Decoupled Power Control Research Articles

A Novel Wired/Wireless Hybrid Multiport Energy Router for Dynamic EV Energy Internet With Grid-Tied and Islanded Operations

Energy routers (ERs) are indispensable in deploying energy Internet for electric vehicles (EVs), which flexibly handle the power flow regulation. Combined with the excellent characteristic of wireless power transfer (WPT) technology for non-contact energy transmission, this paper proposes a novel wired/wireless hybrid multi-port energy router (HMER) for future EV energy Internet. First, multiple bidirectional power ports are provided to control the power flow among the grid, various DC power sources, and EVs. Moreover, with grid-tied and islanded operations, the proposed HMER enables dynamic wireless energy exchange for EVs on the move. When moving along the energy exchange lane, the EVs can receive power from the HMER and conduct energy feedback, relieving mileage anxiety while creating economic benefits. Further, a mathematical model of the system is derived, and a control algorithm is introduced to perform decoupled power control for each transceiver. Finally, a SIC experimental prototype is constructed to verify the effectiveness of the proposed HMER system. Experimental results prove the transceivers can get bidirectional wireless energy interconnection on the energy exchange lane in both grid-tied mode and islanded mode, and each transceiver can realize independent power regulation.

Resource allocation algorithm in Heterogeneous Network Based on Non-orthogonal Multiple Access

The proposed resource allocation algorithm with joint power control and user pairing addresses the problem of degraded uplink user fairness due to cross-cell interference in NOMA uplink and improves user fairness. In the power control section, by decoupling power control from user pairing, the WOA algorithm is proposed in the statistical channel state scenario to solve the nonconvex optimization problem of intra-user pair fairness; in the user pairing section, the PTS algorithm is proposed to introduce randomness into the algorithm to improve the algorithm’s global search performance, solve the local optimum problem of integer programming, and improve inter-user pair fairness. Simulation results show that relative to the α-fairness comparison algorithm, the algorithm in this paper can improve fairness by about 5% under different interfering user densities, cell coverage radius, and tiny area transmit power.

Antisaturation and Power Decoupling Control of Multiwinding Energy Harvester Based on Magnetomotive Force Compensation

With the rapid development of smart grids, numerous monitoring sensors have been widely used for the state inspection of power lines. To ensure reliable operation of these sensors, the problem of their power source needs to be solved urgently. In particular, non-invasive inductive energy harvesters clamped over the lines are suitable as power sources for the monitoring sensors. This paper presents the multiwinding energy harvester (MWEH), equipped with multiple energy output channels. To improve the anti-saturation ability of the magnetic core and eliminate power cross effects between the windings simultaneously, an auxiliary winding is introduced to regulate the magnetomotive force. The method of maintaining the unsaturated working state of the magnetic core and the power decoupling control strategy between the windings are proposed. Hence, the global power fluctuation can be eliminated with a constant unsaturated state when the load and turns of any winding change. The experimental results suggest that regulating the energy harvesting factor of the auxiliary winding can desaturate the magnetic core. Furthermore, based on the linear operation of the MWEH, the problem of power linkage of the windings can also be solved, which stabilizes the output power of one or more windings.

Design and simulation of six-phase UPFC power quality enhancement with improved GWO based decoupled power control strategy

Design and simulation of six-phase UPFC power quality enhancement with improved GWO based decoupled power control strategy

Model predictive control of a microgrid with energy-stored quasi-Z-source cascaded H-bridge multilevel inverter and PV systems

This paper presents a new energy management system (EMS) based on model predictive control (MPC) for a microgrid with solar photovoltaic (PV) power plants and a quasi-Z-source cascaded H-bridge multilevel inverter that integrates an energy storage system (ES-qZS-CHBMLI). The system comprises three modules, each with a PV power plant, quasi-impedance network, battery energy storage system (BESS), and voltage source inverter (VSI). Traditional EMS methods focus on distributing the power among the BESSs to balance their state of charge (SOC), operating in charging or discharging mode. The proposed MPC-EMS carries out a multi-objective control for an ES-qZS-CHBMLI topology, which allows an optimized BESS power distribution while meeting the system operator requirements. It prioritizes the charge of the BESS with the lowest SOC and the discharge of the BESS with the highest SOC. Thus, both modes can coexist simultaneously, while ensuring decoupled power control. The MPC-EMS proposed herein is compared with a proportional sharing algorithm based on SOC (SOC-EMS) that pursues the same objectives. The simulation results show an improvement in the control of the power delivered to the grid. The Integral Time Absolute Error, ITAE, achieved with the MPC-EMS for the active and reactive power is 20 % and 4 %, respectively, lower than that obtained with the SOC-EMS. A 1,3 % higher charge for the BESS with the lowest SOC is also registered. Furthermore, an experimental setup based on an OPAL RT-4510 unit and a dSPACE MicroLabBox prototyping unit is implemented to validate the simulation results.

Investigation and implementation of a nonlinear decoupled power control for a single-phase grid-connected power inverter via an LCL filter

This paper proposes the study and the implementation of a nonlinear decoupled control approach for the active (P) and the reactive (Q) power in a Single-Phase Grid-Connected Power Inverters (SPG-PIs) application, by using the Proportional Multi-Resonant (PM-R) and the IP Anti-Windup (IP/A-W) controllers. The proposed control technique is characterized by a simple structure that requires less calculation. It is designed to ensure the decoupled P/Q power control guarantees high levels of stability and security of the system operation. In the proposed control scheme, internal feedback, employing the P-MR controllers, is designed for controlling the voltage and the current, and external feedback controls and regulates the powers grid by employing the nonlinear IP/A-W regulators capable to ensure the stability of the system operation with the security functioning. The proposed control method is tested in Matlab/Simulink interface and is validated experimentally on a test bench by using the dSPACE 1202. Obtained results validated the proposed controller performance and prove an acceptable efficiency of the P-MR and the IP/A-W controllers with a Total Harmonic Distortion (THD) conformed to the Algerian local Grid-Code (AGC).

Hybrid-Modulation Hysteresis Scheme Based Decoupled Power Control of Grid-Connected Inverter

Most existing power control methods for grid-connected inverter are implemented in synchronous reference frame. In order to achieve soft-switching operation, those methods usually need additional design considerations, which could introduce complex computation. This article presents a control strategy for single-phase grid-connected inverter system with LCL filter that can be used for grid-connected battery/photovoltaic (PV) system, with the target to implement decoupled active and reactive power control capability in stationary frame and achieve soft-switching behavior for higher efficiency. In order to improve system efficiency, a new hybrid-modulation-based hysteresis current scheme is used to achieve soft-switching while improving the inherent zero-crossing distortion issue existing in traditional unipolar hysteresis current control. Multiproportional and resonant compensators are utilized to mitigate output low-frequency distortions further, together with a capacitor current feedback-based active damping design embedded in an inner loop. The proposed controller also demonstrates good robustness and immunity to distorted grid conditions. Simulation and experimental results are presented in this article with essential theoretical analysis to verify the validity of the proposed control strategy.

Power coupling analysis and improved decoupling control for the VSC connected to a weak AC grid

Conventional vector control (VC) is widely used in the voltage source converter (VSC) due to its simplicity and power decoupling ability. However, this paper reveals that the VC may result in strong active and reactive power coupling under weak AC grid conditions. The linearized relationship between the power and dq-axis currents is built. On this basis, the power coupling mechanism is revealed, and the power coupling process is presented. Finally, an improved decoupled power control is accordingly proposed based on the feedforward compensation method. The improved decoupling control method can realize more accurate decoupled active and reactive power regulation. Moreover, its design is simple, and thus is easy to be implemented in practice. The power coupling characteristics analysis and the improved power decoupling control are verified through PSCAD/EMTDC simulations and experiments.

Seamless transfer control for dual‐mode grid‐connected inverter with automatic PCC voltage regulation

AbstractDistributed generators are more expected with the capability to continue supporting power to local critical loads in both intended and unintended islanding conditions, in addition to its house‐keeping functions of grid‐connected condition. With this purpose, this paper proposes a control strategy of single‐phase grid‐connected inverter with both decoupled power control capability for grid‐connected mode and load voltage regulation capability for standalone mode. It also enables automatic voltage regulation on point of common coupling, which enables seamless transfer after islanding occurrence. An impedance model is disclosed to analyze the operation mechanism during transient state, with further investigations on both the effect of system parameters in different modes and the system operating features. Simulation and experimental results are provided to evaluate its effectiveness.

Experimental investigation of efficient and simple wind-turbine based on DFIG-direct power control using LCL-filter for stand-alone mode

This paper suggests an experimental implementation study of the Wind Energy Conversion System (WECS) based on efficient Direct Power Control (DPC). Stand-alone mode for variable wind speed application using Doubly-Fed Induction Generator (DFIG) is studied and developed in this work. Due to the wind power performance limitation of traditional PI controllers, such as overshoot, response time, and static error; IP (integral–Proportional) controllers is replaced instead of the PI to control rotor current d–q components (Ird and Irq) in a Park frame through AC–DC–AC converter. A comparative experimental study was implemented to improve the power quality using L, LC & LCL passive filters between the DFIG’s rotor circuit and the inverter. Experimental results prove that the proposed DPC under stand-alone mode with LCL-Type filter could operate in several conditions despite the sudden wind speed variations. It improves the unity power factor grid operation (≈0.98), dynamic responses, and the decoupled power control with high wind power performances: good reference tracking, short response time, neglected overshoot, and low power error. The power quality injected into the RL-load satisfied the limit specified by IEEE harmonic standard 519 (less than 5%).

Matlab/Simulink Based Modeling and Simulation of Decoupled Power Control for DFIG Operating in Wind Generation Systems

This paper appraises the performances of two control scenarios, for doubly fed induction generator (DFIG) operating in wind generation system (WGS), which are the direct decoupled control (DDC) and indirect decoupled control (IDC). Both control scenarios studied combines vector control and Maximum Power Point Tracking (MPPT) control theory so as to maximize the captured power through wind turbine. Modeling of DFIG based WGS and details of both control scenarios have been presented, a proportional integral controller is employed in the active and reactive power control loops for both control methods. The performance of the both control scenarios in terms of power reference tracking and robustness against machine parameters inconstancy has been shown, analyzed and compared, which can afford a reference to the operators and engineers of a wind farm. All simulations have been implemented via MATLAB/Simulink.

PV inverter with decoupled active and reactive power control to mitigate grid faults

Abstract This paper proposes a grid-tied PV inverter installed at the low voltage side of a distribution grid. The architecture considers the operation of a grid-tied inverter and its robustness against the grid faults. Unlike previously proposed low-voltage-ride-through (LVRT) operation, the proposed control provides maximum-power-point-tracking (MPPT) in both normal and low-voltage fault conditions. The control strategy prevents the inverter shut-down by maintaining the DC-link. The inverter also supports the grid by reactive power injection during the voltage sags. The paper presents a prediction model of a two-stage voltage-source-inverter. The proposed predictive control can generate the appropriate references for both regular and LVRT modes based on the inverter’s specification and the regulatory grid codes. The salient features of the proposed controller are: (1) decoupled power control in regular operation, (2) low-voltage-ride-through operation with reactive power support, (3) No DC-link fluctuation, and (4) MPPT in every mode. The inverter control is developed by formulating a cost function based on the prediction model of the inverter. A cost function minimization-based control eliminates the conventional cascaded-loop control, thus simplifying the controller implementation. The proposed model-predictive-control (MPC) algorithm is validated with mathematical analysis and simulations of the PV inverter in both standard and faulty grid conditions.

Novel MTDC droop scheme with decoupled power control for enhancing frequency stabilities of weak AC systems

Traditional way to enable frequency support provided by MTDC system for the connected weak AC systems is to modify the power reference of each converter under standard power-sharing droop control based on the weak grid's frequency deviations. However, this scheme artificially couples all asynchronous AC systems to tackle with the frequency disturbances of any connected AC systems, which might result in broader frequency disturbance propagations. To overcome this, this study proposes a decoupled frequency control (DFC) scheme to improve weak AC systems frequency stabilities. First, the relationship between the active power and power set points of each converter is derived by the linearization of MTDC power flow equations. Then, the frequency coupling properties of each AC system with traditional frequency control are derived, and it shows that the frequency disturbance will be propagated to all the connected AC systems with traditional control. Furthermore, the control law of each converter in the proposed DFC is developed through the defined decoupled matrix, and the independent frequency regulation characteristic of each converter can be obtained. Finally, numerical simulations have demonstrated the effectiveness of the proposed DFC scheme in events of load changes and converter loss in the main and weak AC grid.

A general closed-loop power-decoupling control for reduced-switch converter-fed IM drives

Twice ripple power exists in single-phase to three-phase reduced-switch induction motor drives, which degrades the performance of the drive system, such as larger total harmonic distortion of the grid current, the larger ripple voltage in the dc link and the larger torque ripple. Most existing power decoupling schemes are open-loop decoupling methods. However, the open-loop decoupling method has the disadvantages of heavy computation and strong dependency of parameters. This paper analyzes all steady state solutions of the decoupling capacitor voltage from the point of view of solving differential equations and presents a unified multi-proportional-resonant closed-loop decoupling method to suppress the ripple voltage on the dc bus. The whole drive system adopts a hybrid predictive control strategy with dual loops to coordinate the operation of each part. Comprehensive experimental results are presented to verify the effectiveness of the presented method.

A Novel Power Decoupling Control Method to Eliminate the Double Line Frequency Ripple of Two Stage Single-Phase DC-AC Power Conversion Systems

In two-stage single-phase inverters, inherent double line frequency ripple is present at both the input and output of the front-end converter. Generally, large electrolytic capacitors are used to eliminate this double line frequency ripple. It is well known that low frequency ripple shortens the lifespan of capacitors. Hence, the system reliability can get worse. In order to eliminate the double line frequency ripple, additional hardware combined with an energy storage device is required in most of the methods developed so far. In this paper, a novel power-decoupling control method is proposed to eliminate the double line frequency ripple at the front-end converter of two-stage single phase DC/AC power conversion systems. The proposed control algorithm is composed of two loops, a ripple compensation loop and an average voltage control loop, and no extra hardware is required. Since the proposed method does not require information from the phase-locked-loop (PLL) of the inverter, it is independent of inverter control. In order to verify the validity and feasibility of the proposed algorithm a 5 kW Dual Active Bridge (DAB) DC/DC converter and a single-phase inverter are implemented. The effectiveness of the proposed method is verified through the simulation and experimental results.

Multifunction Control Strategy for Single-Phase AC/DC Power Conversion Systems With Voltage-Sensorless Power-Decoupling Function

In this article, a novel voltage-sensorless controller for the single-phase ac/dc power conversion systems with a self-adaptive power-decoupling function is proposed. Existing control strategies for achieving power decoupling usually require additional active switches or extra measurement circuits to a certain power-decoupling controller. By employing the proposed method, the decoupling voltage could be accurately evaluated with the fluctuations of the other measured state variables in the original converter, and the issues of instability and inaccuracy on power-decoupling control under transient conditions could be solved. Furthermore, the proposed control scheme involves a phase-shift modification to improve the power quality as well as achieve accurate power-decoupling reference, which could eliminate the harmonic influence on the original PFC circuit. Finally, a 1.2-kW single-phase PFC prototype using SiC-based semiconductor switching devices is tested to validate the proposed control scheme. The experimental results demonstrate that the power factor of 0.99 with total harmonic distortion around 3%, and a dc-link voltage with 5% ripple could be achieved with the proposed control strategy.

Decoupled Power Control With Indepth Analysis of Single-Phase Electric Springs

Electric spring (ES) as a new effective way to solve the power quality issues caused by the uncertainty of wind and photovoltaic (PV) power, has the advantages of small volume, flexible configuration and low cost. Aiming at improving the dynamic responses of the existing power control for ES-2, a new control with in-depth analysis on the decoupling of the active and reactive powers is proposed in this paper. By introducing second order generalized integrator phase locked loop (SOGI-PLL) and fictitious-axis emulator (FAE) into the control algorithm, the virtual orthogonal voltage and current signals were constructed and the mathematic model of ES-2 in the dq axis synchronous rotating reference frame was established. Then, the control system consisting of three closed loops, namely active power loop, current loop and ES voltage loop, is arranged. Among the three loops, a damped proportional resonance (PR) controller is adopted in the ES voltage loop to ensure the accurate control of the output voltage of ES-2. Instead, traditional PI controllers are used for the current and power loops. Finally, the effectiveness of the proposed decoupled power control is validated by both simulation and experimental results.

Monitoring and control of a permanent magnet synchronous generator-based wind turbine applied to battery charging

ABSTRACT The battery charging control within wind turbine applications is the most important challenge in standalone exploitation mode because of the random nature of wind energy and irregular use of electricity. Within this problematic, this paper deals with monitoring and control of a permanent magnet synchronous generator voltage for battery charging. In the proposed topology, the output direct drive PMSG is linked to the battery through a vector-controlled pulse modulated (PWM) rectifier. Most wind energy conversion systems are based on precise knowledge of the wind speed, which makes the adjustment of the charge voltage relatively complicated, and degrades the powers captured with erroneous measurements of this wind speed. In this context, all the efforts of this work are meant to simplify and improve the dynamic performance of the system. The technique used in this work is devoid of wind measurement. By neglecting different losses, the approach adopted leads us to the reference electromagnetic torque, assuming that the wind speed and consequently the rotational speed of the turbine vary slowly in steady state. Using the load current and voltage measures, the proposed controllers calculate permanently the power reference that corresponds to the fixed battery voltage. A vector control approach is adopted to achieve decoupled power control on the supply side power converter by generating the direct and quadrature control voltages. These voltages are necessary to generate the corresponding duty cycles of the PWM active switching devices. Hence, the PWM rectifier maintains the battery voltage at a fixed value by balancing both the rectifier output current and the load input current. To activate the vector control, two dynamic controllers are designed, simulated, and compared. The first controller is based on simple PI regulators. Meanwhile, the second one, which is a sliding mode technique, is applied to control the battery voltage. In order to assess the effectiveness of the used techniques, simulation models have been subjected to critical conditions of changing in speed and load. Simulation results revealed a poor accuracy of the first technique during transients and its close correlation under load disturbance. Whereas the sliding mode controller has high precision and strong robustness in steady state and during transient phases. The system simulation is performed using MATLAB/SIMULINK.

Decoupled Power Control for Direct-Modulation-Based Modular Multilevel Converter With Improved Stability

Direct modulation principle is widely used in modular multilevel converters (MMCs) for its simplicity and natural stability. However, it results in strong active and reactive power coupling. This paper carefully analyzes and identifies four power coupling paths and two power influence factors with the direct modulation principle. Full power decoupling of the MMC can be realized by cutting off the derived coupling paths and compensating the influence factors. However, this will further deteriorate the already poor damping of the MMC and significantly increase dc-bus current fluctuations. To solve this problem, the sources resulting in poor damping are identified and then a new closed-loop dc-bus current controller is incorporated into the control system. Finally, the proposed power decoupling strategy with the newly designed current controller realizes completely decoupled power regulation, avoids overload operation, and obviously improves the dynamic performance of the MMC. Furthermore, it increases the stability of the MMC system under all possible operation conditions. The proposed control strategy is confirmed by experimental results.

Decoupled Power Control for a Modular-Multilevel-Converter-Based Hybrid AC–DC Grid Integrated With Hybrid Energy Storage

This paper presents a decoupled power control strategy for a modular multilevel converter (MMC)-based hybrid ac–dc grid integrated with a hybrid energy storage system. This system can mitigate the active power fluctuations caused by intermittent renewable generation and also realize reactive power compensation as required by voltage regulation. The proposed hybrid ac–dc system has a novel configuration in which batteries and supercapacitors are distributed into the upper arm and the lower arm of the MMC, respectively. Therefore, it is possible to design fully decoupled power control and simultaneously optimize the performances of batteries and supercapacitors. First, the system modeling and operational principles of the MMC are briefly introduced in this paper. On the basis of these analyses, the power decoupling between the upper arm and the lower arm is presented to realize different control objectives. Moreover, battery state-of-charge balancing control and supercapacitor voltage control are also presented, which are crucial for ensuring the normal operation of these energy storage components and the proposed MMC-based hybrid ac–dc grid. Finally, the proposed system and its control strategies are verified by laboratory experimental results.