A Bidirectional Three-level DC-DC Converter with a Wide Voltage Conversion Range for Hybrid Energy Source Electric Vehicles

Abstract

In order to meet the increasing needs of the hybrid energy source system for electric vehicles, which demand bidirectional power flow capability with a wide-voltage-conversion range, a bidirectional three-level DC-DC converter and some control strategies for hybrid energy source electric vehicles are proposed. The proposed topology is synthesized from Buck and Boost three-level DC-DC topologies with a high voltage-gain and non-extreme duty cycles, and the bidirectional operation principle is analyzed. In addition, the inductor current ripple can be effectively reduced within the permitted duty cycle range by the coordinated control between the current fluctuation reduction and the non-extreme duty cycles. Furthermore, benefitting from duty cycle disturbance control, series-connected capacitor voltages can also be well balanced, even with the discrepant rise and fall time of power switches and the somewhat unequal capacitances of series-connected capacitors. Finally, experiment results of the bidirectional operations are given to verify the validity and feasibility of the proposed converter and control strategies. It is shown to be suitable for hybrid energy source electric vehicles.

A Switched-Capacitor Bidirectional DC–DC Converter With Wide Voltage Gain Range for Electric Vehicles With Hybrid Energy Sources

“…In addition, this converter requires complicated control scheme to balance the flying-capacitor voltage. A high bidirectional voltage conversion ratio with lower voltage stresses across the power semiconductors can be achieved by the converter of [23] with a reasonable duty ratio, but the converter still has many problems such as a large number of components, and a high frequency PWM voltage between the low-voltage and high-voltage sides. The multi-level converter in [24] can achieve a high voltage gain with low voltage stress across the power semiconductors.…”

A Coupled-Inductor DC-DC Converter with Input Current Ripple Minimization for Fuel Cell Vehicles

“…Although a three-level DC-DC boost converter lowers the voltage stress to half of the output voltage, the duty cycle is extreme, while the voltage gain is high. A three-level DC-DC converter with a high voltage gain and without extreme duty cycles was proposed in Reference [13], but it had a greater cost due to the number of semiconductors (eight MOSFETs and four diodes), and the control strategy was also more complicated. In References [14,15], the proposed converters employed switched-capacitor cells to achieve a high voltage gain, while the number of switched-capacitor cells, the volume of the converter, and the cost increased.…”

“…In References [22][23][24], interleaved converters were proposed to cut down the input current ripple. The improved modulation strategy proposed in Reference [13] could also obtain a lower input current ripple. However, as the voltage gain increased, the input current became large, and therefore the increased current ripple was still a disadvantage for fuel cell sources.…”

Damping Optimum-Based Design of Control Strategy Suitable for Battery/Ultracapacitor Electric Vehicles

“…A parallel battery/ultracapacitor HESS topology with independent load control of individual energy storages should be well suited for energy management control tasks [6,7,11,26,27]. In such an arrangement, both the battery and the ultracapacitor system are equipped with high-performance current-controlled power converters [28], providing bidirectional energy management within the EVs through the common direct-current (DC) bus (see Figure 1). This may be a challenging control problem because the supervisory control strategy should simultaneously keep the DC bus voltage within narrow bounds [9,25], while also distributing the DC bus load between the battery and ultracapacitor ESS to facilitate smooth EV power-train operation for a wide range of operating regimes [29,30].…”

“…This may be facilitated through conditioning of the power demanded from the ultracapacitor power converter with respect to the battery by using a rule-based [32] or a proportional load distribution strategy [31]. Naturally, due to low energy density of ultracapacitor ESS, ultracapacitor system voltage should also be monitored and controlled to avoid overcharging or operation at low state of charge [28]. Simultaneous load sharing and DC bus voltage control typically requires an additional control level.…”