Novel direct current energy consumption device adopting active buffer circuit, control method and application

Abstract

The application provides a novel direct current energy consumption device with an active buffer circuit, comprising a plurality of active buffer circuit modules and an energy consumption resistor; the energy consumption resistor is connected in series with the plurality of active buffer circuit modules and is connected in parallel between the positive and negative poles of a direct current bus. The application introduces active devices on the basis of the idea of traditional buffer circuits and proposes a novel direct current energy consumption device combined with an active buffer circuit. The active control of the capacitor voltage is realized through thyristors, so that the turn-off loss is greatly reduced without changing the switching loss.

Description

Technical Field

[0001] This invention relates to the problem of wind farm fault ride-through under flexible DC transmission, specifically to a novel DC energy dissipation device, control method, and application using an active buffer circuit. Background Technology

[0002] In flexible DC transmission, wind farms face fault ride-through issues. When a grid-side low-voltage fault occurs, the AC voltage drop reduces the power transmission capacity of the receiving-end converter station, while the wind farm's input power remains unchanged, leading to a power surplus and system overvoltage. In severe cases, wind turbines may disconnect from the grid. In extreme cases, when the three-phase AC voltage at the receiving end drops to 0, the system completely loses its power transmission capacity. The only recourse is to install energy-dissipating devices or shut down the wind turbines to prevent damage to equipment such as converter valves from the high voltage.

[0003] The fundamental reason for the high turn-off losses in solid-state switches is that they are not ideal components; there is an overlap between voltage and current, and the turn-off time for hundreds of amps is only 3–5 μs. Therefore, the key to reducing turn-off losses lies in introducing capacitors to reduce the voltage rise rate and minimize the voltage-current overlap.

[0004] Figure 1 This demonstrates a commonly used buffer circuit scheme for existing solid-state switches. Figure 1 (a) The paper "Analytical Method for RC Snubber Optimization Design to Eliminate Switching Oscillations of SiC MOSFET" published by X. Yang, M. Xu, Q. Li, Z. Wang and M. He in April 2022, Volume 37, Issue 4 of IEEE Transactions on Power Electronics, proposes an RC snubber circuit. This circuit, by adding an RC circuit, causes the current to drop rapidly when the solid-state switch is turned off, and then charges the capacitor, thereby reducing the voltage change rate of the solid-state switch and lowering losses. However, to ensure that the capacitor voltage is zero before each turn-off, the snubber circuit has a small snubber resistance value, resulting in inrush current during the turn-on process, thus increasing the device's turn-on losses. Furthermore, due to the inductance in the DC system, the capacitor may resonate with the system's inductance after the device is turned off. Therefore, the RC snubber circuit is generally used in low-voltage, small-capacity solid-state switches.

[0005] To overcome the shortcomings of RC circuits and enable buffer circuits to be applied to high-voltage and high-power scenarios, RCD circuits were proposed.

[0006] Figure 1(b) In their revisited paper "RCD snubber," published in IEEE Transactions on Industry Applications, Vol. 32, No. 1, January-April 1996, SJ Finney, BW Williams, and TC Green proposed an RCD circuit using a diode in parallel with a large resistor, which is then connected in series with a capacitor. The large resistor suppresses the inrush current during the turn-on process of the solid-state switch. However, due to the use of a large resistor, the capacitor discharges slowly. If a high voltage exists on the capacitor when the solid-state switch is turned off, its buffering effect is greatly weakened. Furthermore, the losses in the buffer circuit caused by the large resistor also need to be considered during the design.

[0007] Figure 1 (c) In their paper "A Novel Solid-State Switch Scheme With High Voltage Utilization Efficiency by Using Modular Gapped MOV for DC Breakers" published in IEEE Transactions on Power Electronics, Vol. 37, No. 3, March 2022, K. Liu, X. Zhang, L. Qi, X. Qu and G. Tang proposed an RCD circuit that reduces the buffer circuit loss caused by the large resistance in the Type IRCD circuit by connecting resistors in parallel with both sides of the capacitor and diode. It has been widely used in high-voltage, high-capacity solid-state switches. However, it still has the defect that the capacitor has a high voltage when the solid-state switch is turned off. Since DC circuit breakers only operate once in the event of a fault, this defect can be ignored.

[0008] Furthermore, it is common knowledge in the field that RC circuits are not suitable for high-voltage, high-power scenarios, and RCD circuits are not suitable for scenarios involving multiple operations of solid-state switching devices. Because DC power dissipation devices employ pulse width modulation during fault ride-through, not only do the solid-state switches operate continuously for 1.5–2.5 seconds during the fault period, but their duty cycle also varies with the surplus power to be absorbed, ranging from 0% to 100%. Therefore, traditional buffer circuit solutions are unsuitable for DC power dissipation devices, necessitating the development of new solutions. Summary of the Invention

[0009] To overcome the shortcomings of the prior art, this invention provides a novel DC power dissipation device employing an active buffer circuit, comprising several active buffer circuit modules and a power dissipation resistor. The power dissipation resistor is connected in series with the active buffer circuit modules and then in parallel between the positive and negative terminals of the DC bus. The specific technical solution is as follows:

[0010] A novel DC power dissipation device employing an active buffer circuit includes several active buffer circuit modules 1 and a power dissipation resistor 2; characterized in that: the power dissipation resistor 2 is connected in series with several active buffer circuit modules 1 and then connected in parallel between the positive and negative terminals of the DC bus; the active buffer circuit module 1 is composed of a solid-state switch and an active buffer circuit connected in parallel.

[0011] Preferably, the solid-state switch includes a power semiconductor switching transistor 3 and an anti-parallel diode 4; the input terminal of the solid-state switch is connected to the collector of the power semiconductor switching transistor 3, and its output terminal is connected to the emitter of the power semiconductor switching transistor 3; the cathode of the anti-parallel diode 4 is connected to the emitter of the power semiconductor switching transistor 3, and its anode is connected to the collector of the power semiconductor switching transistor 3.

[0012] Preferably, the power semiconductor switch is an IGBT.

[0013] Preferably, the active buffer circuit includes a diode 5, a thyristor 7, a capacitor 6, a resistor 8, and a resistor 9; the input terminal of the active buffer circuit is connected to the anode of the diode 5, and the cathode of the diode 5 is connected to the anode of the thyristor 7; the cathode of the thyristor 7 is connected to the inductor 8, the inductor 8 is connected in series with the resistor 9, and the thyristor 7, inductor 8, and resistor 9 are connected in parallel with the capacitor; the other end of the resistor 9 is connected to the output terminal of the active buffer circuit.

[0014] The present invention also discloses a novel DC power dissipation method using an active buffer circuit.

[0015] Beneficial effects

[0016] The technical solution provided by this invention ingeniously incorporates active devices while drawing upon the concept of traditional buffer circuits, proposing a novel DC power dissipation device that combines an active buffer circuit. Active control of the capacitor voltage is achieved through thyristors, thereby significantly reducing turn-off losses without altering switching losses. Attached Figure Description

[0017] Figure 1 These are electrical topologies of two existing DC power-consuming devices.

[0018] Figure 2 This is an electrical topology diagram of a novel DC power dissipation device using an active buffer circuit, provided by the present invention.

[0019] Figure 3 This is a control diagram of the fault ride-through process of a novel DC power dissipation device using an active buffer circuit, provided by the present invention.

[0020] in Figure 2In the diagram: 1 is an active buffer circuit module, 2 is a power dissipation resistor, 3 is a power semiconductor switch, 4 is an anti-parallel diode, 5 is a diode (D), and 6 is a buffer capacitor (C). s ), 7 is thyristor (S), 8 is inductor (L), 9 is resistor (R) s ). Detailed Implementation

[0021] Below, we examine an existing technology, such as a utility model patent published by Tsinghua University (publication number: CN212392806U; invention patent application publication number: CN111525531A), which discloses a DC power dissipation device containing an inter-electrode capacitor, and provides a device containing an inter-electrode capacitor C. d A DC power dissipation device, the DC power dissipation device comprising: an inter-electrode capacitor C d Power electronic switch module S P Resistance R, S P S is formed by connecting it in series with resistor R. P -R series structure, S P One end of the capacitor is connected to one end of the resistor R; the inter-electrode capacitor C d With the S P -R series structure in parallel, the power electronic switch module S P The other end is connected to the inter-electrode capacitor C d One end of the resistor R is connected to the other end of the inter-electrode capacitor C. d At the other end, the S P -R series structure constitutes the inter-electrode capacitor C d Voltage regulator circuit; S P It includes one or more switch submodules connected in series.

[0022] Compared to the prior art, this invention adds an inductor to the active buffer circuit of its topology, so that after the capacitor is fully discharged, the thyristor can be quickly turned off under reverse voltage, thereby preventing the slow turn-off of the thyristor from limiting the operating frequency of the entire DC power consumption device to kHz.

[0023] Please refer to Figure 2This invention provides a novel DC power dissipation device employing an active buffer circuit, comprising: several active buffer circuit modules and a power dissipation resistor. The power dissipation resistor is connected in series with the active buffer circuit modules and then in parallel between the positive and negative terminals of a DC bus. Each active buffer circuit module consists of a solid-state switch and an active buffer circuit connected in parallel; the solid-state switch includes a power semiconductor switching transistor and an anti-parallel diode. The input terminal of the solid-state switch is connected to the collector of the power semiconductor switching transistor, and its output terminal is connected to the emitter of the power semiconductor switching transistor; the anode of the anti-parallel diode is connected to the emitter of the power semiconductor switching transistor, and its cathode is connected to the collector of the power semiconductor switching transistor. The active buffer circuit includes a diode, a thyristor, a capacitor, an inductor, and a resistor. The input terminal of the active buffer circuit is connected to the anode of the power diode, and its cathode is connected to the anode of the thyristor; the thyristor is connected in series with the resistor and then in parallel with the capacitor, with the cathode of the thyristor connected to the resistor; the other end of the resistor is connected to the output terminal of the active buffer circuit.

[0024] The power semiconductor switch is an IGBT; the addition of diodes is to prevent stray inductance on the line from causing capacitor oscillation.

[0025] The active buffer circuit module 1 is composed of a solid-state switch and an active buffer circuit connected in parallel. It can effectively reduce the loss of the solid-state switch by controlling the thyristor to turn on and off, so that the capacitor charging can share the current when the solid-state switch is turned off.

[0026] Functions of each component in the device: Components 3 and 4 constitute a solid-state switch, which is the core equipment for fault ride-through in offshore wind power VSC-HVDC systems; Components 5, 6, 7, 8, and 9 form a buffer circuit to reduce the losses of the solid-state switch; the addition of the diode in component 5 is used to prevent stray inductance on the line from causing capacitor oscillation; the capacitor in component 6 absorbs electrical energy, reduces the voltage rise rate of the device, and minimizes the overlap area of ​​voltage and current; the thyristor in component 7 is used to control the connection and disconnection of the resistor in component 8; the inductor in component 8 is used to buffer energy changes, allowing the thyristor to withstand reverse voltage and accelerate the thyristor turn-off process; the resistor in component 9 is used to dissipate the energy in the capacitor so that it can absorb electrical energy again when the solid-state switch is turned off to reduce the voltage rise rate of the device.

[0027] The buffer circuits mentioned in the background technology include: RC buffer circuits experience inrush current during the turn-on process of solid-state switches, increasing the turn-on losses of the devices. Furthermore, due to the inductance in the DC system, the capacitor resonates with the system inductance after the device is turned off. Therefore, RC buffer circuits are generally used in low-voltage, small-capacity solid-state switches. RCD buffer circuits use large resistors, resulting in slow capacitor discharge. If a high voltage exists on the capacitor when the solid-state switch is turned off, its buffering effect is greatly weakened, and the large resistance also leads to high losses in the buffer circuit. Even with improvements, RCD buffer circuits are not suitable for scenarios involving repeated operation of solid-state switching devices. These shortcomings are all addressed in new DC power dissipation devices employing active buffer circuits.

[0028] To further illustrate this invention, its working principle is now described in detail:

[0029] When the offshore wind power system is operating normally, the energy-consuming device is not working and is in the off state, and the voltage of the buffer capacitor Cs is equal to the voltage across the solid-state switch.

[0030] When a system fault occurs and the solid-state switch is turned on, the thyristor is turned on to discharge the buffer resistor. When the voltage of the buffer resistor is 0, the thyristor is turned off.

[0031] When the solid-state switch is turned off, the current flowing through the solid-state switch will quickly become 0, and then charge Cs. Since the initial voltage of Cs is 0, it will slowly rise.

[0032] By using an active buffer circuit, the turn-off loss is significantly reduced because the capacitor reduces the rate of voltage change during turn-off.

[0033] Furthermore, the thyristor is turned on to discharge the capacitor only after the solid-state switch is fully turned on, avoiding problems such as incomplete capacitor discharge or increased switching losses caused by traditional buffer circuits.

[0034] The advantage of this invention is that it can actively control the turn-on and turn-off of the thyristor to control the start time of capacitor discharge, and ensure that the capacitor voltage is 0 before turn-off, thereby ensuring that the reduction of turn-off loss in actual operation can achieve the expected effect, while avoiding additional losses.

[0035] Please refer to Figure 3 The device control process is divided into four stages: 0-t0 is the normal operation of the system, with the IGBT off; t0-t1 is the IGBT turn-on process, during which the device starts operating; t2 triggers the thyristor, the resistor absorbs the capacitor energy, and t3-t4 the thyristor withstands reverse voltage and quickly turns off; t5 is the voltage return to the set value, the IGBT turns off, and the capacitor charges. The control process is now described in detail according to the timing sequence:

[0036] During the 0-t0 period, the IGBT is in the off state and it withstands the operating voltage (U). rateAt this time, the IGBT current (U) IGBT When the voltage is 0, the capacitor voltage (U) Cs The voltage is equal to that of the IGBT.

[0037] At time t0, the IGBT receives the turn-on signal. During the period t0-t1, U... IGBT Rapidly reduce to the on-state voltage drop, I IGBT Increase to operating current (I rate Due to the presence of the diode, U Cs The diode voltage (U) remains unchanged. D ) and U Cs Conversely, at time t1, the IGBT is fully turned on;

[0038] At time t2, the IGBT is still in the ON state. At this time, the thyristor (S) is triggered, and the capacitor C... s Discharge causes the capacitor voltage to drop, which is... ;

[0039] At time t3, capacitor C s When the voltage drops to negative and the capacitor withstands reverse voltage, it stops discharging.

[0040] At time t4, the thyristor is quickly turned off;

[0041] At time t5, the DC power consumption device continuously monitors the DC voltage. When the DC voltage drops to a set value, the power semiconductor switch turns off. The current flowing through the IGBT decreases rapidly, and the current flowing through the capacitor I... C The voltage rises, charging Cs. When the IGBT is completely turned off, the system voltage continues to charge Cs, causing the capacitor voltage to rise.

[0042] (C s For capacitor 6, the capacitance value is R. s (for resistor 8 resistance value), until U Cs Reaching U rate .

[0043] This invention addresses the shortcomings of existing DC power dissipation devices in engineering, namely high turn-off losses and high costs associated with solid-state switches. This patent proposes a novel DC power dissipation device using an active buffer circuit. Through the coordinated operation of the thyristor-resistor and diode-capacitor in the buffer circuit, the losses of the solid-state switch are significantly reduced. Its advantage lies in its ability to actively control the start time of capacitor discharge according to the duty cycle requirements of the solid-state switch, ensuring that the capacitor voltage is 0 before turn-off. This guarantees that the reduction in turn-off losses in actual operation achieves the expected effect, while avoiding additional losses. Compared to traditional buffer circuit solutions, this DC power dissipation device is suitable for pulse width modulation during fault ride-through. Not only does the solid-state switch operate continuously for 1.5–2.5 seconds during the fault period, but its duty cycle also varies with the surplus power to be absorbed, changing from 0% to 100% operating scenarios. Furthermore, the novel DC power dissipation device using the active buffer circuit proposed in this invention can significantly reduce the cost of solid-state switches, providing a low-cost, high-reliability solution for fault ride-through of offshore wind power VSC-HVDC systems.

[0044] The foregoing has shown and described the basic principles, main features, and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The embodiments and descriptions in the specification are merely principles of the invention. Various changes and modifications can be made to the invention without departing from its spirit and scope, and all such changes and modifications fall within the scope of the claimed invention. The scope of protection claimed by the appended claims and their equivalents is defined.

Claims

1. A novel DC energy dissipation method employing an active buffer circuit, comprising a novel DC energy dissipation device employing an active buffer circuit, the device comprising a plurality of active buffer circuit modules and an energy dissipation resistor; the energy dissipation resistor is connected in series with the plurality of active buffer circuit modules and then connected in parallel between the positive and negative terminals of a DC bus; each active buffer circuit module comprises a solid-state switch; the solid-state switch comprises a power semiconductor switching transistor and an anti-parallel diode; the input terminal of the solid-state switch is connected to the collector of the power semiconductor switching transistor, and its output terminal is connected to the collector of the power semiconductor switching transistor. The emitter is connected; the cathode of the anti-parallel diode is connected to the emitter of the power semiconductor switch, and its anode is connected to the collector of the power semiconductor switch; the active buffer circuit includes a diode, a capacitor, a thyristor, an inductor, and a resistor RS; the input terminal of the active buffer circuit is connected to the anode of the diode, and the cathode of the diode is connected to the anode of the thyristor; the cathode of the thyristor is connected to the inductor, the inductor and the resistor are connected in series, and the thyristor, inductor, and resistor are connected in parallel with the capacitor; the other end of the resistor is connected to the output terminal of the active buffer circuit; its characteristic is: The control process of the DC power consumption device is divided into two periods: 0-t0, during which the system is in normal operation and the power semiconductor switching transistor is in the off state. The period from t0 to t1 is the turn-on process of the power semiconductor switch, and the device starts operating; at t2, the thyristor is triggered, the resistor absorbs the capacitor energy, and from t3 to t4, the thyristor withstands reverse voltage and quickly turns off; at t5, the voltage returns to the set value, the power semiconductor switch turns off, and the capacitor charges. These four stages include the following steps: Step 1: During the 0-t0 period, the power semiconductor switch is in the off state and it withstands the operating voltage U. rate At this time, the drain-source current I of the power semiconductor switch is... ce The capacitor voltage U is 0. Cs It is equal to the voltage of the power semiconductor switch. Step 2: During the t0-t1 period, the power semiconductor switch receives an on-signal, at which time U IGBT Rapidly reduce to the on-state voltage drop, I IGBT Increase to operating current I rate Due to the presence of the diode, U Cs The diode voltage U remains unchanged. D with U Cs on the contrary; Step 3: At time t1, the power semiconductor switch is fully turned on; Step 4: At time t2, the power semiconductor switch is still in the on state. At this time, the thyristor S is triggered, and the capacitor C... s Discharge causes the capacitor voltage to drop, which is... ; Step 5: At time t3, capacitor C s When the voltage drops to negative and withstands reverse voltage, the capacitor stops discharging, and at time t4, the thyristor quickly turns off. Step 6: At time t5, the DC power consumption device monitors the DC voltage in real time. When the DC voltage drops to the set value, the power semiconductor switch turns off, and the current flowing through it decreases rapidly. The current I flowing through the capacitor... C The voltage rises, charging capacitor Cs; when the power semiconductor switch is completely turned off, the system voltage continues to charge Cs, causing the capacitor voltage to rise further. until U Cs Reaching U rate .

2. A non-volatile storage medium, characterized in that, The non-volatile storage medium includes a stored program, wherein the program, when running, controls the device where the non-volatile storage medium is located to execute the method of claim 1.

3. An electronic device, characterized in that, It includes a processor and a memory; the memory stores computer-readable instructions, and the processor is used to execute the computer-readable instructions, wherein the computer-readable instructions, when executed, perform the method of claim 1.

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