Self-energy-taking circuit for power supply of secondary equipment of direct-current power distribution network and control method of self-energy-taking circuit

Abstract

The invention discloses a self-energy-taking circuit for DC power distribution network secondary equipment power supply and a control method thereof.The self-energy-taking circuit is formed by combining a front-stage circuit and a rear-stage circuit, high-proportion voltage reduction is achieved, and the self-energy-taking circuit has the DC fault self-clearing capacity; a front-stage circuit adopts a half-bridge, full-bridge, clamping and fault current limiting sub-module mixed MMC structure, and a rear-stage circuit adopts an isolated DC / DC circuit. And secondly, a voltage disturbance state observer is constructed for the pre-stage circuit, the output voltage of the pre-stage circuit and the duty ratio signal of the power main circuit are used as the input of the observer, and an error feedback controller is used for adjustment, so that the output voltage robust control under the input disturbance condition is realized. And finally, providing a current model prediction control strategy for a post-stage circuit, taking the exciting current of the transformer and the voltage of an output capacitor as state variables of a model prediction controller to be input, and taking the minimum error of the voltage and the current as a cost function to realize the quick response of the voltage and the current.

Description

Technical Field

[0001] The invention relates to the technical field of direct current distribution networks, and is applicable to a self-energy extraction circuit for powering secondary equipment in a direct current distribution network and a control method thereof. Background Art

[0002] With the rapid development of DC distributed power sources such as large-scale photovoltaic and energy storage power stations, and the increasing number of DC loads such as electric vehicle charging piles, DC distribution networks have received extensive attention and research.

[0003] In traditional AC distribution networks, voltage transformers are widely used to power secondary equipment such as relay protection devices and monitoring devices; however, in DC distribution networks, using inverters to power secondary equipment is no longer the most direct and optimal solution. A secondary equipment power supply self-powering circuit that is suitable for DC distribution networks and can achieve self-clearing of DC faults needs to be studied urgently.

[0004] Patent CN110492740A discloses a step-down self-energy extraction circuit and method for a medium- and high-voltage DC distribution network. The step-down self-energy extraction circuit includes N half-bridge modules and one full-bridge module, where N is an integer greater than or equal to 3. A shift control method is adopted for the N half-bridge modules, and the N half-bridge modules adopt a pulse width modulation waveform with a low switching frequency. The phase of the triangular carrier of each half-bridge module differs by 2π / (NR-1) in sequence. A bipolar modulation strategy is adopted for the full-bridge module, and a square wave waveform is output at both ends of the full-bridge module. This patent does not consider how to deal with a fault, and when the DC bus voltage is disturbed, the shift control is prone to deviation, affecting the stability of the self-energy extraction circuit. Summary of the invention

[0005] Technical purpose: In view of the defects in the prior art, the present invention discloses a self-energy circuit and a control method for powering secondary equipment in a DC distribution network, which is independent of external AC power supply and improves the adaptability of the self-powered circuit under different working conditions and fault conditions.

[0006] Technical solution: In order to achieve the above technical objectives, the present invention adopts the following technical solution.

[0007] A self-powered circuit for powering secondary equipment in a DC distribution network, comprising a front-stage circuit and a rear-stage circuit; The front-stage circuit includes an upper bridge arm inductor, an upper bridge arm and a lower bridge arm connected in series, wherein the upper bridge arm includes a plurality of half-bridge submodules, a plurality of full-bridge submodules and a fault current limiting submodule connected in series; the lower bridge arm includes a filter inductor and a filter capacitor connected in series, and includes a plurality of submodules connected in parallel with the filter inductor and the filter capacitor, wherein the plurality of submodules are a plurality of clamping submodules connected in series and a fault current limiting submodule; the half-bridge submodule, the full-bridge submodule and the clamping submodule all include submodule capacitors; The post-stage circuit is connected in parallel with the filter capacitor. The post-stage circuit is an isolated DC / DC circuit. The isolated DC / DC circuit includes a plurality of cascaded sub-circuits. The post-stage circuit outputs a stable DC voltage for powering secondary equipment in a DC distribution network.

[0008] A control method for a self-powered circuit for powering secondary equipment in a DC distribution network, used to control the self-powered circuit for powering secondary equipment in a DC distribution network described above, the control method comprising: The front-stage circuit adopts a sub-module voltage equalization strategy to obtain the average value of the capacitor voltage of the upper and lower bridge arm sub-modules respectively. According to the direction of the bridge arm current, each sub-module is corrected on the basis of the discharge ratio to obtain its own duty cycle signal; a front-stage circuit controller is constructed for the front-stage circuit, and the front-stage circuit controller includes a voltage disturbance state observer and an error feedback controller. By constructing the voltage disturbance state observer, the output voltage of the front-stage circuit and the duty cycle control signal of each sub-module are used as the input of the voltage disturbance state observer, and the error feedback controller is used for adjustment, thereby realizing robust control of the output voltage under input disturbance conditions; A current model predictive control strategy is proposed for the subsequent circuit. The transformer excitation current and output capacitor voltage in the subsequent circuit are used as state variable inputs of the current model predictive controller. The minimum voltage and current error is taken as the cost function to achieve rapid response of voltage and current.

[0009] Beneficial effect: The self-powered circuit of the present invention adopts a hybrid redundant modular multi-level circuit in the front-stage circuit, which can cope with submodule failures and input / output side inter-pole short-circuit failures; the rear-stage circuit adopts an isolated DC / DC circuit. For the front-stage circuit, a voltage robust control strategy for smoothing the DC bus voltage disturbance on the input side is adopted. For the rear-stage circuit, a current model predictive control strategy for improving the dynamic response speed of the system is proposed. The present invention realizes that the secondary equipment of the DC distribution network is independent of the external AC power supply, and improves the adaptability of the self-powered circuit under different working conditions and fault conditions, and improves the output voltage stability and dynamic response speed of the self-powered circuit. BRIEF DESCRIPTION OF THE DRAWINGS

[0010] Figure 1 A schematic diagram of a self-powered circuit structure for powering secondary equipment in a DC power distribution network according to an embodiment of the present invention; Figure 2 for Figure 1 Schematic diagram of current flow in each switching state of the middle clamp submodule; Figure 3 for Figure 1 Schematic diagram of current flow in each switching state of the fault current limiting submodule; Figure 4It is the control block diagram of the front-stage circuit based on voltage robust control; Figure 5 This is a block diagram of the capacitor voltage balancing control of the bridge arm submodule in the front-stage circuit; Figure 6 This is the capacitor voltage balancing control block diagram of the lower bridge arm submodule of the front-stage circuit; Figure 7 This is the control block diagram of the subsequent circuit based on current-type model predictive control. DETAILED DESCRIPTION

[0011] The following further describes and elaborates a self-powered circuit for powering secondary equipment in a DC distribution network and a control method thereof in conjunction with the accompanying drawings and embodiments. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of them.

[0012] Unless otherwise defined, all technical and scientific terms used in the present invention have the same meaning as those commonly understood by those skilled in the art of the present invention. The terms used in the specification of the present invention are only for the purpose of describing specific embodiments and are not intended to limit the present invention. The term "and / or" used herein includes any and all combinations of one or more related listed items.

[0013] Example: As attached Figure 1 As shown, a self-powered circuit for powering secondary equipment in a DC power distribution network according to this embodiment includes a front-stage circuit and a rear-stage circuit;

[0014] The front-stage circuit includes an upper bridge arm inductor, an upper bridge arm and a lower bridge arm connected in series, and the upper bridge arm includes a plurality of half-bridge sub-modules, a plurality of full-bridge sub-modules and a fault current limiting sub-module connected in series; The lower bridge arm includes a filter inductor and a filter capacitor connected in series, and includes a plurality of submodules connected in parallel with the filter inductor and the filter capacitor, wherein the plurality of submodules are a plurality of clamping submodules connected in series and a fault current limiting submodule; the half-bridge submodule, the full-bridge submodule, and the clamping submodule all include submodule capacitors; The post-stage circuit is connected in parallel with the filter capacitor. The post-stage circuit is an isolated DC / DC circuit. The isolated DC / DC circuit includes a plurality of cascaded sub-circuits. The post-stage circuit outputs a stable DC voltage for powering secondary equipment in a DC distribution network. The secondary equipment in the DC distribution network includes a relay protection device, a measuring device, etc.

[0015] The isolated DC / DC circuit includes several cascaded sub-circuits, each of which includes: an input side voltage stabilizing capacitor C M , output capacitor C o, isolation transformer, switch tube and freewheeling diode. The same-name terminal of the primary side of the isolation transformer and the input side voltage stabilizing capacitor C M One end of the input side voltage stabilizing capacitor C M The other end is connected to the emitter of the switch tube, and the collector of the switch tube is connected to the opposite end of the primary side of the isolation transformer; the opposite end of the secondary side of the isolation transformer is connected to the positive electrode of the freewheeling diode, and the negative electrode of the freewheeling diode is connected to the output capacitor C o Connect to the same terminal of the secondary side of the isolation transformer; the output capacitor C of all sub-circuits o The voltage is the same, that is, the output DC voltage V L .

[0016] The front-stage circuit in this embodiment is a hybrid modular multi-level structure, and the upper bridge arm inductor and the sub-module capacitor operate in a series resonance mode.

[0017] Attached Figure 1 In, V H is the DC voltage of the DC distribution network. The half-bridge submodule is composed of 2 IGBT devices, 2 anti-parallel diodes and 1 submodule capacitor. Among them, 2 IGBT devices and 2 anti-parallel diodes constitute a half-bridge arm. The emitter of one IGBT is connected to the collector of another IGBT device and serves as the midpoint of the arm, which is also the positive electrode of the half-bridge submodule. The collector of one IGBT is connected to the emitter of another IGBT device through the submodule capacitor. Among them, one end of the submodule capacitor connected to the collector of one IGBT is the positive terminal of the submodule capacitor, and the emitter of the other IGBT device is also the negative electrode of the half-bridge submodule. The full-bridge submodule is composed of 4 IGBT devices, 4 anti-parallel diodes and 1 submodule capacitor. 4 IGBT devices and 4 anti-parallel diodes constitute a full-bridge arm. The two midpoints of the full-bridge arm serve as the positive and negative electrodes of the full-bridge submodule respectively. The filter capacitor C f The voltage across the two ends is V M Output voltage for the previous circuit; A clamping submodule, consisting of two IGBT devices, two anti-parallel diodes, two independent diodes and a submodule capacitor, wherein the emitter of the first IGBT device is connected to the positive electrode of the first anti-parallel diode, the collector of the first IGBT device is connected to the negative electrode of the first anti-parallel diode, the emitter of the first IGBT device is connected to the negative electrode of the first independent diode through the submodule capacitor, and the collector of the first IGBT device is connected to the positive electrode of the first independent diode; the emitter of the second IGBT device is connected to the positive electrode of the second anti-parallel diode, the collector of the second IGBT device is connected to the negative electrode of the second anti-parallel diode, the collector of the second IGBT device is connected to the positive electrode of the second independent diode through the submodule capacitor, and the emitter of the second IGBT device is connected to the negative electrode of the second independent diode, wherein the collector of the first IGBT device serves as the negative electrode of the clamping submodule, and the emitter of the second IGBT device serves as the positive electrode of the clamping submodule; By connecting the clamping submodule in series to the lower bridge arm, the current in the lower bridge arm is ensured to flow in one direction, and a reverse electromotive force is generated when a fault occurs. The current path diagram of the clamping submodule in each switching state is shown in Figure 2. Figure 2 When both switch tubes VT1 and VT2 are turned off, Figure 2 As shown in (a), the current charges the submodule at this time, which is the forward input state; and when VT1 and VT2 are both turned on, as shown in Figure 2 As shown in (b), at this time, the submodule is reversely connected to the circuit, the submodule is in reverse input state, and a back electromotive force is generated; when VT1 is turned on and VT2 is turned off or VT1 is turned off and VT2 is turned on, as shown in Figure 2 Middle (c), Figure 2 As shown in (d), the submodule is in the cut-off state and the external output voltage is 0.

[0018] The fault current limiting submodule is composed of two IGBT devices and one current limiting resistor. The emitter of each IGBT device is connected to its collector through the current limiting resistor; the collectors of the two IGBT devices serve as the positive electrodes of the fault current limiting submodule, and the emitters of the two IGBT devices serve as the negative electrodes of the fault current limiting submodule; Figure 3 The figure shows the current path of the fault current limiting submodule. During normal operation, the switch tubes VT1 and VT2 are turned on alternately. At this time, the current limiting resistor R res Bypassed, such as Figure 3 Middle (a), Figure 3 As shown in (b); when a fault occurs, both switch tubes VT1 and VT2 are turned off. Figure 3 As shown in (c), the current limiting resistor R res It is connected in series to the circuit to accelerate the clearing of fault current.

[0019] In the present invention, when the self-energy extraction circuit is in normal working state, in the upper and lower bridge arms of the front-stage circuit, the submodules in redundant state and the fault current limiting submodules are all in bypass state, wherein the redundant submodule of the upper bridge arm is a half-bridge submodule, and the redundant submodule of the lower bridge arm is a clamping submodule; when a submodule fails, the failed submodule is locked and the redundant submodule is put into operation; when an input side / output side inter-pole short circuit fault occurs, the full-bridge submodule and the clamping submodule output back electromotive force, and at the same time the fault current limiting submodule puts the current limiting resistor into operation to accelerate the clearing of the fault current.

[0020] The front-stage circuit operates in the resonant mode, and the bridge arm inductance and the submodule capacitance form a series resonance. At this time, the front-stage circuit is equivalent to a switching circuit, and the resonant frequency The calculation formula is: , Where, L s is the upper arm inductance value, C0 is the submodule capacitance value, N on is the number of submodules in the on state, that is, the total number of on submodules in the upper and lower bridge arms of the previous circuit. The resonant frequency is set to a value near the equivalent switching frequency, so the circuit will be in series resonance mode at the equivalent switching frequency. The bridge arm inductance value L is selected by the resonant frequency calculation formula. s And the submodule capacitance value C0.

[0021] The present invention also discloses a control method for a self-powered circuit for powering secondary equipment in a DC power distribution network, comprising: As attached Figure 4 As shown, the front-stage circuit adopts a sub-module voltage equalization strategy to respectively obtain the average value of the capacitor voltage of the upper and lower bridge arm sub-modules. According to the direction of the bridge arm current, each sub-module is corrected on the basis of the discharge ratio to obtain its own duty cycle signal. A front-stage circuit controller is constructed for the front-stage circuit. The front-stage circuit controller includes a voltage disturbance state observer and an error feedback controller. By constructing the voltage disturbance state observer, the output voltage of the front-stage circuit and the duty cycle control signals of each sub-module are used as the input of the voltage disturbance state observer, and the error feedback controller is used for adjustment, thereby realizing robust control of the output voltage under input disturbance conditions.

[0022] A current model predictive control strategy is proposed for the subsequent circuit. The transformer excitation current and output capacitor voltage in the subsequent circuit are used as state variable inputs of the current model predictive controller. The minimum voltage and current error is taken as the cost function to achieve rapid response of voltage and current.

[0023] When the front-stage circuit operates normally, there are two working modes: Mode 1 and Mode 2.

[0024] In mode 1, the upper bridge arm has N onEach sub-module capacitor is put into the circuit, and the sub-module capacitors in the lower bridge arm clamping sub-module are all bypassed; In mode 2, the upper bridge arm has N on - 1 submodule capacitor input circuit, the lower bridge arm has only one submodule capacitor input circuit in the clamping submodule; The proportion of working mode 1 to the total working mode time is recorded as the discharge ratio , the step-down ratio of the previous stage circuit is: , Among them, V M is the output voltage of the previous circuit, V H is the DC voltage of the DC distribution network; The subsequent circuit uses an isolated DC / DC circuit with series input and parallel output. The number of cascaded sub-circuits is N. f , the input side adopts the input voltage equalization strategy. For a single sub-circuit, the input voltage is V M / N f , let the duty cycle of the sub-circuit in the isolated DC / DC circuit be d, the number of turns of the primary coil in each sub-circuit be N1, the number of turns of the secondary coil be N2, and the step-down ratio of the subsequent circuit be: , Among them, V L Output voltage for the subsequent circuit; The total voltage reduction ratio formula of the self-powered circuit for powering secondary equipment in a DC distribution network is: , In the front-stage circuit, since the bridge arm inductance and the submodule capacitor form a series resonance, the filter inductance and filter capacitor can make the front-stage circuit equivalent to a second-order system. The front-stage circuit adopts a voltage robust control strategy, and estimates the input side DC bus voltage fluctuation in real time through the voltage disturbance state observer. The error feedback controller compensates for the total disturbance observed by the observer in real time to stabilize the output voltage of the front-stage circuit. Discharge ratio The equation is: , Where, L f is the filter inductance value of the previous stage circuit, C f is the filter capacitance value of the previous circuit, R M is the resistance value of the load on the output side of the subsequent circuit converted to the previous circuit. The voltage robust control paradigm is: , therefore, represents the second-order derivative of y; therefore, the expressions of output y, input u, control gain b0 and disturbance f are: , The state space equation of the previous circuit is: , In the formula, the state quantity x1 is the output y, the state quantity x2 is the differential of the output y, the state quantity x3 is the disturbance f, and the state quantity h is the differential of the disturbance f.

[0025] The voltage disturbance state observer equation is: , In the formula, the voltage disturbance state observer outputs z1, z2, and z3 track the state quantities x1, x2, and x3 respectively, and β1, β2, and β3 are the parameters of the voltage disturbance state observer, and their parameters are set as follows: , In the formula, ω o is the voltage disturbance state observer bandwidth.

[0026] The error feedback controller equation is: , in, is the output voltage reference value of the previous circuit, is the error feedback controller parameter, and its parameter setting is: , In the formula, ω c is the bandwidth of the previous stage circuit controller, and ξ is the damping ratio of the previous stage circuit controller.

[0027] In order to make the front-stage circuit have good dynamic performance, the bandwidth of the front-stage circuit controller should be c Selected as 1 / 10 of the switching frequency, the voltage disturbance state observer bandwidth ω o Configuration is (3~5)ω c Among them, the switching frequency is the switching frequency when the previous stage circuit is equivalent to a Buck circuit.

[0028] The voltage balancing strategy for each submodule in the front circuit is: calculate the average value of the capacitor voltage of the upper and lower bridge arm submodules respectively, and according to the direction of the bridge arm current, each submodule has a discharge ratio of Based on this, corrections are made to obtain their respective duty cycle signals.

[0029] like Figure 5 As shown in the figure, it is the block diagram of the voltage balancing control strategy of the upper bridge arm submodule capacitor, and the definition is Indicates the upper bridge arm submodule capacitor reference voltage, and its value is the average value of the upper bridge arm submodule capacitor voltage, that is: , Among them, the number of half-bridge submodules defining the upper bridge arm is N H + R H , N H is the number of half-bridge submodules actually controlled, R H is the number of redundant half-bridge submodules; the number of upper bridge arm full-bridge submodules is defined as N F ; The number of lower bridge arm clamp modules is N C + R C , N C is the number of clamping submodules actually controlled, R C is the number of redundant clamping submodules; is the capacitor voltage sampling value of each submodule in the upper bridge arm, , N is the number of submodules actually controlled by the upper bridge arm. p = N H + N F ; is the upper arm current, and the sign function is the sign function. When the upper arm current flows to the positive electrode of the submodule capacitor, it is defined as the positive direction, and the output is 1 after the sign function is judged. On the contrary, when the upper arm current flows to the negative electrode of the submodule capacitor, it is defined as the reverse direction, and the output is -1 after the sign function is judged. Voltage deviation value of the submodule capacitor The product of the sign value is passed through the upper bridge arm submodule capacitor voltage PI compensator to obtain the duty cycle correction value of each upper bridge arm. , and the upper bridge arm submodule duty cycle given value Superposition to obtain the final duty cycle signal .

[0030] The upper bridge arm submodule capacitor voltage correction link obtains the duty cycle signal of the upper bridge arm submodule , its formula is expressed as: , In the formula, is the proportional coefficient of the PI controller of the voltage balancing loop of the upper bridge arm submodule; is the integral coefficient of the PI controller of the voltage-sharing loop of the upper bridge arm submodule, and the letter s represents a complex frequency domain variable.

[0031] Due to the effect of the independent diode in the clamping submodule in the lower bridge arm, the current in the lower bridge arm can only flow in one direction, so there is no need for current direction determination. The block diagram of the capacitor voltage balancing control strategy of the lower bridge arm submodule is as follows: Figure 6 shown.

[0032] definition Represents the reference voltage of the capacitor of the lower bridge arm submodule, and its value is the average value of the capacitor voltage of the lower bridge arm submodule, that is: , In the formula, is the voltage sampling value of each clamping submodule capacitor of the lower bridge arm, , is the number of clamping submodules actually controlled by the lower bridge arm; similarly, the voltage deviation value of the capacitor of the lower bridge arm submodule After the capacitor voltage PI compensator of the lower bridge arm submodule, the duty cycle correction value of each lower bridge arm is obtained. , the duty cycle correction is inverted and compared with the duty cycle given value of the lower bridge arm submodule Superposition to obtain the final duty cycle signal , the capacitor voltage correction link of the lower bridge arm submodule obtains the duty cycle signal of the lower bridge arm submodule , its formula is expressed as: , In the formula, is the proportional coefficient of the PI controller of the voltage equalizing loop of the lower bridge arm submodule; It is the integral coefficient of the PI controller of the voltage equalizing loop of the lower bridge arm submodule.

[0033] As attached Figure 7 As shown in the figure, the back-stage circuit adopts the current model predictive control strategy. The deviation between the output voltage reference value and the current sampling value is used as the input of the PI controller. The output of the PI controller is used as the current inner loop reference value. At the same time, it is used as the input of the model predictive controller to introduce the excitation inductance current of the transformer in the isolated DC / DC converter. i L The output capacitor voltage of the subsequent circuit As state variables, , taking the output voltage error and the current inner loop error as the minimum cost function, the pulse signal duty cycle of the subsequent circuit is rolling optimized. The excitation inductance current of each cascade circuit in the subsequent circuit is independent and controlled separately. The prediction equation of the state variable of the isolated DC / DC converter is: , In the formula, and is the kth switching cycle, that is, the isolation transformer excitation inductance current and output capacitor voltage of the current switching cycle, and is the magnetizing inductor current and output capacitor voltage of the k+1th switching cycle, that is, the next switching cycle. is the input voltage of the mth subcircuit, ; is the transformer magnetizing inductance, is the output capacitor, is the output load, that is, the actual resistance value of the secondary device when the self-powered circuit supplies power to the secondary device. It is the calculated value of the actual resistance value converted to the previous circuit; is the predicted value of the optimal duty cycle of the pulse signal in the kth switching cycle, T is the switching cycle, is the number of turns of the primary coil of the isolation transformer, is the number of turns of the secondary coil of the isolation transformer.

[0034] The cost function is to minimize the voltage outer loop error and the current inner loop error: , In the formula, u ref is the output voltage reference value, i ref It is the current inner loop reference value output by the PI controller.

[0035] When the partial derivative When , the cost function has a minimum value, let , calculate the isolated DC / DC converter k The optimal duty cycle prediction value of the pulse signal of a switching cycle is: , In summary, the present invention first designs a self-powered circuit for powering the secondary equipment of the DC distribution network, which is composed of a front / rear two-stage circuit to achieve high-proportion voltage reduction and has the ability to self-clear DC faults; the front-stage circuit adopts a hybrid modular multi-level structure, the upper bridge arm adopts a mixture of half-bridge, full-bridge and fault current limiting sub-modules, and the lower bridge arm adopts a mixture of clamping and fault current limiting sub-modules; the rear-stage circuit adopts an isolated DC / DC circuit. Secondly, for the front-stage circuit, a voltage disturbance state observer is constructed, and the output voltage of the front-stage circuit and the duty cycle control signal of the power main circuit are used as the input of the state observer, and the error feedback controller is used for adjustment, so as to realize the robust control of the output voltage under the input disturbance. Finally, a current type model predictive control strategy is proposed for the rear-stage circuit, and the transformer excitation current and capacitor voltage are used as the state variable input of the model predictive controller, and the voltage and current error is minimized as the cost function to realize the rapid response of voltage and current. Through the present invention, the secondary equipment of the DC distribution network is independent of the external AC power supply, and the adaptability of the self-powered circuit in different working conditions and fault conditions is improved, and the output voltage stability and dynamic response speed of the self-powered circuit are improved.

[0036] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principle of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A self-powered circuit for supplying power to secondary equipment in a DC distribution network, characterized in that: Including a front stage circuit and a rear stage circuit; The front-stage circuit includes an upper bridge arm inductor, an upper bridge arm and a lower bridge arm connected in series, wherein the upper bridge arm includes a plurality of half-bridge submodules, a plurality of full-bridge submodules and a fault current limiting submodule connected in series; the lower bridge arm includes a filter inductor and a filter capacitor connected in series, and includes a plurality of submodules connected in parallel with the filter inductor and the filter capacitor, wherein the plurality of submodules are a plurality of clamping submodules connected in series and a fault current limiting submodule; the half-bridge submodule, the full-bridge submodule and the clamping submodule all include submodule capacitors; The post-stage circuit is connected in parallel with the filter capacitor. The post-stage circuit is an isolated DC / DC circuit. The isolated DC / DC circuit includes a plurality of cascaded sub-circuits. The post-stage circuit outputs a stable DC voltage for powering secondary equipment in a DC distribution network.

2. A self-powered circuit for powering secondary equipment in a DC distribution network according to claim 1, characterized in that: The upper bridge arm inductor and the submodule capacitor operate in series resonant mode.

3. The self-powered circuit for powering secondary equipment in a DC distribution network according to claim 1, characterized in that: When the self-energy extraction circuit is in normal working state, in the upper and lower bridge arms of the front-stage circuit, the sub-modules in redundant state and the fault current limiting sub-modules are in bypass state, among which the redundant sub-module of the upper bridge arm is a half-bridge sub-module, and the redundant sub-module of the lower bridge arm is a clamping sub-module.

4. A control method for a self-powered circuit for powering secondary equipment in a DC distribution network, used to control a self-powered circuit for powering secondary equipment in a DC distribution network as claimed in any one of claims 1 to 3, characterized in that: Control methods include: The front-stage circuit adopts a sub-module voltage equalization strategy to obtain the average value of the capacitor voltage of the upper and lower bridge arm sub-modules respectively. According to the direction of the bridge arm current, each sub-module is corrected on the basis of the discharge ratio to obtain its own duty cycle signal; a front-stage circuit controller is constructed for the front-stage circuit, and the front-stage circuit controller includes a voltage disturbance state observer and an error feedback controller. By constructing the voltage disturbance state observer, the output voltage of the front-stage circuit and the duty cycle control signal of each sub-module are used as the input of the voltage disturbance state observer, and the error feedback controller is used for adjustment, thereby realizing robust control of the output voltage under input disturbance conditions; A current type model predictive control strategy is proposed for the subsequent circuit. The excitation current of the isolation transformer and the output capacitor voltage in the subsequent circuit are used as the state variable inputs of the current type model predictive controller. The minimum voltage and current error is taken as the cost function to achieve rapid response of voltage and current.

5. A control method for a self-powered circuit for powering secondary equipment in a DC distribution network according to claim 4, characterized in that: In the previous stage circuit, the duty cycle signal of each upper bridge arm submodule after correction , its formula is expressed as: ， in, , The number of submodules actually controlled by the upper bridge arm; Indicates the upper bridge arm submodule capacitor reference voltage, The capacitor voltage sampling values ​​of each submodule of the upper bridge arm; is the upper arm current, and sign function is the sign function; is the discharge ratio; is the proportional coefficient of the PI controller of the voltage balancing loop of the upper bridge arm submodule; is the integral coefficient of the PI controller of the voltage-sharing loop of the upper bridge arm submodule, and the letter s represents a complex frequency domain variable.

6. A control method for a self-powered circuit for powering secondary equipment in a DC distribution network according to claim 4, characterized in that: In the front stage circuit, the duty cycle signal of each lower bridge arm submodule after correction , its formula is expressed as: ， in, , is the number of clamping submodules actually controlled by the lower bridge arm, The number of submodules actually controlled by the upper bridge arm; is the discharge ratio; Indicates the capacitor reference voltage of the lower bridge arm submodule; is the voltage sampling value of each clamping submodule capacitor of the lower bridge arm; is the proportional coefficient of the PI controller of the voltage equalizing loop of the lower bridge arm submodule; is the integral coefficient of the PI controller of the voltage-sharing loop of the lower bridge arm submodule, and the letter s represents a complex frequency domain variable.

7. A control method for a self-powered circuit for powering secondary equipment in a DC distribution network according to claim 4, characterized in that: In the subsequent circuit, the current model predictive control strategy includes: the deviation between the output voltage reference value and the current sampling value is used as the input of the PI controller, the output of the PI controller is used as the current inner loop reference value, and it is also used as the input of the model predictive controller. The excitation inductance current of the transformer in the isolated DC / DC converter and the output capacitor voltage of the subsequent circuit are introduced as state variables. The duty cycle of the pulse signal of the subsequent circuit is rollingly optimized with the output voltage error and the current inner loop error minimized as the cost function.

8. A control method for a self-powered circuit for powering secondary equipment in a DC distribution network according to claim 7, characterized in that: The optimal duty cycle calculation formula for the isolated DC / DC converter pulse signal is: ， in, For the The optimal duty cycle prediction value of the pulse signal of a switching cycle; is the transformer magnetizing inductance, is the output capacitor, is the output load, is the switching cycle, and is the magnetizing inductance current of the isolation transformer and the output capacitor voltage of the subsequent circuit in the kth switching cycle, and are the magnetizing inductor current and output capacitor voltage of the next switching cycle, is the switching cycle, is the number of turns of the primary coil of the isolation transformer, is the number of turns of the secondary coil of the isolation transformer, is the output voltage reference value, is the input voltage of the mth subcircuit in the isolated DC / DC converter, ; is the number of subcircuits.

Images