Adaptive Wide-Area Damping Control Scheme for Smart Grids with Consideration of Signal Time Delay

Remote signals available from the wide-area monitoring system could be used to enhance the stability of large interconnected power systems with the help of a wide-area damping controller (WADC). Uncertainty in system parameters and signal transmission time delay are the major factors, which could worsen the damping effect and deteriorate the system stability. This study presents a novel adaptive wide-area damping control scheme in which oscillation modes will be identified online using stochastic subspace identification for online tuning of the WADC structure and parameters using the residue method. A simple and practical signal time delay compensation algorithm will also be proposed to measure and compensate the time delay in each wide-area control signal so as to eliminate the effects of signal time delay on the proposed adaptive WADC. The effectiveness and robustness of the proposed adaptive wide-area damping control scheme have been verified with simulation studies on the IEEE 16-generator 5-area test system under various disturbance scenarios.

In this paper, the energy method is employed to analytically investigate the influence of time delay in signal transmission on synchronization between two coupled FitzHugh-Nagumo (FHN) neurons. Unlike pre-existing methods that deal with synchronization problems, our major idea is to consider the change rate of the energy of the synchronization error system, since the original system’s synchronization is equivalent to the disappearance of the energy of the error system. In rewriting the original coupled system in the corresponding energy coordinates based on the energy method, we find that the change rate of energy of the error system can be divided into two parts (periodic and non-periodic). The synchronization criterion for the original system can then be obtained by letting the non-periodic part of the change rate of the energy be less than zero. The correctness of the analysis is illustrated with numerical simulations. Our analytical results show that time delay in signal transmission has very significant effects on the synchronization between two FHN neurons. If the time delay in signal transmission is not taken into account in the two coupled FHN neurons, synchronous spikes cannot be achieved in the system for any given coupling strength. By adjusting the value of the time delay in signal transmission, the neural system can freely switch between neural rest and synchronous spikes. This means that time delay in signal transmission is crucial for the occurrence of synchronous spikes in the FHN neural system, which contributes to our understanding of the interaction between neurons. We analytically show the influence of the time delay on the synchronization between two FHN neurons, which was seldom considered by other researchers.

Design and implementation of a measurement-based adaptive wide-area damping controller considering time delays

Influence of the time delay of signal transmission on synchronization conditions in drive-response systems

Wireless Networked Control System (WNCS) is made up of an actuator, sensor, and controller that communicates through a wireless network rather than typical point-to-point cable connections. Lower maintenance costs, greater flexibility, and increased safety are the main WNCS advantages, so as a result, it has attracted a lot of researchers. Nevertheless, time delays and packet losses in wireless data transmission are classified as complicated problems, which impair WNCS output accuracy and may influence the overall system stability. Integer-Order PI-PD (PI-PD) and Fractional-Order PI-PD (FOPI-FOPD) controllers are proposed to reduce the impact of the control signal transmission's time delay and improve system performance. Matlab Simulink and True-time simulator are used to simulate the WNCS, and ZigBee protocol is used in transceiving the control signal between the controller and the system. Rotary Inverted Pendulum (RIP) acted as the controller's objective. The Grey Wolf Optimization (GWO) technique is utilized to evaluate the best controller parameters. Xbee S2 modules are used to implement the signal transmission process over ZigBee protocol. The FOPI-FOPD controller outperforms the PI-PD controller in the simulation and experimental results in decreasing the influence of time delay on system stability

In this paper, approximate lag synchronization (LS) and anticipating synchronization (AS) between two unidirectionally coupled hyperchaotic Chen systems without time-delay coupling are analytically investigated. Firstly, the synchronization condition for exact LS in two unidirectionally coupled hyperchaotic Chen systems with time delay in signal transmission is analytically obtained. Under such conditions, approximate LS and AS are discussed by replacing the true time-delay terms with their Taylor expansions up to the third order.Differently from other research studies, the condition for exact LS is derived by regarding LS as a special type of generalized synchronization (GS), which has nothing to do with the value of the time delay. It is convenient to individually change the value of the lag and anticipation time of approximate LS and AS without considering the synchronization condition. Our study shows the power of a new method for recreating the past signals or predicting the future signals of a hyperchaotic Chen system by using its current signals. The results provide a simple way to eliminate the negative effects of time delay in the signal transmission between two hyperchaotic systems.

Remote signal transmission time delays are the major factors affecting damping performance of wide-area damping controller (WADC), and it even deteriorates small signal stability of large-scale power system. Traditional time delay damping controller based on linear matrix inequalities (LMI) has relatively large conservatism and complexity. Conventional time delay compensation controller suffers large amount of simulations and there is no general formulation to determine control parameters. In this paper, the design method of wide-area time-delay damping controller based on parametric Lyapunov theory is derived. The explicit expression of the controller parameter value associated with the time delay is determined. The controller is determined according to the system stability original definition (The system energy function is finite and positive and its first derivative is negative), which avoids complex matrix inequalities cyclic solution and reduces the conservatism of the controller. Moreover, it can directly give simple and explicit control law and specific control parameters, which enable this method to adjust its parameters online according to the exact time delay obtained by GPS. Case study is undertaken based on the New England ten-machine 39-bus power system. Compared with the free weight matrix controller, which is a kind of LMI-based design strategy with excellent performance, the effectiveness and superiority of the proposed design method for WADC are verified.

Low frequency oscillation occurs frequently in power systems. Wide-area damping controller (WADC) based on Wide-Area Measurement System (WAMS) can effectively suppress inter-area low frequency oscillations. However, with the introduction of global signals, time delays are inevitable. Electromagnetic torque analysis method(ETA) can establish the analytic relation between electromagnetic torque coefficients and control parameters of power component, which is facilitative to analyze small signal stability. Considering that WADC has inherent characteristics of multiple time delays, based on the ETA for equivalent two-machine system, this paper deduces the general mathematics expression among electromagnetic torque coefficients, WADC parameters and time delays. The influence mechanism of time delay on electromagnetic torque coefficients and small signal stability is further analyzed. Based on these analysis, performance of damping control of WADC can be improved, on one hand, time-delay small signal stability region is established under fixed WADC parameters, on the other hand, if small signal stability is not achieved under the given WADC parameters due to set of the time delays, optimization scheme is proposed to carry out parameters coordination according to the measured time delays. Finally, taking two time delays as an example, the paper verifies the effectiveness of the proposed method by comparing the system dynamic performance considering two time delays with the system only considering single time delay and the system without time delay in a two-area four-machine power system.

With the development of the Wide-Area Measurement System (WAMS), researchers has proposed different kinds of Wide-Area Damping Controller (WADC) to suppress inter-area power oscillations. However time delays in WAMS communication networks have made it less effective to improve dynamic stability of large-scale power system. Traditional methods such as modal analysis and simulation cannot study the time delay impacts on the dynamic characters theoretically and obtain boundary conditions of stability for the optimization of damping controllers. To solve these problems, this paper studies the influence of time delays on the inter-area dynamic characters using two-machine Electric Torque Analysis (ETA) method. The mathematical relationships between the time delay, electric torque coefficients, and damping ratio of a power system installed with a WADC are explored. The stability criteria of inter-area mode and the delay margin are studied. An optimization scheme of WADC is proposed to implement fast online damping control considering time-varying delays. This method is verified in a four-generator-two-machine benchmark installed with a SVC-based WADC. Simulation results show the proposed scheme can improve the robustness of WADC against time delays and has advantages over traditional methods.

This paper presents a new design of a scattering transformation-based wide-area damping controller for static synchronous series compensator (SSSC) to enhance power system stability in the presence of communication latency. The proposed control approach is comprised of a classical structure in addition to two scattering transformation ports. These ports are inserted between the power system and the wide-area damping controller (WADC) to regulate the signal exchange. Since the WADC is a centralized controller, the time delay imperfections are considered in the design stage. The proposed controller design is formulated as an optimization problem where the controller parameters are optimized using the particle swarm optimization (PSO) algorithm. The proposed controller improves the system damping performance due to the achieved time delay compensation. The proposed controller's effectiveness is demonstrated by implementing the controller in several case studies under different disturbance scenarios. The proposed controller performance is benchmarked with the classical WADC based on the lead-lag structure. The results confirm the robustness of the proposed WADC against time delay uncertainty. The proposed controller's efficacy is confirmed to reduce the time delay, resulting in better power system stability.

Integrated motor-transmission (IMT) powertrain systems are widely used in future electric vehicles due to the advantages of their simple structure configuration and high controllability. In electric vehicles, precise speed tracking control is critical to ensure good gear shifting quality of an IMT powertrain system. However, the speed tracking control design becomes challenging due to the inevitable time delay of signal transmission introduced by the in-vehicle network and unknown road slope variation. Moreover, the system parameter uncertainties and signal measurement noise also increase the difficulty for the control algorithm. To address these issues, in this paper a robust speed tracking control strategy for electric vehicles with an IMT powertrain system is proposed. A disturbance observer and low-pass filter are developed to decrease the side effect from the unknown road slope variation and measurement noise and reduce the estimation error of the external load torque. Then, the network-induced delay speed tracking model is developed and is upgraded considering the damping coefficient uncertainties of the IMT powertrain system, which can be described through the norm-bounded uncertainty reduction method. To handle the network-induced delay and parameter uncertainties, a novel and less-conservative Lyapunov function is proposed to design the robust speed tracking controller by the linear matrix inequality (LMI) algorithm. Meanwhile, the estimation error and measurement noise are considered as the external disturbances in the controller design to promote robustness. Finally, the results demonstrate that the proposed controller has the advantages of strong robustness, excellent speed tracking performance, and ride comfort over the current existing controllers.

The time delay of signal transmission in the bilateral teleoperation system remains to be a severe problem for stability and transparency, despite that various methods have been proposed for alleviating the effects. Among those approaches, the neural networks (NN) based method is model-free and adaptable for system uncertainties and disturbances, which have shown great potential for teleoperation signal prediction. In this study, firstly, the concept of Passive Prediction and Active Prediction is clarified, i.e., Passive Predictor makes prediction given the delayed signals, while Active Predictor gives prediction based on raw signals before transmission. Secondly, a new Long Short-Term Memory (LSTM) based Bilateral Active Estimation Model (BAEM) is proposed for estimating the time delay in both directions of the teleoperation system, and the condition and proof of the model stability are provided. Based on the proposed model, another LSTM-based Active predictor is used thereafter, to predict the teleoperation signals with as long time in advance as the estimated time delay provided in its transmission direction. The proposed prediction method is independent of dynamic systems, hence it is applicable for general teleoperation scenarios. Moreover, any predictive methods other than LSTM can be embedded in the model, showing great extensibility.

Summary form only given. The usage of remote signal obtained from a widearea measurement system (WAMS) introduces time delays to a wide-area damping controller (WADC), which would degrade system damping and even cause system instability. The time delay margin is defined as the maximum time delay under which a closed-loop system can retain stable. In this paper, the delay margin is introduced as an additional performance index for the synthesis of classical WADCs for flexible AC transmission systems (FACTS) devices to damp inter-area oscillations. The proposed approach includes three parts: a geometric measure approach for selecting feedback remote signals, a residue method for designing phase compensation parameters, and a Lyapunov stability criterion and linear matrix inequalities (LMI) for calculating the delay margin and determining the gain of the WADC based on a tradeoff between damping performance and delay margin. Three case studies are undertaken based on a four-machine two-area power system for demonstrating the design principle of the proposed approach, a New England 10-machine 39-bus power system and a 16-machine 68-bus power system for verifying the feasibility on larger and more complex power systems. The simulation results verify the effectiveness of the proposed approach on providing a balance between the delay margin and the damping performance.

This paper investigates the global lagged finite-time synchronization of the master-slave Lur’e systems subject to time delay of signal transmission. By designing a variable-substitution and feedback controller, a master-slave finite-time synchronization scheme for the Lur’e systems with time delay is built up. Two delay-independent global lagged finite-time synchronization criteria are proved in the forms of linear matrix inequalities (LMIs), and the corresponding settling time of synchronization is analytically estimated. The obtained LMI criteria are applied to Chua’s oscillators, obtaining some easily implemented algebraic criteria under various single-variable-substitution and feedback controller, which are then optimized to improve their conservative property. Finally, several numerical examples are illustrated to verify the effectiveness of the optimized criteria.

In this paper, the tracking control of relative motion of two spacecraft in a leader-follower form is investigated. The time delay of signal transmission between the two spacecraft and external disturbances are explicitly considered. For time delay, we model the relative motion in a linear form and utilize the Lyapunov-Krasovskii functional combining with free-weighting matrix method to complete the stability analysis. The external disturbances are then attenuated in the H ∞ sense. Besides, we take the integral quadratic of the tracking error and control input as the tracking performance index, which is in the H 2 sense. A set of linear matrix inequalities (LMIs) is then derived incorporating all the design requirements and cone complementarity linearization technique is used to solve the LMIs. The theoretical analysis is completed based on the general motion model of circular reference orbit for leader spacecraft and numerical simulation results demonstrate the validity of the designed controller.