Control Strategy Of Converter Research Articles

Instantaneous Symmetrical Component Theory Based Parallel Grid Side Converter Control Strategy for Microgrid Power Management

This paper proposes a centralized control strategy for power management of hybrid microgrid connected to the grid using a parallel combination of grid side converters (GSCs). An improved version of instantaneous symmetrical component theory is developed and is used for the control of parallel operated GSCs, which results in reduced sensor requirement, control complexity, and communication bandwidth. In addition, a simple power management algorithm is developed to test the efficacy of the proposed parallel grid side converter control strategy for all the microgrid modes considering state of charge limits of hybrid energy storage system, load changes, and renewable power variations. In the proposed system, a better dc link voltage regulation is achieved and usage of supercapacitor reduces the current stresses on the battery. With the proposed control strategy, the essential features of grid side converters like power quality, power injection, bidirectional power flow, and proportional power sharing are achieved. The effectiveness of the developed control strategy for the proposed system is tested using MATLAB based simulink environment and validated experimentally using a laboratory prototype.

Photovoltaic Power Converter Management in Unbalanced Low Voltage Networks with Ancillary Services Support

The proliferation of residential photovoltaic (PV) prosumers leads to detrimental impacts on the low-voltage (LV) distribution network operation such as reverse power flow, voltage fluctuations and voltage imbalances. This is due to the fact that the strategies for the PV inverters are usually designed to obtain the maximum energy from the panels. The most recent approach to these issues involves new inverter-based solutions. This paper proposes a novel comprehensive control strategy for the power electronic converters associated with PV installations to improve the operational performance of a four-wire LV distribution network. The objectives are to try to balance the currents demanded by consumers and to compensate the reactive power demanded by them at the expense of the remaining converters’ capacity. The strategy is implemented in each consumer installation, constituting a decentralized or distributed control and allowing its practical implementation based on local measurements. The algorithms were tested, in a yearly simulation horizon, on a typical Portuguese LV network to verify the impact of the high integration of the renewable energy sources in the network and the effectiveness and applicability of the proposed approach.

Control and operation strategy design of ITER coil power supply system

The large-scale ITER coil power supply system will generate huge current for superconducting magnets by plenty of AC/DC converters, which are based on thyristor technology on various circuits. A comprehensive consideration on design, manufacturing, testing and commissioning is the foundation to guarantee the safety operation of the CPSS system. This paper presents the design of converters control and operation strategies according to different typical circuit topologies. As well as illustrate the corresponding operation systems with associated functions to achieve those operation strategies. 2-Quadrant, 4-Quadrant and sequential control operation strategies are applied in corresponding PF (Poloidal Field), CS (Central Solenoid), CC (Correction Coil) and VS1 (Vertical Stability) converters with associated current closed-loop or voltage open-loop control during plasma operation. Three individual operation systems are comprised of TF, PF/CS and CC conventional systems with two architecture hierarchies to perform the control strategies and fulfill the real-time communication with central system. Typical simulation and test results are presented to verify the control strategies in accordance with the manufacturing and factory acceptance test. The converters will be installed in the ITER site soon and all the control strategies will be tested on the following commissioning phase.

Control Strategies of Mitigating Dead-time Effect on Power Converters: An Overview

To prevent short-circuits between the upper and lower switches of power converters from over-current protection, the dead time is mandatory in the switching gating signal for voltage source converters. However, this results in many negative effects on system operations, such as output voltage and current distortions (e.g., increased level of fifth and seventh harmonics), zero-current-clamping phenomenon, and output fundamental-frequency voltage reduction. Many solutions have been presented to cope with this problem. First, the dead-time effect is analyzed by taking into account factors such as the zero-clamping phenomenon, voltage drops on diodes and transistors, and the parameters of inverter loads, as well as the parasitic nature of semiconductor switches. Second, the state-of-the-art dead-time compensation algorithms are presented in this paper. Third, the advantages and disadvantages of existing algorithms are discussed, together with the future trends of dead-time compensation algorithms. This article provides a complete scenario of dead-time compensation with control strategies for voltage source converters for researchers to identify suitable solutions based on demand and application.

Voltage Ride through Control Strategy of Modular Multilevel Converter under Unbalanced Voltage Sag

This paper develops modeling and describes a control strategy for a modular multilevel converter (MMC) for grid-connected renewable energy systems. The proposed model can be used to simulate MMC activity during normal and faulty situations. Firstly, a dynamic model of a grid-connected MMC (GC-MMC), based upon the symmetrical component of voltages and currents, was designed. Then an adaptive robust control approach was established in order to follow the reference currents of the converter and stabilize the submodule (SM) capacitor voltage. The positive and negative sequences of reference currents that were given from the demanded active and reactive power during grid voltage disturbance and a normal situation were then utilized in control loops. Finally, the numerical results for the performance of the MMC throughout voltage sag conditions and the effect of uncertainties on the filter parameters during changing power demands were evaluated. The results specified that the current control strategy is more potent under voltage sag situations and able to fulfill the stability requirements of the MMC.

Improved droop control strategy of energy storage converter under grid‐side power fluctuation

Improved droop control strategy of energy storage converter under grid‐side power fluctuation

Direct Predictive Current-Error Vector Control for a Direct Matrix Converter

This paper proposes a novel control strategy for matrix converters that is coined “direct predictive current-error vector control.” The proposed control method retains the advantageous features of both a modulation scheme and of a predictive-based controller. The result is a controller that is capable of good dynamic performance and steady-state response with fixed switching frequency operation. Control of load and input currents of a direct matrix converter using the proposed method is demonstrated in this paper by simulation and experimental results.

Feedback noncausal model predictive control of wave energy converters

In this paper, a novel feedback noncausal model predictive control (MPC) strategy for sea wave energy converters (WECs) is proposed, where the wave prediction information can be explicitly incorporated into the MPC strategy to improve the WEC control performance. The main novelties of the MPC strategy proposed in this paper include: (i) the recursive feasibility and robust constraints satisfaction are guaranteed without a significant increase in the computational burden; (ii) the information of short-term wave prediction is incorporated into the feedback noncausal MPC method to maximise the potential energy output; (iii) the sea condition for the WEC to safely operate in can be explicitly calculated. The proposed feedback noncausal MPC algorithm can also be extended to a wide class of control design problems, especially to the energy maximisation problems with constraints to be satisfied and subject to persistent but predictable disturbances. Numerical simulations are provided to show the efficacy of the proposed feedback noncausal MPC.

Zonotope‐based quantification of the impact of renewable power generation on hybrid AC/DC distribution system

Hybrid AC/DC distribution network has developed rapidly owing to its convenience for renewable energy integration, thus the authors are interested in quantifying the impact of uncertainty from renewable power on system static performance. This paper proposes a zonotope-based set-theoretic method for quantifying the impact of renewable power fluctuations on system-state variables in hybrid AC/DC distribution network, both for the assessment of the capabilities for integrating renewable resources by hybrid AC/DC system, and for the appropriate selection of operating method in hybrid power systems. The authors bound the uncertain variations of generation by a zonotope and propagate it through a linearised power flow to get another zonotope, which captures all possible values of the system state variables. The zonotope-based method is computationally tractable and takes less computation than probabilistic methods especially when considering the generation uncertainty of multiple renewable energy resources. The proposed method is applied to a hybrid AC/DC test system with different control strategies of converters. The results show that hybrid AC/DC system with proper control mode may help reduce the impact of generation uncertainty.

Virtual synchronous generator: an overview

The continuous increase in the penetration of renewable energy (RE) based distributed generations (DGs) in the power system network has created a great concern on the stability of the existing grid. Traditional bulk power plants, which are dominated by synchronous machines (SMs) can easily support system instability, due to the inherent rotor inertia and damping characteristic, as well as voltage (reactive power) control ability. Nevertheless, converter based RE has some special characteristics, such as stochastic real and reactive power output, quick active and reactive power response, small output impedance, and little or no inertia and damping property thereby causing frequency and voltage instability in the system. To solve this problem, virtual synchronous generator (VSG) concept was proposed to emulate some of the features of conventional SG through converter control strategy in order to provide additional inertia virtually. Different control schemes for VSG has been proposed in literature. Surprisingly, an overview of these schemes is yet to be efficiently presented. This paper presents an overview of the VSG control schemes. It provides the concepts, the features of the control schemes and the applications of VSG. Finally, the crucial issues regarding VSG control schemes and the necessary improvement that need to be addressed are highlighted. Keywords: Distributed generation, Synchronous generator, Virtual synchronous generator, Power electronic converter, Energy storage system, Frequency control http://dx.doi.org/10.4314/njt.v38i1.20

Electrical and Electronic Technologies in More-Electric Aircraft: A Review

This paper presents a review of the electrical and electronic technologies investigated in more-electric aircraft (MEA). In order to change the current situation of low power efficiency, serious pollution, and high operating cost in conventional aircraft, the concept of MEA is proposed. By converting some hydraulic, mechanical, and pneumatic power sources into electrical ones, the overall power efficiency is greatly increased, and more flexible power regulation is achieved. The main components in an MEA power system are electrical machines and power electronics devices. The design and control methods for electrical machines and various topologies and control strategies for power electronic converters have been widely researched. Besides, several studies are carried out regarding energy management strategies that intend to optimize the operation of MEA power distribution systems. Furthermore, it is necessary to investigate the system stability and reliability issues in an MEA, since they are directly related to the safety of passengers. In terms of machine technologies, power electronics techniques, energy management strategies, and the system stability and reliability, a review is carried out for the contributions in the literature to MEA.

A QPR-Based Low-Complexity Input Current Control Strategy for the Indirect Matrix Converters With Unity Grid Power Factor

Unity grid power factor (GPF) is essential for the indirect matrix converter (IMC) applications to satisfy the grid-friendly requirement. The existing unity GPF control strategies usually consist of high-complexity structures, resulting in difficult parameter adjustments and high-speed processor requirements. In this paper, a low-complexity input current control (LCICC) strategy is proposed for the IMC operating at the unity GPF. Unlike the conventional strategies designed in the $d$ -$q$ synchronous coordinate frame, the proposed LCICC strategy is set up in the $\alpha $ -$\beta $ stationary coordinate frame. Then, the quasi-proportional resonant (QPR) controllers are utilized for a novel input current control manner, which is implemented to regulate the input currents based on the reconstructed grid voltage and current vectors. By this design, the proposed strategy can help to reduce the control complexity, with the advantages of the conventional closed-loop control strategies reserved. The steady-state and dynamic-state performance of the proposed strategy is validated by the experiments on a downscaled prototype. Besides, comparative experimental research with respect to an existing typical strategy indicates that the computational burden can be reduced 14.9% by the proposed strategy.

RECONSTRUCTION OF THE NEARSHORE SURFACE WAVE FIELD VIA ASSIMILATION OF REMOTE SENSING DATA

Typically, phase-resolved observations of the surface wave field are limited to in situ single-point time series. Select locations and field projects may have a handful or more single-point time series, such as for example the USACE FRF “8 meter array”. Recently, phase-resolved wave field observations with more spatial coverage have become available using LIDARs; however, LIDAR scan rates are only fast enough to encompass one horizontal dimension at the necessary phase-resolving sampling rates. Imaging remote sensors, such as optical cameras and marine radars, offer the possibility of full 2D reconstruction of the phase-resolved wave field. Accurate reconstructions from these sensors would essentially be equivalent to having thousands of wave gauges. Applications include short-term wave forecasting for maritime operations (e.g., cargo unloading) and highspeed navigation, as well as control schemes for wave energy converters. Moreover, realistic wave field reconstruction of nearshore wave fields would offer a very valuable new tool for investigating the time and space varying wave forcing in the nearshore.

Study on Topology and Control Strategy of High-Precision and Wide-Range Hybrid Converter for Photovoltaic Cell Simulator

Aiming at the function and technical requirements of high-power photovoltaic cell simulation, high-performance programmable logic power supply and dc motor simulation, a high frequency isolation hybrid topology and control strategy based on current-source/voltage-source converter was studied and proposed. Firstly, according to the performance requirements of photovoltaic cell analog power supply, the control strategy requirements of the high-precision wide-range hybrid topology were proposed. Secondly, the working principle of the new hybrid topology was analyzed. At the same time, the equivalent model of the new hybrid topology was simplified and established, and the overall control strategy of the hybrid topology based on current compensation and sliding mode variable structure was proposed. Finally, simulation and experimental research on the hybrid topology was carried out, and the experimental test of photovoltaic cell simulation was completed. The simulation and experimental results show that the hybrid topology and control strategy proposed in this paper has the characteristics of wide-range output regulation, fast dynamic response, high efficiency and high power factor, and can be used for high performance photovoltaic cell simulation, programmable logic power supply and DC motor simulation.

Adaptive SRF-PLL Based Voltage and Frequency Control of Hybrid Standalone WECS with PMSG-BESS

Abstract The variable-speed Permanent Magnet Synchronous Generator (PMSG) based Wind Energy Conversion System (WECS) attracts the maximum power from wind, but voltage-regulation and frequency-control of the system in standalone operation is a challenging task A modern-control-based-tracking of power from wind for its best utilization is proposed in this paper for standalone PMSG based hybrid-WECS comprising Battery Energy Storage System (BESS). An Adaptive Synchronous Reference Frame Phase-Locked-Loop (SRF-PLL) based control scheme for load side bi-directional voltage source converter (VSC) is presented for the system. MATLAB/Simulink model is developed for simulation study for the proposed system and the effectiveness of the controller for bi-directional-converter is discussed under different operating conditions: like variable wind-velocity, sudden load variation, and load unbalancing. Converter control scheme enhances the power smoothening, supply-load power-matching. Also it is able to regulate the active & reactive power from PMSG-BESS hybrid system with control of fluctuations in voltage & frequency with respect to varying operating conditions. Proposed controller successfully offers reactive-power-compensation, harmonics-reduction, and power-balancing. The proposed scheme is based on proportional & integral (PI) controller. Also system is experimentally validated in the laboratory-environment and results are presented here.

LQR-Based Adaptive Virtual Synchronous Machine for Power Systems With High Inverter Penetration

This paper presents a novel virtual synchronous machine controller for converters in power systems with a high share of renewable resources. Using a linear quadratic regulator-based optimization technique, the optimal state feedback gain is determined to adaptively adjust the emulated inertia and damping constants according to the frequency disturbance in the system, while simultaneously preserving a tradeoff between the critical frequency limits and the required control effort. Two control designs are presented and compared against the open-loop model. The proposed controllers are integrated into a state-of-the-art converter control scheme and verified through electromagnetic transient (EMT) simulations.

Grid‐connected control strategy of modular multilevel converter–battery energy storage system based on VSG

Modular multilevel converter-battery energy storage system (MMC-BESS) has a good engineering application. When MMC-BESS is connected to the grid, the real-time phase angle of grid is an important parameter. When MMC-BESS is connected to the grid, a simulation model based on virtual synchronous generator (VSG) is built in MATLAB. The results show the control algorithm based on VSG can improve the dynamic response of the system and stably detect the phase angle of the grid.

Real-power economic dispatch of AC/DC power transmission systems comprising multiple VSC-HVDC equipment

This paper presents a practical approach for the real-power economic dispatch of AC/DC power transmission systems formed by VSC-HVDC equipment. It uses the Lagrange multipliers method combined with a comprehensive representation of the AC/DC power system. The power losses of the AC systems, DC grid and power converters are considered in this novel formulation by using incremental transmission loss factors. For realistic solutions, the different control strategies of the power converters forming any VSC-based power grid are considered. Interestingly, this approach permits to conclude that the AC grids coupled to converters charged with DC voltage control define the nodal marginal prices in the DC network, and in turn, the energy prices in the VSC-connected passive grids are inherited from the DC network. Overall, this modelling approach yields great flexibility to model any arbitrary VSC-based HVDC power grid interconnecting various AC systems. The developed method has been validated using a two-terminal VSC-HVDC network interconnecting two otherwise independent AC grids. Its results are compared against those obtained by the sequential quadratic programming method available in the optimisation toolbox of Matlab©, with both solutions exhibiting differences inferior to 0.30% in the total generation costs, therefore concurring very well between each other. The practicality of this approach is also demonstrated by carrying out the real-power economic dispatch of an AC/DC transmission system comprising seven VSC units which give rise to a thirteen-node DC grid.

Fuzzy Logic-Based Pulse Density Modulation Scheme for Mitigating Uncertainties in AC–AC Resonant Converter Aided Induction Heating System

Induction heating (IH) applications aided by power electronic control system have become very attractive in the recent past. The power electronics circuits succumb to severe switching loss, lower power density if proper switching methodology is not adhered. A state of uncertainty is indispensable in IH application as the power required by the load varies depending upon the nature of work piece. This uncertain issue makes the selection of the control algorithm and controller very vital. The mundane controllers may not be compatible to combat the uncertainties and leads to exhibit dynamic problems say transients, peak overshoot and poor response. Henceforth, the IH system requires a superlative converter topology and control scheme in order to have reduced switching loss and to improve the system performance there by negating the uncertainties. Here, in this work, a direct AC–AC boost resonant converter fed by pulse density modulation (PDM) is realized in a single stage mode. A fuzzy logic-based PDM control technique improves the efficiency and provides the versatile power control with reduced time domain specifications for dynamic changes in load. The proposed system has been studied using MATLAB/SIMULINK and validated using a hardware prototype employing dsPIC30F4011 microcontroller. The results reveal that efficient control over power can be accomplished by varying the density of the switching pulses, and thereby the efficiency is enhanced even with reduced component count. Also, the single-stage conversion is effective than its two-stage counterpart.

A Modified Hysteresis-Modulation-Based Sliding Mode Control for Improved Performance in Hybrid DC–DC Boost Converter

Sliding-mode (SM) control is a popular nonlinear control strategy for the dc-dc converters as it offers several advantages such as ease of implementation and robust performance against load and line variations. However, the main drawback of the traditional hysteresis-modulation-based SM controller is that its use in the regulation of the dc-dc converters results in a tradeoff between the overshoot and speed of the closed-loop output voltage response. This is due to the use of the traditional proportional-integral (PI) controller which is used to generate the reference inductor current of the controller. To overcome this problem, the traditional PI-based SM controller is modified such that the reference inductor current used in the sliding surface is now generated using an integral whose integrand is a function of the normalized output voltage error of the converter. A key feature of the integrand is that it is bounded by a user-defined constant. The modified SM control strategy is applied to a hybrid dc-dc boost converter. The expression of the equivalent control signal of the proposed SM controller is derived and the detailed stability analysis of the closed-loop controlled system is given. Also, experimental results are provided to show that the proposed SM controller gives an improved performance as compared to that obtained using the existing PI-based SM controller.