Combined resonant tank capacitance and pulse frequency modulation control for ZCS-SR inverter-fed high voltage DC power supply

Abstract

Conventional pulse frequency modulated (PFM) zero current switching (ZCS) series resonant (SR) inverter fed high voltage dc power supplies have nearly zero switching loss. However, they have limitations of poor controllability at light loads and large output voltage ripple at low switching frequencies. To address these problems, this paper proposes a combined resonant tank capacitance and pulse frequency modulation based control approach. For the realization of the proposed control approach, the tank circuit of the resonant inverter is made up of several resonant capacitors that are switched into or out of the tank circuit by electromechanical switches. The output voltage of the converter is regulated by digitally modulating the resonant tank capacitance and narrowly varying the switching frequency. The proposed control scheme has several features, namely a wide range of controllability even at light loads, less output voltage ripple, and less current stress on the inverter's power switches at light loads. Therefore, the proposed control approach alleviates most of the problems associated with conventional PFM. Experimental results obtained from a scaled down laboratory prototype are presented to verify the effectiveness of the proposed system.

LLC resonant DC–DC converter with series‐connected primary windings of transformer

“…Resonant DC-DC converters are widely employed in many lowand high-voltage applications for power processing because of their several advantages such as low switching loss, high-frequency operation, absorption of parasitic components (leakage inductance and parasitic capacitance) of transformer as useful elements into the power topology, and low electromagnetic interference (EMI) [1][2][3][4][5][6][7]. There are three main types of resonant converters: series resonant converters (SRCs), parallel resonant converters (PRCs), and series-parallel converters (SPRCs) [7][8][9]. All of these resonant converters have some merits and demerits.…”

“…For example, SRC is free from possible saturation of the transformer, it absorbs the leakage inductance of transformer, and permits capacitive output filter [3][4][5][6][7][8][9]. However, it has several problems such as poor control and loss of zero-voltage switching (ZVS) operation at light loads [1,[3][4][5][6][7][8][9]. In PRC, both leakage inductance and the winding capacitance of transformer are incorporated into the power topology.…”

“…Besides, it provides good control for both light and heavy loads [7][8][9][10][11][12][13]. However, it has low efficiency at light loads because of circulating currents which are independent of the load current [7][8][9][10][11][12][13]. SPRC, on the other hand, combines the features of both SR and PR converters [7,14,15].…”

“…However, it has low efficiency at light loads because of circulating currents which are independent of the load current [7][8][9][10][11][12][13]. SPRC, on the other hand, combines the features of both SR and PR converters [7,14,15]. It also provides good control for both heavy and light loads, and achieves high efficiency.…”

“…However, this converter is not suitable for applications where the input voltage varies over a wider range. This is because, when its input voltage is increased, the circulating currents become high, leading to higher conduction loss and lower efficiency [6][7][8][9][16][17][18]. Besides, this converter also has complex control characteristics [7].…”