Z-source bidirectional DC-DC converter with circuit breaker and voltage regulation functions

Abstract

The invention belongs to the technical field of circuit breakers and electric energy conversion, and particularly relates to a Z-source bidirectional DC-DC converter with circuit breaker and voltage regulation functions. The converter provided by the invention is symmetrical in structure, and Z-source networks and anti-parallel thyristors are symmetrically configured on two sides of a dual-active bridge; the design not only supports two-way transmission of energy, but also endows the two sides with different functional characteristics: the thyristor, the Z-source network and the full-bridge circuit on the input side realize voltage regulation, and the thyristor, the Z-source network and the full-bridge circuit on the output side have the function of a circuit breaker, so that effective fault protection is provided. In addition, the transformer not only provides electrical isolation, but also widens the voltage regulation range by combining the transformer with the Z-source network, and improves the adaptability and flexibility of the system.

Description

Technical Field

[0001] The present invention belongs to the technical fields of circuit breakers and power conversion, and particularly relates to a Z-source bidirectional DC-DC converter with both circuit breaker and voltage regulation functions. Background Art

[0002] In recent years, with the wide application of new energy and distributed generation, microgrid technology has developed rapidly as a solution for integrating distributed generation. Among them, the DC microgrid has become a research and application hotspot due to its efficient utilization of distributed generation and higher energy efficiency. As a bridge connecting DC buses with different voltages, the bidirectional DC / DC interconnection converter is an important part of the DC microgrid.

[0003] Existing DC / DC converter topologies can be mainly divided into isolated DC / DC converters and non-isolated DC / DC converters according to whether they have electrical isolation functions. Compared with non-isolated DC / DC converters, isolated DC / DC converters achieve electrical isolation between the input and output through a high-frequency transformer, improving system safety and preventing electric shock and equipment damage. In addition, it can effectively suppress common-mode noise and electromagnetic interference, improving the electromagnetic compatibility and stability of the system. This advantage is more obvious in DC microgrids with a large number of distributed generation devices. At the same time, the design of the transformer supports a wider voltage regulation range.

[0004] At the same time, the DC microgrid still faces key problems that need to be solved urgently: fault current limiting and isolation. Due to the wide application of power electronic devices in the DC microgrid, the excessive fault current generated by a short-circuit fault may exceed the tolerance range of the devices, resulting in equipment damage. Therefore, DC short-circuit faults must be quickly cleared. Different from alternating current, direct current has no natural zero-crossing point, making it difficult to extinguish the arc of traditional mechanical circuit breakers in DC applications, and it has problems such as slow breaking speed and short lifespan. The DC solid-state circuit breaker has become increasingly indispensable in DC power supply systems due to its advantages such as high-speed response, no arc, and high reliability. To achieve bidirectional short-circuit protection, solid-state circuit breakers need to be configured on both sides of the bidirectional DC / DC interconnection converter, increasing circuit complexity and system cost.

[0005] In view of this, the inventor expects to design a Z-source bidirectional DC-DC converter with both circuit breaker and voltage regulation functions. Summary of the Invention

[0006] The purpose of the present invention is to overcome the above problems existing in the traditional technology, and provide a Z-source bidirectional DC-DC converter with both circuit breaker and voltage regulation functions. Through structural optimization and device reuse, bidirectional circuit breaker and voltage regulation functions are achieved, thereby reducing manufacturing costs, improving safety, and realizing stable and reliable bidirectional energy flow.

[0007] To achieve the above technical objectives and effects, the present invention is realized through the following technical solutions:

[0008] The present invention provides a Z-source bidirectional DC-DC converter with both circuit breaker and voltage regulation functions. The converter includes two anti-parallel thyristor structures, two Z-source networks, and a dual-active-bridge circuit;

[0009] The two anti-parallel thyristor structures are respectively denoted as anti-parallel thyristor structure I and anti-parallel thyristor structure II;

[0010] The two Z-source networks are respectively denoted as Z-source network I and Z-source network II;

[0011] The dual-active-bridge circuit includes a high-frequency transformer, and a full-bridge circuit is provided on each side of the dual-active-bridge circuit, which are respectively denoted as primary-side full-bridge circuit I and secondary-side full-bridge circuit II;

[0012] The primary-side full-bridge circuit I is cascaded with the Z-source network I, the other side of the Z-source network I is connected in parallel with the DC terminal I, and the anti-parallel thyristor structure I is connected in series between the positive pole of the DC port I and the Z-source network I; the secondary-side full-bridge circuit II is cascaded with the Z-source network II, the other side of the Z-source network II is connected in parallel with the DC terminal II, and the anti-parallel thyristor structure II is connected in series between the positive pole of the DC port I and the Z-source network II.

[0013] Further, in the above Z-source bidirectional DC-DC converter with both circuit breaker and voltage regulation functions, each of the anti-parallel thyristor structures includes two anti-parallel thyristors.

[0014] Further, in the above Z-source bidirectional DC-DC converter with both circuit breaker and voltage regulation functions, the high-frequency transformer is a single-input single-output transformer adapted to the switching frequency.

[0015] Further, in the above Z-source bidirectional DC-DC converter with both circuit breaker and voltage regulation functions, the full-bridge circuit is a full-bridge circuit with two bridge arms and four switches.

[0016] Further, in the above Z-source bidirectional DC-DC converter with both circuit breaker and voltage regulation functions, the switching devices in the full-bridge circuit are all power electronic switching tubes with body diodes.

[0017] Further, in the above Z-source bidirectional DC-DC converter with both circuit breaker and voltage regulation functions, the converter can achieve bidirectional energy transfer and has both circuit breaker and voltage regulation functions; on the DC input side, the anti-parallel thyristor structure, the Z-source network, and the full-bridge circuit work as a Z-source converter and boost the voltage through direct conduction; on the DC output side, the anti-parallel thyristor structure, the Z-source network, and the full-bridge circuit work as a Z-source circuit breaker.

[0018] Furthermore, in the Z-source bidirectional DC-DC converter with both circuit breaker and voltage regulation functions, on the DC input side, when the anti-parallel thyristor structure, Z-source network, and full-bridge circuit operate as a Z-source converter, boost is achieved through shoot-through, inversion is performed through the full-bridge circuit, and it is transmitted to the full-bridge circuit on the output side through a transformer, and the body diodes of the full-bridge circuit rectify; in the shoot-through state, the transformer does not work, the input voltage of the full-bridge circuit on the output side is zero, and the current passes through the body diodes of the full-bridge circuit for freewheeling.

[0019] Furthermore, in the Z-source bidirectional DC-DC converter with both circuit breaker and voltage regulation functions, on the DC output side, when the anti-parallel thyristor structure, Z-source network, and full-bridge circuit operate as a Z-source circuit breaker, when a ground short-circuit fault occurs at the DC output port, a new fault loop is added to the circuit. At this time, the current flowing out of the full-bridge circuit directly grounds through the Z-source inductor; at the same time, due to direct grounding, the Z-source capacitor discharges, in the opposite direction to the current of the Z-source inductor, generating a reverse current component in the circuit. The current flowing out of the full-bridge circuit gradually decreases until the current reaches zero, and the body diodes of the full-bridge circuit naturally turn off; due to the disappearance of the current loop of the full-bridge circuit, the circuit cannot form a path, the fault current drops to 0, and the thyristor turns off.

[0020] The beneficial effects of the present invention are as follows:

[0021] 1. The Z-source bidirectional DC-DC converter provided by the present invention has both circuit breaker and voltage regulation functions, realizing bidirectional voltage regulation and energy transfer. When a short-circuit fault occurs on either side, the circuit can be effectively protected through the Z-source network, enhancing the safety and reliability of the system.

[0022] 2. The present invention simplifies the circuit design and structure by reusing two Z-source networks, reducing the number of required devices, thereby reducing the cost of the converter. At the same time, the reduction in the number of devices helps to reduce losses, thereby improving the overall efficiency of the system.

[0023] 3. The design of the present invention achieves a significant voltage gain through the combination of the Z-source network and the transformer. This design enables the converter to efficiently convert low voltages and high voltages, meeting different application requirements and enhancing the adaptability and flexibility of the system.

[0024] Of course, it is not necessary for any product implementing the present invention to simultaneously achieve all the above advantages. Description of the Drawings

[0025] To more clearly illustrate the technical solutions of the embodiments of the present invention, the following will briefly introduce the drawings required for the description of the embodiments. Obviously, the drawings in the following description are only some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can be obtained based on these drawings.

[0026] Figure 1 It is a schematic diagram of the topology of the Z-source bidirectional DC-DC converter with both circuit breaker and voltage regulation functions of the present invention;

[0027] Figure 2 It is a schematic diagram of the working mode in the inverter state when the converter conducts forward;

[0028] Figure 3 It is a schematic diagram of the working mode in the shoot-through zero state when the converter conducts forward;

[0029] Figure 4 It is a schematic diagram of the Z-source circuit breaker when the converter conducts forward. Detailed implementation manners

[0030] The following will clearly and completely describe the technical solutions in the embodiments of the present invention with reference to the drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts belong to the scope of protection of the present invention.

[0031] As Figure 1 shown, this embodiment proposes a Z-source bidirectional DC-DC converter with both circuit breaker and voltage regulation functions, having the following structure: an antiparallel thyristor structure I, an antiparallel thyristor structure II, a Z-source network I, a Z-source network II, and a dual active bridge circuit.

[0032] The antiparallel thyristor structure includes two antiparallel thyristors. The Z-source network includes two inductors and two capacitors. The dual active bridge includes a high-frequency transformer, a full-bridge circuit connected to the primary side of the transformer, and a full-bridge circuit on the secondary side of the transformer. The switches in the full-bridge circuit are all fully controlled devices and include body diodes.

[0033] The transformer in the dual-active-bridge circuit is a single-input single-output high-frequency transformer adapted to the switching frequency. Its primary side is connected to the full-bridge circuit I, including two terminals H1 and H2, and the secondary side is connected to the full-bridge circuit II, including two terminals X1 and X2, where H1 and X1 are the same-named terminals. The full-bridge circuit I contains two bridge arms, the first bridge arm and the second bridge arm, which are connected in parallel. The first bridge arm contains the upper-bridge-arm switch S1 and the lower-bridge-arm switch S2, and the second bridge arm contains the upper-bridge-arm switch S3 and the lower-bridge-arm switch S4. The coupling point of switch S1 and switch S2 is connected to terminal H1, and the coupling point of switch S3 and switch S4 is connected to terminal H2. The full-bridge circuit II contains two bridge arms, the third bridge arm and the fourth bridge arm, which are connected in parallel. The third bridge arm contains the upper-bridge-arm switch S5 and the lower-bridge-arm switch S6, and the fourth bridge arm contains the upper-bridge-arm switch S7 and the lower-bridge-arm switch S8. The coupling point of switch S5 and switch S6 is connected to terminal X1, and the coupling point of switch S7 and switch S8 is connected to terminal X2.

[0034] The anti-parallel thyristor structure I is connected in series between the positive pole of the DC port I and the Z-source network I. The thyristor Q1 and the thyristor Q2 are connected in parallel and have opposite directions. The anode of the thyristor Q1 is connected to the positive pole of the DC port I, and the cathode of the thyristor Q2 is connected to the positive pole of the DC port I.

[0035] The Z-source network I is connected between the thyristor structure I and the full-bridge circuit I on the primary side of the transformer. The inductor L1 is connected in series between the thyristor structure I and the coupling point of switch S1 and switch S3, and the inductor L1 is connected in series between the negative pole of the DC port I and the coupling point of switch S2 and switch S4. The capacitor C1 is connected between the thyristor structure I and the coupling point of switch S1 and switch S3, and the capacitor C2 is connected between the thyristor structure I and the coupling point of switch S2 and switch S4.

[0036] The anti-parallel thyristor structure II is connected in series between the positive pole of the DC port II and the Z-source network II. The thyristor Q3 and the thyristor Q4 are connected in parallel and have opposite directions. The cathode of the thyristor Q3 is connected to the positive pole of the DC port II, and the anode of the thyristor Q4 is connected to the positive pole of the DC port II.

[0037] The Z-source network II is connected between the thyristor structure II and the full-bridge circuit II on the primary side of the transformer. The inductor L3 is connected in series between the thyristor structure II and the coupling point of switch S5 and switch S7, and the inductor L4 is connected in series between the negative pole of the DC port II and the coupling point of switch S6 and switch S8. The capacitor C3 is connected between the thyristor structure II and the coupling point of switch S5 and switch S7, and the capacitor C4 is connected between the thyristor structure I and the coupling point of switch S6 and switch S8.

[0038] When the energy flows from the DC port I to the DC port II, the thyristor structure I, the Z-source network I and the full-bridge circuit I work as a Z-source converter, and the thyristor structure II, the Z-source network II and the full-bridge circuit II work as a Z-source circuit breaker.

[0039] The thyristor structure I, Z-source network I and full-bridge circuit I constitute the structure of the Z-source converter. A continuous conduction signal is given to thyristor Q1 to make it conduct forward, and its function is similar to that of a diode. No signal is given to thyristor Q2 to keep it in the off state. The conduction signals of switch S1 and switch S4 are the same, and the conduction signals of switch S2 and switch S3 are the same. Switch S1, switch S4 and switch S2, switch S3 conduct alternately at half of the switching period, i.e., Ts / 2, and their duty cycle D>0.5. When switches S1, S2, S3, and S4 are all conducting, direct-through boosting is utilized, and energy is transferred to II through a transformer.

[0040] The thyristor structure II, Z-source network II and full-bridge circuit II constitute the structure of the Z-source circuit breaker. A conduction signal is given to thyristor Q3 to make it conduct forward and turn off completely when the current reverses. No signal is given to thyristor Q4 to keep it in the off state. When a short-circuit fault occurs at DC port II, a new fault loop is added to the circuit. Due to the extremely low impedance of the fault loop, a large fault current will be generated here, affecting the reliability and safety of the circuit. Define the current direction flowing from the coupling point of switches S5 and S7 of the full-bridge circuit II to the Z-source network II as positive. The currents of Z-source inductors L3 and L4 generate a positive component here, and Z-source capacitors C3 and C4 discharge to generate a negative component here. The current here gradually decreases. When the current passes through zero, the body diodes of the right full-bridge circuit turn off naturally. Due to the disappearance of the current loop of the full-bridge circuit, the circuit cannot form a path, and the fault current drops to 0, and thyristor Q3 turns off.

[0041] When energy flows from DC port II to DC port I, the thyristor structure II, Z-source network II and full-bridge circuit II work as a Z-source converter, and the thyristor structure I, Z-source network I and full-bridge circuit I work as a Z-source circuit breaker. The working principle is similar to the above content and will not be elaborated here.

[0042] A specific application of this embodiment is:

[0043] The antiparallel thyristor structure is composed of two identical thyristors connected in antiparallel. The thyristors Q1 and Q2 on the left are connected in antiparallel and are connected in series at the positive pole of DC port V1. The thyristors Q3 and Q4 on the right are connected in antiparallel and are connected in series at the positive pole of DC port V2.

[0044] The Z-source network is composed of two inductors and two capacitors connected in an interleaved manner. Inductors L1, L2, capacitors C1, and C2 are connected in an interleaved manner to form the left Z-source network. Inductors L3, L4, capacitors C3, and C4 are connected in an interleaved manner to form the right Z-source network.

[0045] The dual-active-bridge circuit consists of switching devices and a high-frequency transformer. Both sides of the transformer are composed of full-bridge circuits. The switches S1, S2, S3, and S4 form the full-bridge circuit on the left side (the primary side of the transformer), and the switches S5, S6, S7, and S8 form the full-bridge circuit on the right side (the secondary side of the transformer).

[0046] The switches S1, S2, S3, S4, S5, S6, S7, and S8 are all IGBTs and contain internal body diodes.

[0047] When the energy flows in the forward direction (from the DC port V1 to the DC port V2), the thyristors, Z-source network, and full-bridge circuit on the left side work as a Z-source converter, and the thyristors, Z-source network, and full-bridge circuit on the right side work as a Z-source circuit breaker.

[0048] When the thyristors, Z-source network, and full-bridge circuit on the left side work as a Z-source converter, a continuous conduction signal is given to the thyristor Q1 to make it conduct forward. Its function is similar to that of a diode. No signal is given to the thyristor Q2 to keep it in the off state. The conduction signals of the switches S1 and S4 are the same, and the conduction signals of the switches S2 and S3 are the same. The switches S1, S4 and the switches S2, S3 conduct alternately at half of the switching period, that is, Ts / 2, and their duty cycle D>0.5.

[0049] According to the conduction situation of the full-bridge circuit, there are two working states: the inversion state and the direct-through zero state. In a switching period TS, the time of the inversion state is 2(1 - D)TS, and the time of the direct-through zero state is (2D - 1)TS.

[0050] When the full-bridge circuit is in the inversion state, as Figure 2 shown, that is, when the switches S1 and S4 (or the switches S2 and S3) conduct, the DC power at the DC port V1 is converted into high-frequency alternating current, and the energy is transmitted to the secondary side through the transformer. At this time, the voltage vp on the primary side of the transformer is the output voltage of the Z-source network on the left side.

[0051] When the full-bridge circuit is in the direct-through zero state, as Figure 3 shown, that is, when all the switches S1, S2, S3, and S4 conduct, the Z-source network boosts the voltage of the DC port V1. At this time, the voltage vp on the primary side of the transformer is 0, no current flows through the transformer, and the transformer does not work.

[0052] If the duty cycle D of the switches S1, S2, S3, and S4 is <0.5, there is a traditional zero state in the circuit, that is, when all the switches S1, S2, S3, and S4 do not conduct, the Z-source network cannot boost the voltage through direct-through. At this time, the voltage on the primary side of the transformer is 0, no current flows through the transformer, and the transformer does not work.

[0053] When the thyristor, Z-source network and full-bridge circuit on the right side work as a Z-source circuit breaker, a conduction signal is given to the thyristor Q3 to enable it to conduct forward and turn off completely when the current reverses. No signal is given to the thyristor Q4, keeping it in the off state all the time.

[0054] When the left Z-source converter operates in the inverter state, the high-frequency alternating current generated is rectified by the body diodes of the full-bridge circuit on the right side. The current alternately flows through the switches S5, S8 or the switches S6, S7 with a period of Ts / 2 and is converted into direct current.

[0055] When the left Z-source converter operates in the shoot-through zero state, the transformer does not work at this time. The current continues to flow through the body diodes of the full-bridge circuit on the secondary side, and the current forms a loop by flowing through the body diodes of the switches S5, S6, S7, S8.

[0056] When a short-circuit fault occurs at the DC port V2, as Figure 4 shown, a new fault loop is added to the circuit. Since the impedance of the fault loop is extremely low, a large fault current if will be generated here, affecting the reliability and safety of the circuit. However, at this time, due to the addition of a new fault loop, the Z-source capacitors C3 and C4 discharge, generating a reverse component in the current ifb (taking the left-to-right direction as the reference direction) flowing out of the full-bridge circuit on the right side. The current ifb gradually decreases. When the current ifb passes through zero, the body diodes of the full-bridge circuit on the right side turn off naturally. Due to the disappearance of the current loop of the full-bridge circuit, the circuit cannot form a path, and the fault current if drops to 0, and the thyristor Q3 turns off.

[0057] When the energy flows reversely (from the DC port V2 to the DC port V1), the thyristor, Z-source network and full-bridge circuit on the right side work as a Z-source converter, and the thyristor, Z-source network and full-bridge circuit on the left side work as a Z-source circuit breaker. Its working principle is similar to the above content and will not be elaborated here.

[0058] The Z-source bidirectional DC-DC converter proposed by the present invention, which has both the functions of a circuit breaker and voltage regulation, has bidirectional energy transfer and DC circuit breaker functions. The application of the transformer can achieve isolation between the input and output. At the same time, through the Z-source network and the transformer, a wide voltage regulation range can be achieved.

[0059] The preferred embodiments of the present invention disclosed above are only used to help illustrate the present invention. The preferred embodiments do not describe all the details in detail, nor do they limit the invention to only specific embodiments. Obviously, many modifications and variations can be made according to the content of this specification. These embodiments are selected and specifically described in this specification to better explain the principles and practical applications of the present invention, so that those skilled in the art can well understand and utilize the present invention. The present invention is only limited by the claims and their full scope and equivalents.

Claims

1. A Z-source bidirectional DC-DC converter with both circuit breaker and voltage regulation functions, characterized in that, The converter includes two anti-parallel thyristor structures, two Z-source networks and a dual active bridge circuit; The two anti-parallel thyristor structures are respectively denoted as anti-parallel thyristor structure I and anti-parallel thyristor structure II; The two Z-source networks are respectively denoted as Z-source network I and Z-source network II; The dual active bridge circuit includes a high-frequency transformer, and a full-bridge circuit is provided on each side of the dual active bridge circuit, which are respectively denoted as primary-side full-bridge circuit I and secondary-side full-bridge circuit II; The primary-side full-bridge circuit I is cascaded with the Z-source network I, the other side of the Z-source network I is connected in parallel with the DC terminal I, and the anti-parallel thyristor structure I is connected in series between the positive pole of the DC port I and the Z-source network I; the secondary-side full-bridge circuit II is cascaded with the Z-source network II, the other side of the Z-source network II is connected in parallel with the DC terminal II, and the anti-parallel thyristor structure II is connected in series between the positive pole of the DC port I and the Z-source network II.

2. The Z-source bidirectional DC-DC converter with both circuit breaker and voltage regulation functions according to claim 1, characterized in that, Each of the anti-parallel thyristor structures includes two anti-parallel thyristors.

3. The Z-source bidirectional DC-DC converter with both circuit breaker and voltage regulation functions according to claim 1, characterized in that, The high-frequency transformer is a single-input single-output transformer adapted to the switching frequency.

4. The Z-source bidirectional DC-DC converter with both circuit breaker and voltage regulation functions according to claim 1, characterized in that The full-bridge circuit is a full-bridge circuit with two bridge arms and four switches.

5. The Z-source bidirectional DC-DC converter with both circuit breaker and voltage regulation functions according to any one of claims 4, characterized in that The switching devices in the full-bridge circuit are all power electronic switching tubes with body diodes.

6. The Z-source bidirectional DC-DC converter with both circuit breaker and voltage regulation functions according to any one of claims 1-5, characterized in that, The converter can achieve bidirectional energy transfer and has both circuit breaker and voltage regulation functions; on the DC input side, the anti-parallel thyristor structure, the Z-source network and the full-bridge circuit work as a Z-source converter and boost the voltage through direct conduction; on the DC output side, the anti-parallel thyristor structure, the Z-source network and the full-bridge circuit work as a Z-source circuit breaker.

7. The Z-source bidirectional DC-DC converter with both circuit breaker and voltage regulation functions according to claim 6, characterized in that, On the DC input side, when the anti-parallel thyristor structure, the Z-source network and the full-bridge circuit work as a Z-source converter, they boost the voltage through direct conduction, invert through the full-bridge circuit, and are transmitted to the output-side full-bridge circuit through the transformer, and the body diodes of the full-bridge circuit rectify; in the direct-conduction state, the transformer does not work, the input voltage of the output-side full-bridge circuit is zero, and the current continues to flow through the body diodes of the full-bridge circuit.

8. The Z-source bidirectional DC-DC converter with both circuit breaker and voltage regulation functions according to claim 7, characterized in that, On the DC output side, when the anti-parallel thyristor structure, the Z-source network and the full-bridge circuit work as a Z-source circuit breaker, when a ground short-circuit fault occurs at the DC output port, a new fault loop is added to the circuit, and at this time the current flowing out of the full-bridge circuit directly grounds through the Z-source inductor; at the same time, due to direct grounding, the Z-source capacitor discharges, which is opposite to the direction of the Z-source inductor current, and a reverse current component is generated in the circuit, and the current flowing out of the full-bridge circuit gradually decreases until the current passes through zero, and the body diodes of the full-bridge circuit turn off naturally; due to the disappearance of the current loop of the full-bridge circuit, the circuit cannot form a path, the fault current drops to 0, and the thyristor turns off.

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