Current Proportional-Resonant Control - Control of Power Inverters in Renewable Energy and Smart Grid Integration - page 248

where h is the harmonic order, can be easily added to a PR controller (Timbus et al . 2006b).
It is worth noting that, in order to maintain good performance of the controller, the resonant
frequency should be maintained close to the system frequency. If the system frequency varies
significantly, adaptive mechanisms, e.g. the one reported in(Timbus et al . 2006a), can be
adopted to adjust the resonant frequency according to the system frequency.

16.2 Control Structure
16.2.1

) Frame
A PR controller is usually adopted in the stationary reference (

In the Stationary Reference ( αβ

) frame for inverter control
(Sera et al . 2005; Teodorescu et al . 2006; Timbus et al . 2006a; Zmood et al . 1999, 2001), but
it can easily be implemented in the abc frame as well.
The block diagram of a current-controlled VSI in the stationary reference frame with the
PR controller is shown inFigure 16.1. The three-phase currents are transformed into

αβ

α -,

β → αβ α

-components i α and i β using the abc transformation. The -component is the same

β

as the Phase a component and the -component is the combination of Phase b and Phase c

components (when the currents are balanced). Hence, only two current channels i α and i β
need to be controlled, with two separate PR controllers. A PLL is adopted to generate the
phase information of the grid voltage, which is needed by the dq → αβ transformation to

convert the d -, q -current references I d and I q into the reference currents i α and i β . The PR

controllers, often equipped with the harmonic compensator in (16.2), forces i α and i β to track

the reference currents i α and i β

. The output of the PR controllers is then converted back to
the abc frame before being converted into PWM signals to drive the switches. The real power
and reactive power exchanged with the grid are directly determined by I d and I q because the

voltage is determined by the grid.
The grid voltages are feed-forwarded via a phase-lead low-pass filter to improve the per-
formance, as shown in Chapter 3, etc. The filter, chosen as (3.1), is introduced to compensate

Figure 16.1 Block diagram of a current-controlled VSI in the stationary reference frame ( αβ )