Bidirectional Three-Level DC DC Converter Research Articles

Commutation Behavior and Stray Inductance Analysis of a FC-3L-BDC Phase-Leg PEBB

The bidirectional dc-dc converter is a critical component for extending the use of renewable energy and improving the efficiency of high-power electronic systems. This paper presents the analysis of the stray inductance of a commutation loop and the commutation behavior of IGBT devices in a flying capacitor three-level bidirectional DC-DC converter (FC-3L-BDC) phase-leg power electronic building block (PEBB). An FC-3L-BDC phase-leg PEBB was designed as an example, which can be used to build 400 kW to MW-grade light rail train chargers, battery energy storage interface converters, or metro regenerative braking energy recovery converters with a single PEBB or several PEBBs interleaved parallel. In order to optimize the stray inductance of commutation paths and realize snubberless operation, a five-layer laminated bus bar was carefully designed, and the stray inductance of the bus bar was extracted by three-dimensional finite element analysis simulation. To obtain higher accuracy, the stray inductances of IGBT devices and capacitors were extracted from the test instead of their datasheets. Then, the accuracy of the commutation loop stray inductance analysis method was verified by practical experiments. The impact of the stray inductance of the commutation loop on the commutation behavior of IGBT devices was analyzed, and the switching characteristics of IGBT devices were measured under maximum DC-link voltage and entire current rating range at the temperatures of −40 °C, 25 °C, and 150 °C, respectively, finding that neither the excessive turn-off overvoltage of IGBTs nor the snappy reverse recovery of FWDs was observed.

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

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.

The Ultracapacitor-Based Controlled Electric Drives With Braking and Ride-Through Capability: Overview and Analysis

Two issues are still a great challenge in design and application of advanced controlled electric drives: 1) recovery of the braking energy and 2) ride-through capability of the drive system. Apart from ordinary solutions, such as back-to-back and matrix converters, the ordinary drive converter equipped with an energy storage element is used in specific applications such as traction and lift drives. This approach came into focus recently with rapid development of electrochemical double-layer capacitors, so-called ultracapacitors. The ultracapacitor is an electrochemical capacitor having energy density much greater than that of standard electrolytic capacitors. Additionally, the ultracapacitor power density is much higher than that of the existing electrochemical batteries. In this paper, a regenerative controlled electric drive having extended ride-through capability is discussed. The basic principle has been extensively analyzed, including a detailed analysis of all operational modes. A bidirectional three-level dc-dc converter has been considered as the interface power converter. The ultracapacitor design guideline is given. A control algorithm that allows control of the dc bus voltage and the ultracapacitor voltage and current has been presented and briefly analyzed. The regenerative controlled drive system has been tested, and the results are presented and discussed.