基于分段多次采样提高无刷直流电动机换相精度的方法

A Method for Increasing the Commutation Accuracy of BLDCM Based on Piecewise Sampling

在基于利用A/D检测无刷直流电动机反电动势过零点策略的基础上,提出了一种分段多次采样反电动势的方法。根据无刷直流电动机在不同转速下,全桥的PWM占空比不同,将反电动势的采样方式分为三种,分别对应全桥PWM的低占空比、中占空比以及高占空比。在三种不同的占空比下,采用不同的反电动势过零点检测方法。经软件实时计算,在每个阶段中的不同占空比下最大化地设置A/D采样次数,通过实时调节采样次数达到检测反电动势过零点的最优化。由于在每个PWM周期内最大化地利用A/D采样反电动势,提高了换相精度。在同样的转速下,在保证换相精度的同时,可以降低全桥PWM的频率,从而减小功率开关的损耗。从另一方面看,在不提高A/D转换速率的前提下,该策略可以适用于更高速的电机。

A piecewise sampling method of detecting back EMF was proposed based on the use of A / D detection on the back EMF of BLDCM. Because BLDCM's speed was based on the full bridge PWM duty ratio,the method was classified into three periods,respectively corresponding to low duty cycle,middle duty ratio and high duty ratio. Under the different duty cycle,different methods were adopted to detecting the zero- crossing of back EMF. By calculating,the microprocessor as much as possible sets up the A / D sampling frequency under different duty ratio in each stage. Because of maximizing the use of A / D sampling in detecting the zero- crossing of back EMF in each PWM cycle,this method can improve the precision of commutation. Also under the same speed,in ensuring the precision of commutation,it can reduce the frequency of PWM,so as to reduce the switch loss of the MOSFET. On the other hand,without raising A / D conversion rate it can be applied to more high speed motor.