What is compensation in the control system?
A compensator is a control system component that regulates the operation of another system. Most of the time, this is accomplished by conditioning the system’s input or output. Compensators are divided into three categories: lag, lead, and lag-lead.
When a control system is tweaked to improve its performance, it may exhibit unexpected behavior (e.g., poor stability or even instability by increasing the gain value). To make the system behave as desired, it must be redesigned and a compensator, a device that compensates for the original system’s poor performance, must be added.
What are the types of compensation in the control system?
- Series Compensation or Cascade Compensation
- Feedback compensation or Parallel compensation
- State Feedback Compensation
Series Compensation or Cascade Compensation
Series compensation is the process of connecting a compensating circuit between the error detector and the plants.
Feedback compensation or Parallel compensation
In feedback compensation. Compensators are used in a feedback manner
State Feedback Compensation
This is a system that generates the control signal by feeding the state variables back into the system via constant real gains. The system is known as state feedback.
Control System Compensation Techniques
A compensating network is one that makes adjustments to compensate for system flaws. Compensating devices can be electrical, mechanical, or hydraulic in nature. The most common type of electrical compensator is an RC filter. The lead, lag network is the most basic network used for the compensator.
Various control system compensation techniques are
- Phase lead Compensation
- Phase Lag Compensation
- Phase Lag Lead Compensation
Phase lead Compensation
The term “lead network” refers to a system with one pole and one dominating zero (the zero that is closer to the origin than all other zeros). If we want to compensate for a dominating zero in a control system, we must use the lead compensation network.
The phase lead network’s basic requirement is that all of the network’s poles and zeros must lie on the (-)ve real axis, interlacing each other with a zero at the origin of the nearest origin.
Effect of Phase Lead Compensation
- Kv, the velocity constant, rises.
- At the gain crossover frequency, the slope of the magnitude plot decreases, indicating that relative stability improves and error decreases because the error is proportional to the slope.
- The phase margin widens.
- The response time shortens.
Advantages of Phase Lead Compensation
- It increases the system’s speed by shifting the gain crossover frequency to a higher value.
- Because phase lead compensation is present, the system’s maximum overshoot is reduced.
Disadvantages of Phase Lead Compensation
Steady-state error is not improved.
Phase Lag Compensation
A phase lag network is a system that is a combination of one dominant pole and one zero (The dominating pole is the one that is closest to the origin of all the other poles). We must choose a lag compensation network if we want to add a dominating pole for compensation in a control system.
The phase lag network’s basic requirement is that all of the network’s poles and zeros must lie in the (-)ve real axis, interlacing each other with a pole located or the nearest to the origin.
The phase lag compensation network’s circuit diagram is shown below.
Effect of Phase Lag Compensation
- The frequency of gain crossovers rises.
- Bandwidth is reduced.
- The phase margin will be raised.
- Because of the reduced bandwidth, response times will be slower, and the rise and settling times will be longer.
Advantages of Phase Lag Compensation
- Low frequencies and high frequencies are attenuated using a phase lag network.
- The steady-state accuracy improves due to the presence of phase lag compensation.
Disadvantages of Phase Lag Compensation
The system’s speed will decrease
Phase Lag Lead Compensation
Design specifications may not be met with a single lag or lead compensation. Lead compensation provides a quick response but not enough phase margin for an unbalanced system, whereas lag compensation stabilizes the system but does not provide enough bandwidth. As a result, multiple compensators in a cascade are required.
Advantages of Phase Lag Lead Compensation
- The system’s speed increases as a result of the presence of a phase lag-lead network, which shifts the gain crossover frequency to a higher value.
- The accuracy of the phase lag-lead network is improved due to the presence of phase lag.
What is the need for compensation in the control system?
- Compensating networks are used to achieve the system’s desired performance. Feedforward path gain adjustment is used to apply compensating networks to the system.
- Make a shaky system stable by compensating for it.
- To reduce overshoot, a compensating network is used, and these compensating networks improve the system’s steady-state accuracy. One thing to keep in mind is that as the steady-state accuracy improves, the system becomes more unstable.
- Compensating networks introduce poles and zeros into the system, causing changes in the system’s transfer function. As a result, the system’s performance specifications change.
What is the need for a compensator in the control system?
The compensator is used in the control system to improve system dynamics, open-loop system characteristics, and stability.
The lead/lag compensator, also known as a phase compensator, is used to improve the system’s stability.