Adaptive control scheme for a practical bidirectional DC-DC converter with a 80 kHz switching and a 10 kHz sampling frequency

This paper discusses an adaptive control scheme for a bidirectional boost converter used in a hybrid gasoline-electric vehicle. The converter transforms the voltage of the low-voltage battery, approximately 96 V, to 400 V on the DC-link of the motor inverter. The switching frequency of the inverter is 80 kHz, which enables the usage of rather compact 64 µH inductors. However, the sampling frequency of the control scheme is 10 kHz, so the duty cycle of the switches will only be updated after 8 consecutive switching periods. Due to the large dead-time of the switches in comparison with the switching frequency, the response of the current to changes in the duty cycle is highly non-linear. The low sampling frequency of the control scheme combined with the highly non-linear current response makes it impossible for a simple PI-controller to regulate the current in a satisfactory way. At first the cause of the non-linear response is investigated. Based on that knowledge, a control scheme is developed that adjusts the duty cycle when necessary and switches between two PI-controllers, one for small currents and one for large currents. This current controller is implemented on two interleaved bidirectional boost converters. The current controller´s set point is regulated by the DC-link voltage controller.