External Loop Control Research Articles

Comprehensive compensation method for co‐phase power supply in electrified railways based on V/v transformer and electromagnetic single‐phase var compensator

AbstractTo solve the problem of negative‐sequence and reactive power in electrified railway, this paper proposes a comprehensive compensation method based on V/v transformer and electromagnetic single‐phase var compensator (ESVC) for co‐phase power supply. First, based on the principles of static var generator and single‐phase rotary phase shifting transformer, the topology and model of ESVC have been established, and the compensation mechanism has been analysed. Second, the topological structure and mathematical model of co‐phase power comprehensive compensation device (CPCD) are put forward based on the principles of V/v transformer and ESVC, and the operation mode of CPCD in multiple scenarios is designed. Then the strategy of CPCD with double closed loop control is analysed: corresponding compensation mode is selected according to negative‐sequence unbalance degree and expected power factor value. In this strategy, the compensated current output by ESVC is taken as the quantity of external loop control, and the rotation angle of ESVC is taken as the quantity of internal loop control to realize double‐closed loop control of CPCD. Finally, the comprehensive CPCD compensation model is built on the simulation platform and validated the accuracy of the mathematical model and the effectiveness of the control strategy.

Analysis of medium-frequency oscillation based on bifurcation theory and joint modelling of SVG and direct-drive wind turbine

With the expansion of wind power clusters in power system, medium and high frequency oscillations in wind farm area are preliminarily emerging. At present, linear analysis such as impedance analysis are mainly used to analyse the grid-connected oscillation of renewable energy generation. However, the explanation of the oscillation mechanism is not intuitive and does not take into account the nonlinearity of converter. Considering the influence of external loop control of SVG and direct-drive wind turbine on the medium-frequency characteristics of the parallel system, a reduced-order nonlinear model under voltage time scale is established. The conjoint analysis of Jacobi matrix, bifurcation diagram and phase space trajectory are applied to study the influence rule of machine-side output power and short-circuit ratio on the oscillation behaviour of the parallel system. In addition, the oscillation evolution process is analysed from the dynamic standpoint. It is found that the system operates on the limit-loop state when the medium-frequency oscillation occurs, which reveals the mapping relationship between the oscillation amplitude and the limit-loop trajectory. The experimental results ultimately validate the theoretical analysis conducted on the StarSim-HIL (hardware-in-the-loop) experiment platform.

Unified fractional indirect IMC-based hybrid dual-loop strategy for unstable and integrating type CSTRs

Abstract Controlling unstable and integrating type continuously stirred tank reactors (CSTRs) are more difficult due to the presence of poles in the right half and at the origin of the s-plane respectively. The existence of dead-time needs more efficient control requirements for CSTRs. In this work, a modified indirect fractional-order internal model control proportional-derivative (MIFOIMC-PD) decoupled dual-loop control strategy is suggested for unstable and integrating plants with dead time. The external-loop controller is designed using the MIFOIMC strategy for obtaining adequate servo performance. PD controller is designed such that it stabilizes the plant while disturbances occur. Decoupled nature of the suggested strategy allows this PD controller to be designed without considering the external-loop dynamics. Reference tracking and disturbance elimination capabilities of the suggested method are also quantitatively compared with reported methods. It is established that the suggested MIFOIMC-PD control architecture controls CSTRs more effectively than some lately reported schemes.

Control System Design for 16/6/8 Double-Stator Bearingless Switched Reluctance Motor

The 16/6/8 double-stator bearingless switched reluctance motor (DSBSRM) is used as the object of study in this paper. To solve the problem of torque and levitation force ripples in this motor, a control system direct force control (DFC) and direct instantaneous torque control (DITC) based on the torque sharing function (TSF) are proposed. With the strong nonlinearity and approximation capability of radial basis function neural networks, the torque and levitation force observer are designed. The observed torque and levitation forces are used as feedback for the internal loop control, which is combined with the external loop control to make a double closed-loop control. In order to further improve the output torque and system robustness and suppress the torque ripple in steady-state process, the motor winding method is optimized and a set of switching angles is added on the basis of TSF. The simulation results verify the effectiveness and superiority of the proposed control method. It effectively suppresses speed ripple and reduces torque and levitation force fluctuations and rotor radial displacement jitter.

Intelligent Regulation Method for a Controllable Load Used for Improving Wind Power Integration

Improving the safety and stability of power systems by adjusting the controllable load to improve the wind power integration has become a hot research topic. However, the methodology of accurately controlling the load and fundamentally improving the wind power integration capacity has yet to be studied. Therefore, this paper proposes an intelligent regulation method for a controllable load. This method takes the new energy consumption assessment as feedback, and it combines the wind power acceptance assessment and scheduling plan to form the internal and external loop control structure, and it derives the controllable load intelligent regulation architecture. The load curve is decomposed by an interactive load observer, and the load curve is adjusted by the interactive load controller according to a given standard, thereby improving the new energy acceptance capability. Finally, based on the actual grid operation data of a provincial power grid in Northeastern China, the source grid load balancing process and the interactive load regulation model of the wind power system are simulated. The above method verifies the validity and rationality of the proposed method.

Dynamic Switching of Two Degree-of-Freedom Control for Belt-Driven Servomechanism

This paper proposes a new two degree-of-freedom control structure such that the robustness control of a belt-driven servomechanism is adequately addressed. In conventional design approaches, a trade-off between robust stability and robust tracking performance is unavoidable because the control engineer must take different frequency regions into consideration. In this paper, a frequency-dependent switching control structure is proposed, where the feedback connection to the external-loop controller is dynamically switched between the outputs of the controlled plant and its nominal model. The disturbance attenuation at lower frequencies by the double-loop control, as well as the robust stability at higher frequencies through the reference feedforward control, can be achieved at one fixed two degree-of-freedom control structure. The feasibility of the proposed approach is verified by theoretical analysis and experimental results.

A double-loop structure in the adaptive generalized predictive control algorithm for control of robot end-point contact force

Robot force control is an essential issue in robotic intelligence. There is much high uncertainty when robot end-effector contacts with the environment. Because of the environment stiffness effects on the system of the robot end-effector contact with environment, the adaptive generalized predictive control algorithm based on quantitative feedback theory is designed for robot end-point contact force system. The controller of the internal loop is designed on the foundation of QFT to control the uncertainty of the system. An adaptive GPC algorithm is used to design external loop controller to improve the performance and the robustness of the system. Two closed loops used in the design approach realize the system׳s performance and improve the robustness. The simulation results show that the algorithm of the robot end-effector contacting force control system is effective.

Research on Electric Servo Loading System Based on Disturbance Observer

A novel double-loop control approach for reducing excess torque of the servo loading system based on disturbance observer is proposed.The mathematical model of the loading system is established by mechanism theory and the reasons causing the excess torque are analyzed, the nominal model and disturbance weighting function are determined based on an approximate method. Dis-turbance observer based the inner loop controller is designed by H ∞ mixed sensitivity method and the external-loop controller is designed as the classical PID contro ller. Both the simulation and experi-ments results show that disturbance observer is feasible and effectiv e to eliminate the excess torque, accuracy of the loading system is improved.

Virtual Reference Feedback Tuning (VRFT) design of cascade control systems with application to an electro-hydrostatic actuator

In this work an algorithm for direct design of cascade control system is presented. The algorithm is based on the Virtual Reference Feedback Tuning (VRFT) paradigm and allows tuning both the internal loop controller and the external loop control in a single shot based on an I/O data set collected in a single experiment on the plant. Application of this control tuning procedure will be performed on an Electro-HydroStatic Actuator (EHSA) prototype, a new generation of hydraulic actuator providing the main advantages of both mechanical and hydraulic actuators but reducing most of the drawbacks. Experimental validation is presented showing that the designed control system provides good control accuracy and robustness.

A new framework for two loop disturbance rejection control

In this paper, a new framework of a two loop disturbance rejection control and its design methodology are proposed. The framework consists of a robust internal-loop compensator (RIC) to eliminate disturbances and an external-loop controller to achieve nominal control performance. As the main contribution of this paper, we define the design problem of the RIC as a regulation control problem, then show that this new definition with the RIC structure provides more design flexibility and less implementation constraints, which allows us to design the RIC aggressively against a specific disturbance. This is verified through a comparative structural analysis with a disturbance observer (DOB) and an adaptive robust control (ARC). Two design examples of the RIC are given, along with practical issues that should be considered in the design procedure. The proposed framework is demonstrated by simulations and experiments.