INTRODUCTION POWER ELECTRONIC CIRCUITS

The discussion of energy devices and energy control will be covered in this introduction to power
electronics and power circuits. Electricity and energy conversion are involved in every process we
perform every day. Energy, its conversion, and savings are crucial to all human activity. Circuit design is
difficult in terms of proper energy conversion and saving. Controlling the flow of electrical energy in a
circuit is the goal of the field of power electronics and power circuits. Power electronics and power
circuits are treated equally to radio frequency, digital, and analogue electronics in the study of electrical
engineering. Power electronics and power circuits have a wide range of uses, including in phones,
automobiles, wearable technology, industrial electronics, and other applications. All electrical circuits
control the flow of electricity between the source and the electric load. For instance, Figure 1 depicts a
General Electric power conversion system. The power converter's job is to regulate the flow of energy.
We must consider the system losses when developing such a method. Even though a system's energy
source is very dependable, problems with the converter can still arise with the load. This has an impact
on system reliability.

Generic Power Electronic Circuits:

Line-Frequency Diode Rectifiers: Line Frequency AC to Uncontrolled DC

 • Conversion: line frequency ac → uncontrolled dc (control often in next converter stage)

 Applications: power supplies, ac/dc/ac drives, dc servo drives, ...
 Low cost, popular
 Large capacitor needed for ripple-free dc voltage → distorted line current.
 Filters required
to comply with
standards on
allowable line
current
harmonics.
Single-phase diode rectifiers

Basic rectifier, single diode, inductive load

Single-phase diode rectifiers
Single diode, load with internal dc voltage, load with
large C
Single-phase bridge rectifier

+ rail:
Diode with highest anode potential is conducting)

- rail:
Diode with lowest cathode potential is conducting.
Single-phase bridge rectifier
Resistive load
Output voltage:

For inductive load

Fourier analysis of is:

Three phase full-bridge rectifiers

Commutation

Commutation starts when vac = vcn

Driving voltage in a mesh: vcomm = van - vcn

Uncontrolled and Phase-Controlled AC to DC Converter Circuits

 The unidirectional property of a diode is utilized in uncontrolled rectifiers.

 The SCRs in AC to DC converters allow control over the conduction time or the phase of the

conducting voltage.

 Phase-controlled AC to DC converter circuits are used in traction systems, electrochemical

processes, magnet power supplies, high voltage DC transmission, and DC motor drives.

An uncontrolled AC to DC converter

The most prevalent power electronic circuits in use right now are rectifiers, also known as AC to DC
converters. Current and power flow in a single direction in AC to DC converter circuits, which are referred
to as unidirectional converters. Utility electricity at 50 Hz or 60 Hz is converted via AC to DC converters
into either controlled or uncontrolled DC, depending on the converter circuit type. In this article, let's
talk about AC to DC converter circuits.
The unidirectional property of a diode is utilized in uncontrolled rectifiers. In uncontrolled rectifiers, the
rectified output current and voltage are functions of the applied inputs. The output voltage level cannot
be varied when AC to DC converters with diodes are employed for conversion. Diode rectifier circuit
operations are based on the fundamental property of the PN junction diode to conduct as a closed
switch when forward biased and not to conduct like an open switch when reverse biased. The principal
circuit operation remains the same irrespective of the type of uncontrolled rectifiers, such as half-wave
rectifiers or full-wave rectifiers. Both half-wave and full-wave rectifier types are applicable for single-
phase as well as three-phase applications Uncontrolled half-wave AC to DC converters utilize one diode,
converting only positive half cycle AC to DC, whereas full-wave AC to DC converters produce DC from
both positive and negative half-cycles. The full-wave AC to DC converter types, center-tap rectifiers, and
bridge rectifiers, use two diodes and four diodes, respectively. The pulsating DC output from AC to DC
converters with diodes should be ripple-free. For ripple-free DC voltage, large capacitor filters are
connected to the DC side. The capacitor charges and discharges to smoothen the pulsating DC. The
capacitor charging to the peak of the input voltage draws a large current during the peak of the half-
cycle and discharges thereafter. The current flow can be zero for a finite time in uncontrolled AC to DC
 INTRODUCTION
The power provided to the load can be managed via a controlled rectifier. In an inverter, it is used to
convert an AC supply into a unidirectional DC supply. Based on the necessary voltage and current
demand, controlled rectification is the process of changing alternating current (AC) to direct current
(DC). Line commutated ac to dc power converters called controlled rectifiers are used to transform a
fixed voltage, fixed frequency ac power supply into a variable dc output voltage. A controlled rectifier
receives its input power from an ac supply running at a fixed rms voltage and fixed frequency. Phase-
controlled rectifier operation. A single-phase half wave PCR circuit with an RL load resistive is used to

demonstrate the fundamental operation of a PCR circuit. These controlled rectifiers are in fact line-
frequency phase-controlled rectifiers. We study in this chapter half-wave single-phase controlled
rectifiers (E1), full wave single-phase controlled rectifiers (B2) and fully controlled three-phase rectifiers
(B6).
For each of these types we study voltage form, current flow and the expressions for the average output
voltage. Again and again, we study both cases of load (resistive and resistive-inductive). Current
harmonics at the input and voltage harmonics at the output are calculated.

Line frequency phase-controlled rectifiers inverters: line frequency AC to controlled DC:

A controlled rectifier is the same as the uncontrolled rectifier except that the diode is replaced by
the thyristor, as shown in Fig. 3.21. During the positive half cycle, the thyristor is forward biased but
because of the absence of the gate signal it remains in forward blocking mode. As soon as the thyristor is
turned ON by applying the gate signal at angle �, the thyristor comes into forward conduction mode
and starts conducting. From the waveform of anode to cathode voltage (VAK) in Fig. 3.22, we can see that
the voltage is dropped across the thyristor until the gate signal is applied and after the application of the
gate signal, the voltage starts appearing across the load. From � onward, the input voltage starts
increasing in the reverse direction making the diode reverse biased, but the current through the inductor
starts decaying and voltage across it builds up with opposite polarity until reaching the angle ϕ.
From � to 2�, the thyristor is reverse biased, and all the input voltage is dropped across the thyristor
and zero voltage across the load. After that the cycle repeats itself. Because of the inductive load, the
output current lags behind the output voltage. Phase-Controlled AC to DC Converters
In uncontrolled AC to DC converters, the level of DC voltage is dependent on the peak voltage and
frequency of the applied voltage. In controlled AC to DC converter circuits, silicon-controlled rectifiers
(SCRs) or thyristors are used in the place of diodes. The SCRs in AC to DC converters allow control over
the conduction time or the phase of the conducting voltage. SCRs are three-terminal devices with pins:
anode, cathode, and gate. Phase-controlled AC to DC converters with SCRs act like diode rectifiers when
the gate is triggered (or fired) at the 0° phase angle of the applied AC input voltage. The SCR conducts
whenever the gate is triggered and anode to cathode voltage must be positive. One can initiate the gate
triggering between 0° and 180° phase of the input AC voltage, and thereby the conduction of the SCR
can be controlled. According to the firing of the SCR, the average value of the output DC voltage varies
and thus controlled DC is obtained. Phase-controlled AC to DC converter circuits are used in traction
systems, electrochemical processes, magnet power supplies, high voltage DC transmission, and DC
motor drives. Irrespective of the controllability, AC to DC converter circuits is designed in printed circuit
boards. In the case of phase-controlled AC to DC converters, a gate drive circuit (control circuit) is
required, with proper isolation from the converter circuit (power circuit). Cadence offers the proper PCB
design software to design power circuits as well as control circuits for residential, commercial, and
industrial-power electronic applications. Rectification converts an oscillating sinusoidal AC voltage source
into a constant current DC voltage supply by means of diodes, thyristors, transistors, or converters. This
rectifying process can take on many forms with half-wave, full-wave, uncontrolled and fully controlled
rectifiers transforming a single-phase or three-phase supply into a constant DC level. In this tutorial we
will look at single-phase rectification and all its forms. Rectifiers are one of the basic building blocks of AC
power conversion with half-wave or full-wave rectification generally performed by semiconductor
diodes. Diodes allow alternating currents to flow through them in the forward direction while blocking
current flow in the reverse direction creating a fixed DC voltage level making them ideal for rectification.
However, direct current which has been rectified by diodes is not as pure as that obtained from single
phase. waveform of a fixed voltage and frequency as shown.

INTRODUCTION

When semiconductor technology was in its initial stages, the conversion of direct current (DC) supply
voltage to a higher voltage was done by converting it to alternating current (AC) intermediately using the
vibrator, step-up transformer, and the rectifier assembly. This is feasible for low power applications.
However, for higher power applications, an electric motor was needed to drive a generator of suitable
voltage. Such processes turned out to consume a lot of time for setup procedures, involved exorbitant
costs, and were less efficient overall.
With the rise of semiconductor devices and integrated circuits, the conversion circuits could be designed
and implemented effectively as the components were compact, economically viable, and accessible. The
biggest advantage was the ability to design energy-efficient processes using solid-state switch mode
conversion as opposed to age-old methods that dissipated excess energy in the form of heat.

INTRODUCTION
DC-DC SWITCH MODE CONVERTS

INTRODUCTION
SWITCH-MODE DC-AC INVERTERS

INTRODUCTION
RESONANT CONVERTERS. ZERO-VOLTAGE AND OR ZERO CURRENT SWITCHING