Frequency conversion speed regulation technology is a key development direction in modern electric drive systems. As the core component of variable frequency speed control systems, the performance of the inverter has become increasingly critical in determining the overall speed control performance. While the manufacturing process of the inverter plays an important role, it is equally essential to focus on its control methods. Based on current industrial practices, this article reviews various inverter control techniques and explores future trends in this field.
**Introduction to the Inverter**
1) **Basic Structure of the Inverter**
An inverter is a device that converts standard AC power (50 Hz or 60 Hz) into variable frequency AC power to enable motor speed control. It consists of several key components: the control circuit, which manages the main circuit; the rectifier, which converts AC to DC; the DC link, which smooths the DC output; and the inverter section, which reconverts DC back to AC. For advanced inverters like those used in vector control, additional circuits such as a CPU for torque calculation may be included to handle complex computations.
2) **Classification of the Inverters**
Inverters can be classified in multiple ways. According to the main circuit operation mode, they are divided into voltage-source inverters and current-source inverters. Based on switching modes, they include PAM, PWM, and high-frequency PWM inverters. By working principle, they can be categorized as V/f control, slip frequency control, and vector control inverters. Purpose-based classifications include general-purpose inverters, high-performance special inverters, high-frequency inverters, single-phase inverters, and three-phase inverters.
**Inverter Control Mode Selection Basis**
The choice of control method depends on the specific requirements of the production machinery. For example:
- **Quadratic Law Load**: For centrifugal fans, water pumps, and air compressors, V/f control is typically suitable due to its energy-saving characteristics at low frequencies.
- **Constant Torque Load**: For loads with frequent load changes, no feedback vector control may be preferred. However, self-measurement of motor parameters is necessary.
- **Constant Power Load**: For winding machines, either V/f or no feedback vector control can be used. For metal cutting tools, "with feedback vector control" is recommended due to dynamic response needs.
**Detailed Description of Inverter Control Methods**
1) **U/f=C Sinusoidal Pulse Width Modulation (SPWM)**
This method offers a simple structure, low cost, and good mechanical properties, making it suitable for general applications. However, at low frequencies, stator resistance voltage drop reduces torque, leading to lower performance.
2) **Voltage Space Vector Modulation (SVPWM)**
SVPWM improves upon SPWM by generating a more circular magnetic field, enhancing performance. However, it lacks torque adjustment and involves complex control circuits.
3) **Vector Control (VC)**
Vector control transforms stator currents into a two-phase system, allowing independent control of torque and flux. This mimics DC motor behavior but is limited by rotor flux observation challenges and motor parameter sensitivity.
4) **Direct Torque Control (DTC)**
Proposed in 1985, DTC directly controls flux and torque without equivalent DC motor modeling. It offers fast response, high accuracy, and is widely used in high-power drives.
5) **Matrix Control**
Matrix control eliminates the DC link, reducing size and cost. It enables four-quadrant operation and high power density, though it remains under development.
**Key Features of Matrix Control**
- Speed sensorless operation via flux linkage observers.
- Automatic identification of motor parameters.
- Real-time calculation of torque, flux, and speed.
- Band-Band control for efficient PWM generation.
Matrix inverters offer fast torque response (2ms), high speed accuracy (±2%), and excellent low-speed performance, capable of delivering up to 200% torque at zero speed.
Understanding inverters requires not only theoretical knowledge but also practical application. By combining these concepts with real-world examples, one can fully grasp their working principles and potential in modern industrial systems.
Mccb Breaker,Mccb Circuit Breaker,Overload Protection Mccb,Moulded Case Circuit Breaker
ZHEJIANG QIANNA ELECTRIC CO.,LTD , https://www.traner-elec.com