Bypass method and system for power module fault

Abstract

The invention belongs to the field of overvoltage fault processing, and particularly relates to a bypass method and system for a power module fault. The method comprises the following steps: judging whether a current value is not less than a set value or not under the condition that the voltage of the power module rises to a set action voltage after judging that a bypass switch of the half-bridge power module cannot normally bypass; under the condition that the current direction is not smaller than the set value, if the current direction is the charging direction, a first power device in the module is connected, the power device is connected with a bypass switch in parallel so as to connect a short-circuit loop comprising a capacitor and the power device in the module, and the first power device is short-circuited and fails to be in bidirectional long-pass state; if the direction is the discharging direction, a second power device is switched on to switch on a short-circuit loop comprising a capacitor and a diode connected in parallel with the first power device, so that the diode is short-circuited and fails to be in two-way long pass; otherwise, current is injected into the power module to enable the current value to be not smaller than the set value, and processing is carried out according to the condition that the current value is not smaller than the set value.

Description

Technical Field

[0001] The present invention belongs to the field of overvoltage fault handling, and particularly relates to a bypass method and system for power module faults. Background Art

[0002] Flexible high voltage direct current power transmission technology (MMC-HVDC) based on modular multilevel converter (MMC) is an important means to solve high voltage, large capacity, long-distance power transmission and grid interconnection in the world at present. However, for a modular multilevel converter, a certain number of redundant power modules are provided in each arm; considering that when a power module fails, the most common measure is to use a mechanical bypass switch or an overvoltage breakdown power device to bypass the faulty module. Since there are a certain number of redundant power modules in the arm where the faulty power module is located, after bypassing, as long as the faulty module is controlled within the redundancy limit, the converter valve can operate normally. In summary, even if a power module fails, as long as it can be bypassed in time after the failure occurs, it will not affect the operation of the entire flexible DC power transmission system, that is, reliable bypass of the faulty power module plays a significant role in the reliable and stable operation of the flexible DC power transmission system.

[0003] Generally, the means for bypassing a faulty power module is to use a bypass switch to bypass the faulty power module. However, in fact, there may be a situation where the bypass switch cannot bypass normally (for example, the bypass switch fails to operate due to equipment failure, improper operation, system configuration problems, and other factors). In this case, the faulty power module cannot be bypassed through the bypass switch. If the large current generated by the fault enters the flexible DC power transmission system, serious consequences will occur.

[0004] At present, for the problem that the failure of the bypass switch affects the normal operation of the modular multilevel converter, the existing method is to raise the DC capacitor voltage of the power module to the IGBT breakdown voltage through the converter valve current. Finally, the DC capacitor of the power module discharges directly through one IGBT tube and / or another IGBT tube, breaking down the other IGBT tube to make it lose its function and short-circuiting it to fail, so as to have a reliable bi-directional current-carrying capacity to form a bypass. For example, the flexible DC converter valve sub-module bypass failure protection method disclosed in the Chinese invention patent with the application publication number CN115733122A. However, although the power devices or diodes contained in the IGBT tube will lose their functions and form a bi-directional path after being instantaneously broken down, the power devices and diodes often have self-recovery capabilities, that is, their functions may gradually recover automatically after a certain period of time. When the functions of the power devices or diodes recover automatically to a certain extent, they can no longer be used as bi-directional long-pass devices to achieve the bypass effect during the breakdown failure period, thus affecting the operation of the entire flexible DC transmission system and causing significant losses. Summary of the Invention

[0005] The purpose of the present invention is to provide a bypass method and system for power module failures, which is used to solve the problem in the prior art that due to the self-recovery capabilities of the fully controlled power devices or diodes contained in the IGBT tube, they cannot continue to be used as bi-directional long-pass devices to form a bypass after the functions are restored, and thus cannot achieve long-term bypass of the faulty power devices.

[0006] To achieve the above purpose, the present invention provides a bypass method for power module failures, which includes:

[0007] After determining that the bypass switch of the half-bridge power module cannot bypass normally, under the condition that the voltage of the power module rises to the set action voltage, determine whether the current value of the power module is not less than the set value;

[0008] When it is not less than the set value, if the current direction is the charging direction, turn on the first power device in the power module. The first power device is connected in parallel with the bypass switch to turn on the short-circuit loop in the power module that includes the capacitor and the power device, so that the first power device fails short-circuit to bi-directional long-pass; if the current direction is the discharging direction, turn on the second power device in the power module to turn on the short-circuit loop that includes the capacitor and the diode connected in parallel with the first power device, so that the diode fails short-circuit to bi-directional long-pass;

[0009] Otherwise, inject current into the power module to make the current value not less than the set value, and process it in the same way as when it is not less than the set current value.

[0010] Beneficial effects: The present invention provides a new bypass method for power module failures, which is aimed at the situation where the bypass switch cannot be bypassed normally (i.e., the bypass switch refuses to operate due to some extreme reasons); first, it is judged whether the bypass switch cannot be bypassed normally; if it indeed cannot be bypassed normally, then it is judged whether the voltage value of the power module reaches the set action voltage value; if it has reached this value, then the power device to be turned on is determined according to the judgment result of whether the current value of the power module reaches the set current value, so as to construct a corresponding short - circuit loop. Through the constructed short - circuit loop, the power device or diode device included in the corresponding IGBT tube loses its function (i.e., is broken down); and the device after losing its function becomes a two - way long - through device to form a bypass. Since the device (power device or diode device) has been broken down and lost its function, at this time, the short - term bypass effect of the power module can already be achieved. This method takes into account two situations and takes reasonable measures for both to enable the power device to lose and recover its function. That is, if the original current value is not less than the set current value, this current is sufficient to cause the power device to lose its self - recovery ability after being broken down (i.e., permanently used as a two - way long - through device); and for the case where the original current value is less than the set current value, a current is injected into the power module to make its value reach the set current value, so as to achieve the purpose of causing the power device to lose its self - recovery ability after being broken down. In summary, regardless of the original current value of the power module, it can be ensured that ultimately the power device loses and recovers its function and is used as a two - way long - through device (i.e., making the device permanently lose its function) to achieve the long - term bypass effect of the power module. Since the current magnitude may change with the cycle, if a device that still has the recovery ability is only temporarily broken down, then in subsequent cycles, the device will affect the bypass function constructed by breaking down the device before due to its function recovery, thus affecting the operation of the entire flexible DC power transmission system.

[0011] Therefore, adopting this method can effectively avoid the occurrence of such situations. The bypass constructed by this method has a stable and reliable long - through ability, and even if various parameters change with the cycle, it has no impact on the overall bypass function.

[0012] Furthermore, the method for determining that the bypass switch of the half - bridge power module cannot be bypassed normally includes:

[0013] When an over - voltage fault occurs in the half - bridge power module, if the bypass switch cannot bypass the power module when the voltage value of the power module reaches the set over - voltage setting value, it is determined that the bypass switch of the power module cannot be bypassed normally.

[0014] Furthermore, the lower limit value of the set current value is greater than or equal to the ratio of the instantaneous power tolerance value of the diode in the half - bridge power module to the set action voltage value.

[0015] Further, the upper limit value of the set current value is less than or equal to twice the frequency circulating current value of the flexible DC transmission system.

[0016] The present invention also provides a bypass system for power module failures, including a processor for executing a computer program to implement the steps of the bypass method for power module failures.

[0017] The bypass system for power module failures can achieve the same beneficial effects as the above-mentioned bypass method for power module failures. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 It is a flow example diagram of the bypass method for power module failures in the embodiment of the bypass method for power module failures of the present invention;

[0019] Figure 2 It is a schematic diagram of the circuit of the power module in the charging direction in the embodiment of the bypass method for power module failures of the present invention;

[0020] Figure 3 It is a schematic diagram of the circuit of the power module in the discharging direction in the embodiment of the bypass method for power module failures of the present invention;

[0021] Figure 4 It is a control principle block diagram for injecting current into the power module in the embodiment of the bypass method for power module failures of the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0022] In order to make the objectives, technical solutions and advantages of the present invention clearer, the present invention will be further described in detail below with reference to the accompanying drawings and embodiments.

[0023] Embodiment of the bypass method for power module failures

[0024] This embodiment provides a technical solution for the bypass method of power module faults. This method divides the solution into two cases according to the magnitude relationship between the current value of the faulty power module and the set value. The first case is: when the current value of the power module is not less than the set value, corresponding measures are provided according to whether the current direction is the charging direction or the discharging direction. That is, short - circuit loops for devices that require long - term bidirectional current conduction during breakdown are respectively constructed, and the broken - down device is used as a bidirectional long - conducting device to build a long - conducting bypass for the power device. If the current direction is the charging direction, the device to be broken down is the first power device in series with the bypass switch; if the current direction is the discharging direction, the device to be broken down is the diode in parallel with another power device in the power module. The second case is: when the current value of the power module is less than the set value, current is injected into the power module to make its current value not less than the set value. That is, a situation where the current value of the power module is not less than the set value is artificially created, and the corresponding method of the first case is used for processing. Since this method takes into account different situations and takes corresponding measures for processing, it can ensure that in any case, the device to be broken down can be broken down and its self - recovery ability can be lost, avoiding affecting the bypass effect.

[0025] As Figure 1 shown, when a half - bridge power module fails, software over - voltage protection is first performed; that is, when it is detected that the capacitor voltage of the sub - module (i.e., the half - bridge power module) continues to rise, the bypass switch is preferentially triggered after software delay to bypass the power module. However, the bypass switch may fail to bypass normally for some reasons. When it is determined that the bypass switch of the half - bridge power module cannot bypass normally, under the condition that the voltage of the power module rises to the set action voltage Ut_set, it is judged whether the current value of the power module is not less than the set value Ism_set (that is, on the basis of satisfying that the voltage of the power module rises to Ut_set, it is further judged whether the current value of the power module is not less than Ism_set), and corresponding operations are performed according to the judgment result.

[0026] As Figure 2As shown, when the current is not less than Ism_set and the current direction is the charging direction, the power device T2 at the lower part of the power module (i.e., the first power device in the power module) is turned on; this first power device is connected in parallel with the bypass switch to turn on the short - circuit loop including the capacitor C and the power device T2 in the power module (in this embodiment, the short - circuit loop is actually a series loop including the power device T2, diode D1, and capacitor C in the power module); after the short - circuit loop is turned on, the capacitor C provides a large current sufficient to break down the power device T2, and at the same time, since the current direction is the charging direction, the current flowing into the power module also acts on T2 together with this large current, causing the power device T2 to short - circuit and fail to a two - way long - through state (i.e., after being broken down, it loses its function and can conduct bidirectionally like a wire; and loses its self - recovery ability and cannot restore its own function, permanently acting as a two - way long - through device to form a new bypass of the power module). In the scenario applicable to this embodiment, the power devices T1 and T2 in the power module are both fully - controlled power devices. In other embodiments, the bypass method for the power module failure can also be applied to other turn - on - controllable power devices.

[0027] As Figure 3 shown, if the current direction is the discharging direction, the fully - controlled power device T1 at the upper part of the power module (i.e., the second power device in the power module) is turned on to turn on the short - circuit loop including the capacitor C and the diode D2 connected in parallel with the power device T2 (in this embodiment, the short - circuit loop is actually composed of the power device T1, diode D2, and capacitor C). After the short - circuit loop is turned on, the capacitor C provides a large current sufficient to break down the diode D2, causing the diode D2 to short - circuit and fail to a two - way long - through state.

[0028] Otherwise (i.e., when the current is less than the set value Ism_set), according to the control principle of the circulating - current control of the flexible DC converter valve as Figure 4 shown (i.e., by generating a reference current command through the outer loop and generating an expected reference voltage through the inner - loop current controller), current is injected into the power module to make the current value not less than the set value, and it is processed in the same way as when the current is not less than the set current value; that is, by injecting current into the power module, a situation where the current is not less than the set value Ism_set is artificially created; and the processing is carried out according to the operations corresponding to the situation where the current is not less than the set value Ism_set.

[0029] Figure 4The control principle of the circulating current control of the flexible DC converter valve shown is specifically as follows: Mathematically model the flexible DC converter valve and analyze the mathematical relationships among electrical quantities such as the voltage and current of the converter valve. Then, based on the established mathematical model, construct a circulating current suppression controller for the converter valve according to the preset outer-loop power and voltage control strategies of the converter valve and the inner-loop current control strategy. The controller monitors the current distribution inside the converter valve in real time and adjusts according to the preset control strategy. Then, adjust the relevant parameters of the converter valve according to the output of the circulating current suppression controller to suppress the circulating current and ensure that the injected current meets the system requirements.

[0030] Among them, i sdref represents the D-axis reference value of the injected current quantity; i sqref represents the Q-axis reference value of the injected current quantity; i sd represents the actual value of the D-axis of the injected current quantity; i sq represents the actual value of the Q-axis of the injected current quantity; wL represents the coupled voltage compensation amount; u dref represents the D-axis value of the output modulation voltage; u qref represents the Q-axis value of the output modulation voltage; u ref represents the value of the output sinusoidal modulation voltage; and belong to the parameters commonly used in PI control and will not be elaborated here. Injecting current in the above manner can ensure that the sum of the actual value of the injected current quantity and the current value of the power module meets the set value. In other embodiments, other current injection methods can also be used for injection, as long as the effect of injecting current into the power module is ensured so that the current value after injection is not less than the set value.

[0031] This embodiment can not only ensure that when the original current value is not less than the set value Ism_set, the device to be broken down is broken down and completely loses its self-healing ability (in this case, it has been previously determined that the current is not less than Ism_set, so the corresponding short-circuit loop can be directly connected through the corresponding operation, and the large current provided by the capacitor C is used to break down the power device T2. And since the current already meets the condition of not less than Ism_set in this case, the current is large enough to cause the power device to lose its self-healing ability), but also ensure that when the original current value is less than the set value Ism_set, the device to be broken down is broken down and completely loses its self-healing ability (in this case, it has been previously determined that the current does not meet the condition of not less than Ism_set, so in this case, current is injected into the power module to make it always not less than Ism_set, indirectly enabling the same measures as in the previous case to be taken; that is, even when the self-current is not large enough to cause the power device to lose its self-healing ability, the current can be increased to a value that satisfies the condition for the power device to lose its self-healing ability through current injection).

[0032] In this embodiment, the method for determining that the bypass switch of the half-bridge power module cannot be bypassed normally includes:

[0033] When an overvoltage fault occurs in the half-bridge power module, if the bypass switch cannot bypass the power module when the voltage value of the power module reaches the first-stage overvoltage setting value (i.e., the set overvoltage setting value), it is determined that the bypass switch of the power module cannot be bypassed normally.

[0034] Specifically, in this embodiment, the bypass switch is preferentially selected to bypass the power module, that is, regardless of the situation, the bypass switch is triggered first. If it is determined that the bypass switch cannot be bypassed normally, the set voltage is then introduced for judgment. Specifically, the method for determining that the bypass switch cannot be bypassed normally includes: when an overvoltage fault occurs in the power module and the overvoltage setting value reaches the first-stage overvoltage setting value, the faulty power module is bypassed through the bypass switch; if the power module cannot be bypassed through the bypass switch, it is determined that the bypass switch cannot be bypassed normally.

[0035] In this embodiment, the lower limit value of the set current value Ism_set is greater than or equal to the ratio of the withstand instantaneous power value of the diode in the half-bridge power module to the set action voltage value, that is, it is required that the generated instantaneous power can break down the diode device of the power module; the specific calculation method is as follows:

[0036] Ism_set ≥ Pmax / *Ut_set

[0037] Where, Ism_set is the set current value; Pmax is the withstand instantaneous power of the diode in the power module; Ut_set is the set action voltage value. In this embodiment, the upper limit value of the set current value Ism_set is less than or equal to twice the double-frequency circulating current value of the flexible DC transmission system, generally not higher than the system double-frequency circulating current value Iloop. The specific calculation method is as follows:

[0038] Ism_set ≤ Iloop

[0039] Where, Ism_set is the set current value; Iloop is the system double-frequency circulating current value.

[0040] Embodiment of the bypass system for power module faults

[0041] This embodiment provides a technical solution for a bypass system for power module faults. The system includes a processor, and executable program instructions are stored in the processor. The executable program instructions are used to implement the bypass method for power module faults in the bypass method embodiment of power module faults as described above.

[0042] Since the specific working mode and working principle of the bypass system for power module faults in this embodiment have been described in detail in the above embodiments of the bypass method for power module faults, they will not be elaborated here.

[0043] It should be understood that the above specific embodiments of the present invention are only used for exemplary illustration or explanation of the principle of the present invention, and do not constitute a limitation on the present invention.

Claims

1. A bypass method for power module failure, characterized in that: include: After determining that the bypass switch of the half-bridge power module cannot bypass normally, determining whether the current value of the power module is not less than the set value under the condition that the voltage of the power module rises to the set action voltage; In the case of not less than the set value, if the current direction is the charging direction, the first power device in the power module is turned on, and the first power device is connected in parallel with the bypass switch to connect the short-circuit loop containing the capacitor and the power device in the power module, so that the first power device is short-circuited and failed to turn into a two-way long-on state; if the current direction is the discharging direction, the second power device in the power module is turned on to connect the short-circuit loop containing the capacitor and the diode connected in parallel with the first power device, so that the diode is short-circuited and failed to turn into a two-way long-on state; Otherwise, current is injected into the power module so that the current value is not less than the set value, and the power module is processed in the same manner as when the current value is not less than the set value.

2. The bypass method for power module failure according to claim 1, characterized in that: Ways to determine that the bypass switch of the half-bridge power module cannot bypass normally include: When an overvoltage fault occurs in a half-bridge power module, if the voltage value of the power module reaches the set overvoltage setting value and the power module cannot be bypassed through the bypass switch, it is determined that the bypass switch of the power module cannot be bypassed normally.

3. The bypass method for power module failure according to claim 1 or 2, characterized in that: The lower limit value of the set current value is greater than or equal to the ratio of the withstand instantaneous power value of the diode in the half-bridge power module to the set action voltage value.

4. The bypass method for power module failure according to claim 1 or 2, characterized in that: The upper limit of the set current value is less than or equal to the double frequency circulating current value of the flexible DC transmission system.

5. A bypass system for power module failure, comprising a processor, characterized in that: The processor is used to execute a computer program to implement the steps of the power module fault bypass method according to any one of claims 1 to 4.

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