An ultra-high voltage active power system and method of use thereof

Abstract

The application discloses a kind of for superhigh voltage active power system and its use method, it is aimed at solving the deficiency of traditional series standby switching scheme.The application includes cascaded H bridge main circuit, parallel standby unit, control unit and the auxiliary power supply unit for providing power supply for parallel standby unit, wherein, cascaded H bridge main circuit is composed of several cascaded modules in series, cascaded H bridge main circuit is divided into M groups N cascaded modules, parallel standby unit includes standby module with the same structure as sub-module, standby module is in hot standby state by auxiliary power supply unit power supply, the positive and negative DC terminals of each cascaded module in group are respectively connected in parallel with standby module by high-speed switch, control signal is provided to standby module according to the fault state of cascaded module, system is switched to standby module quickly when fault occurs, avoid the problem of system output voltage imbalance and current and voltage impact, make standby module one-to-many working module, so as to improve the utilization of standby module.

Description

Technical Field

[0001] This invention relates to the field of high-voltage power electronics technology, and more specifically, to an ultra-high-voltage active power system and a method of using it. Background Technology

[0002] The active section of an ultra-high voltage hybrid active power filter (HAPF) requires a cascaded H-bridge (CHB) system. However, due to the relatively low withstand voltage of existing IGBTs, the control schemes used in 220kV and 500kV systems require a large number of modules. When a single module fails in this series-connected system, the switching process involves changes to the PWM of the series modules. Whether it's level-shift modulation or phase-shift modulation, the modulation waveform of the entire PWM system is affected. Fault ride-through is achieved by setting up a backup module to replace the function of the faulty module. Traditional backup schemes use a series backup switching method, which requires recalculating the carrier phase shift angle during switching. This causes an imbalance in the system's output voltage, resulting in significant current and voltage surges. Furthermore, the utilization rate of backup modules is low, making the response of cold backup schemes very slow, while hot backup suffers from significant losses. During system startup, there are current and voltage surges, making it difficult for traditional schemes to guarantee startup safety and reliability. Summary of the Invention

[0003] This invention overcomes the shortcomings of traditional series backup switching schemes and provides a method for using ultra-high voltage active power systems. It can quickly switch to the backup module when a fault occurs, avoiding the problems of system output voltage imbalance and current and voltage surges. It enables the backup module to work with multiple modules, thereby improving the utilization rate of the backup module.

[0004] To solve the above-mentioned technical problems, the present invention adopts the following technical solution: A method for an ultra-high voltage active power system includes a cascaded H-bridge main circuit, a parallel standby unit, a control unit, and an auxiliary power supply unit that provides power to the parallel standby unit. The cascaded H-bridge main circuit is composed of several cascaded modules connected in series. The cascaded H-bridge main circuit is divided into M groups of cascaded modules, each group including N cascaded modules. The parallel standby unit includes standby modules with the same structure as the sub-modules. The standby modules are configured in the cascaded module groups, and the number of standby modules in each group is less than N. The standby modules are powered by the auxiliary power supply unit and are in a hot standby state. The positive and negative DC terminals of each cascaded module in the group are connected in parallel with the standby module through high-speed switches. The control module enables the high-speed switches corresponding to each cascaded module in a timing sequence to connect the standby module in parallel with the corresponding cascaded module. The control module provides control signals to the standby module according to the fault status of the cascaded module.

[0005] Preferably, each cascade module group has one spare module, each cascade module group has six cascade modules, and the total number of cascade modules is 36.

[0006] Preferably, each cascade module group is connected in parallel with an external short-circuit relay. When the number of faulty cascade modules in the cascade module group is greater than the number of spare modules, the relay is closed to close the cascade module group and update the group and phase shift angle of other cascade module groups.

[0007] Preferably, the expression for calculating the phase shift angle is: The number of phase shift steps for the nth cascaded module in the mth group is: The phase shift angle of the nth cascaded module in the mth group is: .

[0008] Preferably, the auxiliary power supply unit includes a transformer and an uncontrolled rectifier circuit.

[0009] As a preferred option, the high-speed switch is a SiC solid-state parallel converter.

[0010] A method of using an ultra-high voltage active power system includes the following steps: S1. Start the cascaded H-bridge main circuit for ultra-high voltage active power systems as described above, charge each cascaded module, establish the component voltage in the cascaded module along the slope, and perform closed-loop control. S2. Power the parallel backup unit through an auxiliary power supply unit isolated from the main circuit of the cascaded H-bridge so that the state of each transistor in the backup module is similar to that of the cascaded module. S3. The control module performs fault detection on the main circuit of the cascaded H-bridge and determines the scale of the fault. S4. When the number of faulty cascaded modules is less than or equal to the number of spare modules in the cascaded module group, it is judged as a module-level fault. The control signal of the faulty cascaded module is blocked, the SiC solid-state parallel circuit is closed, and the control signal is transferred to the spare module in the group where the faulty cascaded module is located. S5. When the number of cascaded modules with faults in the same group is greater than the number of spare modules in the cascaded module group, it is judged as a group-level fault. The control signals of all cascaded modules in the cascaded module group are blocked, the short-circuit relays corresponding to the cascaded module group to which the cascaded module belongs are short-circuited, and the group and phase shift angle of other cascaded module groups are updated. S6. Replace the faulty cascade module, and charge the cascade module connected in parallel with the backup module through the auxiliary power supply unit so that it has a state relative to the other cascade modules. After maintaining this state for several switching cycles, switch the control signal of the backup module to the replaced cascade module.

[0011] As a preferred option, the indicators for judging group-level faults also include: abnormal fluctuations in DC voltage within the group exceeding a first preset limit, and input-output current imbalances between and within groups exceeding a second preset limit.

[0012] Preferably, the sources of faults in the cascaded module are determined by: the DC voltage signal of the module, the current protection signal of the module, the temperature signal of the module, and the IGBT fault signal generated based on the DS voltage of the IGBT built into the cascaded module. These signals are then processed by RC hardware filtering (low-pass filtering) and debouncing algorithm to avoid false triggering.

[0013] Preferably, the DC voltage signal of the module is further filtered by moving average to eliminate transient interference, and 12 sampling points are set to eliminate transient voltage spikes.

[0014] Compared with the prior art, the beneficial effects of the present invention are: (1) When a fault occurs, the system can quickly switch to the backup module through a high-speed switch, thus avoiding the problems of system output voltage imbalance and current and voltage surges. (2) It has the ability to handle group-level faults, and only adjusts the phase angle for group-level faults with low fault probability to achieve stable output current and voltage. Attached Figure Description

[0015] Figure 1 is A schematic diagram of the overall system structure of the present invention. Figure 2 is The cascaded module control method of the present invention. Figure 3 is This invention relates to a cascaded H-bridge main circuit controlled in a grouping manner. Figure 4 is A schematic diagram of the structure within the cascaded module group of the present invention. Figure 5 is A comparative analysis of the phase shift angles between modules in CHBs (cascaded H-bridges) with different numbers of modules in this invention. Figure 6 is The CHB module system control program flowchart of the present invention. Detailed Implementation

[0016] The present disclosure will be further described below with reference to the accompanying drawings and embodiments.

[0017] It should be noted that the following detailed descriptions are illustrative and intended to provide further explanation of this application. Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application pertains.

[0018] It should be noted that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the exemplary embodiments according to this application. As used herein, the singular form is intended to include the plural form as well, unless the context clearly indicates otherwise. Furthermore, it should be understood that when the terms "comprising" and / or "including" are used in this specification, they indicate the presence of features, steps, operations, devices, components, and / or combinations thereof.

[0019] In this disclosure, terms such as "upper," "lower," "left," "right," "front," "back," "vertical," "horizontal," "side," and "bottom" indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are merely relational terms determined for the convenience of describing the structural relationship of the various components or elements in this disclosure, and do not specifically refer to any component or element in this disclosure, nor should they be construed as limiting this disclosure.

[0020] In this disclosure, terms such as "fixed connection," "connected," and "linked" should be interpreted broadly, indicating a fixed connection, an integral connection, or a detachable connection; a direct connection or an indirect connection through an intermediate medium. Those skilled in the art can determine the specific meaning of these terms in this disclosure based on the specific circumstances, and they should not be construed as limitations on this disclosure.

[0021] Example: Reference Figure 1 This invention illustrates an ultra-high voltage active power system, comprising a cascaded H-bridge main circuit, a parallel backup unit, a control unit, and an auxiliary power supply unit providing power to the parallel backup unit. The cascaded H-bridge main circuit serves as part of an ultra-high voltage hybrid active filter, whose input terminals can be connected to HVDC systems, wind farms, and large-capacity off-site loads. The ultra-high voltage hybrid active filter, as a three-phase system, converts the voltage to 1000V via an uncontrolled rectifier through a transformer to provide power to the auxiliary power supply unit.

[0022] The cascaded H-bridge main circuit consists of several cascaded modules connected in series. Each cascaded module includes a sampling circuit, a fault generation signal, a PWM driver, and an H-bridge. The sampling circuit and fault generation signal are used to monitor the operating status of the cascaded modules, cooperating with the upstream MCU or other control chips for fault detection and handling. The PWM driver generates the switching signals for the H-bridge, which is used for level shifting and current output.

[0023] Specifically, the sampling circuit is set in each cascaded module and the backup module to detect its own DC-side voltage. , Grid voltage (providing a basis for subsequent harmonic compensation) Inductor current (detects the current passing through the filter, providing a basis for current closed-loop control).

[0024] Because the various cascaded modules are connected in series, each The total output after series connection is the total output of the ultra-high voltage active power system (HAPF), based on the... The detection can be used to evaluate the output voltage of HAPF.

[0025] Based on the foregoing , The inductor current is used to implement two closed-loop controls.

[0026] Closed-loop control 1: DC voltage outer loop control, comparison via controller. This is achieved through a PI (Proportional-Integral) controller, which takes the difference between the input DC voltage reference value and the actual voltage, and outputs a DC current reference signal. This allows the cascaded H-bridge main circuit to absorb or release appropriate fundamental power, thereby stabilizing the average DC voltage.

[0027] Closed-loop control two: Output voltage harmonic outer loop control, which generates a harmonic current reference by compensating for harmonics. This is controlled by the controller. The PR control is used to evaluate and control harmonic currents. It takes a harmonic voltage reference value as input and outputs a corresponding harmonic current reference signal. Harmonic control is achieved by utilizing the characteristic of PR control having infinite gain at a specific frequency point.

[0028] Using the dq transform, the three-phase AC time-varying signals abc are converted into DC (or slowly varying signals) in a dq rotating coordinate system, paving the way for PI control in the inner current loop. The total current amplitude reference is obtained by using the DC current reference and harmonic current reference signals, and this is used as the reference value for the q-axis in the dq coordinate system, converted into a modulation signal, and then controlled by the controller. The PI controller takes the difference between the reference total current amplitude and the actual current as input, outputs the instantaneous value of the modulated wave based on the dq coordinate system, and then converts it into the modulated wave of the corresponding three phases abc to generate the PWM control signal for each cascaded module.

[0029] Combined with appendix Figure 2, Here is a demonstration of its control flow: The target average DC voltage set for the system, in this case 1000V, is the control target; It is the average DC voltage output by the H-bridge main circuit, which is the actual output; the difference between the two is then passed through... The PI controller outputs a DC current reference signal. .akin, (Harmonic voltage reference value) and (HAPF output voltage) After difference calculation, pass through The PR controller outputs a harmonic current reference signal. . This is the actual output current of the HAPF, used as a negative feedback signal, in conjunction with the aforementioned... as well as After summing and subtracting, proceed to... , with fundamental voltage reference Doing and after Enter Perform a dq to abc inverse transform on the output. and After differential calculation, generate based on inductor response. With grid-side current After differential calculation, the final PWM control signal is output based on the inductor response. The control signal is stabilized by LC filtering to remove high-frequency noise.

[0030] refer to Figure 3, This application employs a group management approach to manage the cascaded H-bridge main circuit. The cascaded H-bridge main circuit is divided into M groups of cascaded modules, each group comprising N cascaded modules. Taking a cascaded H-bridge main circuit consisting of 36 cascaded modules as an example, M=6 and N=6. Parallel backup units include backup modules with the same structure as the sub-modules. These backup modules are configured within the cascaded module groups, and the number of backup modules in each group is less than N. Using the aforementioned cascaded H-bridge main circuit consisting of 36 cascaded modules as an example, one backup module is configured in each cascaded module group, achieving a 6-to-1 redundancy backup.

[0031] The backup module is in a hot standby state, powered by an auxiliary power supply unit. The grid's direct supply to the auxiliary power supply unit directly affects the stability of the internal cascaded modules. The hot standby state means that the state of the transistors inside the backup module is similar to that of the cascaded modules, particularly in terms of drain-source voltage, duty cycle, and phase shift angle. Therefore, when a cascaded module fails, the backup module takes over, providing normal output and thus bridging the fault, buying time for the replacement and restart of the faulty module.

[0032] refer to Figure 4, The backup module uses a dual-busbar connection, with its positive and negative DC terminals connected in parallel to the positive and negative DC terminals of each cascaded module within the group via high-speed switches. Specifically, the positive and negative DC terminals of each cascaded module are connected in parallel to the positive and negative DC terminals of the backup module via high-speed switches, and high-speed switches are installed on the parallel lines. to ), used to control the parallel connection status of the standby module and the cascaded module.

[0033] The control module enables the high-speed switches corresponding to each cascaded module in a timing sequence, allowing the backup module to be connected in parallel with the corresponding cascaded module. Its timing adapts to the fixed timing relationship formed by the cascaded modules based on carrier phase-shift SPWM modulation rules. For example, taking a cascaded module group consisting of N=6 cascaded modules, the control module generates a cyclic sequence number from 0 to 5, corresponding to the enable signals of the 6 cascaded modules within the group. The cyclic sequence number generated by the control module directly enables the module with the corresponding sequence number via broadcast or level signaling, thus sequentially connecting the backup module in parallel with the corresponding sequence number module. Taking sequence number 1 as an example, corresponding to the second cascaded module, the two high-speed switches corresponding to the second cascaded module are in a connected state, connecting it in parallel with the backup module. The high-speed connection speed of the high-speed switches ensures the rapid activation of the backup module. As the sequence number changes to 2, the corresponding third module is activated. Correspondingly, the high-speed switches to the left and right of the second cascaded module are in a disconnected state, and the controller enables the high-speed switches to the left and right of the third cascaded module, connecting them. At this time, the backup module is no longer connected in parallel with the second cascaded module but in parallel with the third cascaded module. To further ensure that the backup module corresponds appropriately to its cascaded module in the correct timing, a hardware signal operation based on AND logic is employed. High and low level logic signals are configured for both the cascaded module and the backup module: PWWX indicates the operation of the nth cascaded module, and SX is the high-speed switch enable signal for the nth cascaded module. For each cascaded module within the group, a hardware AND operation is performed on PWMX and SX. All results are then aggregated into the PWM input circuit of the backup module and ANDed. Since only one SX=1 at any given time, only the PWMX corresponding to that SX can output a high level through the AND operation, thus preventing other cascaded modules from outputting anything.

[0034] Control signals are provided to the backup module based on the fault status of the cascaded modules. The total fault signals FAULT corresponding to the cascaded modules are summed. When there is no fault, FAULT=0. When a cascaded module fails, a fault signal FAULT=1 is sent. When FAULT=0, the PWM signal of the backup module is 0, and there is no PWM action. Although it is in parallel, it is equivalent to a diode in anti-parallel open circuit state. No current flows through the high-speed switches on both sides. At this time, the backup module is equivalent to nothing. Conversely, when FAULT=1, the PWM signal of the backup module is made equal to the PWM of the corresponding faulty cascaded module, and the PWM signal sent to the faulty cascaded module is stopped. It directly inherits its IGBT switching timing, phase shift angle, and duty cycle to achieve seamless switching. At this time, the backup module no longer cycles according to the cycle number. The worst-case scenario is that everything is normal when sequence number = 0, but when sequence number = 1, the cascaded module with sequence number 0 suddenly fails. The fault signal is not transmitted to the main control terminal in the first cycle, and the backup module only returns to sequence number 0 after 5 switching cycles. Through H-bridge power design, the short transition process of 5 switching cycles can be smoothly passed. At the extremely low frequency of 500Hz, 5 switching cycles are only 0.01ms (i.e., 1 / 2 power frequency cycle). Slow faults may not respond in time, therefore this design has high reliability. When the aforementioned fault occurs, the backup module continues to work in place of the faulty cascaded module until it is replaced or maintained to clear the fault signal. At this time, the PWM signal of the backup module is blocked, it is de-enabled, and the normal sequence number cycle resumes. The above circuit perfectly balances parameter alignment, low-loss standby, and fast-response switching.

[0035] The sources of faults in the cascaded module are determined by several factors: the module's DC voltage signal, the module's current protection signal, the module's temperature signal, and the IGBT fault signal generated based on the DS voltage of the IGBTs built into the cascaded module. These signals are then processed by a first-order RC hardware filter (low-pass filter) and a debouncing algorithm to prevent false triggering. The module's DC voltage signal is further filtered using a moving average method to eliminate transient interference, and 12 sampling points are used to eliminate transient voltage spikes. The debouncing algorithm can be implemented using the TI CCS built into the TITMS320F28377D controller chip, or other publicly available debouncing algorithms.

[0036] The high-speed switch is a SiC solid-state parallel circuit. The SiC device is selected with a 1200V / 100A specification, featuring nanosecond-level switching speed and low on-resistance. This embodiment uses a high-temperature, high-current SiC Schottky device developed by the research team of the Institute of Microelectronics, Chinese Academy of Sciences and CRRC Times Electric Co., Ltd. in Zhuzhou. Its drift region resistance is 200 times lower than that of silicon, the switching speed is extremely fast, the reverse recovery current is almost zero, and it has ultra-low switching losses.

[0037] The circuit described above can handle faults in cascaded modules with fewer than or equal to the number of backup modules in each group. However, when the number of faulty cascaded modules in a group exceeds the number of backup modules, the operation of 6 modules would require a maximum of 5 modules, posing a risk of long-term overload. Therefore, an external short-circuit relay is connected in parallel outside each cascaded module group. When the number of faulty cascaded modules in the cascaded module group exceeds the number of backup modules, the relay closes, causing the cascaded module group to close and updating the group and phase shift angle of other cascaded module groups. Indicators for determining that a cascaded module group has failed and requires overall shielding, besides the most direct indication that the number of faulty cascaded modules exceeds the number of backup modules, also include: abnormal DC voltage fluctuations within the group exceeding a first preset limit, and input / output current imbalances between and within groups exceeding a second preset limit.

[0038] The first preset limit is set to 30%. Since the DC voltage of each cascaded module is locally controlled, theoretically, all modules should always maintain the same DC voltage value. If a single module or multiple modules fail, the sum of the DC voltages of the entire group will deviate significantly from the rated value. For example, when modules 1 and 2 fail, the imbalance between power absorption and release on their DC sides will inevitably lead to DC voltage imbalance, thus preventing the module from functioning properly. All modules have a reference voltage of 1kV. If the DC voltage of module 2 suddenly drops to 0, the total voltage of the six modules will be 5kV, a reduction of 1 / 6 compared to normal. This can only be attributed to a single module failure. However, if two modules fail simultaneously, such as modules 2 and 4, the DC voltage will drop by 2kV, 1 / 3 less than normal, exceeding 30%. Therefore, this is a group-level failure.

[0039] The second preset limit is set at 20%. If a single module becomes unbalanced with other modules, given that their modulation waves are the same and only the phase shift angle of the phase shift modulation differs, there must be a significant fault, leading to an unbalanced distribution of module power. Therefore, if the abnormal fluctuation of DC voltage within the group exceeds the limit, it must mean that there is a serious fault in the module within the group that has caused the series mechanism to fail, and the group must be stopped immediately.

[0040] Taking a failure of two cascaded module groups as an example, the process of disconnecting the cascaded module groups is as follows: First, immediately block all PWM signals of the group, blocking all faulty PWM signals of both groups. After blocking, all modules will no longer output noise or unexpected ideal control waveforms to avoid interfering with other modules. Second, close the short-circuit switch of the group's input and output lines. While blocking the fault signals of the two groups, immediately close the clutch of the group's input and output lines, short-circuiting the input and output of the modules through the aforementioned relays. Because the entire group 2 is connected in series, once the PWM stops, group 2 will be equivalent to an infinite resistor, the output impedance of the entire system will be infinite, and the current output capability will be reduced to 0. By actuating the external relays, the input and output lines are short-circuited, that is, group 2 is directly short-circuited using the closed relays, which is equivalent to disconnecting the entire group 2. Additionally, by short-circuiting the node, the output of module 2 will be shorted to point 1, eliminating inter-module circulating current and ensuring the safety of modules without faults. Updating the effective group number Y and group number is crucial in modular multilevel DC-DC converters. If the phase shift angle is not adjusted accordingly after updating the number of modules, it may lead to a subharmonic at 5 times the switching frequency in the output voltage, causing filter overheating. Due to the sudden removal of group 2, the entire system needs to complete the original control parameters using 5 / 6 of the original number of modules; therefore, all existing phase shift angles must be updated. The updated group number Y is obtained through communication broadcast after being aggregated by the system. For example, if 5 groups remain available, then Y=5. Subsequently, the newly obtained group number is assigned to the phase shift angle offset base value of each module. For example, after group 2 is suddenly removed, the group number of group 3 is updated to 2, group 4 to 3, and group 6 to 5. The recalculation process for the phase shift angle is as follows: The number of phase shift steps for the nth cascaded module in the mth group is: The phase shift angle of the nth cascaded module in the mth group is: With M=6 and N=6, the phase shift angle is... When two sets of failures are shielded, the phase shift angle is: , refer to Figure 5, The left image shows the situation before the fault occurred, and the right image shows the situation after the fault occurred and the phase shift angle was adjusted.

[0041] like Figure 6 The following is a method of using an ultra-high voltage active power system, comprising the following steps: S1, starting the cascaded H-bridge main circuit for an ultra-high voltage active power system as described above, charging each cascaded module, establishing the component voltage in the cascaded module along the slope, and performing closed-loop control.

[0042] The cascaded H-bridge main circuit is located in an ultra-high voltage active power system. After the pre-charging circuit of the ultra-high voltage active power system is closed, it pre-charges through the main power grid to charge each cascaded module in the cascaded H-bridge main circuit, maintaining the DC voltage of each cascaded module at around 1kV. A starting resistor with a resistance of 20 ohms or more is set to construct the voltage through the starting resistor. Inductors and capacitors are set before and after the starting resistor to provide a stable, small charge for each cascaded module, thereby achieving a stable, linear voltage along the slope until the operating voltage is reached. In addition, the control module (control chip, in this embodiment, TI's TMS320F28377D) is initialized with all control parameters and state variables, and each component is monitored to prevent subsequent closed-loop control from going out of control. Then, the FPGA communicates with each cascaded module to ensure that there are no fault alarms or communication alarms, and to ensure that the module can work normally.

[0043] Wait for the aforementioned voltage to build up until it reaches 80% of its rated value. Monitor the voltage rise using an averaging control method. Since the cascaded modules are connected in series, the DC voltage of each cascaded module should fluctuate synchronously. The operating voltage of the cascaded modules is 1000V, meaning the pre-charge should reach 800V.

[0044] The system current should also be checked to ensure there is no overcurrent. Before activation, the system should be allowed to run stably for a period of time to eliminate basic parameter mismatch issues. Ensure that no overcurrent occurs when harmonic voltage control is activated. Because harmonic voltage control is high-frequency, the high-frequency component of the inductor has significant nonlinearity. Unless the safety margin is normal, if the component parameters are unqualified, overcurrent and other faults can easily occur.

[0045] Once the voltage stabilizes, disconnect the starting resistor. After the harmonic voltage and DC voltage dual outer loop control stabilize, first reset the harmonic voltage reference to zero, then disconnect the starting resistor for normal operation. Active HAPF front-ends contain large passive components, resulting in a certain reactive power adjustment process. It's necessary to wait for the input and DC voltages to stabilize before proceeding to the next step. Due to the use of voltage outer loop control, the disconnection process is equivalent to disconnecting the load, allowing the system to quickly complete this transition.

[0046] The next stage involves implementing a harmonic detection algorithm and gradually increasing the compensation current until it reaches the set value. Algorithms based on FFT harmonic detection, multiple rotating coordinate systems, and wavelet transform can extract the required harmonic current. Based on the harmonic current, a specified harmonic voltage can be designed to output the harmonic current and enhance resistance to background harmonic voltages. Many traditional algorithms exist, and all are compatible with the hardware architecture designed in this paper. For example, by subtracting the DC current from the d-axis and q-axis currents in the rotating coordinate system obtained through an instantaneous power algorithm, the harmonic current reference in the dq coordinate system can be obtained. The harmonic current reference value can be obtained through an inverse dq transform. Since directly enabling a large compensation current may cause harmonic impacts on the power grid, unwanted harmonic components will be injected when there are errors in the compensation. The compensation current is gradually increased through a control algorithm, slowly rising to the rated level in percentage increments before being put into full operation, thus realizing the startup of the cascaded H-bridge main circuit.

[0047] S2. Power the parallel backup unit through an auxiliary power supply unit isolated from the cascaded H-bridge main circuit to ensure that the states of the transistors in the backup module and the cascaded module are similar. Under the premise of ensuring the normal operation of the cascaded H-bridge main circuit, start the parallel backup unit. Power the parallel backup unit through the auxiliary power supply unit to ensure that the states of the transistors in the backup module and the cascaded module are similar. It is worth noting that the power supply of the backup module is independent, isolated from the cascaded H-bridge main circuit through a transformer to ensure that the power supply of the backup module and the power supply of the main circuit do not interfere with each other. The parallel backup unit sends an enable command, indicating that it is ready for normal use.

[0048] S3. The control module performs fault detection on the main circuit of the cascaded H-bridge and determines the scale of the fault. S4. When the number of faulty cascaded modules is less than or equal to the number of spare modules in the same cascaded module group, it is determined to be a module-level fault. The control signal of the faulty cascaded module is blocked, the SiC solid-state parallel connector is closed, and the control signal is transferred to the spare module in the same group as the faulty cascaded module. The control module generates a cyclic timing sequence number, so that the spare module is cyclically connected in parallel with each corresponding cascaded module. The control module also generates a fault signal. When a fault signal occurs, the spare module receives the fault signal and stops sending the PWM signal corresponding to the faulty cascaded module. Instead, it sends the fault signal to the spare module, so that the spare module takes over the function of the faulty cascaded module. Correspondingly, the SiC solid-state parallel connectors on the left and right sides of the next cascaded module no longer receive the timing sequence number enable, so that the spare module always takes over the function of the faulty cascaded module until the fault signal is canceled.

[0049] S5. When the number of cascaded modules with faults in the same group exceeds the number of spare modules in the same cascaded module group, it is determined to be a group-level fault. The control signals of all cascaded modules in the cascaded module group are blocked, the short-circuit relay corresponding to the cascaded module group to which the cascaded module belongs is short-circuited, and the group and phase shift angle of other cascaded module groups are updated. The update process is as described above and will not be repeated here.

[0050] S6. Replace the faulty cascade module, and charge the cascade module connected in parallel with the backup module through the auxiliary power supply unit to achieve a state relative to the other cascade modules. After maintaining this state for several switching cycles, switch the control signal of the backup module to the replaced cascade module. Since the newly replaced cascade module is in parallel with the backup module, the corresponding SiC solid-state parallel connector is in a connected state, and the auxiliary power supply unit will also charge it. When it is charged to a state similar to that of other normal cascade modules, maintain this state for several cycles (5 cycles in this application) to ensure normal function. After this, it will be normally connected, the backup module will return to the backup state, and continue to be connected in parallel with each cascade module one by one according to the timing sequence number, and will no longer send PWM signals to it.

[0051] Through this implementation scheme, the system demonstrates excellent performance under both module-level and group-level fault conditions: Module-level fault switching: switching time is less than 100μs, and the output voltage is fully overlapped, which fully meets the reliability requirements of high-frequency harmonics in power system output.

[0052] Group-level fault reconfiguration: When only one group of modules fails, it can switch to the working mode of five groups of modules. The new rated power of the system is 5 / 6 of the original rated power. Even if the system is working at the original rated power, the output of each module is only increased by 0.2 times, which is lower than the general design margin of 2 to 3 times.

[0053] Specifically, through this implementation scheme, the system achieves excellent results as shown in the attached figure when operating under a power grid containing background harmonics. Compared with traditional control, the input current waveform of this invention is closer to an ideal sine wave, and the THD is significantly reduced, proving the effectiveness of the method.

[0054] The embodiments described above are merely preferred embodiments of the present invention and are not intended to limit the present invention in any way. Other variations and modifications may be made without departing from the technical solutions described in the claims.

Claims

1. A device for an ultra-high voltage active power system, characterized in that, It includes a cascaded H-bridge main circuit, a parallel backup unit, a control unit, and an auxiliary power supply unit that provides power to the parallel backup unit. The cascaded H-bridge main circuit is composed of several cascaded modules connected in series. The cascaded H-bridge main circuit is divided into M groups of cascaded modules, each group including N cascaded modules. The parallel backup unit includes a backup module with the same structure as the sub-module. The backup modules are configured in the cascaded module groups, and the number of backup modules in each group is less than N. The backup modules are powered by the auxiliary power supply unit and are in a hot standby state. The positive and negative DC terminals of each cascaded module in the group are connected in parallel with the backup module through high-speed switches. The control module enables the high-speed switches corresponding to each cascaded module in sequence to connect the backup module in parallel with the corresponding cascaded module. It provides control signals to the backup module according to the fault status of the cascaded module.

2. The fast fault ride-through method for grouped redundancy (CHB) in ultra-high voltage active power filters according to claim 1, characterized in that, Each cascade module group has one spare module, each cascade module group has 6 cascade modules, and the total number of cascade modules is 36.

3. The fast fault ride-through method for grouped redundancy (CHB) in ultra-high voltage active power filters according to claim 1, characterized in that, Each cascade module group has an external short-circuit relay connected in parallel. When the number of faulty cascade modules in the cascade module group is greater than the number of spare modules, the relay is closed to close the cascade module group and update the group and phase shift angle of other cascade module groups.

4. The fast fault ride-through method for grouped redundancy (CHB) in ultra-high voltage active power filters according to claim 3, characterized in that, The expression for calculating the phase shift angle is: The number of phase shift steps for the nth cascaded module in the mth group is: Phase shift steps = 6(M-1) + N, and the phase shift angle for the nth cascaded module in the mth group is: .

5. The fast fault ride-through method for grouped redundancy (CHB) in ultra-high voltage active power filters according to claim 1, characterized in that, The auxiliary power supply unit includes a transformer and an uncontrolled rectifier circuit.

6. A fast fault ride-through method for grouped redundancy (CHB) in ultra-high voltage active power filters according to any one of claims 1 to 5, characterized in that, The high-speed switch is a SiC solid-state parallel converter.

7. A method of use for an ultra-high voltage active power system, characterized in that, Includes the following steps: S1. Start the cascaded H-bridge main circuit for an ultra-high voltage active power system as described in claim 6, charge each cascaded module, establish the component voltage in the cascaded module along the slope, and perform closed-loop control. S2. Power the parallel backup unit through an auxiliary power supply unit isolated from the main circuit of the cascaded H-bridge so that the state of each transistor in the backup module is similar to that of the cascaded module. S3. The control module performs fault detection on the main circuit of the cascaded H-bridge and determines the scale of the fault. S4. When the number of faulty cascaded modules is less than or equal to the number of spare modules in the cascaded module group, it is judged as a module-level fault. The control signal of the faulty cascaded module is blocked, the SiC solid-state parallel circuit is closed, and the control signal is transferred to the spare module in the group where the faulty cascaded module is located. S5. When the number of cascaded modules with faults in the same group is greater than the number of spare modules in the cascaded module group, it is judged as a group-level fault. The control signals of all cascaded modules in the cascaded module group are blocked, the short-circuit relays corresponding to the cascaded module group to which the cascaded module belongs are short-circuited, and the group and phase shift angle of other cascaded module groups are updated. S6. Replace the faulty cascade module, and charge the cascade module connected in parallel with the backup module through the auxiliary power supply unit so that it has a state relative to the other cascade modules. After maintaining this state for several switching cycles, switch the control signal of the backup module to the replaced cascade module.

8. The fast fault ride-through method for grouped redundancy (CHB) in ultra-high voltage active power filters according to claim 7, characterized in that, Indicators for judging group-level faults also include: abnormal fluctuations in DC voltage within the group exceeding the first preset limit, and input-output current imbalance between and within groups exceeding the second preset limit.

9. A fast fault ride-through method for grouped redundancy (CHB) in ultra-high voltage active power filters according to claim 7, characterized in that, The sources of faults in cascaded modules include: the DC voltage signal of the module, the current protection signal of the module, the temperature signal of the module, and the IGBT fault signal generated based on the DS voltage of the IGBT built into the cascaded module. These signals are then processed by first-order RC hardware filtering (low-pass filtering) and debouncing algorithm to avoid false triggering.

10. A fast fault ride-through method for grouped redundancy (CHB) in ultra-high voltage active power filters according to claim 9, characterized in that, The DC voltage signal of the module is also filtered by moving average to eliminate transient interference, and 12 sampling points are set to eliminate transient voltage spikes.

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