CN113985737A - Research on networked control system with time delay and packet loss - Google Patents

Abstract

The invention discloses a research on a networked control system with time delay and data packet loss. A novel prediction-based controller design is proposed for the random packet loss and time delay in the transmission channel of the networked control system. The sequence of packet losses is modeled as a Bernoulli process, compensated by a zero-sequence bracket (ZOH) based module. The state predictor is used to obtain the predicted state of the delay time. Considering the packet loss compensator and state predictor, a novel modified model predictive controller is designed and proposed. Then, using a logic programming approach, all possible scenarios are incorporated into the forecast. Therefore, the cost function is transformed into a simultaneous minimum linear matrix inequality (LMI) with constraints. Therefore, the toolbox YALMIP is adopted to finally solve this minimal programming problem.

Description

Research on Networked Control System with Time Delay and Packet Loss

technical field

The invention relates to the field of networked control systems, in particular to solving the problems of time delay and data packet loss of the networked control system by means of predictive control.

Background technique

In the past few decades, there has been a lot of interest in the research of networked control systems (NCSs) due to their wide application in unmanned aerial vehicles, intelligent transportation systems, mobile sensor networks, cloud computing, real-time systems, etc. It is well known that NCSs have various advantages, such as: low cost, easy installation and maintenance, and high data exchangeability.

However, unreliable communication networks and limited bandwidth lead to inevitable problems such as time delays and packet loss. Undoubtedly, these factors can greatly degrade the performance of NCSs and, even worse, may generate severe instability. For example, time delays can occur when data is exchanged between devices that are shared over a network. Additionally, packet loss can occur when packets are transmitted from the controller to the actuator through an unreliable communication channel. Therefore, it is necessary to study networked control systems with both time delay and packet loss.

SUMMARY OF THE INVENTION

Aiming at the problems of time delay and data packet loss in a networked control system, the invention discloses a research on a networked control system with time delay and data packet loss.

The technical scheme that the present invention solves the above-mentioned technical problems is:

The sequence of packet loss is modeled as a Bernoulli process, compensated by a zero-sequence bracket (ZOH) based module;

The state predictor is used to obtain the predicted state of the delay time;

Considering the packet loss compensator and the state predictor, a novel modified model predictive controller is proposed. Compared with the cost function of the general model predictive controller, the state variables are replaced by the predictors obtained by the state predictor;

The technical effect of the present invention is that: due to the problems of time delay and data packet loss in the networked control system, the existence of these problems will lead to performance degradation and system instability. Therefore, a packet loss compensator and a state predictor are used to make the networked control system The time delay problem and packet loss problem have been improved;

Description of drawings

Fig. 1 is the research principle block diagram of the networked control system with time delay and data packet loss proposed by the present invention

Fig. 2 is the networked control system after reconstruction proposed in the present invention

Detailed ways

The present invention will be further described in detail below in conjunction with the accompanying drawings.

As shown in FIG. 1 and FIG. 2 , the research principle block diagram of the networked control system with time delay and data packet loss proposed by the present invention and the reconstructed networked control system proposed by the present invention, the present invention is directed to the networked control system There are random packet loss and time delay in the transmission channel of , a novel prediction-based controller design is proposed. Considering both the packet loss compensator and the state predictor, a new modified model predictive controller is designed. By using the toolbox YALMIP to incorporate all possible scenarios into the prediction range, the cost function is transformed into a synchronous minimum linear matrix inequality with constraints. The specific steps are as follows:

Step 1: Assume a networked control system with time delay and packet loss as

where y(t) is the output of the networked control system; ρ _k is the transmission probability of the data packet from the controller to the actuator, ρ _k =1 indicates that the data packet is successfully transmitted from the controller to the actuator; on the contrary, ρ _k =0 is If the transmission fails, packet loss occurs; u _c (t) is a control input directly from the controller; t _d is the delay of the networked control system; x(t) is the state quantity of the networked control system at time t.

Step 2: The state quantity at the next moment can be obtained by formula (2).

At the same time, at the control input end, a zero-order keeper is proposed, so that when a data packet is lost, the transmitted control input data will not drop to zero, but will remain the same as last time, i.e.

u _d (k)=ρ _k u _c (k)+(1-ρ _k )u _d (k-1) (5)

where _ud (k) is the input variable when packet loss occurs.

Step 3: Build Augmented Matrix

For simplicity, formula (6) is abbreviated as:

Z(k+1)=A _zd (k)Z(k)+B _zd (k)u _c (k) (7)

in,

Step 4: Define the performance index of the system (7) as:

Where: e(k)=y(k)-r(k); r(k)--the reference signal of the kth step; Q, R--respectively positive semi-definite and positive definite weighting matrices.

Step 5: Incorporate all scenarios into the forecast:

Among them, β ₀ (k) and β ₁ (k) are uncertain variables. Finally, it is solved by utilizing the MATLAB toolbox YALMIP.

Claims (2)

1. The research on the networked control system with time delay and data packet loss proposed by the present invention, the present invention proposes a new type of prediction based on the situation that random packet loss and time delay exist in the transmission channel of the networked control system. Controller design. Considering both the packet loss compensator and the state predictor, a new modified model predictive controller is designed. By using the toolbox YALMIP to incorporate all possible scenarios into the prediction range, the cost function is transformed into a synchronous minimum linear matrix inequality with constraints. 2. According to the application object and control method of the invention example of claim 1, the packet loss compensator and the state predictor of the networked control system apply relevant data to the closed-loop control of the networked control system. The specific control method steps are as follows: Step 1: Assume a networked control system with time delay and packet loss as

where y(t) is the output of the networked control system; ρ _k is the transmission probability of the data packet from the controller to the actuator, ρ _k =1 indicates that the data packet is successfully transmitted from the controller to the actuator; on the contrary, ρ _k =0 is If the transmission fails, packet loss occurs; u _c (t) is a control input directly from the controller; t _d is the delay of the networked control system; x(t) is the state quantity of the networked control system at time t. Step 2: The state quantity at the next moment can be obtained by formula (2).

At the same time, at the control input end, a zero-order keeper is proposed, so that when a data packet is lost, the transmitted control input data will not drop to zero, but will remain the same as last time, i.e. u _d (k)=ρ _k u _c (k)+(1-ρ _k )u _d (k-1) (5) where _ud (k) is the input variable when packet loss occurs. Step 3: Build Augmented Matrix

For simplicity, formula (6) is abbreviated as: Z(k+1)=A _zd (k)Z(k)+B _zd (k)u _c (k) (7) in,

Step 4: Define the performance index of the system (7) as:

Where: e(k)=y(k)-r(k); r(k)--the reference signal of the kth step; Q, R--respectively positive semi-definite and positive definite weighting matrices. Step 5: Incorporate all scenarios into the forecast:

Among them, β ₀ (k) and β ₁ (k) are uncertain variables. Finally, it is solved by utilizing the MATLAB toolbox YALMIP.

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