A DC energy consumption device

Abstract

The present invention relates to a DC energy consumption device, comprising an energy consumption circuit arranged on a DC line, wherein a centralized energy consumption module and at least one voltage dividing module are arranged in series on the energy consumption circuit; the voltage dividing module comprises a series branch, wherein a first switch tube, a second switch tube and a DC capacitor are arranged in series on the series branch; the first switch tube and the second switch tube are arranged in series in the same direction, the input end of the first switch tube is used to be connected to the positive electrode of the DC capacitor, and the input end and the output end of the first switch tube are respectively arranged in series on the energy consumption circuit as the positive electrode and the negative electrode of the voltage dividing module; the two ends of the second switch tube are connected in reverse parallel with a first diode; a voltage equalization discharge module is arranged in series on the line between the input end of the first switch tube and the positive electrode of the capacitor, and the voltage equalization discharge module comprises a voltage equalization discharge resistor and a second diode arranged in parallel. When the voltage equalization module is cut off due to a high voltage, the present invention discharges the DC capacitor through the voltage equalization discharge resistor by closing the second switch tube to accelerate the voltage equalization speed.

Description

Technical Field

[0001] The invention belongs to the technical field of high-voltage direct current power transmission, and in particular relates to a direct current energy consumption device. Background Art

[0002] Flexible DC transmission technology has the advantages of no commutation failure, low voltage harmonic content, high waveform quality, and the ability to quickly adjust active and reactive power. These technical advantages have led to a wide range of application demands for flexible DC technology in power systems, such as access, collection and transmission of large-scale clean energy, and power supply for isolated passive loads.

[0003] When flexible direct current is used to transmit new energy systems, when a fault occurs at the receiving end and causes the voltage of the AC grid to drop, the active power cannot be transmitted or can only be partially transmitted to the AC grid. The surplus active power causes the voltage of the DC transmission line to increase, endangering the safety of equipment such as flexible direct current converter valves. Therefore, DC energy consumption devices are crucial equipment.

[0004] The current method is to directly connect power semiconductor switching devices in series. When the DC voltage is too high, the power semiconductor switching devices are controlled to input resistors. The input of resistors will cause the DC voltage to drop. When the energy consumption rate of the resistors exceeds the rate of energy accumulation on the DC side, the DC voltage will drop, the resistor discharge loop will be turned off, and the DC voltage will rise again. The DC voltage is controlled by repeatedly opening and closing the resistor branch. However, this method has the following problems: when shutting down, it is technically difficult to shut down multiple power semiconductor switching devices at the same time, and it is difficult to ensure consistency. Once the shutdown is not synchronized, the slow-turning device or the fast-turning device will be damaged by overvoltage.

[0005] In order to solve the above problems, a Chinese invention patent application document with application publication number CN109617108A discloses a chain energy consumption device and a control method thereof. The device includes an energy consumption branch and an energy consumption resistor, and the energy consumption branch is composed of at least one energy consumption sub-module connected in series in the same direction. Each energy consumption sub-module is a voltage divider module. The structure of the energy consumption sub-module is as follows: Figure 1 When the device is started, the DC capacitor in the energy-consuming submodule needs to be charged. During the charging process, the voltage of each energy-consuming submodule needs to be balanced. For example, when the voltage of some energy-consuming submodules is high, these energy-consuming submodules with higher voltages can only be cut off, and these energy-consuming submodules with higher voltages are not charged. After the voltage of other energy-consuming submodules with lower voltages increases, these energy-consuming submodules with higher voltages are put back into use to achieve voltage balance of each energy-consuming submodule. The voltage balance speed of this process is slow. Summary of the invention

[0006] The present invention provides a direct current energy consumption device, which is used to solve the problem of slow voltage balancing speed of each voltage dividing module in the energy consumption device in the prior art.

[0007] In order to solve the above technical problems, the technical solutions and beneficial effects of the present invention are as follows:

[0008] A DC energy consumption device of the present invention comprises an energy consumption circuit arranged on a DC line, wherein a centralized energy consumption module and at least one voltage dividing module are arranged in series on the energy consumption circuit; the voltage dividing module comprises a series branch, wherein a first switch tube, a second switch tube and a DC capacitor are arranged in series on the series branch; the first switch tube and the second switch tube are arranged in series in the same direction, the input end of the first switch tube is used to be connected to the positive electrode of the DC capacitor, and the input end and the output end of the first switch tube are respectively arranged in series on the energy consumption circuit as the positive electrode and the negative electrode of the voltage dividing module; a first diode is connected in reverse parallel at both ends of the second switch tube; a voltage-equalizing discharge module is arranged in series on the line between the input end of the first switch tube and the positive electrode of the capacitor, wherein the voltage-equalizing discharge module comprises a voltage-equalizing discharge resistor and a second diode arranged in parallel, and the direction of the second diode is the same as that of the first diode.

[0009] Its beneficial effects: The DC energy consumption device of the present invention, when charging the DC capacitor in the voltage divider module and performing voltage equalization due to inconsistent voltages of the voltage divider modules, cuts off some voltage equalization modules with higher voltages, and at the same time closes the second switch tubes of these voltage equalization modules with higher voltages to discharge the DC capacitor through the voltage equalization discharge resistor, so as to speed up the voltage equalization speed, realize the voltage equalization control of the module, maintain the voltage balance of the voltage divider module, and improve the performance of the DC energy consumption device.

[0010] Furthermore, in order to reliably bypass the faulty voltage divider module from the energy consumption circuit, a voltage divider bypass switch is connected in parallel between the input and output ends of the first switch tube to bypass the corresponding voltage divider module from the energy consumption circuit.

[0011] Furthermore, in order to reliably realize the switching on and bypassing of the centralized energy consumption module, the centralized energy consumption module includes a centralized energy consumption resistor and an energy consumption bypass switch which are arranged in parallel.

[0012] Furthermore, the centralized energy consumption module also includes a third diode arranged in parallel with the centralized energy consumption resistor, and the anode of the third diode is used to be connected to the negative electrode of the DC line. The third diode is arranged to provide a freewheeling loop for the inductive current in the centralized energy consumption resistor when the voltage divider module turns off the discharge current. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] Figure 1 is a circuit structure diagram of a DC energy consumption device of an embodiment of the device of the present invention;

[0014] Figure 2is a flow chart of pressure-sharing control of a pressure-dividing module according to an embodiment of the device of the present invention;

[0015] Figure 3 It is a control block diagram of generating the number of excisions N1 according to an embodiment of the device of the present invention. DETAILED DESCRIPTION

[0016] Device Example:

[0017] This embodiment provides a DC energy consumption device. The circuit structure of the device is shown in FIG. Figure 1 As shown, the device includes an energy consumption circuit arranged on a DC line, and the energy consumption circuit includes a plurality of voltage dividing modules ( Figure 1 The dotted box in the middle is a voltage divider module) and a centralized energy consumption module, and the centralized energy consumption module includes a centralized energy consumption resistor R2 and a centralized energy consumption bypass switch K2 arranged in parallel.

[0018] The circuit structure of each voltage divider module is the same, including a first switch tube Q1 and a second switch tube Q2, the collector of the first switch tube Q1 is connected to the emitter of the second switch tube Q2 through a voltage-equalizing discharge resistor R1, the emitter of the first switch tube Q1 is connected to the negative electrode of the DC capacitor C1, and the collector of the second switch tube Q2 is connected to the positive electrode of the DC capacitor C1. A first diode D1 is connected in reverse parallel between the collector and the emitter of the second switch tube Q2, a second diode D2 is connected in parallel at both ends of the voltage-equalizing discharge resistor R1, and the anode of the second diode D2 is connected to the collector of the first switch tube Q1. A voltage-dividing bypass switch K1 is connected in parallel between the collector and the emitter of the first switch tube Q1, and the collector of the first switch tube Q1 serves as the positive lead-out point of the voltage divider module, and the emitter of the first switch tube Q1 serves as the negative lead-out point of the voltage divider module. The second diode D2, on the one hand, provides a channel for current when the first switch tube Q1 is turned off, and on the other hand, can provide a freewheeling loop for the inductive current in the voltage-equalizing discharge resistor after the second switch tube is turned off.

[0019] The third diode D3 and the centralized energy consumption bypass switch K2 are connected in parallel at both ends of the centralized energy consumption resistor R2, and the anode of the third diode D3 is connected to the negative electrode of the DC line. The function of the third diode D3 is to provide a freewheeling loop for the inductive current in the centralized energy consumption resistor when the voltage divider module turns off the discharge current.

[0020] The first switch tube Q1 and the second switch tube Q2 are power semiconductor switch devices, the base of the switch tube is the control end, the collector of the switch tube is the input end, and the emitter of the switch tube is the output end.

[0021] The working process of the device is described below. The working process of the device is divided into a startup process and a control process. Figure 2 shown.

[0022] Startup process:

[0023] Step 1: Turn off each switch tube in the voltage divider module and disconnect the centralized energy consumption bypass switch K2.

[0024] Step 2: After the DC line is energized, the voltage divider module is charged. During this process, the concentrated energy consumption resistor acts as a soft start resistor for each voltage divider module. After charging to a certain degree, the concentrated energy consumption bypass switch K2 is closed.

[0025] Step 3: During the charging process, the voltage of each voltage-dividing module is detected in real time and sorted, and a specified number of N voltage-dividing modules with higher voltages (N is a pre-set fixed value) are cut off to achieve voltage balance of each voltage-dividing module. If the voltage of a voltage-dividing module exceeds the voltage setting value, the second switch tube is closed while the voltage-dividing module is cut off, and it is discharged through the voltage-equalizing discharge resistor R1 to speed up the voltage-equalizing speed, further control the voltage, and achieve module voltage control. Among them, the state in which the first switch tube and the second switch tube of the voltage-dividing module are all turned off is defined as the input state of the voltage-dividing module, and the state in which the first switch tube of the voltage-dividing module is closed and the second switch tube is disconnected is defined as the cut-off state of the voltage-dividing module.

[0026] Step 4: After the average voltage of the voltage divider module reaches the set value, the startup process ends and the DC energy consumption device enters the standby state. In the standby state, step 3 needs to be continued to achieve voltage equalization control of each voltage divider module.

[0027] Control process:

[0028] Step 1: Detect the DC line voltage in real time. When the DC circuit voltage does not exceed the DC voltage upper limit Umax, the device is in standby mode and executes step 3 in the startup process to achieve voltage equalization control of each voltage divider module; when the DC circuit voltage exceeds the DC voltage upper limit Umax, the device enters energy consumption mode and executes step 2.

[0029] Step 2: Disconnect the centralized energy consumption bypass switch K2. Figure 3 As shown, the DC line voltage is controlled by the PI regulator, the command value is the rated value of the DC line voltage, the feedback value is the actual value of the DC line voltage, the rated DC line voltage is subtracted from the actual DC line voltage, the difference is closed-loop controlled by the PI regulator, the output value of the regulator is limited and multiplied by -1 and rounded, and the number of cut-off voltage divider modules N1 can be obtained. In the energy consumption mode, step 3 of the startup process needs to be executed at the same time to realize the voltage equalization control of each voltage divider module.

[0030] Step 3: Detect the DC line voltage. When the DC line voltage is less than the DC voltage lower limit Umin, exit the energy consumption mode, close the centralized energy consumption bypass switch K2, and enter the standby mode.

[0031] The following is a specific example to illustrate the above process.

[0032] The device includes 237 voltage-dividing modules connected to a 400kV DC line. When entering standby mode, the 237 voltage-dividing modules divide the 400kV voltage equally, and the centralized energy-consuming resistor R2 does not bear the DC voltage; in this state, the voltage of the voltage-dividing modules is sorted in real time, and the N modules with higher voltages are cut off to achieve voltage-equalizing control. When the voltage exceeds the rated voltage of 1.05pu (i.e., Umax=420kV), it enters the energy-consuming mode, disconnects the centralized energy-consuming bypass switch K2, and controls the number of switching on and off of the voltage-dividing modules through the PI regulator. The voltage of the centralized energy-consuming resistor is no longer zero but changes in real time according to the control result, thereby achieving control of the DC voltage. When the voltage is less than the rated voltage of 0.97pu (i.e., Umin=388kV), it exits the energy-consuming mode, closes the centralized energy-consuming bypass switch, and returns to the standby mode.

[0033] The DC energy consumption device of this embodiment adopts a modular approach, which greatly reduces the difficulty of manufacturing and engineering implementation of the device, improves the reliability of device operation, improves the convenience of maintenance, and is easy to expand to applications with higher voltage levels and larger capacities. At the same time, each switch tube in the device adopts a power semiconductor switch device, which avoids the risk caused by inconsistent breaking in the direct series connection solution, and can achieve fast, flexible and controllable power discharge. Moreover, through the control of the power semiconductor switch device, the voltage balance of the voltage divider module can be maintained in the standby and energy consumption modes.

[0034] In this embodiment, the voltage-equalizing discharge module (including the voltage-equalizing discharge resistor R1 and the second diode D2 arranged in parallel) is connected in series on the line between the collector of the first switch tube Q1 and the emitter of the second switch tube Q2. As another implementation, the voltage-equalizing discharge module can also be connected in series on the line between the collector of the second switch tube Q2 and the positive electrode of the DC capacitor C1.

[0035] Although the content of the present invention has been described in detail through the above preferred embodiments, it should be appreciated that the above description should not be considered as a limitation of the present invention. After reading the above content, it will be apparent to those skilled in the art that various modifications and substitutions of the present invention will occur. Therefore, the protection scope of the present invention should be limited by the appended claims.

Claims

1. A DC energy consumption device, characterized in that: It includes an energy consumption circuit arranged on a DC line, and a centralized energy consumption module and a plurality of voltage dividing modules are serially arranged on the energy consumption circuit; The voltage divider module includes a series branch, on which a first switch tube, a second switch tube and a DC capacitor are connected in series; the first switch tube and the second switch tube are connected in series in the same direction, the input end of the first switch tube is used to be connected to the positive electrode of the DC capacitor, and the input end and the output end of the first switch tube are respectively connected in series on the energy consumption circuit as the positive electrode and the negative electrode of the voltage divider module; A first diode is connected in reverse parallel to both ends of the second switch tube; A voltage-equalizing discharge module is connected in series on the line between the input end of the first switch tube and the positive electrode of the capacitor, and the voltage-equalizing discharge module includes a voltage-equalizing discharge resistor and a second diode connected in parallel, and the direction of the second diode is the same as that of the first diode; During the voltage balancing control process of each voltage divider module, if the voltage of the voltage divider module exceeds the voltage setting value, the second switch tube of the voltage divider module is closed while the voltage divider module is cut off, and the voltage is discharged through the voltage equalizing discharge resistor; the state in which the first switch tube of the voltage divider module is closed and the second switch tube is disconnected is defined as the cut-off state of the voltage divider module.

2. The DC energy dissipation device according to claim 1, characterized in that: A voltage-dividing bypass switch is connected in parallel between the input end and the output end of the first switch tube, and is used to bypass the corresponding voltage-dividing module from the energy-consuming circuit.

3. The DC energy dissipation device according to claim 1 or 2, characterized in that: The centralized energy consumption module includes a centralized energy consumption resistor and an energy consumption bypass switch which are arranged in parallel.

4. The DC energy dissipation device according to claim 3, characterized in that: The concentrated energy consumption module further includes a third diode which is arranged in parallel with the concentrated energy consumption resistor, and an anode of the third diode is used to be connected to a negative electrode of the DC line.

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