This site uniformly uses SPWM control technology for introduction for two reasons: one is to facilitate the comparison of different schemes; the other is because it is the most basic control technology. Other control technologies are derived from SPWM control technology.
With the development of control theory and functional technology, various microcontrollers with excellent performance have developed rapidly, and there have been many discrete control methods (they are being used). The control system can be divided into single-loop, double-loop and multi-loop control from the number of control feedback loops. Generally speaking, the more loops, the better the control effect; in principle, it can be divided into digital PID control, state feedback control, and deadbeat control. Control, single-cycle control, repetitive control, space phasor PWM control, sliding mode variable structure control, fuzzy control, neural network control, predictive control, hysteresis control, etc.
Digital PID control has good adaptability, simple algorithm, easy parameter setting, strong robustness, and easy to realize with single-chip microcomputer or DSP, so it has been widely used. However, it has two limitations: one is that the sampling and quantization error of the system reduces the control accuracy of the algorithm; the other is that the sampling and calculation delay makes the controlled system a system with pure time lag, resulting in the stability of the PID controller. The area is reduced, which increases the design difficulty.
Predictive control can achieve small output current distortion and strong anti-noise ability. However, because this algorithm requires accurate load models and circuit parameters, its robustness is poor, and the delay caused by numerical calculations is also in practical applications. It needs to face a problem.
Hysteresis control has the advantage of fast response speed. It is widely used in switching rectifiers and has relatively high stability. However, its disadvantage is that the switching frequency is not fixed, which makes filtering difficult, the reliability of circuit operation decreases, and the output voltage spectrum becomes worse. , Is not conducive to the improvement of system performance.
Deadbeat Control (Deadbeat Control) is a microprocessor-based PWM scheme. It calculates the pulse width of the next sampling period according to the state equation of the inverter system and the output feedback signal. Therefore, it can theoretically make the output voltage very close to the reference voltage in phase and amplitude, and the output voltage error due to load changes or nonlinear loads can be corrected in one switching cycle. But deadbeat control is a control method based on the precise mathematical model of the controlled object, which has poor robustness and large transient overshoot.
Sliding-Mode Variable Structure Control (Sliding-Mode Variable Structure Control) is a non-linear control whose control characteristic is the discontinuity of control. It can be used in linear systems as well as non-linear systems. The advantage is that it is not sensitive to parameter changes and external interference, and has strong robustness; the disadvantage is that it is very difficult to obtain a satisfactory sliding mode.
Repetitive Control is used to overcome the periodic distortion of the output voltage waveform caused by the rectifier-type nonlinear load. It is usually combined with other PWM control methods. The idea of repetitive control is to assume that the fundamental waveform distortion in the previous cycle will appear repeatedly at the same time in the next fundamental cycle. The controller first determines the required correction signal according to the error between the given signal and the feedback signal, and then in the next cycle. The signal is superimposed on the original control signal at the same time of the fundamental wave cycle to eliminate the repetitive distortion that will appear in each subsequent fundamental wave cycle.
Fuzzy Control belongs to the category of intelligent control. The design of the fuzzy controller does not require an accurate mathematical model of the controlled object, so it has strong robustness and adaptability, similar to traditional PD control. The advantage is that the response speed is fast, but the disadvantage is that the static characteristics are not satisfactory.
Neural network control is a control method that simulates the intelligent activities of the human brain nerve central system. Neural network has the advantages of nonlinear mapping ability, parallel computing ability and strong robustness. It has been widely used in the field of control, especially in the field of nonlinear systems. At present, certain achievements have been made in the structural design of neural networks and learning algorithms. However, due to the limitations of the hardware system, online control of the inverter output voltage waveform cannot be achieved at present. Most applications first use offline learning to obtain an optimized control law, and then use the obtained law to achieve online control.
Harmonic injection PWM technology: The utilization rate of the DC bus voltage has basically reached 100%. This method is to add zero-sequence harmonics or third harmonics to the sine modulation wave to flatten or dent the top of the sine wave, thereby achieving the purpose of improving the utilization rate of the DC voltage. Therefore, it can only be used for three-phase three-wire UPS systems. This method is very effective for voltage open-loop control, but in a closed-loop control system, the initial phase of harmonic injection must be consistent with the fundamental wave. In voltage instantaneous value control, the initial phase of the voltage fundamental wave cannot be accurately positioned, which makes it Application is restricted.
Space phasor PWM control has the advantages of small output voltage (current) distortion, high DC bus voltage utilization, and easy digital realization, and it has many applications.
The above-mentioned various control methods have their own advantages and disadvantages, so you can choose by yourself. At the same time, the use of different control methods to form a composite control program has also been practically applied and achieved relatively good results.