| The energy storage multilevel converter can realize the conversion from multiple low-voltage energy storage units to high-voltage and high-power applications by cascading.It has the advantages of high output waveform quality,modular design and so on.The research on this type of converter is of great significance to the grid connection of distributed energy and the drive of high-voltage and high-capacity motor of electric vehicle(EV).In this paper,the fault-tolerant characteristics of hybrid cascade multilevel converter(HCMC)under fault operation and the balance control of energy storage system are studied.It has certain theoretical significance and practical value to promote the industrial application of this type of converter.Firstly,this paper introduces the topology and operation principle of HCMC,and improves the pulse width modulation(PWM)and the nearest level approximation two traditional multi-level modulation methods.The improved modulation strategy is applied to the 9-level HCMC topology for simulation analysis,which verifies the effectiveness of the improved modulation strategy,and compares the modulation performance of the two modulation methods.In order to study the fault-tolerant operation,the mathematical model of HCMC topology is established and applied to the loaded 17 level HCMC circuit.At the same time,the filter design of the circuit and the selection of the parameters of the closed-loop controller are completed.For the fault-tolerant operation of the converter under the closed-loop control,the fault types and operation characteristics of the basic modules are analyzed,and the fault location is realized by monitoring the voltage and current of the basic modules.At the same time,the simulation analysis is carried out for the two fault operation states of the basic modules of the HCMC.The results show that the fault modules have little impact on the HCMC,and the HCMC has strong fault-tolerant operation ability.For the state balance of HCMC energy storage system,firstly,this paper studies the problem of state separation of energy storage system existing in all energy storage converters,analyzes the causes of voltage separation between energy storage batteries,and summarizes the control method of state balance between energy storage units by changing the modulation ratio of basic modules in combination with the characteristics of independent control of basic modules of HCMC.At the same time,the equalization control strategy of battery voltage sequencing is proposed based on the principle,and it is applied to the single carrier carrier PWM modulation,which simplifies the implementation process of the algorithm.In order to realize voltage sharing control under carrier phase-shift PWM modulation,a voltage ratio equalization strategy is proposed.The ratio of battery voltage and reference voltage is used to replace the traditional closed-loop controller,avoiding the design of complex controller.Finally,the experimental platform of single-phase 17 level HCMC is built,and two equalization control strategies are tested.The experimental results show that the proposed method is effective for the equalization of battery voltage. |
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