Abstract: Pulse width modulation (PWM) has become the standard for electro-hydraulic proportion valve amplifiers for it is efficient, flexible and anti-interference. Meanwhile, the dynamic characteristics of a proportional valve can be improved by superimposing dithers to the valve coil. Aiming at the two control parameters, the frequency and the duty ratio of the PWM, the algorithm of the parasitic dither in low frequency PWM is deduced. The result shows that the amplitude and frequency of the dither cannot be set independently. In a high frequency PWM, dither with independent frequency and amplitude can be generated separately by changing the duty ratio of the pulses. According to the current in inductive loads, the algorithms for two types of dither, one in sine wave envelop and another in triangle wave envelap, are deduced respectively. Numeric emulation agrees with the experiment result. The algorithm particularly suits for digital signal processing and control system.

Key words: Algorithm, Parasitic dither, Independent dither, Pulse width modulation (PWM)