3
Current H∞ Repetitive Control
In this chapter, a current controller is designed for grid-connected inverters based on the H∞ and repetitive control techniques. As a result, the inverter is able to inject clean currents into the grid. Moreover, a simple and effective mechanism for the inverter to quickly synchronise with the grid is also discussed. Experimental results show that the controller is able to achieve very low current THD.
3.1 System Description
The control system, as shown in Figure 3.1, adopts an individual controller for each phase in the abc frame and the system is equipped with a neutral point controller discussed in (Zhong et al. 2006) and Part II. It has a current loop including a repetitive controller so that the current injected into the grid could track the reference current iref, which is generated from the dq-current references 
and 
using the 
transformation. A PLL is used to provide the phase information of the grid voltage needed to generate iref. The real power and reactive power exchanged with the grid are determined by 
and . The inverter is powered by a ...
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