Dq Synchronous Reference Frame Research Articles

Single-phase grid-connected power control in dq synchronous reference frame with space vector modulation using FPGA

This paper presents the performance of controlling the active and reactive power of single-phase grid connected inverter by dq synchronous reference frame and space vector modulation (SVM) which is implemented by using field programmable gate array (FPGA) due to the flexibility they offer in comparison to other digital signal processors, hence it become the standard instruments for implementing various types of pulse width modulation (PWM) digital signal processors (DSPs). The SVM method has used because of its superiority in terms of harmonic distortion, switching losses and utilization of direct current (DC) bus. The synchronization is achieved by using second order generalized integrator (SOGI) due to its simple structure, certain filtering ability and frequency adaptability, in which the phase locked loop (PLL) ensures high performance for single-phase inverter. The active and reactive inverter current has been controlled and decoupled from each other and the dynamic response has been improved and became fast with proper feed-forward and decoupling grid voltage term. The system has simulated by MATLAB and the result shows robust control of injected grid current, active and reactive power control and DC link voltage control.

A novel directional element for transmission line connecting inverter-interfaced renewable energy power plant

The fault currents characteristics of inverter-interfaced renewable energy sources (IIRESs) such as direct-drive permanent magnetic synchronous generator and photovoltaic mainly include weak feed, the variety of source impedance and frequency deviation, which may lead to the false operation of distance protection for transmission line connecting inverter-interfaced renewable energy power plant (IIREPP). The R-L differential equation algorithm based time-domain distance protection is not affected by the fault characteristics of IIRES, but it is difficult to determine the fault direction when faults near the relay. In this paper, a directional element suitable for transmission line connecting IIREPP is proposed, and an improved time-domain distance protection composed of the directional element and the R-L differential equation algorithm based time-domain distance protection is proposed. The characteristics of fault currents of IIRES and traditional AC power grid are analyzed and summarized by deriving the analytical expressions of their fault currents in dq synchronous reference frame. The analysis results show that when the back of the relay is the IIRES and the AC power grid respectively, the change trends of the d-axis component of their fault currents are the same in a short time after faults occur in front of the relay, and the changes of q-axis component of their fault currents are obviously different. The directional element is proposed based on the characteristics of the fault currents on both sides of the transmission line connecting IIREPP. The simulation results verify effectiveness of the proposed protection scheme.

A robust control strategy for a single‐phase grid‐connected multibus microgrid based on adaptive sliding mode control and dynamic phasor concept

Due to the increasing development of distribution networks, the need to use clean energy resources, and the existence of different single-phase and three-phase consumers, the maximum use of both single-phase and three-phase distributed generation (DG) units has become crucial. However, the presence of DG units in microgrids (MGs) requires efficient control strategies, for power control and voltage regulation, to achieve a rapid and proper dynamic response with respect to external disturbances and uncertainties. In this paper, in order to improve the dynamic and steady-state performance of an unbalanced multibus microgrid including inverter-based single-phase DGs, a robust control strategy is proposed for controlling the active and reactive power of DGs. The proposed control scheme is composed of a current controller based on an adaptive sliding mode control method in a virtual synchronous dq reference frame, to control the single-phase inverter output current, and a PI controller to regulate the voltage magnitude of the generation buses connected to DGs. In the proposed control structure, each single-phase inverter is controlled as a virtual balanced three-phase inverter, based on the dynamic phasor concept that makes decoupled control of the active and reactive powers of single-phase inverters possible. In order to evaluate the validity and effectiveness of the presented control structure, a multibus single-phase MG containing several inverter-based single-phase DG units has been simulated in MATLAB software environment, and the performance of the proposed control scheme has been investigated for various scenarios of parametric uncertainties and external disturbances.

Controller Design of an Active Front-End Converter Keeping in Consideration Grid Dynamic Interaction

This paper presents a systematic control design procedure for an active front-end (AFE) converter connected to a power electronics embedded grid. A parametric model of the grid is firstly identified using the AFE itself to excite the system. This model is then integrated with AFE one in order to obtain a global system representation. Subsequently, a globally optimized local controller is synthesised for the AFE keeping in consideration interaction between the converter and the grid. The proposed method is finally tested experimentally and its performance is compared with a traditional Proportional-Integral (PI) controller in a dq synchronous reference frame.

Adaptive Control for Three-Phase Power Converters With Disturbance Rejection Performance

This paper presents voltage regulation and current tracking control strategies for three phase two-level grid-connected power converters. By using power-invariant Park's transformation, an averaged mathematical model of power converters is obtained in dq synchronous reference frame. Then a novel control strategy using adaptive control and H <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">∞</sub> technique is proposed to regulate the dc-link output voltage as well as track a desired current reference for three-phase power rectifiers. More specifically, an efficient adaptive controller is established in the external loop for regulating dc-link output voltage in the presence of external disturbances. A set of H <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">∞</sub> controllers are designed in the internal loop to force the input currents track their desired values. Finally, simulation results obtained from the proposed control method are presented, analyzed, and compared with that of sliding mode control, and the superiority of the proposed control laws is verified.

Fuzzy logic based optimal tip speed ratio MPPT controller for grid connected WECS

Abstract This paper proposes a fuzzy logic based optimal tip speed ratio controlled maximum power point tracking for grid connected variable speed wind energy conversion system. The general system includes a three bladed fixed pitch turbine, permanent magnet synchronous generator (PMSG), three phase uncontrolled rectifier, DC boost chopper, PWM inverter and fuzzy logic controller (FLC). The PMSG is modelled in dq–synchronous reference frame theory. The combination of uncontrolled rectifier and DC chopper is employed to acquire the maximum power by controlling the generator. The dc output voltage of the boost converter is converted into ac voltage by PWM inverter. Fuzzy logic controller is applied to both grid side converter for grid voltage control and generator side converter for optimal tip speed control. Grid side controller is employed to vary the modulation index of PWM inverter to keep up constant grid voltage and generator side controller is utilized to stay up the tip speed ratio at an optimal value to operate the system at maximum power point. The effectiveness of the proposed system is verified through extensive simulation results using MATLAB/SIMULINK environment.

A DQ Synchronous Reference Frame Current Control for Grid Connected Photovoltaic Systems using Single Phase Cascaded H Bridge Multilevel Inverter

This paper projects a high performance decoupled current control using a dq synchronous reference frame for single-phase inverter. For the three-phase inverter the conversion from AC to DC with Proportional Integral controller grants to obtain steady state error for AC Voltages and currents but has a few challenges with the single-phase systems. Hence, an orthogonal pair (β) is created by shifting the phase by one quarter cycle with respect to the real component (α) which is needed for the transformation from stationary to rotating frame. The synchronous reference frame control theory helps in controlling the AC voltage by using DC signal as the reference with the proportional integrator controllers. The implementation of the control is done with two-stage converter with LCL filter for a single-phase photovoltaic system. A modified MPPT Incremental conductance algorithm along with decoupled current control helps in regulating the active and reactive power infused into the grid where the power factor is improved, the efficiency of the system is increased above 95% and total harmonic distortion for current is also reduced to3%. The results have been validated using MATLAB.

Dq Synchronous Reference Frame Model of A Series–Series Tuned Inductive Power Transfer System

A control-oriented circuit model of an inductive power transfer system is needed to design a high-performance controller. In this article, a dq synchronous reference frame model of a series-series tuned resonant inductive power transfer system is proposed. A single-phase dq modeling technique for a resonant converter is used to derive the model. The proposed control-oriented model clearly demonstrates the cross- and mutual-coupling between the state variables of the wireless power transfer system. It is interesting to note that the proposed model is similar to a dq synchronous reference frame model of a three-phase induction motor. The well-known controller design methods, such as proportional-integral controller design, manipulated input decoupling, disturbance input decoupling, state observers, and disturbance observers, etc. can be extended to the inductive power systems with the proposed model. The large- and small-signal responses of the transmitter current versus its input voltage are identified. Considering the frequency response, a new transmitter current controller that has a control bandwidth of 500 Hz is designed to show the validity of the proposed model. The proposed model and the controller are evaluated using simulated and experimental results. The simulated open- and closed-loop frequency responses of the model agree well with the theoretical bode plots of them. Also, the experimental results show that the proportional-integral with feedforward input controller regulates the transmitter current within 1 ms for three conditions: a step change of the reference, a step change of the load, and a step change of the mutual-coupling.

Closed-Loop Control for a Rotational Core Loss Tester

In this paper, a flux density waveform controller is proposed for core loss measurements under rotating magnetic fields in the electrical steel. It is based on a vector control scheme in the synchronous dq reference frame. The proposed dq vector controller eliminates the need of commonly used harmonic compensation techniques; improving the execution and convergence times of the controller. Furthermore, it eliminates the need of filters and transformer isolators, which further reduces delays, thus improving the system's dynamic response. The performance of the controller is analyzed using simulations and validated experimentally. The proposed controller is experimentally shown to control the magnetic flux waveforms within 2% of the reference flux density signals at very high densities (up to 1.9 T) under sinusoidal conditions, and up to 1.2 T under nonsinusoidal conditions.

Improvement of DSOGI PLL Synchronization Algorithm with Filter on Three-Phase Grid-connected Photovoltaic System

Synchronous Reference Frame Phase Locked Loop (SRF PLL) has been widely used for synchronization three-phase grid-connected photovoltaic (PV) system. On the grid fault, SRF PLL distorted by negative sequence component and grid harmonic that caused an error in estimating parameter because of ripple and oscillation. This work combined SRF PLL with Dual Second Order Generalized Integrator (DSOGI) and filter to minimize ripple and minimize oscillation in the phase estimation and frequency estimation. DSOGI was used for filtering and obtaining the 90o shifted versions from the vαβ signals. These signals (vαβ) were generated from three phase grid voltage signal using Clarke transform. The vαβ signal was the inputs to the positive-sequence calculator (PSC). The positive-sequence vαβ was transformed to the dq synchronous reference frame and became an input to SRF-PLL to create the estimation frequency. This estimation frequency from SRF PLL was filtered by the low-pass filter to decrease grid harmonic. Moreover, the output of low-pass filter was a frequency adaptive. The performance of DSOGI PLL with filter is compared with DSOGI PLL, SRF PLL, and IEEE standard 1547(TM)-2003. The improvement of DSOGI PLL with filter gave better performances than DSOGI PLL and SRF PLLbecause it minimized ripples and oscillations in the phase and frequency estimations.

A Novel Fast Voltage Sequence Component Detector of Unbalanced Three-Phase System

The fast and accurate voltage sequence component detection of unbalanced three-phase system is of major importance for the industrial continuous processing. The traditional method is to calculate the voltage in dq synchronous reference frame. This results in low order harmonics and long detection time. A novel fast voltage sequence components detector is proposed in this paper. It is to calculate the sequence component projection on dq rotating reference frame with h times the fundamental angular velocity. Simulation results demonstrate the validity of the algorithm.

Simplified Model of a Three-Phase Induction Motor for Fault Diagnostic Using the Synchronous Reference Frame DQ and Parity Equations

This work is a simplified analysis of a nonlinear model for a three-phase induction motor in steady state behavior to diagnose of additive and parametric faults. Multiple faults are also considered using the parity equation approach and some logical assumptions. The simplified analysis of the nonlinear model in a synchronous reference frame is used and matched with the linear model of d.c. motor, then the parity space is determined, and finally, the residual equations are obtained. The performance of the fault detection system is validated by using the Matlab software.

A control strategy of frequency self-adaptation without phase-locked loop for VSC-HVDC

A control strategy of frequency self-adaptation without phase-locked loop (PLL) under αβ stationary reference frame (αβ-SRF) for a VSC-HVDC system is presented to improve the operational performance of the system under severe harmonic distortion conditions. The control strategy helps to eliminate the cross-coupling under dq synchronous reference frame (dq-SRF), and is achieved through two key technologies: 1) positive phase sequence (PPS) and negative phase sequence (NPS) fundamental components are extracted from the AC grid voltage with an improved multiple complex coefficient filter (IMCF), and 2) grid instantaneous frequency is rapidly and precisely tracked using a frequency self-adaptation tracking algorithm (FATA) without PLL. The proposed strategy is applied to a point-to-point VSCHVDC system and validated by means of simulations. The results are compared to those with the traditional vector control strategy under dq-SRF. Simulation results illustrate that the proposed strategy results in better system performance than that with the traditional strategy in terms of harmonic suppression under normal and severe operating conditions of the AC system.

Model Predictive-Sliding Mode Control for Three-Phase Grid-Connected Converters

This paper focuses on the implementation of an extended model predictive-sliding mode control (EMP-SMC) for three-phase grid-connected converters (GcCs). The proposed control considers the GcC model in the dq synchronous reference frame to forecast possible future behavior of the grid current. After that, the applied voltage vector is selected so that a predefined cost function is minimized. This function is aimed to reduce the grid current ripples during steady-state operation. Compared to the conventional MPC, the proposed EMP-SMC algorithm uses 19 voltage vectors (7 real voltage vectors and 12 additional virtual voltage vectors) for the prediction process. Accordingly, lower grid current THD and lower switching losses are obtained. However, the increase of voltage vectors number will lead to higher computation time delay that may affect the control performances. To overcome this problem, the proposed control uses a sliding mode-based preselection step that limits the prediction process to only ten voltage vectors at the most and a table-based implementation process that reduces significantly the execution time of the whole control algorithm. Simulation and experimental results are presented in order to show performances and effectiveness of the proposed EMP-SMC algorithm.

A Subtractive Feedforward Controller Based on Symmetrical Components Decomposition for DFIG Under Balanced and Unbalanced Loads in Weak Grids

Supplying unbalanced load by a doubly fed induction generator (DFIG) causes power and torque pulsation due to its unbalanced stator and rotor currents. Researchers showed that power and torque pulsation increase the rate of the machine’s tear-and-wear and decrease its life time. This becomes stringier in a weak grid where the DFIG supplies a substantial amount of the load’s power. In order to protect the machine, the torque and power pulsation must be minimized. This paper proposes a subtractive feedforward controller that minimizes the DFIG’s torque and power pulsation of the DFIG machine by forcing the machine to supply the load with balanced current. The remaining unbalanced portion of the current is supplied by the grid. The proposed controller is made up of two main steps: First, we used our symmetrical components decomposition technique to generate dc positive and negative sequences in dq synchronous reference frame without the use of bandpass filters to filter out the $$2\omega _\mathrm{s}$$ components. In the second step, a subtractive feedforward compensator for the negative sequence is added to the generic controller. The compensator removes the negative sequence from the stator currents by adjusting the PWM mechanism at the rotor side. Agreeing with other researchers, the zero sequence was found to be absent in standard internally ungrounded DFIG machines; hence, a zero-sequence compensator was not needed. Our simulation results showed that our proposed controller works very well with balanced as well as the unbalanced loads. Under unbalanced conditions, our simulations showed that the negative sequence stator currents were diminished. This forces the supplied DFIG currents the load to be balanced, which leads to minimize torque and power pulsation. The proposed controller is also proven to be effective by extracting the maximum power under balanced as well as unbalanced loads.

Dynamic Modeling and Control of DFIG for Wind Energy Conversion System Using Feedback Linearization

This paper presents a dynamic modeling and control of doubly fed induction-generator (DFIG) based variable speed wind-turbine. The dynamic model of DFIG is incorporated with all system components which provide simple design and controls. The penetration of wind power is increasing into electrical networks, which necessitates more comprehensive studies to recognize the interaction between the wind farms and the power grid. This paper presents the dynamic model of a DFIG based wind turbine connected to the grid system in the dq-synchronous reference frame. In this article, the feedback linearization method has proposed a controller in order to reduce the oscillation and stabilize the wind turbine system parameters based on feedback linearization concepts. Based on the nonlinear control system, the proposed approach is applied to the rotor side converter and grid side converter. The damping of the DFIG is improved in transient response. In addition, the oscillation of the stator current and DC link voltage during the generator voltage dip are reduced. To the best of author’s knowledge, the proposed control outcomes compared with conventional controller verified the effectiveness, having better performance through simulation tool Matlab.

Modeling FACTS for power flow purposes: A common framework

This paper intends to give a common modeling framework for power flow calculations in power systems with embedded FACTS devices. The proposed method uses the node incidence matrix (Γ) to avoid the problems derived from the widely used admittance matrix.The proposed approach is formulated so that the system of differential equations which are the core of the power flow problem, will be kept invariant regardless of the number of embedded FACTS or their location.As it will be demonstrated, the method provides a very versatile and powerful tool for solving such systems, as it allows for a fast way to change the devices locations, configurations or controls.All the equations have been stated in a synchronous reference frame dq, since it is the most popular reference frame for FACTS control. The main advantage of the proposed problem modeling framework is its simplicity due to the fact that all the equations (both power flow and control equations) are defined in a unique reference.It has to be remarked that what it is proposed in this work, is a common modeling framework, but not an algorithm or solving procedure. The authors tested the proposed framework with the traditional power flow approach and an Optimum Power Flow (OPF) approach.

Multimodel Modeling of Doubly Fed Induction Motor

As the electric drives are highly complex and nonlinear systems subject of several disturbances, it is a great problem to represent them via a unique model with sufficient precision and simple structure. Thus, this paper presents a new doubly fed induction motor (DFIM) model based on multimodel approach as a robust modeling method able to replace the complex system by a set of simpler local models. This approach consists of four steps which are clusters estimation, structure identification, parametric identification and local models combination. The collected data on DFIM are, firstly, clustered into several groups through a Chui’s clustering algorithm. Then, the structure identification is performed on each group using the instrumental ratio (RDI) method. Parameters of each sub model are identified using recursive least square (RLS) method. Finally, obtained sub models are combined using the validity concept. A detailed dynamic model of a DFIM with grid-connected stator and PWM inverter connected rotor, side is presented in the dq-synchronous reference frame in order to generate the input/output data. Simulation results are presented and analyzed up under Matlab/Simulink environment

Control Induced Explicit Time-Scale Separation to Attain DC Voltage Stability for a VSC-HVDC Terminal

This paper proposes a novel control scheme to regulate the DC voltage of a VSC terminal. It significantly simplifies the control design process itself and also results in an uncomplicated and efficient control architecture. First, we present an equivalent state-space model established in a synchronous dq reference frame. Subsequently, we split the overall system into two interconnected subsystems and suppose that they have different dynamics. Based on this assumption, a reduced model is derived by using singular perturbation techniques. The developed control structure is actually based on this reduced model and an explicit time-scale separation. Simulation results clearly demonstrate that the proposed control strategy can regulate the DC voltage with good performances. Moreover, the real DC voltage can be well approximated by the solution of the reduced model.

Singe-Phase Grid-Connected Inverter Based on Voltage-Oriented Control in Photovoltaic Generation Systems

The paper proposes a new control of a transformerless singe-stage single-phase grid-connected inverter in photovoltaic generation systems. The control scheme is mainly based on voltage-oriented control (VOC) with help of second order Generalized Integrator (SOGI). A cascaded control structure with an outer dc link voltage control loop and an inner current control loop is used. The currents are controlled in a synchronous dq reference frame using a decoupled feedback control. The simulated results have proven an excellent performance and verified the validity of proposed system.