A Modulation Strategy for Multilevel Converter

Abstract

The invention discloses a multi-level converter modulation strategy, which includes the following steps: S1. Determine the number N of cascaded H bridges, the switching frequency k of the circuit, and determine the triangular carrier wave V according to the number N of cascaded H bridges. c The phase shift angle θ and the required triangular carrier V c Number N; S2, determine the DC side voltage V of the circuit in , the resistive and inductive loads R and L in the circuit; S3. Determine the modulation degree m to obtain the rotating SPWM modulation wave, and generate the left bridge arm modulation wave and the right bridge arm modulation wave of the corresponding circuit topology under the modulation of the rotating SPWM modulation wave. Both the side bridge arm modulation wave and the right bridge arm modulation wave include a clamping part and a modulating part, and are compared with the triangular carrier wave respectively. During the clamping time, the switch remains normally on or off. During the normal modulation time, the switch High-frequency action, and then drive the circuit, so as to complete the corresponding modulation process.

Description

technical field [0001] The invention relates to the technical field of multilevel inverters, in particular to a multilevel converter modulation strategy. Background technique [0002] In recent years, multilevel inverters have been widely used in high-voltage and high-power systems. Multilevel inverters have the advantages of high voltage system capability, low harmonic distortion, easy expansion and high fault tolerance. Therefore, multilevel inverters are widely used in HVDC transmission systems and renewable energy systems. There are many topologies for multilevel inverters, among which the cascaded H-bridge is one of the most widely used topologies. There are many modulation methods for cascaded H-bridges, including carrier phase shifting, carrier stacking, and discontinuous modulation. The power distribution of each module is unbalanced under carrier cascading modulation. Under discontinuous modulation, it is necessary to balance the relationship between the switchi...

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Problems solved by technology

However, under normal conditions, the switch is always in a high-frequency state, and the switching loss is large, which will reduce the efficiency of the system

[0004] According to the above description, it is not difficult to find that although the output waveform quality of carrier phase-shifting unipolar frequency doubling modulation is good, the switch is always in high-frequency operation. As the number of cascades increases, the circuit efficiency will decrease, and the heat of the switch tube will increase, making it easier to damage. detrimental to circuit stability

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