A direct current power module capacitor fault protection method and power module

Abstract

The application considers that after the power module capacitor breakdown, energy continuously enters the fault capacitor and is converted into heat and ejected arc; while for the normal operation power module, the energy continuously entering the capacitor is average 0, and the total energy of the capacitor is basically constant. The application provides a DC power transmission power module capacitor fault protection method, which continuously monitors the cumulative energy entering the power module capacitor, and compares it with the actual capacitor energy E cf calculated by the capacitor voltage feedback. When the expected capacitor energy E co is obviously higher than the actual capacitor energy E cf , the power module bypass switch is triggered to remove the fault power module; after the power module is removed, the expected capacitor energy E co is continuously monitored. If after a predetermined time T thr , the expected capacitor energy E co is still obviously higher than the actual capacitor energy E cf , the trigger IGBT through of the fault power module is executed to ensure that the fault power module no longer affects the operation of the converter station.

Description

Technical Field

[0001] This invention relates to the field of high-voltage direct current (HVDC) transmission technology, and in particular to a method for capacitor fault protection of a DC transmission power module and a power module thereof. Background Technology

[0002] In the field of high-voltage direct current (HVDC) transmission, the reliability of converter stations is crucial. To ensure this reliability, it is necessary to detect various potential faults in the power modules and disconnect faulty modules using bypass switches. The core technologies involve: how to detect potential power module faults, and how to ensure that a faulty module does not affect the continuous operation of the converter station as a whole if the bypass switch fails to operate. Existing power module fault detection solutions include detecting internal faults within the power module: IGBT and its driver faults, power supply faults, unit control board communication faults, abnormal internal pressure of module capacitors, and overvoltage / undervoltage faults of module capacitors. For example, Chinese Patent Publication No. CN 107516872A discloses a forward overvoltage protection circuit for an MMC converter valve submodule. The protection methods when the bypass switch fails to operate include parallel thyristors (such as the MMC power module overvoltage protection circuit and multi-stage bypass method disclosed in Chinese Patent No. CN110829811A) and asymmetric clamping design (such as the power module fault protection circuit disclosed in Chinese Patent No. CN110380387A).

[0003] However, current methods only protect power module capacitors against overvoltage, undervoltage, and abnormal internal pressure. When a capacitor in an individual power module fails to self-heal due to dielectric breakdown and bursts, energy from the converter station system may continuously enter the faulty capacitor, even though the capacitor voltage is within the normal range and the capacitor pressure detection sensor is damaged and cannot provide fault information. If this situation is not addressed, the faulty capacitor will continuously emit high-temperature arcs, quickly causing surrounding power modules to fail and ultimately leading to a converter station shutdown. Summary of the Invention

[0004] To address the technical problems raised in the background, this invention provides a method for capacitor fault protection of DC transmission power modules and a power module. Considering that after a power module capacitor breaks down, energy always continuously enters the faulty capacitor and is converted into heat and an ejected arc; while for a normally operating power module, the energy continuously entering the capacitor is on average 0, and the total energy of the capacitor remains basically constant. The solution of this invention can detect and control the power module under these circumstances, ensuring that the faulty power module does not affect the operation of the converter station.

[0005] To achieve the above objectives, the present invention employs the following technical solution:

[0006] A method for capacitor fault protection of a DC transmission power module includes the following steps:

[0007] 1) Continuously monitor the accumulated energy entering the power module capacitor, which is called the expected capacitor energy E. co ,

[0008] 2) The expected capacitor energy E co The actual capacitor energy E calculated through capacitor voltage feedback from the power module. cf Compare;

[0009] 3) When the expected capacitor energy E co With actual capacitor energy E cf The difference is greater than the set threshold E thr When the faulty power module is disconnected, the power module bypass switch is triggered.

[0010] 4) Continue monitoring the expected capacitor energy E after disconnecting the power module. co If the predetermined time T is elapsed thr Afterwards, the expected capacitor energy E co With actual capacitor energy E cf The difference is still greater than the set threshold E thr If the faulty power module is triggered, IGBT shoot-through will be executed to ensure that the faulty power module no longer affects the operation of the converter station.

[0011] Furthermore, the actual capacitor energy E cf By detecting the capacitor voltage v cf According to the formula Calculations show that C1 is the capacitance value of the power module.

[0012] Furthermore, the expected capacitance energy E co The calculation is performed by analyzing the detected capacitor voltage v of the power module. cf and capacitor current i cf The product is accumulated to obtain the result. However, considering that the system measurement inevitably has errors, in order to avoid the errors affecting the correctness of the protection, the actual capacitor energy E is introduced. cf Negative feedback:

[0013]

[0014] Where k1 is a preset constant, the expected capacitor energy E can be calculated using any numerical integration method. co .

[0015] Furthermore, the capacitor current i of the power module cf It can be obtained through one of the following methods:

[0016] 1) A current sensor is used in the power module to directly detect the capacitor current i in the power module. cf And send it to the unit's main control board;

[0017] 2) Use a current sensor in the power module to directly measure the bridge arm current i arm The data is then sent to the unit's main control board, which then calculates the capacitor current i based on the current state of the power module. cf ;

[0018] 3) Add bridge arm current i to the downlink communication from valve control to the main control board of the power module unit. arm Then, the unit's main control board calculates the capacitor current i based on the current state of the power module. cf .

[0019] Furthermore, when the power module is a half-bridge power module, the capacitor current i of the power module... cf for:

[0020] When the upper IGBTT1 of the power module is turned on, let i cf =i arm ;

[0021] When the lower IGBTT2 of the power module is turned on, let i cf =0;

[0022] When both the upper IGBTT1 and lower IGBTT2 of the power module are turned off, let i cf =|i arm |

[0023] Furthermore, when the power module is a full-bridge power module, the capacitor current i of the power module... cf for:

[0024] When the first IGBTT1 and the fourth IGBTT4 of the power module are turned on, let i cf =i arm ;

[0025] When the second IGBTT2 and the third IGBTT3 of the power module are turned on, let i cf =-i arm ;

[0026] When the first IGBTT1 and the third IGBTT3 of the power module are turned on, let i cf =0;

[0027] When the second IGBTT1 and the fourth IGBTT4 of the power module are turned on, let i cf =0;

[0028] When the first IGBT1, the second IGBT2, the third IGBT3, and the fourth IGBT4 of the power module are all turned off, let i cf =|i arm |

[0029] Furthermore, a threshold E is set. thr The value should be chosen to ensure that, in a normal power module, the capacitor fault protection does not trip due to sampling errors.

[0030] Furthermore, when the power module is a half-bridge power module or a full-bridge power module, the process for triggering IGBT shoot-through is as follows:

[0031] a. Continuously trigger the upper IGBT T1 and the lower IGBT T2 until an IGBT drive failure occurs;

[0032] b. Pause for 40-60μs to stop triggering the upper IGBT T1 and lower IGBT T2;

[0033] c. Proceed to step a and continue execution.

[0034] Furthermore, when the power module is a full-bridge power module, the process for triggering IGBT shoot-through can also be as follows:

[0035] a. Continuously trigger the third IGBT T3 and the fourth IGBT T4 until an IGBT drive failure occurs;

[0036] b. Pause for 40–60 μs to stop triggering the third IGBT T3 and the fourth IGBT T4;

[0037] c. Proceed to step a and continue execution.

[0038] The present invention also provides a DC power transmission module, including a half-bridge or full-bridge power module and a power module main control board, wherein the power module main control board receives valve control commands and continuously monitors the capacitor voltage V entering the power module. cf and capacitor current i cf It also monitors the bridge arm current i arm By running the aforementioned method, the IGBTs and bypass switches in the half-bridge or full-bridge power modules are triggered and controlled, so that when the power modules continuously enter the fault capacitor and are converted into heat and ejected arcs, the faulty power modules do not affect the operation of the converter station.

[0039] Compared with the prior art, the beneficial effects of the present invention are:

[0040] This invention considers that after a power module capacitor breaks down, energy continuously enters the faulty capacitor and is converted into heat and an ejected arc; while for a normally operating power module, the average energy continuously entering the capacitor is 0, and the total energy of the capacitor remains essentially constant. This invention proposes a fault protection method for DC transmission power module capacitors. This fault protection method continuously monitors the accumulated energy entering the power module capacitor and compares it with the actual capacitor energy E calculated through capacitor voltage feedback. cf In comparison, when the expected capacitor energy E co Significantly exceeds the actual capacitor energy E cf When the faulty power module is disconnected, the power module bypass switch is triggered to disconnect the faulty power module; after disconnecting the power module, the expected capacitor energy E is continuously monitored. co If the predetermined time T is elapsed thr Afterwards, the expected capacitor energy E co It still significantly exceeds the actual capacitor energy E cf The faulty power module is triggered to shoot through the IGBT to ensure that the faulty power module no longer affects the operation of the converter station. Attached Figure Description

[0041] Figure 1 This refers to a half-bridge power module used in existing high-voltage direct current transmission technology.

[0042] Figure 2 This refers to existing full-bridge power modules used for high-voltage direct current transmission.

[0043] Figure 3 This is a schematic diagram illustrating the valve-controlled distribution of bridge arm current in a half-bridge power module according to the present invention.

[0044] Figure 4 This is a schematic diagram illustrating the valve-controlled distribution of bridge arm current by the full-bridge power module according to the present invention.

[0045] Figure 5 This is a schematic diagram illustrating the invention of adding a current sensor to a half-bridge power module to directly measure the capacitor current;

[0046] Figure 6 This is a schematic diagram illustrating the invention of adding a current sensor to a full-bridge power module to directly measure the capacitor current;

[0047] Figure 7 This is a schematic diagram illustrating the invention of adding a current sensor to a half-bridge power module to directly measure the bridge arm current;

[0048] Figure 8 This is a schematic diagram illustrating the invention of adding a current sensor to the full-bridge power module to directly measure the bridge arm current;

[0049] Figure 9This is a logic block diagram of the present invention, which calculates the expected capacitor energy based on capacitor voltage feedback and capacitor current and determines whether to perform protection.

[0050] Figure 10 This is a flowchart illustrating the action of power module protection in this invention.

[0051] Figure 11 This is a flowchart illustrating the action of triggering IGBT shoot-through in this invention. Detailed Implementation

[0052] The specific embodiments provided by the present invention will be described in detail below with reference to the accompanying drawings.

[0053] like Figure 1-2 As shown, in a high-voltage direct current (HVDC) transmission system, the flexible HVDC converter consists of six arms, each of which is composed of power modules connected in series, including half-bridge power modules and full-bridge power modules. Figure 1 The image shows a half-bridge power module. Figure 2 The diagram shows a full-bridge power module. The power module is connected to the valve control system via optical fiber, receives modulation commands from the valve control system, executes these commands, triggers the IGBTs within the module, and feeds back the unit status to the valve control system. A half-bridge power module includes two IGBTs, while a full-bridge power module includes four IGBTs. Each power module includes: capacitor C1, a unit control board (i.e., the main control board of the power module), and a voltage divider circuit. The voltage divider circuit divides the voltage of capacitor C1 and is connected to the unit control board. The unit control board samples the divided voltage to obtain the current capacitor voltage.

[0054] This invention proposes a method for capacitor fault protection of DC transmission power modules, the fault protection method comprising the following steps:

[0055] 1) Continuously monitor the accumulated energy entering the power module capacitor, which is called the expected capacitor energy E. co ,

[0056] 2) The expected capacitor energy E co The actual capacitor energy E calculated through capacitor voltage feedback from the power module. cf Compare;

[0057] 3) When the expected capacitor energy E co Significantly exceeds the actual capacitor energy E cf When the faulty power module is disconnected, the power module bypass switch is triggered.

[0058] 4) Continue monitoring the expected capacitor energy E after disconnecting the power module. co If the predetermined time T is elapsed thr Afterwards, the expected capacitor energy Eco It still significantly exceeds the actual capacitor energy E cf If the faulty power module is triggered, IGBT shoot-through will be executed to ensure that the faulty power module no longer affects the operation of the converter station.

[0059] The actual capacitor energy E cf By detecting the capacitor voltage vcf According to the formula The calculations yielded the results.

[0060] To calculate the expected capacitor energy E co We need to know the capacitor current i cf Considering that valve-controlled systems typically have real-time sampling values ​​of the arm current, the arm current i can be added to the downlink communication between the valve control unit and the main control board of the power module unit. arm ,like Figure 3 and Figure 4 As shown, the unit's main control board then calculates the capacitor current i based on the current state of the power module. cf Alternatively, a current sensor can be used in the power module to directly detect the capacitor current i in the power module. cf ,like Figure 5 and Figure 6 As shown, the signal is sent to the unit's main control board; alternatively, a current sensor can be used in the power module to directly measure the bridge arm current i. arm ,like Figure 7 and Figure 8 As shown, the data is sent to the unit main control board, which then calculates the capacitor current i based on the current state of the power module. cf .

[0061] When the power module is a half-bridge power module, the capacitor current i is calculated based on the current state of the power module and the bridge arm current. cf The method is as follows;

[0062] When the upper IGBTT1 of the power module is turned on, let i cf =i arm ;

[0063] When the lower IGBTT2 of the power module is turned on, let i cf =0;

[0064] When both the upper IGBTT1 and lower IGBTT2 of the power module are turned off, let i cf =|i arm |

[0065] When the power module is a full-bridge power module, the capacitor current i is calculated based on the current state of the power module. cf The method is as follows:

[0066] When the first IGBTT1 and the fourth IGBTT4 of the power module are turned on, let i cf =i arm ;

[0067] When the second IGBTT2 and the third IGBTT3 of the power module are turned on, let i cf =-i arm ;

[0068] When the first IGBTT1 and the third IGBTT3 of the power module are turned on, let i cf =0;

[0069] When the second IGBTT1 and the fourth IGBTT4 of the power module are turned on, let i cf =0;

[0070] When the first IGBT1, the second IGBT2, the third IGBT3, and the fourth IGBT4 of the power module are all turned off, let i cf =|i arm |

[0071] The expected capacitance energy E co Calculation is performed by analyzing the detected capacitor voltage v. cf Capacitor current i cf The product is accumulated to obtain the result. However, considering that the system measurement inevitably has errors, in order to avoid the errors affecting the correctness of the protection, the actual capacitor energy E is introduced. cf Negative feedback:

[0072]

[0073] Where k1 is a preset constant. Thus, the expected capacitance energy E can be calculated using any numerical integration method. co For example, the simplest forward Euler integral method can be used. Taking the forward Euler method as an example, the expected capacitance energy E co The calculation method is as follows:

[0074] E co,n+1 =E co,n +(v cf ·i cf -k1·(E co -E cf ))·ΔT

[0075] in:

[0076] E co,n+1 The expected capacitor energy E for the current control cycle co value;

[0077] E co,nThe expected capacitor energy E in the previous control cycle co value;

[0078] ΔT is the control period.

[0079] The value of k1 can be designed according to the convergence time constant: when the sampling signal error is 0, E co E should be approximated using a typical time constant of 0.1s–1s. cf The typical value is k1 = 1 - 10.

[0080] To determine the expected capacitor energy E co Does it significantly exceed the actual capacitor energy E? cf Introducing a pre-set threshold E thr The basis for judgment is: E co -E cf >E thr .

[0081] E thr The value of should be chosen to ensure that, in a normal power module, the capacitor fault protection does not malfunction due to sampling errors. Typical values ​​are: Where v cn This is the rated operating voltage of the capacitor.

[0082] Figure 9 This is a logic block diagram of an embodiment of the present invention, which calculates the expected capacitor energy based on capacitor voltage feedback and capacitor current, and determines whether to perform protection.

[0083] like Figure 10 As shown, the power module bypass switch is triggered to disconnect the faulty power module after a predetermined time T. thr Then, if the expected capacitor energy E co It still significantly exceeds the actual capacitor energy E cf This indicates that the bypass switch has failed to operate. In this case, the faulty power module should be triggered to shoot through the IGBT. Where T... thr The value of T should be chosen to ensure that sampling errors will not lead to a misjudgment that the bypass switch has failed to operate. A typical value is: T thr =1 / k1.

[0084] Considering that typical IGBT driver boards automatically protect themselves when the IGBT is shot-through or short-circuited, therefore, if Figure 11 As shown, the process that triggers IGBT shoot-through (for half-bridge or full-bridge power modules) is as follows:

[0085] a. Continuously trigger IGBTs T1 and T2 until an IGBT drive failure occurs;

[0086] b. Pause for 50μs to stop triggering IGBTs T1 and T2;

[0087] c. Proceed to step a and continue execution.

[0088] If it is a full-bridge power module, the process for triggering IGBT shoot-through can also be:

[0089] a. Continuously trigger IGBTs T3 and T4 until an IGBT drive failure occurs;

[0090] b. Pause for 50μs to stop triggering IGBTs T3 and T4;

[0091] c. Proceed to step a and continue execution.

[0092] This invention also provides a DC transmission power module, including a half-bridge or full-bridge power module and a power module main control board (unit control board), the hardware structure of which is as follows: Figure 1-8 Any of the above, with the particular feature that the power module main control board (unit control board) receives valve control commands and continuously monitors the capacitor voltage v entering the power module. cf and capacitor current i cf It also monitors the bridge arm current i arm By running the aforementioned method, the IGBTs and bypass switches in the half-bridge or full-bridge power modules are triggered and controlled, so that when the power modules continuously enter the fault capacitor and are converted into heat and ejected arcs, the faulty power modules do not affect the operation of the converter station.

[0093] The above embodiments are implemented based on the technical solution of the present invention, providing detailed implementation methods and specific operation processes. However, the scope of protection of the present invention is not limited to the above embodiments. Unless otherwise specified, the methods used in the above embodiments are conventional methods.

Claims

1. A method for capacitor fault protection of a DC transmission power module, characterized in that, Includes the following steps: 1) Continuously monitor the accumulated energy entering the power module capacitor, which is called the expected capacitor energy E. co , 2) The expected capacitor energy E co The actual capacitor energy E calculated through capacitor voltage feedback from the power module. cf Compare; 3) When the expected capacitor energy E co With actual capacitor energy E cf The difference is greater than the set threshold E thr When the faulty power module is disconnected, the power module bypass switch is triggered. 4) Continue monitoring the expected capacitor energy E after disconnecting the power module. co If the predetermined time T is elapsed thr Afterwards, the expected capacitor energy E co With actual capacitor energy E cf The difference is still greater than the set threshold E thr If the faulty power module is triggered, IGBT shoot-through will be executed to ensure that the faulty power module no longer affects the operation of the converter station; The expected capacitor energy E co The calculation is performed by analyzing the detected capacitor voltage v of the power module. cf and capacitor current i cf The product is accumulated to obtain the result. However, considering that the system measurement will inevitably have errors, in order to avoid the errors affecting the correctness of the protection, the actual capacitor energy E is introduced. cf Negative feedback: Where k1 is a preset constant, the expected capacitor energy E can be calculated using any numerical integration method. co ; When the power module is a half-bridge power module or a full-bridge power module, the process for triggering IGBT shoot-through is as follows: a. Continuously trigger the upper IGBT T1 and lower IGBT T2 of the half-bridge power module or the first IGBT T1 and second IGBT T2 of the full-bridge power module until an IGBT drive failure occurs; b. Pause for 40~60μs to stop triggering the upper IGBT T1 and lower IGBT T2 of the half-bridge power module or the first IGBT T1 and second IGBT T2 of the full-bridge power module; c. Proceed to step a and continue execution; When the power module is a full-bridge power module, the process for triggering IGBT shoot-through is as follows: a. The third IGBT T3 and the fourth IGBT T4 are continuously triggered until an IGBT drive failure occurs. b. Pause for 40~60μs to stop triggering the third IGBT T3 and the fourth IGBT T4; c. Proceed to step a and continue execution.

2. The method for capacitor fault protection of a DC transmission power module according to claim 1, characterized in that, Actual capacitor energy E cf By detecting the capacitor voltage v cf According to the formula The calculations yielded the following results: This refers to the capacitance value of the power module.

3. The method for capacitor fault protection of a DC transmission power module according to claim 1, characterized in that, The capacitor current i of the power module cf It can be obtained through one of the following methods: A current sensor is used in the power module to directly detect the capacitor current i in the power module. cf And send it to the unit's main control board; The power module uses a current sensor to directly measure the bridge arm current i. arm The data is then sent to the unit's main control board, which then calculates the capacitor current i based on the current state of the power module. cf ; Add bridge arm current i to the downlink communication from valve control to the main control board of the power module unit. arm Then, the unit's main control board calculates the capacitor current i based on the current state of the power module. cf .

4. The method for capacitor fault protection of a DC transmission power module according to claim 3, characterized in that, When the power module is a half-bridge power module, the capacitor current i of the power module cf for: When the upper IGBT T1 of the power module is turned on, ; When the lower IGBT T2 of the power module is turned on, ; When both the upper IGBT T1 and the lower IGBT T2 of the power module are turned off, let .

5. A method for capacitor fault protection of a DC transmission power module according to claim 3, characterized in that, When the power module is a full-bridge power module, the capacitor current i of the power module cf for: When the first IGBT T1 and the fourth IGBT T4 of the power module are turned on, ; When the second IGBT T2 and the third IGBT T3 of the power module are turned on, ; When the first IGBT T1 and the third IGBT T3 of the power module are turned on, ; When the second IGBT T1 and the fourth IGBT T4 of the power module are turned on, ; When the first IGBT T1, the second IGBT T2, the third IGBT T3, and the fourth IGBT T4 of the power module are all turned off, let .

6. The method for capacitor fault protection of a DC transmission power module according to claim 1, characterized in that, Set threshold E thr The value should be chosen to ensure that, in a normal power module, the capacitor fault protection does not trip due to sampling errors.

7. A DC power transmission module, characterized in that, The power module includes a half-bridge or full-bridge power module and a main control board. The main control board receives valve control commands and continuously monitors the capacitor voltage V entering the power module. cf and capacitor current i cf It also monitors the bridge arm current i arm The method described in any one of claims 1-6 is used to trigger and control the IGBTs and bypass switches in the power modules of the half-bridge or full-bridge power modules, so that when energy continuously enters the fault capacitor and is converted into heat and ejected arc, the IGBTs are triggered to conduct a short circuit, ensuring that the faulty power modules do not affect the operation of the converter station.

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