Self-healing DC system with intelligent bus undervoltage compensation function

Abstract

The self-healing DC system with intelligent bus undervoltage compensation function includes two interconnected DC systems, 1# and 2#. A bidirectional DC-DC compensator DC1 is installed between the power supply DC buses. The bidirectional DC-DC compensator DC1 consists of three modules B1, B2 and B3, each containing an H-bridge. The H-bridges in module B3 are connected by an isolation transformer T1. Through the fixed turns ratio and bidirectional flow of the isolation transformer T1, combined with the current flow direction control of module B1 / module B2, bidirectional compensation between the two DC systems is achieved. Furthermore, module B3 implements zero-current switching (ZCS), and module B1 / module B2 implements zero-voltage switching (ZVS), thereby avoiding high-voltage spikes in the MOSFETs within the H-bridges. This system is suitable for high-power DC power supply systems.

Description

Technical Field

[0001] This invention relates to the field of DC system technology for substations, and specifically to a self-healing DC system with intelligent bus undervoltage compensation function. Background Technology

[0002] Taking the DC system of a substation as an example, to ensure the continuous operation of its power supply equipment, it is usually equipped with two busbars. The two busbars at both ends are continuously powered by two chargers and battery banks respectively. When one of the busbars fails and loses voltage, the bus coupler switch between the two busbars is closed, so that the busbar that has not lost voltage provides power to the busbar that has lost voltage, ensuring the stable operation of the load on both busbars. However, since the chargers and battery banks of the two busbars operate independently, the voltage value of the two busbars is determined by their respective chargers and battery banks. The voltage values ​​of the two busbars may be unequal, and the voltage of one of them may exceed the threshold. At this time, since the load on the busbar can still work normally, it may cause the load to be unstable or reduce the life of the load equipment.

[0003] To address the aforementioned issues, a voltage undervoltage compensation device is employed between the two busbars. For instance, Chinese patent document CN211351821U describes a battery pack open-circuit monitoring and voltage undervoltage compensation device. This device uses an H-bridge circuit between the two busbars, with the H-bridge achieving electrical isolation through transformer mutual inductance coils. This allows for voltage compensation from the other busbar when one busbar experiences voltage undervoltage, thus achieving electrical isolation. During compensation, there is no direct hardware connection between the two busbars, and a fault in one busbar can be promptly disconnected from the other busbar by turning off a MOSFET, resulting in high safety.

[0004] When the two busbars are connected to an H-bridge, the leakage inductance of the mutual inductance coils will cause high voltage spikes in the switching MOSFETs. This means that the H-bridge can only be used as a DC-DC converter in small substations. When there are many DC loads in large substations, the MOSFETs of the H-bridge will be subjected to large voltage surges. Summary of the Invention

[0005] The technical problem to be solved by the present invention is to provide a self-healing DC system with intelligent bus undervoltage compensation function, which can form high-efficiency voltage compensation between two DC buses of a high-power DC system.

[0006] To solve the above-mentioned technical problems, the technical solution adopted by the present invention is as follows:

[0007] The self-healing DC system with intelligent bus undervoltage compensation function includes two interconnected DC systems, #1 and #2.

[0008] The No. 1 DC system is equipped with power supply DC bus KM1+ and KM1-;

[0009] The No. 2 DC system is equipped with power supply DC bus KM2+ and KM2-;

[0010] A bidirectional DC-DC compensator DC1 is installed between the power supply DC bus KM1+, KM1- and DC bus KM2+, KM2-. The two ends of the bidirectional DC-DC compensator DC1 are connected to DC bus #1 and DC bus #2 respectively.

[0011] The aforementioned bidirectional DC-DC compensator DC1 is controlled by controller U1;

[0012] Voltage detection devices 1DV3 and 2DV3 are respectively installed on the DC power supply bus KM1+, KM1- and the DC power supply bus KM2+, KM2-;

[0013] Voltage detection devices 1DV3 and 2DV3 are electrically connected to the input terminal of controller U1.

[0014] The aforementioned bidirectional DC-DC compensator DC1 consists of three modules B1, B2, and B3, each containing an H-bridge. The H-bridges within module B3 are connected by an isolation transformer T1. One end of the H-bridge in module B1 is electrically connected to the power supply DC bus KM1+ and KM1-. ​​The other end of the H-bridge in module B1 is electrically connected to one end of the H-bridge in module B2. The other end of the H-bridge in module B2 is also electrically connected to the power supply DC bus KM1+ and KM1-. ​​The positive and negative terminals of the connection points of the H-bridges in modules B1 and B2 are connected to the input terminals of the H-bridges in module B3. The output terminals of the H-bridges in module B3 are connected to the power supply DC bus KM2+ and KM2-.

[0015] The H-bridge in module B3 is composed of MOSFETs Q9-Q12. The two ends of MOSFETs Q9 and Q10 are electrically connected to the positive and negative terminals of the H-bridge in module B1 and the H-bridge in module B2. The series capacitors C6 and C7 are connected in parallel with the two ends of MOSFETs Q9 and Q10. One end of the primary coil of the isolation transformer T1 is connected to the midpoint of MOSFETs Q9 and Q10, and the other end is connected to the midpoint of capacitors C6 and C7.

[0016] The secondary coil of isolation transformer T1 is divided into two sections with the midpoint as the boundary. The upper and lower ends of the secondary coil are connected in series with MOSFETs Q11 and Q12 of the H-bridge, respectively. The other ends of MOSFETs Q11 and Q12 are connected in parallel and then electrically connected to the DC power supply bus KM2+. The midpoint of the secondary coil of isolation transformer T1 is electrically connected to the DC power supply bus KM2-.

[0017] The primary coil of the aforementioned isolation transformer T1 is connected in series with capacitor C8. The two ends of the primary coil and capacitor C8 are electrically connected to the midpoint of MOSFETs Q9 and Q10 and the midpoint of capacitors C6 and C7, respectively.

[0018] The connection terminals of module B3 with the power supply DC bus KM2+ and KM2- are equipped with capacitor C9, and the connection terminals of module B3 with modules B1 / B2 are equipped with capacitor C5.

[0019] The H-bridge in module B1 is composed of MOSFETs Q1-Q4. MOSFETs Q1 and Q2 are connected in series, and MOSFETs Q3 and Q4 are connected in series. An inductor L1 is provided between the midpoints of the two series branches. The two ends of MOSFETs Q3 and Q4 are electrically connected to module B2.

[0020] The H-bridge in module B2 is composed of MOSFETs Q5-Q8. MOSFETs Q5 and Q6 are connected in series, and MOSFETs Q7 and Q8 are connected in series. An inductor L2 is provided between the midpoints of the two series branches. The two ends of MOSFETs Q7 and Q8 are electrically connected to module B1.

[0021] The connection section between module B1 and the power supply DC bus KM1+ and KM1- is equipped with capacitor C1, and the connection end between module B1 and module B3 is equipped with capacitor C3.

[0022] The connection section between module B2 and the power supply DC bus KM1+ and KM1- is equipped with capacitor C3, and the connection end between module B2 and module B3 is equipped with capacitor C4.

[0023] This invention provides a self-healing DC system with intelligent bus undervoltage compensation. It involves installing modules B1 and B2 (containing an H-bridge) on the bus side of one DC system, and module B3 (containing an H-bridge and an isolation transformer T1) on the bus side of another DC system. The fixed turns ratio and bidirectional flow of the isolation transformer T1, combined with the current flow control of modules B1 and B2, enable bidirectional compensation between the two DC systems. Furthermore, module B3 implements zero-current switching (ZCS), and zero-voltage switching (ZVS) is implemented at modules B1 and B2, thereby avoiding high-voltage spikes in the MOSFETs within the H-bridge. This system is suitable for high-power DC power supply systems. Attached Figure Description

[0024] The present invention will be further described below with reference to the accompanying drawings and embodiments:

[0025] Figure 1 This is a simplified circuit diagram of the DC system of the present invention;

[0026] Figure 2 This is a circuit diagram of the bidirectional DC-DC compensator DC1;

[0027] Figure 3 This is a schematic diagram of the bidirectional flow of the primary and secondary resonant currents within module B3. Detailed Implementation

[0028] like Figure 1-3 As shown, the self-healing DC system with intelligent bus undervoltage compensation function includes two interconnected DC systems 1# and 2#.

[0029] The No. 1 DC system is equipped with power supply DC bus KM1+ and KM1-;

[0030] The No. 2 DC system is equipped with power supply DC bus KM2+ and KM2-;

[0031] A bidirectional DC-DC compensator DC1 is installed between the power supply DC bus KM1+, KM1- and DC bus KM2+, KM2-. The two ends of the bidirectional DC-DC compensator DC1 are connected to DC bus #1 and DC bus #2 respectively.

[0032] The aforementioned bidirectional DC-DC compensator DC1 is controlled by controller U1;

[0033] Voltage detection devices 1DV3 and 2DV3 are respectively installed on the DC power supply bus KM1+, KM1- and the DC power supply bus KM2+, KM2-;

[0034] Voltage detection devices 1DV3 and 2DV3 are electrically connected to the input terminal of controller U1.

[0035] The aforementioned bidirectional DC-DC compensator DC1 consists of three modules B1, B2, and B3, each containing an H-bridge. The H-bridges within module B3 are connected by an isolation transformer T1. One end of the H-bridge in module B1 is electrically connected to the power supply DC bus KM1+ and KM1-. ​​The other end of the H-bridge in module B1 is electrically connected to one end of the H-bridge in module B2. The other end of the H-bridge in module B2 is also electrically connected to the power supply DC bus KM1+ and KM1-. ​​The positive and negative terminals of the connection points of the H-bridges in modules B1 and B2 are connected to the input terminals of the H-bridges in module B3. The output terminals of the H-bridges in module B3 are connected to the power supply DC bus KM2+ and KM2-.

[0036] The isolation transformer T1 in module B3 enables electrical isolation between the power supply DC bus KM1+, KM1- and the power supply DC bus KM2+, KM2-, and allows bidirectional current flow between the buses. It can supply power from DC system 1 to DC system 2, and vice versa.

[0037] Meanwhile, the H-bridge connection structure of module B1 / module B2 can achieve precise voltage regulation by adjusting the duty cycle of the internal H-bridge MOSFETs. When the 1# DC system supplies power to the 2# DC system, the power supply DC bus KM1+ and KM1- serve as the input terminals of module B1, and module B3 provides power to the power supply DC bus KM2+ and KM2-. When the 2# DC system supplies power to the 1# DC system, the power supply DC bus KM2+ and KM2- serve as the input terminals of module B3, and module B2 provides power to the DC bus KM1+ and KM1-.

[0038] The H-bridge in module B3 is composed of MOSFETs Q9-Q12. The two ends of MOSFETs Q9 and Q10 are electrically connected to the positive and negative terminals of the H-bridge in module B1 and the H-bridge in module B2. The series capacitors C6 and C7 are connected in parallel with the two ends of MOSFETs Q9 and Q10. One end of the primary coil of the isolation transformer T1 is connected to the midpoint of MOSFETs Q9 and Q10, and the other end is connected to the midpoint of capacitors C6 and C7.

[0039] The secondary coil of isolation transformer T1 is divided into two sections with the midpoint as the boundary. The upper and lower ends of the secondary coil are connected in series with MOSFETs Q11 and Q12 of the H-bridge, respectively. The other ends of MOSFETs Q11 and Q12 are connected in parallel and then electrically connected to the DC power supply bus KM2+. The midpoint of the secondary coil of isolation transformer T1 is electrically connected to the DC power supply bus KM2-.

[0040] The isolation transformer T1 in module B3 has the function of electrically isolating the two ends of the bidirectional DC-DC compensator DC1, and the primary and secondary coils can be bidirectionally switched, so that DC1 has bidirectional voltage conversion capability and current can flow bidirectionally. At the same time, the fixed turns ratio of the primary and secondary coils of the isolation transformer T1, together with the switching of MOSFETs Q9-Q12, provides a fixed ratio of voltage rise and fall.

[0041] The primary coil of the aforementioned isolation transformer T1 is connected in series with capacitor C8. The two ends of the primary coil and capacitor C8 are electrically connected to the midpoint of MOSFETs Q9 and Q10 and the midpoint of capacitors C6 and C7, respectively.

[0042] By adding a small capacitor C8 on the primary coil side, the self-resonant frequency of capacitor C8 can provide zero-current switching ZCS with the leakage inductance of isolation transformer T1. That is, by utilizing the inherent resonant frequency of the current on the primary coil side of isolation transformer T1, the MOSFET of module B3 can switch at zero point at its resonant part. When the resonant current reaches zero, Q9-Q12 will always be on and off. Specifically, the operating mode of module B3, taking the DC system from 1# to 2# as an example, when Q9 and Q11 are on, that is, during the period from t1 to t2, the primary side resonant current I3 flows in the form of a sine wave until it reaches zero. After that, Q10 and Q12 will be on, that is, during the period from t2 to t3, and the primary side resonant current I3 still maintains the shape of a sine wave and flows in the opposite direction.

[0043] The switching loss of the bidirectional DC-DC compensator DC1 is close to zero, so the switches in modules B1-B3 can operate at extremely high switching frequencies, achieving extremely high power density. Furthermore, it achieves complete zero-current switching (ZCS) on the secondary coil and partial ZCS on the primary coil.

[0044] The connection terminals of module B3 with the power supply DC bus KM2+ and KM2- are equipped with capacitor C9, and the connection terminals of module B3 with modules B1 / B2 are equipped with capacitor C5.

[0045] The H-bridge in module B1 is composed of MOSFETs Q1-Q4. MOSFETs Q1 and Q2 are connected in series, and MOSFETs Q3 and Q4 are connected in series. An inductor L1 is provided between the midpoints of the two series branches. The two ends of MOSFETs Q3 and Q4 are electrically connected to module B2.

[0046] The H-bridge in module B2 is composed of MOSFETs Q5-Q8. MOSFETs Q5 and Q6 are connected in series, and MOSFETs Q7 and Q8 are connected in series. An inductor L2 is provided between the midpoints of the two series branches. The two ends of MOSFETs Q7 and Q8 are electrically connected to module B1.

[0047] The connection section between module B1 and the power supply DC bus KM1+ and KM1- is equipped with capacitor C1, and the connection end between module B1 and module B3 is equipped with capacitor C2.

[0048] The connection section between module B2 and the power supply DC bus KM1+ and KM1- is equipped with capacitor C3, and the connection end between module B2 and module B3 is equipped with capacitor C4.

[0049] Modules B1 and B2 provide precise voltage regulation and stabilization. B1 and B2 have the same structure and provide bidirectional compensation voltage and current in the power supply system. Therefore, their current directions are opposite, and the current direction is formed by the switching of the MOSFETs in the internal H-bridge. When one busbar supplies power to another busbar, the voltage of the powered busbar can be steadily increased by adjusting the duty cycle of modules B1 and B2, instead of directly increasing to the voltage of the supply busbar. This achieves flexible voltage boost, allowing the load sufficient response time and reducing the current surge caused by sudden voltage increase.

[0050] During the conversion process of module B1 / module B2, the controller U1 can be placed in the zero voltage switch boost / drop control mode to achieve zero voltage conversion. Due to the use of zero voltage switch ZVS, high efficiency and high power density can be achieved in module B1 / module B2.

Claims

1. A self-healing DC system with intelligent bus undervoltage compensation function, comprising two interconnected DC systems 1# and 2#, characterized in that: The No. 1 DC system is equipped with power supply DC bus KM1+ and KM1-; The No. 2 DC system is equipped with power supply DC bus KM2+ and KM2-; A bidirectional DC-DC compensator DC1 is installed between the power supply DC bus KM1+, KM1- and DC bus KM2+, KM2-. The two ends of the bidirectional DC-DC compensator DC1 are connected to DC bus #1 and DC bus #2 respectively. The bidirectional DC-DC compensator DC1 is controlled by controller U1; Voltage detection devices 1DV3 and 2DV3 are respectively installed on the DC power supply bus KM1+, KM1- and the DC power supply bus KM2+, KM2-; Voltage detection devices 1DV3 and 2DV3 are electrically connected to the input terminal of controller U1; The bidirectional DC-DC compensator DC1 consists of three modules B1, B2, and B3, each containing an H-bridge. The H-bridges within module B3 are connected by an isolation transformer T1. One end of the H-bridge in module B1 is electrically connected to the power supply DC bus KM1+ and KM1-. ​​The other end of the H-bridge in module B1 is electrically connected to one end of the H-bridge in module B2. The other end of the H-bridge in module B2 is also electrically connected to the power supply DC bus KM1+ and KM1-. ​​The positive and negative terminals of the connection points of the H-bridges in modules B1 and B2 are connected to the input terminals of the H-bridges in module B3. The output terminals of the H-bridges in module B3 are connected to the power supply DC bus KM2+ and KM2-. The H-bridge in module B3 is composed of MOSFETs Q9-Q12. The two ends of MOSFETs Q9 and Q10 are electrically connected to the positive and negative terminals of the H-bridge in module B1 and the H-bridge in module B2. The series capacitors C6 and C7 are connected in parallel with the two ends of MOSFETs Q9 and Q10. One end of the primary coil of the isolation transformer T1 is connected to the midpoint of MOSFETs Q9 and Q10, and the other end is connected to the midpoint of capacitors C6 and C7. The secondary coil of isolation transformer T1 is divided into two sections with the midpoint as the boundary. The upper and lower ends of the secondary coil are connected in series with MOSFETs Q11 and Q12 of the H-bridge, respectively. The other ends of MOSFETs Q11 and Q12 are connected in parallel and then electrically connected to the DC power supply bus KM2+. The midpoint of the secondary coil of isolation transformer T1 is electrically connected to the DC power supply bus KM2-.

2. The self-healing DC system with intelligent bus undervoltage compensation function according to claim 1, characterized in that, The primary coil of the isolation transformer T1 is connected in series with capacitor C8. The two ends of the primary coil and capacitor C8 are electrically connected to the midpoint of MOSFETs Q9 and Q10 and the midpoint of capacitors C6 and C7, respectively.

3. The self-healing DC system with intelligent bus undervoltage compensation function according to claim 2, characterized in that, The connection terminals of module B3 with the power supply DC bus KM2+ and KM2- are equipped with capacitor C9, and the connection terminals of module B3 with modules B1 / B2 are equipped with capacitor C5.

4. The self-healing DC system with intelligent bus undervoltage compensation function according to claim 3, characterized in that, The H-bridge in module B1 is composed of MOSFETs Q1-Q4. MOSFETs Q1 and Q2 are connected in series, and MOSFETs Q3 and Q4 are connected in series. An inductor L1 is provided between the midpoints of the two series branches. The two ends of MOSFETs Q3 and Q4 are electrically connected to module B2. The H-bridge in module B2 is composed of MOSFETs Q5-Q8. MOSFETs Q5 and Q6 are connected in series, and MOSFETs Q7 and Q8 are connected in series. An inductor L2 is provided between the midpoints of the two series branches. The two ends of MOSFETs Q7 and Q8 are electrically connected to module B1.

5. The self-healing DC system with intelligent bus undervoltage compensation function according to claim 4, characterized in that, The connection section between module B1 and the power supply DC bus KM1+ and KM1- is equipped with capacitor C1, and the connection end between module B1 and module B3 is equipped with capacitor C3. The connection section between module B2 and the power supply DC bus KM1+ and KM1- is equipped with capacitor C3, and the connection end between module B2 and module B3 is equipped with capacitor C4.

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