With the expansion of the market and the diversification of customer needs, VFD products have been improving and increasing in functionality, integration and systemisation, and the emergence of special VFD products. It is understood that in recent years, the VFD market in China has maintained a growth rate of 12-15% and is expected to maintain a growth rate of over 10% for at least the next 5 years. The current growth rate of installed VFDs (electricity) in the Chinese market is actually around 20%. The VFD market is expected to saturate and mature in at least 10 years' time.
1. Intelligent
After the system is installed with an intelligent VFD, it is easy to operate and use, not so multi-functional settings, the working status display is obvious, fault diagnosis and troubleshooting can be achieved, and even automatic component conversion can be carried out. Internet remote monitoring can be used to realise multiple sets of VFDs linked by process flow, forming an optimised integrated VFD control system.
2. Specialisation
Specialised VFDs can be manufactured in a targeted manner according to the characteristics of a certain type of load, which not only helps to control the motor of the load economically and effectively, but also reduces manufacturing costs. For example: fan and pump VFDs, crane VFDs, lift control VFDs, tension control VFDs, air conditioning VFDs, etc.
3. Integration
VFDs selectively integrate relevant functional components such as parameter recognition systems, PID regulators, PLC controllers and communication units into the internal all-in-one machine, which not only enhances the functionality and increases the reliability of the system, but also effectively reduces the size of the system and the connection of external circuits. It is reported that an integrated combination machine for VFDs and motors has been developed, making the whole system smaller and more convenient to control.
4. Environmental protection
Protecting the environment and manufacturing "green" products is the new philosophy of mankind. In the future VFDs will focus more on energy saving and low pollution, i.e. minimising noise and harmonics to the grid and other electrical equipment during use.
5. The main circuit power switching components are self-closing, modular, integrated and intelligent, with increasing switching frequency and further reduction of switching losses.
6. VFD main circuit topology.
VFD network-side converters usually use 6-pulse converters for low-voltage small-capacity equipment, and multi-pulse converters above 12-pulse for medium-voltage large-capacity equipment. The load-side converter is usually a two-level bridge inverter for low-voltage small-capacity equipment and a multi-level inverter for medium-voltage large-capacity equipment. For transmission operating in four quadrants, in order to achieve VFD renewable energy back to the grid and save energy, the net-side converter should be a reversible converter, while a bi-directional power flow with dual PWMVFD appears. proper control of the net-side converter can make the input current close to a sinusoidal wave, reducing pollution to the grid. Such products are currently available for low and medium voltage VFDs.
7. Pulse width modulated converter VFD's can be controlled by sine wave pulse width modulation (SPWM) control, PWM control to eliminate specified harmonics, current tracking control and voltage space vector control (magnetic chain tracking control).
8. Advances in AC motor frequency control methods are mainly reflected in the development from scalar control to vector control and direct torque control with high dynamic performance as well as the development of vector control and direct torque control systems without speed sensors.
9. Microprocessor advances make digital control become the development direction of modern controllers: motion control system is a fast system, especially the high-performance control of AC motors need 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 introduced a DSP (digital signal processor) as the core, with the peripheral functions required for motor control circuit. DSP monolithic motor controller integrated in a single chip, greatly reducing the price, reduce the size, compact structure, easy to use, improve reliability. Compared to ordinary microcontrollers, the DSP has 10 ~ 15 times more processing power, thus ensuring superior control performance of the system.The digital control simplifies the hardware, the flexible control algorithm makes the control very flexible, complex control rules can be implemented, making the application of modern control theory in the motion control system a reality, easy to connect with the upper system for data transmission, facilitate fault diagnosis, strengthen the protection and monitoring function, making the system intelligent (such as the VFD with self-regulation function).
10. AC synchronous motors have become a new star in the field of AC speed control, especially permanent magnet synchronous motors. The motor has a brushless structure, a high power factor, high efficiency and a rotor speed that is strictly synchronised with the working frequency. There are two main types of synchronous motor frequency control systems, independent frequency control and automatic frequency control. In principle, an automatic frequency controlled synchronous motor is very similar to a DC motor. It replaces the mechanical commutator of a DC motor with a power electronic converter. For example, when the AC-DC-AC voltage is VFD, this is called a "commutatorless DC motor" or "BLDC motor". Conventional speed control systems for automatic inverter synchronous motors have rotor position sensors, but systems without rotor position sensors are under development. Vector control can also be used as a stand-alone inverter for synchronous motors, which is simpler than for asynchronous motors based on the vector control of the rotor field orientation.
In short, the development trend of VFD technology is towards intelligence, simple operation, perfect functionality, safety and reliability, environmental protection, low noise, low cost and miniaturisation.