2019 Volume 8 Issue 5 Pages 787-794
This paper proposes voltage control of two battery-operated high-efficiency energy conversion system choppers, which have a very high efficiency of 99.3% and are suitable for power trains of electrical vehicles. However, due to the topology of the choppers, one disadvantage is that the chopper output voltage control has a large transient response, for example, when the duty ratio is changed from zero to a finite value, because of the inherent dead time in the switching phenomena. The minimum pulse width of the gate signal is physically determined by the delay time in the switching phenomena. As a result, there exists a dead time when the duty ratio is changed in this case. Similar phenomena occur when the duty ratio is changed around unity. Consequently, an overcurrent is observed during these types of transient periods and the system shuts down due to overcurrent protection. To solve this problem, intermittent pulse density modulation is proposed such that the output voltage is controlled by the average duty ratio. This makes it possible to output both the very low and the very high average duty ratios with multiple sampling periods. As a result, the transient response was experimentally verified to be improved even though the voltage ripple under this control increased compared with that under simple pulse width modulation (PWM) control.