Development Of A Novel Soft-switching Ozone Generator Based On Phase-shifted Control

Ozone is a environment-friendly strong oxidant, which has been widely used inmany fields such as water treatment, industrial oxidation, aquaculture, medical andhealth, etc. However, the development of ozone technology is not mature enough,ozone equipment has high power loss, high cost and low efficiency, which restrict theapplication of ozone still as the key factor. In order to improve the efficiency of theinverter, reduce the switching loss and device size, soft-switching technology andclosed-loop control strategy is proposed as an effective way to solve these problems.In this paper, a novel main circuit topology is used. With an auxiliarycapacitance for commutation and two IGBT switches to control DC bus on and offintroduced at DC bus side of full-bridge inverter circuit, it can achieve each switch ofthe inverter circuit working on the ZVS/ZCS soft switching condition by controllingthe pulse timing and the dead zone of six IGBTs. The conditions to achievesoft-switching and the six modes at half cycle of power supply are analyzed. Based onthe analysis of the circuit topology, hardware and software implementation andcontrol strategies of ozone generating system are mainly studied in this paper.Software phase-locked loop technology achieves frequency tracking and phasecompensation for load current, so that the ozone generator is always working in thequasi-resonant state. According to that switching power supply is a higher order andnonlinear system and it is hard to establish an accurate model of ozone cell, the fuzzyself-tuning PID control strategy is applied in the control of ozone power. Thephase-shifted angle is calculated with fuzzy PID algorithm by real-time detection ofthe inverter output current, thus closed-loop control of load current is achievedindirectly through the phase-shifted PWM regulation, which greatly enhances thestability and reliability of the whole system. Using IPM as the power switches andTMS320F28335as the controller, an ozone generator prototype with ozone productionof160g/h was designed. Some design methods are concretely given such as the maincircuit, control circuit and protection circuit. Software flowcharts are also given suchas PWM control pulses, phase-shifted PWM control, fuzzy PID control, faultdiagnosis, and etc. The dielectric barrier equivalent parameters, the drive pulse timing,phase-shifted PWM regulation, and load voltage and current waveforms in the processof operation of the prototype are tested. The test waveforms are in good agreement with the theoretical analysis. The long-term operation and experiments for theprototype shows the scheme is feasible and the reliability of the system is alsoconfirmed.