Adaptive control method for fault-controlled SiC module economically integrated medium-voltage grid-connected equipment

Abstract

The invention discloses an adaptive control method for SiC module economic integrated medium-voltage grid-connected equipment oriented to fault control, comprising: calculating a three-phase bridge arm modulation wave and a fourth bridge arm modulation wave; obtaining a three-phase bridge arm NPC circuit switch signal according to the three-phase bridge arm modulation wave, and obtaining a three-phase bridge arm NPC circuit output voltage according to the three-phase bridge arm NPC circuit switch signal; obtaining a fourth bridge arm NPC circuit switch signal according to the fourth bridge arm modulation wave, and obtaining a fourth bridge arm NPC circuit output voltage according to the fourth bridge arm NPC circuit switch signal; calculating a voltage-stabilizing active power vector of each submodule of a CHB circuit; obtaining a three-phase bridge arm CHB circuit switch signal according to the three-phase bridge arm modulation wave, the three-phase bridge arm NPC circuit output voltage and the voltage-stabilizing active power vector of each submodule of the CHB circuit; obtaining a fourth bridge arm CHB circuit switch signal according to the fourth bridge arm modulation wave, the fourth bridge arm NPC circuit output voltage and the voltage-stabilizing active power vector of each submodule of the CHB circuit; and completing the adaptive control of the grid-connected equipment according to the CHB circuit switch signal.

Description

Technical Field

[0001] The present invention relates to the field of single-phase grounding fault support in distribution networks, and in particular to an adaptive control method for fault-control-oriented SiC module economically integrated medium-voltage grid-connected equipment. Background Art

[0002] The distribution network goes deep into the user terminal, and random faults occur frequently, among which single-phase grounding fault (SPG) accounts for the highest proportion. With the increasing proportion of cables in the distribution network and the large-scale access of nonlinear loads, the active component and harmonic component of the grounding fault current have increased significantly, making it difficult for traditional passive arc suppression equipment to effectively suppress single-phase grounding faults.

[0003] The IFCD (Integrated fault control device) based on CHB (Cascaded H-bridge) can give full play to the flexible control characteristics of power electronics, realize efficient and high-quality control of power quality and ground faults, and effectively improve the asset utilization rate of distribution network. However, considering the asymmetric characteristics of single-phase ground faults, the three-arm IFCD structure needs to bear the line voltage, resulting in a large number of cascaded submodules and high costs, which seriously restricts its application and promotion. In order to reduce the number of cascaded IFCDs, the four-arm IFCD has received extensive attention and research. In the prior art, there is a four-arm CHB-IFCD with energy supply equipment. This structure uses the CHB circuit of the fourth bridge arm to bear the fault phase voltage, thereby reducing the voltage borne by the remaining three bridge arms to the phase voltage, effectively reducing the number of sub-module cascades; in the prior art, there is also a four-arm HCM-IFCD (Hybrid Cascade Multilevel-IFCD) with energy supply equipment. This structure gives full play to the advantages of high withstand voltage of NPC (Neutral Point Clamped) converter and high switching frequency of CHB, further reducing the number of sub-module cascades, and effectively improving the power density of the equipment. However, when the four-arm IFCD fully compensates for the fault current, it needs to consume the energy stored in the DC side capacitor of the fourth bridge arm CHB, and it is necessary to add power supply equipment to provide energy support, which seriously affects the cost and power density advantages of the four-arm IFCD.

[0004] Therefore, a new technical solution is urgently needed to solve the technical problem of how to achieve full compensation of fault current by a four-arm IFCD while ensuring self-stabilization of the DC side of the IFCD, that is, without the need for additional power supply equipment. Summary of the invention

[0005] The present invention provides an adaptive control method for SiC module economic integrated medium voltage grid-connected equipment for fault control, which is used to solve the technical problem of how to achieve full compensation of fault current by a four-arm IFCD while ensuring self-stabilization of the DC side of the IFCD, i.e., without the need for additional power supply equipment.

[0006] To achieve the above object, the present invention provides an adaptive control method for SiC module economic integrated medium voltage grid-connected equipment oriented to fault control, comprising:

[0007] Calculate the three-phase bridge arm modulation wave and the fourth bridge arm modulation wave; obtain the three-phase bridge arm NPC circuit switching signal according to the three-phase bridge arm modulation wave, and obtain the three-phase bridge arm NPC circuit output voltage according to the three-phase bridge arm NPC circuit switching signal; obtain the fourth bridge arm NPC circuit switching signal according to the fourth bridge arm modulation wave, and obtain the fourth bridge arm NPC circuit output voltage according to the fourth bridge arm NPC circuit switching signal; perform feedback closed-loop control on the capacitor voltage of each sub-module of the CHB circuit, and obtain the voltage stabilization active power vector of each sub-module of the CHB circuit.

[0008] A three-phase bridge arm CHB circuit switching signal is obtained according to the three-phase bridge arm modulation wave, the three-phase bridge arm NPC circuit output voltage and the voltage stabilization active power vector of each sub-module of the CHB circuit; a fourth bridge arm CHB circuit switching signal is obtained according to the fourth bridge arm modulation wave, the fourth bridge arm NPC circuit output voltage and the voltage stabilization active power vector of each sub-module of the CHB circuit.

[0009] The adaptive control of the grid-connected equipment is completed according to the switching signal of the three-phase bridge arm CHB circuit and the switching signal of the fourth bridge arm CHB circuit.

[0010] Preferably, calculating the three-phase bridge arm modulation wave and the fourth bridge arm modulation wave comprises:

[0011] Calculate the three-phase bridge arm modulation wave:

[0012] Obtain the DC side voltage of the NPC circuit to obtain a first voltage; obtain the sum of the capacitor voltages of the CHB circuit submodules to obtain a second voltage; subtract the first voltage and the second voltage from the third voltage to obtain a first difference; the third voltage includes the sum of a preset reference value of the DC side voltage of the NPC circuit and a preset reference value of the sum of the capacitor voltages of the CHB circuit submodules.

[0013] The first difference is subjected to feedback closed-loop control to obtain a reference value of the voltage-stabilizing active current; a reference value of the reactive compensation current is obtained according to a preset reactive compensation instruction; a sampling value of the voltage-stabilizing active current and a sampling value of the reactive compensation current of the three-phase bridge arm are obtained, and the sampling values ​​are subtracted from the reference values ​​of the voltage-stabilizing active current and the reactive compensation current to obtain a second difference and a third difference, respectively; the second difference and the third difference are subjected to feedback closed-loop decoupling control to obtain a three-phase bridge arm modulation wave.

[0014] The reactive compensation current reference value obtained according to the preset reactive compensation instruction includes:

[0015] The preset reactive power compensation instruction is issued by the superior dispatcher. To express; then the reactive compensation current reference value It can be expressed by the following relationship:

[0016]

[0017] Among them, U d is the grid voltage active vector.

[0018] Calculate the modulation wave of the fourth bridge arm:

[0019] Calculate the output current reference value of the fourth bridge arm according to the distribution network information; obtain the output current sampling value of the fourth bridge arm, subtract the sampling value from the output current reference value of the fourth bridge arm to obtain a fourth difference; perform feedback closed-loop control on the fourth difference, and add output voltage feedforward control of the fourth bridge arm to obtain a modulation wave of the fourth bridge arm.

[0020] Preferably, feedback closed-loop decoupling control is performed on the second difference and the third difference respectively to obtain a three-phase bridge arm modulation wave, which includes:

[0021]

[0022]

[0023] in, and is the three-phase bridge arm modulation wave; θ is the angle between the d axis and the phase reference axis; ω is the grid angular frequency; L is the filter inductance value; V d Represents the d-axis component of the three-phase bridge arm modulation wave; V q Represents the q-axis component of the three-phase bridge arm modulation wave; U q Represents the grid voltage reactive vector; K pi Indicates the proportional coefficient of the PI controller; K ii Represents the integral coefficient of the PI controller; Indicates the reference value of the voltage-stabilized active current; I zd Indicates the sampling value of the voltage-stabilized active current; I zq represents the reactive compensation current sampling value; s represents the complex frequency domain variable.

[0024] Preferably, calculating the fourth bridge arm output current reference value according to the distribution network information includes:

[0025] When a single-phase grounding fault occurs on phase x, the fourth bridge arm outputs a current reference value It can be expressed by the following relationship:

[0026]

[0027] in, is the phase voltage of the x-phase power grid; and is the grid phase voltage of the remaining two phases except phase x; r 0y and r 0w is the resistance to ground of the remaining two phases except phase x; C 0y and C 0w is the capacitance to ground of the remaining two phases except phase x; j represents the imaginary unit of the complex number.

[0028] Preferably, the fourth difference is subjected to feedback closed-loop control, and the fourth bridge arm output voltage is additionally subjected to feedforward control, so as to obtain the fourth bridge arm modulation wave, which includes:

[0029]

[0030] in, is the modulation wave of the fourth bridge arm; K p and K r are the proportional coefficient and integral coefficient of the PR controller respectively; ω c is the resonant frequency band width; ω0 is the resonant frequency point; I z0 is the output current of the fourth bridge arm; u0(t) is the output voltage of the fourth bridge arm.

[0031] Preferably, obtaining a three-phase bridge arm NPC circuit switch signal according to the three-phase bridge arm modulation wave, and obtaining a three-phase bridge arm NPC circuit output voltage according to the three-phase bridge arm NPC circuit switch signal comprises:

[0032] The three-phase bridge arm NPC circuit switch signal is obtained according to the three-phase bridge arm modulation wave, including:

[0033]

[0034]

[0035] Among them, U dc Indicates the DC side voltage reference value of the NPC circuit, S x1 and S x2 They represent the switching functions of the upper bridge arm and the lower bridge arm of the x-th phase NPC circuit respectively; Represents the modulation wave of the x-phase bridge arm.

[0036] The output voltage of the three-phase bridge arm NPC circuit is obtained according to the switch signal of the three-phase bridge arm NPC circuit, including:

[0037]

[0038] Among them, u npcx (t) represents the output voltage of the x-phase NPC circuit.

[0039] Preferably, obtaining a fourth bridge arm NPC circuit switch signal according to the fourth bridge arm modulation wave, and obtaining a fourth bridge arm NPC circuit output voltage according to the fourth bridge arm NPC circuit switch signal comprises:

[0040] The fourth bridge arm NPC circuit switch signal is obtained according to the fourth bridge arm modulation wave, including:

[0041] Assuming that the switching angle of the NPC circuit of the fourth bridge arm in the unit period of the modulation wave of the fourth bridge arm is θ1~θ4, it can be expressed by the following relationship:

[0042]

[0043] Then the output voltage of the fourth bridge arm NPC circuit is u npc0 The calculation formula of (t) can be expressed by the following relationship:

[0044]

[0045] Among them, S 01 and S 02 They are the switching functions of the upper arm and the lower arm of the fourth bridge arm NPC circuit, respectively, and can be expressed by the following relationship:

[0046]

[0047] Wherein, ω=2π / T, T is the grid voltage period.

[0048] Assume that the time domain expression of the modulation wave of the fourth bridge arm is and the fourth bridge fault compensation current They are:

[0049]

[0050] Among them, U m ,I m are the modulation voltage amplitude and compensation current amplitude respectively, is the power factor angle.

[0051] Then the energy fluctuation ΔE of the fourth bridge arm CHB circuit in a unit period can be expressed by the following relationship:

[0052]

[0053] in, Represents the modulation voltage of the fourth bridge arm CHB circuit.

[0054] When the energy fluctuation ΔE in the unit cycle is 0, the capacitor voltage of the CHB submodule is stable. When the capacitor voltage of the CHB circuit submodule is stable, the switching angle θ1 can be expressed by the following relationship:

[0055]

[0056] Then the switching functions S of the upper and lower arms of the fourth bridge arm NPC circuit are 01 and S 02 Can be corrected to S 001 and S 002 :

[0057]

[0058] According to S 001 and S 002 The fourth bridge arm NPC circuit switching signal is obtained by combining the fourth bridge arm modulation wave with the fourth bridge arm.

[0059] The output voltage u of the fourth bridge arm NPC circuit is obtained according to the switch signal of the fourth bridge arm NPC circuit npc0 (t), including:

[0060]

[0061] Preferably, feedback closed-loop control is performed on the capacitor voltage of each submodule of the CHB circuit to obtain the voltage stabilization active power vector of each submodule of the CHB circuit, including:

[0062]

[0063] Where Δv xj represents the voltage stabilization active power vector of the jth CHB circuit submodule of the xth phase; U cxj represents the capacitor voltage of the jth CHB circuit submodule of the xth phase; Indicates the capacitance voltage reference value of the CHB circuit submodule; Indicates the output current phase of the xth phase.

[0064] Preferably, obtaining the three-phase bridge arm CHB circuit switch signal according to the three-phase bridge arm modulation wave, the three-phase bridge arm NPC circuit output voltage and the voltage stabilization active power vector of each submodule of the CHB circuit includes:

[0065] Calculate the modulation voltage of the x-phase CHB circuit The calculation method for each phase in the three-phase bridge arm is the same, which can be expressed by the following relationship:

[0066]

[0067] in, represents the bridge arm modulation wave of the xth phase; u npcx (t) represents the output voltage of the NPC circuit of the xth phase.

[0068] According to the modulation voltage of the x-phase CHB circuit The switching function of the CHB circuit submodule is calculated to obtain the switching signal of the CHB circuit of the xth phase, which can be expressed by the following relationship:

[0069]

[0070] Among them, S xj (j=1,2,...,N) represents the switching function of the x-phase CHB circuit submodule, u trj The carrier is modulated for the jth CHB unit submodule, and its corresponding phase is π / N.

[0071] Preferably, obtaining the fourth bridge arm CHB circuit switch signal according to the fourth bridge arm modulation wave, the fourth bridge arm NPC circuit output voltage and the voltage stabilization active power vector of each submodule of the CHB circuit includes:

[0072] Calculate the modulation voltage of the fourth bridge arm CHB circuit It can be expressed by the following relationship:

[0073]

[0074] According to the modulation voltage of the fourth bridge arm CHB circuit The switching function of the CHB circuit submodule is calculated to obtain the switching signal of the fourth bridge arm CHB circuit, which can be expressed by the following relationship:

[0075]

[0076] Among them, S 0j (j=1,2,...,N) represents the switching function of the fourth bridge arm CHB circuit submodule, u trj The carrier is modulated for the jth CHB unit submodule, and its corresponding phase is π / N.

[0077] The present invention has the following beneficial effects:

[0078] The adaptive control method of the SiC module economic integrated medium-voltage grid-connected equipment for fault control of the present invention obtains the switching signals of the three-phase bridge arm NPC circuit and the CHB circuit by acquiring the equipment data and performing mathematical operations, so that the present invention can realize the reactive power compensation function through the switching signals of the three-phase bridge arm NPC circuit and the CHB circuit in both the normal mode and the fault mode of the distribution network. The switching signal of the fourth bridge arm NPC circuit is also obtained by acquiring the equipment data and performing mathematical operations, so that the present invention can ensure the stability of the capacitor voltage of the fourth bridge arm CHB circuit submodule through the switching signals of the fourth bridge arm NPC circuit and the CHB circuit, that is, to ensure the self-stabilization of the DC side of the IFCD; and realize high-quality control of single-phase grounding faults in the distribution network fault mode. The method of the present invention effectively solves the problem of the contradiction between the voltage stabilization and arc extinguishing control targets of the grid-connected equipment during the SPG period, without the need to add power supply equipment to the fourth bridge arm, thereby improving the power density and economy of the equipment.

[0079] In addition to the above-described purposes, features and advantages, the present invention has other purposes, features and advantages. The present invention will be further described in detail below with reference to the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0080] The drawings constituting a part of this application are used to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute an improper limitation of the present invention. In the drawings:

[0081] Figure 1 It is a schematic diagram of the structure of the grid-connected equipment according to the preferred embodiment of the present invention.

[0082] Figure 2 It is a control block diagram of the control method of the preferred embodiment of the present invention.

[0083] Figure 3 It is a simulation waveform diagram of the phase voltage and phase current of the power grid according to the preferred embodiment of the present invention.

[0084] Figure 4 It is a fault voltage and fault current simulation waveform diagram of a preferred embodiment of the present invention.

[0085] Figure 5 It is a simulation waveform diagram of the DC capacitor voltage of the NPC circuit according to the preferred embodiment of the present invention.

[0086] Figure 6 It is a capacitor voltage simulation waveform diagram of the C-phase CHB circuit submodule of the preferred embodiment of the present invention.

[0087] Figure 7 It is a capacitor voltage simulation waveform diagram of the fourth bridge arm CHB circuit submodule of the preferred embodiment of the present invention. DETAILED DESCRIPTION

[0088] The embodiments of the present invention are described in detail below with reference to the accompanying drawings, but the present invention can be implemented in many different ways as defined and covered by the claims.

[0089] See also Figure 1 The SiC module economic integrated medium-voltage grid-connected equipment for fault control of the present invention includes a first bridge arm, a second bridge arm, a third bridge arm and a fourth bridge arm; any bridge arm includes a CHB circuit and an NPC circuit connected in series; the CHB circuit end of the fourth bridge arm is grounded; the CHB circuit ends of the first bridge arm, the second bridge arm and the third bridge arm are connected to a three-phase distribution network.

[0090] The CHB circuit includes N sub-modules connected in series, where N is a positive integer, and each sub-module is composed of 4 fully-controlled SiC MOSFET devices, which are named S1, S2, S3 and S4 in sequence; wherein the collectors of S1 and S3 are respectively connected to the positive electrode of the sub-module capacitor, and the emitters are connected to the first lead-out terminal; the emitters of S2 and S4 are respectively connected to the negative electrode of the sub-module capacitor, and the collectors are connected to the second lead-out terminal; the first lead-out terminal of the sub-module close to the distribution network in the CHB circuits of the first bridge arm, the second bridge arm and the third bridge arm is connected to the distribution network after passing through the filter inductor L, and the second lead-out terminal of the sub-module close to the NPC circuit is connected to the output end of the NPC circuit of the first bridge arm, the second bridge arm and the third bridge arm; the first lead-out terminal of the sub-module close to the NPC circuit in the CHB circuit of the fourth bridge arm is connected to the output end of the NPC circuit of the fourth bridge arm; the remaining first lead-out terminals and second lead-out terminals are used to connect the sub-modules end to end.

[0091] The NPC circuit includes a first clamping diode, a second clamping diode and four fully controlled SiC MOSFET devices; the four fully controlled SiC MOSFET devices are connected in series; the collector of the first SiC MOSFET device is connected to the positive electrode of the NPC DC capacitor, and the emitter of the fourth SiC MOSFET device is connected to the negative electrode of the NPC DC capacitor; the NPC circuits of the first bridge arm, the second bridge arm, the third bridge arm and the fourth bridge arm all share the same NPC DC capacitor. The anode of the first clamping diode is connected to the emitter of the first SiC MOSFET device, and the cathode is connected to the neutral point of the NPC circuit; the anode of the second clamping diode is connected to the neutral point of the NPC circuit, and the cathode is connected to the collector of the fourth SiC MOSFET device. The output end of the NPC circuit is located between the emitter of the second SiC MOSFET device and the collector of the third SiC MOSFET device.

[0092] See also Figure 1 , for medium voltage distribution network, is the grid phase voltage; is the grid voltage, C 0x(x=a,b,c) is the line capacitance to ground; r 0x (x=a,b,c) is the line resistance to ground; R f is the ground fault resistance. For HCM-IFCD, u npcx (x=a,b,c,0) is the output voltage of the NPC circuit; u chbx (x=a,b,c,0) is the output voltage of CHB circuit; U dc1 , U dc2 is the DC side voltage of the NPC circuit; is the output current of each bridge arm; C N is the DC capacitance of the NPC circuit; C h is the DC capacitor of the CHB circuit; L is the filter inductor; A, B and C represent the three phases of the distribution network respectively.

[0093] See also Figure 2 The preferred embodiment of the present invention provides an adaptive control method for SiC module economic integrated medium voltage grid-connected equipment oriented to fault control, comprising:

[0094] Superior control strategy:

[0095] Obtain the DC side voltage of the NPC circuit to obtain a first voltage; obtain the sum of the capacitor voltages of the CHB circuit submodules to obtain a second voltage; subtract the first voltage and the second voltage from the third voltage to obtain a first difference; the third voltage includes the sum of a preset reference value of the DC side voltage of the NPC circuit and a preset reference value of the sum of the capacitor voltages of the CHB circuit submodules.

[0096] The first difference is subjected to feedback closed-loop control to obtain a voltage-stabilized active current reference value.

[0097] Obtaining a reactive compensation current reference value according to a preset reactive compensation instruction; specifically including:

[0098] The preset reactive power compensation instruction is issued by the superior dispatcher. To express.

[0099] The reactive compensation current reference value is It can be expressed by the following relationship:

[0100]

[0101] Among them, U d is the grid voltage active vector.

[0102] The voltage-stabilizing active current sampling value and the reactive compensation current sampling value of the three-phase bridge arm are obtained, and the sampling values ​​are subtracted from the reference values ​​of the voltage-stabilizing active current and the reactive compensation current to obtain the second difference and the third difference respectively.

[0103] The second difference and the third difference are respectively subjected to feedback closed-loop decoupling control to obtain a three-phase bridge arm modulation wave; specifically comprising:

[0104]

[0105] in, and is the three-phase bridge arm modulation wave; θ is the angle between the d-axis and the phase reference axis; ω is the grid angular frequency; L is the filter inductance value.

[0106] Calculate the output current reference value of the fourth bridge arm according to the distribution network information; specifically include:

[0107] When a single-phase grounding fault occurs on phase x, the fourth bridge arm outputs a current reference value It can be expressed by the following relationship:

[0108]

[0109] in, is the phase voltage of the x-phase power grid; and is the grid phase voltage of the remaining two phases except phase x; r 0y and r 0w is the resistance to ground of the remaining two phases except phase x; C 0y and C 0w is the capacitance to ground of the remaining two phases except phase x.

[0110] Obtain the fourth bridge arm output current sampling value, subtract the sampling value from the fourth bridge arm output current reference value, and obtain a fourth difference. Perform feedback closed-loop control on the fourth difference, and perform additional fourth bridge arm output voltage feedforward control to obtain a fourth bridge arm modulation wave; specifically including:

[0111]

[0112] in, is the modulation wave of the fourth bridge arm; K p and K r are the proportional coefficient and integral coefficient of the PR controller respectively; ω c is the resonant frequency band width; ω0 is the resonant frequency point; I z0 is the output current of the fourth bridge arm; u0(t) is the output voltage of the fourth bridge arm.

[0113] Lower-level control strategy:

[0114] The three-phase bridge arm NPC circuit switch signal is obtained according to the three-phase bridge arm modulation wave, and the three-phase bridge arm NPC circuit output voltage is obtained according to the three-phase bridge arm NPC circuit switch signal; specifically including:

[0115] The three-phase bridge arm NPC circuit switch signal is obtained according to the three-phase bridge arm modulation wave, and the nearest level approximation modulation method is adopted, including:

[0116]

[0117] Among them, U dc Indicates the DC side voltage reference value of the NPC circuit, S x1 and S x2 They represent the switching functions of the upper bridge arm and the lower bridge arm of the x-th phase NPC circuit respectively; Represents the modulation wave of the x-phase bridge arm.

[0118] In order to prevent the DC side capacitor from being damaged by the potential fluctuation at the midpoint of the NPC circuit, the zero-sequence voltage injection method is adopted to ensure the voltage balance of the DC split capacitors, thereby achieving the potential balance at the midpoint of the NPC circuit; that is, the voltage of the first DC capacitor of the NPC circuit is subtracted from the voltage of the second DC capacitor of the NPC circuit, the reference value 0 is subtracted from this difference, and the difference is controlled through a feedback closed loop to obtain the required injected zero-sequence voltage. This zero-sequence voltage is superimposed on the modulation wave of the three-phase bridge arm, thereby achieving the balance of the midpoint voltage on the NPC DC side.

[0119] The output voltage of the three-phase bridge arm NPC circuit is obtained according to the switch signal of the three-phase bridge arm NPC circuit, including:

[0120]

[0121] Among them, u npcx (t) represents the output voltage of the x-phase NPC circuit.

[0122] Obtaining a fourth bridge arm NPC circuit switch signal according to the fourth bridge arm modulation wave, and obtaining a fourth bridge arm NPC circuit output voltage according to the fourth bridge arm NPC circuit switch signal; specifically comprising:

[0123] The fourth bridge arm NPC circuit switch signal is obtained according to the fourth bridge arm modulation wave, including:

[0124] Assuming that the switching angle of the NPC circuit of the fourth bridge arm in the unit period of the modulation wave of the fourth bridge arm is θ1~θ4, it can be expressed by the following relationship:

[0125]

[0126] Then the output voltage of the fourth bridge arm NPC circuit is u npc0 The calculation formula of (t) can be expressed by the following relationship:

[0127]

[0128] Among them, S 01 and S 02They are the switching functions of the upper arm and the lower arm of the fourth bridge arm NPC circuit, respectively, and can be expressed by the following relationship:

[0129]

[0130] Wherein, ω=2π / T, T is the grid voltage period.

[0131] Assume that the time domain expression of the modulation wave of the fourth bridge arm is and the fourth bridge fault compensation current They are:

[0132]

[0133] Among them, U m ,I m are the modulation voltage amplitude and compensation current amplitude respectively, is the power factor angle.

[0134] Then the energy fluctuation ΔE of the fourth bridge arm CHB circuit in a unit period can be expressed by the following relationship:

[0135]

[0136] When the energy fluctuation ΔE in the unit cycle is 0, the capacitor voltage of the CHB submodule is stable. When the capacitor voltage of the CHB circuit submodule is stable, the switching angle θ1 can be expressed by the following relationship:

[0137]

[0138] Then the switching functions S of the upper and lower arms of the fourth bridge arm NPC circuit are 01 and S 02 Can be corrected to S 001 and S 002 :

[0139]

[0140] According to S 001 and S 002 The fourth bridge arm NPC circuit switching signal is obtained by combining the fourth bridge arm modulation wave with the fourth bridge arm.

[0141] The output voltage u of the fourth bridge arm NPC circuit is obtained according to the switch signal of the fourth bridge arm NPC circuit npc0 (t), including:

[0142]

[0143] Feedback closed-loop control is performed on the capacitor voltage of each submodule of the CHB circuit to obtain the voltage stabilization active power vector of each submodule of the CHB circuit; specifically, it includes:

[0144]

[0145] Where Δv xj represents the voltage stabilization active power vector of the jth CHB circuit submodule of the xth phase; U cxj represents the capacitor voltage of the jth CHB circuit submodule of the xth phase; Indicates the capacitance voltage reference value of the CHB circuit submodule; Indicates the output current phase of the xth phase.

[0146] The three-phase bridge arm CHB circuit switch signal is obtained according to the three-phase bridge arm modulation wave, the three-phase bridge arm NPC circuit output voltage and the voltage stabilization active power vector of each submodule of the CHB circuit; the CHB circuit switch signal modulation method is a PWM modulation method; specifically including:

[0147] Calculate the modulation voltage of the x-phase CHB circuit The calculation method for each phase in the three-phase bridge arm is the same, which can be expressed by the following relationship:

[0148]

[0149] in, represents the bridge arm modulation wave of the xth phase; u npcx (t) represents the output voltage of the NPC circuit of the xth phase.

[0150] According to the modulation voltage of the x-phase CHB circuit The switching function of the CHB circuit submodule is calculated to obtain the switching signal of the CHB circuit of the xth phase, which can be expressed by the following relationship:

[0151]

[0152] Among them, S xj (j=1,2,...,N) represents the switching function of the x-phase CHB circuit submodule, u trj The carrier is modulated for the jth CHB unit submodule, and its corresponding phase is π / N.

[0153] The switch signal of the CHB circuit of the fourth bridge arm is obtained according to the modulation wave of the fourth bridge arm, the output voltage of the NPC circuit of the fourth bridge arm and the voltage stabilization active power vector of each submodule of the CHB circuit; the modulation method of the switch signal of the CHB circuit is a PWM modulation method; specifically including:

[0154] Calculate the modulation voltage of the fourth bridge arm CHB circuit It can be expressed by the following relationship:

[0155]

[0156] According to the modulation voltage of the fourth bridge arm CHB circuit The switching function of the CHB circuit submodule is calculated to obtain the switching signal of the fourth bridge arm CHB circuit, which can be expressed by the following relationship:

[0157]

[0158] Among them, S 0j (j=1,2,...,N) represents the switching function of the fourth bridge arm CHB circuit submodule, u trj The carrier is modulated for the jth CHB unit submodule, and its corresponding phase is π / N.

[0159] Adaptive control of the grid-connected equipment can be achieved based on the switching signal of the three-phase bridge arm CHB circuit and the switching signal of the fourth bridge arm CHB circuit.

[0160] Verification part:

[0161] In order to verify the effectiveness of the adaptive control method of the SiC module economic integrated medium voltage grid-connected equipment for fault control of the present invention, the following operating conditions are set: at 1s, a single-phase grounding fault occurs in phase A; during the 1s-1.1s period, the HCM-IFCD still operates in the reactive power compensation mode; at 1.1s, the HCM-IFCD performs fault control. The HCM-IFCD fault control simulation waveform is as follows: Figures 3 to 7 shown.

[0162] like Figure 3 As shown in the figure, during fault control, HCM-IFCD can provide reactive power support for the power grid. Before and after the fault occurs, the power supply side of the power grid always maintains unity power factor operation. Figure 4 As shown in the figure, when HCM-IFCD does not perform arc extinguishing, the residual current I f Reach 65.49A, residual pressure at fault point U f The voltage reaches 6550.99V, which seriously threatens the safe and reliable operation of the distribution network. After the HCM-IFCD performs fault control, the arc extinguishing current I is injected through the fourth bridge arm. z0 , residual fault current I f The current is suppressed to 0.71A, and the residual voltage at the fault point is suppressed to 65V, effectively suppressing the single-phase grounding fault. Figure 5 As shown in the figure, in the fault control mode, the DC side voltage U of the NPC circuit dc1 , U dc2 All fluctuate around the reference value of 6800V; Figure 6 As shown, taking phase C as an example, the DC side voltage U c1 ~U c3 Fluctuates around the reference value of 1200V; Figure 7 As shown, the DC side voltage U of the CHB circuit of the fourth bridge arm01 ~U 03 Fluctuates around the reference value of 1200V.

[0163] Analysis of the simulation results shows that the adaptive control method of the SiC module economic integrated medium-voltage grid-connected equipment for fault control of the present invention realizes the self-voltage stabilization of the four-arm HCM-IFCD, effectively solves the contradiction between the voltage stabilization and arc extinguishing control targets of the grid-connected equipment during the SPG period, and does not require additional power supply equipment for the fourth arm, thereby improving the power density and economy of the equipment.

[0164] In summary, the adaptive control method of the SiC module economic integrated medium-voltage grid-connected equipment for fault control of the present invention obtains the switching signals of the three-phase bridge arm NPC circuit and the CHB circuit by acquiring the data of the equipment and performing mathematical operations, so that the present invention can realize the reactive power compensation function through the switching signals of the three-phase bridge arm NPC circuit and the CHB circuit in both the normal mode and the fault mode of the distribution network. The switching signal of the fourth bridge arm NPC circuit is also obtained by acquiring the data of the equipment and performing mathematical operations, so that the present invention can ensure the stability of the capacitor voltage of the fourth bridge arm CHB circuit submodule through the switching signals of the fourth bridge arm NPC circuit and the CHB circuit, that is, to ensure the self-voltage stabilization of the DC side of the IFCD; and realize high-quality control of single-phase grounding faults in the distribution network fault mode. The method of the present invention effectively solves the problem of the contradiction between the voltage stabilization and arc extinguishing control targets of the grid-connected equipment during the SPG period, without the need to add power supply equipment to the fourth bridge arm, thereby improving the power density and economy of the equipment.

[0165] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. An adaptive control method for fault-controlled SiC module economic integrated medium-voltage grid-connected equipment, characterized in that: include: Obtain the DC side voltage of the NPC circuit to obtain a first voltage; obtain the sum of the capacitor voltages of the CHB circuit submodules to obtain a second voltage; Subtracting the first voltage and the second voltage from the third voltage to obtain a first difference; the third voltage includes the sum of a preset reference value of the DC side voltage of the NPC circuit and a preset reference value of the sum of the capacitor voltages of the CHB circuit submodules; Performing feedback closed-loop control on the first difference to obtain a voltage-stabilized active current reference value; A reactive compensation current reference value is obtained according to a preset reactive compensation instruction; a voltage-stabilizing active current sampling value and a reactive compensation current sampling value of the three-phase bridge arm are obtained, and the reference values ​​of the voltage-stabilizing active current and the reactive compensation current are subtracted from the sampling values ​​to obtain a second difference and a third difference respectively; feedback closed-loop decoupling control is performed on the second difference and the third difference respectively to obtain a three-phase bridge arm modulation wave; Calculate the output current reference value of the fourth bridge arm according to the distribution network information; Obtain a sampling value of the fourth bridge arm output current, subtract the sampling value from the fourth bridge arm output current reference value, and obtain a fourth difference; perform feedback closed-loop control on the fourth difference, and perform additional fourth bridge arm output voltage feedforward control to obtain a fourth bridge arm modulation wave; According to the three-phase bridge arm modulation wave, a three-phase bridge arm NPC circuit switch signal is obtained, and according to the three-phase bridge arm NPC circuit switch signal, a three-phase bridge arm NPC circuit output voltage is obtained; according to the fourth bridge arm modulation wave, a fourth bridge arm NPC circuit switch signal is obtained, and according to the fourth bridge arm NPC circuit switch signal, a fourth bridge arm NPC circuit output voltage is obtained; feedback closed-loop control is performed on the capacitor voltage of each submodule of the CHB circuit respectively, to obtain a voltage stabilization active vector of each submodule of the CHB circuit; A three-phase bridge arm CHB circuit switch signal is obtained according to the three-phase bridge arm modulation wave, the three-phase bridge arm NPC circuit output voltage and the voltage stabilization active power vector of each submodule of the CHB circuit; a fourth bridge arm CHB circuit switch signal is obtained according to the fourth bridge arm modulation wave, the fourth bridge arm NPC circuit output voltage and the voltage stabilization active power vector of each submodule of the CHB circuit; The adaptive control of the grid-connected equipment is completed according to the three-phase bridge arm CHB circuit switching signal and the fourth bridge arm CHB circuit switching signal.

2. The adaptive control method for fault-controlled SiC module economic integrated medium-voltage grid-connected equipment according to claim 1, characterized in that: The obtaining of the reactive compensation current reference value according to the preset reactive compensation instruction comprises: The preset reactive power compensation instruction is issued by the superior dispatcher. To express; then the reactive compensation current reference value It can be expressed by the following relationship: Among them, U d is the grid voltage active vector.

3. The adaptive control method for fault-controlled SiC module economic integrated medium-voltage grid-connected equipment according to claim 2, characterized in that: The second difference and the third difference are respectively subjected to feedback closed-loop decoupling control to obtain a three-phase bridge arm modulation wave including: in, and is the three-phase bridge arm modulation wave; θ is the angle between the d axis and the phase reference axis; ω is the grid angular frequency; L is the filter inductance value; V d Represents the d-axis component of the three-phase bridge arm modulation wave; V q Represents the q-axis component of the three-phase bridge arm modulation wave; U q Represents the grid voltage reactive vector; K pi Indicates the proportional coefficient of the PI controller; K ii Represents the integral coefficient of the PI controller; Indicates the reference value of the voltage-stabilized active current; I zd Indicates the sampling value of the voltage-stabilized active current; I zq represents the reactive compensation current sampling value; s represents the complex frequency domain variable.

4. The adaptive control method for fault-controlled SiC module economic integrated medium-voltage grid-connected equipment according to claim 3, characterized in that: Calculating the output current reference value of the fourth bridge arm according to the distribution network information includes: When a single-phase grounding fault occurs on phase x, the fourth bridge arm outputs a current reference value It can be expressed by the following relationship: in, is the x-phase grid phase voltage; and is the grid phase voltage of the remaining two phases except phase x; r 0y and r 0w is the resistance to ground of the remaining two phases except phase x; C 0y and C 0w is the capacitance to ground of the remaining two phases except phase x; j represents the imaginary unit of the complex number.

5. The adaptive control method for fault-controlled SiC module economic integrated medium-voltage grid-connected equipment according to claim 4, characterized in that: The fourth difference is subjected to feedback closed-loop control, and the fourth bridge arm output voltage is additionally subjected to feedforward control, so as to obtain the fourth bridge arm modulation wave including: in, is the modulation wave of the fourth bridge arm; K p and K r are the proportional coefficient and integral coefficient of the PR controller respectively; ω c is the resonant frequency band width; ω0 is the resonant frequency point; I z0 is the output current of the fourth bridge arm; u0(t) is the output voltage of the fourth bridge arm.

6. The adaptive control method for fault-controlled SiC module economic integrated medium-voltage grid-connected equipment according to claim 5, characterized in that: Obtaining a three-phase bridge arm NPC circuit switch signal according to the three-phase bridge arm modulation wave, and obtaining a three-phase bridge arm NPC circuit output voltage according to the three-phase bridge arm NPC circuit switch signal includes: Obtaining a three-phase bridge arm NPC circuit switch signal according to the three-phase bridge arm modulation wave includes: Among them, U dc Indicates the DC side voltage reference value of the NPC circuit, S x1 and S x2 They represent the switching functions of the upper bridge arm and the lower bridge arm of the x-th phase NPC circuit respectively; Represents the modulation wave of the x-phase bridge arm; Obtaining a three-phase bridge arm NPC circuit output voltage according to the three-phase bridge arm NPC circuit switch signal includes: Among them, u npcx (t) represents the output voltage of the x-phase NPC circuit.

7. The adaptive control method for fault-controlled SiC module economic integrated medium-voltage grid-connected equipment according to claim 6, characterized in that: Obtaining a fourth bridge arm NPC circuit switch signal according to the fourth bridge arm modulation wave, and obtaining a fourth bridge arm NPC circuit output voltage according to the fourth bridge arm NPC circuit switch signal comprises: Obtaining a fourth bridge arm NPC circuit switch signal according to the fourth bridge arm modulation wave includes: Assuming that the switching angle of the fourth bridge arm NPC circuit in the unit period of the fourth bridge arm modulation wave is θ1-θ4, it can be expressed by the following relationship: Then the output voltage of the fourth bridge arm NPC circuit is u npc0 The calculation formula of (t) can be expressed by the following relationship: Among them, S 01 and S 02 They are the switching functions of the upper arm and the lower arm of the fourth bridge arm NPC circuit, respectively, and can be expressed by the following relationship: Where, ω = 2π / T, T is the grid voltage period; Assume that the time domain expression of the modulation wave of the fourth bridge arm is and the fourth bridge fault compensation current They are: Among them, U m ,I m are the modulation voltage amplitude and compensation current amplitude respectively, is the power factor angle; Then the energy fluctuation ΔE of the fourth bridge arm CHB circuit in a unit period can be expressed by the following relationship: in, represents the modulation voltage of the fourth bridge arm CHB circuit; When the energy fluctuation ΔE in the unit cycle is 0, the capacitor voltage of the CHB submodule is stable. When the capacitor voltage of the CHB circuit submodule is stable, the switching angle θ1 can be expressed by the following relationship: Then the switching functions S of the upper and lower arms of the fourth bridge arm NPC circuit are 01 and S 02 Can be corrected to S 001 and S 002 : According to S 001 and S 002 and the fourth bridge arm modulation wave to obtain a fourth bridge arm NPC circuit switch signal; The output voltage u of the fourth bridge arm NPC circuit is obtained according to the switch signal of the fourth bridge arm NPC circuit npc0 (t), including: 。 8. The adaptive control method for fault-controlled SiC module economic integrated medium-voltage grid-connected equipment according to claim 7, characterized in that: Feedback closed-loop control is performed on the capacitor voltage of each submodule of the CHB circuit to obtain the voltage stabilization active vector of each submodule of the CHB circuit, including: Where Δv xj represents the voltage stabilization active power vector of the jth CHB circuit submodule of the xth phase; U cxj represents the capacitor voltage of the jth CHB circuit submodule of the xth phase; Indicates the capacitance voltage reference value of the CHB circuit submodule; Indicates the output current phase of the xth phase.

9. The adaptive control method for fault-controlled SiC module economic integrated medium-voltage grid-connected equipment according to claim 8, characterized in that: Obtaining a three-phase bridge arm CHB circuit switch signal according to the three-phase bridge arm modulation wave, the three-phase bridge arm NPC circuit output voltage and the voltage stabilization active power vector of each submodule of the CHB circuit includes: Calculate the modulation voltage of the x-phase CHB circuit The calculation method for each phase in the three-phase bridge arm is the same, which can be expressed by the following relationship: in, represents the bridge arm modulation wave of the xth phase; u npcx (t) represents the output voltage of the NPC circuit of phase x; According to the modulation voltage of the x-phase CHB circuit The switching function of the CHB circuit submodule is calculated to obtain the switching signal of the CHB circuit of the xth phase, which can be expressed by the following relationship: Among them, S xj (j=1,2,...,N) represents the switching function of the CHB circuit submodule of the xth phase, u trj The carrier is modulated for the jth CHB unit submodule, and its corresponding phase is π / N.

10. The adaptive control method for fault-controlled SiC module economic integrated medium-voltage grid-connected equipment according to claim 9, characterized in that: The fourth bridge arm CHB circuit switch signal is obtained according to the fourth bridge arm modulation wave, the fourth bridge arm NPC circuit output voltage and the voltage stabilization active power vector of each submodule of the CHB circuit, including: Calculate the modulation voltage of the fourth bridge arm CHB circuit It can be expressed by the following relationship: According to the modulation voltage of the fourth bridge arm CHB circuit The switching function of the CHB circuit submodule is calculated to obtain the switching signal of the fourth bridge arm CHB circuit, which can be expressed by the following relationship: Among them, S 0j (j=1,2,...,N) represents the switching function of the fourth bridge arm CHB circuit submodule, u trj The carrier is modulated for the jth CHB unit submodule, and its corresponding phase is π / N.

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