1434 PIERS Proceedings, Marrakesh, MOROCCO, March 2023, 2011

Applications of Resonant and Soft Switching Converters

V. Sladecek, P. Palacky, T. Pavelek, and P. HudecekDepartment of Electronics, Faculty of Electrical Engineering and Computer Science

VSB-Technical University of Ostrava, 17, listopadu 15, Ostrava-Poruba 70833, Czech Republic

Abstract This paper covers the circuit modification of the power part of the inverter withauxiliary resonant poles utilising configuration of switches realised with routinely produced IGBTmodules. Covered is also the control optimisation which goal is the minimisation of switching ofthe auxiliary resonant pole. Presented results were gained on a prototype of an inverter laboratorysample.

1. INTRODUCTION

High frequency operations of PWM converters allow reduction of the size and weight of theirmagnetic components. However, at high switching frequency, switching losses and EMI emissionsbecome significant and must be reduced. Traditional high frequency switch mode supplies, whichrely on generating an AC waveform have used power transistors to hard-switch the unregulatedinput voltage at this rate. This means that a transistor turning on will have the whole raw inputvoltage, across it as it changes state. During the actual switching interval (less than 50 microsec-onds) there is a finite period as the transistor begins to conduct where the voltage begins to fallat the same time as current begins to flow. This simultaneous presence of voltage across the tran-sistor and current through it means that, during this period, power is being dissipated within thedevice. A similar event occurs as the transistor turns off, with the full current flowing through it.More recently, new power conversion topologies have been developed which dramatically reduce thepower dissipated by the main power transistors during the switching interval. The most commontechnique employed has been a constant frequency resonant switching scheme, which ensures thatthe actual energy being dissipated by the active device is reduced to nearly zero. This method,commonly called is Zero Voltage Switching (ZVS), Zero Current Switching or SoftSwitching. These converters use the LC resonance circuit. When using resonant circuits to re-duce switching losses, by resonant inductance connected or disconnected from the resonant circuitat zero current passing through this inductance, or that connects or disconnects the resonance ca-pacity at zero voltage. Leader in this area are quasiresonant converters, which use the properties ofresonant LC circuit, only in moments of commutation switches. Reduction in the steepness of thestarting and trailing edge of the output voltage when using resonant inverter also has a favorableinfluence on the electromagnetic interference.

2. POWER PART OF AN INVERTER WITH RESONANT POLE

In Fig. 1, there is shown a block scheme of the power part of used three-phase converter with softswitching. The converter with resonant poles consists of a conventional voltage source inverterwith zero (reverse) diodes and resonant poles. Each branch of the inverter bridge contains switchesVT11 and VT12 (VT21, VT22 and VT31, VT32). The switches activate circuits Lr1, Cr1, respectiveLr2, Cr2 and Lr3, Cr3 (see Fig. 1). These circuits are initialized in the instants, when the currentof load is too low for fast overcharging, or wrong polarity for overcharging of resonant capacitors.If the current of load is high enough and right polarity it is possible to overcharge without resonantcircuit utilization. The main switches of the converter use zero voltage switching and the auxiliaryswitches use zero current switching.

3. DESIGN OF METHODS FOR OPTIMIZATION OF RESONANT CIRCUIT CONTROLWITH RESPECT TO LOAD CURRENT

For design of optimalization of resonant circuit control it is used the scheme for one phase ofresonant circuit (Fig. 2). It is clear that switching of IGBT transistors has to be realised in suchway to no IGBTs use hard switching. It is possible to perform optimization of switching algorithmwith respect to the value of load current in the following way to minimal number of resonantcircuit activation occurs and to short-term currents of resonant circuit have a necessary value only.The optimization can be divided into two basic problems.

Progress In Electromagnetics Research Symposium Proceedings,Marrakesh,Morocco,Mar. 2023, 2011 1435

M

VT11

VT 12

LR1

C R1A

C R1B VT 2

VT 1 VT 3

VT 4

VT 5

VT 3

VD 1

VD 2

VD 3

VD 4

VD 5

VD 6

XR 1 XR 2 XR 3

U

V

W

Ud

Figure 1: Inverter with resonant poles power part.

ILUd

VT11

VT 12

LR1

C R1A

C R1B

VT 2

VT 1 VD 1

VD 2

iLR

uV1

uV2

Figure 2: One phase of quasi-resonant inverter.

Optimization of switching algorithm of the switches in the bridge with respect to the value ofIL.

Optimization of current impulse size in the resonant circuit with respect to the value of IL.If the load current achieves sufficient value and right direction it is possible to overcharge theresonant capacitors by the current without resonant circuit activation. In the second case thesituation is following, load current has right direction, but it is not high enough for fast overchargingthe resonant capacitors. In this case the load current overcharges the resonant capacitors with thehelp of the resonant circuit without its activation. For right understanding it is presented detailedexplanation. Each situation follows from waveforms of the load current. The first assumption wetake into account an ideal load current, we substitute it by a sinusoidal waveform. The waveformis divided into a few sectors according to size and direction of load current (see Fig. 3). Currentdirections, positive and negative, correspond to labelling in Fig. 2. The load current is also dividedinto sectors I, II, III with respect to its absolute value. Switching algorithm for control of one phaseof quasi-resonant converter depends on the direction and sector, where load current IL lies. Fromthe fact follows that it exists five switching sequences of each IGBT in the quasi-resonant bridge.

4. BLOCK SCHEME OF THE CONTROL PART FOR ONE PHASE OF THECONVERTER USING SOFT-SWITCHING

In Fig. 4, it is shown a block scheme of the control part for one phase of the converter using soft-switching. The input is a PWM signal connected to the analog part, where it is compared the loadcurrent and resonant current, it is evaluated position of load current with respect to the positionin the given sector (see Fig. 4) and it is chosen a switching sequence for logical part of the controlcircuits.

1436 PIERS Proceedings, Marrakesh, MOROCCO, March 2023, 2011

5. EXPERIMENTAL RESULTS

In Figs. 5 to 9 there are depicted the time responses of output voltage and current together withthe current of resonant coil during small and large values of the output current. On the picturesare also included the details of switching in various regimes.

IL

t

0

Sector I

Sector II

Sector III

Sector II

Sector III

Sector I

Figure 3: Waveform of load current and its di-vision into particular sectors.

SENSOR UVT1=0

SENSOR UVT2=0

SENSOR ILr

SENSOR IL

ANALOGPART

DIGITALPART

POWERPART

PWM

Figure 4: Block scheme of the control part for one phaseof the converter using soft-switching.

Figure 5: Inverter with resonant circuit.

Figure 6: Voltage UVT2 (blue) and resonant currentiLR (red) for small IL.

Figure 7: Voltage UVT2 (blue) and resonant currentiLR (red) for one switching cycle VT2 and small IL.

Progress In Electromagnetics Research Symposium Proceedings,Marrakesh,Morocco,Mar. 2023, 2011 1437

Figure 8: Output voltage, current and resonant cur-rent for f = 50Hz and small output current.

Figure 9: Output voltage, current and resonant cur-rent for f = 50Hz and large output current.

ACKNOWLEDGMENT

The paper was created with the support of the projects MSM: 618910007, ENET: CZ.1.05/2.1.00/-03.0069.

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