এসি ভোল্টেজ কন্ট্রোল কুইজ

AC Voltage Controllers

• AC voltage controllers are converters that control voltage, current, and average power delivered to an AC load from an AC source.
• Applications include light dimmer circuits, speed control of induction motors, industrial heating, electric welding, and on-load tap changing of transformers.

Course Details

• Course Title: Power Electronics
• Course Code: EEE 361
• Credits: 3.00
• Presented by: Sancoy Barua
• Assistant Professor, Department of EEE, CUET

References and Chapter Details

• Reference: M.H. Rashid, Power Electronics: Circuits, Devices and Applications, 3rd Edition, 2016-2017
• Chapter: 11, Articles 11.1, 11.2, 11.3, 11.4 (Continued)
• Additional content: Derivations and Examples

Working Principle

• Phase Control: Adjusts the phase angle of the AC voltage by delaying the triggering of semiconductors (thyristors or triacs). This controls the energy delivered to the load. A longer delay results in less power.
• Firing Angle: Delay introduced in triggering the device; a smaller firing angle uses more of the AC cycle, leading to higher average voltage and power to the load.

Types of Control

• Phase Control (Firing Angle Control): Most common method adjusting the firing angle of thyristors or triacs to control the duration of AC cycle energy delivery to the load. Simple and effective for resistive loads but generates higher harmonic distortion, affecting inductive loads.

• Pulse Width Modulation (PWM): Switches the output on and off rapidly changing the width of pulses (duty cycle). More efficient and minimizes harmonic generation compared to phase control. Suitable for various loads, including inductive and resistive loads. More complex control circuitry is needed.

• On-Off Control (Integral Cycle Control): Switches the load completely on or off. Simple and inexpensive for low-cost applications, such as heating. Less efficient, causing voltage spikes, and not suitable for applications needing variable control.

• Closed-Loop Control: Uses feedback from the output to dynamically adjust the control mechanism. Employing sensors to continuously adjust firing angle or PWM signal to maintain the desired output levels. Precise control and stability, compensating for variations in load and supply; however, more complex and costly due to the necessity of sensors and advanced algorithms.

• Open-Loop Control: Operates without feedback using predefined settings based on expected load characteristics. Simple and cost-effective for applications where precise control is unnecessary. Less adaptive to changing load conditions, leading to inefficiencies.

Classification

• AC voltage controllers are classified based on types like on/off, single-phase, three-phase; directional and bidirectional, half-wave, and full-wave control.

Performance Parameters

• RMS Output (Load) Voltage: The output voltage is calculated using formulas.
• Duty Cycle: This is a key parameter to calculate the power delivered.
• RMS Load Current: Calculated using specific formulas
• Output AC (Load) Power: Determined by formulas.
• Input Power Factor: Computed using formulas.
• Average Current of Thyristor: Calculated using formulas relating to the thyristor current.
• RMS Current of Thyristor: Another parameter calculated using specific formulas.

Additional Information

• Specific equations and formulas are provided for calculating RMS output voltage, duty cycle, RMS load current, output AC power, input power factor, average thyristor current, RMS thyristor current, and others, which are important to understand AC voltage controllers.