the first heterogeneous unit cooperative converter and reactive power , through active power Calculate the reference active current , through reactive power Calculate the reference reactive current , the actual active current , Reference active current and actual reactive current , Reference reactive current After the proportional integral controller, the active modulation wave is obtained respectively. , reactive modulation wave , the active modulation wave , reactive modulation wave After dq-abc transformation, the initial three-phase modulation wave is obtained , and ; Step S-A2: Input the first capacitor of the ANPC unit DC side Voltage and the second capacitor on the DC side Voltage The difference between the two is passed through the proportional integral controller to output the modulated wave voltage stabilization component , the modulation wave voltage stabilization component The initial three-phase modulation wave and Add them together to get the modulation wave of each phase of the first ANPC unit. Through the ANPC nearest level approximation modulation strategy, the switch of the first ANPC unit is obtained. , Signal; Step S-A 3: Input Actual voltage on the DC side of each submodule of the first CCM unit of the phase and the DC side reference voltage of each submodule of the first CCM unit , each reference voltage The actual voltage After passing through the proportional controller, the output current of the first heterogeneous unit coordinated with the normalized converter Multiply them to get the modulation wave voltage-balanced component of the current submodule , the modulation wave voltage component With modulation wave The total modulation wave of the front submodule is formed by superposition , the total modulation wave of the front submodule The current submodule switch of the first CCM unit is obtained by CCM carrier superposition modulation signal; modulated wave is the initial modulation wave With the first ANPC unit output voltage The difference, for or or .

7. The control method of the medium voltage flexible interconnection device based on the cooperation of SiC and Si heterogeneous units according to claim 6 is characterized in that: In step S-A3: the specific calculation formula is: (1) (2) (3) In the formula, is the proportionality coefficient, is the integration coefficient, is a complex variable; the normalized output current of the first heterogeneous unit cooperative converter Expressed as , is the normalized reference value, that is The amplitude of .

8. The control method of the medium voltage flexible interconnection device based on the cooperation of SiC and Si heterogeneous units according to claim 5, characterized in that: For the second heterogeneous unit cooperative converter, the control method is as follows: Step S-B1: Input the DC side reference voltage of the second ANPC unit and the actual voltage on the DC side The difference between the DC side reference voltage of the second CCM unit and the actual voltage on the DC side The difference is passed through the proportional integral controller to obtain the regulated active current ; Step S-B2: Input the reactive power set by the second heterogeneous unit cooperative converter , calculate the reference reactive current , the actual active current , Stabilized active current and actual reactive current , Reference reactive current After the proportional integral controller, the active modulation wave is obtained respectively. , reactive modulation wave , the active modulation wave , reactive modulation wave After dq-abc transformation, the initial three-phase modulation wave is obtained and ; Step S-B3: Input the first capacitor of the ANPC unit DC side Voltage and the second capacitor on the DC side Voltage The difference between the two is passed through the proportional integral controller to output the modulated wave voltage stabilization component , the modulation wave voltage stabilization component The initial three-phase modulation wave and Add them together to get the modulation wave of each phase of the second ANPC unit. Through the ANPC nearest level approximation modulation strategy, the switch of the second ANPC unit is obtained. , , Signal; Step S-B4: Input Actual voltage on the DC side of each submodule of the second CCM unit and the DC side reference voltage of each submodule of the second CCM unit , each reference voltage The actual voltage After passing through the proportional controller, the output current of the converter is coordinated with the second heterogeneous unit in the unitized state. Multiply them to get the modulation wave voltage-balanced component of the current submodule , the modulation wave voltage component With modulation wave The total modulation wave of the front submodule is formed by superposition , the total modulation wave of the front submodule The current submodule switch of the second CCM unit is obtained through CCM carrier superposition modulation signal; modulated wave is the initial modulation wave The second ANPC unit output voltage The difference, for or or .

9. The control method of the medium voltage flexible interconnection device based on the cooperation of SiC and Si heterogeneous units according to claim 8, characterized in that: In step S-B4: the specific calculation formula is: (4) (5) (6) In the formula, is the proportionality coefficient, is the integration coefficient, is a complex variable; the normalized output current of the second heterogeneous unit cooperative converter Expressed as , is the normalized reference value, that is The amplitude of .

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