# Types of Power Electronic Converters

- Link: https://studyelectrical.com/2024/03/power-electronic-converters-types.html
- Published: 2024-03-13T14:30:20+00:00
- Author: Tesla

Electric power control or conditioning requires converting power from one form to
another. **Power electronic converters** perform these power conversion tasks.

A **power electronic system **consists of one or more power electronic converters.
A power electronic converter is made up of power semiconductor devices controlled
by [integrated circuits](https://www.easybom.com/c/integrated-circuits-ics).

The switching characteristics of **power semiconductor devices** permit a power 
electronic converter to shape the input power of one form to output power of some
other form. **Static power converters** perform these functions of power conversion
very efficiently.

Static power converters are electrical networks made of semiconductor devices called
switches (SCR, MOSFET, IGBT). They operate by switching these components in a specific
sequence to transfer energy between two sources with different electrical properties.

A converter can be seen as a **switching matrix.** One or more switches are turned
on and connected to the supply source to obtain the desired output voltage or current.

## Classification of Power Electronic Converters

Power electronics converters (or circuits) can be classified into six types:

 1. Diode rectifiers
 2. DC-DC converters (DC choppers)
 3. DC-AC converters (inverters)
 4. AC-DC converters (controlled rectifiers)
 5. AC-AC converters (AC voltage controllers)
 6. Static switches

The switching devices in the following converters are used to illustrate the basic
principles only. The switching action of a converter can be performed by more than
one device. The choice of a particular device depends on the voltage, current, and
speed requirements of the converter.

### 1. Diode Rectifiers

A diode rectifier circuit converts AC input voltage into a fixed DC voltage. The
input voltage may be single-phase or three-phase.

![Diode Rectifier](https://studyelectrical.com/wp-content/uploads/2024/03/Diode-
Rectifier.webp)

Diode Rectifier

 * A diode conducts when its anode voltage is higher than the cathode voltage, typically
   with a voltage drop around 0.7 V.
 * A diode acts as an open circuit when its cathode voltage is higher than the anode
   voltage, offering high resistance, ideally infinite.

![Voltage Waveform of Diode Rectifier](https://studyelectrical.com/wp-content/uploads/
2024/03/Voltage-Waveform-of-Diode-Rectifier.webp)

Voltage Waveform of Diode Rectifier

 * The output voltage of the rectifier is pulsating DC, containing harmonics and
   distortion.
 * The average output voltage can be calculated using the formula **V_(o(AVG)) =
   2Vm/π.**
 * The input voltage to the rectifier can be either single-phase or three-phase.

**Application:** Diode rectifiers find wide use in [electric traction](https://studyelectrical.com/2014/05/how-electric-locomotives-work.html),
battery charging, electroplating, electrochemical processing, power supplies, welding,
and uninterruptible power supply (UPS) systems.

### 2. DC-DC Converters (DC Chopper)

A DC chopper converts fixed DC input voltage to a controllable DC output voltage.
Chopper circuits require **forced or load commutation** to turn off the thyristors.
For lower power circuits, thyristors are replaced by power transistors.

![Chopper DC DC Converter](https://studyelectrical.com/wp-content/uploads/2024/03/
Chopper-DC-DC-Converter.webp)

Chopper DC DC Converter

 * A DC-DC converter are also known as a **chopper or switching regulator** is shown
   in the figure.
 * When transistor Q_(1) is turned on by applying a gate voltage V_(GE), the DC 
   supply connects to the load, resulting in an instantaneous output voltage of 
   V_(o) = +V_(s).
 * When transistor Q_(1) is turned off by removing the gate voltage V_(GE), the 
   DC supply disconnects from the load, causing the instantaneous output voltage
   to be V_(o) = 0.

![Chopper Waveform](https://studyelectrical.com/wp-content/uploads/2024/03/Chopper-
Waveform.webp)

Chopper Waveform

 * The average output voltage becomes **V_(o(AVG)) = t_(1)V_(s)/T = δ V_(s)**, where
   δ is the duty cycle.
 * Therefore, the average output voltage can be varied by controlling the **duty
   cycle**.
 * The average output voltage V_(o) is controlled by varying the **conduction time
   t **of transistor Q_(1).
 * If T is the chopping period, then **t_(1) = δT**, where δ is the duty cycle of
   the chopper.

**Application:** Choppers find wide applications in DC drives, subway cars, trolley
trucks, battery-driven vehicles, etc.

### 3. DC to AC Converters (Inverters)

An inverter converts fixed DC voltage to a variable AC voltage. The output may be
a variable voltage and variable frequency. These converters use **line, load, or
forced commutation** for turning off the thyristors.

Conventional thyristors are being replaced by **GTOs in high-power applications**
and by **power transistors in low-power applications**.

![DC to AC Converters (Inverters)](https://studyelectrical.com/wp-content/uploads/
2024/03/DC-to-AC-Converters-Inverters.webp)

DC to AC Converters (Inverters) Circuit Diagram

 * A single-phase transistor inverter is depicted in the figure above.
 * When MOSFETs M1 and M2 are turned on by applying gate voltages, the DC supply
   voltage Vs appears across the load, resulting in an instantaneous output voltage
   of **Vo = +Vs**.
 * Similarly, when MOSFETs M3 and M4 are turned on by applying gate voltages, the
   DC supply voltage Vs appears across the load in the opposite direction, yielding
   an instantaneous output voltage of **Vo = −Vs**.

![Inverter Voltage Waveform](https://studyelectrical.com/wp-content/uploads/2024/
03/Inverter-Voltage-Waveform.webp)

Inverter Voltage Waveform

 * If transistors M1 and M2 conduct for one half of a period and M3 and M4 conduct
   for the other half, the output voltage takes on an alternating form.
 * The root mean square (rms) value of the output voltage becomes **V_(o(rms)) =
   V_(S)**.
 * However, the output voltage contains harmonics which could be filtered out before
   supplying to the load.

**Application:** Inverters find wide use in [induction-motor](https://studyelectrical.com/2014/11/how-three-phase-induction-motor-work.html)
and synchronous-motor drives, induction heating, UPS, [HVDC transmission](https://studyelectrical.com/2018/12/what-is-hvdc-transmission-system-components.html),
etc.

### 4. **AC to DC Converters (Phase-controlled rectifiers)**

These power electronic converter convert constant AC voltage to variable DC output
voltage. These rectifiers use line voltage for their commutation, hence also called**
line-commutated or naturally-commutated **AC to DC converters. Phase-controlled 
converters may be fed from 1-phase or 3-phase sources.

![AC to DC Converters (Phase-controlled rectifiers) Power Electronic Converter](
https://studyelectrical.com/wp-content/uploads/2024/03/AC-to-DC-Converters-Phase-
controlled-rectifiers.webp)

AC to DC Converters (Phase-controlled rectifiers)

 * A single-phase converter with two naturally commutated thyristors is depicted
   in the figure.
 * Thyristors normally remain in an off-state and can be turned on by applying a
   gate pulse of approximately 10 V with a duration of 100 μs.
 * When thyristor T1 is turned on at a delay angle of ωt = α, the supply voltage
   appears across the load, and thyristor T1 is turned off automatically when its
   current falls to zero at ωt = π.
 * When thyristor T2 is turned on at a delay angle of ωt = π + α, the negative part
   of the supply voltage appears across the load in the positive direction, and 
   thyristor T2 is turned off automatically when its current falls to zero at ωt
   = 2π.

![Phase-controlled-rectifier-voltage-waveform](https://studyelectrical.com/wp-content/
uploads/2024/03/Phase-controlled-rectifier-voltage-waveform.webp)

Phase controlled rectifier voltage waveform

 * The average output voltage can be found from **Vo(AVG) = (1 + cos α)Vm/π**.
 * At a delay angle of α = 0, this converter operates as a diode rectifier, as shown
   above.
 * The average value of the output voltage v0 can be controlled by varying the conduction
   time of thyristors or firing delay angle, α.
 * The input could be a single- or three-phase source.
 * These converters are also known as controlled rectifiers.

These are used in DC drives, metallurgical and chemical industries, excitation systems
for synchronous machines, etc.

### 5. **AC to AC Converters**

These type of power electronic converter convert fixed AC input voltage into variable
AC output voltage. Two types include:

 1. **AC Voltage Controllers (AC Voltage Regulators):** Convert fixed AC voltage directly
    to variable AC voltage at the same frequency. Widely used for lighting control,
    speed control of fans, pumps, etc.
 2. **Cycloconverters:** Convert input power at one frequency to output power at a 
    different frequency through one-stage conversion. Primarily used for slow-speed
    large AC drives like rotary kiln, etc.

![AC to AC Converter Power Electronic Converter](https://studyelectrical.com/wp-
content/uploads/2024/03/AC-to-AC-Converter.webp)

AC to AC Converter

 * A single-phase converter with a [TRIAC ](https://eepower.com/technical-articles/an-introduction-to-triac-basics/#)
   is illustrated in the figure above. This types of converters are also known as**
   AC voltage controllers**.
 * These converters are utilized to obtain a variable AC output voltage (vo) from
   a fixed AC source.
 * A **TRIAC **permits current flow in both directions.
 * It can be turned on by applying gate voltages at ωt = α for a current flow in
   the positive direction and also at ωt = π + α for a current flow in the negative
   direction.

![AC to AC Converter Voltage Waveform](https://studyelectrical.com/wp-content/uploads/
2024/03/AC-to-AC-Converter-Voltage-Waveform.webp)

AC to AC Converter Voltage Waveform

 * The output voltage is controlled by varying the conduction time of a TRIAC or
   firing delay angle, α.

### 6. **Static Switches**

Power semiconductor devices can operate as **static switches or contactors**, offering
advantages over mechanical and electromechanical circuit breakers. Depending on 
the input supply, static switches are called **AC static switches or DC static switches.**

**Static Transfer Switches (STS)** are specifically designed to transfer power supply
between independent one-phase or three-phase AC power sources. Unlike traditional
[automatic transfer switches (ATS)](https://studyelectrical.com/2023/12/automatic-transfer-switch.html),
STS offers significantly faster load transfer, typically completing the transfer
in just 1/4 of a cycle, ensuring uninterrupted operation of sensitive electronic
equipment. Additionally, load retransfer to a preferred input source is nearly instantaneous,
typically taking only 100 microseconds.

## Multiple Conversion

Below is the block diagram of an **uninterrupted power supply** (UPS). It has multiple
power electronic converter circuits such as rectifier, inverter and static switch.

![Block diagram of UPS](https://studyelectrical.com/wp-content/uploads/2024/03/Block-
diagram-of-UPS.webp)

Block diagram of UPS

 * Multiple conversion stages are often cascaded to produce the desired output, 
   as depicted in the block diagram of UPS.
 * Mains 1 supplies the normal AC supply to the load through the static bypass.
 * The AC-DC converter charges the standby battery from mains 2.
 * The DC-AC converter supplies emergency power to the load through an isolating
   transformer.
 * Mains 1 and mains 2 are normally connected to the same AC supply.
 * The input voltage to a rectifier circuit could be either single-phase or three-
   phase.
 * Similarly, an inverter can produce either single-phase or three-phase AC output
   voltage.
 * Consequently, a converter could be either single-phase or three-phase type.

## Summary

Table below summarizes different types of power electronic converters, their functions,
and their symbols.

| Conversion From/To | Converter Name | Converter Function | Converter Symbol | 
| AC to DC | Rectifier | Converts AC to unipolar (DC) current | ⌊AC to DC Converter Symbol⌉ | 
| DC to DC | Chopper | Converts constant DC to a variable DC or vice versa | ⌊DC to DC Converter Symbol⌉ | 
| DC to AC | Inverter | Converts DC to AC of desired output voltage and frequency | ⌊DC to AC Converter Symbol⌉ | 
| AC to AC | AC Voltage Controller, Cycloconverter, Matrix Converter | Converts AC of desired frequency and/or magnitude from generally line supply AC | ⌊AC to AC Converter Symbol⌉ |

Table summarizes different power electronic converters, their functions, and their
symbols.

### Related posts:

 [ ⌊Schottky Power Diode⌉Schottky Power Diode](https://studyelectrical.com/2024/03/schottky-power-diode.html)
[ ⌊Typical switching waveform⌉Ideal and Typical Power Switching Waveforms](https://studyelectrical.com/2024/07/ideal-typical-power-switching-waveforms.html)
[ ⌊garage door opener⌉How To Program Garage Door Opener](https://studyelectrical.com/2024/08/how-to-program-garage-door-opener.html)