Week 10/11

Development of PI and PR controllers:

Since the considered inverter is grid-connected, a PQ control system was developed using MATLAB Simulink.
Two controllers; one using Proportional Integral (PI) and the other using Proportional Resonant (PR) control algorithms were created and simulated.

DQ control strategy (PI control):

In this case, ac voltages are converted into dq reference frame.
PI controller is used for the inner current loop while the outer loop works in the feed-forward manner where the Active power reference (Pref) and Reactive power reference (Qref) is used directly to generate reference currents in dq frame.
The basic block diagram of the control system is shown below.

Basic block diagram for power controller in dq frame

PR control strategy:

Here, a proportional control algorithm is used for the controller loop.
The reference current is obtained using the Pref and Qref values.
The basic block diagrams of the system are shown below.

Basic block diagram for power controller using PR control

PR controller block diagram

Simulation results:

The performance of the developed controllers was compared using the simulation results.
PI method

Can control P and Q independently.
Fast response time can be achieved.
Cannot achieve zero steady-state error.
Can be very sensitive to grid variations.

PR method
- Can eliminate steady-state error.
- Can compensate for low order harmonics.
- Sensitivity can be reduced.
- Slow response time compared to PI method.

Reference tracking of active power for PI method

Reference tracking of reactive power for PI method

Reference tracking of active power for PR method

Reference tracking of reactive power for PR method

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