This paper proposes the new non-inverting buck-boost ac-ac converter, which can minimize the reverse recovery loss by disabling the body diodes of switches and using the external fast recovery diodes for its current freewheeling. In particular, the proposed ac-ac converter takes advantages of metal-oxide semiconductor field effect transistors (MOSFET) and external fast recovery diodes to achieve the high efficiency. Also, it has the high reliability without the shoot-through and dead-time considerations in the circuit. Moreover, it can be simply implemented without employing the conventional commutation control. This results in decreasing the control complexity. As its proper application, a new type of dynamic voltage restorer (DVR) based on the proposed non-inverting buck-boost converter is described. It enables to solve the voltage sag and swell problems by utilizing both positive and negative gains of converter. Then, the hardware prototype of proposed ac-ac converter and DVR are implemented to verify their practical effectiveness.

This article proposes a family of single-phase transformer based Z-source ac-ac converters (ZSACs). The proposed converters inherit all the benefits associated with the classical single-phase ZSAC, which are providing the buck-boost operation, maintaining or reversing the phase angle, and improving reliability. The proposed converters also have the improved input profile, continuous input current, and shared ground between input and output. Moreover, they use the turns ratio of transformers to produce the required voltage gain, which can be tuned by either increasing or decreasing the turns ratio of transformer depending on the configuration of Z-source structure. A safe-commutation strategy is also presented to achieve the soft commutation, which eliminates the voltage and current spikes without any additional snubber circuits. The features of proposed converters are comprehensively discussed with the detailed theoretical analysis. Thereafter, its performances are evaluated by both simulation and experimental tests.

This article proposes a novel sawtooth-carrier based pulsewidth-modulation (SCPWM) method for quasi-Z-source inverter (qZSI) with the zero-voltage-switching (ZVS) operation to reduce the total harmonic distortion (THD) and inductor current ripple. The conventional variable-duty pulsewidth-modulation (VDPWM) method has been being used for qZSIs because it causes the low switching loss. However, this method has the limitation not only to improve the THD of output current but also to reduce the size of inductor when it is applied to the qZSI. To figure it out, the proposed SCPWM method uses the sawtooth-carrier signal while keeping the benefit from the use of variable duty. In particular, the ZVS operation occurs whenever the edge of sawtooth-carrier signal is located in the time interval of shoot-through state. This allows to increase the carrier frequency of qZSI without any additional switching loss. Thus, both the THD of output current and the inductor current ripple can be reduced while keeping the high efficiency of system. The operating principle of the proposed SCPWM method is first explained in detail. Thereafter, its performance is mathematically analyzed and compared with that of conventional VDPWM method. Finally, its practical effectiveness is verified by the hardware experimental test.

This paper presents a new type of Z-source inverter (ZSI) that replaces two inductors in the original quasi-ZSI with two transformers. It can produce very high output voltage with the high value of modulation index. Moreover, it enables both to provide the better power quality of output and to reduce switching loss. In particular, the proposed quasi-clamped ZSI with two transformers gives a unique solution to obtain the high gain by reducing the turns ratio, rather than increasing it. Also, the leakage inductance of transformer might cause huge voltage spikes across the inverter bridge. To deal with this problem, the effective clamping technique is proposed. As the result, this increases the overall efficiency of system by utilizing the low power switching devices. The characteristics of proposed quasi-clamped ZSI with two transformers are comprehensively discussed with the detailed theoretical analysis. Thereafter, its performances are evaluated by both simulation and experimental tests.

In this paper, a new constant power generation (CPG) method for photovoltaic (PV) systems is proposed to mitigate the power variations due to changes in external conditions. A power grid with the high penetration of renewables might face both voltage and frequency instability when the power variations from PV systems are large. The proposed CPG method estimates the constant power point (CPP) in real-time without requiring the time step used in the conventional methods. Thus, it can rapidly track the CPP, and it is able to generate the constant power effectively even for sudden changes in external conditions. The practical effectiveness of proposed CPG method is verified by experimental and hardware-in-the-loop tests. The results clearly show that the proposed CPG method provides a much faster response with a less tracking error than the conventional methods in different operating conditions. Thus, it can be an effective solution to further increase the penetration level of PV systems to power grid.

This paper proposes an energy-efficient current control strategy for drive modules of permanent magnetic actuators (PMAs) to reduce the cost and volume of DC-link capacitors. The drive module of the PMA does not receive the input power from an external power source during operation. Instead, the externally charged DC-link capacitors are used as internal backup power sources to guarantee the reliable operation even in the case of an emergency. Therefore, it is important to use the charged energy efficiently within the limited DC-link capacitors. However, conventional control strategies using a voltage open loop have trouble reducing the energy waste. This is because the drive module with the voltage open loop uses unnecessary energy even after the PMA mover has finished its movement. To figure it out, the proposed control strategy adopts a current control loop to save energy even if the displacement of the PMA mover is unknown. In addition, the proposed strategy can ensure the successful operation of the PMA by using the driving force analysis. The efficacy of the proposed strategy is verified through the experimental test. It would be expected that the proposed strategy can reduce the cost and volume of the PMA drive system.