Aug 29, 2020
Six characteristics of inverter development
The frequency converter is the power converter in the motion control system. Today's motion control systems include technical fields of multiple disciplines. The general development trend is: AC drive, high frequency power converter, digital control, intelligent and networked control. Therefore, the frequency converter, as an important power conversion component of the system, provides a controllable high-performance variable-voltage and variable-frequency AC power source and has developed rapidly. With the application of new power electronic devices and high-performance microprocessors as well as the development of control technology, the performance-to-price ratio of frequency converters is getting higher and higher, and the volume is getting smaller and smaller, and manufacturers are still constantly improving the reliability of the frequency converter. New efforts are being made to further reduce the size and weight, improve performance, multi-function, and pollution-free. The performance of the frequency converter depends on the impact of the harmonics of its output AC voltage on the motor; the harmonic pollution on the grid and the input power factor; and the energy loss (ie efficiency) of the inverter. Here only take the AC-DC-AC inverter with a large quantity and a wide range as an example to illustrate its development trend: self-shut-off, modularization, integration, and intelligence of the main circuit power switching components; the switching frequency continues to increase, and the switching The loss is further reduced. The topology of the inverter main circuit. The grid-side converter of the frequency converter often uses 6-pulse converters for low-voltage and small-capacity devices, and uses multiple 12-pulse converters for medium-voltage and large-capacity devices. Load-side converters often use two-level bridge inverters for low-voltage and small-capacity devices, and multi-level inverters for medium-voltage and large-capacity devices. For the rotation of four-quadrant operation, in order to realize the regenerated energy of the inverter to feed back to the grid and save energy, the grid-side converter should be an invertible converter. At the same time, dual PWM inverters with bidirectional power flow have appeared. Proper control of the current device can make the input current close to a sine wave and reduce the pollution to the power grid. The control method of pulse width modulation variable voltage inverter can adopt sine wave pulse width modulation control, PWM control to eliminate specified harmonics, current tracking control, and voltage space vector control (flux tracking control). The progress of AC motor variable frequency adjustment control methods is mainly reflected in the development of vector control and direct torque control from scalar control to high dynamic performance and the development of speed sensorless vector control and direct torque control systems. The advancement of microprocessors makes digital control the development direction of modern controllers. The motion control system is a fast system, especially the high-performance control of AC motors needs to store a variety of data and process a large amount of information quickly and in real time. In recent years, major foreign companies have launched cores based on DSP (digital signal processor), equipped with peripheral function circuits required for motor control, and integrated in a single chip called DSP single-chip motor controller. It is greatly reduced, the volume is reduced, the structure is compact, the use is convenient, and the reliability is improved. Compared with ordinary single-chip microcomputers, DSP can increase the processing capacity of digital operation by 10 to 15 times, which can ensure that the system has better control performance. Digital control simplifies the hardware, flexible control algorithm makes the control very flexible, can realize complex control laws, make the application of modern control theory in the motion control system a reality, easy to connect with the upper system for data transmission, and facilitate fault diagnosis , Strengthen the protection and monitoring functions, make the system intelligent (for example, some inverters have self-adjustment function). AC synchronous motors have become a new star in AC adjustable rotation, especially permanent magnet synchronous motors. The motor has a brushless structure, high power factor and high efficiency, and the rotor speed is strictly synchronized with the power frequency. Synchronous motor frequency conversion speed regulation system has two major types: separate control frequency conversion and automatic control frequency conversion. The principle of automatic frequency conversion synchronous motor is very similar to DC motor. Power electronic converter replaces the mechanical commutator of DC motor, such as AC- DC-AC variable voltage frequency converter is called "DC commutatorless motor" or "brushless DC motor". The traditional automatic control variable frequency synchronous motor speed control system has a rotor position sensor, and a system without a rotor position sensor is now being developed. The other control frequency conversion method of synchronous motor can also adopt vector control, and its vector control based on the rotor field orientation is simpler than asynchronous motor.