Voltage H Repetitive Control with a Frequency-adaptive Mechanism - Control of Power Inverters in Renewable Energy and Smart Grid Integration - page 122

voltage u A was lagging the reference voltage when the grid frequency was above 50 00 Hz,

as shown in Figure 5.15. When the frequency-adaptive mechanism was activated, the tracking
error was kept almost constant.
Because the grid frequency was maintained within a tight band in reality, the experiments
were carried out only for the above grid frequencies.

.

5.5 Summary
Based on (Hornik and Zhong 2010a 2010b), the H ∞ repetitive control strategy is presented
for the voltage control of grid-connected inverters, focusing on reducing the complexity of
the voltage controller and improving the control performance. The current feedback used in
the previous chapter is removed and the output voltage only is taken as feedback for the
voltage controller. Moreover, a frequency adaptive mechanism is introduced to cope with grid-
frequency variations. The experimental results with the designed controller have shown that
the H ∞ repetitive controller offers excellent performance in the stand-alone mode in terms
of voltage quality, even with non-linear loads connected to the system. In the grid-connected
mode, the quality of the local voltage is controlled well, even better than that of the grid
voltage, but the power quality of the grid current is well above the requirements when the local
load is non-linear.