Unified Control Algorithm Research Articles

Long-Horizon Sequential FCS-MPC Approaches for Modular Multilevel Matrix Converters

The Modular multilevel matrix converter (M3C) is a direct ac-ac power converter that presents several features such as scalable and flexible structure, high efficiency, fault-tolerant capability, and high power quality. However, this converter requires a complex control strategy to govern the cluster currents and balance the internal floating capacitor voltages among clusters and cells. To fulfill these requirements, this work proposes a long-horizon sequential finite-control-set model predictive control (sFCS-MPC). The resulting predictive strategy is formulated to perform both the local cell balancing control and to regulate cluster currents of the M3C in a unified control algorithm, considering the nonlinear and coupled dynamic model of each cluster. Additionally, the total available combinations and the average cell switching frequency are reduced. The proposed sFCS-MPC is implanted for a prediction horizon from one to four, and compared with some previous FCS-MPC approaches. Experimental results on a 3 kW prototype are provided to demonstrate the effectiveness and high-quality performance of the proposed strategy.

Reduced dynamics and geometric optimal control of nonequilibrium thermodynamics: Gaussian case

This paper introduces a control-theoretic formulation of nonequilibrium thermodynamic systems with Gibbs states of Gaussian distributions, i.e., thermodynamic systems characterized by Gaussian probability densities. The distinct features of the paper are three-fold. First, the dynamics of a thermodynamic system is studied by transferring the original state variable from the non-Euclidean and nonlinear manifold state space to a Lie group, and further to the dual space of a Lie algebra, which is endowed with vector space structures. Consequently, the resulting reduced dynamics significantly reduces the high nonlinearity appearing in the original non-Euclidean state space of a thermal process. Second, the obtained equations of motion interestingly indicate that thermodynamics can be naturally viewed as a generalization of rigid body motions, and this bridges control theory, thermodynamics, information theory, and rigid body dynamics. Third, the optimality conditions for the energy-minimum optimal control problem of probability densities are derived via geometric Pontryagin’s principle by regarding the reduced dynamics as dynamical constraints, and a unified control algorithm is developed. Finally, the proposed approach is applied to three different scenarios including two benchmark examples to demonstrate the applicability and effectiveness. The purpose of the paper is to provide a deeper understanding of thermodynamics from a control perspective, and also to draw intrinsic connections between control theory, thermodynamics, information theory, and rigid body dynamics.

Enhanced Natural Fault-Tolerant Model Predictive Current Control in Nine-Phase Motor Drives Under Open-Phase Faults

For the open-phase fault (OPF) tolerant operation of multi-phase motors based on model predictive current control (MPCC), the fault diagnosis and control scheme reconfiguration are difficult to avoid, which leads to the increase of control complexity. A natural fault-tolerant (NFT) MPCC method based on virtual voltage vectors (V <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$^{3}$</tex-math></inline-formula> ) can simplify this procedure and realize the fault-tolerant operation by using a unified control algorithm during pre- and post-faults. However, there is no effective control scheme to deal with the V <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$^{3}$</tex-math></inline-formula> shifting after the fault, which will lead to the control errors. To overcome this problem, an enhanced NFT-MPCC strategy is proposed in this paper. Firstly, this paper analyzes the causes of the control error in NFT, and elaborates the influence of V <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$^{3}$</tex-math></inline-formula> shifting on the current tracking performance. Then, a duty ratio optimization based on an PI regulator is proposed for the first time. After the fault occurs, the PI regulator automatically corrects the duty ratio calculation result to eliminate the control error caused by vector shifting, and the proposed method is versatile to different OPF scenarios. Compared with existing NFT-MPCC technologies, the experimental results show that the proposed method significantly suppresses the torque ripple in post-fault, and provides a satisfactory control performance before and after fault without the need of software reconfiguration.

A Comparative Study of Different Capacitor Voltage Control Design Strategies for Z-Source Inverter

The Z-source inverter (ZSI) is a prominent single-stage power conversion topology compared to traditional voltage source inverter (VSI)/ current source inverter (CSI). It adds the additional buck–boost capability to input voltage with improved reliability. However, the non-minimum phase (NMP) behavior is the major disadvantage of ZSI due to the existence of the right half plane (RHP) zero in the converter transfer functions. The existences of RHP zero destabilize the wideband feedback loops, which imply high gain instability and introduce the constraints on controller design. This paper presents different types of controllers and its design to maintain the required capacitor voltage with better transient response for non-minimum phase ZSI. Different tuning algorithms have been considered for both proportional–integral (PI), and integral–proportional (IP) control schemes. Also, the unified control algorithm has been implemented with both simple boost pulse width modulation (SBPWM) and a modified space vector pulse width modulation (MSVPWM) schemes to obtain the required capacitor voltage. The converter performance is comprehensively analyzed for different controllers and observations are tabulated. The complete analysis has been carried out using the MATLAB/Simulink environment for the proposed models.

Operation modes and control algorithms of anisotropic permanent magnet synchronous motor (IPMSM)

This paper represents control strategy of anisotropic permanent magnet synchronous motor (IPMSM) in the field-weakening region. Field weakening controller allows to increase maximum achievable speed with output torque reduction. Proposed control system consists of four general modes: MTPA (maximum torque per ampere), MC (maximum current), FW (field weakening), and MTPV (maximum torque per voltage) which must be chosen accordingly to motor speed, current and torque references. Operation point is found as an intersection of torque hyperbola and voltage ellipse curves in d-q motor’s current reference frame involving motor parameters’ limits. However, due to nonlinear dependence between torque and voltage equations, it is quite complicated to obtain both right control mode selection and reference output calculation. In order to solve this problem, a unified control algorithm adopted for wide speed and torque reference with online constraints calculation is proposed. Matlab/Simulink control model of PMSM motor and control system were designed in order to show developed strategy performance. Simulation results shows increasing of speed limit by more than 2.5 times related to nominal speed with high controller’s response. However, speed limit increasing leads to a decrease in motor’s output torque. Due to this fact, presented control strategy is not suitable for applications where nominal torque level is essential for all speed operation points.

A unified control strategy for active distribution networks via demand response and distributed energy storage systems

As part of the transition to a future power grid, distribution systems are undergoing profound changes evolving into Active Distribution Networks (ADNs). The presence of dispersed generation, local storage systems and responsive loads in these systems incurs severe impacts on planning and operational procedures. This paper focuses on the compelling problem of optimal operation and control of ADNs, with particular reference to voltage regulation and lines congestion management. We identify the main challenges and opportunities related to ADNs control and we discuss recent advances in this area. Finally, we describe a broadcast-based unified control algorithm designed to provide ancillary services to the grid by a seamless control of heterogeneous energy resources such as distributed storage systems and demand-responsive loads.

A New VSAS approach for Maximum Power Tracking for Renewable Energy Sources (RES)

This paper presents, after a comparative review of the most often used algorithms, a control methodology that clarifies the control problems and shows how to design a robust control to track the maximum power point in VSAS. This approach clarifies the rationale behind MPP dynamic tracking problem and shows how to be optimal. This technique called VSAS (Variable Structure Automated Systems) is compared with some techniques existing in literature like PO, HC, InCond and SMC approach. The maximum power is computed online using a Modified Enhanced Perturb and Observe (MEPO) algorithm and a Robust Unified Control Algorithm (RUCA). The proposed MPPT has several advantages: simplicity, high convergence speed, robustness and is independent on PV array characteristics. The algorithm is tested under various operating conditions. The results show that the MPPT is tracked even under sudden change of irradiation level.

Unified control algorithm for torques delivered to wheels of all-wheel-drive vehicles

This paper proposes the unified control algorithm for torques delivered to wheels of all-wheel-drive vehicles with “intellectual” transmission. The algorithm provides the determination of torques delivered to each wheel of multi-axis vehicle with minimal loss of power regarding to road conditions: solid surface or deformable ground. Results of calculations were confirmed by experimental research.

Research on Modify Proportion-Integration Control Strategy of Three-Phase Four-Leg Inverter

A general PI control algorithm is not a perfect solution to control ac signal. Because it is not able to eliminated steady-state error. The radical reason of the problem is investigated in few literatures. So the reason is explored, and an important conclusion is reached. The conclusion is that zero steady-state error control is obtained when the control algorithm has infinite gain at the excited frequency. Based on this conclusion, a modified PI algorithm is proposed for a four-leg inverter. The method that parameters of the modified PI algorithm are defined is given. To control the component in the 0 axis, the virtual component leading the component in the 0 axis by 90 degree is constructed. So the unified control algorithm is implemented in reference frame. The effectiveness of the proposed algorithm has been investigated and verified through simulation.

Formation Control of Mobile Robots with Active Obstacle Avoidance

In this paper, the formation control and obstacle avoidance problems are dealt with a unified control algorithm, which allows the follower to avoid obstacle while maintaining desired relative bearing or relative distance from the leader. In the known leader-follower robot formation control literature, absolute motion states of the leader robot are required to control the followers, which may not be available in some environments. In this research, the leader-follower robot formation is modelled and controlled in terms of the relative motion states between the leader and follower robots. The absolute motion states of the leader robot are not required in the proposed formation controller. Furthermore, the research has been extended to a novel obstacle avoidance scheme based on sensing the relative motion between robot and obstacle. Experimental investigation has been conducted using the platform consisted of three nonholonomic mobile robots and computer vision system, and the results have demonstrated the effectiveness of the proposed methods.

A unified approach to position and force control by fuzzy logic

This paper proposes a unified control strategy of position and force. The authors' technique is based on impedance control with fuzzy logic and realizes the smooth shift from position control to force control and vice versa. At first, a robust impedance controller based on a disturbance observer is shown, and the method to unify the position and the force control through one controller is described. Next, an algorithm to estimate the dynamic characteristics of the environment is shown, and a force tracking control using the estimated parameters is proposed. Finally, the unified control algorithm of position and force based on fuzzy logic is established. The validity of this method is confirmed by several experimental results.