A multiple bypass protection method for power modules of flexible DC transmission converter valve fault

Abstract

The present invention discloses a multiple bypass protection method for power modules of a flexible direct current transmission converter valve failure. The faulty power module is bypassed by software overvoltage protection and hardware overvoltage protection. When the capacitor voltage value to the power module exceeds the software overvoltage protection action threshold value, the power module is bypassed; when the software overvoltage protection fails, the hardware overvoltage protection is automatically started. When the capacitor voltage of the power module exceeds the hardware overvoltage protection threshold value, the hardware overvoltage protection circuit automatically locks the trigger pulses of all fully controlled power electronic devices of the power module and closes the bypass switch, wherein the software overvoltage protection threshold value is less than the hardware overvoltage protection threshold value. It is ensured that the faulty power module can be reliably cut off from the power main circuit under any fault, thereby preventing the converter valve system from tripping due to a single power module fault, and greatly improving the system reliability of the flexible direct current converter station.

Description

Technical Field

[0001] The invention belongs to the technical field of flexible direct current transmission, and in particular relates to a power module multiple bypass protection method of a flexible direct current transmission converter valve. Background Art

[0002] Flexible DC transmission is a new generation of DC transmission system with self-commutation capability. It can realize long-distance grid connection of large-scale renewable energy power generation and offshore wind power grid connection. It is a key core equipment technology to promote my country's energy transformation.

[0003] Each bridge arm of the flexible DC transmission converter valve is composed of multiple power modules connected in series. When a single power module fails, it is necessary to bypass the faulty power module from the main power circuit in time so as not to affect the operation of the system. At present, most of my country's flexible DC transmission systems use mechanical bypass switches to bypass the faulty power modules. When the bypass switch refuses to operate, the downlink communication link from the valve control system to the power module fails, or the power supply of the power module fails, the faulty module cannot be effectively bypassed from the main power circuit, causing the flexible DC converter valve to trip. Summary of the invention

[0004] In order to solve the above problems, the present invention provides a multiple bypass protection method for power modules of flexible direct current transmission converter valve faults, which bypasses the faulty power modules through software overvoltage protection and hardware overvoltage protection. When it is monitored that the capacitor voltage value of the power module exceeds the software overvoltage protection action threshold value, the power module applies for bypass to the valve control system. After the valve control system issues a bypass permission command, the power module performs bypass. When the software overvoltage protection fails, the hardware overvoltage protection is automatically started. When the capacitor voltage of the power module exceeds the hardware overvoltage protection threshold value, the hardware overvoltage protection circuit locks the trigger pulses of all fully controlled power electronic devices of the power module and closes the bypass switch, wherein the software overvoltage protection threshold value is less than the hardware overvoltage protection threshold value.

[0005] Furthermore, the calculation formula of the software overvoltage protection threshold Upsoft is: Upsoft = Vpk (1-ε) - (1-kmar) * (Ipk / Csm * τ), where Vpk is the transient maximum shutdown voltage of the fully controlled power electronic device, ε is the measurement error of the capacitor voltage, τ is the link delay, Csm is the minimum capacitance value of the power module, Ip k is the maximum fault current, and kmar is the margin of the overvoltage protection threshold value.

[0006] Furthermore, the calculation formula of the hardware overvoltage protection threshold Uphard is: Uphard = Ucmax (1 + ε) + ΔU, ε is the measurement error of the capacitor voltage, Ucmax is the maximum capacitor voltage that can be reached after the power module is locked under various fault conditions, and ΔU is the regulation voltage.

[0007] Furthermore, an electronic bypass switch can automatically break down under an overvoltage in parallel at the port of the power module. When both the software overvoltage protection and the hardware overvoltage protection fail, the capacitor voltage and the port voltage of the faulty power module rise. When the port voltage of the power module exceeds the breakdown threshold of the electronic bypass switch, the electronic bypass switch automatically breaks down to bypass the faulty power module from the main power circuit of the flexible DC transmission system. The hardware overvoltage protection threshold value is less than the overvoltage automatic breakdown action threshold value of the power electronic bypass switch.

[0008] Furthermore, the method for determining the protection threshold of the overvoltage self-breakdown power electronic bypass switch is as follows: let the collector-emitter rated voltage of the fully-controlled power electronic device be Ucemax, the difference between the maximum and minimum breakdown voltages of the overvoltage self-breakdown power electronic bypass switch be Uband, and the protection threshold of the overvoltage self-breakdown power electronic bypass switch be (Ucemax-Uband)~Ucemax.

[0009] Furthermore, interconnection communication is set between each pair of power modules, a pair of power modules refers to two adjacent power modules, and the valve control system continuously sends bypass commands to the current module through the communication link of the adjacent power modules and the communication of the current power module.

[0010] Furthermore, two energy-taking power supplies are configured inside each power module.

[0011] Furthermore, each power module is internally configured with a main power supply and an auxiliary power supply. The main power supply supplies power to the secondary control board of the power module, and the auxiliary power supply is used to supply power to the secondary control board of the power module adjacent to the power module.

[0012] Furthermore, it is characterized in that, for a half-bridge power module, before closing the bypass switch, the lower fully-controlled power electronic device of the half-bridge power module is opened in advance.

[0013] Compared with the prior art, the present invention has at least the following beneficial technical effects:

[0014] The present invention designs a multiple bypass protection technology for faulty modules to ensure that under any fault, the faulty power module can be reliably cut off from the main power circuit, thereby preventing a single power module failure from causing the converter valve system to trip, greatly improving the system reliability of the flexible DC converter station.

[0015] Taking the flexible direct current converter valve with the largest power as an example, its single-pole power is 2.5 million kW. When the method of the present invention is not adopted, the number of unplanned tripping times per year reaches 3 times / year, and the fault recovery time is 24 hours. The corresponding electricity loss is about 180 million yuan. If the technology provided by the patent of this invention is adopted, the loss cost of unplanned power outages can be reduced to 0.

[0016] Furthermore, interconnection communication is set up between each pair of power modules. A pair of power modules refers to two adjacent power modules. When the valve control system of each pair of power modules issues a module bypass command, the bypass command of the current module is continuously issued through the communication link of the adjacent power module and the communication of the current power module, so as to avoid the valve control system being unable to issue a bypass command to the current power module when the communication link between the current module and the valve control system is disconnected.

[0017] Furthermore, each power module is internally configured with two energy-taking power supplies. When any of the energy-taking power supplies fails, the failed power module still has a power supply to provide it with the energy required for bypass. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 A schematic diagram of power module protection provided by an embodiment of the present invention;

[0019] Figure 2 This is a schematic diagram of redundant configuration of energy supply for an embodiment of the present invention;

[0020] Figure 3 This is a schematic diagram of a cross-redundancy configuration of an energy supply according to an embodiment of the present invention;

[0021] Figure 4 This is an example of redundancy of communication links between adjacent modules in an embodiment of the present invention;

[0022] Figure 5 An example of the relationship between different protection thresholds of the power module. DETAILED DESCRIPTION

[0023] In order to make the purpose and technical solution of the present invention clearer and easier to understand, the present invention is further described in detail below in conjunction with the accompanying drawings and embodiments. The specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0024] Figure 1 A schematic diagram of power module protection is given. The power module includes an upper tube fully controlled power electronic device 1, a lower tube fully controlled power electronic device 2, an upper tube diode 3, a lower tube diode 4, a power module port bypass switch 5, which is a mechanical switch, a DC capacitor 6, an overvoltage breakdown power electronic bypass switch 7 connected in parallel to the output port of the power module, and a power module discharge resistor 8. The sampling circuit collects the DC voltage on both sides of the DC capacitor 6. When the software determines that the voltage of the DC capacitor 6 exceeds the software overvoltage protection limit, the power module software overvoltage protection outlet applies for a bypass request to the valve control system. After receiving the bypass permission command from the valve control system, the power module locks the trigger pulse of its fully controlled power electronic device and closes the bypass switch 5.

[0025] Reference Figure 1The present invention also sets up hardware overvoltage protection. When the software overvoltage protection fails, the DC capacitor 6 of the power module will be further charged, causing the DC capacitor voltage to rise. When the DC capacitor voltage exceeds the hardware overvoltage protection threshold, the hardware overvoltage protection circuit automatically locks the trigger pulses of all fully controlled power electronic devices of the power module and closes the bypass switch 5, reporting the bypass status signal of the power module to the valve control system.

[0026] For a half-bridge power module, before closing the bypass switch 5, the lower tube fully-controlled power electronic device 2 of the half-bridge power module is turned on in advance to prevent the upper tube diode 3 of the half-bridge power module from being damaged due to excessive reverse recovery current at the moment of closing the mechanical bypass switch 5.

[0027] When the hardware overvoltage protection also fails, the voltage of the DC capacitor 6 and the voltage of the power module output port 16 will further increase under the action of the bridge arm current charging. When the voltage value of the power module output port 16 exceeds the action voltage of the overvoltage self-breakdown power electronic bypass switch 7, the overvoltage self-breakdown power electronic bypass switch 7 will be short-circuited due to the overvoltage, thereby short-circuiting the output port of the faulty module and cutting off the faulty power module from the main circuit. Figure 2 The configuration of the power supply for the power module is shown. Two power supplies are configured in the power module - the first power supply 9 and the second power supply 10, so as to prevent any power supply from failing. The failed power module still has a power supply to provide it with the energy required for bypass, and there is still a redundant power supply to power the secondary control board of the power module.

[0028] Figure 3 The cross-configured redundant power supply inside the power module is shown. Each power module is configured with a main power supply and an auxiliary power supply, where the main power supply supplies power to the secondary control board of the module, and the auxiliary power supply supplies power to the secondary board of the adjacent power module. This prevents a single power module from failing to work due to low capacitor voltage under fault conditions, resulting in the inability to effectively bypass the faulty power module because there is no working power supply. The role of the secondary board in multiple protection is to measure the capacitor voltage value, transmit signals to the valve control system, receive instructions from the valve control system, and send opening commands and locking commands to the fully controlled power electronic devices; the secondary control board can control software overvoltage protection, and hardware overvoltage protection is implemented through hardware analog circuits.

[0029] Figure 4The redundant communication configuration between adjacent power modules is illustrated. Taking two adjacent power modules as an example, the valve control system 11 sends control commands to the two power modules 14 and the power module 15 respectively through the first communication link 12 and the second communication link 13. The control command includes a bypass instruction to the adjacent modules, that is, when the valve control system sends a bypass command to a certain module, it also sends a bypass command to the current module through the communication link of the adjacent module, and sends the bypass instruction of the current module to the current module through the communication link between the adjacent modules, so as to avoid the situation that the valve control system cannot send a bypass command to the current power module when the communication link between the current module and the valve control system is disconnected; when the communication link between the current module and the valve control system fails, the bypass instruction sent by the valve control system can be received through the communication link of the adjacent module.

[0030] Figure 5 The relationship between the software overvoltage protection threshold, hardware overvoltage protection threshold, and overvoltage self-breakdown power electronic bypass switch protection threshold is illustrated. The relationship between the thresholds is software overvoltage protection threshold < hardware overvoltage protection threshold < overvoltage self-breakdown power electronic bypass switch protection threshold, so that a protection level difference is formed between the protections. According to the severity of the fault, the corresponding protection is activated. The typical value of the difference between adjacent overvoltage protection thresholds is 150V.

[0031] The software overvoltage protection threshold calculation method is:

[0032] The software overvoltage protection threshold value is Upsoft, the maximum transient shutdown voltage of the fully controlled power electronic device is Vpk, the measurement error of the capacitor voltage is ε, the link delay is τ, the minimum capacitance value of the power module is Csm, the maximum fault current is Ipk, and the margin of the overvoltage protection threshold value is kmar. The calculation method of the software overvoltage protection threshold value Upmax is:

[0033] Upsoft=Vpk(1-ε)-(1-kmar)*(Ipk / Csm*τ)

[0034] The link delay τ is the sum of the following link delays, including: capacitor voltage sampling delay, calculation processing time for comparing the capacitor voltage with the software overvoltage protection threshold value to determine whether the capacitor voltage exceeds the limit, communication link delay for the power module secondary control board to send a bypass request instruction to the valve control system, the valve control system processes the instruction and issues a logic operation processing delay to allow bypass, link delay for allowing bypass instructions to be transmitted to the power module secondary control board, power module control board calculation processing and issuing a locking instruction to the fully controlled power electronic device drive control board, processing time of the fully controlled power electronic device drive control board, and delay for shutting down the fully controlled power electronic device.

[0035] The calculation method of hardware overvoltage protection threshold is:

[0036] The hardware overvoltage protection threshold is Uphard. Under various fault conditions, the maximum capacitor voltage that can be reached after the power module is locked is Ucmax. The Uphard calculation formula is: Uphard=Ucmax(1+ε)+ΔU

[0037] Among them, the typical value of ε is 0.01, ΔU is the adjustment voltage, and the value of ΔU is related to the overvoltage self-breakdown protection threshold of the power electronic bypass switch. Usually, by adjusting the value of ΔU, Uphard is made to be in the middle value between Ucmax(1+ε) and (Ucemax-Uband).

[0038] The calculation method for the protection threshold of the overvoltage self-breakdown power electronic bypass switch is:

[0039] The rated collector-emitter voltage of the fully controlled power electronic device is Ucemax. Due to the dispersion of the process, the difference between the maximum and minimum breakdown voltages of the overvoltage self-breakdown power electronic bypass switch is Uband. The protection threshold of the overvoltage self-breakdown power electronic bypass switch is (Ucemax-Uband)~Ucemax.

[0040] For a certain type of power module using fully controlled power electronic devices with a rated voltage of 4500V and a rated current of 2000A, the typical values ​​of the above variables are: Vpk=3400V, ε=0.01, τ=0.00013s, Csm=0.0012F, Ipk=4000A, kmar=0.1, Ucmax=3950V, Ucemax=4500V, Uband=200V, ΔU=110.5V, and Upsoft=3322V and Uphard=4100V are calculated.

[0041] The above contents are only for explaining the technical idea of ​​the present invention and cannot be used to limit the protection scope of the present invention. Any changes made on the basis of the technical solution in accordance with the technical idea proposed by the present invention shall fall within the protection scope of the claims of the present invention.

Claims

1. A method for multiple bypass protection of power modules of a flexible DC transmission converter valve fault, characterized in that: The faulty power module is bypassed through software overvoltage protection and hardware overvoltage protection. When the capacitor voltage of the power module is detected to exceed the software overvoltage protection action threshold, the power module applies to the valve control system for bypass. After the valve control system sends a bypass permission command, the power module is bypassed. When the software overvoltage protection fails, the hardware overvoltage protection automatically starts. When the capacitor voltage of the power module exceeds the hardware overvoltage protection threshold, the hardware overvoltage protection circuit blocks the trigger pulses of all fully controlled power electronic devices of the power module and closes the bypass switch, where the software overvoltage protection threshold value < the hardware overvoltage protection threshold value; The calculation formula of software overvoltage protection threshold Upsoft is: Among them, Vpk is the maximum transient shutdown voltage of the fully controlled power electronic device. ε is the measurement error of the capacitor voltage, τ is the link delay, Csm is the minimum capacitance of the power module, Ipk is the maximum fault current, and kmar is the margin of the overvoltage protection threshold; The calculation formula of the hardware overvoltage protection threshold Uphard is: Uphard=Ucmax(1+ ε )+ , ε is the measurement error of the capacitor voltage, Ucmax is the maximum capacitor voltage that can be reached after the power module is locked under various fault conditions, To regulate the voltage.

2. A method for multiple bypass protection of power modules of a faulty flexible DC transmission converter valve according to claim 1, characterized in that: An overvoltage self-breakdown power electronic bypass switch (7) is connected in parallel to the port of the power module. When both the software overvoltage protection and the hardware overvoltage protection fail, the capacitor voltage and the port voltage of the faulty power module rise. When the port voltage of the power module exceeds the breakdown threshold of the electronic bypass switch, the electronic bypass switch automatically breaks down, bypassing the faulty power module from the main power circuit of the flexible DC transmission system. The hardware overvoltage protection threshold value is less than the overvoltage automatic breakdown power electronic bypass switch action threshold value.

3. A method for multiple bypass protection of power modules of a flexible DC transmission converter valve fault according to claim 2, characterized in that: The method for determining the protection threshold of the overvoltage self-breakdown power electronic bypass switch (7) is as follows: let the collector-emitter rated voltage of the fully controlled power electronic device be Ucemax, and the difference between the maximum and minimum breakdown voltages of the overvoltage self-breakdown power electronic bypass switch be Uband, then the protection threshold of the overvoltage self-breakdown power electronic bypass switch is (Ucemax-Uband)~Ucemax.

4. A method for multiple bypass protection of power modules of a faulty flexible DC transmission converter valve according to claim 1, characterized in that: Interconnection communication is set between each pair of power modules. A pair of power modules refers to two adjacent power modules. The valve control system continuously sends the bypass command of the current module through the communication link of the adjacent power module and the communication of the current power module.

5. A method for multiple bypass protection of power modules of a faulty flexible DC transmission converter valve according to claim 1, characterized in that: Two energy-taking power supplies are configured inside each power module.

6. A method for multiple bypass protection of power modules of a flexible DC transmission converter valve fault according to claim 1, characterized in that: Each power module is internally configured with a main power supply and an auxiliary power supply. The main power supply supplies power to the secondary control board of the power module, and the auxiliary power supply is used to supply power to the secondary control board of the power module adjacent to the power module.

7. A method for multiple bypass protection of power modules of a faulty flexible DC transmission converter valve according to any one of claims 1 to 6, characterized in that: For a half-bridge power module, before closing the bypass switch, the lower fully-controlled power electronic device of the half-bridge power module is turned on in advance.

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