Shunt Active Power Filters

Summary

This detailed technical presentation covers the design and selection of components for a three-phase active filter, focusing on impedance, voltage, and current ratings. It highlights the importance of careful calculations for losses and dynamic conditions, ultimately leading to efficient component choices like IGBTs and RLE filters. Key parameters such as capacitance, inductance, and harmonic currents are analyzed to ensure optimal performance in filtering applications, demonstrating a comprehensive approach to modern power electronics design.

Takeaways

• 😀 The impedance at 50 Hz is calculated to be 0.414 ohms, resulting in minimal losses of only 5.14 watts.
• 📏 Voltage rating selection requires considering the highest expected voltage and a 10% overshoot, leading to a nominal voltage of 770 volts.
• ⚡ A safety factor is applied to voltage ratings, typically selecting a 1200-volt IGBT for the voltage source converter.
• 🔌 Current ratings are determined by factoring in ripple current, resulting in a calculated rating of 300 amps for the 1200-volt system.
• 📊 A three-phase four-wire active filter design incorporates specific parameters such as source resistance of 0.0 ohms and source inductance of 1 mH.
• 🔄 The rectifier output current is approximately 86.28 amps, with harmonic currents calculated as the difference from the fundamental current.
• 🔋 The DC link voltage is selected based on system requirements, arriving at a value around 700 volts.
• 📏 Capacitor values are determined through dynamic equations, leading to a selection of 5500 microfarads for balancing purposes.
• 🔄 Interfacing inductance and neutral conductor values are calculated to meet system specifications, ensuring optimal performance.
• 🔧 The design of an RLE filter is crucial for reducing noise, with calculated impedance showing sufficient performance at both fundamental and switching frequencies.

Q & A

What is the calculated impedance at 50 Hz mentioned in the script?

The impedance at 50 Hz is calculated to be 0.414 ohms.

How are the losses in the three-phase system calculated?

The losses are calculated using the formula for losses in all three phases, resulting in a total of 5.14 watts.

What is the recommended voltage rating for solid-state devices in this design?

The recommended voltage rating for solid-state devices is 1200 volts, considering a 10% overshoot based on the highest expected voltage.

What is the significance of the 1.25 factor in current rating calculations?

The 1.25 factor is applied to the ripple current plus the current flowing into the passive filter to determine the total switch current needed.

Describe the load characteristics used in the three-phase four-wire active filter design.

The load consists of three single-phase rectifiers, with specified resistance of 2.5 ohms and inductance of 25 mH, classified as a nonlinear load.

How is the RMS value of the fundamental current calculated?

The RMS value of the fundamental current is calculated as 0.9 times the input current, leading to approximately 77.65 amperes.

What is the selected capacitance value for the DC link, and how is it determined?

The selected capacitance value for the DC link is 5500 microfarads, derived from dynamic equations involving voltage and ripple current.

What are the selected parameters for the RLE filter?

The selected parameters for the RLE filter include a resistance of 10 ohms and a capacitance of 5.5 microfarads, designed to filter noise effectively.

What method is used to calculate the losses in the RLE filter?

The losses in the RLE filter are calculated using the relationship 3 * I^2 * R, where I is the fundamental current and R is the resistance.

What is the reason for selecting a 2.5 mH inductance leg in the design?

A 2.5 mH inductance leg is selected based on calculations that ensure appropriate performance and stability in the filtering process.