Photovoltaic (PV) systems containing a rechargeable battery as an energy buffer require multiple dc-dc converters for PV panel control and battery regulation, and hence, they are prone to be complex and costly. To simplify the system by reducing the number of converters, this paper proposes the non-isolated switched capacitor converter (SCC)-based multi-port converter (SC-MPC) for standalone PV systems. The proposed SC-MPC can be derived by integrating a bidirectional PWM converter, series-resonant converter (SRC), and an SCC with sharing switches. PWM and PFM controls are employed for the PWM converter and SRC, respectively, to regulate either a battery voltage, output voltage, or input power from a PV panel, depending on power balance among the input, battery, and load. The 150-W prototype was built for an experimental verification, and the results demonstrated the output voltage could be regulated independently on the battery voltage or input port of PV panels.

Photovoltaic (PV) systems having rechargeable batteries are prone to be complex and costly because multiple converters are necessary to individually regulate a load, PV panel, and battery. This paper proposes novel nonisolated multiport converters (MPCs) integrating a bidirectional PWM converter and phase-shift switched capacitor converter (PS-SCC) for standalone PV systems. A PWM converter and PS-SCC are integrated with reducing the total switch count, realizing the simplified system and circuit. In the proposed MPCs, two control freedoms of duty cycle and phase shift angle are manipulated to individually regulate the load, PV panel, and/or battery. The detailed operation analysis was performed to mathematically derive gain characteristics and ZVS operation boundaries. For the battery discharging mode, in which the PV panel is not available and the MPC behaves as a single-input-single-output converter with two control freedoms available, the optimized control scheme achieving the lowest RMS current is also proposed to maximize power conversion efficiencies. Various kinds of experimental verification tests using a 200-W prototype were performed to verify the theoretical analysis and to demonstrate the performance of the proposed MPC.

High step-down voltage conversion is necessary to bridge the voltage gap between main power converters and low-voltage auxiliary electronics in power conversion systems. Switched capacitor converters (SCCs) are an attractive candidate as a high step-down converter, but their poor voltage regulation capability may limit their applications. PWM SCCs with adjustable high step-down voltage conversion are proposed in this paper. The proposed PWM SCCs can be derived from traditional SCCs by replacing an energy transfer capacitor with a switched-capacitor-inductor (SCL) cell that comprises inductors, capacitors, and diodes to realize PWM-controllable voltage conversion. The voltage step-down ratio of the proposed PWM SCCs is not only PWM-controllable but also adjustable with structures of SCCs and SCL cells. Two representative PWM SCCs were taken as examples to perform the operational analysis. The prototypes of both representative PWM SCCs were built and tested to demonstrate the proposed concept.

Voltages of series-connected batteries gradually become imbalanced due to non-uniformity in terms of not only battery characteristics but also self-discharge rate that is significantly dependent on temperature. In large-scale energy storage systems, a large temperature gradient is very likely because of its huge geometry, and therefore, equalizers capable of relatively large equalization current would be necessary to eliminate voltage imbalance originating from uneven temperature distribution. A two-switch string-to-battery voltage equalizer using a half-bridge converter with multi-stacked current doublers (MSCDs) is proposed for series-connected batteries in this paper. The proposed equalizer is capable of providing relatively large equalization currents without increasing ripple current thanks to the interleaved operation of the MSCDs. Fundamental operational analysis for discontinuous conduction mode (DCM), in which currents in the equalizer can be limited to desired levels without feedback control, is performed. The experimental result of equalization tests performed for four supercapacitor modules and lithium-ion batteries connected in series demonstrated the equalization performance of the proposed equalizer.

Multiport converters (MPCs) that can regulate multiple input/output ports have been proposed to reduce the converter count in electric vehicle battery systems consisting of multiple batteries (12-V, 48-V, and high-voltage batteries). Conventional MPCs consist of an interleaved PWM converter and DAB converter, and an active current balancing control is indispensable for the interleaved converter. Furthermore, the transformer utilization unavoidably decreases because switches are driven with a nominal duty cycle of 0.75 for 48-/12-V batteries. This article proposes a novel MPC with an automatic current balancing capability and improved transformer utilization. A flying capacitor (FC) is added to the interleaved PWM converter to automatically balance inductor currents. The added FC also allows operations with a nominal duty cycle of 0.5 for 48-/12-V batteries, improving the transformer utilization. The experimental verification tests using a 1-kW prototype demonstrated the automatic current balancing capability, improved transformer utilization, and flexible power exchange among three batteries.

Recent power systems, such as renewable energy systems consisting of solar panels and rechargeable batteries, contain multiple power sources and need multiple converters in proportion to the number of power sources, resulting in increased system complexity and cost. This paper proposes a multiport converter (MPC) integrating a bidirectional PWM converter and series-resonant converter. Not only is the switch count halved with the proposed MPC, but also magnetic components can be integrated, reducing the circuit complexity and volume. A 150-W prototype of the proposed MPC was built for the experimental verification. The measured voltage conversion characteristics and transient responses demonstrated that the proposed MPC could control load and battery voltages independently by pulse width modulation and pulse frequency modulation controls, respectively.