PWM_SPEED_CONTROLAND_ENERGY_RECOVERING_BRAKE

Published:2009/7/8 4:48:00 Author:May | From:SeekIC

This circuit uses the main drive motor as a generator/brake to recover the battery charge during vehicle braking. When this is done, it can increase the overall range and efficiency of an electric vehicle. In the accelerate mode, Q1 through Q3 receive gate pulses from U1, an on-line, current-mode, PWM controller IC. Assuming negligible effects of R, when Q1 through Q3 turn on, current I1 builds up through the motor at a rate of: d/I1=VB-VA where: VA = Battery voltage VB= Motor's back EMF LA = Motor inductance in henries Motor current and torque continue to rise until the voltage on the ISENSE line is greater than IRESET, as determined by the speed potentiometer. At this time, Q1 through Q3 are switched off, current I2 begins to flow and decreases at a rate of: dI2 VA — = — dt LA until the next clock period begins.As vehicle braking occurs, accelerate PWM IC U1 is switched off and braking PWM IC U2 and Q2 through Q4 are switched on. During this time, the back EMF source voltage causes current I3 to begin to flow at the rate of: dI3 VA — = — dt LA The current I3 continues to rise until ISENSE is greater than IRESET. Now, Q2 through Q4 are switched off and IB is forced to flow back into the storage battery, thus energy is recovered. The braking torque produced by the motor is proportional to the average reverse current that flows through the motor on the duty cycle of Q2 through Q4. The braking force can continue until: VA =0 For reliable performance, voltage supplies should be independent of the main battery voltage.



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