Rectifier: Line commutated 1 phase and 3 phase half (semi) & fully controlled bridge converters
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### Rectifiers: Line Commutated 1-Phase and 3-Phase Half (Semi) & Fully Controlled Bridge Converters
#### Introduction
Rectifiers are power electronic devices that convert alternating current (AC) into direct current (DC). They are widely used in power supplies, motor drives, and other electronic devices that require DC power. There are two main types of rectifiers:
- **Half-controlled (semi-controlled) rectifiers**: Consist of both diodes and thyristors (SCRs). They allow control over only part of the AC cycle.
- **Fully-controlled rectifiers**: Composed entirely of thyristors, providing full control over the AC waveform.
Both types can be implemented in single-phase and three-phase systems and are known as bridge converters.
### 1-Phase Half and Fully Controlled Bridge Converters
#### 1-Phase Half-Controlled Bridge Converter
A **half-controlled bridge converter** in a 1-phase system consists of two diodes and two thyristors arranged in a bridge configuration.
##### Working:
- **Positive half-cycle**: During the positive half-cycle of the AC input, one thyristor and one diode conduct, allowing current to flow through the load.
- **Negative half-cycle**: During the negative half-cycle, the other thyristor and diode conduct, allowing current in the reverse direction.
- **Control of output voltage**: The thyristors are controlled by firing at a specific angle (called the **firing angle α**) during the positive and negative cycles. The diodes automatically conduct based on the polarity of the input voltage.
##### Output:
- The output voltage is pulsating DC with some control over the magnitude, depending on the firing angle of the thyristors.
##### Applications:
- Used in applications requiring simple control of DC power but where full control over the entire waveform is not necessary, such as battery chargers.
#### 1-Phase Fully Controlled Bridge Converter
A **fully-controlled bridge converter** in a 1-phase system consists of four thyristors instead of diodes.
##### Working:
- **Positive half-cycle**: During the positive half-cycle, two thyristors (T1 and T2) are triggered at the appropriate firing angle (α).
- **Negative half-cycle**: During the negative half-cycle, the other two thyristors (T3 and T4) are triggered at the same firing angle.
##### Output:
- The output voltage is fully controlled, depending on the firing angle of all thyristors. By adjusting the firing angle, the average output voltage can be varied from positive maximum to negative maximum.
- The output is a controlled DC waveform with reduced ripple compared to a half-controlled converter.
##### Applications:
- Used in applications where precise control of DC output is needed, such as motor drives, industrial power supplies, and variable DC sources.
### 3-Phase Half and Fully Controlled Bridge Converters
#### 3-Phase Half-Controlled Bridge Converter
A **3-phase half-controlled bridge converter** consists of three thyristors and three diodes arranged in a bridge configuration.
##### Working:
- **Positive half-cycle**: During each positive half-cycle of the AC input from any phase, one thyristor and one diode conduct.
- **Negative half-cycle**: During the negative half-cycle of the AC input from any phase, a different thyristor and diode conduct.
- **Control of output voltage**: The thyristors can be triggered at a specific firing angle to control the output DC voltage.
##### Output:
- The output voltage is a pulsating DC waveform with reduced ripple compared to a 1-phase system due to the three-phase input.
- The magnitude of the DC voltage depends on the firing angle of the thyristors.
##### Applications:
- Used in high-power applications like DC motor drives and large rectifier systems where full control over the waveform is not required.
#### 3-Phase Fully Controlled Bridge Converter
A **3-phase fully controlled bridge converter** consists of six thyristors arranged in a bridge configuration, with each phase having two thyristors.
##### Working:
- **Operation per phase**: Each phase of the AC input is controlled by two thyristors. During the positive half-cycle of each phase, one thyristor is triggered, and during the negative half-cycle, the other thyristor is triggered.
- **Control of output voltage**: The firing angle of each thyristor can be adjusted to control the average DC output voltage. The firing sequence is synchronized with the AC waveform.
##### Output:
- The output is a fully controlled DC waveform with low ripple. By varying the firing angle of the thyristors, the output voltage can be adjusted over a wide range.
- The ripple in the output voltage is smaller compared to the single-phase converters due to the three-phase input, which improves the quality of the output.
##### Applications:
- Widely used in high-power applications like industrial motor drives, power supplies for large equipment, and HVDC power transmission systems.
### Key Concepts
- **Firing Angle (α)**: The angle at which a thyristor is triggered in each cycle of the AC waveform. By delaying the firing angle, the average DC output voltage can be controlled.
- For a **half-controlled converter**, the firing angle only affects part of the AC cycle.
- For a **fully controlled converter**, the firing angle affects the entire AC cycle.
- **Commutation**: In line-commutated rectifiers, the thyristors turn off automatically when the current reaches zero in the AC cycle, known as natural commutation.
### Comparison of Half and Fully Controlled Converters
| Feature | Half-Controlled Converter | Fully Controlled Converter |
|------------------------------|-------------------------------------|-----------------------------------|
| **Control Elements** | Thyristors + Diodes | Thyristors only |
| **Control** | Partial control of the waveform | Full control of the waveform |
| **Output Voltage Control** | Limited control via firing angle | Complete control via firing angle |
| **Applications** | Simpler control applications | Precision control applications |
| **Cost** | Lower due to fewer thyristors | Higher due to more thyristors |
### Conclusion
Line-commutated rectifiers, both half and fully controlled, play a critical role in power electronics, allowing for the conversion and control of AC to DC power. The choice between half-controlled and fully controlled rectifiers depends on the application's need for control, complexity, and cost.
- **1-phase** rectifiers are simpler but produce more ripple in the output.
- **3-phase** rectifiers offer better performance with less ripple and are more suitable for high-power applications.
Understanding the difference between these configurations helps in choosing the right rectifier for specific industrial and electronic applications.
#### Introduction
Rectifiers are power electronic devices that convert alternating current (AC) into direct current (DC). They are widely used in power supplies, motor drives, and other electronic devices that require DC power. There are two main types of rectifiers:
- **Half-controlled (semi-controlled) rectifiers**: Consist of both diodes and thyristors (SCRs). They allow control over only part of the AC cycle.
- **Fully-controlled rectifiers**: Composed entirely of thyristors, providing full control over the AC waveform.
Both types can be implemented in single-phase and three-phase systems and are known as bridge converters.
### 1-Phase Half and Fully Controlled Bridge Converters
#### 1-Phase Half-Controlled Bridge Converter
A **half-controlled bridge converter** in a 1-phase system consists of two diodes and two thyristors arranged in a bridge configuration.
##### Working:
- **Positive half-cycle**: During the positive half-cycle of the AC input, one thyristor and one diode conduct, allowing current to flow through the load.
- **Negative half-cycle**: During the negative half-cycle, the other thyristor and diode conduct, allowing current in the reverse direction.
- **Control of output voltage**: The thyristors are controlled by firing at a specific angle (called the **firing angle α**) during the positive and negative cycles. The diodes automatically conduct based on the polarity of the input voltage.
##### Output:
- The output voltage is pulsating DC with some control over the magnitude, depending on the firing angle of the thyristors.
##### Applications:
- Used in applications requiring simple control of DC power but where full control over the entire waveform is not necessary, such as battery chargers.
#### 1-Phase Fully Controlled Bridge Converter
A **fully-controlled bridge converter** in a 1-phase system consists of four thyristors instead of diodes.
##### Working:
- **Positive half-cycle**: During the positive half-cycle, two thyristors (T1 and T2) are triggered at the appropriate firing angle (α).
- **Negative half-cycle**: During the negative half-cycle, the other two thyristors (T3 and T4) are triggered at the same firing angle.
##### Output:
- The output voltage is fully controlled, depending on the firing angle of all thyristors. By adjusting the firing angle, the average output voltage can be varied from positive maximum to negative maximum.
- The output is a controlled DC waveform with reduced ripple compared to a half-controlled converter.
##### Applications:
- Used in applications where precise control of DC output is needed, such as motor drives, industrial power supplies, and variable DC sources.
### 3-Phase Half and Fully Controlled Bridge Converters
#### 3-Phase Half-Controlled Bridge Converter
A **3-phase half-controlled bridge converter** consists of three thyristors and three diodes arranged in a bridge configuration.
##### Working:
- **Positive half-cycle**: During each positive half-cycle of the AC input from any phase, one thyristor and one diode conduct.
- **Negative half-cycle**: During the negative half-cycle of the AC input from any phase, a different thyristor and diode conduct.
- **Control of output voltage**: The thyristors can be triggered at a specific firing angle to control the output DC voltage.
##### Output:
- The output voltage is a pulsating DC waveform with reduced ripple compared to a 1-phase system due to the three-phase input.
- The magnitude of the DC voltage depends on the firing angle of the thyristors.
##### Applications:
- Used in high-power applications like DC motor drives and large rectifier systems where full control over the waveform is not required.
#### 3-Phase Fully Controlled Bridge Converter
A **3-phase fully controlled bridge converter** consists of six thyristors arranged in a bridge configuration, with each phase having two thyristors.
##### Working:
- **Operation per phase**: Each phase of the AC input is controlled by two thyristors. During the positive half-cycle of each phase, one thyristor is triggered, and during the negative half-cycle, the other thyristor is triggered.
- **Control of output voltage**: The firing angle of each thyristor can be adjusted to control the average DC output voltage. The firing sequence is synchronized with the AC waveform.
##### Output:
- The output is a fully controlled DC waveform with low ripple. By varying the firing angle of the thyristors, the output voltage can be adjusted over a wide range.
- The ripple in the output voltage is smaller compared to the single-phase converters due to the three-phase input, which improves the quality of the output.
##### Applications:
- Widely used in high-power applications like industrial motor drives, power supplies for large equipment, and HVDC power transmission systems.
### Key Concepts
- **Firing Angle (α)**: The angle at which a thyristor is triggered in each cycle of the AC waveform. By delaying the firing angle, the average DC output voltage can be controlled.
- For a **half-controlled converter**, the firing angle only affects part of the AC cycle.
- For a **fully controlled converter**, the firing angle affects the entire AC cycle.
- **Commutation**: In line-commutated rectifiers, the thyristors turn off automatically when the current reaches zero in the AC cycle, known as natural commutation.
### Comparison of Half and Fully Controlled Converters
| Feature | Half-Controlled Converter | Fully Controlled Converter |
|------------------------------|-------------------------------------|-----------------------------------|
| **Control Elements** | Thyristors + Diodes | Thyristors only |
| **Control** | Partial control of the waveform | Full control of the waveform |
| **Output Voltage Control** | Limited control via firing angle | Complete control via firing angle |
| **Applications** | Simpler control applications | Precision control applications |
| **Cost** | Lower due to fewer thyristors | Higher due to more thyristors |
### Conclusion
Line-commutated rectifiers, both half and fully controlled, play a critical role in power electronics, allowing for the conversion and control of AC to DC power. The choice between half-controlled and fully controlled rectifiers depends on the application's need for control, complexity, and cost.
- **1-phase** rectifiers are simpler but produce more ripple in the output.
- **3-phase** rectifiers offer better performance with less ripple and are more suitable for high-power applications.
Understanding the difference between these configurations helps in choosing the right rectifier for specific industrial and electronic applications.
A **rectifier** is an electrical device that converts alternating current (AC) into direct current (DC). Rectifiers are essential components in various power supply systems, such as in motor drives, battery charging, and in high-voltage DC transmission systems. Among the different types of rectifiers, **line commutated** rectifiers are widely used, especially in industrial and power electronics applications. Let’s break down the different types of line-commutated rectifiers: **1-phase and 3-phase half-controlled and fully-controlled bridge converters.**
### **Line Commutated Rectifiers (LCRs)**
In a line commutated rectifier, the process of commutation (i.e., the switching from conducting to non-conducting state) is controlled by the AC supply voltage. In simpler terms, the rectifier relies on the natural zero-crossings of the AC waveform to turn off the conducting thyristors or diodes. Since this commutation is based on the AC line frequency, these rectifiers are often referred to as **line commutated**.
These rectifiers can be classified based on their configuration and control methods, primarily into **half-controlled** and **fully-controlled** types.
---
### **1. 1-Phase Half-Controlled Bridge Converter**
In a 1-phase half-controlled bridge converter, the rectifier uses both **diodes** (which are uncontrolled) and **thyristors** (which are controlled).
#### Working Principle:
- The **diodes** allow current to pass during the positive half-cycle of the AC input voltage.
- The **thyristors** are controlled and allow current to flow during the negative half-cycle of the AC input voltage, but only after being triggered by a gate signal.
Since the triggering of thyristors is controlled, the average output DC voltage can be adjusted by varying the firing angle (delay of the thyristor triggering). This control gives flexibility in regulating the DC output.
#### Key Points:
- **Output waveform**: The output is a pulsating DC, and the average output voltage depends on the firing angle of the thyristor.
- **Control**: The main feature of the half-controlled bridge converter is that it provides partial control of the rectifier, allowing for some adjustment of the output voltage.
- **Commutation**: The diodes automatically turn off when the AC voltage reverses, while the thyristors turn off when the AC voltage crosses zero, and their control depends on the firing angle.
---
### **2. 1-Phase Fully-Controlled Bridge Converter**
In a 1-phase fully-controlled bridge converter, all the devices in the converter are **thyristors**, which means every part of the current flow is controlled. This configuration allows for full control over the output DC voltage.
#### Working Principle:
- During the positive half-cycle of the AC input, the thyristors are triggered to conduct, allowing current to flow and converting AC to DC.
- During the negative half-cycle of the AC input, the thyristors are again triggered to conduct, and the output DC is obtained.
- The firing angle of the thyristors can be adjusted over the entire AC cycle, allowing for a much greater range of control over the output voltage.
#### Key Points:
- **Output waveform**: Similar to the half-controlled converter, the output is a pulsating DC, but since all devices are controlled, there is better control over the output voltage.
- **Control**: Full control is provided by the firing angle of the thyristors. The converter can operate at higher output voltages and greater efficiency compared to the half-controlled version.
- **Commutation**: Since all the devices are controlled, the turn-off of the thyristors happens when the AC voltage crosses zero or when the gate signal is removed.
---
### **3. 3-Phase Half-Controlled Bridge Converter**
The 3-phase half-controlled bridge converter operates in a similar way to the 1-phase half-controlled converter but uses three-phase AC power. It uses a combination of **diodes** and **thyristors**.
#### Working Principle:
- The **diodes** conduct during the positive half-cycles of each phase.
- The **thyristors** are triggered to conduct during the negative half-cycle of the AC input. Their firing angle determines how much of the negative cycle is used to convert to DC.
In a three-phase system, the voltage waveform is smoother and less pulsating than in a single-phase system, making this converter suitable for industrial applications where three-phase power is commonly available.
#### Key Points:
- **Output waveform**: The output is smoother than the 1-phase half-controlled converter, but it is still a pulsating DC signal.
- **Control**: The main control in this converter is through the thyristors, whose firing angle can be varied to regulate the output voltage.
- **Commutation**: Just like in the 1-phase half-controlled converter, the diodes automatically turn off at the voltage zero-crossings, while the thyristors are turned off when the AC supply voltage crosses zero.
---
### **4. 3-Phase Fully-Controlled Bridge Converter**
In the 3-phase fully-controlled bridge converter, all the devices are **thyristors**, providing full control of the rectifier circuit, similar to the 1-phase fully-controlled converter.
#### Working Principle:
- During both the positive and negative half-cycles of each phase, the thyristors are triggered to conduct at the appropriate times. The output is a smoother DC voltage, with the thyristors conducting according to the firing angle.
- Since all devices are controlled, there is a significant reduction in ripple compared to the half-controlled version.
#### Key Points:
- **Output waveform**: The output is a smoother, more constant DC signal compared to the half-controlled converters.
- **Control**: The output DC voltage is highly controllable by adjusting the firing angles of the thyristors. This gives high flexibility and efficiency.
- **Commutation**: As with the fully-controlled 1-phase converter, the thyristors are turned off when the AC voltage crosses zero or when their gate signal is removed.
---
### **Comparison Summary:**
| Type | Devices Used | Control Type | Output DC Ripple | Applications |
|----------------------------------|-----------------|--------------------|-------------------|---------------------------------------------------|
| 1-Phase Half-Controlled | Diodes & Thyristors | Partial Control | High Ripple | Small to medium power applications |
| 1-Phase Fully-Controlled | Thyristors | Full Control | Medium Ripple | Small to medium power applications |
| 3-Phase Half-Controlled | Diodes & Thyristors | Partial Control | Medium Ripple | Industrial equipment and motor drives |
| 3-Phase Fully-Controlled | Thyristors | Full Control | Low Ripple | High-power industrial and commercial applications |
---
### **Applications:**
- **1-phase half-controlled**: These are typically used in low-power applications where cost is a concern, and the quality of the DC voltage is not a primary concern.
- **1-phase fully-controlled**: Used in systems where better control of output voltage is required and can tolerate moderate ripple.
- **3-phase half-controlled**: These are often used in industrial motor control circuits where three-phase power is available but full control is not necessary.
- **3-phase fully-controlled**: These are used in high-power applications, such as large motor drives, where a smooth DC output is essential, and the full control over the DC voltage is required.
### Conclusion:
Line commutated rectifiers with half-controlled and fully-controlled configurations are important in both 1-phase and 3-phase systems. The choice between half-controlled and fully-controlled depends on the level of control required over the output voltage and the ripple tolerance for the specific application.
### **Line Commutated Rectifiers (LCRs)**
In a line commutated rectifier, the process of commutation (i.e., the switching from conducting to non-conducting state) is controlled by the AC supply voltage. In simpler terms, the rectifier relies on the natural zero-crossings of the AC waveform to turn off the conducting thyristors or diodes. Since this commutation is based on the AC line frequency, these rectifiers are often referred to as **line commutated**.
These rectifiers can be classified based on their configuration and control methods, primarily into **half-controlled** and **fully-controlled** types.
---
### **1. 1-Phase Half-Controlled Bridge Converter**
In a 1-phase half-controlled bridge converter, the rectifier uses both **diodes** (which are uncontrolled) and **thyristors** (which are controlled).
#### Working Principle:
- The **diodes** allow current to pass during the positive half-cycle of the AC input voltage.
- The **thyristors** are controlled and allow current to flow during the negative half-cycle of the AC input voltage, but only after being triggered by a gate signal.
Since the triggering of thyristors is controlled, the average output DC voltage can be adjusted by varying the firing angle (delay of the thyristor triggering). This control gives flexibility in regulating the DC output.
#### Key Points:
- **Output waveform**: The output is a pulsating DC, and the average output voltage depends on the firing angle of the thyristor.
- **Control**: The main feature of the half-controlled bridge converter is that it provides partial control of the rectifier, allowing for some adjustment of the output voltage.
- **Commutation**: The diodes automatically turn off when the AC voltage reverses, while the thyristors turn off when the AC voltage crosses zero, and their control depends on the firing angle.
---
### **2. 1-Phase Fully-Controlled Bridge Converter**
In a 1-phase fully-controlled bridge converter, all the devices in the converter are **thyristors**, which means every part of the current flow is controlled. This configuration allows for full control over the output DC voltage.
#### Working Principle:
- During the positive half-cycle of the AC input, the thyristors are triggered to conduct, allowing current to flow and converting AC to DC.
- During the negative half-cycle of the AC input, the thyristors are again triggered to conduct, and the output DC is obtained.
- The firing angle of the thyristors can be adjusted over the entire AC cycle, allowing for a much greater range of control over the output voltage.
#### Key Points:
- **Output waveform**: Similar to the half-controlled converter, the output is a pulsating DC, but since all devices are controlled, there is better control over the output voltage.
- **Control**: Full control is provided by the firing angle of the thyristors. The converter can operate at higher output voltages and greater efficiency compared to the half-controlled version.
- **Commutation**: Since all the devices are controlled, the turn-off of the thyristors happens when the AC voltage crosses zero or when the gate signal is removed.
---
### **3. 3-Phase Half-Controlled Bridge Converter**
The 3-phase half-controlled bridge converter operates in a similar way to the 1-phase half-controlled converter but uses three-phase AC power. It uses a combination of **diodes** and **thyristors**.
#### Working Principle:
- The **diodes** conduct during the positive half-cycles of each phase.
- The **thyristors** are triggered to conduct during the negative half-cycle of the AC input. Their firing angle determines how much of the negative cycle is used to convert to DC.
In a three-phase system, the voltage waveform is smoother and less pulsating than in a single-phase system, making this converter suitable for industrial applications where three-phase power is commonly available.
#### Key Points:
- **Output waveform**: The output is smoother than the 1-phase half-controlled converter, but it is still a pulsating DC signal.
- **Control**: The main control in this converter is through the thyristors, whose firing angle can be varied to regulate the output voltage.
- **Commutation**: Just like in the 1-phase half-controlled converter, the diodes automatically turn off at the voltage zero-crossings, while the thyristors are turned off when the AC supply voltage crosses zero.
---
### **4. 3-Phase Fully-Controlled Bridge Converter**
In the 3-phase fully-controlled bridge converter, all the devices are **thyristors**, providing full control of the rectifier circuit, similar to the 1-phase fully-controlled converter.
#### Working Principle:
- During both the positive and negative half-cycles of each phase, the thyristors are triggered to conduct at the appropriate times. The output is a smoother DC voltage, with the thyristors conducting according to the firing angle.
- Since all devices are controlled, there is a significant reduction in ripple compared to the half-controlled version.
#### Key Points:
- **Output waveform**: The output is a smoother, more constant DC signal compared to the half-controlled converters.
- **Control**: The output DC voltage is highly controllable by adjusting the firing angles of the thyristors. This gives high flexibility and efficiency.
- **Commutation**: As with the fully-controlled 1-phase converter, the thyristors are turned off when the AC voltage crosses zero or when their gate signal is removed.
---
### **Comparison Summary:**
| Type | Devices Used | Control Type | Output DC Ripple | Applications |
|----------------------------------|-----------------|--------------------|-------------------|---------------------------------------------------|
| 1-Phase Half-Controlled | Diodes & Thyristors | Partial Control | High Ripple | Small to medium power applications |
| 1-Phase Fully-Controlled | Thyristors | Full Control | Medium Ripple | Small to medium power applications |
| 3-Phase Half-Controlled | Diodes & Thyristors | Partial Control | Medium Ripple | Industrial equipment and motor drives |
| 3-Phase Fully-Controlled | Thyristors | Full Control | Low Ripple | High-power industrial and commercial applications |
---
### **Applications:**
- **1-phase half-controlled**: These are typically used in low-power applications where cost is a concern, and the quality of the DC voltage is not a primary concern.
- **1-phase fully-controlled**: Used in systems where better control of output voltage is required and can tolerate moderate ripple.
- **3-phase half-controlled**: These are often used in industrial motor control circuits where three-phase power is available but full control is not necessary.
- **3-phase fully-controlled**: These are used in high-power applications, such as large motor drives, where a smooth DC output is essential, and the full control over the DC voltage is required.
### Conclusion:
Line commutated rectifiers with half-controlled and fully-controlled configurations are important in both 1-phase and 3-phase systems. The choice between half-controlled and fully-controlled depends on the level of control required over the output voltage and the ripple tolerance for the specific application.