THE DESIGNING OF POWER SUPPLY WITH DOUBLE CONVERSION OF ENERGY

Oleynik I.N., Besh A.N.

Donbass State Machinebuilding Academy

The work’s object is designing of pulsed power supply (PPS) of AC/AC type with the following parameters: input voltage is 127 V, frequency is 50 Hz; output voltage is 260 V, frequency is 140 Hz, output power is 300 W.

Having analyzed the circuit prototypes in technical literature [1-3] the decision has been taken: half-bridge topology with current mode control; soft start; voltage and current protection; high-power MOSFET transistors; input bridge rectifier with LC filter; output filter of impulse noise on dual choke. The thermistor and safety device are at the input. The electric circuit is presented in Pic. 1.

High-frequency transducer works with frequency 80 kHz. The potential transformer with a ring core made of ferrite 1500NM3 was calculated for this frequency. The number of turns of the primary winding - 23, of the secondary winding - 107. The wires were chosen according to the international standard IECR20 with core diameter d_1c=1,6 mm and d_2c=0,56 mm. High-power MOSFET transistors IRF 740 were chosen as power keys. For them V_dss=400 v, R_DS(on)=0,55 Ω, I_d=10 A. For control circuit the current control strategy [4] was applied, standard controller UC1825 was chosen, RC elements of internal clock, trigger circuit, and soft start were calculated.

Input impulse noise filter is needed for suppression of higher harmonic present in a supply-line voltage. Filter parameters are f=80 kHz, R_L=1 Ω, ζ=0,707, С=0,1∙10^-6 F, L=2,8∙10^-6 H.

Input rectifier is realized on rectifier bridge KBU1004 and has a capacitive filter.

Voltage feedback loop is isolated and realized on optron and controllable current source ТL431. Simple amplifier with common emitter is performed on optron transistor.

Current feedback loop is calculated so that one can create the voltage sufficient for operation of internal comparator UC1825. The current transformer with the number of turns W1=1, and W2=115 of standard wire IEC R20 with core diameter d_1c=0,56 mm and d_2c=0,15 mm was calculated as a current sensor. The current transformer is loaded on ballast resistor.

For consequent convertion of direct voltage into alternative one with frequency 140 Hz the bridge inverter is used. It is made on two power intelligent moduli of International Rectifier IR3101 company which contain high-power MOSFET, driver for gate handling, and bootstrap diode. The moduli have overheat and current overload protection as well as the protection against line low voltage and steady leakage current. The advanced technology IMS provides less area.

Conclusions.

In the course of designing of PPS the prototypes of power supply were analyzed, the knowledge of impulse power supplies was generalized and secured. The PWM controller satisfying the preset parameters was chosen. The power parts (keys, transformers) were calculated; current reading circuits and voltage and current feedback loops were designed. The topology was selected and the selection was justified, the computations of PPS of the given type was evaluated.

The results of the operation show that the use of pulsed power supplies in many cases is more profitable and cheaper in production than linear voltage transducers. Their small dimensions and high power is a great advantage to linear voltage transducers, but when designing PPS of high power the complexity of designing increases.

Picture 1 - Circuit scheme of power supply with double conversion of energy

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