Method for determining duty ratio of universal pulse width controlled by three-phase AD motor PWM

Abstract

The invention provides a method for determining duty ratio of universal pulse width for control of a three-phase AD motor PWM (pulse width modulation). The method comprises the following steps: determining normalization three-phase current set values Ia, Ib and Ic of the three-phase AD motor; calculating each two-phase current difference Iab, Ibc and Iac according to the normalization three-phase current set values Ia, Ib and Ic; calculating the maximum value max{|Iab|, |Ibc| and |Iac|} of absolute values of each two-phase current difference; determining the duty ratios ka, kb and kc according to three conditions of the max{|Iab|, |Ibc| and |Iac|} through four arithmetic operations. Compared with the conventional six sector vector decomposition method for determining the duty ratio of three-phase pulse, the method has the same result; but because of simple process and prevention of complicated vector determination and trigonometric function operation, the method has less realized code amount, small occupied hardware resources and high operation efficiency, can realize multiple PWM control modes including control modes of SPWM (sine pulse width modulation) and SVPWM (space vector pulse width modulation), and is particularly applicable to high-precision SVPWM control of the three-phase AD motor.

Description

technical field [0001] The present invention relates to a method for determining the general pulse width duty ratio of PWM (pulse width modulation) control of a three-phase AC motor, in particular to a method for avoiding complex sector judgment and vector decomposition, and can realize a method including SPWM (sinusoidal pulse Width Modulation) and SVPWM (Space Vector Pulse Width Modulation) methods to determine the general duty cycle of the pulse width. Background technique [0002] At present, PWM control has become the most widely used control method in switching power supply, motor control and other devices that need to realize power inverter function. The theoretical basis of PWM control is the principle of impulse conservation in sampling control theory, that is, when narrow pulses with equal impulse but different shapes act on the inertial link, the effects are basically the same. PWM control technology is based on this principle, by controlling the on and off of se...

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Problems solved by technology

[0006] Compared with SPWM, the advantage of SVPWM is that it can increase the utilization efficiency of DC power by 15.47%. However, due to the need for vector decomposition, the three-phase vector space is divided into six sectors, as shown in the attached figure 2 As shown, Vr in the figure is the reference vector that needs to be decomposed. Firstly, it is necessary to judge which sector Vr is in, and then select the action vector, and decompose Vr into the action vector components corresponding to the sector (for example figure 2 V in 1 ’ and V 2 ’), but also calculate and determine its action time T (pulse width) and sampling period T according to the size of each vector component s ratio (duty cycle), where the sector judgment and vector decomposition need to perform trigonometric and inverse trigonometric operations, not only the algorithm is complex, the amount of programming code is large, and the amount of calculation is also large, the cost is the computing power of the processor more demanding

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