Working Principle:
An Active Power Filter consists of power electronics devices, such as Insulated Gate Bipolar Transistors (IGBTs), which act as controllable switches.
These devices are capable of generating current in real-time, which is injected into the electrical system to counteract the undesired harmonic currents. The APF monitors the system's current and voltage waveforms using sensors, and based on this data, it generates corrective currents to eliminate or reduce harmonics.
Harmonic Mitigation:
The primary function of an APF is to mitigate harmonics. It continuously monitors the harmonic content in the system and generates a corresponding, but opposite, current to neutralize the harmonic currents. This effectively cancels out the harmonic components, resulting in a nearly sinusoidal current waveform.
Types of Active Power Filters:
There are mainly two types of Active Power Filters:
a. Current-Controlled APF: This type of APF injects current in parallel with the load to cancel out the harmonics. It ensures that the load receives only the fundamental frequency component, leading to a near-ideal sinusoidal current waveform.
b. Voltage-Controlled APF: In this type, the APF injects current in series with the supply voltage to correct the harmonic distortion at the source itself. It ensures that the source voltage remains unaffected by the harmonic load currents.
Filtering Performance:
The filtering performance of an APF is a critical aspect of its specification. It is measured by its ability to reduce Total Harmonic Distortion (THD) in the system. A well-designed APF can achieve THD levels well below the acceptable limits defined by relevant standards, resulting in a cleaner power supply.
Response Time:
The response time of an APF is the time it takes to detect a harmonic disturbance and generate a corrective current. A faster response time ensures that harmonics are swiftly mitigated, minimizing the impact on sensitive equipment and reducing the risk of potential damage.
System Capacity:
The system capacity of an APF refers to its ability to handle a certain level of harmonic load. This specification depends on the maximum current it can inject into the system and its rated voltage. A higher system capacity allows the APF to handle larger non-linear loads and more substantial harmonic distortions.
Communication and Control:
APFs are often integrated into the overall control and monitoring system of the electrical network. They may support communication protocols like Modbus, Profibus, or Ethernet to allow for remote monitoring, control, and data logging.
Efficiency:
The efficiency of an APF is essential to ensure minimal losses during operation.
An efficient APF design contributes to overall energy conservation and reduces operational costs.
Protection Features:
APFs should include protection features such as overcurrent protection, overtemperature protection, and short-circuit protection to ensure safe and reliable operation.
Benefits:
APFs offer several advantages, including:
Improved power quality by reducing harmonic distortion and maintaining near-ideal sinusoidal waveforms.
Enhanced efficiency and reduced losses in electrical systems.
Extended lifespan and improved performance of sensitive equipment.
Compliance with power quality standards and regulations.
Reduced risk of penalties due to non-compliance with power quality requirements.
