Wide load

Abstract

Researchers working at the National Yunlin University of Science and Technology in Taiwan present a new resonant converter. The converter has two advantages; firstly, it uses two flying capacitors to balance input split voltages and secondly, it has a wide input-voltage range of operation, along with variable secondary winding turns, due to use of an AC switch. Resonant converters are power electronics devices containing a network of inductors and capacitors known as a ‘resonant tank’. They can be tuned to resonate at specific frequencies and find a multitude of applications in electronics as parts of integrated circuits. Power converters for medium and high voltage applications are widely used for reactive power control and in AC motor-drives. Whilst full-bridge converters are excellent for high-voltage uses, the materials used to produce them (silicon carbide or gallium nitride) are very expensive, and so it is more economically efficient to use cheaper devices and optimise their performance. Circuit diagram of the proposed device. Experimental waveforms of the proposed converter. a Vin, VCin1, VCin2 at Vin = 260 V and the rated power b Vin, VCin1, VCin2 at Vin = 800 V and the rated power c iD1, iD2, Vo, Io at Vin = 260 V and the rated power d iD3, iD4, Vo, Io at Vin = 800 V and the rated power As we move to more renewable energy sources, such as solar and wind power, we find that the voltage output of harvesting devices, such as solar panels and wind turbines, fluctuates over time. Due to this fluctuation, it is important that power electronics used to transfer the energy from these devices are equipped to deal with a range of voltages. The basic circuit topology for these applications is a two-stage power converter. An alternative topology is a series or parallel connection of full bridge converters. Both topologies have drawbacks however, two-stage converters suffer from low circuit efficiency, whilst series/parallel full bridge converters require a large number of circuit components and also introduce additional power losses. The device presented in this issue of Electronics Letters boasts zero-voltage switching on active devices and a wide input-voltage operation range, between 260 and 800 V. The proposed device comprises a two-part circuit. Input voltage is provided by a unstable input, such as a solar panel or wind turbine device. Two split capacitors and two half bridge legs are included on the input-side of the circuit to reduce the voltage rating on the 4 power switches. Power MOSFETS (metal-oxide-semiconductor field-effect transistors) in the circuit are able to withstand ∼800 V of input voltage. The other side of the converter is a voltage double rectifier, effectively doubling the output voltage. Different parts of the second half of the converter are active depending on the voltage coming across from the input-half of the converter, ensuring that the converter is working optimally across the input-voltage range. Frequency modulation is adopted in the converter to control load voltage and to generate pulse-width modulation (PWM) signals of active devices. Experimental verification of the converter is provided by the authors. It can be seen that the device clearly performs well across the wide input range of 260–800 V. The two split capacitor voltages are well balanced, showing the device is stable. As the device does not rely on expensive semiconductor materials such as silicon carbide or gallium nitride, the device is more economically viable for mass production. This device is promising as a candidate for resonant converter applications such as renewable energy conversion, especially for renewable energy sources with unstable voltage outputs (such as solar and wind power). Future experiments could look at the feasibility of improving the input voltage range of the device even further, or further improving the amount by which the input voltage is increased post-conversion.