Optimized fault-tolerant control method suitable for cascaded solid-state transformer

Abstract

The invention discloses an optimized fault-tolerant control method suitable for a cascaded solid-state transformer. On the basis of the basic control link of the cascade converter, the bus voltage of each normally operating cascade module in the switching process and the bus voltage of the redundant module are detected, and according to the current modulation signal of each cascade module, the new modulation signal of each cascade module is dynamically calculated and obtained; the fluctuation of voltage and current in each stage of the switching process can be reduced. According to the invention, the problem that the current impact is too large when the whole system is switched due to the fault of one cascade module in the cascade converter is solved. According to the method, no additional circuit needs to be added, smooth switching of the cascade converter can be achieved when the fault occurs, the whole system can continue to work stably, and collapse of the whole system caused by over-current protection is prevented.

Description

Technical Field

[0001] The invention belongs to the technical field of medium voltage power distribution power electronic converters, and relates to a cascade solid-state transformer control method, and in particular to an optimized fault-tolerant control method suitable for cascade solid-state transformers. Background Art

[0002] In the cascade solid-state transformer system, the number of power electronic switch tube devices used is proportional to the number of modules, and the power electronic switch tube is the part of the power electronic device that is most prone to failure. Therefore, the probability of switch tube failure in the cascade converter is much greater than that of the ordinary converter. Moreover, if the failure of a module in the cascade system is not properly handled in time, the large changes in voltage and current caused by it can easily affect the normal operation of other modules, cause more module failures, and even paralyze the entire system. Therefore, in order to ensure the continuous normal operation of the power supply system, it is of great significance to design a reliable fault-tolerant control strategy.

[0003] Common faults of power electronic devices include short circuit faults and open circuit faults. Short circuit faults are caused by the switch tube entering a normally closed state due to breakdown or other reasons. The characteristics of short circuit faults are fast fault occurrence, great damage to the circuit, and obvious fault characteristics. Open circuit faults are caused by the switch tube failing to open and being in a normally closed state. After a fault occurs, a suitable fault-tolerant strategy is needed to ensure that the system continues to operate without being damaged in the event of a fault. Common fault-tolerant strategies mainly include reconstructing the circuit according to the fault type and adding redundancy. The circuit reconstruction method is generally to isolate the faulty switch and change the control method to allow the remaining part of the circuit to continue to operate. Although this fault-tolerant method can make the circuit run in a fault-tolerant manner, the quality of its output power will be reduced to a certain extent, and the working effect before the fault cannot be fully restored. In contrast, the fault-tolerant scheme based on redundancy can usually better ensure that the system achieves the same effect as normal operation during fault-tolerant operation. The fault-tolerant scheme of redundant switch tubes is to connect a redundant switch tube in series or in parallel to each switch tube in the circuit, and the corresponding redundant switch tube will replace the faulty switch tube in the event of a fault. However, this fault-tolerant method requires twice as many switches as normal, which greatly increases the cost. In addition, there is a redundant bridge arm solution, which adds a redundant bridge arm to each H bridge, isolates the faulty bridge arm during fault-tolerant operation, and replaces the faulty bridge arm with the redundant bridge arm. Compared with the redundant switch tube solution, this solution greatly reduces the number of redundant devices required, but in cascaded application scenarios, the cost of redundant devices will still increase with the increase in the number of modules.

[0004] For easily modularized cascade circuits, another commonly used redundancy solution is to add a redundant module to the system, so that in the event of a fault, the faulty module can be directly bypassed and replaced by the redundant module to continue operation.

[0005] Depending on whether it is put into the circuit to operate with other modules under normal operation, the redundant module solution is divided into two types: cold standby module solution and hot standby module solution.

[0006] Since the number of system modules in the module hot standby scheme is less during fault-tolerant operation than during normal operation, it is impossible to maintain the normal operating state during fault-tolerant operation. At the same time, because the bus voltage needs to be raised during fault-tolerant operation, additional margin needs to be reserved when designing the withstand voltage parameters of components such as the switch tube in the circuit, which results in the inability to fully utilize the capacity of the device during normal operation. Moreover, after the bus voltage of the module is raised, the gain of the subsequent isolation DC / DC must also be adjusted, which will cause it to deviate from the rated operating point. For popular isolation DC / DC schemes such as LLC, deviation from the rated operating point often means a reduction in converter efficiency, thereby reducing the overall efficiency of the system.

[0007] Compared with the hot standby solution, the number of modules put into operation in the cold standby solution is the same when the system is operating normally and when the system is operating in fault tolerance, and the voltage and current in the system do not change. Therefore, the cold standby solution can theoretically fully restore the normal operation state when the system is operating in fault tolerance. However, the disadvantage of the cold standby solution is that after a fault occurs, in order to prevent the fault from spreading, the faulty module needs to be bypassed immediately and the redundant module is connected. However, the redundant module needs to be charged until the bus voltage reaches the rated value before it can completely replace the faulty module. In conventional applications, in order to ensure the stability of the bus voltage and reduce the second harmonic pulsation on the bus during AC input, the bus capacitor of the module is generally selected with a larger capacitance, so the charging time of the redundant module will also be longer. During this period of time, the system has been in a state of dynamic adjustment. How to keep the system stable and reduce the fluctuation of input and output voltage and current during this module switching process has become the main problem that the cold standby solution needs to solve.

[0008] The process of removing the faulty module and fully charging the bus capacitor of the redundant module in the module cold standby fault-tolerant control is essentially the module switching process between the faulty module and the redundant module. To reduce the fluctuation of voltage and current in the system from the time the redundant module is cut in to the time it is charged to the rated value, it is necessary to achieve smooth switching of modules in the cascaded solid-state transformer system. Summary of the invention

[0009] The purpose of the present invention is to provide an optimized fault-tolerant control method suitable for cascade solid-state transformers, reduce the current surge caused by module fault fault-tolerant switching in the cascade solid-state transformer system, and realize smooth fault-tolerant switching.

[0010] The present invention provides an optimized fault-tolerant control method suitable for a cascade solid-state transformer. The cascade solid-state transformer is composed of a plurality of cascade modules with input ends connected in series and output ends connected in parallel. The input ends of each cascade module are connected in series with a filter inductor and then connected to an AC power grid. Each module includes a front-stage H-bridge converter and a rear-stage isolated LLC resonant converter. The method includes: in normal operation, controlling the output voltage through a front-stage CHB controller; and performing closed-loop control of the intermediate bus voltage through a rear-stage LLC resonant converter. When a module fails, the faulty module is bypassed through the IGBT connected in parallel to its input end, and the redundant module is put into operation in the system. At the same time, the drive of the faulty module is forwarded to the redundant module for use, and all switch tubes of the faulty module are blocked. Furthermore, in order to reduce the current stress of the traditional fault-tolerant control strategy when removing the faulty module and charging the redundant module, on the basis of the above control method, the present invention adopts an optimized fault-tolerant control strategy, which is to control the bus voltage V of each module according to the bus voltage V busi (i=1,2…N,r ≠F,module M F is the faulty module, module M r is a redundant module) and the original duty cycle modulation signal (i.e. the original modulation voltage) v m Dynamically adjust the modulation voltage v of each normal module mn Therefore, the fluctuation of input voltage can be reduced, thus avoiding input current surge.

[0011] The specific implementation of the fault-tolerant control strategy of the cascade solid-state transformer includes setting a front-stage CHB controller (referred to as the front-stage controller) and a rear-stage LLC controller (referred to as the rear-stage controller). The front-stage controller is used to control the front-stage H-bridge converter in the cascade module, and the rear-stage controller controls the rear-stage isolated LLC converter of the cascade module. The front-stage controller is used to control the output voltage and realize the grid-side power factor correction, and the rear-stage controller is used to control the intermediate bus voltage of the cascade unit.

[0012] Optionally, the front-stage controller includes a voltage control module, a current control module and a carrier phase-shift SPWM modulation module. The voltage control module is used to control the output voltage V of the entire power distribution system. o , and the output signal it generates is used as the grid current reference value. The current control module is used to control the grid current to achieve power factor correction, and its output signal is the duty cycle modulation signal of the front-stage H-bridge converter of all cascaded units; the PWM modulation module is used to generate the switching pulses of each switch tube of all the front-stage H-bridge converters. More importantly, in the present invention, the front-stage controller also includes a modulation voltage optimization module, and during the module switching process, the modulation voltage optimization module is used to adjust the modulation voltage of the normal module in real time to reduce the fluctuation of the input voltage.

[0013] Optionally, the modulation voltage optimization module calculates the modulation wave v of each module calculated by the normal front-stage control loop. m Dynamic adjustment is performed, specifically: during the module switching process, the modulation signal v of the normal module is adjusted according to the bus voltage value of the normal module and the redundant module. m Dynamically adjust to generate a new modulation signal v mn , the modulation voltage signal v of the redundant module m The modulation voltage v mn With v m The relationship is:

[0014]

[0015] Where V busfr is the bus voltage of the redundant module, which changes with the charging of the redundant module during the fault-tolerant control process. busfi Module M for fault-tolerant control i The bus voltage, V bus_rated It is the rated value of the bus voltage, which is also the bus voltage value of each module during normal operation.

[0016] Optionally, the post-stage LLC controller includes a bus voltage control module and a pulse frequency modulation module. The intermediate bus voltage of the cascade module is the input signal of the post-stage controller. The bus voltage control module is used to generate the switching frequency of the LLC converter, and as the input signal of the pulse frequency modulation module, the switching pulse is obtained through pulse frequency modulation and sent to each switch tube of the post-stage LLC resonant converter. When a fault occurs, the LLC controller of the faulty module stops running, and the LLC controller of the redundant module starts working.

[0017] The present invention aims at the unit module failure problem of the cascade solid-state transformer system. On the basis of the basic control link of the cascade converter, by detecting the bus voltage and the bus voltage of the redundant module during the switching process of each normally operating cascade module, and dynamically adjusting the modulation voltage of the front stage of each module during the switching process, the new modulation signal of each cascade module is calculated, and the voltage and current smoothing in each stage of the switching process can be achieved, and the inductor voltage fluctuation during the switching process is significantly reduced, thereby weakening the front-stage input current stress. The present invention solves the problem of excessive current impact when the entire system is switched due to the failure of a cascade module in the cascade converter through control. The method does not require the addition of additional circuits, and can achieve smooth switching of the cascade converter when a fault occurs, so that the entire system can continue to work stably, and prevent overcurrent protection from causing the entire system to collapse. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 It is a circuit diagram of a cascaded solid-state transformer in one embodiment of the present invention.

[0019] Figure 2 yes Figure 1 The front-end control block diagram of the instance under normal operating conditions.

[0020] Figure 3 yes Figure 1 The back-end control block diagram when the instance is operating normally.

[0021] Figure 4 yes Figure 1 Block diagram of the front-end control under the instance fault state.

[0022] Figure 5 yes Figure 1 Block diagram of the subsequent control under the instance fault state.

[0023] Figure 6 Yes Figure 1 The example adopts the control method of the present invention in the front-stage control block diagram under fault state.

[0024] Figure 7 It is the phasor diagram of each voltage phasor on the input side under normal working conditions.

[0025] Figure 8 It is the phasor diagram of the voltage phasors on the input side at the moment the fault module is removed.

[0026] Fig. 9 It is the voltage phasor diagram at the moment when the faulty module is removed.

[0027] Fig.10 It is the voltage phasor diagram during the charging process of the redundant module.

[0028] Fig.11 is the fault-tolerant switching process v mn With v m Ratio change curve.

[0029] Fig.12 It is the modulation wave change curve of each module during the fault-tolerant switching process. DETAILED DESCRIPTION

[0030] The technical solution of the present invention is further described in detail below in conjunction with the accompanying drawings and specific embodiments. The embodiments are only used to illustrate and explain the specific implementation and corresponding effects of the present invention, and are not intended to limit the present invention.

[0031] According to a specific embodiment of the present invention, Figure 1This is the circuit diagram of a single-phase solid-state transformer, which consists of multiple cascade modules with inputs connected in series and outputs connected in parallel. The input end of each cascade module is connected in series with the filter inductor and then connected to the AC power grid. The output ends are connected in parallel to maintain a stable DC voltage. The cascade module consists of a front-stage H-bridge converter (CHB) and a rear-stage isolated LLC resonant converter. The front-stage H-bridge converter of each cascade module processes the energy of the medium-voltage power grid, reduces the equivalent input voltage of each cascade unit by series connection, and converts it into a lower DC bus voltage. The energy is then sent to the rear-stage LLC resonant converter. After high-frequency isolation, the output ends of all cascade units are connected in parallel to provide energy for the DC load. In the illustrated example, M 1 、M 2 and M 3 The three modules are normal operating modules, M r It is a redundant module.

[0032] Figure 2 This is the control block diagram of the front-stage CHB of the solid-state transformer under normal operating conditions. Figure 3 This is the control block diagram of the LLC of the back stage of each module of the solid-state transformer under normal operation. When a module in the solid-state transformer fails, the faulty module is bypassed through the IGBT connected in parallel at its input end, and the redundant module is put into use. Figure 4 This is the front-stage control block diagram under fault conditions. When module M 3 When a fault occurs, the driver forwards the fault to the redundant module M. r When a fault occurs, such as Figure 5 As shown, the fault module M 3 The LLC controller stops running, the redundant module M r The LLC controller starts working. Figure 6 This is a control block diagram of the front-stage CHB under the fault state of the present invention, in the bypass fault module M 3 During the process of inserting the redundant module, the normal module M is adjusted in real time according to the modulation voltage optimization module 604. 1 and M 2 The modulation voltage is used to compensate for the input voltage drop caused by the bypass fault module, thereby avoiding input current surge.

[0033] Alternatively, if Figure 6 As shown, the front-stage CHB controller under fault condition of the present invention includes four parts: voltage control module 601, current control module 602, PWM modulation module 603 and modulation voltage optimization module 604. Voltage control module 601 is used to control the output voltage V of the whole solid-state transformer system. o , which is specifically: the output voltage reference value V o_ref Subtract the output voltage sampling value V o, the obtained error value is used as the input of the voltage controller, and the output signal of the voltage controller is used as the input signal of the current control module 602, wherein the voltage controller is a proportional integral controller (PI controller).

[0034] The current control module 602 is used to control the grid current to achieve power factor correction, specifically as follows: First, the grid current i g Perform abc / dq coordinate transformation to obtain the d-axis component and the q-axis component, and use the output signal of the voltage control module 601 as the reference value i of the d-axis component of the grid current. d_ref , and the reference value of the q-axis component is 0, the d-axis component and q-axis component of the grid current are subtracted from the d-axis and q-axis reference values ​​respectively, and the errors are passed through the current controller to generate the d-axis component v of the modulation signal md and the q-axis component v mq , and then v md and v mq According to the grid voltage phase, the dq / abc coordinate transformation is performed to obtain the duty cycle fundamental modulation signal v of the previous H-bridge converter. m , where the current controller is a proportional integral controller (PI controller).

[0035] The modulation voltage optimization module 604 modulates the signal v of the front-stage H-bridge converter m Dynamic adjustment is performed. The specific implementation method is as follows: during the module switching process, according to the bus voltage value V of the normal module and the redundant module busi (i=1,2,r) for normal module M 1 and M 2 The modulation signal v m Dynamically adjust to generate a new modulation signal v mn , the modulation voltage signal v of the redundant module m Remain unchanged.

[0036] The PWM modulation module 603 is used to generate switching pulses for each switch tube of all the H-bridge converter modules of the previous stage, and compare the duty cycle fundamental modulation signal with the high-frequency carrier signal to obtain a square wave pulse signal whose duty cycle changes with the modulation signal as the switching signal of each switch tube of the H-bridge converter module of the previous stage.

[0037] Optionally, the adjusted modulation voltage signal v mn According to the bus voltage V of each module busi (i=1,2,r), original modulation voltage signal v m The specific derivation process is as follows:

[0038] Under normal working conditions, the phasor diagram of each voltage phasor on the input side is as follows Figure 7 As shown, where v Lg is the voltage on the grid inductor, vsi (i=1,2,3) is the input voltage of each module. Lg The phasor representation of is as follows:

[0039]

[0040] The phasor diagram of each voltage phasor on the input side at the moment the fault module is removed is as follows Figure 8 As shown, where v Lgf Cut off the voltage on the instantaneous grid inductance for the fault module. Lgf The phasor representation of is as follows:

[0041]

[0042] In order to reduce the input current surge caused by module switching, the voltage on both sides of the inductor needs to remain unchanged. Therefore, assuming that the inductor voltage remains unchanged, the voltage phasor diagrams at the moment of removing the faulty module and during the charging process of the redundant module are: Fig. 9 and Fig.10 The voltage phasor at the moment of removing the faulty module is expressed as follows:

[0043]

[0044] The voltage phasor during the redundant module charging process is expressed as follows:

[0045]

[0046] Formula (1) can be written as:

[0047]

[0048] Substituting equation (5) into equation (3) and equation (4), since the voltage directions of each module are the same during normal operation and fault-tolerant control, the scalar form can be obtained:

[0049] v s ' 1f +v s ' 2f =v s1 +v s2 +v s3 (6)

[0050] v s1f +v s2f +v srf =v s1 +v s2 +v s3 (7)

[0051] Formula (6) can be regarded as Formula (7) when the redundant module input voltage v srfTherefore, the moment of fault module removal and the charging process of redundant modules can be processed uniformly, and the average of the switching cycle at both ends of equation (7) is obtained:

[0052] <v s1f > Ts +<v s2f > Ts +<v srf > Ts =<v s1 > Ts +<v s2 > Ts +<v s3 > Ts (8)

[0053] Taking module 1 as an example, derive its input voltage v s1 With bus voltage V bus1 The relationship is as follows. In different switching states, v s1 They are:

[0054]

[0055] Assume S 11 The duty cycle is D. When bipolar SPWM modulation is adopted, equation (9) can be written as:

[0056]

[0057] Where T s is the switching period, and the average of the switching period is obtained for equation (10):

[0058] <v s1 > Ts =V bus1 ·D+(-V bus1 )·(1-D)=V bus1 (2D-1) (11)

[0059] In a switching cycle, the amplitude of the modulation wave can be regarded as unchanged. According to the basic principle of SPWM, the duty cycle D can be expressed as follows:

[0060]

[0061] where v m is the modulation wave, V tri is the amplitude of the triangular carrier. Substituting equation (12) into equation (11), we can obtain:

[0062]

[0063] Set the carrier amplitude V tri If is taken as 1, then formula (13) can be simplified as:

[0064] <v s1 > Ts =V bus1 ·v m (14)

[0065] Similarly, the input voltage v of other modules can be written si With the respective bus voltage V busi (i=1,2,3,r) relationship:

[0066]

[0067] Substituting formula (15) into formula (8), we can obtain:

[0068] V busf1 ·v mf1 +V busf2 ·v mf2 +V busfr ·v mfr =(V bus1 +V bus2 +V bus3 )·v m (16)

[0069] Where V busi (i=1,2,r) and v m They are respectively the bus voltage of each module under normal working conditions and the modulation voltage of the module front stage.

[0070] Under normal working conditions, under the control of the LLC at the rear stage of each module, the bus of each module is basically stable at the rated bus voltage value, so it can be regarded as a constant, and equation (16) can be further written as:

[0071] V busf1 ·v mf1 +V busf2 ·v mf2 +V busfr ·v mfr =3V bus_rated ·v m (17)

[0072] Where V bus_rated is the module bus voltage rating.

[0073] In equation (17), the only variable that changes due to external factors is the redundant module bus voltage V which increases as the redundant module is charged. busr , and the modulation wave v of each module can be controlled and adjusted mfi (i=1,2,r)3 variables, so in order to avoid unnecessary complex calculations, it is advisable to add some restrictions to the modulation wave, for example, let:

[0074]

[0075] That is, the modulation wave voltage v of the redundant module CRM in charging mfr Set it to the same as normal operation, and make the module M that was working normally 1 With M 2 The modulation wave remains equal to v mn At this point, the only thing that needs to be determined is v mn The value of .

[0076] Substituting formula (18) into formula (17), we can obtain:

[0077] (V busf1 +V busf2 )·v mn +V busfr ·v m =3V bus_rated ·v m (19)

[0078] The modulation voltage v can be derived from the above formula mn Relationship with other quantities:

[0079]

[0080] Where V busfr is the bus voltage of the redundant module, which changes with the charging of the redundant module during the fault-tolerant control process. busf1 With V busf2 They are normal modules M 1 With M 2 The bus voltage, V bus_rated is the rated value of the bus voltage, which is also the bus voltage value of each module during normal operation, v m The modulation wave of each module calculated for the normal control loop.

[0081] That is, in fault-tolerant control, the modulation voltage value v calculated by the control loop is m According to equations (18) and (20), dynamic adjustments can be made according to the bus voltage of each module to maintain the stability of the system input and output.

[0082] According to formula (20), the modulation voltage v in the fault-tolerant control process can be plotted mn The modulation voltage v calculated by the control loop m The ratio change curve is as follows Fig.11 As shown in the figure, the modulation voltage v of the normal module mnAt the moment of failure, the ratio suddenly changes to 1.5 to cope with the removal of the module, and as the redundant module is charged, the ratio gradually decreases until it is restored to v after charging is completed. mn =v m relationship.

[0083] Under the condition of AC input and using CPS-SPWM as the modulation method, the modulation wave v of the front stage during normal operation m Usually it is a sinusoidal waveform. By combining equations (18) and (20), we can draw the changes of the modulation waveforms of each module before and after the fault occurs and during the fault-tolerant control process as the charging process of the redundant module changes. Fig.12 shown.

[0084] In different stages Fig.12 To perform the analysis:

[0085] 1)t 0 Before this moment, the system works normally. Since the modulation mode adopted by the previous stage is CPS-

[0086] SPWM, so the modulation waves of all modules before the fault are the same sine wave signal. 2)t 0 At the instant of time, according to the formula (18) in the improved fault-tolerant control strategy studied in this paper, the new

[0087] The modulation wave signal v of the redundant module added to the circuit mrf Still maintain the normal working condition of the modulation wave v m In order to make the two normal modules bear the input voltage originally borne by the faulty module, the modulation wave v mn According to the control strategy formula (20), it was adjusted and increased to 1.5 times of the original value.

[0088] 3)t 0 Time to t 1 During this time, as the redundant module is charged, its contribution to the input voltage gradually increases, and the input voltage that the two normal modules need to bear additionally decreases, and its modulation wave v mn With v m The curves are gradually approaching.

[0089] 4)t 1 After a certain time, the redundant module is fully charged and the redundant module completely replaces the faulty module.

[0090] The modulation wave of each module returns to the state during normal operation.

[0091] The present invention aims at the fault tolerance problem of unit modules in the cascade solid-state transformer system, mainly analyzes the module cold standby redundancy scheme, and studies a fault-tolerant control method based on a switching modulation calculation method for reducing current impact in the process of switching the faulty module to the redundant module. When a module fails, the faulty module is bypassed by the IGBT connected in parallel at the input end, and the redundant module is put into operation. At the same time, the drive originally sent to the faulty module is forwarded to the redundant module. In order to reduce the input current impact caused by the module switching, the modulation signal voltage of the normal module is dynamically adjusted according to the bus voltage of each module, and the modulation signal voltage of the redundant module is kept unchanged during the charging process, the input inductor voltage is stabilized, and the input current impact is suppressed.

[0092] The above-described embodiments are only partial solutions of the present invention, but they are not intended to limit the present invention. A person skilled in the relevant technical field may make various changes and modifications without departing from the spirit and scope of the present invention. Therefore, any technical solution obtained by equivalent replacement or equivalent conversion falls within the protection scope of the present invention.

Claims

1. An optimized fault-tolerant control method for a cascade solid-state transformer, wherein the cascade solid-state transformer is composed of a plurality of low-voltage cascade modules with input ends connected in series and output ends connected in parallel, wherein the input end of each low-voltage cascade module is connected in series with a filter inductor and then connected to an AC power grid, and each low-voltage cascade module includes a front-stage H-bridge converter and a rear-stage isolated LLC resonant converter; characterized in that: The method includes setting a front-stage CHB controller, bypassing the faulty module when a cascade module fails, switching the redundant module to operate, forwarding the drive of the faulty module to the redundant module, and modulating the bus voltage and the original duty cycle of each cascade module according to the bus voltage and the original duty cycle of each cascade module during the module switching process. m Dynamically adjust the modulation voltage of each normal module.

2. The optimized fault-tolerant control method for cascaded solid-state transformers according to claim 1, characterized in that: The front-stage CHB controller comprises four parts: a voltage control module (601), a current control module (602), a PWM modulation module (603) and a modulation voltage optimization module (604); the voltage control module (601) is used to control the output voltage V of the entire solid-state transformer system. o The output signal generated by the current control module (602) is used as the input signal of the current control module (602); the current control module (602) is used to control the grid current to achieve power factor correction, and the output signal thereof is the duty cycle modulation signal of the preceding H-bridge converter in all cascaded modules; the modulation voltage optimization module (604) modulates the duty cycle modulation signal v of the preceding H-bridge converter m Dynamic adjustment is performed and output to a PWM modulation module (603), and the PWM modulation module (603) is used to generate switching pulses of all switch tubes of all H-bridge converters.

3. The optimized fault-tolerant control method for cascaded solid-state transformers according to claim 2, characterized in that: Consider a system with N modules, namely modules M1, M2, ...M N Cascade and add a spare redundant module M r system, in module M F When a fault occurs, during the module switching process, the modulation voltage optimization module (604) modulates the voltage according to the normal module and the redundant module M r The bus voltage value V busi ,i=1,2,…N,r ≠F,for the normal modules M1,M2,…M N The duty cycle modulation signal v m Dynamically adjust to generate a new modulation signal v mn , Redundancy module M r The modulation voltage signal v m remains unchanged; the modulation voltage v mn With v m The relationship is: Among them, V busfr For redundant module M r The bus voltage changes as the redundant modules are charged during the fault-tolerant control process, V busfi Module M for fault-tolerant control i The bus voltage, V bus_rated It is the rated value of the bus voltage, which is also the bus voltage value of each module during normal operation.

Images