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Converters with impedance source networks combine their one-stage energy conversion with the function as buck and boost converters. Due to this fact, they are very attractive to the dc–ac applications. Many literatures have focused on the stress analysis and control enhancement of the impedance network in the dc side. For a better system design and control, the synthesis and interaction principle between the ac and dc side of the converters is required. This paper first presents small-signal modeling for the bidirectional quasi-Z-source converter by the circuit-averaging technique. Compared with previous modeling based on the shoot-through duty ratio, the modulation ratio is included for the ac-side analysis. It is revealed that the oscillation in the modulation ratio could be triggered by the ac current controller, due to the magnitude margin issue caused by the impedance network, and then instability in the impedance network can be observed, including the system input current. Based on the theoretical analysis, a design guideline for the ac current controller is provided. Experimental validation for both the model and analysis is demonstrated and the results are in good agreement with the theoretical analysis. [ABSTRACT FROM AUTHOR]

The impedance-source network converter, utilizing a unique LC network and previously forbidden shoot-through states, provides the ability to buck and boost the input voltage in a single stage. However, the inrush shoot-through current (STC) in startup or transient process might cause undesired current stresses on converter devices. This paper focuses on the STC sensing for an effective inrush current limitation by the combined current sensing technique in the quasi-Z-source inverter. STC and phase currents for the inverter control strategy are obtained simultaneously. No extra hardware is needed and the effects of current sensor bandwidth and duty cycle on the sensing accuracy are analyzed mathematically. The voltage spike gets avoided by integrating the stray inductance into the impedance network. Finally, an STC control loop based on proposed method are embedded in the field-oriented control strategy. The inrush STC and the device current stress in the transient process get suppressed. Simulation and experimental results from a quasi-Z-source inverter validate the feasibility of the proposed methods. [ABSTRACT FROM PUBLISHER]

An ultracapacitor–battery hybrid energy storage system (HESS) for an electric vehicle (EV) based on a bidirectional quasi-Z-source inverter (qZSI) is proposed in this paper. The buck/boost characteristic in the qZSI enables the HESS incorporated into the traction inverter system. The battery converter can be eliminated and the rated voltages for the battery package and UCs are reduced. The steady power distribution principle is explained under various operation modes. An enhanced frequency dividing coordinated control strategy is established to optimize the dynamic power regulation and the battery current stress in short timescale. Both the simulation and experimental results in time and frequency domain validate the performance of the proposed HESS. [ABSTRACT FROM PUBLISHER]

This paper proposes an ultracapacitor (UC)-battery hybrid energy storage system (HESS) for electric vehicle based on asymmetric bidirectional Z-source topology. Compared with the conventional two-stage design, the HESS can be incorporated into the traction inverter system, leading to better performance and lower cost. The UC energy can be effectively utilized due to the buck/boost characteristic in the Z-source converter; meanwhile, the battery converter gets eliminated in this case. The assumption about the symmetry in the Z-source topology impendence network states for the conventional analysis no longer applies to the proposed HESS configuration. The asymmetric characteristic related with the uneven power distribution of UCs and battery is mathematically excavated in detail. The frequency dividing coordinated control is proposed to exploit the advantages of UCs and battery. The battery peak current estimation is then investigated. Finally, the steady performance and transient response in both traction and regenerative modes are verified by simulation and experimental results. [ABSTRACT FROM PUBLISHER]