A multifunctional grid-connected converter based on heterogeneous module hybrid and its modulation method

Abstract

This invention belongs to the field of grid-connected converter technology, specifically providing a multifunctional grid-connected converter and modulation method based on heterogeneous module hybridization. It includes four phases: a, b, c, and n. Each phase includes a set of series-connected diode-clamped square wave circuit units and cascaded H-bridge shaping circuit units. The four phases share two DC-side energy storage capacitors C. T1 C T2 The diode-clamped square wave circuit unit includes a single-bridge-arm NPC converter, which comprises four high-voltage SiIGBTs and two clamping diodes; the cascaded H-bridge shaping circuit unit comprises multiple series-connected sub-modules, each sub-module including two SiIGBT devices. 11 T 12 and two SiC MOSFET devices T 21 T 22 This invention enables the simultaneous operation of reactive power compensation and flexible arc suppression functions, which not only improves the utilization and practicality of the equipment but also ensures the safe and reliable operation of the power distribution network; it also reduces the total number of cascaded connections and increases power density.

Description

Technical Field

[0001] This invention relates to the field of grid-connected converter technology, and more specifically, to a multifunctional grid-connected converter and modulation method based on heterogeneous module hybridization. Background Technology

[0002] With the increasing integration of power electronics into distribution networks, the problems of single-function power electronic devices and high idle rates are becoming increasingly serious. Therefore, various multifunctional power electronic devices have gradually attracted the attention of many scholars (such as current-limiting dynamic voltage restorers and unified power quality controllers). Furthermore, the continuous expansion of distribution network capacity has led to frequent single-phase grounding faults. To better achieve flexible arc suppression in distribution networks, active flexible arc suppression devices based on power electronic components have become an important research direction in the field of arc suppression. However, in medium-voltage distribution networks, the cost of active arc suppression devices is too high, severely restricting their application and promotion. To further reduce the cost of active arc suppression devices and improve the utilization rate of distribution network assets, multifunctional power electronic devices with flexible arc suppression and power quality regulation have become a current research hotspot.

[0003] The proposed static var compensators (SVCs) with arc suppression capabilities compensate the grid for reactive power when the grid is normal; during single-phase ground faults in the distribution network, the device switches to a flexible arc suppression mode. Because the device withstands line voltage in arc suppression mode, this structure requires more cascaded units than traditional SVCs, resulting in lower power density. In addition, there is a hybrid structure multi-functional SVC. This structure utilizes high-voltage NPC modules to withstand most of the voltage, significantly reducing the number of cascaded units and effectively improving the power density and efficiency of the device.

[0004] For example, in patent CN114784779A, the power electronic withstand voltage of the NPC circuit unit in the proposed hybrid structure multifunctional static var compensator is selected to be 6500V, and the DC side capacitor voltage Udc1=Udc2=4000V. During the arc suppression period, the maximum withstand voltage of the grounded phase and the non-faulty phase of the NPC unit is 8000V, so the maximum withstand voltage of each phase of the CHB unit is 64142V. Therefore, each phase of the CHB unit has 9 H-bridge sub-modules, and a total of 27 H-bridge modules are needed for the three phases. The large number of H-bridge modules not only burdens the household circuit but also increases the cost.

[0005] Furthermore, the power quality control and flexible arc suppression functions of the two types of multi-functional grid-connected converters mentioned above can only be switched and performed in a time-sharing manner. Therefore, in flexible arc suppression mode, the multi-functional device cannot perform power quality control, which will seriously affect the high-quality, high-efficiency, and high-reliability operation of the distribution network system. Thus, while ensuring the high efficiency, high power density, and low cost characteristics of the multi-functional device, further improving its operational reliability is of great significance for its application and promotion. Summary of the Invention

[0006] This invention addresses the technical problem that existing multifunctional devices cannot simultaneously achieve power quality regulation and flexible arc suppression.

[0007] This invention provides a multifunctional grid-connected converter based on heterogeneous module hybrid design, comprising phase a, phase b, phase c, and phase n. Each phase includes a set of diode-clamped square wave circuit units and cascaded H-bridge shaping circuit units connected in series, and the four phases share two DC-side energy storage capacitors C. T1 C T2 ;

[0008] Each phase of the diode-clamped square wave circuit unit includes a single-bridge-arm NPC converter, wherein the single-bridge-arm NPC converter includes four high-voltage Si IGBTs and two clamping diodes.

[0009] Each phase of the cascaded H-bridge shaping circuit unit comprises two sub-modules connected in series, each sub-module including two low-voltage Si IGBT devices. 11 T 12 and two low-voltage SiC MOSFET devices T 21 T 22 ;

[0010] Among them, the output of the sub-module at the end of the series connection in phase n is grounded.

[0011] Preferably, in phase a, the single-arm NPC converter includes a first clamping diode D. a1 Second clamping diode D a2 The first Si IGBT T is connected in series through the collector node and the emitter node. a1 Second Si IGBT T a2 Third SiIGBT T a3 Fourth Si IGBT T a4 There are a total of four high-voltage Si IGBTs, of which D a1 Negative electrode, T a1 emitter, T a2 Collector connection, D a1 Positive terminal connected to D a2 Negative electrode, D a2 Positive electrode, T a3 emitter, T a4 Collector connection;

[0012] The a-phase AC output port of the single-bridge arm NPC converter is from T a2 Emitter and T a3 It is led out at the collector connection node and connected to a sub-module of phase a of the cascaded H-bridge shaping circuit unit;

[0013] Another submodule of the cascaded H-bridge shaping circuit unit within the n-phase is grounded.

[0014] Preferably, each Si IGBT contains an anti-parallel diode.

[0015] Preferably, the DC-side energy storage capacitor C T1 C T2 Installed on the DC side of each of the single-bridge arm NPC converters, C T1 The positive terminal of the capacitor is connected to the collector node of the first high-voltage Si IGBT in each phase;

[0016] C T1 The negative terminal of the capacitor, the positive terminal of the first clamping diode of each phase, and the negative terminal of the second clamping diode of each phase are connected to point O. T2 The positive terminal of the capacitor is connected to point O, C T2 The negative terminal of the capacitor is connected to the emitter node of the fourth high-voltage Si IGBT in each phase.

[0017] Preferably, phases a, b, and c have identical structures and each includes two sub-modules. The first port of one of the sub-modules in each phase (a, b, or c) is connected via a T... 11 Emitter and T 12 The collector node is connected to the filter inductor L and then to the power distribution network. The second port is connected to T. 21 Source and T 22 The drain node is connected to the first port of another submodule, and the second port of the other submodule is connected to the output of the single-bridge NPC converter.

[0018] Preferably, the n-phase includes two sub-modules SM. nn and SM n1 Submodule SM n1 Grounded via a filtered inductor; Submodule SM nn Connect to the output terminal of the corresponding single-bridge arm NPC converter.

[0019] Preferably, the DC-side energy storage capacitor C H Installed on the DC side of a single-phase full-bridge capacitor, the DC side energy storage capacitor C H Positive electrode, T 11 collector node, T 21 The drain is connected, C H Negative electrode, T 12 emitter, T 22 The source poles are connected.

[0020] The present invention also provides a modulation method for a multifunctional grid-connected converter based on heterogeneous module hybrid technology, the modulation method being used in a multifunctional grid-connected converter based on heterogeneous module hybrid technology, comprising:

[0021] The phase a modulation method is as follows: In During the positive half-cycle, when When the amplitude is greater than the DC-side capacitor voltage of the diode-clamped square wave circuit unit, that is... The diode-clamped square wave circuit unit outputs a positive voltage U. dc ;exist During the negative half-cycle, when At that time, the single-bridge arm NPC converter outputs a negative voltage -U. dc ;

[0022] in, This is the reference voltage for phase a output; It consists of two parts: one part is the high-voltage three-level voltage output by the diode-clamped square wave circuit unit. The other part is the shaped voltage output from the cascaded H-bridge shaping circuit unit.

[0023] The modulation methods for the other phases are the same as those for phase a.

[0024] Preferably, the shaping voltage output by the cascaded H-bridge shaping circuit unit shapes the high-voltage three-level voltage output by the diode-clamped square wave circuit unit into a sine wave of a reference value, wherein the modulation reference voltage of the cascaded H-bridge shaping circuit unit... Calculated by the following formula:

[0025]

[0026] The cascaded H-bridge shaping circuit unit uses unipolar carrier phase shift control, which concentrates the high-frequency switching action on the SiC MOSFET device of the sub-module, while the Si IGBT device operates in low-frequency mode.

[0027] Preferably, the The per-unit value is used as the modulation wave for each submodule, and the triangular carrier phase of each submodule is successively out of phase by π / N, where N is a natural number.

[0028] Beneficial Effects: This invention provides a multifunctional grid-connected converter and modulation method based on heterogeneous module hybridization. The multifunctional grid-connected converter includes phases a, b, c, and n, each phase including a set of diode-clamped square wave circuit units and cascaded H-bridge shaping circuit units connected in series. Each diode-clamped square wave circuit unit includes a single-arm NPC converter and two DC-side energy storage capacitors C. T1 C T2 The single-bridge arm NPC converter includes four high-voltage Si IGBTs and two clamping diodes; each cascaded H-bridge shaping circuit unit comprises multiple series-connected sub-modules, each sub-module including two low-voltage Si IGBT devices. 11T 12 and two low-voltage SiC MOSFET devices T 21 T 22 The MF-GCC device can simultaneously perform reactive power compensation and flexible arc suppression functions, which not only improves the utilization and practicality of the equipment but also ensures the safe and reliable operation of the distribution network. Furthermore, the MF-GCC employs a four-phase symmetrical design, with each phase consisting of an NPC converter and a cascaded H-bridge connected in series. During arc suppression, each phase only bears the phase voltage, resulting in a smaller total number of cascaded units and higher power density. Attached Figure Description

[0029] Figure 1 A topology diagram of a multifunctional grid-connected converter based on heterogeneous module hybridization is provided for this invention;

[0030] Figure 2 The schematic diagram of MF-GCC modulation provided by this invention;

[0031] Figure 3 The CHB circuit unit modulation principle diagram provided by this invention;

[0032] Figure 4 The reactive current flow diagram during reactive power compensation provided by this invention;

[0033] Figure 5 The present invention provides a flow diagram of reactive current and arc suppression current during the arc suppression period;

[0034] Figure 6 The voltage vector relationship diagram during arc suppression provided by this invention;

[0035] Figure 7 The schematic diagram shows the control method for a multifunctional grid-connected converter based on heterogeneous module hybrid technology provided by this invention. Detailed Implementation

[0036] The specific embodiments of the present invention will be described in further detail below with reference to the accompanying drawings and examples. The following examples are for illustrative purposes only and are not intended to limit the scope of the invention.

[0037] Figure 1 To address the problems of existing multifunctional power electronic devices, this invention proposes a multifunctional grid-connected converter (MF-GCC) based on heterogeneous module hybridization.

[0038] The topology of MF-GCC consists of four phases (a, b, c, and n), each of which is composed of a diode-clamped (NPC) square wave circuit unit and a cascaded H-bridge (CHB) shaping circuit unit connected in series.

[0039] Figure 1 middle This is the three-phase power supply voltage. The voltage at the grid connection point. The zero-sequence voltage at the neutral point; R f L is the ground fault resistance, and L is the filter inductance. This is the output voltage of the CHB shaping circuit unit; U is the output voltage of the NPC square wave circuit unit relative to point O; c U represents the DC-side capacitor voltage value of the CHB submodule. dc1 =U dc2 This is the DC-side capacitor voltage value of the NPC.

[0040] The NPC square wave circuit unit (diode-clamped square wave circuit unit) includes a single-bridge-arm NPC converter and two DC-side energy storage capacitors C. T1 C T2 Each single-arm NPC converter includes four high-voltage Si IGBTs and two clamping diodes. Each phase has one single-arm NPC converter, therefore, a total of four single-arm NPC converters (four-arm NPC) are formed by four phases. Each single-arm NPC converter consists of 16 high-voltage Si-based insulated-gate bipolar transistors (IGBTs; note: each SiIGBT contains one anti-parallel diode) and eight clamping diodes. The single-arm NPC converters in each phase are identical.

[0041] The specific connection method is described using phase a as an example: The single-bridge arm NPC converter includes the first clamping diode D. a1 Second clamping diode D a2 The first Si IGBT T is connected in series through the collector node and the emitter node. a1 Second Si IGBTT a2 Third Si IGBT T a3 Fourth Si IGBT T a4 Four high-voltage Si IGBTs, of which D a1 Negative electrode, T a1 emitter, T a2 Collector connection, D a1 Positive terminal connected to D a2 Negative electrode, D a2 Positive electrode, Ta3 emitter, T a4 Collector connection; the a-phase AC output port of the single-bridge arm NPC is from T a2 Emitter and T a3 The collector is led out at the connection node and connected to a sub-module of phase a of the CHB circuit unit; phases b, c and n have the same structure as phase a, and another sub-module of the CHB circuit unit in phase n is grounded.

[0042] Among them, the two DC-side energy storage capacitors C T1 C T2 Installed on the DC side of the NPC converter, C T1 The positive terminal of the capacitor and the first high voltage Si IGBT (T) of each phase a1 T b1 T c1 T n1 The collector nodes of ) are connected. C T1 capacitor negative terminal and clamping diode D a1 D b1 D c1 D n1 Positive electrode (D) a2 D b2 D c2 D n2 The negative electrode is connected to point O, and C T2 The positive terminal of the capacitor is connected to point O, C T2 The negative terminal of the capacitor and the fourth high-voltage Si IGBT (T) of each phase a4 T b4 T c4 T n4 The emitter nodes are connected.

[0043] The CHB shaping circuit unit (cascaded H-bridge shaping circuit unit) has four identical phases, with each phase consisting of n identical sub-modules connected in series. Each sub-module includes two low-voltage Si IGBT devices T. 11 T 12 And two low-voltage SiC power field-effect transistors (MOSFETs). Note: Each SiC MOSFET contains an anti-parallel diode. 21 T 22 .

[0044] The specific connection method is described using phase a as an example: phase a includes the submodule SM. a1 and submodule SM an Submodule SM a1 Port 1 via T 11 Emitter and T12 The collector node is connected to the filter inductor L, and port 2 is connected to T. 21 Source and T 22 The drain node is connected to another submodule SM. an Port 1 of phase b, phase c and phase n are the same as phase a above; however, port 2 of another submodule of phase b and phase c is connected to their respective single-bridge arm NPC converters, while the other submodule of phase n is grounded.

[0045] DC-side energy storage capacitor C H Installed on the DC side of a single-phase full-bridge capacitor, the DC side energy storage capacitor C H Positive electrode, T 11 collector node, T 21 The drain is connected, C H Negative electrode, T 12 emitter, T 22 The source poles are connected. Submodules are connected in series, with submodule SM in phase a. a1 SM, a submodule in phase b b1 SM, a submodule in phase c c1 The filtered inductor is directly connected to the distribution network, and the submodule SM in phase n is... n1 Grounded via a filtered inductor; Four-phase neutron module SM an SM bn SM cn SM nn Each phase is connected to the output terminal of one of the four corresponding single-bridge arm NPC converters; the other phases have the same structure as phase a.

[0046] Compared with traditional solutions, the structure described in this application has at least the following two advantages:

[0047] 1) Flexible arc suppression and reactive power compensation can operate simultaneously without affecting each other.

[0048] 2) Regardless of whether the topology of this solution is time-extinguishing or reactive power compensation mode, each phase only bears the phase voltage. Under the same voltage level, fewer modules are required to be cascaded.

[0049] The modulation method for a multifunctional grid-connected converter based on heterogeneous module hybrid is as follows:

[0050] The modulation strategy of MF-GCC (Multifunctional Grid-Connected Converter Based on Heterogeneous Module Hybridization) can be divided into two parts: NPC three-level circuit unit modulation and CHB shaping circuit unit modulation. Figure 2 This is a schematic diagram of MF-GCC modulation.

[0051] Since the four-phase structure is symmetrical (or identical), we will use phase a as an example for explanation: The reference voltage for phase a of the MF-GCC is given by the small voltage drop across the filter inductor. The amplitude is approximately equal to the voltage amplitude E from the grid connection point to point O. a . It consists of two parts: one part is the high-voltage three-level voltage output by the NPC circuit unit. The other part is the shaping voltage output by the CHB circuit unit.

[0052] 1) NPC modulation principle

[0053] exist During the positive half-cycle, when When the amplitude is greater than the DC side capacitor voltage of the NPC (i.e.) NPC outputs positive voltage U dc ;exist During the negative half-cycle, when At that time, the NPC outputs a negative voltage level -U. dc The switching states of the a-phase devices of the NPC are shown in Table 1.

[0054] Table 1. Three-level switch status table

[0055]

[0056] 2) CHB modulation principle

[0057] The shaping voltage output of the CHB circuit unit High voltage three-level voltage The sine wave is shaped to be close to the reference value, where the modulation reference voltage of the CHB circuit unit is... It can be calculated using the following formula:

[0058]

[0059] The CHB circuit unit uses unipolar carrier phase-shift control, which concentrates the high-frequency switching action on the SiCMOSFET devices in the sub-module, while the Si IGBT devices operate in low-frequency mode. The per-unit value is used as the modulation wave for each submodule, and the triangular carrier phase of each submodule differs by π / N sequentially. The CHB output voltage... like Figure 3 As shown.

[0060] This invention also provides a modulation method for a multifunctional grid-connected converter based on heterogeneous module hybrid technology. The modulation method is used in the aforementioned multifunctional grid-connected converter based on heterogeneous module hybrid technology (MF-GCC), and includes: within phase a, in... During the positive half-cycle, when When the amplitude is greater than the DC side capacitor voltage of the NPC (i.e.) The NPC outputs a positive voltage U. dc ;exist During the negative half-cycle, when At that time, the NPC outputs a negative voltage level -U. dc ;

[0061] in, The a-phase output reference voltage of the MF-GCC; It consists of two parts: one part is the high-voltage three-level voltage output by the NPC circuit unit. The other part is the shaping voltage output by the CHB circuit unit. The modulation methods for the other phases are the same as those for phase a.

[0062] The working principle of the modulation method is as follows:

[0063] (1) Normal operating conditions of distribution network

[0064] When the power grid is normal, all devices in phase n of the MF-GCC are locked, and the MF-GCC operates in reactive power compensation mode. During reactive power compensation, the reactive current flow diagram of the MF-GCC compensation is as follows: Figure 4 As shown.

[0065] Using instantaneous power theory, the relationship between instantaneous active and reactive power is as follows:

[0066]

[0067] In the formula, u d u q These are the d-axis and q-axis components of the grid connection point voltage, respectively; i d i q These represent the active and reactive components of the MF-GCC compensation current, respectively. In pure reactive compensation mode, i d =0. Through Park transformation, the q-axis reference value of the reactive component of the compensation current can be obtained:

[0068]

[0069] In the formula, Q ref The target value is given for reactive power.

[0070] By performing the inverse Park transformation on equation (3), we obtain the reference values ​​of the reactive current injected into phases a, b, and c:

[0071]

[0072] Where T is the Park transformation:

[0073]

[0074] In the formula, ω is the angular frequency.

[0075] (2) Single-phase grounding condition of distribution network

[0076] Assuming a single-phase ground fault occurs in phase a of the distribution network, the MF-GCC adds arc suppression functionality to its compensation capabilities. Arc suppression current is injected into the n-phase arm of the MF-GCC, and after being shunt through phases b and c, it compensates for the distribution network's ground capacitance current, suppressing the grounding point current to zero. The flow diagrams of reactive current and arc suppression current compensated by the MF-GCC in this mode are as follows: Figure 5 As shown.

[0077] According to the KCL equation:

[0078] i ca +i c b+i cc +if-i z =0 (4)

[0079] In the formula, i ca i cb i cc These are the three-phase ground capacitance currents of the distribution network, i f For the grounding fault current, i z Arc suppression current injected into MF-GCC.

[0080] Substituting the distribution network system parameters into equation (4), we get:

[0081]

[0082] In the formula, The neutral point voltage, R is the power supply voltage. f For grounding resistance, Y a Y b Y c This refers to the three-phase ground admittance of the distribution network.

[0083] Therefore When (i.e., the equivalent control point O voltage is) If the grounding point current is suppressed to zero, then the arc-suppression current injected by the MF-GCC at this time is:

[0084]

[0085] The arc-suppression current injected through phases b and c can be expressed as:

[0086]

[0087] Therefore, the arc-suppression current injected by phase n satisfies equation (6), and the arc-suppression current injected by phases b and c superimposed satisfies equation (7).

[0088] At this point, the vector relationship of the output voltage of each bridge arm satisfies Figure 6 As can be seen from the figure, the voltage across each arm of the MF-GCC is the phase voltage.

[0089] like Figure 7 As shown, this embodiment of the invention also provides a control method for a multifunctional grid-connected converter based on heterogeneous module hybrid technology, including:

[0090] The injected active component is set to 0, and the reactive power compensation current reference value i is calculated according to formula (4) in this application. qref The active and reactive components of the sampled compensation current are compared with the reference value, and the d-axis component i is obtained through a PI controller. dr q-axis component i qr If the device does not extinguish the arc, then the 0-axis component is equal to 0 (i.e., i... 0r =0); If the device extinguishes the arc, the arc extinguishing current reference value i is calculated by formula (6) in this application. zref And divide by 3 as the 0-axis component. dr i qr i 0r The three-phase stationary coordinate system components a, b, and c are obtained through dq transformation, and are respectively compared with the voltage difference from point O to the grid connection point (i.e., The sum of these values ​​yields the reference values ​​for the modulation voltages of phases a, b, and c. The sampling of n-phase output voltage and i zref The n-phase stationary coordinate system components are obtained by performing a differential operation using a PI controller and compared with the voltage at point O. The summation yields the reference value of the modulation voltage for the n-phase. After obtaining the reference voltages for each phase, respectively, the following methods are used: Figure 4 and Figure 5 The modulation strategy controls the multifunctional grid-connected converter.

[0091] The following is an analysis of the number pairs of submodules:

[0092] Taking a cascaded H-bridge submodule with a power electronic device withstand voltage of 1700V and a DC side voltage Uc = 800V as an example. In a 10kV distribution network, the arc suppression device withstands the line voltage (peak value 14142V) during arc suppression. A traditional cascaded H-bridge type multi-functional static var compensator requires 21 H-bridge submodules per phase, so a total of 63 H-bridge submodules are needed for three phases.

[0093] Traditionally, the power electronic withstand voltage of the NPC circuit unit in a hybrid structure static var compensator is selected as 6500V, and the DC side capacitor voltage U... dc1 =U dc2=4000V. During the arc suppression period, the maximum voltage that the grounded phase and non-faulty phase of the NPC unit can withstand together is 8000V. Therefore, the maximum voltage that each phase of the CHB unit can withstand is 64142V. Thus, each phase of the CHB unit has 9 H-bridge sub-modules, and a total of 27 H-bridge modules are required for the three phases.

[0094] The structure proposed in this invention allows each phase to independently withstand only the phase voltage (peak value 8165V) during arc suppression. Therefore, the NPC unit can withstand a maximum of 4000V, and the maximum voltage that each phase of the CHB unit can withstand is 4165V. Thus, each phase of the CHB unit has 6 H-bridge sub-modules, and a total of 24 H-bridge sub-modules are required for four phases.

[0095] In summary, compared with existing multi-functional grid-connected converters, the proposed MF-GCC hybrid topology cascaded H-bridge sub-modules are further reduced, the number of power electronic devices and DC-side capacitors is less, and the power density and efficiency of active devices are higher.

[0096] Although preferred embodiments of the invention have been described, those skilled in the art, upon learning the basic inventive concept, can make other changes and modifications to these embodiments. Therefore, the appended claims are intended to be interpreted as including both the preferred embodiments and all changes and modifications falling within the scope of the invention.

[0097] Obviously, those skilled in the art can make various modifications and variations to this invention without departing from its spirit and scope. Therefore, if these modifications and variations fall within the scope of the claims of this invention and their equivalents, this invention also intends to include these modifications and variations.

Claims

1. A multifunctional grid-connected converter based on heterogeneous module hybrid design, characterized in that, It includes phases a, b, c, and n. Each phase includes a set of diode-clamped square wave circuit units and cascaded H-bridge shaping circuit units connected in series. The four phases share two DC-side energy storage capacitors C. T1 C T2 ; Each phase of the diode-clamped square wave circuit unit includes a single-bridge-arm NPC converter, wherein the single-bridge-arm NPC converter includes four high-voltage Si IGBTs and two clamping diodes. Each phase of the cascaded H-bridge shaping circuit unit comprises two sub-modules connected in series, each sub-module including two low-voltage Si IGBT devices. 11 T 12 and two low-voltage SiC MOSFET devices T 21 T 22 ; Among them, the output of the sub-module at the end of the series connection in phase n is grounded; In phase a, the single-bridge arm NPC converter includes a first clamping diode D. a1 Second clamping diode D a2 The first Si IGBT T is connected in series through the collector node and the emitter node. a1 Second Si IGBT T a2 Third Si IGBT T a3 Fourth Si IGBT T a4 There are a total of four high-voltage Si IGBTs, of which D a1 Negative electrode, T a1 emitter, T a2 Collector connection, D a1 Positive terminal connected to D a2 Negative electrode, D a2 Positive electrode, T a3 emitter, T a4 Collector connection; The a-phase AC output port of the single-bridge arm NPC converter is from T a2 Emitter and T a3 It is led out at the collector connection node and connected to a sub-module of phase a of the cascaded H-bridge shaping circuit unit; Phases a, b, and c have identical structures and each includes two sub-modules. The first port of one of the sub-modules in each of phases a, b, and c is connected via T... 11 Emitter and T 12 The collector node is connected to the filter inductor L and then to the power distribution network. The second port is connected to T. 21 Source and T 22 The drain node is connected to the first port of another submodule, and the second port of the other submodule is connected to the output of the single-bridge arm NPC converter; The n-phase includes two sub-modules SM. nn and SM n1 Submodule SM n1 Grounded via a filtered inductor; Submodule SM nn Connect to the output terminal of the corresponding single-bridge arm NPC converter.

2. The multifunctional grid-connected converter based on heterogeneous module hybrid as described in claim 1, characterized in that, Each SiIGBT contains an anti-parallel diode.

3. The multifunctional grid-connected converter based on heterogeneous module hybrid as described in claim 1, characterized in that, The DC-side energy storage capacitor C T1 C T2 Installed on the DC side of each of the single-bridge arm NPC converters, C T1 The positive terminal of the capacitor is connected to the collector node of the first high-voltage Si IGBT in each phase; C T1 The negative terminal of the capacitor, the positive terminal of the first clamping diode of each phase, and the negative terminal of the second clamping diode of each phase are connected to point O. T2 The positive terminal of the capacitor is connected to point O, C T2 The negative terminal of the capacitor is connected to the emitter node of the fourth high-voltage Si IGBT in each phase.

4. The multifunctional grid-connected converter based on heterogeneous module hybrid as described in claim 1, characterized in that, The DC-side energy storage capacitor C H Installed on the DC side of a single-phase full-bridge capacitor, the DC side energy storage capacitor C H Positive electrode, T 11 collector node, T 21 The drain is connected, C H Negative electrode, T 12 emitter, T 22 The source poles are connected.

5. A modulation method for a multifunctional grid-connected converter based on heterogeneous module hybrid technology, characterized in that, The modulation method is used in the multifunctional grid-connected converter based on heterogeneous module hybrid as described in any one of claims 1-4, comprising: The phase a modulation method is as follows: In During the positive half-cycle, when When the amplitude is greater than the DC-side capacitor voltage of the diode-clamped square wave circuit unit, that is... >U dc The diode-clamped square wave circuit unit outputs a positive voltage U. dc ;exist During the negative half-cycle, when >U dc At that time, the single-bridge arm NPC converter outputs a negative voltage -U. dc ; in, This is the reference voltage for phase a output; It consists of two parts: one part is the high-voltage three-level voltage output by the diode-clamped square wave circuit unit. The other part is the shaped voltage output from the cascaded H-bridge shaping circuit unit. ; The modulation methods for the other phases are the same as those for phase a.

6. The modulation method for a multifunctional grid-connected converter based on heterogeneous module hybrid technology according to claim 5, characterized in that, The shaping voltage output by the cascaded H-bridge shaping circuit unit shapes the high-voltage three-level voltage output by the diode-clamped square wave circuit unit into a sine wave of a reference value, wherein the modulation reference voltage of the cascaded H-bridge shaping circuit unit... Calculated by the following formula: (1) The cascaded H-bridge shaping circuit unit uses unipolar carrier phase shift control, which concentrates the high-frequency switching action on the SiCMOSFET device of the sub-module, while the Si IGBT device operates in low-frequency mode.

7. The modulation method for a multifunctional grid-connected converter based on heterogeneous module hybrid technology according to claim 6, characterized in that, The The per-unit value is used as the modulation wave for each submodule, and the triangular carrier phase of each submodule is sequentially phased. N is a natural number.

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