CN109283916B - Data packet loss compensation method for multi-sensor networked control system - Google Patents
Data packet loss compensation method for multi-sensor networked control system Download PDFInfo
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Abstract
A compensation method for data packet loss of a multi-sensor networked control system comprises the following steps: step 1) in the initial state of a control system, a controller is switched to form a system model of the invention; step 2) a plurality of sensors in the control system respectively acquire state information of the control system, and the state information is respectively and independently sent to a controller end; step 3) after receiving the information sent by the sensor, the controller firstly judges whether the loss phenomenon of partial data packets occurs, if so, in order to maintain the stability of the control system, the lost data of the control system is predicted according to the system model switched in the step one; and 4) integrating the predicted sensor signal and the signal actually sent by the sensor by the controller to form a new state vector, calculating the control quantity, storing the formed state vector to the local, and then sending the calculated control quantity to the actuator.
Description
Technical Field
The invention relates to the technical engineering field, in particular to a control system which is provided with a plurality of sensors and realizes data exchange between the sensors and a controller through a network channel.
Background
As the information system and the physical system are becoming more closely related, the communication network also plays an increasingly important role in the engineering field. The close integration of traditional industrial control fields and communication technologies forms a special type of networked control system. Compared with the traditional control system, the control system can greatly reduce the cost of hardware configuration (such as wiring and the like), and in addition, the networked control system has the advantages that the traditional control system cannot compare favorably with the networked control system in terms of expansibility and a hardware system composition structure, so the rapidly developed networked control system becomes a research hotspot in the industrial field and the engineering field.
The networked control system is particularly advantageous because it is significantly different in its composition and structure from conventional control systems. In the conventional control system, information transmission among the three sensor controllers and actuators is carried out through a special line, and the defect is that signal lines are required to be connected among the three sensors and actuators for achieving information exchange among the three sensors and actuators, so that the wiring cost per se is a very large problem, and secondly, in terms of expansibility, the control system connected through the special line is limited in structural expansion, and the whole body is easily pulled. Therefore, the conventional control system is greatly limited in specific practical applications due to the structure of the control system, and the limitation may cause great trouble to users when more than one sensor data needs to be collected by one control system. The networked control system formed by the introduction of the communication channel solves the problems well in terms of hardware composition. The communication network includes the so-called ethernet and the like in addition to the more used CAN bus technology and DN technology of the industrial control network. With the existence of the communication channels, the signal transmission among the sensor controller and the actuator can be free from the influence of wiring, thereby solving the problems, in particular having the advantages incomparable to the traditional control system in expansibility, and in addition, benefiting from the advantages of the system architecture, the networked control system has the advantages of easy maintenance, easy data collection and the like. However, the communication channel may be affected by the communication channel itself during data transmission to cause unstable transmission, such as data packet loss or time lag, and such problems caused by the communication system may affect the stability of the control system to some extent.
Some methods and technologies applied to the field of networked control systems solve problems that may be caused during data packet transmission to some extent, but for a networked control system with a plurality of sensors, when each sensor transmits a data packet to a controller, the data packets may compete with each other or with other data, or a part of the data packets may be lost due to interference of an external electromagnetic environment. For such a networked control system composed of a plurality of sensors, there is no effective method to solve such a problem when a partial packet loss occurs, and a novel method is needed. The main object of the present invention is to solve such problems.
For a networked control system with multiple sensors, each sensor sends sensor data to the controller over a separate communication channel. In such a multi-path situation, due to the characteristics of the communication channel, part of the data packets are necessarily lost within a certain time, and therefore, for the controller, the data sent by all the sensors cannot be received within a sampling period in some cases. How to reduce the unstable phenomenon of the control system caused by the data packet loss is a main problem to be solved by the invention.
Disclosure of Invention
The present invention is directed to overcoming the above-mentioned drawbacks of the prior art and providing a method for compensating for packet loss in a multi-sensor networked control system.
The present invention provides a strategy that is significantly different from existing methods based on the method of simultaneous use of predictive compensation methods with controller-side data. The general can be summarized as follows:
a compensation method for data packet loss of a multi-sensor networked control system comprises the following steps:
step 1) in the initial state of a control system, a controller is switched to form a system model of the invention;
step 2) a plurality of sensors in the control system respectively acquire state information of the control system, and after the sensors acquire the information, the state information can be respectively and independently sent to a controller end;
step 3) after receiving the information sent by the sensor, the controller firstly judges whether the loss phenomenon of partial data packets occurs, if so, in order to maintain the stability of the control system, the lost data of the control system is predicted according to the system model switched in the step one;
and 4) integrating the predicted sensor signal and the signal actually sent by the sensor by the controller to form a new state vector, calculating the control quantity according to an improved model-based method, storing the formed state vector to the local, and sending the calculated control quantity to the actuator.
The above-described method will be further described below.
In step 1), after the controller receives data sent by the sensor, because the method of the invention is different from the traditional system model, the method firstly converts the model of the system at the controller end. Assume a general system of
Then the system model after conversion can be expressed as x (k +1) ═ ax (k) + bu (k), in the above equation,
in step 2), the sensors transmit data through the communication channel, and the transmission may be performed in a manner that each sensor has a separate communication channel to the controller, which is common when the sensors and the controller are geographically distant.
Step 3) after the controller receives the data signal sent by the sensor, firstly, the data signal is processed according to a formula
Predicting the signal of the missing sensor. In the above formula represent
The amount of the signal that is predicted is,
representing the semaphore at the last time saved by the controller. If the data of the ith sensor is lost, the prediction formula can be expressed as
Wherein
Representing the ith semaphore stored in the controller.
Step 4) the controller according to the formula
And calculating the control quantity of the system and sending the control quantity to the actuator. Herein, the
K is the feedback gain matrix.
The invention has the advantages that: the lost partial sensor data is compensated, so that the control quantity of the system can be calculated when the partial sensor data is lost, the performance of the system is improved, and compared with other methods, the method has higher convergence speed and smaller stability margin.
Drawings
FIG. 1 is a block diagram of a networked control system with multi-packet transmission that implements the method of the present invention;
FIG. 2 is a graph of loss of three sensor data for a networked control system having three sensors;
FIG. 3 is a state diagram of a networked control system with three sensors using the method of the present invention in numerical simulation under Matlab software;
FIG. 4 is a state diagram of a networked control system with three sensors simulated using the specialized network simulation toolkit Treutime.
Detailed Description
For a better understanding of the method of the present invention, reference is made to the following further description taken in conjunction with the accompanying drawings for the purpose of providing a better understanding of the reader and of the method.
The method comprises the following steps: in a control system, a model of a controlled object is reconstructed first, and as a result of the reconstruction, a general system model is used
Converted into x (k +1) ═ ax (k) + bu (k), the relationships among some mathematical expressions in the above formula are
The conversion is described in detail below in the case of a control system in which the data of the i-th sensor is represented by x at the k-th timei(k) Is shown corresponding to
Element c in (1)iSimultaneously reconstructing a state vector
Predicting the system quantity of the ith sensor. Assuming a sequence x of statesT(k) The jth element of (a) is
U inij. It is thus possible to construct a matrix of columns, where the columns are represented as
Step two: as shown, it is a structural diagram of a networked control system having a plurality of sensors, and in this step, the sensors 1-r adopt different state quantities respectively and are packaged and then sent to the controller through a communication network.
Step three: after receiving a data packet sent by a sensor, a controller firstly judges whether the sensor data packet is lost or not according to the following judgment basis:
wherein
If it is detected that a portion of the data packets are lost during transmission, the state of the lost sensor is predicted, and a specific prediction method is as follows. For a linear system can be expressed as
X herej(k) Is an incomplete data packet received by the controller, wherein
q represents the number of sensors. If it is used
Representing the sensor state reconstructed at time k +1, then
Can be expressed as a process of sensor data reconstruction, here
That is, the state information of the actual control quantity used at the last moment stored in the controller, and after the system state is rebuilt, the actually received state information and the predicted state information are based on
Vector containing all system states integrated into a new mixture
Here, the
Step four: after the controller obtains all the mixed sensor data, the controller calculates the control amount based on the state information. In the case of a linear system, for example,
is unfolded to form
After the controller calculates the control quantity u (k), the control quantity u (k) is sent to the actuator through the communication network, and after the actuator takes corresponding action according to the control signal, the sensor acquires relevant informationTo the controller.
The embodiments described in this specification are merely illustrative of implementations of the inventive concept and the scope of the present invention should not be considered limited to the specific forms set forth in the embodiments but rather by the equivalents thereof as may occur to those skilled in the art upon consideration of the present inventive concept.
Claims (1)
1. A compensation method for data packet loss of a multi-sensor networked control system comprises the following steps:
step 1) in the initial state of a control system, firstly, establishing a model of the system at a controller end; the process of modeling is represented as follows:
specifically, after the controller receives data sent by the sensor, the model of the system is converted at the controller end; the specific process is as follows:
for a generally discrete linear system
In other words, the system model after transformation can be expressed as
x (k +1) ═ ax (k) + bu (k), where,
step 2) a plurality of sensors in the control system respectively acquire one state information of the control system, and after the information acquisition of the sensors is finished, the state information is respectively and independently sent to the controller end, and the state x of the sensors is generally represented by the following formulaT(k)＝[x1(k),x2(k),…xr(k)]T；
The reason for this is mainly that the sensors are geographically isolated and distributed in different places, and the data sent from the sensors to the controller cannot be packed into one data packet, so these data packets have to be sent to the controller through separate communication channels, and further more than one communication channel exists between the sensors and the controller, but each separate channel can ensure the normal sending and receiving of the data packet, and there is a problem that more than one data packet is lost when multiple data packets transmit data in the communication channel;
step 3) after receiving the information sent by the sensor, the controller firstly judges whether the loss phenomenon of partial data packets occurs;
if the loss phenomenon of part of data packets occurs, in order to maintain the stability of the control system, predicting the lost data of the control system according to the corresponding system model switched by the content in the step 1), and reconstructing the system state; the detailed process of system state reconstruction can be expressed as follows:
for a typical discrete linear system,
x(k+1)＝Ax(k)+Bu(k)
x∈Rn,u∈Rn,A∈Rn×n,B∈Rn×m；
the first step of state reconstruction is to perform block processing on a system matrix, split a and B into block matrices of qxq and qx1, where q represents the number of sensors, and the specific process is as follows:
the information of the missing sensor can be obtained by the following equation:
wherein
For complete state information at the last moment in the system,
herein, the
The method comprises two parts, namely a predicted value of the system control quantity at the last moment and a measured value of the system actual at the last moment; step 4), integrating the predicted sensor signal and a signal actually sent by a sensor by a controller to form a new state vector;
then, the calculation of the control quantity is carried out according to an improved model-based method, the state vector is stored locally for the next use, and the control signal of the system at the current moment is calculated according to the following formula:
herein, the
K is a feedback gain matrix;
after the system calculates the current control signal u (k), u (k) is sent to the actuator through the communication network, and after the actuator takes corresponding action according to the control signal, the sensor collects relevant information and sends the information to the controller.
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