In the traditional virtual flux estimation for a three phase P WM rectifier, the integration element causes problems for the initial value and DC bias. And the unstable grid voltage induces a non constant flux amplitude. To address these issues, an improved direct power control (D PC) scheme is proposed. It is based on an adaptive sliding mode observer (AS MO). The observer employs a s i g mo id function as switch function to estimate the grid side source voltage.
an adaptive com pen sat or instead of pure integral element is also designed to dynamically adjust compensation. The stability of this observer is proved by the L ya p u no v function; moreover, simulations and experimental results indicate that this new virtual flux observer substantially improves the observation accuracy based on voltage sensor less control. The application of this strategy successfully suppresses the fluctuation of the dynamic voltage response in the DC bus, eliminating high frequency noise from the grid side, whilst simultaneously boosting the power quality.
Fig. 1. System structure of traditional voltage sensor less (VF Direct Power Control)
EXPECTED SIMULATION RESULTS:
Fig. 2. Comparison of steady state curve under four methods.
Fig. 3. Dynamic simulation I of saturation suppression and adaptive sliding mode.
Fig. 4. Dynamic simulation II of saturation suppression and adaptive sliding mode.
Fig. 5. Dynamic simulation of traditional voltage sensor less control.
Fig. 6. Dynamic simulation of adaptive sliding mode.
Fig. 7. Comparison of bus voltage during load step.
Fig. 8. Comparison of phase current and voltage during load step.
This paper introduces sliding mode control in a virtual flux observer, based on the three phase P WM rectifier model under virtual flux D PC; moreover, the systematic design of an orthogonal feedback compensation method to calibrate the flux estimation has been proposed. An improved sensor less control algorithm with an adaptive sliding mode observer has been simulated and experimentally verified. Results show that the combination of sliding control and virtual flux observer has improved dynamic response over traditional control strategies. This scheme can significantly improve the observation accuracy and dynamic response performance of the observer, and suppress the dynamic fluctuation and harmonic disturbance, increasing the overall power quality and delivery.
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