Industrial Power Supplies, Inverters and Converters:
Objectives and Overview

The objectives of this section are to:

1. Explain the operation of a single-diode halfwave rectifier and draw its input and output waveforms.
2. Schematically illustrate the output waveform for a two-diode center-tapped rectifier that produces a fullwave output and explain its operation.
3. Explain the operation of a four-diode fullwave bridge rectifier and draw its input and output waveforms.
4. Calculate the average dc output voltage from the input rms voltage for the single-diode hall wave rectifier, two-diode center-tapped recti­fier, and the four-diode full-wave rectifier.
5. Show how the capacitor and inductor are connected in a power supply and explain their function.
6. Explain the function of a zener diode in a power supply.
7. Explain the operation of a metal-oxide varistor (MOV) as it's used in a power supply.
8. Explain the operation of six-phase rectifiers.
9. Compare the differences between half-wave and full-wave rectifiers.
10. Explain the operation of a crowbar circuit.
11. Discuss the operation of an uninterruptible power supply.
12. Draw the diagram of an inverter and explain its operation.
13. Identify three types of inverter circuits (variable-voltage input, pulse-width modulation. and current-source input) and explain their operation.
14. Explain the operation of a cycloconverter.
15. Schematically illustrate the diagram for a linear power supply and explain its operation.
16. Explain the operation of a switch-mode power supply.
17. Explain the operation of the buck converter, the boost converter, and the buck-boost converter.
18. Identify typical voltages that would be found in power supplies used in industrial electronic circuits.
19. Provide examples of power supplies used in industrial applications.

Overview

Solid-state electronics have become integrated into all aspects of industrial power supplies, converters, inverters, and choppers. Industrial power supplies are used in applications where a variety of voltages is required, such as power for PLC processors and their analog modules and other specialty modules. Power supplies are also used in all types of digital displays and cathode ray tube (CRT) color displays. One will find a power supply in virtually every electrical device on the factory floor. Any equipment that has electronic circuits in it must have a dc supply voltage available. Since all power in the factory originates as ac voltage, converters must be used in the power supplies to convert ac power to dc power. These circuits called converters will be similar to the diode rectifier circuits you may have encountered in basic electronic courses. Larger industrial systems such as motor drives, welding equipment, and battery chargers will require larger three-phase rectifier circuits.

Some industrial applications such as ac variable-frequency motor drives and welders will have a section where ac voltage is converted to dc and another section where the dc voltage must be converted back to ac voltage. The circuit that changes dc voltage to ac voltage is called an inverter. The inverter circuit is needed to change the dc voltage back to ac voltage because the frequency of the incoming ac voltage is fixed at 60 Hz and the output section of the drive needs to be able to provide the frequency of the output voltage between 0-120 Hz.

Choppers are special inverter circuits that take the dc voltage and convert it to a variety of other dc voltages. This is a useful circuit in dc motor drives where the dc voltage must be manipulated to provide changes in current and voltage for changing motor speed and torque characteristics. Chopper circuits are also used in welding power supplies and dc power supplies for a variety of other solid-state devices. This section will help one understand how solid-state devices are used in industrial power supplies to provide the correct voltages and frequencies through converters, inverters, and choppers.

Industrial Rectifier Circuits: AC-to-DC Conversion