IEEE TRANSACTIONS ON POWER ELECTRONICS, VOL. 28, NO. 12, DECEMBER 2013 5477 Development of an 85-kW Bidirectional Quasi-Z-Source Inverter With DC-Link Feed-Forward Compensation for Electric Vehicle Applications Feng Guo, Student Member, IEEE, Lixing Fu, Student Member, IEEE, Chien-Hui Lin, Cong Li, Student Member, IEEE, Woongchul Choi, and Jin Wang, Member, IEEE Abstract—This paper presents a detailed operation analysis, controller design, and realization of a high-power, bidirectional quasi-Z-source inverter (BQ-ZSI) for electric vehicle applications. The circuit analysis shows that with a bidirectional switch in the quasi-Z-source network, the performance of the inverter under small inductance and low power factor can be improved. Based on the circuit analysis, a small signal model of the BQ-ZSI is derived, which indicates that the circuit is prone to oscillate when there is disturbance on the dc input voltage. Therefore, a dedicated voltage controller with feed-forward compensation is designed to reject the disturbance and stabilize the dc-link voltage during a non-shoot- through state. An 85-kW prototype has been built. Both simulation and experimental results are presented to prove the functionality of the circuit and the effectiveness of the proposed control strategy. Index Terms—Bidirectional quasi-Z-source inverter (BQ-ZSI), electric vehicle (EV) applications, feed-forward compensation, re- verse power flow, small signal model. I. INTRODUCTION T HE global push for greenhouse gas emission reduction and higher fuel economy standards have made the development of electric vehicles (EVs) more urgent than ever [1]–[3]. In an EV, the traction drive system is one of the key subsystems. Cur- rently, the topology of a voltage source inverter (VSI) cascaded with a dc–dc converter is widely used. Although the dc–dc con- verter increases the overall efficiency of the traction drive system by properly regulating the dc-link voltage, it brings additional cost. In 2001, the Z-source inverter (ZSI) [4] was proposed to combine the functions of the dc–dc converter and VSI. It can realize the boost function and dc–ac conversion in one active Manuscript received August 14, 2012; revised November 11, 2012; accepted December 20, 2012. Date of current version June 6, 2013. This work was supported in part by the Korean Electric Vehicle-Transportation Convergence System Research Consortium from the Ministry of Land, Transportation, and Maritime affairs of Korea and in part by the Kookmin University. Recommended for publication by Associate Editor S. Wirasingha. F. Guo, L. Fu, C.-H. Lin, C. Li, and J. Wang are with the Ohio State Univer- sity, Columbus, OH 43210 USA (e-mail: guo.135@osu.edu; fu.141@osu.edu; lin.1158@osu.edu; li.1012@osu.edu; wang@ece.osu.edu). W. Choi is with the Kookmin University, Seoul 136-702, Korea (e-mail: danchoi@kookmin.ac.kr). Color versions of one or more of the figures in this paper are available online at http://ieeexplore.ieee.org. Digital Object Identifier 10.1109/TPEL.2012.2237523 stage and decrease the total average switching device power (SDP) by 15% over the dc–dc converter with the VSI topology, which reduces the total cost and further improves the efficiency of the traction drive system [5]. However, the input current of ZSI is not continuous, which will shorten the lifetime of the bat- tery pack and degrade the vehicle performance. By rearranging the components in the Z-source network, a new topology called quasi-Z-source inverter (QZSI) is proposed in [6]. The QZSI realizes the continuous input current, at the same time retaining all the merits of the ZSI, which makes it a good candidate for EV applications. However, the traditional QZSI only allows unidirectional power flow from the dc to the ac side. The traction drive system requires the reverse power flow to realize the regeneration break of the EV. To achieve the bidirectional power flow capability, the same approach as in [6]–[8] is utilized in this paper and the diode in the quasi-Z-source network (QZSN) is replaced by an active switch. A similar approach is also utilized in the bidirec- tional ZSI in [9]–[12]. However, much of the previous operation mode analysis was based on the topology of the ZSI and mainly focused on the power flow from the dc to the ac side. To better understand the circuit, this paper first gives a detailed circuit analysis of the bidirectional quasi-Z-source inverter (BQ-ZSI) during the regeneration mode, i.e., when the power flows from the ac to the dc side. The analysis proves that with the active switch, the inductor currents in the QZSN can be reversed and the energy from the ac side can be delivered to the dc source. The analysis also shows that, unlike in the ZSI, part of the dc- link ripple current will be absorbed by the two capacitors in the QZSN and not go through the dc source, which provides a better operating condition for the battery pack in EV. Further- more, with the additional switch, the discontinuous conduction mode (DCM) can be avoided and the BQ-ZSI can have a better performance with small inductance or under low power factor condition [13], such as when the electric motor is operated with a light load. Based on the circuit analysis, the small signal model can be obtained, and the control algorithm of the BQ-ZSI in EV appli- cations can be developed. Several papers were focused on the research on the control of the ZSI and QZSI for different appli- cations [14]–[18]. Li et al. [14] presented a control strategy of the QZSI for photovoltaic (PV) applications, where the voltage of a quasi-Z-source capacitor is controlled to be constant. In the 0885-8993/$31.00 © 2013 IEEE