There are three commonly used controllable DC power supplies:
1. **Rotary Converter Unit** – This system consists of an AC motor and a DC generator, which together produce an adjustable DC voltage. It was one of the earliest methods for controlling DC power and was widely used in early industrial applications. The AC motor acts as a prime mover, driving the DC generator, which in turn supplies power to a DC motor requiring speed control. A small excitation generator (GE) is often included to provide the necessary DC excitation for both the generator and the motor. By adjusting the excitation current, the output voltage can be controlled, allowing for speed regulation of the DC motor. However, this system is bulky, inefficient, and noisy, which has led to its replacement by more modern technologies.
2. **Static Controllable Rectifier** – This method uses solid-state devices such as thyristors to convert AC power into adjustable DC power. Unlike the rotary converter, it doesn't rely on mechanical components, making it more efficient and compact. The rectifier can be controlled electronically, allowing for precise voltage regulation. This system is commonly used in modern DC drive systems and is known for its fast response and high efficiency. It forms the basis of the VM (Voltage-Controlled Motor) system, where the thyristor's firing angle determines the output voltage, thus controlling the motor speed.
3. **DC Chopper or PWM Converter** – This type of power supply uses power electronic switches, such as thyristors or MOSFETs, to chop the input DC voltage into a series of pulses. These pulses are then filtered to produce a variable average DC voltage. This method is highly efficient and allows for precise control of motor speed through pulse width modulation (PWM). The chopper circuit can rapidly switch the power on and off, creating a waveform that mimics a lower DC voltage over time. This technique is widely used in electric traction systems and high-performance servo drives due to its dynamic response and energy efficiency.
Controllable DC power supplies are classified based on their power source and control method. The **rotary converter unit** was one of the first, but it has largely been replaced by more advanced technologies. The **thyristor rectifier** offers better performance, while the **DC chopper** provides even greater flexibility and precision. Each system has its own advantages and is suited for different applications depending on the required speed control, efficiency, and system complexity.
2.2mm Pitch
2.2mm Pitch
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