1-Phase Controlled Half Wave Rectifier: R Load

Circuit Diagram
The circuit diagram of the single phase half wave controlled rectifier with resistive load is given
in Fig. 1. The single phase half wave controlled rectifier circuit consists of a Thyristor switch
only. An ac voltage source (vs) is connected at the input while a resistive (R) load is connected at
the output. The thyristor is turned on after applying a firing pulse.

Waveform Characteristics

 The output waveform will show the half-wave form, starting from the triggering angle (α)
and extending to π\piπ.
 As α increases, the average output voltage decreases, leading to lower output current.
1-Phase Controlled Half Wave Rectifier: RL Load

In a single-phase controlled half-wave rectifier with an inductive load, the thyristor is triggered at a
specific firing angle \( \alpha \), allowing the load voltage to follow the source voltage. Due to the
inductance, the current rises gradually, peaks, and then decreases, continuing even after the voltage
drops to zero at \( \pi \). The thyristor conducts until the current reaches zero at the extinction angle \( \
beta \), and the conduction period is from \( \alpha \) to \( \beta \). After \( \beta \), the thyristor
remains off until the next cycle starts.

During the positive half cycle of the input voltage, the thyristor T is forward biased but it does
not conduct until a gate signal is applied to it. • When a gate pulse is given to the thyristor T at
ωt= α, it gets turnedON and begins to conduct. • When the thyristor is ON, the input voltage is
applied to the load but due to the inductor present in the load, the current through the load builds
up slowly.

During the negative half cycle • During the negative half cycle, the thyristor T gets reverse
biased. • At this instant i.e at ωt = π, the load current shift its path from the thyristor to the
freewheeling diode. • When the current is shifted from thyristor to freewheeling diode, the
thyristor turns OFF. • The current through the inductor slowly decays to zero through the loop
freewheeling diode-R-L. • So here the thyristor will not conduct in the negative half cycle and
turns off at ωt=π. • So the load receives voltage only during the positive half cycle. • The average
value of output voltage can be varied by varying the firing angle α.

1-Phase Controlled Half Wave Rectifier: Free Wheeling Diode , give working

In a 1-phase controlled half-wave rectifier with a free wheeling diode (FWD), the setup includes
a thyristor and a diode connected in parallel with the load. When the thyristor is triggered at a
certain angle, it allows current to flow through the load, matching the input AC voltage. For
inductive loads, like motors, the current doesn’t drop to zero immediately when the input voltage
goes off; it gradually decreases because of the energy stored in the inductor. This is where the
free wheeling diode comes into play. When the thyristor turns off, the diode provides a path for
the current to continue flowing, allowing it to circulate through the load until it fully decays. This
helps prevent abrupt changes in current, which could damage the circuit components. Once the
current drops to zero, the diode also turns off, and the cycle can repeat when the thyristor is
triggered again. Overall, the free wheeling diode ensures smoother operation and improved
stability in the circuit.
Single Phase Full Bridge Converter with R Load

a. Positive Half-Cycle

The thyristor is triggered into conduction at α (firing angle) during the positive half-cycle of the
input AC voltage. The conductivity of the thyristor enables current to move through the load (R)
and thyristor (T1 & T2) simultaneously. The input voltage changes polarity at the conclusion of
the positive half-cycle, resulting in the thyristor’s natural shutdown.
b. Negative Half-Cycle:

The thyristor (T1&T2) is reverse-biased and does not conduct during the negative half-cycle of
the input AC voltage. However, during this half-cycle, the thyristors (T3 & T4) conduct, and
current flows through the load.

Both the output voltage and current are positive cycles in this setup. This is a result of the load
being positive with regard to the ground throughout both cycles.

Similar to this, the thyristor (T3 & T4) is off during the positive cycle, and the input voltage
changes polarity causing the thyristor to naturally turn off.

Single Phase Full Bridge Converter With RL Load

a. Positive Half-Cycle:

During the positive half-cycle of the input AC voltage, the thyristor (T1 & T2) is triggered at α
(firing angle) into conduction. The thyristor conducts, allowing the current to flow through the
inductive load (RL) and the thyristor. The load current rises, and energy is stored in the inductor.

At the end of the positive half-cycle, the input voltage reverses polarity, causing the thyristor (T1
& T2) to naturally turn off.

The inductive load tries to maintain the current flow after the thyristor turns off. However, since
the thyristor is off, the load continuously conducts until the charges are present in the inductor.
But the inductor discharges current in the reverse direction.

b. Negative Half-Cycle:

During the negative half-cycle of the input AC voltage, both the thyristor (T1 & T2) do not
conduct. No current flows through the load during this half-cycle using T1 & T2.

Thyristor T3 & T4 conducts during the negative cycle. Similarly, the inductor stores the charges
during the negative cycle.

At the end of the negative half-cycle, the input voltage reverses polarity, causing the thyristor
(T3 & T4) to naturally turn off. However, the load continuously conducts until the charges are
present in the inductor in the reverse direction.

### 3-Phase Diode Rectifier with RL Load

A 3-phase diode rectifier converts 3-phase AC voltage into DC voltage using diodes. When
connected to an RL (resistive-inductive) load, the circuit operates as follows:
1. **Basic Configuration**:
- The rectifier consists of three diodes connected to a 3-phase AC source. Each diode conducts
in turn as the AC voltage changes, allowing current to flow to the load.
2. **Operation**:
- In a 3-phase system, the voltage waveform is more consistent than in a single-phase system.
The diodes are arranged so that at any given time, two diodes are conducting, allowing the load
to receive power continuously.
- The conduction sequence occurs as follows: when one diode turns on, the current flows
through the load, and as the voltage peaks for the next phase, the corresponding diode turns on,
keeping the current flowing.
3. **Current and Voltage Waveforms**:
- The output voltage is a series of pulses rather than a smooth DC voltage. The average output
voltage can be calculated from the peak phase voltage, which is higher than in single-phase
systems.
- The load current (i.e., the combination of resistive and inductive effects) will not follow the
voltage immediately due to the inductance. The current builds up gradually when the voltage
rises and decays slowly when the voltage drops.
4. **Inductive Behavior**:
- The inductor in the load stores energy when the current is flowing. When the diode turns off
(as the input AC voltage decreases), the inductor releases this stored energy, allowing the current
to continue flowing, which helps smooth out the output current.
- The presence of the inductor results in a phase shift between the voltage and current
waveforms, and the current will have a tendency to lag behind the voltage.
5. **Output Characteristics**:
- The output DC voltage is relatively constant compared to a single-phase rectifier, thanks to
the overlapping conduction of the diodes. However, it still has ripple due to the nature of the
rectification process.
- The ripple voltage can be minimized further by adding filtering components (like capacitors)
in parallel with the load.
### Summary
A 3-phase diode rectifier with an RL load effectively converts 3-phase AC into DC by allowing
diodes to conduct in sequence. The output voltage is pulsed but averages out to a more stable
level compared to single-phase rectification. The inductive load smooths the current waveform,
reducing abrupt changes and improving overall performance.

### 3-Phase Diode Rectifier with RL Load(on less lines)

A 3-phase diode rectifier converts 3-phase AC voltage into DC using three diodes.
1. **Basic Configuration**:
- The rectifier connects to a 3-phase AC source, with diodes conducting in sequence to allow
continuous current flow.
2. **Operation**:
- In a 3-phase system, two diodes conduct at any time, ensuring the load receives power
consistently.
3. **Current and Voltage Waveforms**:
- The output voltage consists of pulses, resulting in a higher average voltage. The load current
lags behind the voltage due to inductance, gradually building and decaying.
4. **Inductive Behavior**:
- The inductor stores energy, releasing it when the diode turns off, which smooths the current
waveform and introduces a phase shift.
5. **Output Characteristics**:
- The output DC voltage is more stable than in single-phase rectifiers, though some ripple
remains. Adding filtering components can further reduce this ripple.
### Summary
A 3-phase diode rectifier with an RL load efficiently converts 3-phase AC into pulsed DC,
achieving a stable output voltage while the inductive load smooths current fluctuations.

### Working of 3-Phase Full Bridge Diode Rectifiers

A 3-phase full bridge diode rectifier is a circuit that converts 3-phase AC voltage into DC
voltage using six diodes arranged in a bridge configuration. Here’s an overview of its working
and features:
#### 1. **Basic Configuration**
- The rectifier comprises six diodes (D1, D2, D3, D4, D5, D6) connected in a bridge
arrangement. Each diode is connected to one of the three phases of the AC supply.
- The load is connected across the output terminals of the bridge.
#### 2. **Operation**
- The operation utilizes the three-phase AC supply, where the voltage levels of the three phases
(A, B, and C) are offset by 120 degrees.
- At any moment, two of the three phases will have a higher voltage, allowing current to flow
through the corresponding diodes. This continuous conduction ensures that the load receives
power without interruption.

#### 3. **Conduction Sequence**

- The conduction pattern is cyclical, as follows:
- When phase A is positive, diodes D1 and D2 conduct.
- When phase B is positive, diodes D2 and D3 conduct.
- When phase C is positive, diodes D3 and D1 conduct.
- This sequence continues as the AC waveform cycles, resulting in smooth, pulsating DC output.

#### 4. **Output Voltage Waveform**

- The output voltage consists of a series of pulses that approximate a smooth DC voltage.

#### 5. **Current Waveform**

- The output current will mirror the output voltage, but for inductive loads, it will lag behind due
to the inductance, resulting in a smoother current waveform.
#### 6. **Ripple and Filtering**
- Although the output voltage is smoother than that of single-phase rectifiers, it still contains
ripple. Additional filtering (using capacitors) can be implemented to further smooth the output.
#### 7. **Advantages**
- **Higher Efficiency**: The full bridge configuration optimally utilizes the 3-phase supply,
leading to better efficiency.
- **Reduced Ripple**: The continuous conduction results in lower ripple in the output voltage.
- **Improved Stability**: The average output voltage is more stable, making it suitable for
various applications requiring reliable DC power.
### Summary
The 3-phase full bridge diode rectifier is an effective solution for converting 3-phase AC to
stable DC. By utilizing six diodes in a bridge configuration, it ensures continuous current flow,
resulting in a higher average output voltage and improved performance compared to other
rectification methods.