Open-loop VAr compensator for industrial applications, using a single PWM pattern

The authors present the analysis of an open-loop, three-phase static VAr compensator (SVC) based on a voltage source inverter, using only one fixed pulse width modulation (PWM) pattern. The VAr generation is controlled by shifting this PWM pattern according to the ACmains voltage. Because the system is naturally stable, there is no need to control the capacitor DC voltage, which takes a particular stable voltage for each power factor operation condition. To prove this particular behaviour, a stability analysis, based on the d-q frame is developed. From this analysis, the circle diagram of the VAr compensator is obtained, which gives all the operating characteristics related to the DC voltage, power angle operation, and reactive power generated. The main characteristics of this compensator are its simplicity and its strong stability, which are particularly suitable for use in industrial loads, such as induction motors, thyristor rectifiers and other low power factor loads. This open-loop system is suitable in the range 1-20 kvar. The experimental results confirm the operating characteristics given by computer simulations and analysis.