Voltage-based Control Research Articles

Busbar voltage-based control strategy for energy flexibility in farmhouse coupled to photovoltaic systems

Control strategy is a crucial technology for solving the mismatch between supply and demand in photovoltaic (PV) systems. Model predictive control (MPC) has high accuracy but high system complexity and cost, thus limiting its application. This study proposes a busbar-voltage-based control strategy and applies it to a farmhouse equipped with a PV system in Northern China. The core of the busbar-voltage-based control strategy is that the converter in the system automatically adjusts the operating conditions to ensure that the busbar voltage is stabilized within a specific range. Field test results revealed that the busbar voltage-based control strategy improved the energy flexibility of the farmhouse PV system. We developed a predictive model for the control system and analyzed its performance during different seasons. The simulation results confirmed that the farmhouse PV system's energy flexibility, self-satisfaction rate, and self-consumption rate under the proposed control strategy were similar to those under the conventional MPC approach. This study provides a novel control approach that enables MPC-level performance without the need for communication systems and controllers, which reduces costs and helps promote PV systems.

Application of Modeling and Control Approaches of Piezoelectric Actuators: A Review

Piezoelectric actuators find extensive application in delivering precision motion in the micrometer to nanometer range. The advantages of a broader range of motion, rapid response, higher stiffness, and large actuation force from piezoelectric actuators make them suitable for precision positioning applications. However, the inherent nonlinearity in the piezoelectric actuators under dynamic working conditions severely affects the accuracy of the generated motion. The nonlinearity in the piezoelectric actuators arises from hysteresis, creep, and vibration, which affect the performance of the piezoelectric actuator. Thus, there is a need for appropriate modeling and control approaches for piezoelectric actuators, which can model the nonlinearity phenomenon and provide adequate compensation to achieve higher motion accuracy. The present review covers different methods adopted for overcoming the nonlinearity issues in piezoelectric actuators. This review highlights the charge-based and voltage-based control methods that drive the piezoelectric actuators. The survey also includes different modeling approaches for the creep and hysteresis phenomenon of the piezoelectric actuators. In addition, the present review also highlights different control strategies and their applications in various types of piezoelectric actuators. An attempt is also made to compare the piezoelectric actuator’s different modeling and control approaches and highlight prospects.

Design of Stand-Alone O&G Water Injection System Fed by Wind Generation with Battery Support

The promising area of offshore wind power has encouraged wind generation to supply Oil & Gas (O&G) facilities. A potential arrangement comprises a Water Injection System (WIS), as a method for oil recovery in reservoirs, connected to a wind turbine and a Battery Energy Storage System (BESS). However, the wind intermittency poses a challenge for an isolated wind-powered system operation. Therefore, this paper considers a design of a stand-alone system comprised of: a WIS, wind turbine, and BESS based on DC-link interconnection; and proposes a methodology to operate this system aiming to reduce the number of WIS stops. The methodology is based on two perspectives: an energetic analysis in which an energy analytical tool is developed to size the BESS; and a dynamic evaluation performed considering a DC-link voltage-based control to assist the load operation by reducing the WIS stops. The results have shown an adequate performance of the WIS even during moments of lower-wind power generation to the proposed methodology.

A Fast Model Predictive Control Method for a Single DC Source Driven Dual Inverter Fed Open-end Winding Induction Motor Drive

Multi-level inversion can be obtained from a dual two-level inverter fed open-end winding induction motor (OEWIM) powered from a single dc power supply and a floating capacitor. In this paper, two new model predictive control (MPC) variants are proposed for this drive by simple use of a voltage-based control approach in place of current-based control to reduce the number of computations in the digital controller. With both the proposed MPC variants, the floating capacitor voltage is initialized and is tightly regulated. Improved computational efficiencies are accomplished with both the proposed MPC variants, and superior performance of the drive is obtained with reduced sampling time achievable by exploiting the reduced computational burden. Performance of the entire drive system is demonstrated over a wide motor speed range by extending into field weakening operation also. Besides tight capacitor voltage regulation, the rugged performance of the proposed MPC variants under speed and load changes is demonstrated through simulations and are experimentally validated. Faster execution times owing to a dramatic reduction in computations, compared to some of the existing control methods, superior current and motor torque characteristics of OEWIM are also showcased in support of the proposed MPC variants.

Prototype design of an extended range electric sightseeing bus with an air-cooled proton exchange membrane fuel cell stack based on a voltage control logic of hydrogen purging

Range Extender (RE) is one means to enhance the driving range of battery electric vehicles by applying an electricity-generating equipment onto the vehicle. Air-cooled PEMFCs are used in some light-duty vehicle for lowering cost and simplify system. In this work, to increase system intergradation and adaptivity, an air-cooled PEMFC with a rated power of 1.1 kW is designed and fabricated. A prototype RE-FCEV with the air-cooled PEMFC serving as a sightseeing bus is designed and tested in a trial run. The PEMFC can extend the vehicle range from 40 km to 70 km. The voltage-based control logic of purging for durable operation is proposed and verified in a trial run. The effectiveness of the voltage-based control logic of purging is proved to maintain a fuel utilization of 97.84% with a sufficient voltage recovery. Based on the trial run results, the driving characteristics of three typical powertrain systems, FCEV, Hybrid battery electric vehicle (HBEV), and RE-FCEV are compared. The RE-FCEV combines the advantages of FCEV and HBEV with providing a stable output of PEMFC, decreasing the hydrogen consumption from 15.504 mol to 11.14 mol and extending the state of charge from 0.871 to 0.94 under the same operating condition.

MAF-DCGI Based Single-Phase Uninterrupted PV-Battery System Under Unintentional Islanding

The unintentional islanding is a critical issue in grid-connected solar battery systems in case of grid loss. This interrupts the power supply to the loads. Therefore, in this paper, an uninterrupted photovoltaic (PV)-battery energy storage (BES) system is presented to improve the reliability of the power supply. Besides, this system also furnishes the mitigation of load harmonics current and nonactive power compensation along with peak energy optimization for the PV array. The PV-battery system comprises a battery control by converter and an inverter regulated by an adaptive algorithm. The bidirectional controller regulates the voltage of the DC link capacitor. The moving average filter (MAF) - dual cascaded generalized integrator (DCGI) based adaptive control algorithm is used for utility-interactive operation and a voltage-based control algorithm is used for a standalone mode of operation. MAF-DCGI based phase-locked loop (PLL) is used for synchronization and islanding detection mechanism. An energy management system is used to manage the power flow between the devices in different modes of operation and smooth connection to the grid satisfying the IEEE 1547-2018 standard.

Nonlinear band gap characteristics of piezo-electro-magnetic phononic crystal micro and nanobeams based on size-dependent continuum mechanics models

This paper presents size-dependent continuum mechanics models for the nonlinear band gap (BG) characteristics of a piezo-electro-magnetic phononic crystal (PC) micro and nanobeam under voltage-based control (VBC) and negative capacitance-based control (CBC) methods. Taking various size-dependent effects into account, the BG properties of a piezo-electro-magnetic PC micro/nanobeam are analyzed based on Rayleigh beam theory (RBT), plane wave expansion (PWE), Bloch theorem, and nonlinear von-Kármán method. The effects of electro-magneto-mechanical coupling fields, geometric parameters, and micro/nanobeam dimensions on BG properties are discussed. It is found that all BGs frequencies can be controlled by the applied physical fields and elastic medium.

Voltage Control of Flexible-Joint Robot Manipulators using Singular Perturbation Technique for Model Order Reduction

Background and Objectives: Robot manipulator with flexible-joints is very complex nonlinear system whose control is one of the most challenging issues in the control word. Therefore, the design of voltage-based controller in addition, using of order reduction methods can reduce the complexity of the control law in such systems. Methods: This paper proposes a voltage controller for flexible-joint robot manipulators based on singular perturbation method. The presented control approach has all three advantages of the singular perturbation method for model order reduction, the proper structure of Port-Hamiltonian systems, and voltage control strategy (VCS). In this approach, the robot manipulator model is divided into three sub-systems, slow, medium and fast sub-systems. Each of the sub-systems is controlled using separate controller. In addition, the stability of these sub-systems and ultimately the whole system are proved. Unlike other related works, in this work the tracking error system is considered from the beginning, and by singular perturbation method, a controller is designed to stabilize the tracking system. Moreover, in the suggested voltage-based controller unlike torque control strategy, the electrical model of actuators is used. Results: The main advantages of proposed approach are simple structure, using only velocity of motors, the position of the joints as a control signal and considering the electrical model of the actuators. So, practical implementation of this controller will be with much less effort, compared to the methods like feedback linearization or other controllers in related works. Moreover, using the Lyapunov-based method, the ultimate bounded stability of the closed loop system is proved. Then, some simulations are provided for tracking, regulation, robustness and response speed purposes. Conclusion: Since, the controllers for every sub-system are designed separately, also, the control signal parameters such as joints position, motors velocity, and motors current can be simply measured, therefore, the structure of designed controller is very simple and practically implementable. As the simulation results confirm, the performance of this controller is appropriate, even when external disturbances are present or the frequency of reference signal increases. At last, by comparison and analysis of the simulation results between the presented approach and a related work, the suitable tracking performance of the suggested controller is shown.

Rotor Position Synchronization in Central-Converter Multi-Motor Electric Actuation Systems

The aerospace industry is increasingly transitioning from hydraulic and pneumatic drives to power-electronic based drive systems for reduced weight and maintenance. Electromechanical thrust reverse actuation systems (EM-TRAS) are currently being considered as a replacement for mechanical based TRAS for future aircraft. An EM-TRAS consists of one or more power-electronic drives, electrical motors, and gear-trains that extend/retract mechanical members to produce a drag force that decelerates the aircraft upon landing. The use of a single (“central”) power electronic converter to simultaneously control a set of parallel induction machines is a potentially inexpensive and robust method for implementing EM-TRAS. However, because the electrical motors may experience different shaft torques—arising from differences in wind forces and a flexible nacelle—a method to implement rotor position synchronization in central-converter multi-motor (CCMM) architectures is needed. This paper introduces a novel method for achieving position synchronization within CCMM architecture by using closed-loop feedback of variable stator resistances in parallel induction machines. The feasibility of the method is demonstrated in several case studies using electromagnetic transient simulation on a set of parallel induction machines experiencing different load torque conditions, with the central converter implementing both voltage-based and current-based primary control strategies. The key result of the paper is that the CCMM architecture with proposed feedback control strategy is shown in these case studies to dynamically drive the position synchronization error to zero. The initial findings indicate that the CCMM architecture with induction motors may be a viable option for implementing EM-TRAS in future aircraft.

A Novel Concept for Energy-Optimal, Independent-Phase Control of Brushless Motor Drivers

Abstract In this work, a new drive concept for brushless direct current (BLDC) motors is introduced. Energy regeneration is optimally managed with the aim of improving the energy efficiency of robot motion controls. The proposed scheme has three independent regenerative drives interconnected in a wye configuration. An augmented model of the robot, joint mechanisms, and BLDC motors is formed, and then a voltage-based control scheme is developed. The control law is obtained by specifying an outer-loop torque controller followed by minimization of power consumption via online constrained quadratic optimization. An experiment is conducted to assess the performance of the proposed concept against an off-the-shelf driver. It is shown that, in terms of energy regeneration and consumption, the developed driver has better performance. Furthermore, the proposed concept showed a reduction of 15% energy consumption for the conditions of the study.

Event-triggered adaptive control for upper-limb robot-assisted passive rehabilitation exercises with input delay

In this article, an adaptive tracking control strategy is designed for uncertain electrically driven end-effector type upper-limb rehabilitation robots subject to an input delay and a limited bandwidth channel. This control scheme is implemented to perform upper-limb passive rehabilitation training for different subjects. Primarily, dynamic analysis of the rehabilitation robot is carried out using the Euler–Lagrange principle, which incorporates motor dynamics to allow the voltage-based control commands as desirable in practical implementations. Thereafter, an adaptive backstepping control law with input delay compensation is designed to estimate the unknown dynamical parameters of the rehabilitation robot during the training sessions. Furthermore, a Lyapunov-based triggering mechanism is developed to deal with the limited bandwidth challenge and reduce the transmissions over the network. The experimental validation is conducted for different scenarios, and a comparison study is carried out with two time-triggered control schemes to investigate the potential of the proposed approach. From the experimental runs and the comparative analysis, the proposed control scheme is found to achieve a promising tracking performance with input delay compensation. Moreover, a significant saving in the network resources is attained during the passive rehabilitation training of the subjects.

Voltage-Based Droop Control of Electric Vehicles in Distribution Grids under Different Charging Power Levels

If left uncontrolled, electric vehicle charging poses severe challenges to distribution grid operation. Resulting issues are expected to be mitigated by charging control. In particular, voltage-based charging control, by relying only on the local measurements of voltage at the point of connection, provides an autonomous communication-free solution. The controller, attached to the charging equipment, compares the measured voltage to a reference voltage and adapts the charging power using a droop control characteristic. We present a systematic study of the voltage-based droop control method for electric vehicles to establish the usability of the method for all the currently available residential electric vehicle charging possibilities considering a wide range of electric vehicle penetrations. Voltage limits are evaluated according to the international standard EN50160, using long-term load flow simulations based on a real distribution grid topology and real load profiles. The results achieved show that the voltage-based droop controller is able to mitigate the under voltage problems completely in distribution grids in cases either deploying low charging power levels or exhibiting low penetration rates. For high charging rates and high penetrations, the control mechanism improves the overall voltage profile, but it does not remedy the under voltage problems completely. The evaluation also shows the controller’s ability to reduce the peak power at the transformer and indicates the impact it has on users due to the reduction in the average charging rates. The outcomes of the paper provide the distribution grid operators an insight on the voltage-based droop control mechanism for the future grid planning and investments.

Solar photovoltaic-based microgrid hosting capacity evaluation in electrical energy distribution network with voltage quality analysis

In this paper, solar photovoltaic hosting capacity within the electrical distribution network is estimated for different buses, and the impacts of high PV penetration are evaluated using power hardware-in-loop testing methods. It is observed that the considered operational constraints (i.e. voltage and loadings) and their operational limits have a significant impact on the hosting capacity results. However, with increasing photovoltaic penetration, some of the network buses reach maximum hosting capacity, which affects the network operation (e.g. bus voltages, line loading). The results show that even distributing the maximum hosting capacity among different buses can increase the bus voltage rise to 9%. To maintain the network bus voltages within acceptable limits, reactive power voltage-based droop control is implemented in the photovoltaic conditioning devices to test the dynamics of the network operation. The results show that implementation of the droop control technique can reduce the maximum voltage rise from 9% to 4% in the considered case. This paper also presents the impact of forming a mesh type network (i.e. from radial network) on the voltage profile during PV penetration, and a comparative analysis of the operational performance of a mesh type and radial type electrical network is performed. It is observed that the cumulative effect of forming a mesh type network along with a droop control strategy can further improve the voltage profile and contribute to increase photovoltaic penetration. The results are verified using an experimental setup of digital real-time simulator and power hardware-in-loop test methods. The results from this work will be useful for estimating the appropriate photovoltaic hosting capacity within a distribution network and implementation of a droop control strategy in power conditioning devices to maintain the network operational parameters within the specified limits.HighlightsVoltage and line loading constraints’ combination can reduce PV hosting capacity by 50% as compared to only voltage as a constraint.Implementation of reactive power versus voltage droop control in PV power conditioning device can reduce voltage variation from 9% to 4%.In a PV integrated electrical energy network, line loading can be reduced by 20% if the network is configured from radial to mesh type.

General Classification and Comprehensive Performance Assessment of Multi-Objective DC Voltage Control in Multi-Terminal HVDC Networks

The recent massive global movement towards green energy in power systems has raised the efforts of integrating large-scale Renewable Energy Sources (RESs) through Multi-Terminal HVDC (MTDC) systems. The configuration of the MTDC system and the possibility of transnational interconnection impose some challenges and raise the potential of single or multi-objective control for the DC voltage control. Additional requirements from the Transmission System Operator (TSO) and/or AC grids may influence the action taken for the DC voltage control. In this paper, a generalized classification for the DC voltage control methods in an MTDC system is delivered. The DC voltage control methods are classified into conventional control (i.e., reference voltage-based control) and non-conventional control (i.e., virtual resistance-based control) methods. The DC voltage control objective may cover a range of the following targets: power-sharing based on converters' rating capacity, ratio priority of the power distribution, available headroom, and/or loading factor. The control objective may include transmission losses minimization of the MTDC system with optimal or sub-optimal power flow. The design approaches of the control methods for post-contingency operation are presented. The control methods are evaluated and simulated with a 4-terminal radial MTDC network during normal and abnormal system operation. A comprehensive performance assessment is also presented considering the control methods from the perspective of the control method and objective, system efficiency, grid-code violation, communication requirement, and design complexity and flexibility.

Enhanced Frequency Droop Method for Decentralized Power Sharing Control in dc Microgrids

This article proposes two novel approaches to improve the superimposed frequency droop scheme for the control of dc microgrids (MGs). Conventional voltage-based control strategies suffer from issues such as undesirable voltage regulations, poor power sharing among the sources, and negative effects of line resistances on the equivalent droop characteristics. To overcome these challenges, a superimposed frequency droop scheme has been introduced. However, this method suffers from three major issues: 1) instability in terms of load variation, which is due to the location of system dominant poles; 2) limitation in system loading due to the limitation in the transferred reactive power; and 3) poor voltage quality caused by injection of the ac voltage. In this article, two methods are presented to stabilize the system and enhance its loading condition, consequently improving its viability for control of the dc MG. Furthermore, the system voltage quality is improved by limiting the amplitude of the injected ac voltage. The effectiveness of the proposed schemes is shown by different simulations and is further validated by experiments.

Model-free control of electrically driven robot manipulators using an extended state observer

This paper deals with the robust control of robot manipulators by presenting a novel voltage-based control approach. For this purpose, an Extended State Observer (ESO) is utilized to estimate the dynamical behaver of the system without any need to use the equations of motion including robot dynamics, actuator dynamics and their parameters in the proposed method. Convergence analysis proves that the estimated parameters converge to actual parameters asymptotically. The boundedness of tracking error is guaranteed through the Lyapunov theorem. Simulation results on an articulated robot driven by permanent magnet DC motors, and experimental implementation on a SCARA robot show that the proposed model-free controller has a satisfactory performance as compared to an adaptive uncertainty estimation-based controller.

A Simulation Analysis of Nanofluidic Ion Current Rectification Using a Metal-Dielectric Janus Nanopore Driven by Induced-Charge Electrokinetic Phenomena.

We propose herein a unique mechanism of generating tunable surface charges in a metal-dielectric Janus nanopore for the development of nanofluidic ion diode, wherein an uncharged metallic nanochannel is in serial connection with a dielectric nanopore of fixed surface charge. In response to an external electric field supplied by two probes located on both sides of the asymmetric Janus nanopore, the metallic portion of the nanochannel is electrochemically polarized, so that a critical junction is formed between regions with an enriched concentration of positive and negative ions in the bulk electrolyte adjacent to the conducting wall. The combined action of the field-induced bipolar induced double layer and the native unipolar double layer full of cations within the negatively-charged dielectric nanopore leads to a voltage-controllable heterogenous volumetric charge distribution. The electrochemical transport of field-induced counterions along the nanopore length direction creates an internal zone of ion enrichment/depletion, and thereby enhancement/suppression of the resulting electric current inside the Janus nanopore for reverse working status of the nanofluidic ion diode. A mathematical model based upon continuum mechanics is established to study the feasibility of the Janus nanochannel in causing sufficient ion current rectification, and we find that only a good matching between pore diameter and Debye length is able to result in a reliable rectifying functionality for practical applications. This rectification effect is reminiscent of the typical bipolar membrane, but much more flexible on account of the nature of a voltage-based control due to induced-charge electrokinetic polarization of the conducting end, which may hold promise for osmotic energy conversion wherein an electric current appears due to a difference in salt concentration. Our theoretical demonstration of a composite metal-dielectric ion-selective medium provides useful guidelines for construction of flexible on-chip platforms utilizing induced-charge electrokinetic phenomena for a high degree of freedom ion current control.

Analysis and Assessment of Modular Multilevel Converter Internal Control Schemes

Adoption of distributed submodule (SM) capacitors in a modular multilevel converter (MMC) necessitates complex controllers to ensure the stability of its internal dynamics. This paper presents comprehensive analysis and assessment of different proportional resonant (PR)-based control schemes proposed to stabilize the internal dynamics and ensure ac and dc sides power quality of the MMC within a dc transmission system. With the consideration of passive component tolerances, different energy- and voltage-based control schemes under various conditions are analyzed. It has been established that without vertical voltage balance control, unequal passive component values in the upper and lower arms of the same phase leg may cause: unbalanced fundamental currents in the arms, unequal dc voltage across the arms, and fundamental oscillations in the common-mode currents that lead to fundamental frequency ripple in the dc-link current. The theoretical analysis that explains this mechanism is presented, and is used to show that vertical voltage balancing is necessary for the nullification of arm voltage difference and suppression of odd oscillations caused by capacitive/inductive asymmetry between arms of the same phase leg. Simulations support the theoretical analysis and the effectiveness of voltage balancing in ensuring correct operation, independent of tolerances of the MMC passive elements, and operating conditions. A new direct method for elimination of fundamental oscillations in the common-mode and dc-link current is proposed. Experimental results from a single-phase MMC prototype validate the presented theoretical discussions and simulations.

Optimal Placement and Dispatch of LV-SVCs to Improve Distribution Circuit Performance

In this paper, a two-stage optimization framework is proposed for optimal placement and centralized real-time control of low-voltage static var compensators (LV-SVCs) in unbalanced distribution circuits to achieve feeder level benefits namely voltage regulation and energy loss minimization. The number, locations, and the optimal real-time reactive power injections from the LV-SVCs are determined from a proposed three-phase unbalanced ac optimal power flow (ACOPF). The ACOPF is formulated as a multi-objective optimization with operating constraints written in rectangular coordinates. The resulting nonlinear nonconvex problem is solved using the predictor-corrector primal-dual interior point method. The proposed approach is scalable for application to large distribution circuits, treats the constraints of physical space limitations effectively, and can take advantage of communication capabilities of LV-SVCs for centralized real-time control. The benefits of the proposed real-time control of LV-SVCs as compared to their operation with local autonomous voltage-based distributed control is demonstrated. The results show that, the proposed approach addresses the LV-SVC placement and control problem effectively to minimize energy losses while maintaining the voltage regulation.

Distributed Generation Systems: An Approach in Instrumentation and Monitoring

This paper presents an active instrumentation approach for distributed generation systems. The basic inherent tasks of such active instrumentation are (1) measurement, (2) control, (3) operation, (4) monitoring, and (5) correction of undesirable power quality issues in response to power parameters deviations, with the particularity of presenting the control scheme flexible and easy-to-adapt to new grid codes. The technology discussed in this paper is an approach to improve the life-cycle cost applied to distributed generation systems for instrumentation and monitoring in smart grids. It is based on designing an intelligent instrument to achieve the highest performance, to allow for flexibility in generating data suitable for each destination, to involve validation for the credibility of operation, and to adapt itself to new grid codes. Such intelligent power instruments are implemented with knowledge of measurement processes, their variables, and parameters, with a response to the universe of data that must be monitored and controlled. Also, the active instrumentation performs efficient, reliable, and safe operation of distributed power plants enhancing the power quality and economy. Such approach is based on triple loop control, and it can be expanded to any distributed generators ranging from grid-feeding to grid-supporting, whether using current-based or voltage-based control schemes ensuring immunity against power line impedances change without the previous knowledge of their values. This approach in instrumentation, i.e., ACTSENSOR Power Instrument is thoroughly described and analyzed by simulation results developed in the MatLab platform. Hardware-in-the-loop simulation through Typhoon HIL is used to validate its control, and experimental results validate its dynamic during transition between grid-connected and islanded modes.