Direct-current-based self-power-taking topology system and control and optimization method thereof

Abstract

The invention discloses a direct-current-based self-power-taking topology system and a control and optimization method thereof. The system comprises a first-stage circuit for realizing voltage reduction and fault ride-through functions; the second-stage circuit realizes voltage control and isolation functions; moreover, the modular multi-level structure of the first-stage circuit operates in a resonant mode, parameter setting needs to be performed on a series resonant inductor and a series resonant capacitor, and the problem of difficulty in total loss optimization caused by a plurality of resonant parameters is solved through a parameter design optimization algorithm based on a particle swarm optimization algorithm. The method improves the adaptability and operation convenience of power equipment in a DC power grid, promotes the development of DC power distribution, guarantees that distributed new energy is more safely and efficiently accessed to the DC power grid, guarantees the high-reliability power supply of important loads, improves the operation reliability and operation efficiency of the equipment, and has significant significance.

Description

Technical Field

[0001] The present invention relates to the technical field of direct current self-powering in a medium voltage direct current distribution network, and in particular to a direct current self-powering topology system and a control and optimization method thereof. Background Art

[0002] With the rapid development of large-scale DC-type distributed new energy such as photovoltaics, and the increasing number of DC loads such as electric vehicle charging piles and data centers, the DC characteristics of power sources and loads in distribution networks are becoming increasingly obvious. Compared with AC distribution networks, DC distribution networks can effectively reduce the conversion links, improve the access capacity and energy utilization efficiency of distributed new energy such as photovoltaics and wind power, and have received extensive attention and research.

[0003] In traditional AC power grids, most of the secondary circuit power supply for high-voltage power equipment comes from 220V low-voltage AC or UPS (Uninterruptible Power System) circuits. This power supply solution has a very natural advantage in AC systems. A common power supply solution is to use the secondary side of the voltage transformer (PT) to obtain energy, and then perform relevant processing to power the control circuit board card of the power secondary equipment.

[0004] However, the solution of using 220V AC to supply power to the secondary circuit in medium and high voltage DC power grids is no longer the most direct and optimal solution, and it increases the dependence of DC distribution network construction on AC power. At the same time, under the traditional capacitor voltage balance control algorithm, all submodules need to be sorted and calculated at any time, which increases the amount of computer calculations; moreover, the switching state of the submodules changes frequently, and the switching frequency of the switching devices is high, which will cause greater switching losses. Overcoming the above problems is currently an urgent problem to be solved. Summary of the invention

[0005] The purpose of the present invention is to overcome the problem that the existing solution of secondary circuit power supply through AC 220V in medium and high voltage DC power grid is no longer the most direct and optimal solution. The present invention provides a DC self-powered topology system and its control and optimization method, the first-level circuit realizes the functions of voltage reduction and fault ride-through; the second-level circuit realizes the functions of voltage control and isolation; and the modular multi-level structure of the first-level circuit operates in the resonance mode, and the series resonant inductor and the series resonant capacitor need to be parameterized. Through the parameter design optimization algorithm based on the particle swarm optimization algorithm, the problem of total loss optimization difficulties caused by multiple resonance parameters is solved, the adaptability and operation convenience of power equipment in the DC power grid are improved, the development of DC power distribution is promoted, and the distributed new energy is guaranteed to be more safely and efficiently connected to the DC power grid, and the high-reliability power supply of important loads is guaranteed. The reliability and efficiency of equipment operation are improved, which has significant significance and good application prospects.

[0006] To achieve the above object, the present invention provides the following technical solutions:

[0007] A DC self-powered topology system, comprising:

[0008] The first-stage circuit adopts a modular multi-level structure, including an upper bridge arm unit and a lower bridge arm unit. The upper bridge arm unit includes a plurality of half-bridge sub-modules connected in series, and the lower bridge arm unit includes a plurality of chopper sub-modules connected in series. The first half-bridge sub-module in the upper bridge arm unit is connected to the bridge arm inductor L S , and operates in a resonant mode; the two ends of the lower bridge arm unit serve as output ends of the first stage circuit and output an intermediate stage voltage;

[0009] The second-stage circuit is a double-overlap flyback circuit, the input end of which is connected to the two ends of the lower bridge arm unit, and the intermediate-stage voltage output by the first-stage circuit is input. The intermediate-stage voltage is stepped down by adjusting the duty cycle and the turns ratio of the isolation transformer, so that the output end of the double-overlap flyback circuit obtains a constant DC voltage to power the secondary equipment.

[0010] Preferably, each half-bridge sub-module includes a first IGBT device, a second IGBT device and a first capacitor.

[0011] The emitter of the second IGBT device is electrically connected to the collector of the first IGBT device, and in steady-state operation, the first IGBT device and the second IGBT device are complementary-conducted;

[0012] One end of the first capacitor is connected to the collector of the first IGBT device, and the other end of the first capacitor is electrically connected to the emitter of the second IGBT device.

[0013] Preferably, each chopper sub-module includes a third IGBT device, a first diode device, and a second capacitor.

[0014] The cathode of the first diode device is electrically connected to the emitter of the third IGBT device, one end of the second capacitor is connected to the collector of the third IGBT device, and the other end of the second capacitor is connected to the anode of the first diode device.

[0015] Preferably, the double overlap flyback circuit is used to realize power conversion and isolation between the input side and the output side, and includes a transformer, a fully controlled device, a second diode device, and a third capacitor.

[0016] The same-name end of the primary winding of the transformer serves as the positive terminal of the input side, the fully-controlled device is a switch device for controlling the current flow on the input side, and is connected in series to the non-same-name end of the primary winding as the negative terminal of the input side. The input end of the fully-controlled device serves as the input end of the double-overlap flyback circuit and is connected to the two ends of the lower bridge arm unit to input the intermediate-level voltage output by the first-level circuit;

[0017] The second diode device is used to control the flow of energy, the positive electrode of the second diode device is connected to the non-same-name end of the secondary winding of the transformer, and the negative electrode of the second diode device serves as the positive terminal of the output side of the transformer;

[0018] The third capacitor is used to smooth the output voltage and store energy. The positive electrode of the third capacitor is connected to the negative electrode of the diode, and the negative electrode of the third capacitor is connected to the same end of the secondary winding of the transformer as the negative terminal of the transformer output side.

[0019] Preferably, the primary winding of the transformer is divided into two completely identical parts N1 and N2, and N1 and N2 are controlled to be on and off by fully controlled devices VT1 and VT2 respectively. N1 and N2 are the turns on the upper and lower sides of the primary coil of the isolation transformer in the second-stage circuit respectively.

[0020] Preferably, the upper bridge arm unit includes four half-bridge sub-modules connected in series, the lower bridge arm unit includes two chopper sub-modules connected in series, the first stage circuit operates in a resonant mode, and the high-voltage side inductor L S The upper bridge arm unit includes four first capacitors C1, C2, C3, C4 corresponding to the half-bridge sub-modules connected in series, and a low-voltage side capacitor C L The series connection constitutes series resonance, and the resonant frequency is given by:

[0021]

[0022] Wherein, C is the capacitance value corresponding to the first capacitors C1, C2, C3, and C4 in the half-bridge submodule, and N is the number of upper bridge arm submodules, which is 4;

[0023] In the resonant mode, operation mode 1: one submodule capacitor of the upper bridge arm unit and the lower bridge arm unit is short-circuited, and the output voltage of the upper bridge arm unit circuit of the previous stage is the voltage across one of the chopper submodule capacitors of the lower bridge arm; operation mode 2: both submodule capacitors of the lower bridge arm unit are short-circuited, and the output voltage of the upper bridge arm unit circuit of the previous stage is zero;

[0024] Assume that the ratio of operation mode 2 to the total time T of operation mode 1 and operation mode 2 is δ. According to the volt-second balance law of inductor current, the increase and decrease of inductor current in a cycle remain the same under stable conditions, thus obtaining:

[0025]

[0026] Wherein, j=5, 6, indicating the capacitor numbers of two chopper submodules connected in series in the lower bridge arm unit. The chopper submodule capacitor of the lower bridge arm can be expressed as:

[0027]

[0028] Assume that the number of chopper submodules of the lower bridge arm unit is M, M=2, and the high-voltage side voltage V H It can be expressed as:

[0029]

[0030] Then the voltage conversion ratio is:

[0031]

[0032] Among them, v Cj is the voltage across the capacitor of the submodule labeled j, V H is the input voltage of the first stage circuit; V M is the output voltage of the first stage circuit and the input voltage of the second stage circuit; V L is the output voltage of the second stage circuit.

[0033] Preferably, the second-stage circuit performs secondary voltage reduction by adjusting the duty cycle and the number of turns of the isolation transformer, and the formula is:

[0034]

[0035] Among them, V L is the output voltage of the second stage circuit, V M is the input voltage of the second-stage circuit, n is the number of turns of the secondary coil of the isolation transformer in the second-stage circuit, and d is the duty cycle of the pulse signal of the secondary circuit.

[0036] Preferably, the first-stage circuit and the second-stage circuit are structurally combined, and the relationship between the output voltage and the input voltage is:

[0037]

[0038] A control method based on a DC self-powered topology system specifically includes the following steps:

[0039] Step (A), control of the output voltage of the first-stage circuit: sampling the output voltage of the lower bridge arm unit, subtracting the output voltage reference value, sending the error to a low-pass filter to obtain a DC component, and then passing through a PI controller and limiting, adding a rated duty cycle, and obtaining a modulation signal of each submodule in the first-stage circuit;

[0040] Step (B), realizing capacitor voltage balance control of each submodule in the upper bridge arm unit and the lower bridge arm unit by feedback of modulation signals of each submodule in the first-stage circuit, so that the total voltage of the upper bridge arm unit and the lower bridge arm unit is complementary to achieve constant DC voltage output;

[0041] Step (C), control of the output voltage of the second stage circuit: sampling the output voltage of the latter stage, subtracting the output voltage reference value, sending the error to a low-pass filter to obtain a DC component, and then adding the rated duty cycle after passing through a PI controller and limiting, thereby obtaining a driving signal for the fully controlled device in the second stage circuit;

[0042] Step (D) is to achieve a constant DC voltage at the output end of the double overlap flyback circuit of the second stage circuit by feeding back the driving signal of the fully controlled device in the second stage circuit.

[0043] An optimization method based on a DC self-powered topology system takes the total loss of a modular multi-level DC self-powered topology as the objective function of the optimization design, and uses a particle swarm optimization algorithm to obtain the resonance parameters when the total loss is the lowest, including the series resonant inductor L S And the series resonant capacitor C, based on the resonant parameters when the total loss is lowest, build a model based on the DC self-powered topology system.

[0044] The beneficial effects of the present invention are as follows: the present invention is based on a DC self-powered topology system and a control and optimization method thereof, wherein the first-stage circuit based on the DC self-powered topology system adopts a modular multi-level structure, the upper bridge arm unit adopts a half-bridge sub-module, and the lower bridge arm unit adopts a chopper sub-module, and power is taken from both ends of the lower bridge arm chopper sub-module to obtain an intermediate-level voltage; the second-stage circuit adopts a double overlapping flyback circuit, and the intermediate-level voltage is further reduced by adjusting the duty cycle and the turns ratio of the isolation transformer, and the double overlapping flyback circuit performs closed-loop control on the output voltage, and finally obtains a constant DC voltage to power secondary equipment, and the first-stage circuit realizes the functions of voltage reduction and fault ride-through; the second-stage circuit realizes the functions of voltage control and isolation; and the modular multi-level structure of the first-stage circuit operates in a resonant mode, and it is necessary to perform parameter setting on the series resonant inductor and the series resonant capacitor. The parameter design optimization algorithm of the present invention based on the particle swarm optimization algorithm solves the problem of difficulty in optimizing the total loss caused by multiple resonant parameters. It is of great significance to improve the adaptability and operational convenience of power equipment in the DC power grid, promote the development of DC power distribution, ensure the safer and more efficient access of distributed new energy to the DC power grid, ensure high-reliability power supply for important loads, and improve the operational reliability and efficiency of equipment. BRIEF DESCRIPTION OF THE DRAWINGS

[0045] Figure 1 It is a schematic diagram of the DC self-powered topology system of the present invention;

[0046] Figure 2Schematic diagram of the circuit structure of the half-bridge submodule of the present invention;

[0047] Figure 3 It is a schematic structural diagram of a double overlapping flyback circuit of the present invention;

[0048] Figure 4 It is a schematic diagram of the driving signal waveform of each submodule 1 to 6 in the first-stage circuit of the present invention;

[0049] Figure 5 It is a schematic diagram of the step-down operation mode of the first stage circuit of the present invention;

[0050] Figure 6 A feedback control diagram of the output voltage of the first stage circuit of the present invention;

[0051] Figure 7 It is a block diagram of the capacitor voltage balance control of the half-bridge submodules 1 and 3 of the upper bridge arm unit of the present invention;

[0052] Figure 8 It is a block diagram of the capacitor voltage balance control of the half-bridge submodules 2 and 4 of the upper bridge arm unit of the present invention;

[0053] Fig. 9 This is a block diagram of the capacitor voltage balance control of the chopper submodules 5 and 6 of the lower bridge arm unit of the present invention;

[0054] Fig.10 A feedback control diagram of the output voltage of the second stage circuit of the present invention;

[0055] Fig.11 A flow chart of the resonance parameter optimization design based on the particle swarm optimization algorithm of the present invention;

[0056] Fig.12 The present invention is a flow chart of the particle swarm optimization design algorithm for optimizing resonance parameters. DETAILED DESCRIPTION

[0057] The present invention will be further described below in conjunction with the accompanying drawings.

[0058] The DC self-powered topology system of the present invention improves the adaptability and operation convenience of power equipment in the DC power grid, promotes the development of DC power distribution, ensures that distributed new energy sources are more safely and efficiently connected to the DC power grid, ensures high-reliability power supply for important loads, and improves the reliability and efficiency of equipment operation. Figure 1 As shown, specifically including

[0059] The first-stage circuit adopts a modular multi-level structure, including an upper bridge arm unit and a lower bridge arm unit. The upper bridge arm unit includes a plurality of half-bridge sub-modules connected in series, and the lower bridge arm unit includes a plurality of chopper sub-modules connected in series. The first half-bridge sub-module in the upper bridge arm unit is connected to the bridge arm inductor LS , and operates in a resonant mode; the two ends of the lower bridge arm unit serve as output ends of the first stage circuit and output an intermediate stage voltage;

[0060] The second-stage circuit is a double-overlap flyback circuit, the input end of which is connected to the two ends of the lower bridge arm unit, and the intermediate-stage voltage output by the first-stage circuit is input. The intermediate-stage voltage is stepped down by adjusting the duty cycle and the turns ratio of the isolation transformer, so that the output end of the double-overlap flyback circuit obtains a constant DC voltage to power the secondary equipment.

[0061] The present invention effectively integrates a double overlapping flyback circuit (second-stage circuit) with a first-stage circuit, and realizes the transmission and matching of electric energy by connecting capacitors in parallel. The double overlapping flyback circuit is usually used to realize isolation and electric energy conversion, and the connection with the first-stage circuit can provide the specific functions required by the medium-voltage DC self-collecting topology in the DC distribution network.

[0062] The first-stage circuit and the second-stage circuit are a composite circuit, which is a composite circuit that combines the modular multi-level structure and the double-overlap flyback circuit structure, and obtains the intermediate voltage from the two ends of the chopper submodule of the lower bridge arm unit as the input of the second-stage circuit. Specifically, the first-stage circuit and the second-stage circuit are designed as an integrated composite circuit, which means that the modular multi-level structure and the double-overlap flyback circuit structure are organically combined to form an overall system.

[0063] Structural compounding: The modular multi-level structure and the dual overlap flyback circuit structure are physically and electrically compounded. This may involve the comprehensive design of connections, layouts, and component arrangements to ensure that the two circuits cooperate with each other and achieve the intended functions.

[0064] Intermediate-stage voltage output: The intermediate-stage voltage is output across the capacitor of the chopper submodule, which means that the output of the primary circuit is introduced into the secondary circuit through the capacitor as the input signal of the secondary circuit.

[0065] Such a design creates a synergistic effect between the primary circuit and the secondary circuit, and realizes the function of the composite circuit through the output of the intermediate voltage. This structural composite method may help optimize system performance, improve the efficiency of energy conversion, and meet the requirements of specific medium-voltage DC self-powered topology.

[0066] like Figure 2 As shown, each half-bridge sub-module includes a first IGBT device, a second IGBT device and a first capacitor.

[0067] The emitter of the second IGBT device is electrically connected to the collector of the first IGBT device, and in steady-state operation, the first IGBT device and the second IGBT device are complementary-conducted;

[0068] One end of the first capacitor is connected to the collector of the first IGBT device, and the other end of the first capacitor is electrically connected to the emitter of the second IGBT device.

[0069] The half-bridge sub-module realizes the conversion and control functions of electric energy by controlling the conduction state of the first IGBT device and the second IGBT device and utilizing the electrical properties of the first capacitor. This design enables the half-bridge sub-module to effectively achieve complementary conduction during steady-state operation and meet specific circuit requirements with the assistance of capacitors.

[0070] Each chopper sub-module includes a third IGBT device, a first diode device, and a second capacitor.

[0071] The cathode of the first diode device is electrically connected to the emitter of the third IGBT device, one end of the second capacitor is connected to the collector of the third IGBT device, and the other end of the second capacitor is connected to the anode of the first diode device.

[0072] like Figure 3 As shown, the double overlap flyback circuit is used to realize the power conversion and isolation between the input side and the output side, and includes a transformer, a fully controlled device, a second diode device, and a third capacitor.

[0073] The same-name end of the primary winding of the transformer serves as the positive terminal of the input side, the fully-controlled device is a switch device for controlling the current flow on the input side, and is connected in series to the non-same-name end of the primary winding as the negative terminal of the input side. The input end of the fully-controlled device serves as the input end of the double-overlap flyback circuit and is connected to the two ends of the lower bridge arm unit to input the intermediate-level voltage output by the first-level circuit;

[0074] The second diode device is used to control the flow of energy, the positive electrode of the second diode device is connected to the non-same-name end of the secondary winding of the transformer, and the negative electrode of the second diode device serves as the positive terminal of the output side of the transformer;

[0075] The third capacitor is used to smooth the output voltage and store energy. The positive electrode of the third capacitor is connected to the negative electrode of the diode, and the negative electrode of the third capacitor is connected to the same end of the secondary winding of the transformer as the negative terminal of the transformer output side.

[0076] The primary winding of the transformer is divided into two identical parts N1 and N2, which are controlled on and off by fully controlled devices VT1 and VT2, respectively. N1 and N2 are the turns on the upper and lower sides of the primary coil of the isolation transformer in the second-stage circuit, respectively.

[0077] The upper bridge arm unit includes four half-bridge sub-modules connected in series, and the lower bridge arm unit includes two chopper sub-modules connected in series. The first-stage circuit operates in a resonant mode, and the high-voltage side inductor L S The upper bridge arm unit includes four first capacitors C1, C2, C3, C4 corresponding to the half-bridge sub-modules connected in series, and a low-voltage side capacitor C L The series connection constitutes series resonance, and the resonant frequency is given by:

[0078]

[0079] Wherein, C is the capacitance value corresponding to the first capacitors C1, C2, C3, and C4 in the half-bridge submodule, and N is the number of upper bridge arm submodules, which is 4;

[0080] like Figure 4 As shown, the first-stage circuit adopts a shift control strategy. In order to ensure that the upper bridge arm can have four or three submodules inject voltage at any time, the duty cycle of each submodule must be higher than 75%. The pulse signal of each submodule of the upper bridge arm lags behind by 2π / 4 in turn, the switching frequency of the lower bridge arm submodule is twice that of the upper bridge arm submodule, and submodule 5 is complementary to submodules 1 and 3; submodule 6 is complementary to submodules 2 and 4, so it can be ensured that there are always 4 submodule capacitors connected to the circuit in the upper and lower bridge arms, so that the total voltage of the upper and lower bridge arms is complementary, ensuring a constant DC voltage.

[0081] like Figure 5 As shown, in the resonant mode, operation mode 1: one submodule capacitor of the upper bridge arm unit and the lower bridge arm unit is short-circuited, and the output voltage of the upper bridge arm unit circuit of the previous stage is the voltage across one of the chopper submodule capacitors of the lower bridge arm; operation mode 2: both submodule capacitors of the lower bridge arm unit are short-circuited, and the output voltage of the upper bridge arm unit circuit of the previous stage is zero;

[0082] Assume that the ratio of operation mode 2 to the total time T of operation mode 1 and operation mode 2 is δ. According to the volt-second balance law of inductor current, the increase and decrease of inductor current in a cycle remain the same under stable conditions, thus obtaining:

[0083]

[0084] Wherein, j=5, 6, indicating the capacitor numbers of two chopper submodules connected in series in the lower bridge arm unit. The chopper submodule capacitor of the lower bridge arm can be expressed as:

[0085]

[0086] Assume that the number of chopper submodules of the lower bridge arm unit is M, M=2, and the high-voltage side voltage V H It can be expressed as:

[0087]

[0088] Then the voltage conversion ratio is:

[0089]

[0090] Among them, v Cj is the voltage across the capacitor of the submodule labeled j, V H is the input voltage of the first stage circuit; V M is the output voltage of the first stage circuit and the input voltage of the second stage circuit; V L is the output voltage of the second stage circuit.

[0091] Preferably, the second-stage circuit performs secondary voltage reduction by adjusting the duty cycle and the number of turns of the isolation transformer, and the formula is:

[0092]

[0093] Among them, V L is the output voltage of the second stage circuit, V M is the input voltage of the second-stage circuit, n is the number of turns of the secondary coil of the isolation transformer in the second-stage circuit, and d is the duty cycle of the pulse signal of the secondary circuit.

[0094] Preferably, the first-stage circuit and the second-stage circuit are structurally combined, and the relationship between the output voltage and the input voltage is:

[0095]

[0096] The control method based on the DC self-collecting topology system of the present invention specifically includes the following steps:

[0097] Step (A), control of the output voltage of the first-stage circuit: sampling the output voltage of the lower bridge arm unit, subtracting the output voltage reference value, sending the error to a low-pass filter to obtain a DC component, and then passing through a PI controller and limiting, adding a rated duty cycle, and obtaining a modulation signal of each submodule in the first-stage circuit;

[0098] Step (B), realizing capacitor voltage balance control of each submodule in the upper bridge arm unit and the lower bridge arm unit by feedback of modulation signals of each submodule in the first-stage circuit, so that the total voltage of the upper bridge arm unit and the lower bridge arm unit is complementary to achieve constant DC voltage output;

[0099] Step (C), control of the output voltage of the second stage circuit: sampling the output voltage of the latter stage, subtracting the output voltage reference value, sending the error to a low-pass filter to obtain a DC component, and then adding the rated duty cycle after passing through a PI controller and limiting, thereby obtaining a driving signal for the fully controlled device in the second stage circuit;

[0100] Step (D) is to achieve a constant DC voltage at the output end of the double overlap flyback circuit of the second stage circuit by feeding back the driving signal of the fully controlled device in the second stage circuit.

[0101] The control method based on the DC self-powered topology system of the present invention is specifically implemented as follows according to the above steps:

[0102] like Figure 6 As shown, the output voltage of the first stage circuit is controlled by sampling the output voltage V M , minus the output voltage reference value V M * , the error is sent to the low-pass filter to obtain the DC component, and then after the PI controller and limiting, the rated duty cycle D is added to obtain the modulation signal D of each submodule * ;

[0103] like Figure 7 , 8 As shown in the figure, the capacitor voltage balance control of the upper bridge arm unit: first, the voltage across the capacitor of each sub-module of the upper bridge arm is measured by the voltage transformer, v c1 、v c3 With v c2 、v c4 The voltage deviation is recorded as Δu1=v c1 -v c3 and Δu2=v c2 -v c4 ; Obtain the upper arm current i through the sign function N The positive and negative signs of the output value are multiplied by the error Δu1, and then the duty cycle fine-tuning signal ΔD1 is output through PI adjustment, and the duty cycle signal D of the upper bridge arm module 1 and module 3 can be obtained. * +ΔD1,D * -ΔD1; Similarly, the voltages at both ends of capacitors 2 and 4 are processed accordingly, and the output of the corresponding voltage deviation signal is superimposed on the modulation signal of the upper bridge submodule after proportional control;

[0104] like Fig. 9 As shown, the capacitor voltage balance control of the lower bridge arm unit: first sample the capacitor voltage value v of the lower bridge arm, calculate the reference voltage v of the lower bridge arm submodule ref , v ref Represents the average voltage of the lower bridge arm submodule; compare the voltage signal v of each module of the lower bridge alarm with the reference voltage v ref Subtract the voltage deviation signal, send it to the low-pass filter, and then after PI control and limit adjustment, add it to the modulation signal D * The voltage modulation signal D of the lower bridge arm submodule can be obtained by superposition. j (j=5, 6);

[0105] like Fig.10 As shown, the output voltage of the second stage circuit is controlled, and the output voltage V L , minus the output voltage reference The error is sent to a low-pass filter to obtain the DC component, which is then passed through a PI controller and limited, and then added to the rated duty cycle d * , thereby obtaining the driving signal d of the upper and lower switch tubes. The loss of the first-stage circuit of the modular multi-level DC self-collecting topology includes the switch tube driving loss, the switch tube conduction loss, the series resonant capacitor loss and the rectifier diode loss. In order to reduce the rectifier diode loss, silicon carbide diodes are used, so the reverse recovery loss can be ignored. The loss of the high-voltage rectifier diode is the conduction loss, that is,

[0106]

[0107] Among them, P D is the high voltage rectifier diode loss, V o is the output voltage, V D is the tube voltage drop of the high-voltage rectifier diode, R D is the converter load. The driving loss of the main switch tube,

[0108] P dr =4Q g V dr f s

[0109] Among them, Q g is the gate drive charge, V dr is the driving voltage of the switch tube, f s is the resonant frequency.

[0110] Combined with the calculation formula of the effective value of the resonant current, the conduction loss of the main switch tube is

[0111]

[0112] Among them, V o is the output voltage, T s is the switching period, T rs For L s and the resonant period of C, R o For load.

[0113] The total loss of the first-stage circuit of the modular multi-level DC self-collecting topology is

[0114]

[0115] The optimization method based on the DC self-collecting topology system of the present invention takes the total loss of the modular multi-level DC self-collecting topology as the objective function of the optimization design, and obtains the resonance parameters when the total loss is the lowest through the particle swarm optimization algorithm, including the series resonant inductor L S And the series resonant capacitor C, based on the resonance parameters when the total loss is the lowest, build a model based on the DC self-powered topology system. Fig.11 As shown in the figure, the specific optimization process is as follows:

[0116] Step 1: Determine the main switch tube and rectifier diode models according to the input voltage, output voltage, and operating frequency of the first-stage circuit of the modular multi-level DC self-powered topology. Substitute the parameters of the main switch tube, rectifier diode, and magnetic core into the total loss formula of the converter;

[0117] Step 2: Use the particle swarm optimization design algorithm to optimize the total loss of the converter, and calculate the optimized resonant parameters and the optimized total loss;

[0118] Step 3: Based on the optimized parasitic parameters in step 2, build the first-stage circuit of the modular multi-level DC self-powered topology;

[0119] Step 4: Test the first-level circuit of the modular multi-level DC self-powered topology;

[0120] like Fig.12 As shown in the figure, the particle swarm optimization design algorithm flow chart for resonant parameter optimization design includes the following steps:

[0121] Step 2.1: Initialize the particle swarm optimization algorithm. The parameters of the particle swarm optimization algorithm, including Velocity.min, Velocity.max, Position.min and Position.max, are initialized. The number of particles Npa is 20, and the maximum number of iterations Max.Iteration is 100. Each particle is assigned an arbitrary L s and C value. The resonance parameters are input into the particle swarm optimization design algorithm, and the total loss of the converter is used as the objective function of the particle swarm optimization algorithm.

[0122] Step 2.2: Total loss calculation. In this step, the objective function value of each particle and the total loss of the converter are calculated. The objective function value will be used to evaluate the fitness of each particle.

[0123] Step 2.3: Update global optimal value and individual optimal value. Based on the total loss calculated in step 2, the global optimal value of all particles, the individual optimal value of each particle, Velocity and Position will be updated.

[0124] Step 4: Repeat steps 2 and 3 until the loop termination condition is met. If the average objective function value is stable or the maximum number of iterations is reached, the loop process will be terminated. Otherwise, the process of steps 2 and 3 will be repeated.

[0125] Step 5: Output the optimized resonance parameter value and the optimized total loss. When the loop termination conditions of step 2 and step 3 are met, the particle swarm optimization algorithm will output the optimized resonance parameter value and the total loss.

[0126] At this point, the particle swarm optimization algorithm ends. When the particle swarm optimization algorithm ends, the optimized resonance parameters will be obtained, including L s and C. Next, the first-level circuit will be built using the optimized resonance parameters and experimental tests will be performed.

[0127] In summary, the present invention is based on a DC self-powered topology system and its control and optimization method, wherein the first-stage circuit based on the DC self-powered topology system adopts a modular multi-level structure, the upper bridge arm unit adopts a half-bridge sub-module, and the lower bridge arm unit adopts a chopper sub-module, and the intermediate-level voltage is obtained by taking power from both ends of the lower bridge arm chopper sub-module; the second-stage circuit adopts a double overlapping flyback circuit, and the intermediate-level voltage is further reduced by adjusting the duty cycle and the turns ratio of the isolation transformer. The double overlapping flyback circuit performs closed-loop control on the output voltage, and finally obtains a constant DC voltage to power the secondary equipment. The first-stage circuit realizes the step-down and fault ride-through functions; the second-stage circuit realizes the voltage control and isolation functions; and the modular multi-level structure of the first-stage circuit operates in a resonant mode, and it is necessary to set the parameters of the series resonant inductor and the series resonant capacitor. The parameter design optimization algorithm of the present invention based on the particle swarm optimization algorithm solves the problem of difficulty in optimizing the total loss caused by multiple resonant parameters. It is of great significance to improve the adaptability and operational convenience of power equipment in the DC power grid, promote the development of DC power distribution, ensure the safer and more efficient access of distributed new energy to the DC power grid, ensure high-reliability power supply for important loads, and improve the operational reliability and efficiency of equipment.

[0128] The above shows and describes the basic principles, main features and advantages of the present invention. It should be understood by those skilled in the art that the present invention is not limited to the above embodiments. The above embodiments and descriptions are only for explaining the principles of the present invention. Without departing from the spirit and scope of the present invention, the present invention may have various changes and improvements, which fall within the scope of the present invention to be protected. The scope of protection of the present invention is defined by the attached claims and their equivalents.

Claims

1. Based on the DC self-powered topology system, it is characterized by: include The first-stage circuit adopts a modular multi-level structure, including an upper bridge arm unit and a lower bridge arm unit. The upper bridge arm unit includes a plurality of half-bridge sub-modules connected in series, and the lower bridge arm unit includes a plurality of chopper sub-modules connected in series. The first half-bridge sub-module in the upper bridge arm unit is connected to the bridge arm inductor L S , and operates in a resonant mode; the two ends of the lower bridge arm unit serve as output ends of the first stage circuit and output an intermediate stage voltage; The second-stage circuit is a double-overlap flyback circuit, the input end of which is connected to the two ends of the lower bridge arm unit, and the intermediate-stage voltage output by the first-stage circuit is input. The intermediate-stage voltage is stepped down by adjusting the duty cycle and the turns ratio of the isolation transformer, so that the output end of the double-overlap flyback circuit obtains a constant DC voltage to power the secondary equipment.

2. The DC self-powered topology system according to claim 1 is characterized in that: Each half-bridge sub-module includes a first IGBT device, a second IGBT device and a first capacitor. The emitter of the second IGBT device is electrically connected to the collector of the first IGBT device, and in steady-state operation, the first IGBT device and the second IGBT device are complementary-conducted; One end of the first capacitor is connected to the collector of the first IGBT device, and the other end of the first capacitor is electrically connected to the emitter of the second IGBT device.

3. The DC self-powered topology system according to claim 1 is characterized in that: Each chopper sub-module includes a third IGBT device, a first diode device, and a second capacitor. The cathode of the first diode device is electrically connected to the emitter of the third IGBT device, one end of the second capacitor is connected to the collector of the third IGBT device, and the other end of the second capacitor is connected to the anode of the first diode device.

4. The DC self-powered topology system according to claim 1 is characterized in that: The double overlap flyback circuit is used to realize the power conversion and isolation between the input side and the output side, and includes a transformer, a fully controlled device, a second diode device, and a third capacitor. The same-name end of the primary winding of the transformer serves as the positive terminal of the input side, the fully-controlled device is a switch device for controlling the current flow on the input side, and is connected in series to the non-same-name end of the primary winding as the negative terminal of the input side. The input end of the fully-controlled device serves as the input end of the double-overlap flyback circuit and is connected to the two ends of the lower bridge arm unit to input the intermediate-level voltage output by the first-level circuit; The second diode device is used to control the flow of energy, the positive electrode of the second diode device is connected to the non-same-name end of the secondary winding of the transformer, and the negative electrode of the second diode device serves as the positive terminal of the output side of the transformer; The third capacitor is used to smooth the output voltage and store energy. The positive electrode of the third capacitor is connected to the negative electrode of the diode, and the negative electrode of the third capacitor is connected to the same end of the secondary winding of the transformer as the negative terminal of the transformer output side.

5. The DC self-powered topology system according to claim 4 is characterized in that: The primary winding of the transformer is divided into two identical parts N1 and N2, which are controlled on and off by fully controlled devices VT1 and VT2, respectively. N1 and N2 are the turns on the upper and lower sides of the primary coil of the isolation transformer in the second-stage circuit, respectively.

6. The DC self-powered topology system according to claim 1 is characterized in that: The upper bridge arm unit includes four half-bridge sub-modules connected in series, and the lower bridge arm unit includes two chopper sub-modules connected in series. The first-stage circuit operates in a resonant mode, and the high-voltage side inductor L S The upper bridge arm unit includes four first capacitors C1, C2, C3, C4 corresponding to the half-bridge sub-modules connected in series, and a low-voltage side capacitor C L The series connection constitutes series resonance, and the resonant frequency is given by: Wherein, C is the capacitance value corresponding to the first capacitors C1, C2, C3, and C4 in the half-bridge submodule, and N is the number of upper bridge arm submodules, which is 4; In the resonant mode, operation mode 1: one submodule capacitor of the upper bridge arm unit and the lower bridge arm unit is short-circuited, and the output voltage of the upper bridge arm unit circuit of the previous stage is the voltage across one of the chopper submodule capacitors of the lower bridge arm; operation mode 2: both submodule capacitors of the lower bridge arm unit are short-circuited, and the output voltage of the upper bridge arm unit circuit of the previous stage is zero; Assume that the ratio of operation mode 2 to the total time T of operation mode 1 and operation mode 2 is δ. According to the volt-second balance law of inductor current, the increase and decrease of inductor current in a cycle remain the same under stable conditions, thus obtaining: Wherein, j=5, 6, which represent the capacitor numbers of two chopper submodules connected in series in the lower bridge arm unit. The chopper submodule capacitor of the lower bridge arm can be expressed as: Assume that the number of chopper submodules of the lower bridge arm unit is M, M=2, and the high-voltage side voltage V H It can be expressed as: Then the voltage conversion ratio is: Among them, v Cj is the voltage across the capacitor of the submodule labeled j, V H is the input voltage of the first stage circuit; V M is the output voltage of the first stage circuit and the input voltage of the second stage circuit; V L is the output voltage of the second stage circuit.

7. The DC self-powered topology system according to claim 4 is characterized in that: The second stage circuit performs secondary voltage reduction by adjusting the duty cycle and the number of turns of the isolation transformer. The formula is: Among them, V L is the output voltage of the second stage circuit, V M is the input voltage of the second-stage circuit, n is the number of turns of the secondary coil of the isolation transformer in the second-stage circuit, and d is the duty cycle of the pulse signal of the secondary circuit.

8. The DC self-powered topology system according to claim 5 is characterized in that: The first-stage circuit and the second-stage circuit are structurally combined, and the relationship between the output voltage and the input voltage is:

9. The control method based on the DC self-powered topology system according to any one of claims 1 to 8, characterized in that: The specific steps include: Step (A), control of the output voltage of the first-stage circuit: sampling the output voltage of the lower bridge arm unit, subtracting the output voltage reference value, sending the error to a low-pass filter to obtain a DC component, and then passing through a PI controller and limiting, adding a rated duty cycle, and obtaining a modulation signal of each submodule in the first-stage circuit; Step (B), realizing capacitor voltage balance control of each submodule in the upper bridge arm unit and the lower bridge arm unit by feedback of modulation signals of each submodule in the first-stage circuit, so that the total voltage of the upper bridge arm unit and the lower bridge arm unit is complementary to achieve constant DC voltage output; Step (C), control of the output voltage of the second stage circuit: sampling the output voltage of the latter stage, subtracting the output voltage reference value, sending the error to a low-pass filter to obtain a DC component, and then adding the rated duty cycle after passing through a PI controller and limiting, thereby obtaining a driving signal for the fully controlled device in the second stage circuit; Step (D) is to achieve a constant DC voltage at the output end of the double overlap flyback circuit of the second stage circuit by feeding back the driving signal of the fully controlled device in the second stage circuit.

10. The optimization method based on the DC self-powered topology system according to any one of claims 1 to 8, characterized in that: The total loss of the modular multi-level DC self-collecting topology is used as the objective function of the optimization design. The particle swarm optimization algorithm is used to obtain the resonance parameters when the total loss is the lowest, including the series resonant inductor L. S And the series resonant capacitor C, based on the resonant parameters when the total loss is lowest, build a model based on the DC self-powered topology system.

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