Positive Sequence Detector Research Articles

A Novel Frequency and Positive Sequence Detector for Utility Applications and Power Quality Analysis.

Based on multi-dimensional representation and vector calculus definitions, this paper proposes two novel and quite simple algorithms for utility applications and power quality analysis. The first one is a synchronizing procedure, based on a digital PLL (Phase Locked Loop). Its design and dynamic behavior are analyzed for single and three-phase systems. The second one is a positive sequence detector, which uses the proposed PLL to ensure that the positive sequence components can be calculated even under distorted waveform conditions or frequency variations. Since it is not based on Fortescue’s classical decomposition and no special input filtering are needed, its dynamic response may be as fast as one fundamental cycle. In order to validate the proposed models, simulations are shown and experimental results were obtained by means of a DSP-based system and a prototype of Power Quality Monitor. Furthermore, the PLL algorithm was implemented in a selective active filter to confirm the expectations in a closed-loop application.

The Current Synchronous Detection Method Combined with Positive Sequence Detector for Active Power Filters

The Current Synchronous Detection Method Combined with Positive Sequence Detector for Active Power Filters

An FPGA Based Novel Digital Controller for DSTATCOM to Enhance Power Quality in Distribution System

This paper proposes an FPGA based all-on-chip novel digital controller for DSTATCOM to compensate harmonics and reactive power existing in power distribution system. The proposed technique extracts reference current by considering instantaneous symmetrical component active power (ISCAP) theory based phase delay compensation (PDC) control technique. The proposed controller comprises positive sequence detector, PI-controller, low-pass filters (LPF) and hysteresis current controller. All these segments are configured on high speed, low cost field programmable gate arrays (FPGA) hardware resources intended to mitigate harmonics and compensate reactive power in power distribution network. Very high speed hardware description language (VHDL) implementation for each module are produced through system generator and implemented on SPARTAN-3 XC3S5000 FPGA chip through RT-XSG toolbox in Opal-RT platform. The performance of proposed controller is demonstrated through VHDL test bench, simulation and real-time experimental results with consideration of total harmonic distortion (THD) and power factor correction in steady state condition.

Performance Analysis of ANN Based three-phase four-wire Shunt Active Power Filter for Harmonic Mitigation under Distorted Supply Voltage Conditions

This paper presents the design and implementation of three-phase four-wire shunt active power filter (SAPF). It consists of insulated gate bipolar transistors, IGBT based current-controlled voltage source inverter (CC-VSI), series coupling inductor and self-supported DC bus. Power electronics based converters and non-linear loads generate waveform-driven power quality issue as harmonics. Three-phase four-wire SAPF mitigates harmonics, compensates for reactive power, neutral current and power factor correction. Conventionally, the positive sequence detection control strategy using phase-locked loop (PLL) is applied as the synchronizing unit vector element to generate reference source currents. Conventional controller tuning process is difficult and fails to perform satisfactorily under supply voltage variation conditions. In this paper, Levenberg-Marquardt back propagation training algorithm based artificial neural network (ANN) controller is proposed to regulate DC link voltage due to its self-adapting and rapid calculation characteristics that allow the controller to handle high nonlinearity and uncertainty in a non-linear system. Weights of a neuron are adapted to minimize total harmonic distortion (THD) of source current under the step, ramp, time series amplitude variation and frequency and amplitude of modulation conditions. The proposed system is modelled in MATLAB/SIMULINK environment and laboratory prototype with dSpace1104 control card is developed. Experimentation results validate the simulated results of the proposed scheme under supply voltage variations for three-phase four-wire distribution system.

Grid integration of single stage SPV-STATCOM using cascaded 7-level VSC

A multi-functional single-stage grid-tied solar photovoltaic (SPV) system with STATCOM (Static Compensator) capabilities using a cascaded three phase seven level voltage source converter (VSC) is presented in this paper. PS-PWM (Phase Shifted Pulse Width Modulation) technique with a low switching frequency (450Hz) is used to operate the VSC. The proposed SPV-STATCOM system works in three modes i.e. in Mode-1, only active power is supplied to the grid; in Mode-2, both active and reactive powers are supplied to the grid and in Mode-3, only reactive power is supplied to the grid thereby utilizing the proposed system to its fullest capacity in 24h of a day. To extract the maximum power from the SPV array, the incremental conductance maximum power point tracking scheme is utilized. To synchronize the SPV-STATCOM power to the grid and to maintain power factor close to unity, a decoupled current controller, feed-forward term and positive sequence detector dq phase locked loop (PSD-dqPLL) control approach are used. Lower switching losses, harmonic distortions, high output voltage and power are some of the advantages of using a single-stage 7-level cascaded H-bridges. The design and the control scheme performances in all modes are simulated in MATLAB and validated through real time hardware in loop (HIL) system.

Overview and comparative study of two control strategies used in 3-phase grid-connected inverters for renewable systems

In this paper, an overview of grid-connected renewable systems is presented, then two current-control strategies for 3-phase grid-connected inverters are analyzed: firstly, the well-known d–q control in the rotating synchronous reference frame (d–q axes) using Proportional Integral regulators is described, and secondly, the Proportional Resonant controller in the Stationary Reference Frame (αβ axes). In order to obtain a high efficiency of the system when the 3-phase utility grid voltages are affected by harmonic pollution, a Harmonic Compensator (HC) structure is used with the Proportional Resonant controller, this due to the ease way to compensate harmonics when a Proportional Resonant control is utilized instead of a d–q control. Then both control strategies (d–q control and PR + HC) are analyzed under harmonic pollution condition. For both strategies, a Positive Sequence Detector plus a Synchronous Reference Frame Phase-Look Loop (PSD + dqPLL) is used as the synchronization algorithm. After the study, it was observed that the PR controller provides a greater facility for carrying out the harmonic compensation process helping to fulfill with the international standards. A model of a grid-connected photovoltaic system with a nominal power of 10 kW is used to evaluate and compare the performance of the current-control strategies. For this, a Real-Time Digital Simulator (RTDS) platform is used.

IDA-PBC controller design for grid connected Front End Converters under non-ideal grid conditions

A passivity-based non-linear controller design for three-phase front-end converters used to connect renewable energy sources to the grid is proposed in this paper. The control objective is to inject all the generated power to the grid, while adjusting the reactive power exchanged with the power system. Besides, generated currents must have very low distortion, in order to satisfy the standards, even when grid voltages are distorted or unbalanced. The proposed controller is first designed using the Interconnection and Damping Assignment strategy, which allows obtaining controller parameters while ensuring the closed-loop system stability. In order to ensure that the output currents have very low harmonic distortion, the obtained control laws are modified based on the fundamental positive sequence grid voltage, obtained from a positive sequence detector. The proposal allows controlling both injected powers and DC-link voltage, from a unique controller design. Simulation and experimental results are presented to validate the proposed controller.

Sensorless control of inverter dc-bus voltage combined with modified PQ control using extended Kalman filter in a photovoltaic system

this paper presents a sensorless control approach of inverter dc-bus voltage using extended Kalman Filter (EKF). A positive sequence detection of grid voltage and load current is also proposed. The dc-bus voltage estimated by EKF is combined with the modified instantaneous power (p–q) control technique for photovoltaic system application to improve electrical energy quality at the grid under photovoltaic (PV) varying temperature and radiation and also distorted grid voltage ensuring at the same time the supply of unbalanced nonlinear load. The ac grid receives the required active power from the PV cells through boost converter, dc-bus and inverter. It supplies the energy to unbalanced nonlinear load in case of absence of PV energy. The boost converter control extracts the maximum power point from PV cells by Disturb and Observe (P&O) algorithm. Mathematical relationships of different parts of PV system are described and studied. The control system is simulated using the SimPower blockset of Matlab/Simulink. Simulation results have showed that the proposed methodology is an efficient solution to PV control system.

Control Directo de Potencia Predictivo Robusto con Sincronismo Intrínseco

A new type of PLL-less Direct Power Control with robust implementation and deadbeat response is presented for grid-tie inverters. In this work a novel positive sequence detector is also implemented which ensures the elimination of perturbation at the output current due to harmonics content. The control algorithm has an intrinsic synchronization scheme which avoids an additional three-phase PLL. This maximizes the response time and power tracking achieving precise power step reference change in less than 200 μs. The results obtained are shown with both simulations and experiential results in a 15kW three-phase inverter that verifies the performance of the proposed controller, yielding low-harmonics output currents even in abnormal operating situations.

Robust Predictive Control of Grid-Tied Converters Based on Direct Power Control

This study focuses on the control of instantaneous complex power of a grid-connected voltage-source inverter (VSI). In this study, a new space-vector-modulation-based direct power control approach is proposed: the robust predictive direct power control (RP-DPC). The proposed predictive control algorithm ensures that both, instantaneous real and imaginary powers, track the reference with high speed and accuracy reducing steady-state errors. In order to reduce the total harmonic distortion (THD) in the output currents, a fundamental frequency positive sequence detector is used in conjunction with a prediction grid voltage observer. Comparative simulations and experimental results of a $10$ -kW three-phase grid-connected VSI showing the steady-state and transient performance of the proposed RP-DPC are given. A low THD and balanced output currents are maintained even under severe voltage unbalance conditions.

Performance study of a synchronization algorithm for a 3-phase photovoltaic grid-connected system under harmonic distortions and unbalances

In a distributed generation (DG) system, several renewable agents are connected to the low-voltage 3-phase utility grid through an inverter which is used as power condition and must guarantee the higher efficiency of the renewable agent. To attain this level of efficiency, a unitary power factor (FP) between the inverter currents and the utility grid voltages is necessary, and a synchronization algorithm is needed for the perfect synchronization between the renewable agent and the 3-phase utility grid. Within this context, this paper gives a performance study of the Positive Sequence Detector plus a Synchronous Reference Frame Phase-Locked Loop (PSD+dqPLL) as the synchronization algorithm, evaluating its accuracy under different conditions and studying their advantages and drawbacks. A grid-connected photovoltaic system with a nominal power of 6kW is used so as to evaluate the behavior of the synchronization algorithm when the 3-phase utility grid is affected by some disturbances such as voltage unbalances, frequency variations and harmonic distortions. Firstly, several simulations with a disturbed 3-phase utility grid using MATLAB/SIMULINK from The MathWorks, Inc. are shown, and secondly, the previous tests are run in a Real-Time Digital Simulation (RTDS) platform in order to validate the obtained results with simulations.

Fryze Current Controller Based Active Power Filter

Harmonics in a power system can result in communication interference, transformer heating, or solid-state device malfunctions. Active power line conditioners (APLC) or Active power filter (APF) are one important way to achieve harmonic reduction. The purpose of this work is to present shunt active power filter which mitigates harmonic contents in source current due to non linear load present in the system. The novel active power filter is based on Fryze current controller with a positive sequence detector, an approach different from conventional method; the aim is to guarantee the reduction in harmonic from source current. The shunt APF system is implemented with current controlled Voltage Source Inverter (VSI) and is connected to the distribution network for canceling current harmonics. The reference currents are generated using Fryze current minimization (FCM) algorithm and switching signals for VSI are generated from hysteresis current controller (HCC). The shunt APLC system is tested and the performance parameters are obtained under various non-linear and unbalanced load conditions. This is a time domain approach, easy to understand and implement.

Grid Sequence Detector Based on a Stationary Reference Frame

This paper proposes a new three-phase positive sequence detector. The structure is based on a stationary reference frame and a Moving Average Filter (MAF) that guarantees the complete cancellation of harmonics and grid imbalances. Performance of the MAF is analyzed mathematically for a proper selection of the window width of the optimal filter in this application. The time delay introduced by MAFs is constant and known; hence, it can be compensated. Furthermore, it completely eliminates any oscillation multiple of the frequency for what it is designed; The proposed detector operates in open loop and there is no PI controller to be tuned. Thus, the dynamic response and simplicity is improved compared to other solutions. Performance of the proposed detector is verified through simulation and experiment. It shows very good performance under extreme grid voltage conditions, allowing fast detection of the grid voltage positive sequence (within one grid voltage cycle).

Decoupled Double Synchronous Reference Frame PLL for Power Converters Control

This paper deals with a crucial aspect in the control of grid-connected power converters, i.e., the detection of the fundamental-frequency positive-sequence component of the utility voltage under unbalanced and distorted conditions. Specifically, it proposes a positive-sequence detector based on a new decoupled double synchronous reference frame phase-locked loop (DDSRF-PLL), which completely eliminates the detection errors of conventional synchronous reference frame PLL's (SRF-PLL). This is achieved by transforming both positive- and negative-sequence components of the utility voltage into the double SRF, from which a decoupling network is developed in order to cleanly extract and separate the positive- and negative-sequence components. The resultant DDSRF-PLL conducts then to a fast, precise, and robust positive-sequence voltage detection even under unbalanced and distorted grid conditions. The paper presents a detailed description and derivation of the proposed detection method, together with an extensive evaluation using simulation and experimental results from a digital signal processor-based laboratory prototype in order to verify and validate the excellent performance achieved by the DDSRF-PLL