Title :
Dynamic digital control schemes for three-phase UPS inverters
Author :
Uys, J.J. ; Beukes, H.J.
Author_Institution :
Dept. of Electr. Eng., Stellenbosch Univ., Matieland, South Africa
Abstract :
The purpose of a voltage controller is to produce stable three-phase output voltages with low distortion under all loading conditions. This paper presents the design of such a three-phase, closed-loop voltage controller, implementing a deadbeat controller on the output voltage and the inductor current. A digital signal processor is used to implement the digital closed-loop control algorithms. This, together with delays introduced by sampling the analog quantities, introduces a delay in the control law that causes system instability. The system model is augmented to compensate for these dynamics, hereby including a third deadbeat controlled variable. System stability is then ensured. Load current feed-forward is used to compensate for changes in the load current before the output voltages get distorted, in order to improve the output voltage waveform quality. Practical results show that the designed voltage controller can produce output voltage waveforms that can meet the specifications for balanced and unbalanced loads. This is verified by using a three-phase, four-wire, 250 kW inverter, which shows that the constructed pulse-width modulated control scheme can achieve fast dynamic response as well as low total harmonic distortion. Nonlinear loads, however, produce undesirable harmonics that cause large distortion in output voltage.
Keywords :
PWM invertors; digital control; feedforward; harmonic distortion; power harmonic filters; power supply quality; signal processing; uninterruptible power supplies; voltage control; voltage regulators; waveform analysis; 250 KW; analog quantity sampling; closed-loop voltage controller; control law delay; deadbeat controller; digital signal processor; dynamic digital control algorithm; harmonic distortion; inductor current; load current feed-forward; loading condition; nonlinear load; output voltage waveform quality; pulse-width modulated control scheme; system instability; three-phase UPS inverters; Delay; Digital control; Digital signal processors; Inductors; Low voltage; Pulse width modulation inverters; Signal processing algorithms; Signal sampling; Uninterruptible power systems; Voltage control;
Conference_Titel :
Power Electronics Specialist Conference, 2003. PESC '03. 2003 IEEE 34th Annual
Print_ISBN :
0-7803-7754-0
DOI :
10.1109/PESC.2003.1216794