Series-resonant Voltage Multiplier Research Articles

Variable switching frequency modulation scheme for PWM converter integrating series‐resonant voltage multiplier‐based voltage equalizer for photovoltaic strings under partial shading

Conventional photovoltaic (PV) systems require not only a converter for string control but also preferably a voltage equalizer to preclude partial shading issues, which increases the system complexity because two separate converters are necessary. A single‐switch, single‐magnetic pulse width modulation (PWM) converter integrating a series‐resonant voltage multiplier (SRVM) as a voltage equalizer has been proposed in previous work to simplify PV systems by reducing the converter count. The equalization performance of the integrated converter employing a traditional PWM control scheme, however, is unavoidably impaired because the effective operation period of the SRVM in a switching cycle is relatively short at a fixed switching frequency fS. This paper proposes a variable‐fS PWM control technique to improve the voltage equalization performance of the SRVM. The proposed modulation scheme adjusts fS according to the duty cycle variation so that the SRVM's effective operation period is extended. Detailed mathematical analysis revealed that the proposed modulation scheme could improve the equalization performance of the integrated converter. The experimental equalization tests for three PV modules connected in series were performed emulating a partial shading condition. With the proposed modulation scheme, the extractable maximum power from the partially shaded string increased by up to 7%, demonstrating the improved equalization performance of the SRVM. © 2018 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.

Single-Switch Single-Magnetic PWM Converter Integrating Voltage Equalizer for Partially Shaded Photovoltaic Modules in Standalone Applications

To prevent partial-shading issues in photovoltaic (PV) systems, various kinds of voltage equalizers that virtually unify characteristics of shaded and unshaded modules have been proposed. Although PV string utilization can be dramatically improved, PV systems tend to be complex and costly because, in addition to the main converter for string control, voltage equalizers are separately necessary. This paper proposes the single-switch single-magnetic pulse width modulation (PWM) converter integrating the voltage equalizer using the series-resonant voltage multiplier (SRVM) for standalone PV systems. By utilizing a square wave voltage generated across a filter inductor in a PWM buck converter for driving the SRVM, the main PWM converter and voltage equalizer can be integrated into a single unit with reducing the total switch and magnetic component counts, achieving not only system-level but also circuit-level simplifications. The experimental test using the prototype for three PV modules connected in series was performed emulating a partial-shading condition. The integrated converter effectively precluded the partial-shading issues and significantly improved the power available at a load, demonstrating its efficacy.

PWM Converter Integrating Switched Capacitor Converter and Series-Resonant Voltage Multiplier as Equalizers for Photovoltaic Modules and Series-Connected Energy Storage Cells for Exploration Rovers

Power systems for exploration rovers tend to be complex as three separate converters are necessary; in addition to a main dc–dc converter and cell equalizer for rechargeable energy storage cells, an equalizer for photovoltaic (PV) modules is desirably equipped in order to preclude negative impacts of partial shading. This paper proposes the pulse width modulation (PWM) converter integrating voltage equalizers for PV modules and energy storage cells. The proposed integrated converter comprises a switched capacitor converter, PWM buck converter, and series-resonant voltage multiplier that perform PV equalization, power conversion from the PV modules to the load, and cell equalization, respectively. Three converters can be integrated into a single unit with reducing the total switch counts, achieving not only system-level but also circuit-level simplifications. The derivation procedure of the integrated converter is explained, followed by the operation analysis. Experimental tests were performed using series-connected supercapacitor (SC) modules and solar array simulators to emulate a partial shading condition. With the integrated converter, the extractable maximum power from the PV modules significantly increased while voltage imbalance of SC modules was adequately eliminated, demonstrating the integrated performance of the proposed converter.

太陽電池用部分影補償器を統合したPWMコンバータ

Partial shading on a photovoltaic (PV) panel comprising of multiple substrings connected in series leads to major issues, such as decreased power generation and occurrence of multiple power point maxima. Various PV equalizers have been proposed to preclude partial shading issues. However, system complexity increases because of the addition of PV equalizers, and circuits are prone to complexity because each PV equalizer contains switches. This study proposes a single-switch PWM converter integrating a PV equalizer using a series-resonant voltage multiplier (SRVM) for PV panels under partial shading. A PWM converter and PV equalizer can be integrated into a single unit, which decreases the switch count, achieving system- and circuit-level simplifications. Detailed operation analysis was performed for the SRVM, using which a dc equivalent circuit was mathematically derived. Experimental tests using a prototype for three substrings connected in series were performed with solar array simulators. The integrated converter successfully precluded the occurrence of multiple power point maxima and significantly improved the extractable maximum power as compared to that without equalization, demonstrating its efficacy.

Bidirectional PWM Converter Integrating Cell Voltage Equalizer Using Series-Resonant Voltage Multiplier for Series-Connected Energy Storage Cells

In conventional energy storage systems using series-connected energy storage cells such as lithium-ion battery cells and supercapacitors (SCs), an interface bidirectional converter and cell voltage equalizer are separately required to manage charging/discharging and ensure years of safe operation. In this paper, a bidirectional PWM converter integrating cell voltage equalizer is proposed. This proposed integrated converter can be derived by combining a traditional bidirectional PWM converter and series-resonant voltage multiplier (SRVM) that functionally operates as an equalizer and is driven by asymmetric square wave voltage generated at the switching node of the converter. The converter and equalizer can be integrated into a single unit without increasing the switch count, achieving not only system-level but also circuit-level simplifications. Open-loop control is feasible for the SRVM when operated in discontinuous conduction mode, meaning the proposed integrated converter can operate similarly to conventional bidirectional converters. An experimental charge-discharge cycling test for six SCs connected in series was performed using the proposed integrated converter. The cell voltage imbalance was gradually eliminated by the SRVM while series-connected SCs were cycled by the bidirectional converter. All the cell voltages were eventually unified, demonstrating the integrated functions of the proposed converter.

Two-Switch Voltage Equalizer Using a Series-Resonant Voltage Multiplier Operating in Frequency-Multiplied Discontinuous Conduction Mode for Series-Connected Supercapacitors

Two-Switch Voltage Equalizer Using a Series-Resonant Voltage Multiplier Operating in Frequency-Multiplied Discontinuous Conduction Mode for Series-Connected Supercapacitors