Medium-Voltage Flexible Interconnection Device Based on the Collaboration of SiC and Si Heterogeneous Units and Its Regulation Method

Abstract

Medium-voltage flexible interconnection device based on the cooperation of SiC and Si heterogeneous units and its control method. The device includes a first and a second heterogeneous unit cooperative converter. The first heterogeneous unit cooperative converter includes a three-phase bridge arm, and the three-phase bridge arm includes a first ANPC unit and a first CCM unit. The second heterogeneous unit cooperative converter includes a three-phase bridge arm, and the three-phase bridge arm includes a second ANPC unit and a second CCM unit. It also includes a control method for the medium-voltage flexible interconnection device based on the cooperation of SiC and Si heterogeneous units. The method includes 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; controlling the neutral point potential balance of the ANPC unit and outputting the corresponding ANPC unit switching signals; at the same time, controlling the capacitor voltage balance of the CCM unit and outputting the corresponding CCM unit switching signals. The present invention reduces the requirements for the number of power devices and sub-module capacitors, and improves the economy and power density.

Description

Technical Field

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

[0002] With the access of a high proportion of renewable energy and a high proportion of power electronic devices, problems such as overload of distribution network loads and bidirectional power flow have become increasingly severe, and the problems of renewable energy consumption difficulties and power quality in new distribution networks need to be solved urgently. In order to cope with challenges such as bidirectional power flow, voltage balance, and reactive power control in distribution networks, interconnection devices that support the complementary spatio-temporal characteristics of multiple distribution networks have been widely studied by relevant scholars.

[0003] According to whether the device contains power electronic devices, existing interconnection devices are mainly divided into traditional interconnection devices and flexible interconnection devices. Traditional distribution networks mostly have a radial grid structure, and traditional interconnection devices are often set at the end of the feeder, generally a tie switch. In order to limit the short-circuit capacity and avoid the problem of electromagnetic loop networks, 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 power flow is naturally distributed according to the circuit parameters and load demands. Although network reconfiguration can be carried out by operating the tie switch to change the power flow direction, the control ability is limited. In recent years, the concept of flexible interconnection devices (FID) has gradually emerged and has received extensive attention from the academic and engineering circles. Its basic idea is to use advanced power electronic technology to upgrade and transform the key branches and nodes of the primary distribution network, so that the distribution network can operate in a closed loop and has the ability to actively control the power flow.

[0004] The main difficulty in realizing a flexible interconnection device lies in the topology design. The existing topologies of flexible interconnection devices are mainly the half-bridge modular multilevel flexible interconnection device (HBMM-FID) and the full-bridge modular multilevel flexible interconnection device (FBMM-FID). However, limited by the modular multilevel topology structure, both HBMM-FID and FBMM-FID have a large number of power devices and sub-module capacitors, resulting in a low power density and high cost of the device. To improve the power density and economy of the FID, Zhejiang University proposed a hybrid cascaded multilevel flexible interconnection device (HCM-FID), which significantly reduces the number of power devices and sub-module capacitors through the coordinated cooperation of high-voltage units and cascaded H-bridge modules. However, the withstand voltage of the switching devices in the high-voltage unit of HCM-FID is the same as the DC bus voltage, increasing the number of series power devices in the high-voltage unit and thus reducing the operating reliability of the device. Summary of the Invention

[0005] The technical problem to be solved by the present invention is to overcome the deficiencies of the above background technology and provide a medium-voltage flexible interconnection device based on the cooperation of SiC and Si heterogeneous units and its control method, which effectively reduces the number of power devices and sub-module capacitors required, 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 three-phase bridge arms, and the three-phase bridge arms include a first ANPC unit and a first CCM unit, and the first ANPC unit and the first CCM unit are connected in series; the second heterogeneous unit cooperative converter includes three-phase bridge arms, and the three-phase bridge arms include a second ANPC unit and a second CCM unit, and the second ANPC unit and the second CCM unit are connected in series.

[0007] Furthermore, the first ANPC unit includes a three-phase ANPC unit, and each phase ANPC unit includes Si IGBT switches , Si IGBT switches connected in series, Si IGBT switches connected in series, Si IGBT switches connected in series structure and Si IGBT switches The series structure is in parallel; the second ANPC unit includes a three-phase ANPC unit, and each phase ANPC unit includes Si IGBT switches , the Si IGBT switches are in series, and the Si IGBT switches are in series, and the Si IGBT switches The series structure is in parallel with the Si IGBT switches ; further includes a first capacitor and a second capacitor , the first capacitor is in series with the second capacitor , and the first ANPC unit, the second ANPC unit, the first capacitor are in parallel with the second capacitor .

[0008] Furthermore, the first CCM unit includes a three-phase CCM unit, and each phase CCM unit includes N series-connected sub-modules; each sub-module includes a SiC MOSFET switch and a capacitor , the SiC MOSFET switch is in series with the SiC MOSFET switch and then in parallel with the capacitor , the SiC MOSFET switch is in series with the SiC MOSFET switch and then in parallel with the capacitor , the input end of the capacitor is connected to the output end of the capacitor through the SiC MOSFET switch , and the output end of the capacitor is connected to the input end of the capacitor through the SiC MOSFET switch ; the second CCM unit includes a three-phase CCM unit, and each phase CCM unit includes N series-connected sub-modules; the sub-modules of the second CCM unit include a SiC MOSFET switch and a capacitor , the SiC MOSFET switch is in series with the SiC MOSFET switch and then in parallel with the capacitor , the SiC MOSFET switch is in series with the SiC MOSFET switch and then in parallel with the capacitor , the 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:

[0011] 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;

[0012] 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.

[0013] Furthermore, for the first heterogeneous unit cooperative converter, the control method is as follows:

[0014] 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 ;

[0015] 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 regulated voltage component of the modulation wave is respectively added to the initial three-phase modulation wave and to obtain the modulation waves of each phase of the first ANPC unit. Through the ANPC nearest level approximation modulation strategy, the switching , , signals of the first ANPC unit are obtained;

[0016] Step S-A3: Input the actual DC-side voltage of each sub-module of the first CCM unit of phase and the reference DC-side voltage of each sub-module of the first CCM unit . The reference voltages are multiplied by the corresponding actual voltages after passing through a proportional controller and then multiplied by the per-unit output current of the first heterogeneous unit coordinated converter to obtain the voltage equalization component of the modulation wave of the current sub-module . The voltage equalization component of the modulation wave is superimposed on the modulation wave to form the total modulation wave of the previous sub-module . The total modulation wave of the previous sub-module is subjected to CCM carrier superposition modulation to obtain the switching signal of the current sub-module of the first CCM unit; The modulation wave is the difference between the initial modulation wave and the output voltage of the first ANPC unit. is or or .

[0017] Furthermore, in step S-A3: The specific calculation formula is:

[0018] (1)

[0019] (2)

[0020] (3)

[0021] In the formula, is the proportional coefficient, is the integral coefficient, is the complex variable; The per-unit output current of the first heterogeneous unit coordinated converter is expressed as . is the per-unit reference value, that is, the amplitude of.

[0022] Furthermore, for the second heterogeneous unit collaborative converter, the control method is as follows:

[0023] Step S-B1: Input the difference between the reference DC voltage of the second ANPC unit and the actual DC voltage, and the difference between the reference DC voltage of the second CCM unit and the actual DC voltage. After passing through a proportional-integral controller, the regulated active current and the actual DC voltage are obtained; and the actual DC voltage is obtained. After passing through a proportional-integral controller, the regulated active current is obtained;

[0024] Step S-B2: Input the reactive power Q set by the second heterogeneous unit collaborative converter 2 , calculate the reference reactive current . Pass the actual active current , the regulated active current , the actual reactive current , and the reference reactive current through a proportional-integral controller respectively to obtain the active modulation wave and the reactive modulation wave . Pass the active modulation wave and the reactive modulation wave through dq-abc transformation to obtain the initial three-phase modulation waves and ;

[0025] Step S-B3: Input the voltage of the first capacitor on the DC side of the ANPC unit and the voltage of the second capacitor on the DC side of the ANPC unit. Pass the difference between the two through a proportional-integral controller to output the regulated component of the modulation wave. Add the regulated component of the modulation wave to the initial three-phase modulation waves and respectively to obtain the modulation waves of each phase of the second ANPC unit. Through the ANPC nearest level approximation modulation strategy, obtain the switching and signals of the second ANPC unit; 、 signals;

[0026] Step S-B4: Input the actual DC voltage of each sub-module on the DC side of the phase second CCM unit and the reference DC voltage of each sub-module on the DC side of the second CCM unit. Subtract the corresponding actual voltage from each reference voltage After passing through the proportional controller, it is multiplied by the per-unit second heterogeneous unit cooperative converter output current to obtain the modulation wave voltage equalization component of the current sub-module . The modulation wave voltage equalization component is superimposed with the modulation wave to form the total modulation wave of the previous sub-module . The total modulation wave of the previous sub-module is subjected to CCM carrier superposition modulation to obtain the switching signal of the current sub-module of the second CCM unit ; the modulation wave is the difference between the initial modulation wave and the output voltage of the second ANPC unit , is or or .

[0027] Furthermore, in step S-B4: The specific calculation formula is:

[0028] (4)

[0029] (5)

[0030] (6)

[0031] In the formula, is the proportional coefficient, is the integral coefficient, is the complex variable; the per-unit second heterogeneous unit cooperative converter output current is expressed as , is the per-unit reference value, that is, the amplitude of

[0032] Compared with the prior art, the advantages of the present invention are as follows:

[0033] Aiming at the problems 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 its control method, realizing 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 cross-connected module (CCM) unit. Through the cooperation of the ANPC unit and the CCM unit, the requirements for the number of power devices and sub-module capacitors are effectively reduced, and the economy and power density of the flexible interconnection device are significantly improved. Description of the Drawings

[0034] Figure 1 It is the topological structure diagram of the flexible interconnection device in the embodiment of the present invention.

[0035] Figure 2 is Figure 1 The structure diagram of the CCM unit sub-module of the shown embodiment.

[0036] Figure 3 is Figure 1 The structure diagram of the ANPC unit of the shown embodiment.

[0037] Figure 4 is Figure 1 The schematic diagram of hierarchical control of the shown embodiment.

[0038] Figure 5 is Figure 1 The power transmission waveform of the first heterogeneous unit cooperative converter of the shown embodiment.

[0039] Figure 6 is Figure 1 The power transmission waveform of the second heterogeneous unit cooperative converter of the shown embodiment. Detailed Embodiments

[0040] The present invention will be further described in detail below with reference to the drawings and specific embodiments.

[0041] Referring to Figure 1-3 , the flexible interconnection device of this embodiment includes a first heterogeneous unit cooperative converter (HUCC) and a second heterogeneous unit cooperative converter.

[0042] The first heterogeneous unit collaborative 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.

[0043] The first CCM unit includes a three-phase CCM unit, and each phase of the CCM unit includes N a certain number of series-connected sub-modules (SMs). Each sub-module includes a SiC MOSFET switch and a capacitor . The SiC MOSFET switch is connected in series with the SiC MOSFET switch and then connected in parallel with the capacitor . The SiC MOSFET switch is connected in series with the SiC MOSFET switch and then connected in parallel with the capacitor . The input terminal of the capacitor is connected to the output terminal of the capacitor through the SiC MOSFET switch . The output terminal of the capacitor is connected to the input terminal of the capacitor through the SiC MOSFET switch .

[0044] The first ANPC unit includes a three-phase ANPC unit, and each phase of the ANPC unit includes a Si IGBT switch , the Si IGBT switch is connected in series, the Si IGBT switch is connected in series, and the series structure of the Si IGBT switch is connected in parallel with the series structure of the Si IGBT switch .

[0045] The second heterogeneous unit collaborative converter includes a three-phase bridge arm. The three-phase bridge arm includes a second ANPC (active neutral point clamped) unit and a second CCM (cross connected module) unit, and the second ANPC unit is connected in series with the second CCM unit.

[0046] The second CCM unit includes a three-phase CCM unit, and each phase of the CCM unit includes NA number of series-connected sub-modules (SMs). The structure of the second CCM unit sub-module is the same as that of the first CCM unit sub-module, and the second CCM unit sub-module includes SiC MOSFET switches and capacitors , the SiC MOSFET switch is connected in series with the SiC MOSFET switch and then connected in parallel with the capacitor , the SiC MOSFET switch is connected in series with the SiC MOSFET switch and then connected in parallel with the capacitor , the input terminal of the capacitor is connected to the output terminal of the capacitor through the SiC MOSFET switch , the output terminal of the capacitor is connected to the input terminal of the capacitor through the SiC MOSFET switch .

[0047] The second ANPC unit includes a three-phase ANPC unit, and each phase ANPC unit includes Si IGBT switches , the Si IGBT switch is connected in series, the Si IGBT switch is connected in series, and the series structure of the Si IGBT switch is connected in parallel with the series structure of the Si IGBT switch .

[0048] It also includes a first capacitor and a second capacitor , the first capacitor is connected in series with the second capacitor , and the series structure of the first ANPC unit, the second ANPC unit, the first capacitor and the second capacitor is connected in parallel.

[0049] 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.

[0050] 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, is the grid connection point voltage of the second heterogeneous unit cooperative converter. is the filter inductance of each arm.

[0051] , indicating three phases. 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 voltage of the second capacitor, 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 collaborative converter, where x is a or b or c, is the sub-module switch of the first CCM unit, is the sub-module capacitor of the first CCM unit.

[0052] is the switch of 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 collaborative converter, is the sub-module switch of the second CCM unit, is the sub-module capacitor of the second CCM unit.

[0053] The control method of the flexible interconnection device in this embodiment includes the following steps:

[0054] Step S1: Superior control: Control the overall DC-side voltage of the flexible interconnection device to be stable at a given value, and generate an initial three-phase modulation wave for reactive power compensation;

[0055] Step S2: Inferior control: Control the midpoint potential balance of the ANPC unit and output the corresponding ANPC unit switch signal; at the same time, control the capacitor voltage balance of the CCM unit and output the corresponding CCM unit switch signal.

[0056] Refer to Figure 4 , for the first heterogeneous unit collaborative converter, the control method is as follows:

[0057] Step S-A1: Input the set active power P 1 and reactive power Q 1 of the first heterogeneous unit collaborative converter, and calculate the reference active current 1 through the active power P , calculate the reference reactive current 1 through the reactive power Q , and compare the actual active current , reference active current and actual reactive current , reference reactive current After passing through a proportional-integral (PI) controller respectively, the active modulation wave is obtained respectively , and the reactive modulation wave . The active modulation wave and the reactive modulation wave are transformed through dq-abc transformation to obtain the initial three-phase modulation wave and .

[0058] Step S-A2: Input the voltage of the first capacitor on the DC side of the ANPC unit and the voltage of the second capacitor on the DC side . Pass the difference between the two through a proportional-integral (PI) controller to output the voltage stabilization component of the modulation wave . Add the voltage stabilization component of the modulation wave to the initial three-phase modulation wave and respectively to obtain the modulation wave of each phase of the first ANPC unit. Through the ANPC nearest level approximation modulation strategy, the switching , , signals of the first ANPC unit are obtained .

[0059] Step S - A3: Input x ( x is a or b or c) the actual voltage of each sub-module on the DC side of the first CCM unit in the phase (that is, the voltage of the capacitor of each sub-module of the first CCM unit or the voltage of the capacitor ) and the reference voltage of each sub-module on the DC side of the first CCM unit . After passing the reference voltage through a proportional controller (P), multiply it by the per-unit output current of the first heterogeneous unit's coordinated converter to obtain the voltage equalization component of the modulation wave of the current sub-module . Superimpose the voltage equalization component of the modulation wave with the modulation wave to form the total modulation wave of the previous sub-module . Pass the total modulation wave of the previous sub-module through CCM carrier superposition modulation to obtain the switching , , signals of the current sub-module of the first CCM unit. The specific calculation formula is:

[0060] (1)

[0061] (2)

[0062] (3)

[0063] Modulation wave is the initial modulation wave and the output voltage of the first ANPC unit The difference of is or or . is the proportionality coefficient, is the integral coefficient, is a complex variable. The per-unit first heterogeneous unit coordinated converter output current is expressed as , is the per-unit reference value, that is, The amplitude of

[0064] For the second heterogeneous unit coordinated converter, the control method is as follows:

[0065] Step S-B1: Input the difference between the reference voltage of the DC side of the second ANPC unit and the actual voltage of the DC side, and the difference between the reference voltage of the DC side of the second CCM unit and the actual voltage of the DC side. After passing through a proportional-integral (PI) controller, the regulated active current is obtained;

[0066] Step S-B2: Input the reactive power Q 2 set by the second heterogeneous unit coordinated converter, calculate the reference reactive current , and pass the actual active current , the regulated active current and the actual reactive current , the reference reactive current through a proportional-integral (PI) controller respectively, and obtain the active modulation wave and the reactive modulation wave respectively. Pass the active modulation wave and the reactive modulation wave through a dq-abc transformation to obtain the initial three-phase modulation wave and ;

[0067] Step S-B3: Input the voltage of the first capacitor on the DC side of the ANPC unit and the voltage of the second capacitor , the difference between the two is passed through a proportional-integral (PI) controller to output the regulated component of the modulation wave. , the regulated component of the modulation wave is separately added to the initial three-phase modulation wave and to obtain the modulation waves of each phase of the second ANPC unit. Through the ANPC nearest-level approximation modulation strategy, the switching , , signals of the second ANPC unit are obtained.

[0068] Step S-B4: Input x ( x is a or b or c) the actual DC-side voltage of each sub-module of the second CCM unit in the phase (i.e., the capacitor voltage or capacitor voltage of each sub-module of the second CCM unit) and the reference DC-side voltage of each sub-module of the second CCM unit . After passing each reference voltage through a proportional controller (P), it is multiplied by the per-unit output current of the second heterogeneous unit co-converter to obtain the voltage equalization component of the modulation wave of the current sub-module . The voltage equalization component of the modulation wave is superimposed on the modulation wave to form the total modulation wave of the previous sub-module . The total modulation wave of the previous sub-module is modulated by CCM carrier superposition to obtain the switching of the current sub-module of the second CCM unit , , signals. The specific calculation formula is:

[0069] (4)

[0070] (5)

[0071] (6)

[0072] The modulation wave is the difference between the initial modulation wave and the output voltage of the second ANPC unit. is or or . is the proportional coefficient, is the integral coefficient, is a complex variable. The per-unit second heterogeneous unit cooperative converter output current is expressed as , is the per-unit reference value, that is the amplitude of

[0073] Aiming at the problems 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 its control method, realizing 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 cross-connected module (CCM) unit. Through the cooperation of the ANPC unit and the CCM unit, the requirements for the number of power devices (SiC MOSFET switches, Si IGBT switches) and sub-module capacitors are effectively reduced, and the economy and power density of the flexible interconnection device are significantly improved.

[0074] Based on the hierarchical control idea, the upper-level control strategy includes the overall voltage stabilization outer loop and the three-phase bridge arm current inner loop; the lower-level control strategy includes the neutral point potential balance control of the ANPC unit, the modulation of the ANPC unit, the sub-module capacitor voltage equalization outer loop of the CCM unit, and the modulation of the CCM unit. An active vector parallel to the output current direction is superimposed on the modulation wave obtained by the upper-level control. When the voltage of the sub-module of the CCM unit is low, a vector in the same direction as the current is superimposed, and when the voltage of the sub-module of the CCM unit is high, a vector in the opposite direction to the current is superimposed, so as to realize the reasonable distribution of active power among the sub-modules of each unit. The per-unit output current amplitude is close to 1, and when the load fluctuates or changes suddenly, it is not easy to cause large changes in the output of the proportional controller and limit saturation. Compared with the existing flexible interconnection devices, the present invention effectively improves the output waveform quality and power density, and significantly reduces the device cost.

[0075] Simulation waveform

[0076] To verify the feasibility and effectiveness of the proposed HUC-FID, an HUC-FID and a 10 kV distribution network simulation model are built based on Matlab / Simulink. The specific simulation parameters are shown in Table 1:

[0077] Table 1 Main simulation parameters

[0078] ,

[0079] To verify the effectiveness of the proposed HUC-FID under the condition of changing transmission power, the following two simulation conditions are set:

[0080] (1) Condition 1: During 0.40 s to 0.48 s, the HUCC 1 (the first heterogeneous unit collaborative converter) outputs 1 MW of active power and 1.4 MVar of reactive power; the HUCC 2 (the second heterogeneous unit collaborative converter) absorbs 1 MW of active power and outputs 0.4 MVar of reactive power.

[0081] (2) Condition 2: During 0.48 s to 0.60 s, the HUCC 1 outputs 1.4 MW of active power and 1 MVar of reactive power; the HUCC 2 absorbs 1.4 MW of active power and outputs 1.0 MVar of reactive power.

[0082] As Figure 5 、 6 shown, during 0.48 s to 0.60 s, the active power output by the HUCC 1 increases from 1 MW to 1.4 MW, and the reactive power output decreases from 1.4 MVar to 0.4 MVar; the active power absorbed by the HUCC 2 increases from 1 MW to 1.4 MW, and the reactive power output increases from 0.4 MVar to 1.0 MVar. Analyzing the simulation results, it can be seen that the HUC-FID has the ability to quickly respond to the change of the transfer power of the interconnected feeder.

[0083] Those skilled in the art can 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 its equivalent technologies, then these modifications and variations are also within the protection scope of the present invention.

[0084] The content not described in detail in the specification is the prior art well 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: The invention comprises a first heterogeneous unit cooperative converter and a second heterogeneous unit cooperative converter, wherein the first heterogeneous unit cooperative converter comprises a three-phase bridge arm, wherein the three-phase bridge arm comprises a first ANPC unit and a first CCM unit, wherein the first ANPC unit is connected in series with the first CCM unit; the second heterogeneous unit cooperative converter comprises a three-phase bridge arm, wherein the three-phase bridge arm comprises a second ANPC unit and a second CCM unit, wherein the second ANPC unit is connected in series with the second CCM unit, wherein the first ANPC unit and the second ANPC unit are both composed of Si IGBT switches, and the first CCM unit and the second CCM unit are both composed of SiC MOSFET switches and capacitors; and further comprises a first capacitor C N1 , the second capacitor C N2 , the first capacitor C N1 With the second capacitor C N2 Series connection, first ANPC unit, second ANPC unit, first capacitor C N1 With the second capacitor C N2 Series structure in parallel.

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 S 1x1 , S 1x2 , S 1x3 , S 1x4、 S 1x5 , S 1x6 , Si IGBT switch S 1x5 , S 1x6 Series, Si IGBT switch S 1x2 , S 1x3 Series, Si IGBT switch S 1x5 , S 1x6 Series structure and Si IGBT switch S 1x2 , S 1x3 The series structure is connected in parallel with the Si IGBT switch S 1x1 , S 1x4 The second ANPC unit includes a three-phase ANPC unit, each phase ANPC unit includes a Si IGBT switch S 2x1 , S 2x2 , S 2x3 , S 2x4、 S 2x5 , S 2x6 , SiIGBT switch S 2x5 , S 2x6 Series, Si IGBT switch S 2x2 , S 2x3 Series, Si IGBT switch S 2x5 , S 2x6 Series structure and SiIGBT switch S 2x2 , S 2x3 The series structure is connected in parallel with the Si IGBT switch S 2x1 , S 2x4 series; also includes a first capacitor C N1 , the second capacitor C N2 , the first capacitor C N1 With the second capacitor C N2 Series connection, first ANPC unit, second ANPC unit, first capacitor C N1 With the second capacitor C N2 Series structure in parallel; x =a,b,c, indicating three phases.

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 S 3x1 , S 3x2 , S 3x3 , S 3x4 , S 3x5 , S 3x6 and capacitor C h1x1 , C h2x1 , SiC MOSFET switch S 3x1 With SiC MOSFET switch S 3x2 After connecting in series with capacitor C h1x1 Parallel, SiC MOSFET switches S 3x3 Switching with SiC MOSFET S 3x4 After connecting in series with capacitor C h2x1 In parallel, capacitor C h1x1 The input is switched by SiC MOSFET S 3x6 With capacitor C h2x1 Output connection, capacitor C h1x1 The output is switched by SiC MOSFET S 3x5 With capacitor C h2x1 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 S 4x1 , S 4x2 , S 4x3 , S 4x4 , S 4x5 , S 4x6 and capacitor C h1x2 , C h2x2 , SiC MOSFET switch S 4x1 Switching with SiC MOSFET S 4x2 After connecting in series with capacitor C h1x2 Parallel, SiC MOSFET switches S 4x3 Switching with SiC MOSFET S 4x4 After connecting in series with capacitor C h2x2 In parallel, capacitor C h1x2 The input is switched by SiC MOSFET S 4x6 With capacitor C h2x2 Output connection, capacitor C h1x2 The output is switched by SiC MOSFET S 4x5 With capacitor C h2x2 Input connection.

4. 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 one of claims 2 or 3, 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.

5. The control method of the medium voltage flexible interconnection device based on the cooperation of SiC and Si heterogeneous units according to claim 4 is characterized in that: For the first heterogeneous unit cooperative converter, the control method is as follows: Step S-A1: Input the active power P1 and reactive power Q1 set by the first heterogeneous unit cooperative converter, and calculate the reference active current through the active power P1 , the reference reactive current is calculated by the reactive power Q1 , 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 C N1 Voltage U dc1 and the second capacitor on the DC side C N2 Voltage U dc2 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. S 1a1 ~ S 1a6 , S 1b1 ~ S 1b6 , S 1c1 ~ S 1c6 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 S 3a1 ~ S 3a6 , S 3b1 ~ S 3b6 , S 3c1 ~ S 3c6 signal; modulated wave is the initial modulation wave With the first ANPC unit output voltage The difference, for or or .

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: 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 .

7. The control method of the medium voltage flexible interconnection device based on the cooperation of SiC and Si heterogeneous units according to claim 4 is 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 Q2 set by the second heterogeneous unit cooperative converter to 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 C N1 Voltage U dc1 and the second capacitor on the DC side C N2 Voltage U dc2 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. S 2a1 ~ S 2a6 , S 2b1 ~ S 2b6 , S 2c1 ~ S 2c6 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 S 4a1 ~ S 4a6 , S 4b1 ~ S 4b6 , S 4c1 ~ S 4c6 signal; modulated wave is the initial modulation wave The second ANPC unit output voltage The difference, for or or .

8. The control method of the medium voltage flexible interconnection device based on the cooperation of SiC and Si heterogeneous units according to claim 7 is 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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