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An error detection-based droop-boost control method for the capacitive-coupling grid-connected inverter

English Abstract

The concept of microgrid has been introduced in order to have reduced transmission loss, increased reliability, and improved power quality and to electrify the rural area. Inverters play an important role in the microgrid to realize active and reactive power flow balance and sharing among distributed generators (DGs). The droop method has been applied to control inductive-coupling grid-connected inverter (IGCI) since 1990’s and many improved droop methods have been developed. The droop-controlled inverters use only local measurement and does not need a communication link among the DG units. It is able to realize the “plug and play” function of DGs and loads. The capacitive-coupling grid-connected inverter (CGCI) was applied to integrate renewable energy sources since 2012. Its operational voltage is lower and is fit for injecting bulky leading reactive power to the grid. In order to apply the CGCI to the microgrid and coordinative control it with other inverters, droop control of the CGCI is studied in this work. The basic operational principle of the droop control is to decouple active power and reactive power and control them by frequency- and iv voltage-droop independently. The valid power control range of the IGCI and CGCI was first analyzed and compared. Results indicate that the conventional droop control is only valid for a very limited range for the CGCI due to high coupling impedance value. Hence, improved droop control method should be developed for the CGCI in order to extend its power control range. Since the conventional droop control only implement power decoupling control when the phase angle of the inverter output voltage varies near zero. The power decoupling control of the CGCI is extended to the region when the phase angle varies near , /2 and –/2. A droop-boost control is developed for the CGCI and the operational region is much wider than the conventional droop, especially for the reactive power control range. The validity of the droop-boost control is verified by simulation results. However, the droop-boost control is still not able to extend the power control range of the CGCI to all that theoretically can be reached. An error detection-based droop-boost control is proposed, in which the phase angle and amplitude of the inverter output voltage is determined from two parts. The first is the output from the droop-boost controller and the second is the adjustment coefficient deduced from the power control errors. The adjustment coefficient is obtained from a step-by-step approach. The step size is selected to meet the requirement of both dynamic performance and error convergence. The simulation results are provided to show the validity of the error detection-based droop boost control for the CGCI. A scaled-down prototype of the CGCI was built up. Experimental results indicate that the CGCI can achieve simultaneous active and reactive power control with a lower DC-link voltage in comparison with that required by the IGCI. The power control range of the CGCI is able to reach the theoretical boundary by using the error detection-based droop-boost control.

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Sheng, Jing Jing


Faculty of Science and Technology


Department of Electrical and Computer Engineering




Electric inverters


Dai, Ning Yi

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