DC / DC converter with short-circuit current blocking function and control method and system

Abstract

The application discloses a DC / DC converter with a short-circuit current blocking function and a control method and system, and belongs to the field of AC / DC hybrid distribution networks. The DC / DC converter comprises an isolation boost full-bridge converter and a short-circuit current component blocking module. The DC / DC converter is designed with a thyristor which can be automatically turned off after a short-circuit fault occurs at the DC output side, thereby blocking the short-circuit current flowing from the distributed current branch to the DC line. Moreover, the blocked short-circuit current component is safely consumed on a small resistor of the controlled branch, and the design can achieve the beneficial effect of greatly reducing the short-circuit current on the DC circuit.

Description

Technical Field

[0001] This invention belongs to the field of AC / DC hybrid power distribution networks, and more specifically, relates to a DC / DC converter with short-circuit current blocking function and a control method and system. Background Technology

[0002] With the increasing penetration of large-scale distributed power sources such as photovoltaics and wind power in distribution networks, the structure of distribution networks has undergone fundamental changes. Among these, hybrid AC / DC distribution networks have significant advantages in integrating distributed power sources and distributed energy storage systems, and have become the future development trend of distribution networks. However, the resistance and inductance of DC lines in hybrid AC / DC distribution networks are often very small. When a short-circuit fault occurs on a DC line, the short-circuit current can reach an extremely high level in a very short time, causing serious damage to electrical equipment. However, current research on hybrid AC / DC distribution networks often lacks reliable and low-cost DC short-circuit fault protection measures, or relies on expensive DC circuit breakers to address short-circuit faults. Therefore, technologies that can effectively limit DC short-circuit current are of great significance to the development of hybrid AC / DC distribution networks. Summary of the Invention

[0003] In view of the shortcomings of the prior art, the purpose of this invention is to provide a DC / DC converter and control method and system with short-circuit current blocking function, aiming to solve the problem of difficulty in limiting DC short-circuit current.

[0004] To achieve the above objectives, the present invention provides a DC / DC converter with short-circuit current blocking function, including an isolated boost full-bridge converter and a short-circuit current component blocking module;

[0005] The isolated boost full-bridge converter includes a capacitor C1 connected in parallel at the input voltage port, a single-phase bridge PWM inverter, and a three-winding high-frequency transformer T. hf The first single-phase bridge uncontrolled rectifier, wherein the output port of the single-phase bridge PWM inverter is connected to the three-winding high-frequency transformer T. hf The primary winding and the three-winding high-frequency transformer T hf The main secondary winding is connected to the input port of the first single-phase bridge uncontrolled rectifier. The single-phase bridge PWM inverter converts the DC power generated by the distributed power source into AC power. The first single-phase bridge uncontrolled rectifier converts the boosted AC voltage into DC power. The first output voltage port of the first single-phase bridge uncontrolled rectifier is connected in parallel with capacitor C2 and in series with smoothing reactor L, which serves to filter and smooth the output voltage.

[0006] The short-circuit current component blocking module includes a negative DC power supply module and a thyristor switch V. T1 Control V T1Controlled branch L that is turned off fh The negative DC power supply module includes components connected to the three-winding high-frequency transformer T. hf The second single-phase bridge uncontrolled rectifier on the secondary winding, the capacitor C3 connected in parallel to the output port of the second single-phase bridge uncontrolled rectifier, and the controlled branch L fh The first end is connected in parallel to the thyristor switch V. T1 The anode of the circuit is connected in series with the negative terminal of the output port of the negative DC power supply module; the controlled branch L fh Including thyristor switches V T2 and small resistance R p Used to connect the negative terminal of the negative DC power supply module output and the thyristor switch V after a fault occurs. T1 The anode pulls down V T1 The effect of anode voltage.

[0007] Furthermore, the small resistance R p Resistance value R p The restrictions are

[0008]

[0009] Among them, U C3 Let i be the voltage across capacitor C3. k (t1) represents the thyristor switch V. T2 The short-circuit current at the moment of conduction.

[0010] Preferably, the single-phase bridge PWM inverter includes: four IGBTs, which operate as switching devices in high-frequency mode, and four diodes, which serve to ensure continuous load current; wherein, the collectors and emitters of the first and second IGBTs are connected in series to form a first bridge arm, the collectors and emitters of the third and fourth IGBTs are connected in series to form a second bridge arm, the first bridge arm and the second bridge arm are connected in parallel, and each IGBT is connected in anti-parallel to a diode; the two ends of the parallel connection between the first and second bridge arms are led out to the input terminal of the single-phase bridge PWM inverter, and the middle end of the two bridge arms is led out to the output terminal of the single-phase bridge PWM inverter.

[0011] Preferably, the first single-phase bridge uncontrolled rectifier includes: four diodes; wherein, the anode and cathode of every two diodes are connected in series to form a bridge arm, the two bridge arms are connected in parallel, the two parallel nodes are led out to the input terminal of the first single-phase bridge uncontrolled rectifier, and the midpoint of the two bridge arms is led out to the output terminal of the first single-phase bridge uncontrolled rectifier.

[0012] Preferably, the first single-phase bridge uncontrolled rectifier includes: four diodes; wherein, the anode and cathode of every two diodes are connected in series to form a bridge arm, the two bridge arms are connected in parallel, the two parallel nodes lead out to the input terminal of the second single-phase bridge uncontrolled rectifier, and the midpoint of the two bridge arms leads out to the output terminal of the second single-phase bridge uncontrolled rectifier.

[0013] Another objective of this invention is to provide a control method for the aforementioned DC / DC converter with short-circuit current blocking function, wherein, under normal operating conditions, the thyristor switch V T1 When in the ON state, the thyristor switch V T2 When the short-circuit fault occurs on the DC line, the thyristor switch V is in the open state. T2 It is triggered to conduct, and at the same time the thyristor switch V T1 Automatic shutdown, simultaneously shutting off the positive pulse signal on its control electrode, thus completely blocking the DC short-circuit current component flowing to the fault point on the distributed power supply branch.

[0014] When a short-circuit fault occurs, the thyristor switch V T2 The conduction condition is: U fg <ηU DCN And i L >γI LN , where η<1 and γ>1, U fg For thyristor switch V T1 The voltage between the anode and the positive terminal of the negative DC power supply module output, U DCN i is the rated voltage on the DC circuit. L For the current flowing through the smoothing reactor L, I LN This is the rated current flowing through the smoothing reactor L.

[0015] The present invention also provides a control system for a DC / DC converter with short-circuit current blocking function, comprising: a computer-readable storage medium and a processor;

[0016] The computer-readable storage medium is used to store executable instructions;

[0017] The processor is used to read executable instructions stored in the computer-readable storage medium and execute the control method described above.

[0018] Compared with the prior art, the above technical solution conceived by this invention adds a thyristor on the DC output side that can automatically turn off after a short-circuit fault occurs, thus blocking the flow of short-circuit current from the distributed current branch to the DC line. Furthermore, the blocked short-circuit current component will be safely consumed by the small resistance of the controlled branch. This design can achieve the beneficial effect of greatly reducing the short-circuit current in the DC circuit. Attached Figure Description

[0019] Figure 1 It is the general network structure of an AC / DC hybrid distribution network;

[0020] Figure 2 It is a DC / DC converter with short-circuit current component blocking function;

[0021] Figure 3 It is the equivalent circuit of a distributed power supply branch;

[0022] Figure 4 This is a functional diagram of a DC / DC converter with short-circuit current component blocking function. Detailed Implementation

[0023] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention. Furthermore, the technical features involved in the various embodiments of this invention described below can be combined with each other as long as they do not conflict with each other.

[0024] The typical network structure of an AC / DC hybrid distribution network is as follows: Figure 1 As shown, the DC line integrates an energy storage system (ESS), distributed generation (DG), and DC load using a DC / DC converter. When a short-circuit fault occurs at point k on the DC line, the short-circuit current i k This can be viewed as consisting of four short-circuit current components: 1) the short-circuit current component from the energy storage system branch; 2) the short-circuit current component from the distributed power generation branch; 3) the short-circuit current component from the DC load branch; and 4) the short-circuit current component from the DC side of the AC / DC converter. Based on this, the present invention provides a DC / DC converter with short-circuit current blocking function, thereby limiting the DC short-circuit current.

[0025] Based on the aforementioned research background, this invention proposes a DC / DC converter with short-circuit current component blocking function. This DC converter can block the flow of short-circuit current components from distributed power supply branches to the fault point in the event of a short-circuit fault in a DC line, thereby achieving significant current limiting in short-circuit circuits on DC lines.

[0026] The DC / DC converter with short-circuit current component blocking function proposed in this invention, such as Figure 2 As shown, it includes an isolated boost full-bridge converter and a short-circuit current component blocking module.

[0027] Isolated boost full-bridge converter, such as Figure 2 As shown in the red box in the middle, it consists of a capacitor C1 connected in parallel at the input voltage port; a single-phase bridge PWM inverter; and a three-winding high-frequency transformer T. hf ; connected in T hf The system consists of a single-phase bridge uncontrolled rectifier 1 on the primary secondary winding; a capacitor C2 connected in parallel at output voltage port 1; and a smoothing reactor L. The isolated boost full-bridge converter converts the DC power from the distributed power source into AC power through a single-phase bridge PWM inverter. Simultaneously, a capacitor C1 is connected in parallel at the input port of the single-phase bridge PWM inverter to maintain stable DC voltage operation. The output port of the single-phase bridge PWM inverter is connected to the three-winding high-frequency transformer T. hf A primary winding, a three-winding high-frequency transformer T hf The primary secondary winding is connected to the input port of the first single-phase bridge uncontrolled rectifier; the first single-phase bridge uncontrolled rectifier converts the boosted AC voltage into DC voltage, and its output port is connected in parallel with capacitor C2 and in series with smoothing reactor L, which plays the role of filtering and smoothing the output voltage.

[0028] Short-circuit current component blocking module, such as Figure 2 As shown in the green box in the middle, it consists of a negative DC power supply module; a thyristor switch V T1 Control V T1 Controlled branch L that is turned off fh Composition. The negative DC power supply module consists of components connected to T. hf The single-phase bridge uncontrolled rectifier 2 on the secondary winding; the capacitor C3 connected in parallel at the output voltage port 2, and the controlled branch L fh Transistor switch V T2 and small resistance R p Composition. The negative DC power supply module consists of components connected to T. hfThe second single-phase bridge uncontrolled rectifier on the secondary winding and capacitor C3 connected in parallel to the output voltage port of the second single-phase bridge uncontrolled rectifier constitute the circuit. The negative DC power supply module forms a stable small voltage across capacitor C3, between points g and h, to quickly pull down the thyristor switch V in the event of a short-circuit fault. T1 The anode voltage, and make it less than V. T1 The cathode voltage is thus achieved under short-circuit fault conditions, V T1 The effect of automatic shutdown. Controlled branch L fh Transistor switch V T2 and small resistance R p Composition. Among them, the thyristor switch V T2 After a short-circuit fault occurs, the controller turns the circuit on, thereby enabling the negative DC power supply module to pull down the voltage at point f.

[0029] The working principle of this DC / DC converter with short-circuit current component blocking function will be analyzed in detail next.

[0030] (1) Under normal working conditions

[0031] Distributed power generation supplies power to the DC line through an isolated boost full-bridge converter. At this time, the voltage U across capacitor C2 is... C2 Equal to the rated voltage U of the DC line DCN The voltage U across capacitor C3 C3 Maintain at a small value (U) C3 < C2 ). Thyristor switch V T1 It is in the ON state, while the thyristor switch V T2 It is currently disconnected.

[0032] (2) Short circuit fault situation

[0033] When a short-circuit fault occurs on a DC line, the thyristor switch V... T2 It will be triggered to conduct by the controller. This is because the voltage U at point h relative to the negative terminal of the DC line... h equal to -U C3 Therefore V T2 At the instant of conduction, the voltage U at point f relative to the negative terminal of the DC line f It will be rapidly pulled down and reduced to a value less than the cathode voltage. At this point, V T1 It is automatically shut down, and the positive pulse signal on its control electrode is also turned off. From this point on, the DC short-circuit current component flowing to the fault point on the distributed power supply branch is completely blocked.

[0034] controller such as Figure 2 As shown in the blue box in the diagram. When a short-circuit fault occurs, the thyristor switch V... T2 ​The conduction condition is: U fg <ηU DCN And i L >γI LN (η < 1 and γ > 1, for example, η = 0.8, γ = 1.2). When the above conditions are met, the triggering unit will send a signal to the thyristor switch V. T2 The control electrode sends a trigger signal and simultaneously sends a stop signal to the isolated boost full-bridge converter (a signal that shuts down the PWM control unit of the single-phase bridge PWM inverter). The controller also includes a trigger for V during DC / DC converter startup / restart. T1 The control unit.

[0035] Furthermore, the small resistance R will be given below. p The parameter design method. To make the controlled branch L... fh The thyristor V in T2 It can be successfully turned on; at the moment of conduction, the voltage drop U across the small resistor is... R Must be less than U C3 Small resistance R p Resistance value R p The constraints can be derived through the following process.

[0036] From the occurrence of a DC short circuit fault to the thyristor V T2 During the period when it is turned on, the isolated boost full-bridge converter still outputs voltage U. DCN At this point, the equivalent circuit of the distributed power supply branch is as follows: Figure 3 As shown.

[0037] Assuming the circuit operates under rated conditions before the fault occurs, the short-circuit current can be obtained through transient analysis.

[0038]

[0039] Suppose that when t = t1, the thyristor switch V T2 The conduction condition is met, and the magnitude of the short-circuit current is i. k (t1). Therefore, the small resistance R p Resistance value R p The restrictions are

[0040]

[0041] To verify the short-circuit current component blocking capability of the proposed DC / DC converter with short-circuit current component blocking function, according to Figure 2 A simulation model was built in Matlab / Simulink. The parameters of the simulation circuit are shown in the table.

[0042] Table 1 Parameters of the Simulation Circuit

[0043]

[0044] In the simulation, a short circuit fault occurs at point k on the DC line at t = 0.04s. Figure 4 This demonstrates the effectiveness of the short-circuit current blocking function of a DC / DC converter equipped with short-circuit current component blocking capability. The red and blue curves represent the short-circuit current component i on the regenerative power supply branch with and without short-circuit current component blocking capability, respectively. k The curve of the change of (t). As can be seen from the figure, this measure can effectively block the DC short-circuit current component flowing from the renewable power supply branch to the fault point.

[0045] Those skilled in the art will readily understand that the above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A DC / DC converter with short-circuit current blocking function, characterized in that, Includes an isolated boost full-bridge converter and a short-circuit current component blocking module; The isolated boost full-bridge converter includes a capacitor C1 connected in parallel at the input voltage port, a single-phase bridge PWM inverter, and a three-winding high-frequency transformer T. hf The first single-phase bridge uncontrolled rectifier, wherein the output port of the single-phase bridge PWM inverter is connected to the three-winding high-frequency transformer T. hf A primary winding, a three-winding high-frequency transformer T hf The main secondary winding is connected to the input port of the first single-phase bridge uncontrolled rectifier. The single-phase bridge PWM inverter converts the DC power generated by the distributed power source into AC power. The first single-phase bridge uncontrolled rectifier converts the boosted AC voltage into DC power. The first output voltage port of the first single-phase bridge uncontrolled rectifier is connected in parallel with capacitor C2 and in series with smoothing reactor L, which serves to filter and smooth the output voltage. The short-circuit current component blocking module includes a negative DC power supply module and a thyristor switch V. T1 Control V T1 Controlled branch L that is turned off fh The negative DC power supply module includes components connected to the three-winding high-frequency transformer T. hf The second single-phase bridge uncontrolled rectifier on the secondary winding, the capacitor C3 connected in parallel to the output port of the second single-phase bridge uncontrolled rectifier, and the controlled branch L fh The first end is connected in parallel to the thyristor switch V. T1 The anode of the circuit is connected in series with the negative terminal of the output port of the negative DC power supply module; the controlled branch L fh Including thyristor switches V T2 and small resistance R p Used to connect the negative terminal of the negative DC power supply module output and the thyristor switch V after a fault occurs. T1 The anode pulls down V T1 The effect of anode voltage.

2. The DC / DC converter according to claim 1, characterized in that, Small resistor R p Resistance value R p The restrictions are Among them, U C3 Let i be the voltage across capacitor C3. k (t1) represents the thyristor switch V. T2 The short-circuit current at the moment of conduction.

3. The DC / DC converter according to claim 1, characterized in that, The single-phase bridge PWM inverter includes: four IGBTs, which operate as switching devices in high-frequency mode, and four diodes, which serve to ensure continuous load current. The emitters of the first IGBT and the collectors of the second IGBT are connected in series to form the first bridge arm; the emitters of the third IGBT and the collectors of the fourth IGBT are connected in series to form the second bridge arm; the first and second bridge arms are connected in parallel, and each IGBT is connected in anti-parallel to a diode. The two ends of the parallel connection between the first and second bridge arms are led out to the input terminal of the single-phase bridge PWM inverter, and the middle end of the two bridge arms is led out to the output terminal of the single-phase bridge PWM inverter.

4. The DC / DC converter according to claim 1, characterized in that, The first single-phase bridge uncontrolled rectifier includes four diodes; wherein, the anode and cathode of every two diodes are connected in series to form a bridge arm, the two bridge arms are connected in parallel, the two parallel nodes are led out to the input terminal of the first single-phase bridge uncontrolled rectifier, and the midpoint of the two bridge arms is led out to the output terminal of the first single-phase bridge uncontrolled rectifier.

5. The DC / DC converter according to claim 1, characterized in that, The first single-phase bridge uncontrolled rectifier includes four diodes; wherein, the anode and cathode of every two diodes are connected in series to form a bridge arm, the two bridge arms are connected in parallel, the two parallel nodes lead out to the input terminal of the second single-phase bridge uncontrolled rectifier, and the midpoint of the two bridge arms leads out to the output terminal of the second single-phase bridge uncontrolled rectifier.

6. A control method for a DC / DC converter with short-circuit current blocking function as described in any one of claims 1 to 5, characterized in that, Under normal operating conditions, the thyristor switch V T1 When in the ON state, the thyristor switch V T2 When the short-circuit fault occurs on the DC line, the thyristor switch V is in the open state. T2 It is triggered to conduct, and at the same time the thyristor switch V T1 Automatic shutdown, simultaneously shutting off the positive pulse signal on its control electrode, thus completely blocking the DC short-circuit current component flowing to the fault point on the distributed power supply branch.

7. The control method according to claim 6, characterized in that, When a short circuit fault occurs, the thyristor switch V T2 The conduction condition is: U fg <ηU DCN And i L >γI LN , where η<1 and γ>1, U fg For thyristor switch V T1 The voltage between the anode and the positive terminal of the negative DC power supply module output, U DCN i is the rated voltage on the DC circuit. L For the current flowing through the smoothing reactor L, I LN This is the rated current flowing through the smoothing reactor L.

8. A control system for a DC / DC converter with short-circuit current blocking function, characterized in that, include: Computer-readable storage media and processors; The computer-readable storage medium is used to store executable instructions; The processor is used to read executable instructions stored in the computer-readable storage medium and execute the control method according to claim 6 or 7.

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