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A direct ac–ac resonant switched-capacitor converter (SCC) for both noninverting and inverting output voltages is proposed here, which is suitable for bidirectional power transmission including different applications such as dynamic voltage restorer (DVR), constant current regulator (CCR), and constant current regulator. Zero voltage switching and zero current switching operation conditions are easily realized for its power switches, which effectively reduce the switching losses, as well as the electromagnetic interference noise. Consequently, high-frequency operation is possible, which improves the converter power density, in practice. Continuous voltage-gain, transformerless connection of the converter output port to the gird, no commutation problems without using extra components, and improving the electrical specifications are some other advantages of the given resonant SCC. The converter operation principles, its key waveforms and different operational states, its mathematical analysis and normalized state-plane trajectories, simulation results, as well as its design procedure, are also given here, in detail. To verify the given theoretical analyses and simulation results, a 500 W prototype converter for a 2 kW DVR with 220 Vrms nominal output voltage has been implemented successfully, which realizes 96.55% efficiency at its rating power value.

Magnetic resonance imaging (MRI) systems gradient driver (GD) circuits, which drive current through gradient coils, have essential roles in imaging quality and speed. They drive large current values, higher than 1000 A, with high fidelity to the commands, low current ripples, and fast transient responses, which lead to high voltage values, larger than 2 kV, to properly drive the coils. Till now, some solutions with parallel and stacked structures have been reported to fulfill such requirements, which need several independent isolated voltages to deliver the necessary output current. Thus, other parts are generally needed to generate these voltages, separately. In this article, a new GD circuit with only a single independent voltage source and output voltage boosting capability is proposed to drive such gradient coils. It reduces the semiconductor and magnetic element counts, in the MRI gradient driver power chain. It also reduces the pulsed power demand from the facility, by storing energy. The proposed circuit has been mathematically analyzed, here. A 2.34 MVA,1300 A/1800 V GD circuit has been designed and simulated based on the proposed topology to verify its performance. Finally, a laboratory 700 V, 10 A scaled-down prototype converter has been implemented, based on the proposed topology to verify the given analyses and simulation results.

An extendable nonisolated resonant dc–dc converter based on current-fed voltage multiplier (VM) technique is proposed in this article for high step-up applications. These VM cells capacitors participate in a resonant network; therefore, no additional elements are required to provide a resonant tank circuit to realize soft switching conditions for power switches. Zero voltage switching and zero current switching conditions are realized here for switches and diodes, respectively. Consequently, mosfets dominant switching losses and the diodes reverse recovery problems are well overcome. Furthermore, the input source current waveform is continuous. Also, using the VM cells reduces the power devices voltage stresses. Accordingly, low voltage rating devices can be used, which reduce conduction losses and cost, and improve the converter efficiency. Also, by using more VM cells, the proposed converter can be used for high-voltage applications, without using extremely high duty cycle values to regulate the output voltage. The operation principles, steady-state analysis, design guidelines, and main characteristics of the proposed converter are given here, in detail. Finally, an 800 W prototype converter, with 80–100 V input voltage and 2 kV output voltage, has been implemented to validate the given analyses, simulation results, as well as to show the proposed converter main advantages.

In this article, a bidirectional transformerless multilevel direct ac–ac switched-capacitor converter (SCC) is proposed with both in-phase and out-of-phase output voltage capabilities. This converter can be used for series compensator applications, such as dynamic voltage restorers (DVRs), to compensate grid voltage sag and swell phenomena by incorporating its input–output common ground. Its input-series output-parallel capabilities reduce voltage and current stresses of the converter components in multilevel configurations, which lead to higher efficiency and lower manufacturing costs for high-power applications. Furthermore, proper utilization of an interleaving control scheme can provide lower input and output currents ripples values and smaller filter sizes. The proposed SCC operation principle and its mathematical analyses are given, in detail. Additionally, its switching patterns have been developed with a safe-commutation strategy to obtain various output voltages. Subsequently, both single- and two-level SCC prototypes are implemented as series compensators for DVR applications. Moreover, experimental results are given to generate in-phase and out-of-phase regulated output voltages. The experimental results at 2 kW show that the output voltage changes are less than 3% under the steady-state conditions, despite the large input voltage changes from 140 to 300 V. The converter maximum efficiency value is equal to 95.4% at maximum output power value.