Multi-level converter modulation strategy

Abstract

The invention discloses a multi-level converter modulation strategy which comprises the following steps: S1, determining the number N of cascaded H bridges and the switching frequency k of a circuit, and determining the phase shift angle theta of triangular carriers Vc and the number N of required triangular carriers Vc according to the number N of the cascaded H bridges; S2, determining a direct current side voltage Vin of the circuit and resistive and inductive loads R and L in the circuit; and S3, determining a modulation degree m, obtaining a rotary SPWM modulation wave, generating a left side bridge arm modulation wave and a right side bridge arm modulation wave of a corresponding circuit topology under the modulation of the rotary SPWM modulation wave, wherein each of the left side bridge arm modulation wave and the right side bridge arm modulation wave comprises a clamping part and a modulation part which are respectively compared with a triangular carrier wave, and enabling ing the switch to be kept in a normally-on or off state within the clamping time and to act at high frequency within normal modulation time, and then driving the circuit, so that the corresponding modulation process is completed.

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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