Neutral-point voltage balance control method and system for electroless capacitor NPC three-level inverter

Abstract

The invention discloses a neutral-point voltage balance control method and system for an electroless capacitor NPC (Neutral Point Clamped) three-level inverter. The neutral-point voltage balance control method is based on a carrier comparison PWM modulation strategy, that is, a CB-PWM modulation strategy, and includes the steps: calculating a three-phase modulated wave according to a voltage vector, and obtaining a modulated wave Vmax having the maximal amplitude and a modulated wave Vmin having the minimum amplitude at the same time; detecting the voltage of the upper and lower capacitors bya voltage detecting circuit, and calculating the voltage difference; determining whether the motor is running in the electric or braking state; and according to the two conditions, determining that the Vmax and the Vmin are clamped to P or N of the bus voltage, reselecting the redundant vector, and modifying the switching sequence of the IGBT to ensure voltage balance. The neutral-point voltage balance control method and system for an electroless capacitor NPC three-level inverter have the advantages of being low in the switching loss, being less in the time of achieving simple CPU calculation, being able to control the fluctuation of the neutral point voltage in a reasonable range, and being high in the adjusting speed.

Description

technical field [0001] The invention relates to the technical field of AC servo drive control, in particular to a neutral point voltage balance control method and system for a non-electrolytic capacitor NPC (NeutralPoint Clamped) three-level inverter. Background technique [0002] NPC three-level inverters are widely used in medium and high voltage drive systems. Nowadays, this topology is as follows: figure 1 As shown, it has also begun to be gradually applied in low-voltage systems. This topology consists of two capacitors C connected in series 1 , C 2 , the point between the two capacitors is called the midpoint, so the midpoint-clamped inverter is also called a diode-clamped inverter; each phase contains four groups of IGBT / Diode (insulated gate gate thyristor / diode) TX1, TX2, TX3 and TX4; two clamping diodes D X5 and D X5 (X=A, B, and C, representing three phases respectively). Compared with the traditional two-level inverter, the NPC three-level inverter shows signi...

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Problems solved by technology

[0004] The technical problem to be solved by the present invention is that in the prior art, film capacitors or ceramic capacitors are used to replace traditional electrolytic capacitors, the capacitance value of the busbar capacitance is only a few microfarads or tens of microfarads, there is no energy storage device such as electrolytic capacitors, and the busbar voltage cycle This kind of fluctuation makes it more difficult to control the balance of the three-level midpoint voltage. The traditional method may not be able to meet the technical defects of this small capacitor inverter system. A non-electrolytic capacitor NPC three-level inverter is provided. Transformer neutral point voltage balance control method and system

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