In the industrial control system, the controller is an important device to realize the regulation and control of the controlled object. Among them, the proportional-integral (PI) controller is a commonly used controller, whose role is to process the error signal through the proportional and integral links in order to realize the precise control of the controlled object. According to the different connection methods of proportional and integral links, PI controllers can be categorized into two types: series-type PI controllers and parallel-type PI controllers. This paper will compare and analyze these two types of PI controllers.
I. Series PI controller
Series PI controller refers to the proportional link and integral link in series, that is, the error signal is first processed by the proportional link and then by the integral link.
The characteristics of series type PI controller are:
1. The outputs of the proportional and integral links are added together as the output of the controller. Therefore, the output of series PI controller is proportional to the size of the error signal and inversely proportional to the speed of change of the error signal.
2. The proportional gain and integral gain of the series PI controller can be adjusted independently, so it can be adjusted according to the actual needs.
3. The response speed of series type PI controller is faster, but there is overshooting phenomenon. When the error signal is large, the output of the controller will increase rapidly, resulting in the controlled object's response speed is too fast, and even the phenomenon of overshooting.
II. Parallel type PI controller
Parallel PI controller refers to the proportional and integral links are connected together in parallel, that is, the error signal is processed by the proportional and integral links at the same time.
The parallel type PI controller is characterized by:
1. The outputs of the proportional and integral links are added together as the output of the controller. Therefore, the output of the parallel PI controller is proportional to the size of the error signal and inversely proportional to the speed of change of the error signal.
2. The proportional gain and integral gain of the parallel PI controller can be adjusted independently, so it can be adjusted according to the actual needs.
3. The response speed of parallel type PI controller is slow, but there is no overshooting phenomenon. Because the proportional and integral links act on the error signal at the same time, the output of the controller will not increase rapidly, avoiding the occurrence of too fast response speed and overshooting phenomenon of the controlled object.
III. Comparison of series-type PI controller and parallel-type PI controller
1. Response speed: the response speed of the series-type PI controller is faster, while the response speed of the parallel-type PI controller is slower. This is because the proportional and integral links of the series PI controller are connected serially, and the processing time of the error signal is shorter; while the proportional and integral links of the parallel PI controller are connected in parallel, and the processing time of the error signal is longer.
2. Overshooting phenomenon: The serial PI controller has overshooting phenomenon, while the parallel PI controller does not have overshooting phenomenon. This is because when the proportional gain of the series PI controller is large, it will lead to a rapid increase in the output of the controller, which will cause the response speed of the controlled object to be too fast and the overshooting phenomenon occurs; and when the proportional gain of the parallel PI controller is small, it can avoid this situation.
3. Stability: the stability of the series-type PI controller is poor, and the stability of the parallel type PI controller is better. This is because the series-type PI controller proportional gain and integral gain is independent, when the proportional gain is too large or integral gain is too small, it is easy to cause system instability; and parallel PI controller proportional gain and integral gain is mutual influence, can better ensure the stability of the system.
4. Parameter adjustment: The proportional gain and integral gain of series PI controller can be adjusted independently, while the proportional gain and integral gain of parallel PI controller can also be adjusted independently. However, due to the existence of overshooting phenomenon in series PI controller, it is necessary to limit the proportional gain in practical application; while parallel PI controller does not have overshooting phenomenon, so it can be more flexible to adjust the proportional gain and integral gain.
In summary, the series PI controller and parallel PI controller have their own advantages and disadvantages. In practical applications, the appropriate type should be selected according to the characteristics of the controlled object and control requirements. If you need fast response and large control accuracy, you can choose series PI controller; if you need stable control performance and small overshoot, you can choose parallel PI controller. In addition, the control performance can be further improved by reasonable parameter adjustment and optimized design.