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Summary: Varied control applications in electrical engineering find the utility of the theory of transformation of three‐phase quantities from abc to αβ0 and dq0 reference frames. These transformations are vital in simplifying the control equations and their implementation. However, for different applications, different orientations of the abc‐, αβ‐, and dq‐axes are used. This results in a different transformation matrix for each such orientation. In this paper, a generalized abc to αβ0 and dq0 transformation matrix is proposed which can be utilized for any possible orientation and thus effectuates faster derivation of the transformation matrix. This is achieved by defining two parameters l and m whose values are obtained by observing the orientation of the axes. The transformation equation can therefore be obtained without having to undergo the steps of resolving abc quantities into their components along the αβ‐ or dq‐axes. Furthermore, this paper discusses the visual understanding of transformed electrical quantities. It is shown that the complex plots of real versus imaginary parts of instantaneous positive and negative symmetrical components have shapes which exhibit specific characteristics of electrical quantities and give a direct understanding about unbalance and presence of harmonics in the system. [ABSTRACT FROM AUTHOR]

In the conventional sliding mode control, the four-leg distribution static compensator (DSTATCOM) currents are controlled based on a current error in each phase. However, the four currents in a four-wire system can not be independently controlled variables and hence one of the four controllers is redundant in conventional schemes. Further, the current dynamics of a DSTATCOM converter are coupled through converter pole voltages in the natural reference frame. This leads to cross-coupling in the sliding variable equations with respect to four manipulated input variables. Considering the above points, in this paper, the current due to Thevenin’s equivalent load neutral-point voltage is considered as a fourth independent controlled variable and the corresponding system dynamic equations are presented. To get a decoupled feature, a new sliding surface function is structured. The performance of a DSTATCOM with the proposed control scheme under various operating conditions is validated through a detailed simulation study and experimental results, obtained from a laboratory prototype of four-leg DSTATCOM. [ABSTRACT FROM AUTHOR]

In this paper, an optimization-based control algorithm for the compensation of steady-state load under distorted supply voltages is presented. For balanced and sinusoidal supply voltages, load compensation using shunt active filter produces perfect harmonic cancellation (PHC) and unity power factor (UPF) source currents. However, when the supply voltages are distorted, compensation for PHC will not provide UPF, as the harmonics in the supply voltages are not utilized for delivering the average power. In the same way, to achieve UPF source currents, the compensated source currents should have the same harmonics, unbalance, shape, and be in phase with the respective supply voltages, thereby violating the perfect harmonic cancellation objective. Hence, there should be an optimal operation between these two important compensation characteristics. The optimization-based control algorithm presented in this paper gives the best power factor while satisfying the constraints such as total harmonic distortion limits and average power balance of source currents. It is also flexible to adopt different compensation characteristics based upon the supply voltage conditions. MATLAB and its optimization toolbox are used for simulation studies and solving the nonlinear optimization problem, respectively. The algorithm is validated by using a prototype of digital signal processor (TMS320F2812PGFA)-based shunt active power filter. Detailed experimental results are presented. Index Terms--Active power filter (APF), digital signal processor (DSP), load compensation, optimization, perfect harmonic cancellation, unity power factor.

In this paper, the theory of instantaneous symmetrical components is applied to explore various control strategies of load compensation, under different supply voltages. When the supply voltages are balanced and sinusoidal, all of these strategies converge to the same compensation characteristics. However, when the supply voltages are not balanced sinusoids, these control strategies result in different degrees of compensation in harmonics, power factor, neutral current, and compensator ratings. These control strategies are discussed in detail and a comparative study of their performance in terms of the rms value, total harmonic distortion, power factor of source currents, and compensator ratings is presented. Based on this study, it is possible to select the best strategy to meet the required load compensation characteristics for available supply voltages. A three-phase four-wire distribution system supplying an unbalanced and nonlinear load is considered for simulation study. The detailed simulation results using MATLAB are presented to support the proposed compensation strategies. Index Terms--Active power filter (APF), instantaneous symmetrical component theory, load compensation, perfect harmonic cancellation, unbalanced and distorted supply voltages, unity power factor.

In this paper, load compensation techniques under unbalanced and distorted voltages have been discussed. Two kinds of compensation methods are considered. In the first category, synchronous detection and modified equal current strategies are used under the unbalanced but sinusoidal source voltages. In the second method, load compensation based on instantaneous symmetrical component theory with positive sequence extraction is proposed and is shown to work under unbalanced and the non-sinusoidal source voltages. To support the proposed method, a 440 V (L-L) three-phase, four-wire distribution system is considered. The compensator is realized using a three-phase voltage source inverter (VSI) operated in the current control mode. Detailed digital simulation and experimental results are presented to validate the approach. Index Terms--Load compensation, unbalanced and distorted voltages, voltage source inverter.

The authors propose a control algorithm for a single-phase active-power filter working under a non-stiff voltage source. The method provides compensation for harmonics and reactive power and has an excellent dynamic performance. A detailed synchronization circuit is presented for proper sequencing of operation of the active power filter even when the source voltage contains multiple zero crossings. Experimental study has been carried out under a non-stiff voltage source to verify the proposed control scheme. Index Terms--Harmonic current distortion, non-stiff voltage source, zero crossings.

Voltage imbalance in capacitors is a well-known problem in compensator topologies which use two or more capacitors. This imbalance may exist even if the load does not contain any dc component, due to practical factors. However, when the load contains a dc part, the voltage imbalance problem becomes critical. In this paper, a two-quadrant chopper has been used to regulate the capacitor voltages in a two-capacitor compensator structure. Two different control strategies for the two-quadrant chopper to equalize the voltage of the capacitors have been proposed. The strategies are validated through detailed simulation studies. Experiments have also been carried out to validate the hysteresis control of chopper. Index Terms--Active shunt compensators, chopper control, dc load, voltage equalization, voltage imbalance.

The paper presents the operating principles of a distribution static compensator (DSTATCOM) that is used to maintain the voltage of a distribution bus. A three-phase, four-wire distribution system is assumed in this study. A three-phase bridge inverter circuit that is supplied by two neutral-clamped dc storage capacitors realizes the DSTATCOM. Three filter capacitors, one for each phase, are connected in parallel with the DSTATCOM to eliminate high-frequency switching components. The voltage across the filter capacitor is controlled by a dead-beat controller to maintain the ac bus voltage. The magnitude of the bus voltage is chosen as nominal value, i.e., 1.0 p.u., while its phase angle is obtained through a feedback loop that maintains the voltage across the dc storage capacitors. Through detailed simulation and experimental results, it has been shown that the DSTATCOM can maintain the voltage against any unbalance and distortion in either the load or supply side. Index Terms--Deadbeat control and neutral clamped inverter, distribution static compensator (DSTATCOM), voltage regulation.

Synchronverter (SV) control has emerged as a popular method for distributed energy resources (DERs), to emulate response of a synchronous generator. In this work, a simple gradient descent based pre‐synchronization control for SV scheme is proposed that varies the reference frequency in SV control alone. Thus, local load connection to DER can remain intact during synchronization with proposed pre‐synchronization method, unlike virtual current based methods. Normally, phase‐locked loop used for synchronization purpose, uses a first order loop filter such as a PI controller. In the proposed pre‐synchronization control, the inherent low pass filter of SV scheme itself is used as a loop filter. Transient response analysis is presented in this work, based on small signal transfer functions derived from the proposed method. From the theoretical analysis of proposed pre‐synchronisation control, design of the parameters is presented. Thus, there is no trial and error basis for parameters tuning in the proposed method, as compared to virtual current based methods. Validation of proposed pre‐synchronisation control through experiments are presented for all initial conditions. The transient response analysis, effectiveness of proposed method during local load changes and grid integration are verified by experimental results. [ABSTRACT FROM AUTHOR]

Point wind velocity measurement given by nacelle-top mounted sensor may not be same as effective wind velocity, which strikes the wind turbine rotor blades. This article proposes a new method for the computation of effective wind velocity by inverting the turbine's aerodynamic model after estimating the turbine torque and its rotor speed. Nonlinear control theory-based sliding mode observers are used to estimate the wind turbine generator induced speed emfs, rotor speed, and aerodynamic torque imparted to generator shaft. While satisfying the Lyapunov inequality condition, design aspects of sliding mode observers are discussed in detail. The performance of the proposed wind velocity estimation method is evaluated by using permanent magnet synchronous generator-based wind turbine emulator in laboratory. Simulation and experimental studies confirm that the estimated wind velocity under different wind profile conditions is accurate and can be used in various control algorithms in wind energy conversion systems. [ABSTRACT FROM AUTHOR]

This paper proposes a new control algorithm for effective power management in the dc microgrid with renewable energy sources (RES) and energy storage system (ESS). This scheme overcomes the average power sharing and bus voltage regulation problems with maximum utilization of source power. In the source, the additional power available beyond its average rated value is treated as virtual generation. The new references are generated considering virtual generation. The novelty of the proposed algorithm is to bring the virtual generation effectively in operation. The virtual generation of the individual source is based on available power source. The proposed algorithm reduces the charging/discharging cycles of ESS and, hence, enhances the life span of ESS. It reduces the stress on interfaced converters, regulates the system bus voltage, reduces power fluctuations on the sources, and enhances stability. The proposed control algorithm is verified in MATLAB simulation and in real-time simulator. [ABSTRACT FROM AUTHOR]

This paper deals with the design and stability analysis of a dc microgrid with battery-supercapacitor energy storage system under variable supercapacitor operating voltage. The conventional design method reported in the literature considers the rated supercapacitor voltage in the modeling and design of controllers. However, the supercapacitor unit can discharge as low as 10% of its rated voltage due to self discharge. It is observed that the conventional method of controller design can potentially make the system unstable or introduce ringing in the dc link voltage at low supercapacitor voltage. In this paper, the sensitivity of dc microgrid stability with respect to supercapacitor voltage variation is analyzed, an optimal supercapacitor voltage to be considered in the design is calculated and a design method is proposed to ensure the stability of dc microgrid in all operating modes. The stability of the dc microgrid with controllers designed using the proposed method is evaluated with digital simulation and experimental studies. [ABSTRACT FROM AUTHOR]

This paper deals with the protection of critical loads from voltage-related power quality issues using a dynamic voltage restorer (DVR). A generalized control algorithm based on instantaneous space phasor and dual $P$ - $Q$ theory has been proposed to generate the instantaneous reference voltages to compensate the load voltages with direct power flow control. The proposed algorithm adapts energy-optimized series voltage compensation, which results in a reduction of energy storage requirement. The proposed DVR control scheme can support the load from voltage-related power quality issues irrespective of the load current profile. Each leg of the three-phase three-leg split capacitor inverter is used to inject series compensation voltage in respective phases of the system. Model-based computer simulation studies and real-time experimental results validate the effectiveness of the proposed control algorithm. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Single-stage DC-AC converter systems (SSCSs) are developed by merging both DC-DC and DC-AC conversion processes. These SSCS transfer power from photovoltaics (PV) to loads/grid in one stage. In this study, a PV-based grid tied single-stage DC-AC converter system (GTSS) for low-voltage PV systems is presented. Generally, when SSCSs are connected to the grid, grid voltage template is used to generate reference current which is to be tracked. In doing so, the GTSS delivers power to the grid at a power factor other than unity. A suitable control scheme is implemented in this study to control active and reactive powers' flow from the GTSS to the grid while continuously operating PV at maximum power point. The proposed control scheme of GTSS has attributes such as less complexity and requires simple proportional integral controller. Modelling of control loops in the proposed control scheme is mentioned. A detailed MATLAB/SIMULINK-based simulation and experimental studies are conducted to validate the proposed control scheme. [ABSTRACT FROM AUTHOR]

In a variable switching frequency control scheme, it is challenging to design the voltage source inverter (VSI) parameters without knowing the maximum and minimum switching frequencies. The switching frequency variation depends on the system parameters. Therefore, the expression for frequency variation in one inverter topology does not hold in other topologies. The design of hysteresis current controlled four-leg shunt active power filter (APF) requires the switching dynamics analysis to ensure satisfactory performance of the inverter. In this study, a detailed analysis on the switching dynamics of hysteresis current controlled four-leg VSI and design of various inverter components for compensating unbalanced and nonlinear loads are presented. The results obtained from these analyses can be used in any applications involving hysteresis current controlled four-leg VSI. These results are supported by detailed simulation studies conducted on a three-phase four-leg shunt APF system using Matlab/Simulink. The theoretical studies and design of passive components are also verified by conducting experiments on a prototype of four-leg shunt APF developed in the laboratory. [ABSTRACT FROM AUTHOR]

The power generation from renewable power sources is variable in nature, and may contain unacceptable fluctuations in case of the wind power generation. High fluctuations in power generation may negatively impact the voltage stability of the microgrid. This problem can be alleviated by using hybrid energy storage system consisting of batteries and supercapacitors (SCs) at dc grid. A new control scheme is proposed to control the power sharing between batteries and SCs to match the generation-demand mismatch and hence to regulate the grid voltage. In the proposed control strategy, the SC supplies error component of the battery current in addition to the fast transient power demand. This added feature not only improves the dc grid voltage regulation capability but also reduces the stress levels on the battery and hence increases the life span of the battery. The main advantage of the scheme is that, the uncompensated power due to slow dynamics of the battery is diverted to the SC and keeps the state of charge within the limits for longer duration, as compared to the conventional strategy. The proposed scheme is validated through detailed experimental studies. [ABSTRACT FROM PUBLISHER]

Converter system that does both dc–dc conversion and dc–ac conversion in a single stage is called a single-stage converter system (SSCS). Compared to a two-stage converter, SSCS is more efficient and compact in size. In this paper, a grid-connected SSCS (GCSS) system for photovoltaic (PV) applications is presented. This GCSS transfers power from PV to grid while tracking maximum power point (MPP) continuously. The proposed system has several desirable features such as low switching loss, high gain, and compact size that makes this GCSS suitable for PV systems, where the PV system output voltage is low and varies with time. Design of the presented GCSS components with necessary equations and derivation of both current control loop and voltage control loop required for operation are given. Proposed GCSS is simulated using MATLAB/SIMULINK. Detailed simulation and experimental results are given to verify the efficacy of the proposed GCSS. [ABSTRACT FROM AUTHOR]

A distribution static compensator (DSTATCOM) is used for load voltage regulation, and its performance mainly depends upon the feeder impedance and its nature (resistive, inductive, stiff, nonstiff). However, a study for analyzing voltage regulation performance of DSTATCOM depending upon network parameters is not well defined. This paper aims to provide a comprehensive study of design, operation, and flexible control of a DSTATCOM operating in voltage control mode. A detailed analysis of the voltage regulation capability of DSTATCOM under various feeder impedances is presented. Then, a benchmark design procedure to compute the value of external inductor is presented. A dynamic reference load voltage generation scheme is also developed, which allows DSTATCOM to compensate load reactive power during normal operation, in addition to providing voltage support during disturbances. Simulation and experimental results validate the effectiveness of the proposed scheme. [ABSTRACT FROM PUBLISHER]

This paper presents an adaptive maximum power point tracking (MPPT) algorithm for small-scale wind energy conversion systems (WECSs) to harvest more energy from turbulent wind. The proposed algorithm combines the computational behavior of hill climb search, tip speed ratio, and power signal feedback control algorithms for its adaptability over wide range of WECSs and fast tracking of maximum power point. In this paper, the proposed MPPT algorithm is implemented by using buck–boost featured single-ended primary inductor converter to extract maximum power from full range of wind velocity profile. Evaluation of the proposed algorithm is done on a laboratory-scaled dc motor drive-based WECS emulator. TMS320F28335, 32-bit floating point digital signal controller, is used to execute the control schemes of the in-lab experimental setup. Experimental results show that tracking capability of the proposed algorithm under sudden and gradual fluctuating wind conditions is efficient and effective. [ABSTRACT FROM PUBLISHER]

Interturn short-circuit faults are the leading cause of power transformer's failure. If not detected at the incipient stage, these faults usually develop into more severe faults that would result in irreversible damage to the transformer, unexpected outages, and consequential losses. This paper presents a transformer interturn fault detection system (TIFDS) for the detection of an interturn fault at the inception stage in power transformers. TIFDS is immune to supply voltage imbalance, constructional asymmetries, and instrumental errors. It also takes care of unequal load distribution. The TIFDS algorithm makes the transformer symmetrical in its entire three phases and sets primary-side neutral current to zero value. This is achieved by computing and applying various correction coefficients. However, under the interturn fault condition, TIFDS characterizes the behavior of neutral current. Simulation and experimentation studies are carried out on the 400/110-V, 3 \times 2.5 kVA power transformer. Presented test results demonstrate the effectiveness of the proposed system. [ABSTRACT FROM AUTHOR]

In this paper, a unified energy management scheme is proposed for renewable grid integrated systems with battery–supercapacitor hybrid storage. The intermittent nature of renewable-energy resources (RES), coupled with the unpredictable changes in the load, demands high-power and high-energy-density storage systems to coexist in today's microgrid environment. The proposed scheme dynamically changes the modes of renewable integrated systems based on the availability of RES power and changes in load as well. The participation of battery–supercapacitor storage to handle sudden/average changes in power surges results in fast dc link voltage regulation, effective energy management, and reduced current stress on battery. In addition, the proposed energy management scheme enables the real power transfer along with ancillary services such as current harmonic mitigation, reactive power support, and power factor improvement at the point of common coupling. The proposed scheme is validated through both simulation and experimental studies. [ABSTRACT FROM PUBLISHER]