MATLAB Simulation of Single Phase Shunt Active Filter
Introduction to the Single-Phase System
The system used in this simulation consists of a single-phase voltage source, an inductor, and an inductive (non-linear) load. Non-linear loads, such as rectifiers, cause distortion in the source current. Normally, a source current would be sinusoidal, but when a non-linear load is connected, the current becomes non-sinusoidal and includes higher harmonics.
Challenges with Non-Linear Loads
Non-linear loads can lead to several problems:
Increased harmonic distortion in the source current.
Higher reactive power consumption, which negatively affects the system's power quality.
To address these issues, it is necessary to use a shunt active filter that can correct these problems by injecting compensating currents into the system, which helps to make the source current sinusoidal again.
The Role of the Single Phase Shunt Active Filter
The single-phase shunt active filter consists of:
Inverter: Controlled by a PI controller.
Capacitor: Supplies the reactive power required to balance the non-linear load.
The active filter helps in compensating the reactive power and reducing the harmonic distortion in the system. The capacitor voltage is maintained at 700V, which is achieved by the PI controller.
Control Strategy and PI Controller
The filter is controlled using a PI (Proportional-Integral) controller. The capacitor voltage is continuously measured and compared with a reference voltage. The controller adjusts the inverter to ensure the capacitor voltage stays at the desired value of 700V.
In the control process:
The load current and source voltage are measured.
A three-phase signal is generated based on a delay signal, which is then used to calculate the power components such as real and reactive power.
The power values are filtered using a low-pass filter to determine the compensating current needed by the system.
The reference current is calculated based on the power requirements and used to drive the inverter for compensating reactive power.
Generating the Compensating Current
Once the reference current is generated, the active filter compares it with the actual current. The inverter is controlled to inject the compensating current that balances the reactive power in the system, thus improving the overall power quality by making the source current sinusoidal.
The compensating current is injected into the system in such a way that the source current becomes sinusoidal, despite the presence of a non-linear load.
Simulation Results and Observations
Upon simulating the system, the following observations were made:
Capacitor Voltage: The capacitor voltage initially starts at 670V and gradually charges up to 700V.
Source and Load Currents: Without the active filter, the source current was non-sinusoidal due to the non-linear load. However, after the filter was activated, the source current became sinusoidal.
Total Harmonic Distortion (THD):
The THD for the load current was observed to be high initially.
After the filter injected compensating current, the THD for the source current significantly reduced.
For the source current, the THD dropped to approximately 0.58%.
This confirms that the active filter successfully reduced harmonic distortion and made the source current sinusoidal.
Effect of Disconnecting the Filter
To highlight the importance of the active filter, the simulation was rerun with the filter disconnected. Without the filter, the load and source currents showed similar non-sinusoidal behavior, and the THD values remained high (46% for the source current and 36% for the load current). When the filter was reconnected, the source current was restored to a sinusoidal waveform, and the THD values dropped significantly.
Conclusion
The MATLAB simulation of the single-phase shunt active filter demonstrates its effectiveness in improving power quality in systems with non-linear loads. The active filter successfully compensates for reactive power and reduces harmonic distortion, ensuring that the source current remains sinusoidal. This type of filter can be widely used in practical applications to enhance the performance of power systems affected by non-linear loads.
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