CALCULATION OF THE PARAMETERS ON OUTPUT CURRENT IN FULL─BRIDGE SERIAL RESONANT POWER CONVERTER Assos. prof. Dr. Eng. Stefanov G. 1 , Prof. Dr. Eng. Sarac V. 2 , Assist. M.Sc. Kukuseva Paneva M. 3 , Assis. M.Sc. Citkuseva Dimitrovska B. 4 , Assis. M.Sc. Veta Buralieva J. 5 Faculty of Electrical Engineering- Radovish, University „Goce Delcev‟-Stip, Macedonia 1,2,3,4 FI- Stip, University „Goce Delcev‟-Stip, Macedonia 5 goce.stefanov@ugd.edu.mk, vasilija.sarac@ugd.edu.mk, maja.kukuseva@ugd.edu.mk, biljana.citkuseva@ugd.edu.mk, jasmina.buralieva@ugd.edu.mk Abstract: In this paper for full─bridge serial resonant converter, exact general equations for dependencies of phase angle, the maximum voltage of the capacitor and the maximum value of the output current are derived. Mathematical analysis of the this dependence on the reso- nant circuit dumping frequency when it is excited with pulse voltage with a different frequency than the resonant one is made. This depen- dences derived in wide a band around the resonant frequency. Keywords: POWER CONVERTER, PHASE ANGLE, OUTPUT CURRENT, EQUATIONS 1. Introduction In the analysis of serial resonant converters it is usual to use the resonant circuit frequency ω 0 for two reasons: 1) assuming that the value of the resistance of the resonant tank is very small the dump- ing is negligible and thus resonant ω 0 and damping ω d angular fre- quencies have very close values; 2) active power is calculated using the phase angle between voltage and current first harmonics [1], [2], [3], [4]. However, at these converters in applications of induction heating there is an equivalent resistance of the resonant circuit and the resonant and dumping are different [5], [6], [7]. Also in these converters, the voltage waveforms are pulse and the current has a dumped sinusoidal form [8], [9]. In such cases is required the phase angle and maximum value on the output current of the converter be calculated in respect to the dumping frequency. In this paper for H–bridge serial the resonant converter the explicit dependence of the output current of the converter from the deviation on the switching from damping frequency is determined. This calculation is made in a wide band around the resonant fre- quency. 2. Calculated of the output current of the serial reso- nant bridge converter Calculation of the current in wide band around the resonant fre- quency based on calculate the value of the phase angle and maximal value on current in this wide band. 2.1 Phase angle dependence analysis The knowledge of the dependence of the phase angle between the output voltage and current of the bridge converter is convenient for maintence operating the converter with constant power [10], [11], [12]. Fig. 1 shows a block diagram of the feedback control circuitry used in the direct phase control of full-bridge serial reso- nant converter [13], [14]. The microcontroller program has predefined values for the initial value of the switching frequency fs, ref0 (or period Ts, ref0 = 1/fs, ref0 ) and the desired or the reference phase difference between the output voltage and current φ ref [15]. This phase difference would be zero or close to zero if maximum power transfer is needed, or have a spe- cific value that corresponds to the desired output power when we like to control the power transfer. Analysis of the series-resonant converters usually use the voltage and current first harmonics to determine the circuit parameters and behavior. Assuming that the resistance in the circuit is small, the resonant frequency ω 0 is used in the calculations. Fig. 1 Block diagram of the full-bridge series-resonant converter. When a series resonant circuit, Fig. 2 is excited by a sine wave vol- tage, all waveforms have the same shape. Fig. 2 Serial resonant circuit supply with voltage ±UDC. When the supply voltage of serial resonant circuit is in form of the Heaviside step function, then the current oscillates around zero with angular dumping frequency ω d , as shown in Fig. 3. When the voltage has square pulses waveform (duty ratio D = 0.5) and ampli- tude ± U DC , then in every half-period the current is a piece of the dumped oscillation of Fig. 3. Fig. 3. Current waveform in the series-resonant circuit when excited by a Heaviside step voltage with amplitude UDC = 60 V. Parameters' values are R = 0.24 Ω, L = 26.5 μH and C = 26.6 μF with initial values iL(0+) = –165 A and uC(0+) = –163 V. When the circuit excitation with voltage pulses, the current is in the form:   ) 1 ( ) ( sin ) sin( ) ( d d  t t ω K e φ t ω K e t i αt αt       310 INTERNATIONAL SCIENTIFIC JOURNAL "MACHINES. TECHNOLOGIES. MATERIALS." WEB ISSN 1314-507X; PRINT ISSN 1313-0226 YEAR XIII, ISSUE 7, P.P. 310-313 (2019)