Suppliers of frequency converter supporting equipment remind you that frequency converters are power converters in motion control systems. The current motion control system is a technical field that involves multiple disciplines, and the overall development trend is: AC driven, high-frequency power converters, digital, intelligent, and networked control. Therefore, as an important power conversion component of the system, frequency converters have developed rapidly by providing controllable high-performance variable voltage and variable frequency AC power sources.
In the 21st century, the substrate of power electronics has been transformed from Si (silicon) to SiC (silicon carbide), ushering in an era of high voltage, large capacity, high frequency, modular components, miniaturization, intelligence, and low cost for new power electronic devices. Various new electrical equipment suitable for variable frequency speed regulation is currently being developed and researched. The rapid development of IT technology and the continuous innovation of control theory will affect the development trend of frequency converters.
With the expansion of the market and the diversification of user demands, the functions of domestic frequency converter products are constantly improving and increasing, with higher integration and systematization, and some specialized frequency converter products have already emerged. It is reported that in recent years, the market for frequency converters in China has maintained a growth rate of 12-15%, and it is expected to maintain a growth rate of over 10% for at least the next 5 years. At present, the growth rate of installed capacity (power) of frequency converters in the Chinese market is actually around 20%. It is expected that the frequency converter market will reach saturation and gradually mature at least 10 years later.
1. Intelligence
After the intelligent frequency converter is installed in the system, there is no need to perform so many functional settings, it can be easily operated and used, with obvious working status display, and can achieve fault diagnosis and troubleshooting, and even automatic component conversion. The Internet can be used for remote monitoring to realize the linkage of multiple inverters according to the process procedures, forming an optimized inverter integrated management and control system.
2. Specialization
Based on the characteristics of a certain type of load, manufacturing specialized frequency converters is not only beneficial for economically and effectively controlling the motor of the load, but also can reduce manufacturing costs. For example, frequency converters for fans and pumps, frequency converters for lifting machinery, frequency converters for elevator control, frequency converters for tension control, and frequency converters for air conditioning.
3. Integration
The frequency converter selectively integrates relevant functional components such as parameter identification system, PID regulator, PLC controller, and communication unit into an integrated machine, which not only enhances functionality and increases system reliability, but also effectively reduces system volume and minimizes external circuit connections. According to reports, an integrated combination machine of frequency converter and electric motor has been developed, making the entire system smaller in size and easier to control.
4. Environmental Protection
Protecting the environment and manufacturing 'green' products is a new concept for humanity. In the future, frequency converters will focus more on energy conservation and low pollution, that is, minimizing the pollution and interference of noise and harmonics on the power grid and other electrical equipment during use.
5. The self turn off, modularization, integration, and intelligence of the power switching components in the main circuit have continuously increased the switching frequency and further reduced the switching losses.
6. In terms of the topology structure of the main circuit of the frequency converter:
The grid side converter of the frequency converter often uses a 6-pulse converter for low voltage and small capacity devices, while a multiplexed 12 pulse or more converter is used for medium voltage and large capacity devices. Load side converters often use two-level bridge inverters for low-voltage small capacity devices, while multi-level inverters are used for medium voltage large capacity devices. For the transmission of four quadrant operation, in order to achieve regenerative energy feedback to the grid and save energy, the grid side inverter should be a reversible inverter. At the same time, a dual PWM inverter with bidirectional power flow has emerged. Proper control of the grid side inverter can make the input current approach sine wave and reduce pollution to the grid. At present, both low and medium voltage frequency converters have such products.
7. The control methods for pulse width modulation variable voltage inverters can include sine wave pulse width modulation (SPWM) control, PWM control to eliminate specified harmonic orders, current tracking control, and voltage space vector control (magnetic flux tracking control).
8. The progress of frequency conversion adjustment control methods for AC electric motors is mainly reflected in the development of vector control and direct torque control systems without speed sensors, which have shifted from scalar control to high dynamic performance vector control and direct torque control.
9. The advancement of microprocessors has made digital control the development direction of modern controllers: motion control systems are fast systems, especially high-performance control of AC motors that require storage of various data and fast real-time processing of large amounts of information. In recent years, major foreign companies have successively launched DSP (Digital Signal Processor) based cores, combined with peripheral functional circuits required for motor control, integrated into a single chip called DSP single-chip motor controller. The price is greatly reduced, the volume is reduced, the structure is compact, the use is convenient, and the reliability is improved. Compared with ordinary microcontrollers, DSP has increased its digital processing power by 10-15 times to ensure superior control performance of the system.
Digital control simplifies hardware, and flexible control algorithms provide great flexibility in control, enabling the implementation of complex control laws and making modern control theory a reality in motion control systems. It is easy to connect with upper level systems for data transmission, facilitates fault diagnosis, strengthens protection and monitoring functions, and makes the system intelligent (such as some frequency converters having self-adjusting functions).
10. AC synchronous motors have become a new star in AC adjustable transmission, 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. There are two main types of synchronous motor variable frequency speed control systems: external control variable frequency and automatic control variable frequency. The principle of self controlled variable frequency synchronous motor is very similar to that of DC motor, replacing the mechanical commutator of DC motor with power electronic converter. When using AC-DC-AC voltage converter, it is called "DC commutatorless motor" or "brushless DC motor (BLDC)". The traditional self controlled variable frequency synchronous machine speed control system has a rotor position sensor, and a system without a rotor position sensor is currently being developed. The variable frequency control method of synchronous motors can also use vector control, which is simpler than asynchronous motors in terms of vector control oriented according to the rotor magnetic field.
In short, the development trend of frequency converter technology is towards intelligence, easy operation, sound functionality, safety and reliability, environmental protection, low noise, low cost, and miniaturization.