Weight coefficient-free model prediction control method for single-phase cascaded H-bridge converter

Abstract

The invention provides a weight coefficient-free model prediction control method for a single-phase cascaded H-bridge converter. The weight coefficient-free model prediction control method comprises the following steps: constructing a two-dimensional control region based on a switching function; according to the input voltage of the converter, dividing the two-dimensional control area into 2N + 2 sub-areas, wherein N is the total number of cascade units of the single-phase cascade H-bridge converter; determining a sub-region where the input voltage reference value is located as an optimal sub-region, and taking all switching states corresponding to the two voltage vectors in the optimal sub-region as candidate switching states of the corresponding voltage vectors; constructing a cost function based on a current error, and calculating the optimal action time corresponding to each voltage vector; constructing a cost function based on a voltage error, and respectively selecting the corresponding optimal switching state from the candidate switching states corresponding to the two voltage vectors; and controlling the single-phase cascaded H-bridge converter by taking the optimal action time and the optimal switching state as output. According to the method, the parameter setting and readjusting process of the controller can be avoided, the control structure is simple, and the algorithm execution time is shortened.

Description

technical field [0001] The invention relates to the technical field of power electronics and converter control, in particular to a weightless coefficient model predictive control method for a single-phase cascaded H-bridge converter. Background technique [0002] Cascaded H-bridge converter is one of the main topological structures of multilevel converters. It has the advantages of low harmonic distortion rate of AC output voltage, good electromagnetic environment, high degree of modularization and easy expansion, and is widely used in traction drives. , Photovoltaic power generation and wind power generation and other medium and high voltage and high power occasions. [0003] The main control objectives of the cascaded H-bridge converter are to achieve fast tracking of the grid-side current and balanced control of the DC-side capacitor voltage. Traditional control strategies include PI control and hysteresis control, etc. Among them, the parameter setting of PI control str...

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Problems solved by technology

Traditional control strategies include PI control and hysteresis control, etc. Among them, the parameter setting of PI control strategy is complex, the dynamic response speed of the system is slow, and the delay of PI controller causes steady-state error in current tracking; the design of hysteresis control strategy Simple, good transient performance, but its disadvantages are: the switching frequency is not fixed, the controllability is poor, the harmonic spectrum is wide, and the design of the post-stage filter is difficult

However, due to the large number of switches in the cascaded H-bridge, the model-based predictive control strategy is more complicated and the response speed is slower

At the same time, due to the need to control the grid-side current and DC voltage, traditional predictive control usually introduces weight coefficients into the cost function, and the design process takes a lot of time, and when the system parameters or working conditions change, the weight coefficients also need to be adjusted. Carry out secondary design to increase the difficulty of the controller

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