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Main Applications of Thyristors

Introduction

Thyristors, commonly known as silicon-controlled rectifiers (SCRs), find widespread applications in various electronic systems owing to their unique electrical properties. These semiconductor devices are primarily employed in power control and conversion circuits. One significant application involves their use in voltage regulation, where thyristors play a crucial role in maintaining stable and controlled electrical output. Additionally, thyristors are integral components in phase-locked loop (PLL) circuits, ensuring precise synchronization and frequency control in electronic systems. Moreover, they are extensively utilized in motor control applications, contributing to the efficient and controlled operation of electric motors. The versatility of thyristors extends to their use in pulse-width modulation (PWM) techniques for achieving variable speed control in diverse applications, such as industrial drives and robotics. In summary, the main applications of thyristors encompass power control, voltage regulation, phase synchronization, motor control, and pulse-width modulation, making them indispensable components in modern electronic systems.

Standard Gate-Turn-Off Thyristors1
Standard Gate-Turn-Off Thyristors1
Standard Gate-Turn-Off Thyristors2
Standard Gate-Turn-Off Thyristors3
Standard Gate-Turn-Off Thyristors4
Standard Gate-Turn-Off Thyristors4
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Phase-Controlled Rectifiers

This technology is primarily applied in scenarios involving controllable rectifiers, AC switches, and AC power regulation.

  1. High-Power Rectification Power Supplies:
    • Electrochemical Power Sources: Notably in electroplating and electrolysis processes.
    • Rail Traction Power Supplies: Applied in railway traction systems for efficient power delivery.
  2. AC Switching:
    • Static Bypass Switches (STS): Utilized for seamless power transfer and backup in critical applications.
    • High-Voltage Valve Groups: Found in systems requiring high-voltage switching capabilities.
  3. AC Power Regulation:
    • Soft Startups: Implemented for gradual and controlled power startup.
    • Induction Furnace Heating Power Supply: Applied in the heating process of induction furnaces.

Applications in Uninterruptible Power Supplies (UPS):

  1. Phase-Controlled Rectifiers:
    • Used in UPS systems to regulate and control the rectification process.
  2. Static Bypass Switches:
    • Integrated into UPS setups for rapid and reliable power transfer during system failures.
  3. DC Soft Startups:
    • Employed in UPS configurations to ensure smooth and controlled startups in DC power systems.
Pic1 Phase Controlled Rectifier
Pic1 Phase Controlled Rectifier
Pic1a Phase Controlled Rectifier Formula

F=1.73

A Phase-Controlled Rectifier is a type of rectifier circuit that allows controlled conversion of AC (alternating current) to DC (direct current). This device is characterized by its ability to adjust the output voltage by controlling the firing angle of the thyristors within the circuit. Here’s a detailed explanation of the schema and formula associated with a Phase-Controlled Rectifier:

Schema:

  • Components:
    • Transformer: The input AC voltage is fed through a transformer to adjust the voltage levels.
    • Diode Bridge: A diode bridge is employed to rectify the AC voltage, converting it into pulsating DC.
  • Controlled Element:
    • Thyristors (SCRs): The crucial element in a Phase-Controlled Rectifier. The firing angle of the thyristors determines when during each AC cycle the rectification occurs.
  • Filter:
    • Capacitor/Inductor Filter: Depending on the application, a filter is often used to smooth the pulsating DC and reduce harmonics.

Working Principle:

  • The thyristors are triggered at a specific point in the AC waveform by controlling the firing angle (α). The firing angle represents the delay in turning on the thyristors after the zero-crossing point of the AC waveform.
  • By adjusting the firing angle, the effective value of the output voltage is controlled, allowing for regulation of the DC output.

Formula:

  • The output voltage (V_dc) of a Phase-Controlled Rectifier can be calculated using the following formula: Vdc​=Vpeak​​/π⋅cos(α)

Where:

  • Vdc​ is the average or DC output voltage.
  • Vpeak​ is the peak value of the AC input voltage.
  • α is the firing angle.

Adjusting the firing angle α allows for control over the average output voltage, providing a means of regulating the DC power in applications such as motor drives, heating systems, and certain power supplies.

Application of Thyristor-based UPS Power Supply: Battery Soft Start

The circuit diagram of a soft starter is a crucial element in motor control systems, designed to mitigate the inrush current during the starting phase of electric motors. A key component enhancing the functionality of this circuit is the thyristor. The soft starter circuit typically consists of a thyristor-based voltage control mechanism that regulates the power supplied to the motor during startup. The importance of the thyristor in this context lies in its ability to control the conduction angle, allowing for a gradual and controlled increase in voltage to the motor. By employing the thyristor, the soft starter ensures a smooth and step-less acceleration of the motor, preventing sudden spikes in current that could lead to mechanical stress and electrical disturbances. This controlled startup not only reduces mechanical wear and tear on the motor but also enhances the overall efficiency of the system. The thyristor’s role in the soft starter circuit is indispensable, providing a reliable means to optimize motor performance and prolong equipment lifespan in various industrial applications.

Pic2 Soft Starter
Pic2 Soft Starter

The formula provided is related to thyristor calculations in the context of electrical circuits. Let’s break down the components and their meanings:

  1. IT​(AV)=Id​:
    • IT​(AV) represents the average thyristor current over a complete cycle.
    • Id​ is the DC current delivered to the load.
    • This equation signifies that the average thyristor current equals the DC current supplied to the load.
  2. PT​(AV)=VT​(TO)IT​(AV)+rTI2T​(AV):
    • PT​(AV) denotes the average power dissipated in the thyristor.
    • VT​(TO) is the threshold voltage of the thyristor.
    • IT​(AV) is the average thyristor current.
    • rT​ is the dynamic resistance of the thyristor.
    • I2T​(AV) is the average squared current through the thyristor.
    • This equation expresses the average power dissipation in the thyristor, taking into account the threshold voltage and dynamic resistance. It is a crucial formula for assessing the thermal performance and power handling capability of the thyristor in a given circuit.

In summary, these formulas provide insights into the relationship between average thyristor current, DC current delivered to the load, and the average power dissipated in the thyristor. Understanding these relationships is essential for designing and optimizing circuits involving thyristors, ensuring efficient and reliable operation within specified parameters.

Applications of Thyristors in UPS Power Supplies – Modularization

Pic3 UPS Circuit Diagram
Pic3 UPS Circuit Diagram

The circuit diagram of a modular UPS main circuit is designed with modularity in mind, enhancing the flexibility and scalability of uninterruptible power supply (UPS) systems. In this setup, thyristors play a pivotal role in controlling power flow and facilitating seamless transitions between different modules within the UPS system. Thyristors efficiently regulate and switch high-power loads, allowing the modular UPS to distribute power among various modules, optimizing energy usage, and improving overall system reliability. The modular architecture enables easy expansion or maintenance without disrupting the entire system, making the UPS adaptable to changing power requirements. Therefore, the inclusion of thyristors in the modular UPS main circuit is crucial for creating a robust and scalable power supply solution capable of meeting diverse needs in a dynamic operational environment.

Applications of Thyristors - Static Bypass Switches (STS)

Pic4 STS
Pic4 STS

A static bypass switch circuit diagram typically comprises a set of components designed to allow for the seamless transfer of electrical power from the main supply to an alternative path. In this circuit, the inclusion of a thyristor is of paramount importance. The thyristor serves as a key switching element that enables the controlled diversion of power when needed. The circuit design ensures that, under normal operating conditions, the thyristor remains non-conductive, allowing power to flow through the primary path. However, in the event of a fault or maintenance requirement, the thyristor can be triggered to conduct, creating a low-resistance path and facilitating the transfer of power to the bypass route. This controlled switching is crucial for ensuring uninterrupted power supply during critical moments without causing disruption or downtime. The thyristor’s role in the static bypass switch circuit is central to achieving a reliable and efficient mechanism for diverting power when necessary, thus enhancing the overall reliability and availability of the electrical system.

𝐼𝑇(𝐴𝑉)=𝐼𝑅𝑀𝑆 (√2/𝜋)

𝐼𝑇𝑅𝑀𝑆 = 𝐼𝑅𝑀𝑆/√2

PTAV=VTO × ITAV + rTO × ITRMS2 = VTO × ITAV + rTO × ITAV2 × F2


Let’s break down the three formulas:

  1. IT​(AV)=IRMS​(√2/π​​):
    • IT​(AV) represents the average thyristor current over a complete cycle.
    • IRMS​ is the root mean square current.
    • This formula establishes the relationship between the average thyristor current and the root mean square current by a factor of √2/π​​. It’s commonly used in thyristor calculations to convert between average and RMS values.
  2. ITRMS​=IRMS​​/√2:
    • ITRMS​ is the RMS thyristor current.
    • IRMS​ is the root mean square current.
    • This formula simplifies the calculation of the RMS thyristor current by dividing the root mean square current by the square root of 2.
  3. PTAV​=VTO​×ITAV​+rTO​×I2TRMS=VTO​×ITAV​+rTO​×I2TAV​×F2:
    • PTAV​ denotes the average power dissipated in the thyristor.
    • VTO​ is the threshold voltage of the thyristor.
    • ITAV​ is the average thyristor current.
    • rTO​ is the dynamic resistance of the thyristor.
    • ITRMS​ is the RMS thyristor current.
    • F is the frequency of the AC input.
    • This formula expresses the average power dissipation in the thyristor, considering the threshold voltage, dynamic resistance, and frequency. It is crucial for assessing the thermal performance and power handling capacity of the thyristor in a given circuit.

Conclusion

In summary, the main application of thyristors spans across various electrical systems, where their unique characteristics are harnessed for specific purposes. Whether employed in high-power rectification for electrochemical processes or rail traction systems, as static bypass switches in critical applications, or as integral components in soft starters for controlled motor acceleration, thyristors play a pivotal role in optimizing energy usage and enhancing system efficiency. Furthermore, their application extends to modular UPS main circuits, contributing to the adaptability and reliability of power supply solutions. The discussed formulas elucidate the intricacies of thyristor behavior, emphasizing their significance in circuit design, power regulation, and overall system performance. As demonstrated, the versatility of thyristors positions them as indispensable components in modern electronic systems across diverse industrial applications.

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