A redundant control method for a three-phase cascaded h-bridge

Abstract

This invention relates to the field of power electronic transformer technology, specifically a redundancy control method for a three-phase cascaded H-bridge, comprising three phases A, B, and C, each phase containing multiple series modules, with a bypass switch installed before each module. The voltage of each phase is controlled by carrier phase shifting. Compared with the prior art, this invention does not add additional redundant modules. When a module fails, the voltage of that phase in the system is reduced, while the voltage of the other two phases in the system is increased, thus achieving normal operation of the system without affecting the grid voltage.

Description

Technical Field

[0001] This invention relates to the field of power electronic transformer technology, specifically a redundancy control method for a three-phase cascaded H-bridge. Background Technology

[0002] With the development of the new energy sector, the development of high-voltage DC charging for new energy vehicles and grid-connected photovoltaic power generation has created a demand for equipment that converts 10kV AC to 750V~1kV DC. Among these, the cascaded H-bridge (CHB), composed of multiple modules connected in series, can convert high-voltage AC to DC output. Connecting one cascaded H-bridge to each phase of a 10kV three-phase AC grid achieves the 10kV AC to DC conversion function. Furthermore, its modular design offers advantages such as high power factor and minimal harmonic impact on the power grid.

[0003] The CHB (Chain Bus) rectifies the 10kV AC grid into DC power through a series H-bridge full-bridge module, and then uses a DC / DC converter to achieve parallel output between multiple modules. The grid-side current is controlled by controlling the voltage of each phase. Since the phase voltage of a 10kV grid is approximately 8165V, the CHB needs a maximum output higher than 8165V. If each module outputs 900V, then at least 10 modules are required for the system to function properly. When the system requires redundant control—that is, to ensure normal operation even if a module fails—at least one more module is needed. This adds a total of three modules across the three phases, increasing both cost and losses.

[0004] Existing technologies, such as CN108599540A, "A Redundancy Structure for a Cascaded H-Bridge Three-Phase Electronic Power Transformer," change the redundancy of the three phases to sharing a single redundant module. This can only support redundancy when one module fails, and cannot support redundancy when each of the three phases has only one module failed. Another example is CN111934570A, "A Fault-Tolerant Control Method for a Cascaded H-Bridge Photovoltaic-Storage Hybrid Energy Router," which can handle the failure of a single or multiple H-bridge tubes, but cannot handle the complete failure of the H-bridge or the failure of the DC output photovoltaic energy storage H-bridge module. CN111600494A, "A Control Method for Improving the Operational Performance of Power Electronic Transformers After Redundancy," CN109802571A, "A Redundancy Control System and Method Applied to Three-Phase Solid-State Transformers," and CN109450265A, "A Multi-Module Redundancy Structure for a Cascaded H-Bridge Three-Phase Electronic Power Transformer," all require the addition of redundant modules and redundant power modules, which increases costs and losses. Therefore, a redundant control method for a three-phase cascaded H-bridge needs to be designed. This method can achieve redundant control without adding modules. When one module fails, the peak voltage of that phase is reduced, while the peak voltages of the other two phases are increased, thus restoring normal operation. This method only affects the internal structure of the energy router and does not alter the voltage and current on the 10kV grid side. Summary of the Invention

[0005] The purpose of this invention is to overcome the shortcomings of existing technologies and provide a redundancy control method for a three-phase cascaded H-bridge. This method achieves redundancy control without adding modules. When one module fails, the peak voltage of that phase is reduced, while the peak voltages of the other two phases are increased, thus restoring normal operation. This method only affects the internal structure of the energy router and does not alter the voltage and current on the 10kV grid side.

[0006] To achieve the above objectives, the present invention provides a redundancy control method for a three-phase cascaded H-bridge, comprising three phases A, B, and C, each phase containing multiple series modules, each module having a bypass switch in front of it, and the voltage of each phase being controlled by carrier phase shifting, including the following steps: S1, when a module in a certain phase is damaged, the module is bypassed and the peak voltage of the system in that phase is limited to within the threshold ±k. When the phase grid voltage exceeds the threshold k, the voltage of the three phases A, B, and C of the system is simultaneously reduced by the value ue, where ue is the difference between the grid voltage of the phase with the damaged module and the system voltage, so that the voltage of the damaged phase is maintained at k. Since the voltage of the three phases of the system is reduced by ue at the same time, the voltage difference between any two phases of the system, i.e. the line voltage, remains unchanged, and the line voltage on the grid side is not changed, so there is no effect on the phase voltage on the grid side. S2, when the voltage on the grid side of the damaged phase is positive and greater than k, it is limited to k. At this time, the difference between the grid side voltage and k, ue, is positive. When the voltage on the grid side of the damaged phase is negative and less than -k, it is limited to -k. At this time, the difference between the grid side voltage and -k, ue, is negative. S3, k is determined by the number of damaged modules. k is lower than the highest output voltage of the phase where the module is damaged. If multiple modules are damaged, if the damaged modules are in the same phase, the more damaged modules there are, the smaller k will be. If they are in different phases, different k can be set for different phases. The minimum value of k is determined by the maximum output voltage of each phase of the system after the damage. S4, under redundant control, intact modules can still operate at rated power, and the maximum output power of the system is only lost by the power corresponding to the damaged module.

[0007] Compared with the prior art, this invention does not add extra redundant modules. When a module fails, it reduces the voltage of this phase in the system and increases the voltage of the other two phases in the system, so as to achieve normal operation of the system without affecting the grid voltage. Attached Figure Description

[0008] Figure 1 This is a schematic diagram of the circuit structure of the present invention; Figure 2 This is a schematic diagram of the grid-side and system phase voltages when a single phase fails according to the present invention; Figure 3This is a schematic diagram of the grid-side and system phase voltages when two phases are damaged according to the present invention; Figure 4 This is a schematic diagram of the grid-side and system phase voltages when three phases are damaged according to the present invention; Figure 5 This is a schematic diagram of the maximum redundancy state when the three phases of the present invention are damaged; Implementation

[0009] The present invention will now be further described with reference to the accompanying drawings.

[0010] See Figures 1-5 This invention provides a redundancy control method for a three-phase cascaded H-bridge, comprising three phases A, B, and C, each phase containing multiple series modules, with a bypass switch before each module, and the voltage of each phase controlled by carrier phase shifting, including the following steps: S1, when a module in a certain phase is damaged, the module is bypassed and the peak voltage of the system in that phase is limited to within the threshold ±k. When the phase grid voltage exceeds the threshold k, the voltage of the three phases A, B, and C of the system is simultaneously reduced by the value ue, where ue is the difference between the grid voltage of the phase with the damaged module and the system voltage, so that the voltage of the damaged phase is maintained at k. Since the voltage of the three phases of the system is reduced by ue at the same time, the voltage difference between any two phases of the system, i.e. the line voltage, remains unchanged, and the line voltage on the grid side is not changed, so there is no effect on the phase voltage on the grid side. like Figure 1 As shown, each module has a bypass switch S1. When a module in phase A fails, this module is bypassed, limiting the maximum voltage of this phase to within the maximum output value k. This value k is called the threshold.

[0011] When the voltage of phase A of the power grid exceeds the threshold k, the voltage of phase A of the system remains unchanged at k. At this time, there is a difference ue between the voltage of the grid side and the voltage of phase A of the system, while the voltages of phases B and C are reduced by this difference ue from the original voltages.

[0012] For example, the grid-side voltages ua, ub, and uc are sinusoids with the same amplitude but a phase difference of 120°, while ua', ub', and uc' are the system voltages. If one module in phase A is damaged, the voltage of ua' will be limited to the threshold (-k, k), where k is slightly lower than the maximum voltage that phase A can output at this time.

[0013] For example, if Vin = 1000V, and each item takes n = 9 modules connected in series, if one module is damaged, then (n-1) × Vin = 8000V < 8165V, and k takes a value slightly lower than 8000V, for example, k = 7500V; When ua is a positive voltage: When 0 < ua ≤ k, ua' = ua, ub' = ub, uc' = uc When u > k: Keep ua'=k, At this point, there is a difference ue between ua and k:

[0014] ub' and uc' are obtained by subtracting this difference from ub and uc respectively: ; ;

[0015] At this time, the system's line voltages uab', ubc', and uca' are: ; ;

[0016] Since the 10kV power grid only includes three wires of phases A, B, and C, and does not include the ground wire, it is only necessary to ensure that the voltage difference between the three wires under redundant control is consistent with the original state, so as not to affect the power grid.

[0017] The same applies when ua is a negative voltage.

[0018] like Figure 2 As shown, when the grid-side phase A voltage is positive, the system phase A voltage is limited to no higher than a threshold, during which the voltages of phases B and C both decrease. When the grid-side phase A voltage is negative, the system phase A voltage is limited to a negative value no lower than this threshold, during which the voltages of phases B and C both increase. This redundancy control, when the number of damaged modules is small, results in a 60° difference between the peak value of phase A and the negative peak value of phases B and C. When the phase A voltage reaches near its peak value, phases B and C are not near their peak values. Therefore, when the number of redundant modules is small, it will not affect the peak voltage of phases B and C. The number of modules that can provide redundancy depends on the maximum voltage that phases B and C can withstand.

[0019] When damage occurs in different phases, thresholds can be set separately for each phase.

[0020] like Figure 3 As shown, when damage occurs in two phases, the voltage of the two damaged phases is limited to the threshold range, and the redundancy depends on the maximum voltage that phase C can withstand. like Figure 4 As shown, when damage occurs in three phases, the three phases A, B, and C are limited to the threshold range.

[0021] like Figure 5 As shown, when the damage occurs in three phases, in order to ensure that the redundant regions of the three phases A, B, and C do not overlap, the minimum threshold voltage is [value missing]. If the value is lower than this, the redundant areas of the three phases will overlap, resulting in an increase in the system voltage peak and the inability to achieve the redundancy function.

[0022] in Figure 4 and Figure 5 The only difference is the size of the threshold.

[0023] S2, when the voltage on the grid side of the damaged phase is positive and greater than k, it is limited to k. At this time, the difference between the grid side voltage and k, ue, is positive. When the voltage on the grid side of the damaged phase is negative and less than -k, it is limited to -k. At this time, the difference between the grid side voltage and -k, ue, is negative. S3, k is determined by the number of damaged modules. k is lower than the highest output voltage of the phase where the module is damaged. If multiple modules are damaged, if the damaged modules are in the same phase, the more damaged modules there are, the smaller k will be. If they are in different phases, different k can be set for different phases. The minimum value of k is determined by the maximum output voltage of each phase of the system after the damage. S4, under redundant control, intact modules can still operate at rated power, and the maximum output power of the system is only lost by the power corresponding to the damaged module.

[0024] The above are merely preferred embodiments of the present invention, intended only to aid in understanding the method and core ideas of this application. The scope of protection of the present invention is not limited to the above embodiments; all technical solutions falling within the scope of the present invention's concept are within its protection. It should be noted that for those skilled in the art, any improvements and modifications made without departing from the principles of the present invention should also be considered within the scope of protection of the present invention.

[0025] This invention comprehensively solves the problem in the prior art where, when a system has redundant control requirements, additional redundant modules are needed to ensure normal operation when a module in the system fails, thus increasing costs and losses. By reducing the voltage of this phase in the system and increasing the voltage of the other two phases, the normal operation of the system can still be achieved without affecting the grid voltage.

Claims

1. A redundant control method for a three-phase cascaded H-bridge, characterized in that, It consists of three phases, A, B, and C, each phase containing multiple series modules. Each module is equipped with a bypass switch. The voltage of each phase is controlled by carrier phase shifting. The process includes the following steps: S1, when a module in a certain phase is damaged, the module is bypassed and the peak voltage of the system in that phase is limited to within a threshold ±k. When the phase grid voltage exceeds the threshold k, the voltage of all three phases (A, B, and C) of the system is simultaneously reduced by a value ue, where ue is the difference between the grid voltage of the damaged phase and the system voltage, so that the voltage of the damaged phase is maintained at k. Since the voltage of all three phases of the system is reduced by ue, the voltage difference between any two phases of the system, i.e., the line voltage, remains unchanged, and the line voltage on the grid side is not changed, so there is no effect on the phase voltage on the grid side. S2, when the voltage on the grid side of the damaged phase is positive and greater than k, it is limited to k. At this time, the difference between the grid side voltage and k, ue, is positive. When the voltage on the grid side of the damaged phase is negative and less than -k, it is limited to -k. At this time, the difference between the grid side voltage and -k, ue, is negative. S3, k is determined based on the number of damaged modules. k is lower than the highest voltage that the phase in which the module is damaged can output. If multiple modules are damaged, if the damaged modules are in the same phase, the more damaged modules there are, the smaller k will be. If they are in different phases, different k will be set for different phases. The minimum value of k is determined based on the maximum voltage that each phase of the system can output after the damage. S4, under redundant control, intact modules can still operate at rated power, and the maximum output power of the system is only lost by the power corresponding to the damaged module.

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