Dual-modulating wave dual-carrier modulation method for voltage type three-level neutral point clamped converter

Abstract

The invention discloses a dual-modulating wave dual-carrier modulation method for a voltage type three-level neutral point clamped converter. The method comprises the following steps of (1) obtaining three phases of modulating waves according to a carrier PWM (pulse width modulation) method; (2) decomposing the modulating wave Ux of each phase into an upper modulating wave Uxp and a lower modulating wave Uxn; and (3) comparing the upper and lower modulating waves Uxp and Uxn with carriers, and outputting a final PWM pulse to the voltage type three-level neutral point clamped converter. According to the method, the upper and lower modulating waves Uxp and Uxn are solved according to the principle that average neutral point current in each carrier cycle is 0, and influence on the balance of direct current capacitance and voltage is avoided.

Description

【Technical field】 [0001] The invention relates to the technical field of power electronics, in particular to a modulation method for a voltage-type three-level midpoint clamp converter. 【Background technique】 [0002] In recent years, the application of three-level neutral-point clamped inverters in the medium and high voltage fields has become more and more extensive, and the technology has become more and more mature. However, its inherent neutral-point potential balance problem still needs to be improved. [0003] The modulation methods of the three-level inverter include a carrier PWM method and a space vector PWM (space vector PWM, SVPWM) method. [0004] SVPWM has been widely welcomed because of its high voltage utilization rate and flexible vector selection, but this method has complex algorithms and a large amount of calculation. On the contrary, the basic carrier PWM has the advantages of simple algorithm and easy implementation. However, since the three-level NPC ...

AI Technical Summary

Problems solved by technology

[0004] SVPWM has been widely welcomed due to its high voltage utilization rate and flexible vector selection, but this method has complex algorithms and a large amount of calculation

On the contrary, the basic carrier PWM has the advantages of simple algorithm and easy implementation. However, since the three-level NPC inverter needs to control the neutral point potential balance, and the method of zero-sequence voltage injection is generally used, this brings the carrier PWM The following disadvantages are overcome: 1) The calculation of the exact value of the required injected zero-sequence voltage is very complicated, which offsets the simple advantages of the basic carrier PWM algorithm; 2) Under partial modulation and power factor, the low-frequency fluctuation of the midpoint potential still cannot be completely eliminated , which not only needs to increase the capacitance of the DC node, but also increases the low-frequency harmonics of the inverter output

Images