A fault-tolerant control method for SiC / Si hybrid power electronic transformer

Abstract

The application discloses a fault-tolerant control method suitable for SiC / Si hybrid power electronic transformers, and specific steps are as follows: 1) converting to obtain a pulse waveform V st (t) and V PWM (t); 2) distributing low-frequency control voltages to each full-Si high-voltage sub-module; 3) balancing the voltages of two capacitors in SiC / Si hybrid high-voltage sub-modules by switching the redundancy state of the SiC / Si hybrid high-voltage sub-modules in a high-frequency working state; and 4) realizing the control of each high-voltage sub-module after a fault. According to the system structure adopted by the application, only two SiC / Si hybrid high-voltage sub-modules are used, the high-frequency control voltages are distributed to the two SiC / Si hybrid high-voltage sub-modules through the nearest level pulse width modulation strategy and the complementary control average of high-frequency control and low-frequency control interlacing, and the remaining high-voltage sub-modules only need to undertake low-frequency switching tasks. The advantages of SiC devices and Si devices are fully exerted, and the effective balance of economy and performance is realized.

Description

Technical Field

[0001] This invention relates to the field of power electronic converter technology, specifically to a fault-tolerant control method for a SiC / Si hybrid power electronic transformer. Background Technology

[0002] Recent studies have found that using SiC devices can increase the switching frequency of converters and reduce switching losses, effectively improving converter efficiency. Furthermore, higher switching frequencies can reduce the size of magnetic components, increasing the power density of the converter. Therefore, multilevel converters using SiC devices are increasingly widely used in fields such as fast charging for electric vehicles and aerospace. However, SiC devices are expensive; at high rated currents, SiC devices can be up to eight times more expensive than Si devices. To balance the performance advantages and economic disadvantages of SiC devices, a widely adopted solution is to use a hybrid topology combining SiC and Si devices, leveraging the high performance of SiC devices while saving costs by using Si devices.

[0003] In SiC / Si hybrid topologies, one type employs a full-bridge NPC as a submodule. Through nearest-nearest-level pulse width modulation (PWM), the AC sine wave in the AC-DC conversion is decomposed into a high-frequency PWM wave and a low-frequency stepped wave. This topology uses only one SiC / Si hybrid high-voltage submodule to handle high-frequency switching events, while the remaining submodules use only all-Si submodules for low-frequency switching events. This topology leverages the performance advantages of SiC devices in high-frequency switching while also utilizing the cost advantages of Si devices. However, the existing high-frequency modulation strategy in this topology uses only the average value of the parallel upper and lower capacitors for voltage sorting in the capacitor voltage balance control strategy. This may cause voltage imbalances between the upper and lower capacitors within the submodule. Furthermore, in this operating mode, only one submodule handles high-frequency switching events. If this submodule fails, the entire system will lose high-frequency modulation, leading to more severe consequences than with conventional topologies. Summary of the Invention

[0004] The purpose of this invention is to provide a fault-tolerant control method applicable to SiC / Si hybrid power electronic transformers to solve the problems of uneven distribution of upper and lower capacitors of high-voltage submodules under high-frequency control and fault tolerance in existing SiC / Si hybrid full-bridge NPC power electronic transformers.

[0005] To achieve the above objectives, the technical solution of this invention is as follows: A fault-tolerant control method applicable to SiC / Si hybrid power electronic transformers is provided. Its innovation lies in the fact that the control method is implemented in the following fault-tolerant topology: the fault-tolerant topology consists of a voltage source V... ac (t) It consists of a high-voltage stage, an isolation stage, and a low-voltage stage, with voltage source Vac (t) and the high-voltage AC side are connected in series, and the high-voltage stage and the low-voltage stage are electrically isolated by an isolation stage;

[0006] The high-voltage stage is composed of N+2 high-voltage submodules connected in series, namely high-voltage submodule 1 to high-voltage submodule N+2; each high-voltage submodule is equipped with a bypass switch on the AC side, corresponding to K1-K respectively. N+2 Each high-voltage submodule has an upper capacitor C connected to its DC terminal. u and lower capacitor C l Of the N+2 high-voltage submodules, two are SiC / Si hybrid full-bridge ANPC topologies, and the remaining N are all-Si DNPC topologies. In the SiC / Si hybrid full-bridge ANPC topology, one bridge arm uses a half-bridge DNPC structure and uses all Si devices, while the other bridge arm uses a hybrid half-bridge ANPC topology, in which two switching transistors use SiC devices and the remaining switching transistors are all Si devices.

[0007] The isolation stage includes N+2 isolation sub-modules. The isolation sub-modules adopt a series half-bridge three-level LLC converter. The primary side of the isolation stage adopts fixed frequency and fixed duty cycle control, and the secondary side of the isolation stage adopts uncontrolled rectification control. The N+2 high-voltage sub-modules are connected in series with the N+2 isolation sub-modules respectively.

[0008] The low-voltage stage includes several DC / DC converters. The DC port of the low-voltage stage is connected to the photovoltaic power generation system and new energy vehicle through the DC / DC converters to realize power transmission.

[0009] The specific steps of the control method based on the above fault-tolerant topology are as follows:

[0010] 1) Use the nearest-level pulse width modulation method to convert the AC voltage source V ac The AC voltage generated by (t) is converted into a pulse waveform V that can be used to control the high-voltage submodule. st (t) and V PWM (t);

[0011] 2) Under normal operating conditions, collect the capacitance C of each high-voltage submodule. u and lower capacitor C l The capacitor voltages are sorted using a parallel sorting method; based on the current direction and the absolute value of the upper and lower capacitors of each high-voltage submodule relative to the current stepped wave |V st The magnitude relationship of (t)| is used to allocate low-frequency control voltage to each full-Si high-voltage submodule;

[0012] 3) Based on the capacitor voltage sorting results in step 2), perform complementary control of high-frequency and low-frequency control on the two SiC / Si hybrid high-voltage submodules according to the power frequency cycle, and balance the voltage of the two capacitors in the SiC / Si hybrid high-voltage submodule by switching the redundant state of the SiC / Si hybrid high-voltage submodule in the high-frequency operating state.

[0013] 4) After a fault occurs, disconnect the faulty high-voltage submodule, reorder the remaining high-voltage submodules, block the control signals of the faulty high-voltage submodule, and realize the control of each high-voltage submodule after the fault.

[0014] Furthermore, in step 1), the nearest-level pulse width modulation method is used to modulate the AC voltage source V. ac The AC voltage generated by (t) is converted into a modulated waveform V that can be used to control the high-voltage submodule. st (t) and V PWM The specific steps for (t) are as follows:

[0015] (11) Set the modulation ratio M o According to the withstand voltage rating U of each component in the high voltage submodule r and AC voltage source voltage peak V peak Determine the DC voltage V output by each high-voltage submodule. dc The number of submodules is N+2;

[0016] (12) According to the modulation ratio M described in step (11) o and the DC bus voltage V output by the high voltage submodule dc Through the AC voltage source voltage waveform V ac (t), calculate the stepped wave V used to control the high-voltage submodule of the entire Si. st (t) and the modulation wave V used to control the SiC / Si hybrid high-voltage submodule m (t), the calculation formula is:

[0017]

[0018]

[0019] (13) Set the high-frequency carrier frequency f c Determine 1 / f c High-frequency triangular carrier V with periodicity c (t);

[0020] (14) The modulation wave V according to steps (12) and (13) m (t) and high-frequency triangular carrier V c (t), calculate the high-frequency pulse signal V PWM (t), the calculation formula is:

[0021]

[0022] Furthermore, step 2) specifically includes the following steps:

[0023] (21) Take the average value of the upper and lower capacitor voltages of one of the SiC / Si hybrid high voltage submodules and sort them in ascending order with the upper and lower capacitor voltages of the other high voltage submodules to calculate the capacitor voltage ranking rank1; take the average value of the upper and lower capacitor voltages of another SiC / Si hybrid high voltage submodule and sort them in ascending order with the upper and lower capacitor voltages of all the other high voltage submodules to calculate the capacitor voltage ranking rank2.

[0024] (22) Based on the capacitor voltage obtained in step (21), sort rank1 and assign low-frequency voltage control signals to the remaining high-voltage submodules;

[0025] (23) Based on the capacitor voltage sorting rank2 obtained in step (21), assign low-frequency voltage control signals to the remaining high-voltage submodules;

[0026] (24) According to steps (22) and (23), when the current direction is positive, if the sorting results of the upper and lower capacitor voltages of a certain high-voltage submodule are both less than |V st If (t)|, then all capacitors of the high-voltage submodule will be connected, and the switching action will be [1 1 0 0 0 01 1]; if a high-voltage submodule only has the upper capacitor C u The sorting result is less than |V st (t)|, then the high-voltage submodule only has the upper capacitor C u When activated, the switch action is [1 1 0 0 0 1 1 0]; otherwise, the high-voltage submodule only has the lower capacitor C. l It will be activated, and the switch action will be [0 1 1 0 0 0 1 1];

[0027] When the current direction is negative, if the sorting results of a certain high-voltage submodule are both less than |V st If (t)|, then all capacitors in the high-voltage submodule will be connected, and the switching action will be [0 0 1 1 1 1 0 0]; if a high-voltage submodule only has the upper capacitor C u The sorting result is less than |V st (t)|, then the high-voltage submodule only has the upper capacitor C u When activated, the switch action is [0 0 1 1 0 1 10]; otherwise, the high-voltage submodule only has the lower capacitor C. l The circuit will be activated, and the switching action will be [0 1 1 0 1 1 0 0]; if the voltage of both the upper and lower capacitors of a certain high-voltage submodule is greater than |V stIf (t)|, then regardless of the positive or negative current, the upper and lower capacitors will be cut off, and the switching action is [0 1 1 0 0 1 1 0].

[0028] Furthermore, the specific steps of step 3) are as follows:

[0029] (31) The control mode for controlling the high voltage submodule is switched with the power frequency as the cycle. If the ranking result rank1 is used to control all high voltage submodules in the current power frequency cycle, that is, the high voltage submodule of SiC / Si hybrid corresponding to the ranking result rank1 will work under high frequency control, and all other high voltage submodules will work under low frequency control; at the same time, in the next power frequency cycle, the high voltage stage will use the ranking result rank2 to control all high voltage submodules, that is, the high voltage submodule of SiC / Si hybrid corresponding to the ranking result rank2 will work under high frequency control, and all other high voltage submodules will work under low frequency control.

[0030] (32) Select the SiC / Si hybrid high-voltage submodule for high-frequency control according to step (31); when the current direction is positive, if the average voltage sorting result of the upper and lower bridge arms of the high-voltage submodule under high-frequency control is less than |V st (t)|, this high-voltage submodule will switch frequently between +2 level and +1 level, with switching actions of [1 1 0 0 0 1 0 0 1 1] and [1 0 1 0 01 0 0 1 1]; when the current direction is positive and the sorting result is greater than |V st When (t)|, the high-voltage submodule will switch between +1 and 0 levels at high frequency, with switching actions of [1 1 0 0 0 1 0 1 1 0] and [1 1 0 0 0 1 0 1 1 0]. At this time, only the upper capacitor C is active. u In charging state; when the current direction is negative and the sorting result of the high-voltage submodule is greater than |V st When (t)|, the high-voltage submodule will rapidly switch between 0 and -1 levels, with switching actions of [0 1 0 1 1 0 0 1 1 0] and [0 0 1 1 10 0 1 1 0]. At this time, only the lower capacitor C... l In charging state; when the current direction is negative and the sorting result of the high-voltage submodule is less than |V st When (t)|, the high-voltage submodule will quickly switch between -1 level and -2 level, with the switching action being [0 1 0 1 1 01 1 0 0] and [0 0 1 1 1 0 1 1 0 0];

[0031] (33) Based on the high-frequency control method for the high-voltage submodule in step (32), the switching action mode is reselected according to the relationship between the upper and lower capacitor voltages of the high-voltage submodule under high-frequency control. Let Δuc =u cu -u cl , where u cu The voltage across the upper capacitor, u cl The voltage of the lower capacitor; when the current direction is positive and the sorting result of the high-voltage submodule is greater than |V st When (t)|, if Δu c If the value is greater than 0, redundant switching actions [0 1 0 0 1 0 0 0 1 1] and [0 0 1 0 1 0 0 0 1 1] will be used. At this time, the high-voltage submodule will switch rapidly between +1 level and 0 level, and only the lower capacitor C will be active. l In charging state; when the current direction is negative and the sorting result of the high-voltage submodule is greater than |V st When (t)|, if Δu c If the value is greater than 0, redundant switching actions [0 0 1 0 01 1 1 0 0] and [0 1 0 0 0 1 1 1 0 0] will be used. At this time, the high-voltage submodule will switch rapidly between +1 level and 0 level, and only the upper capacitor C will be active. u The module is in a charging state; if it is in another state, the control method of step (32) is still used to control the high-voltage submodule of SiC / Si hybrid under high-frequency control.

[0032] (34) Set the voltage threshold u lim Only when Δu c >u lim Only when necessary will the normal switching state be switched to the redundant switching state to reduce the number of times the Si devices in the SiC / Si hybrid high voltage submodule are activated.

[0033] Furthermore, the specific steps of step 4) include:

[0034] (41) Set a fault tolerance cut-off time. After a fault occurs in a switching device in a high voltage submodule or an isolation submodule connected in series with it, the faulty high voltage submodule is cut off within the fault tolerance time using the bypass switch corresponding to the high voltage submodule.

[0035] (42) The control method for the faulty high-voltage submodule and the isolation submodule connected in series with it is: by pulse control, all switch states of the faulty high-voltage submodule and the isolation submodule connected in series with it are set to zero, and at the same time, the sorting result of the faulty high-voltage submodule is set to the highest.

[0036] (43) The control method for a normally functioning high-voltage submodule is as follows: If the faulty high-voltage submodule is a SiC / Si hybrid high-voltage submodule corresponding to the sorting result, the sorting result and its corresponding control method are used for control. The other SiC / Si hybrid high-voltage submodule will always be under high-frequency control and will no longer perform complementary switching between high and low frequencies. If the faulty high-voltage submodule is an all-Si high-voltage submodule, the sorting result and its corresponding control method are used for control. The SiC / Si hybrid high-voltage submodule corresponding to the sorting result will undertake the high-frequency switching task, and the other SiC / Si hybrid high-voltage submodule will always work under low-frequency control.

[0037] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0038] (1) Regarding the system structure adopted in this invention, only two SiC / Si hybrid high-voltage submodules are used. The high-frequency control voltage is distributed to the two SiC / Si hybrid high-voltage submodules through the nearest-level pulse width modulation strategy and the complementary control of alternating high-frequency and low-frequency control. The remaining high-voltage submodules only need to undertake the low-frequency switching task. This fully utilizes the advantages of SiC devices and Si devices, and achieves an effective balance between economy and performance.

[0039] (2) To address the issue that existing SiC / Si hybrid high-voltage submodules only sort the upper and lower capacitors by their average values ​​while neglecting voltage balance control between them, this invention adds four new redundant states to the SiC / Si hybrid high-voltage submodule. This allows the SiC / Si hybrid high-voltage submodule under high-frequency control to freely select and charge one side of the capacitor individually in each half-cycle based on the voltage relationship between the upper and lower capacitors, thus improving the problem of capacitor voltage imbalance.

[0040] (3) Addressing the problem of system loss of high-frequency voltage modulation and subsequent system malfunction caused by a fault in the existing SiC / Si hybrid high-voltage submodule under high-frequency control in SiC / Si hybrid power electronic transformers, this invention adds an additional SiC / Si hybrid high-voltage submodule for redundancy. Under normal system operation, this submodule shares the high-frequency switching task with the other SiC / Si hybrid high-voltage submodule. In the event of a fault, it can replace the SiC / Si hybrid high-voltage submodule to perform high-frequency switching tasks and also replace the all-Si high-voltage submodule to achieve low-frequency control. This ensures that the system can continue to operate normally after a fault. Attached image description:

[0041] Figure 1 Schematic diagram of redundancy control and fault-tolerant control methods applicable to SiC / Si hybrid power electronic transformers

[0042] Figure 2This is a fault-tolerant topology diagram illustrating the fault-tolerant control method for SiC / Si hybrid power electronic transformers according to the present invention.

[0043] Figure 3 Schematic diagram of the nearest-level pulse width modulation for power electronic transformers applicable to SiC / Si hybrids.

[0044] Figure 4 Schematic diagram of parallel sequencing of capacitor voltages for selecting different SiC / Si hybrid high-voltage submodules to undertake high-frequency control.

[0045] Figure 5 Control principle diagram for an all-Si high-voltage submodule of a power electronic transformer suitable for SiC / Si hybrid power electronics.

[0046] Figure 6 Schematic diagram of high-frequency control for SiC / Si hybrid high-voltage submodule with redundant switching states applicable to SiC / Si hybrid power electronic transformers.

[0047] Figure 7 This is the input voltage of SiC / Si hybrid high voltage submodule 1.

[0048] Figure 8 It is the input voltage of SiC / Si hybrid high-voltage submodule N+2.

[0049] Figure 9 The SiC / Si hybrid high-voltage submodule 1 failed at 0.39s, and the input voltage of the high-voltage stage of the power electronic transformer was cut off at 0.4s.

[0050] Figure 10 At 0.39s, the SiC / Si hybrid high-voltage submodule 1 failed, and after being disconnected at 0.4s, the input current of the high-voltage stage of the power electronic transformer...

[0051] Figure 11 At 0.39s, the SiC / Si hybrid high-voltage submodule 1 failed, and after being disconnected at 0.4s, the bus voltage of the high-voltage stage of the power electronic transformer...

[0052] Figure 12 At 0.39s, the SiC / Si hybrid high-voltage submodule 1 failed, and after being disconnected at 0.4s, the bus voltage of the low-voltage stage of the power electronic transformer... Detailed implementation method:

[0053] The present invention will be further described below with reference to the accompanying drawings and specific embodiments.

[0054] This invention provides a fault-tolerant control method for power electronic transformers applicable to SiC / Si hybrid transformers. The control method is applicable to situations such as... Figure 2 Implemented in the fault-tolerant topology: The fault-tolerant topology used consists of voltage source Vac (t) It consists of a high-voltage stage, an isolation stage, and a low-voltage stage, with voltage source V ac (t) and the high-voltage AC side are connected in series, and the high-voltage stage and the low-voltage stage are electrically isolated by an isolation stage;

[0055] The high-voltage stage is composed of N+2 high-voltage submodules connected in series, namely high-voltage submodule 1 to high-voltage submodule N+2; each high-voltage submodule is equipped with a bypass switch on the AC side, corresponding to K1-K respectively. N+2 Each high-voltage submodule has an upper capacitor C connected to its DC terminal. u and lower capacitor C l Of the N+2 high-voltage submodules, two are SiC / Si hybrid full-bridge ANPC topologies, and the remaining N are all-Si DNPC topologies. In the SiC / Si hybrid full-bridge ANPC topology, one bridge arm uses a half-bridge DNPC structure, employing all Si devices, while the other bridge arm uses a hybrid half-bridge ANPC topology, where two switches use SiC devices, and the remaining switches are all Si devices. In this embodiment, as... Figure 2 As shown, the SiC / Si hybrid high-voltage submodule in this invention is located at both ends of the series connection of the high-voltage submodules, namely high-voltage submodule 1 and high-voltage submodule N+1. In the high-voltage submodules, the drive signals used to control the SiC MOSFETs in the SiC / Si hybrid high-voltage submodule are labeled S2 and S3, and the remaining Si IGBT drive signals are labeled S1, S3-S... 10 In the all-Si high-voltage submodule, the drive signals used to control the Si IGBTs are labeled S1-S8, and they are transmitted through a matrix [S1 S2 ... S...]. i [] indicates the on / off state of the drive signal, where i = 8 when controlling the all-Si high-voltage submodule and i = 10 when controlling the SiC / Si hybrid high-voltage submodule.

[0056] The isolation stage includes N+2 isolation sub-modules. The isolation sub-modules adopt series half-bridge three-level LLC converters. The primary side of the isolation stage adopts fixed frequency and fixed duty cycle control, and the secondary side of the isolation stage adopts uncontrolled rectification control. The N+2 high-voltage sub-modules are connected in series with the N+2 isolation sub-modules respectively.

[0057] The low-voltage stage includes several DC / DC converters. The DC port of the low-voltage stage is connected to the photovoltaic power generation system and new energy vehicles through the DC / DC converters to realize power transmission.

[0058] The specific steps and flow of the control method based on the above fault-tolerant topology are as follows: Figure 1 As shown, specifically:

[0059] 1) Use the nearest-level pulse width modulation method to convert the AC voltage source V acThe AC voltage generated by (t) is converted into a pulse waveform V that can be used to control the high-voltage submodule. st (t) and V PWM (t); The specific steps are as follows:

[0060] (11) Set the modulation ratio M o According to the withstand voltage rating U of each component in the high voltage submodule r and AC voltage source voltage peak V peak Determine the DC voltage V output by each high-voltage submodule. dc The number of submodules is N+2;

[0061] (12) According to the modulation ratio M described in step (11) o and the DC bus voltage V output by the high voltage submodule dc Through the AC voltage source voltage waveform V ac (t), calculate the stepped wave V used to control the high-voltage submodule of the entire Si. st (t) and the modulation wave V used to control the SiC / Si hybrid high-voltage submodule m (t), the calculation formula is:

[0062]

[0063]

[0064] (13) Set the high-frequency carrier frequency f c Determine 1 / f c High-frequency triangular carrier V with periodicity c (t);

[0065] (14) The modulation wave V according to steps (12) and (13) m (t) and high-frequency triangular carrier V c (t), calculate the high-frequency pulse signal V PWM (t), the calculation formula is:

[0066]

[0067] Figure 3 The diagram shows the modulation principle using the nearest level pulse width modulation. The normalized AC voltage source voltage is calculated using the following formula:

[0068]

[0069] like Figure 3 visible V st (t) and V PWM (t) summation yields:

[0070]

[0071] 2) Under normal operating conditions, collect the capacitance C of each high-voltage submodule. u and lower capacitor C l The capacitor voltages are sorted using a parallel sorting method; based on the current direction and the absolute value of the upper and lower capacitors of each high-voltage submodule relative to the current stepped wave |V st The magnitude relationship of (t)| is used to allocate low-frequency control voltage to each full-Si high-voltage submodule;

[0072] Specifically, the steps include the following:

[0073] (21) Take the average value of the upper and lower capacitor voltages of one of the SiC / Si hybrid high voltage submodules and sort them in ascending order with the upper and lower capacitor voltages of the other high voltage submodules to calculate the capacitor voltage ranking rank1; take the average value of the upper and lower capacitor voltages of another SiC / Si hybrid high voltage submodule and sort them in ascending order with the upper and lower capacitor voltages of all the other high voltage submodules to calculate the capacitor voltage ranking rank2.

[0074] Figure 4 The schematic diagram shows the arrangement of SiC / Si hybrid high-voltage submodule 1 or N+2 as the high-frequency control module.

[0075] The voltage of the upper and lower capacitors of the submodule using high-frequency control will be averaged.

[0076]

[0077] H is the sequence number of the module capacitor voltage under high-frequency control. When the high-voltage submodule 1 is under high-frequency control, H = 1; when the high-voltage submodule N+2 is under high-frequency control, H = 2N+3.

[0078] Furthermore, parallel sorting is used to sort the capacitor voltages in each high-voltage submodule.

[0079]

[0080] Where n i (k) represents the sorting of the k-th capacitor voltage when the i-th sorting strategy is selected. When i=1, the SiC / Si hybrid high voltage submodule 1 adopts a high-frequency control strategy. When i=2, the SiC / Si hybrid high voltage submodule N+2 adopts a high-frequency control strategy. sign(x) is the sign function, which outputs +1, -1 and 0 according to the positive or negative sign of the independent variable x.

[0081] Furthermore, the sorting results of the capacitor voltages of all sub-modules are stored in rank. i In the middle, it is represented as rank i =[ni (1) n i (2) … n i (k) … n i (2N+3)], and the stepped wave control signal V st (t) is compared.

[0082] (22) Based on the capacitor voltage obtained in step (21), sort rank1 and assign low-frequency voltage control signals to the remaining high-voltage submodules;

[0083] (23) Based on the capacitor voltage sorting rank2 obtained in step (21), assign low-frequency voltage control signals to the remaining high-voltage submodules;

[0084] (24) According to steps (22) and (23), when the current direction is positive, if the sorting results of the upper and lower capacitor voltages of a certain high-voltage submodule are both less than |V st If (t)|, then all capacitors of the high-voltage submodule will be connected, and the switching action will be [1 1 0 0 0 01 1]; if a high-voltage submodule only has the upper capacitor C u The sorting result is less than |V st (t)|, then the high-voltage submodule only has the upper capacitor C u When activated, the switch action is [1 1 0 0 0 1 1 0]; otherwise, the high-voltage submodule only has the lower capacitor C. l It will be activated, and the switch action will be [0 1 1 0 0 0 1 1];

[0085] When the current direction is negative, if the sorting results of a certain high-voltage submodule are both less than |V st If (t)|, then all capacitors in the high-voltage submodule will be connected, and the switching action will be [0 0 1 1 1 1 0 0]; if a high-voltage submodule only has the upper capacitor C u The sorting result is less than |V st (t)|, then the high-voltage submodule only has the upper capacitor C u When activated, the switch action is [0 0 1 1 0 1 10]; otherwise, the high-voltage submodule only has the lower capacitor C. l The circuit will be activated, and the switching action will be [0 1 1 0 1 1 0 0]; if the voltage of both the upper and lower capacitors of a certain high-voltage submodule is greater than |V st If (t)|, then regardless of the positive or negative current, the upper and lower capacitors will be cut off, and the switching action is [0 1 1 0 0 1 1 0].

[0086] The flowchart for selecting the capacitor operating state of the all-Si high-voltage submodule is as follows: Figure 5 As shown. In Figure 5In this model, each all-Si high-voltage submodule is divided into two parts: [S1 S2 S3 S4] and [S5 S6 S7 S8]. Since there is no redundant state in the all-Si high-voltage submodule, the charging and bypassing actions of the upper capacitor under positive and negative currents can be represented as [1 1 0 0], [00 1 1], and [0 1 1 0]; the charging and bypassing actions of the lower capacitor under positive and negative currents can be represented as [0 0 1 1], [1 1 0 0], and [0 1 1 0]. These can be determined by the rank matrix. i The matrix index i and capacitor voltage index k of (k) determine whether the capacitor voltage is under the control of [S1 S2 S3 S4] or [S5 S6 S7 S8]. After obtaining the final result, [S1 S2 S3 S4] and [S5 S6 S7 S8] are merged into a matrix [S1 S2 ... S8] to jointly control the high voltage submodule.

[0087] exist Figure 5 In the middle, by setting the judgment condition: |V st (t)|Whether to change; This judgment condition reduces the frequent changes in sorting caused by the capacitor voltages of each submodule being too close, which leads to the sorting result being inconsistent with |V. st To mitigate the rapid changes in the relationship between (t)|, reduce unnecessary switching of low-frequency Si devices;

[0088] Meanwhile, the time interval between each judgment node is:

[0089]

[0090] Where k∈(-N-2,0]∪[0,N+2) and k is an integer, f s The power frequency is typically taken as 50Hz. At the nodes k = -N-2 and k = N+2, due to the modulation wave V... m (t)≠0, therefore it is not a decision node; and the time interval between decision nodes between k=-N-1 and k=N+1 is...

[0091] Each judgment node is in the stepped wave V st The nodes of change (t) were not missed, and no valid judgment nodes were omitted.

[0092] The operating conditions of each voltage in the all-Si high-voltage submodule and the corresponding capacitor charging and discharging conditions are shown in Table 1. Where u cu n i (k) represents the capacitor voltage on the all-Si high-voltage submodule under low-frequency control and the sorting result under the i-sorting method, respectively. cl n i(k+1) represents the capacitor voltage under this high-voltage submodule and the sorting result under sorting i, respectively; F1-F8 represent the control modes of each switch action of the full-Si high-voltage submodule. The switching actions of the full-Si high-voltage submodule under low-frequency control are shown in Table 1:

[0093] Table 1

[0094]

[0095]

[0096] 3) Based on the capacitor voltage sorting results in step 2), perform complementary control of high-frequency and low-frequency control on the two SiC / Si hybrid high-voltage submodules according to the power frequency cycle, and balance the voltage of the two capacitors in the SiC / Si hybrid high-voltage submodule by switching the redundant state of the SiC / Si hybrid high-voltage submodule in the high-frequency operating state.

[0097] The specific steps are as follows:

[0098] (31) The control mode for controlling the high voltage submodule is switched using the power frequency as the cycle. If the ranking result rank1 is used to control all high voltage submodules in the current power frequency cycle, that is, the high voltage submodule of SiC / Si hybrid corresponding to the ranking result rank1 will work under high frequency control, and all other high voltage submodules will work under low frequency control; at the same time, in the next power frequency cycle, the high voltage stage will use the ranking result rank2 to control all high voltage submodules, that is, the high voltage submodule of SiC / Si hybrid corresponding to the ranking result rank2 will work under high frequency control, and all other high voltage submodules will work under low frequency control.

[0099] (32) For the SiC / Si hybrid high-voltage submodule under high-frequency control, since the SiC devices in the submodule are constantly switching rapidly, the submodule will switch at high frequency between complementary switch groups consisting of two levels at any given time. The selection of the high-frequency switching complementary switch group is related to the current direction, the average voltage sorting result of the upper and lower bridge arms, and the magnitude of the absolute value of the current step wave. st (t)|Related.

[0100] According to step (31), a SiC / Si hybrid high-voltage submodule is selected for high-frequency control; when the current direction is positive, if the average voltage ranking result of the upper and lower bridge arms of the high-voltage submodule under high-frequency control is less than |V st (t)|, this high-voltage submodule will switch between +2 level and +1 level at high frequency, with switching actions of [1 1 0 0 0 1 0 0 1 1] and [1 0 1 0 0 10 0 1 1]; when the current direction is positive and the sorting result is greater than |V stWhen (t)|, the high-voltage submodule will switch between +1 and 0 levels at high frequency, with switching actions of [1 1 0 0 0 1 0 1 1 0] and [1 1 0 0 0 1 0 1 1 0]. At this time, only the upper capacitor C is active. u In charging state; when the current direction is negative and the sorting result of the high-voltage submodule is greater than |V st When (t)|, the high-voltage submodule will rapidly switch between 0 and -1 levels, with switching actions of [0 1 0 1 1 0 0 1 1 0] and [0 0 1 1 1 00 1 1 0]. At this time, only the lower capacitor C is active. l In charging state; when the current direction is negative and the sorting result of the high-voltage submodule is less than |V st When (t)|, the high-voltage submodule will quickly switch between -1 level and -2 level, with the switching action being [0 1 0 1 1 0 11 0 0] and [0 0 1 1 1 0 1 1 0 0];

[0101] (33) Assuming that the power supplied by the AC voltage source to the SiC / Si hybrid high-voltage submodule under high-frequency control does not decrease during the entire phase of the control of two complementary switches, the power difference between the upper and lower capacitors of the submodule can be expressed as:

[0102]

[0103] Where t p and t n The starting time points for the rapid switching between +1 and +2 levels in the submodule during the positive half-cycle and the starting time points for the switching between -1 and -2 levels during the negative half-cycle; t l+ and t u- These are the charging times of the lower capacitor in the positive half-cycle and the upper capacitor in the negative half-cycle of this submodule, respectively; Z eq The equivalent impedance is assumed to be the same within one cycle.

[0104] Because the SiC / Si hybrid high-voltage submodule under high-frequency control uses the average voltage of the upper and lower capacitors for sorting, it cannot flexibly modulate the voltage of the upper and lower capacitors. During the positive half-cycle, if the lower capacitor voltage is lower than the upper capacitor voltage, the upper capacitor will be charged simultaneously with the lower capacitor. As the overall capacitor voltage increases, the sorting result of the submodule's average voltage will increase, causing the submodule's switching state to fall back to the 0 and +1 level operating range during the positive half-cycle, charging only the upper capacitor. The same applies during the negative half-cycle, resulting in the lower capacitor charging for a longer period than the upper capacitor. Although both the upper and lower capacitors have periods with longer charging times than each other throughout the cycle, deviations still occur because the switching device operation is controlled by the average capacitor voltage in each cycle. Therefore, four redundancy modes are added to balance the deviations of the upper and lower capacitors.

[0105] Based on the high-frequency control method for the high-voltage submodule in step (32), and according to the relationship between the upper and lower capacitor voltages of the high-voltage submodule under high-frequency control, the switching action mode is reselected, and Δu is set. c =u cu -u cl , where u cu The voltage across the upper capacitor, u cl The voltage of the lower capacitor; when the current direction is positive and the sorting result of the high-voltage submodule is greater than |V st When (t)|, if Δu c If the value is greater than 0, redundant switching actions [0 1 0 0 1 0 0 0 1 1] and [0 0 1 0 1 0 0 0 1 1] will be used. At this time, the high-voltage submodule will switch rapidly between +1 level and 0 level, and only the lower capacitor C will be active. l In charging state; when the current direction is negative and the sorting result of the high-voltage submodule is greater than |V st When (t)|, if Δu c If the value is greater than 0, redundant switching actions [0 0 1 0 0 1 11 0 0] and [0 1 0 0 0 1 1 1 0 0] will be used. At this time, the high-voltage submodule will switch rapidly between +1 level and 0 level, and only the upper capacitor C will be active. u If it is in a charging state, the control method of step (32) is still used to control the high voltage submodule of SiC / Si hybrid under high frequency control.

[0106] The switching actions of each submodule under high-frequency control are shown in Table 2.

[0107] Table 2

[0108]

[0109] (34) Set the voltage threshold u lim Only when Δu c >u lim Only when necessary will the normal switching state be switched to the redundant switching state to reduce the number of times the Si devices in the SiC / Si hybrid high voltage submodule are activated.

[0110] In the six complementary switch action control modes P2 and P shown in Table 2, 11 P 12 N 12 N 11Within N2, only SiC devices S2 and S3 switch rapidly, without any switching of Si devices. Switching of Si devices occurs between control modes, and the number of Si device switching cycles during the switching of modes that may switch between groups is shown in Table 3. Based on Tables 2 and 3, the following analysis can be made:

[0111] Table 3

[0112]

[0113]

[0114] Define P 12 and N 12 For redundant control mode, P2, P 11 N 11 N2 represents the normal control mode. As shown in Table 3, when the SiC / Si hybrid high-voltage submodule under high-frequency control is switching between the +1 to +2 level control range and the 0 to +1 level control range, if it switches from normal control mode P2 to normal control mode P... 11 The required number of Si device switching operations is 2; while the transition from normal control mode P2 to redundant control mode P... 12 Therefore, the required number of Si device switching operations is 4. When this submodule is switching from the -1 to -2 level control range to the 0 to -1 level control range, it can be seen that the switch from normal control mode N2 to normal control mode N... 11 The required number of Si device operations is still higher than when switching to redundant control mode N2. 12 The Si device operates less than twice. The switching mode with the most Si device operations is the redundant state P. 12 and N 12 The switching between modes involved the Si device performing up to 8 actions. As shown in Table 3, the switching between each control mode varies with the current direction and Δu. c Positive and negative and |V st Any change in the magnitude of (t) can occur and is unavoidable. To reduce the large number of actions of Si devices caused by switching between control modes, especially from normal operating state to redundant operating state,

[0115] Therefore, a voltage threshold u is set. lim Only when Δu c >u lim Only when necessary will the normal switching state be switched to the redundant switching state to reduce the number of times the Si devices in the SiC / Si hybrid high voltage submodule are activated.

[0116] The control flowchart of the SiC / Si hybrid high-voltage submodule under high-frequency control is as follows: Figure 6 As shown.

[0117] 4) After a fault occurs, disconnect the faulty high-voltage submodule, reorder the remaining high-voltage submodules, block the control signals of the faulty high-voltage submodule, and realize the control of each high-voltage submodule after the fault.

[0118] The specific steps include:

[0119] (41) Set a fault tolerance cut-off time. After a fault occurs in a switching device in a high voltage submodule or an isolation submodule connected in series with it, the faulty high voltage submodule is cut off within the fault tolerance time using the bypass switch corresponding to the high voltage submodule.

[0120] (42) The control method for the faulty high-voltage submodule and the isolation submodule connected in series with it is as follows: The switching states of the faulty high-voltage submodule and the isolation submodule connected in series with it are set to zero via pulse control. That is, the high-voltage stage switching state is set to [0 0 0 0 0 0 0 0 0] or [0 0 0 0 0 0 0 0 0 0], and the primary side switching state of the isolation stage is [0 0 0 0]. Simultaneously, the sorting result of the faulty high-voltage submodule is placed at the highest level.

[0121] (43) The control method for a normally functioning high-voltage submodule is as follows: If the faulty high-voltage submodule is a SiC / Si hybrid high-voltage submodule corresponding to the ranking result rank2, then the ranking result rank2 and its corresponding control method are used for control. The other SiC / Si hybrid high-voltage submodule will always be under high-frequency control and will no longer perform complementary switching between high and low frequencies. If the faulty high-voltage submodule is an all-Si high-voltage submodule, then the ranking result rank1 and its corresponding control method are used for control. The high-frequency switching task is undertaken by the SiC / Si hybrid high-voltage submodule corresponding to the ranking result rank1, and the other SiC / Si hybrid high-voltage submodule will always work under low-frequency control.

[0122] To further describe the fault-tolerant control method for power electronic transformers applicable to SiC / Si hybrid transformers proposed in this invention, the following examples illustrate the invention:

[0123] In this embodiment of the invention, the high-voltage stage is a 4-module single-phase cascaded hybrid full-bridge NPC multilevel converter. The high-voltage AC power input voltage is 800V, the high-voltage stage DC bus voltage is 1.6kV, and the low-voltage stage DC bus voltage is 260V. In the high-voltage stage, high-voltage submodule 1 and high-voltage submodule 4 are SiC / Si hybrid high-voltage submodules.

[0124] Based on step (1), determine the modulation ratio. High-frequency carrier frequency f c The frequency is 3kHz, and the step wave V is calculated. st(t), Modulation wave V m (t) and high-frequency pulse signal V PWM (t).

[0125] According to step (21), the average value of the upper and lower capacitors of the SiC / Si hybrid high voltage submodule 4 is sorted in ascending order with the upper and lower capacitor voltages of the other high voltage submodules to calculate the capacitor voltage ranking rank2. The average value of the upper and lower capacitors of the high voltage submodule 1 is sorted in ascending order with the upper and lower capacitor voltages of the other high voltage submodules to calculate the capacitor voltage ranking rank1.

[0126] According to steps (22) and (23), low-voltage control signals are assigned to the high-voltage submodules except high-voltage submodule 1 when the capacitor voltage ranking is rank1, and voltage control signals are assigned to the high-voltage submodules except high-voltage submodule 4 when the ranking result is rank2.

[0127] According to the control method described in (24), the stepped wave signal is distributed to the high-voltage submodule controlled by the low frequency. Figure 7 and Figure 8 These are the input voltage waveforms of SiC / Si hybrid high-voltage submodules 1 and 4 under normal operating conditions, respectively. It can be seen that... Figure 8 During the 0.1s-0.12s interval, because the system is under the control of the ranking result rank2, the high-voltage submodule 1 is controlled by a low-frequency signal, and the input voltage is a stepped wave; Figure 7 During the 0.12-0.14s period, as the system is under the control of the sorting result rank1, the high-voltage submodule 4 is controlled by the low-frequency signal, and the input voltage is a stepped wave.

[0128] Simultaneously, according to the control in step (31), the control mode for controlling the high-voltage submodule is switched periodically with the power frequency as the cycle, realizing the high-frequency complementary control strategy of the SiC / Si hybrid high-voltage submodule. At the same time, the normal switching action and redundant switching action control in steps (32), (33) and (34) are used, and the voltage threshold u is set. lim =0.5V, for high-frequency control of the SiC / Si hybrid high-voltage submodule. It can be seen that... Figure 7 During the 0.1s-0.12s interval, high-voltage submodule 1 is controlled by a high-frequency switch. Figure 8 During the 0.12s-0.14s interval, the high-voltage submodule is controlled by a high-frequency switch. It is also evident that only one of these two high-voltage submodules is under high-frequency control at any given time.

[0129] Figure 9 The 0.35s-0.39s range represents the high-voltage input voltage when the system is operating normally. As can be seen, the input voltage is as follows: Figure 3The waveform shown is the closest level pulse width modulation waveform. Since the SiC / Si hybrid high voltage submodule is used as a redundant system, it does not increase the number of input voltage levels. Figure 10 The 0.35-0.39s interval represents the high-voltage stage input current under normal operating conditions. It can be seen that the input current operates under a sinusoidal waveform, indicating stable system operation. Furthermore, due to the addition of redundant switching states, neither the high-voltage stage input voltage nor the input current exhibits distortion due to capacitor voltage imbalance.

[0130] Figure 9 The waveform of the high-voltage stage input voltage during the 0.39s-0.4s interval is the system operating with a fault. According to step (41), the fault tolerance clearing time t is set. r =0.01s, which is half a power frequency cycle. During this time period, the device in SiC / Si hybrid high voltage submodule 1 malfunctioned and was not switched off. It can be seen that during this time period, the entire high voltage stage of the system lost high frequency signal control. Without a corresponding fault resolution strategy, the system will continue to operate in a state of high frequency signal absence. The system switched off the faulty submodule at 0.4s and adopted the control strategy of step (42). The high voltage stage switch state was set to [0 0 0 0 0 0 0 0 0 0], the isolation stage primary side switch state was set to [0 0 0 0], and the sorting result of the faulty high voltage submodule was placed at the highest.

[0131] In step (43), different control strategies are selected based on the faulty high-voltage submodule. Since the faulty submodule is SiC / Si hybrid high-voltage module 1, the ranking result rank2 and its corresponding control method are used for control. High-voltage submodule 4 takes over the high-frequency switching task, and the complementary control of high-frequency and low-frequency control is no longer performed. Therefore, after 0.4s, the input voltage waveform quickly recovers to high-frequency control, and the system returns to steady state.

[0132] Similarly, Figures 10-12 The waveforms represent the high-voltage input current, high-voltage bus voltage, and low-voltage bus voltage of the power electronic transformer, respectively. It can be seen that each waveform exhibited varying degrees of instability within the 0.39s-0.4s time period, resulting in unstable operation. After the fault was cleared at 0.4s, all waveforms recovered to a stable state after a transient period. Therefore, the control strategy proposed in this patent enables the SiC / Si hybrid power electronic transformer to operate stably after a fault.

[0133] The above description is merely a preferred embodiment of the invention and not a limitation thereof. Any variations or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in this invention should be included within the protection scope of this invention.

Claims

1. A fault-tolerant control method for power electronic transformers applicable to SiC / Si hybrid transformers, characterized in that: The control method is implemented in the following fault-tolerant topology: the fault-tolerant topology uses a voltage source It consists of a high-voltage stage, an isolation stage, and a low-voltage stage, forming a voltage source. It is connected in series with the AC side of the high-voltage stage, and the high-voltage stage and the low-voltage stage are electrically isolated by an isolation stage; The high-voltage stage is composed of N+2 high-voltage submodules connected in series, namely high-voltage submodule 1 to high-voltage submodule N+2; each high-voltage submodule is equipped with a bypass switch on the AC side, corresponding to respectively... - Each high-voltage submodule has an upper capacitor connected to its DC terminal. and lower capacitor Of the N+2 high-voltage submodules, two are SiC / Si hybrid full-bridge ANPC topologies, and the remaining N are all-Si DNPC topologies. In the SiC / Si hybrid full-bridge ANPC topology, one bridge arm uses a half-bridge DNPC structure and uses all Si devices, while the other bridge arm uses a hybrid half-bridge ANPC topology, in which two switching transistors use SiC devices and the remaining switching transistors are all Si devices. The isolation stage includes N+2 isolation sub-modules. The isolation sub-modules adopt a series half-bridge three-level LLC converter. The primary side of the isolation stage adopts fixed frequency and fixed duty cycle control, and the secondary side of the isolation stage adopts uncontrolled rectification control. The N+2 high-voltage sub-modules are connected in series with the N+2 isolation sub-modules respectively. The low-voltage stage includes several DC / DC converters. The DC port of the low-voltage stage is connected to the photovoltaic power generation system and new energy vehicle through the DC / DC converters to realize power transmission. The specific steps of the control method based on the above fault-tolerant topology are as follows: 1) Use the nearest-level pulse width modulation method to convert the AC voltage source The generated AC voltage is converted into a pulse waveform that can be used to control the high-voltage submodule. and ; 2) Under normal operating conditions, collect the capacitance data of each high-voltage submodule. and lower capacitor The capacitor voltages are sorted using a parallel sorting method; the sorting is based on the current direction and the absolute values ​​of the upper and lower capacitors of each high-voltage submodule relative to the current stepped waveform. The magnitude relationship is used to allocate low-frequency control voltage to each full-Si high-voltage submodule; 3) Based on the capacitor voltage sorting results in step 2), perform complementary control of high-frequency and low-frequency control on the two SiC / Si hybrid high-voltage submodules according to the power frequency cycle, and balance the voltage of the two capacitors in the SiC / Si hybrid high-voltage submodule by switching the redundant state of the SiC / Si hybrid high-voltage submodule in the high-frequency operating state. 4) After a fault occurs, disconnect the faulty high-voltage submodule, reorder the remaining high-voltage submodules, block the control signals of the faulty high-voltage submodule, and realize control of each high-voltage submodule after the fault. In step 1), the nearest-level pulse width modulation method is used to convert the AC voltage source. The generated AC voltage is converted into a modulated waveform that can be used to control the high-voltage submodule. and The specific steps are as follows: (11) Set the modulation ratio Based on the withstand voltage rating of each component in the high-voltage submodule and AC voltage source voltage peak Determine the DC voltage output of each high-voltage submodule. Number of submodules ; (12) According to the modulation ratio described in step (11) and the DC bus voltage output by the high voltage submodule Through the voltage waveform of the AC voltage source Calculate the stepped waveform used to control the high-voltage submodule of the all-Si system. and the modulation wave used to control the SiC / Si hybrid high-voltage submodule The calculation formula is: (13) Set the high-frequency carrier frequency , determined to High-frequency triangular carrier wave with periodicity ; (14) Modulation wave according to steps (12) and (13) and high-frequency triangular carrier Calculate high-frequency pulse signals The calculation formula is: 。 2. The fault-tolerant control method for SiC / Si hybrid power electronic transformers according to claim 1, characterized in that, Step 2) specifically includes the following steps: (21) Take the average value of the upper and lower capacitor voltages of one of the SiC / Si hybrid high-voltage submodules, and sort them in ascending order with the upper and lower capacitor voltages of the other high-voltage submodules to obtain the capacitor voltage ranking. Take the average value of the upper and lower capacitor voltages of another SiC / Si hybrid high-voltage submodule, and sort them in ascending order with the upper and lower capacitor voltages of all other high-voltage submodules to obtain the capacitor voltage ranking. ; (22) Sort the capacitor voltages obtained in step (21). Low-frequency voltage control signals are allocated to the remaining high-voltage submodules; (23) Sort the capacitor voltages obtained in step (21). Low-frequency voltage control signals are allocated to the remaining high-voltage submodules; (24) According to steps (22) and (23), when the current direction is positive, if the sorting results of the upper and lower capacitor voltages of a certain high-voltage submodule are both less than If all capacitors in the high-voltage submodule are connected, the switching action will be [1 1 0 0 0 0 11]; if only the capacitors in a high-voltage submodule are connected... The sorting result is less than Then the high-voltage submodule only has an upper capacitor. It will be activated, and the switch action will be [1 1 0 0 0 1 1 0]; Conversely, this high-voltage submodule only has a lower capacitor. It will be activated, and the switch action will be [0 1 1 0 0 0 1 1]; When the current direction is negative, if the sorting results of a certain high-voltage submodule are both less than 1, then... If all capacitors in the high-voltage submodule are connected, the switching action will be [0 0 1 1 1 1 0 0]; if only the capacitors in a high-voltage submodule are connected... The sorting result is less than Then the high-voltage submodule only has an upper capacitor. When activated, the switch action is [0 0 1 1 0 1 1 0]; otherwise, the high-voltage submodule only has the lower capacitor. It will be activated, and the switch action will be [0 1 1 0 1 1 0 0]; If the voltages of both the upper and lower capacitors of a certain high-voltage submodule are greater than Then, regardless of whether the current is positive or negative, the upper and lower capacitors will be cut off, and the switching action is [0 1 10 0 1 1 0].

3. The fault-tolerant control method for SiC / Si hybrid power electronic transformers according to claim 1, characterized in that, The specific steps of step 3) are as follows: (31) The control mode for controlling the high voltage submodule is switched using the power frequency as the cycle. If the sorting result is used in the current power frequency cycle... Control all high-voltage submodules, i.e., according to the sorting results. The corresponding SiC / Si hybrid high-voltage submodule will operate under high-frequency control, while all other high-voltage submodules will operate under low-frequency control; simultaneously, in the next power frequency cycle, the high-voltage stage will adopt the sorting result. Control all high-voltage submodules, i.e., according to the sorting results. The corresponding SiC / Si hybrid high-voltage submodule will operate under high-frequency control, while all other high-voltage submodules will operate under low-frequency control. (32) Select a SiC / Si hybrid high-voltage submodule for high-frequency control according to step (31); when the current direction is positive, if the average voltage ranking result of the upper and lower bridge arms of the high-voltage submodule under high-frequency control is less than This high-voltage submodule will switch between +2 level and +1 level at high frequency, with switching actions of [1 1 0 0 0 1 0 0 1 1] and [1 0 1 0 0 1 00 1 1]; When the current direction is positive and the sorting result is greater than At this time, the high-voltage submodule will switch frequently between +1 and 0 levels, with switching actions of [1 1 0 0 0 1 0 1 1 0] and [1 1 0 0 0 1 0 1 1 0]. Only the upper capacitor is active at this time. In charging state; when the current direction is negative and the sorting result of the high-voltage submodule is greater than... At this time, the high-voltage submodule will rapidly switch between 0 and -1 levels, with switching actions of [0 1 0 1 1 0 0 1 1 0] and [0 0 1 1 1 0 0 11 0]. Only the lower capacitor is active at this time. In charging state; when the current direction is negative and the sorting result of the high-voltage submodule is less than At this time, the high-voltage submodule will quickly switch between -1 level and -2 level, with switching actions of [0 1 0 1 1 0 1 10 0] and [0 0 1 1 1 0 1 1 0 0]; (33) Based on the high-frequency control method for the high-voltage submodule in step (32), and according to the relationship between the upper and lower capacitor voltages of the high-voltage submodule under high-frequency control, the switching action mode is reselected, and the following is set: ,in The voltage across the upper capacitor. The voltage of the lower capacitor; when the current direction is positive and the sorting result of the high-voltage submodule is greater than... At that time, if Then, redundant switching actions [0 1 0 0 1 0 0 0 1 1] and [0 0 1 0 1 0 0 0 1 1] are used. At this time, the high-voltage submodule will quickly switch between +1 level and 0 level, and only the lower capacitor is used. In charging state; when the current direction is negative and the sorting result of the high-voltage submodule is greater than... At that time, if Then, redundant switching actions [0 0 1 0 0 11 1 0 0] and [0 1 0 0 0 1 1 1 0 0] are used. At this time, the high-voltage submodule will quickly switch between +1 level and 0 level, and only the upper capacitor is used. The module is in a charging state; if it is in another state, the control method of step (32) is still used to control the high-voltage submodule of SiC / Si hybrid under high-frequency control. (34) Set voltage threshold Only when Only when necessary will the normal switching state be switched to the redundant switching state to reduce the number of times the Si devices in the SiC / Si hybrid high voltage submodule are activated.

4. The fault-tolerant control method for SiC / Si hybrid power electronic transformers according to claim 1, characterized in that, The specific steps of step 4) include: (41) Set a fault tolerance cut-off time. After a fault occurs in a switching device in a high voltage submodule or an isolation submodule connected in series with it, the faulty high voltage submodule is cut off within the fault tolerance time using the bypass switch corresponding to the high voltage submodule. (42) The control method for the faulty high-voltage submodule and the isolation submodule connected in series with it is: by pulse control, all switch states of the faulty high-voltage submodule and the isolation submodule connected in series with it are set to zero, and at the same time, the sorting result of the faulty high-voltage submodule is set to the highest. (43) The control method for a normally functioning high-voltage submodule is as follows: If the faulty high-voltage submodule is a SiC / Si hybrid high-voltage submodule corresponding to the sorting result, the sorting result and its corresponding control method shall be used for control. The other SiC / Si hybrid high-voltage submodule shall always be under high-frequency control and shall no longer perform complementary switching between high and low frequencies. If the faulty high-voltage submodule is an all-Si high-voltage submodule, the sorting result and its corresponding control method shall be used for control. The high-frequency switching task shall be undertaken by the SiC / Si hybrid high-voltage submodule corresponding to the sorting result, and the other SiC / Si hybrid high-voltage submodule shall always work under low-frequency control.

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