A Single Phase Full Wave Controlled Rectifier is a power electronic device that converts alternating current (AC) to direct current (DC) while allowing control over the output voltage. Unlike uncontrolled rectifiers that use only diodes, this rectifier employs semiconductor devices such as thyristors (SCRs), which can be triggered at specific points in the AC cycle. This feature provides precise regulation of the output voltage, making the circuit suitable for applications requiring variable DC power. In this configuration, both the positive and negative halves of the AC input are utilized, enhancing efficiency and reducing ripple compared to half-wave rectifiers. The circuit typically operates in a bridge arrangement using four SCRs, which are fired in pairs to conduct current during each half-cycle. By varying the firing angle (the point in time at which the SCRs are turned on), the average output voltage can be adjusted according to the load requirements. Single Phase Full Wave Controlled Rectifier (or Converter) both positive and negative halves of AC supply are used and, therefore, the effective value of DC voltage is increased and ripple content is reduced compared to half-wave rectifiers. Basically, there are two types of FWR.

1.  center-tap transformer 
2.  Bridge Converter

In this article, we will learn about Single Phase Full Wave Controlled Rectifier along with its definition, construction, working, classification, advantages, disadvantages and applications in detail. The information in this article helps you extensively in your SSC JE Electrical and GATE Electrical preparation journey.

What is the Single Phase Full Wave Controlled Rectifier

In Single phase full wave controlled rectifier (1- Phase FWR), all four are SCR used, hence we get output voltage for both positive and negative cycles.

These devices are used to convert alternating current (AC) to direct current (DC) with the ability to control the output voltage. This is achieved by adjusting the firing angle (or phase angle) of thyristors, which are semiconductor devices capable of switching large currents.

When the rectifier is connected to a resistive load (R load), the output voltage across the load directly correlates with the input AC voltage, albeit rectified. This simplicity makes the Single Phase Full Wave Controlled Rectifier with resistive load a fundamental configuration, crucial for understanding more complex load scenarios.

This circuit primarily consists of thyristors and a transformer, instrumental in converting AC voltage into a controllable DC output. The rectifier circuit can be designed using either a center-tap transformer setup or a bridge configuration, each having its unique advantages and application areas.

The circuit diagram of single phase full wave controlled rectifier with resistive load is given below

 Fig- single phase full wave controlled rectifier circuit diagram

single-phase full-wave controlled rectifier (also known as a converter) utilizes a center-tapped transformer and two thyristors (semiconductor devices that act as switches). The center-tapped transformer serves a dual purpose: it adapts the input AC voltage to the required level and provides two phases of output, each 180° out of phase with the other. That is why it is also known as single phase full wave controlled rectifier with center tap transformer

The thyristors are connected such that each one is responsible for rectifying one half-cycle of the AC input. The center tap of the transformer acts as a common return path for the circuit, creating a complete electrical path for current during each half-cycle operation.

Principle of Operation

The operation works on the alternation of the AC supply, where each half-cycle sees a different thyristor being triggered into conduction at a controlled firing angle (α). 

The control in firing angle allows modulation of the output characteristics (i.e., output voltage and current) by effectively delaying the point within the AC cycle at which the thyristor starts conducting.

• Positive Half-cycle Operation: When terminal A of the transformer secondary winding is positive with respect to the midpoint (N), thyristor TH1 is triggered at a specific angle α. This allows current to flow from A, through TH1, the load, and back to N until the AC supply reaches its zero crossing. The flow of current through the load generates a voltage across it, which can be observed as the first pulse of the output waveform.
• Negative Half-cycle Operation: As the AC supply enters the negative half-cycle, terminal B becomes positive relative to N, and thyristor TH2 is triggered at the same controlled angle α. This results in a second pulse of current and voltage across the load, following a similar path from B, through TH2, the load, and back to N.

Characteristics of Load Current with Pure Resistive Load

• Load Current: With a purely resistive load, the current directly follows the voltage applied across the load without any phase shift since resistors do not store electrical energy. However, due to the nature of controlled rectification, the load current is inherently discontinuous, meaning it only flows during the portions of the AC cycle when each thyristor is conducting.
• Ripple Frequency: As each half of the AC supply cycle results in a pulse of current across the load, the resulting ripple frequency (the frequency of the voltage and current fluctuations seen at the output) is twice the frequency of the input AC supply. This is because, within one complete cycle of the input (360°), two pulses of current are delivered to the load.

Fig- single phase full wave controlled rectifier waveform

The configuration of a single-phase full-wave controlled rectifier with a purely resistive load gives a fundamental application of power electronics in controlling AC power. By adjusting the firing angles of the thyristors, one can control the output characteristics, catering to various application needs. However, the discontinuous nature of the load current and the increased ripple frequency are essential considerations in the design and application of these circuits, particularly in scenarios requiring smooth and continuous power delivery.

Single Phase Full Wave Controlled Rectifier Formula

The output DC voltage for the resistive load is 

The average load current will be

Single Phase Full Wave Controlled Rectifier With Inductive Load

Introducing an inductive load to the rectifier circuit complicates the behavior due to the inductor's tendency to resist changes in current. This setup necessitates a more sophisticated control strategy to manage the inductor's reactance, crucial for applications requiring a smooth and stable DC output.

Fig- Circuit Diagram Of Single Phase Full Wave Controlled Rectifier With Inductive Load

a single phase full converter with an R-L load provides two pulses in each cycle as in the case of mid-point full-wave converter. Firing angles for both the thyristor pairs are assumed to be equal. A large value of L will result in a continuous steady current in the load. A small value of L will produce a discontinuous load current for large firing angles. The waveforms with two different firing angles are shown below

Fig- Output waveform of Single phase full wave controlled rectifier with RL load

The voltage waveform at the DC terminals comprises a steady DC component superimposed with an AC ripple component, having a fundamental frequency equal to twice that of the AC supply.

Advantages Of Single Phase Full Wave Controlled Rectifier

• Enhanced Efficiency: Achieves higher efficiency compared to half-wave rectifiers.
• Improved Power Quality: Reduced harmonic distortion and smoother DC output.
• Versatility: Adaptable to various load types and applications

Single Phase Full Wave Controlled Rectifier Applications

Single Phase Full Wave Controlled Rectifiers find their applications in various field

• battery charging systems, and power supply units
• Mobile phones, laptops, charger circuits.
• Uninterruptible Power Supply (UPS) circuits to convert AC to DC.
• Our home inverters convert AC to DC.
• LCD, LED TVs.
• Car Alternator to charge the batteries during the running of the car.
• LED Driver Circuits.
• Audio Amplifier.
• Radios.

This article summarises all the information related to Single Phase Half Wave Controlled Rectifier, which helps in propelling your preparation for various AE/JE and ESE examinations. You can visit the Testbook app to keep yourself updated with all the exam-oriented information related to the upcoming examination, like SSC JE, GATE, ESE, RRB JE, and state AE/JE Exams.