Active Power Filter Of Arc Welding Power Source Based On DSP Technology

With the development of power electronics, electric equipments have been widely used in the field of material manufacture today. Due to their nonlinearity, a lot of harmonic pollution has been brought to power systems and results in a series of power quality and reliability problems of power system. At the same time, the harmonics existing in input current give the limit to advance the power factor further, and result in a low efficiency, which means an enormous waste of capacity of power system. For welding inverter's input circuit is made up by a capacitor as filter after a diode bridge rectifier, it injects harmonics to the power as a voltage source. Based on the theoretical analysis and simulation to the welding inverter as harmonic sources, the relation between the input performance and the parameter of the circuit is given. The results can be used as a reference to select the parameter on the balance of input and output performance. The mathematical model of 3-phase voltage source inverter (VSI) is presented in this paper. The reason why VSI can be used to compensate harmonics is interpreted. The DC side control of APF imposes the direct effect on the performance and the stable running of APF system. Based on intensive analysis of the DC control of APF, the correction of DC voltage loop is proposed, and the simulation result is shown. From the theory of DC voltage regulation, a novel control method, based on the active power balance theory, is proposed. Only two current sensors and one voltage sensor are needed in this method. The control of APF is simplified adopting this method. Because APF is a complicated control system with two closed-loop, higher performance is required for the design of the control circuit. The digital control system is designed based on TMS320LF2407 DSP. Through the control system and high real-time software, harmonic detection, digital filter, current correction, voltage correction, PWM and so on are achieved. Based on the above work, the test sample of APF is installed. The tests are done on how to compensate the current harmonic source with parallel APF.