Method for compensating for unknown network time delay in forward path of network cascade control system

Abstract

The invention provides a method for compensating for an unknown network time delay in a forward path of a network cascade control system and belongs to the technical field of network control systems. A real network data transmission process between forward path nodes is adopted to substitute for a network time delay compensation model between the nodes; the measurement, the observation, the estimation or the identification of a network data transmission unknown time delay between the forward path nodes are eliminated; and the requirement on the synchronization of a node clock signal is eliminated. By the method, the influence of the unknown network time delay on the stability of the system can be reduced and the control performance quality of the system is improved. The method is applied to the dynamic compensation and control of the unknown network time delay only existing in the forward path of the network cascade control system, in which the main and secondary controlled target mathematical models are known or unknown, the network has a certain amount of packets, and the network time delay can be more than several even over ten sampling periods.

Description

Technical field [0001] The present invention relates to a method for compensating the unknown network time delay of the forward path of a network cascade control system, and belongs to the technical field of network control systems. Background technique [0002] Networked control systems (Networked control systems, NCS) refers to the real-time closed-loop control system formed by connecting the various components of the control system (transmitter, controller and actuator, etc.) through the communication network. It is similar to the previous point-to-point control system. In comparison, network control systems have the advantages of resource sharing, easy installation and maintenance, and low overhead. However, due to the limited network bandwidth resources, there are inevitably problems such as network resource competition and network congestion in the network, resulting in data packet loss or transmission time Delay issues. [0003] In the actual industrial process control, the...

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Problems solved by technology

[0009] Since the denominator of the closed-loop transfer function shown in equation (1) includes the network delay τ 1 and τ 2 index term of and The existence of time delay will deteriorate the control performance quality of the system, and even cause the system to lose stability, and in severe cases, the system may fail.

[0010] The key to reducing the impact of delay on system stability is whether the network delay τ between the main transmitter (controller) node and the auxiliary transmitter (controller) node can be realized. 1 index term of and the network delay τ between the secondary transmitter (controller) node and the actuator node 2 index term of It is removed from the denominator of equation (1), that is, the exponential term of all network delays is not included in the closed-loop characteristic equation of the system, and then the compensation of network delay is realized. However, to realize the compensation of network delay, first, Know the size of the network delay. At present, the method commonly used at home and abroad is to measure the network delay τ 1 and τ 2 measurement to compensate for the time delay τ 1 and τ 2 The impact on system stability. However, due to the network delay τ 1 and τ 2 The accurate measurement of the node needs to meet the synchronization requirements of the node clock signal. If hardware is used to realize the complete synchronization of the node clock signal, a large economic investment is required; if the software is used to correct the clock signal, the correction signal may encounter Due to the influence of network delay, it is difficult to achieve complete synchronization of node clocks; if the method of estimating, observing, identifying or predicting network delay is used to obtain the size of network delay, the accurate probability distribution of network delay must first be known, or An accurate mathematical model, but because the network delay is related to factors such as specific network protocols, network load, and network topology, there may be deviations in the estimation, observation, identification or prediction of network delay.

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