Stationary Αβ Reference Frame Research Articles

Angular position estimation error extraction for speed and angular position estimation of IPMSM using a parameter-free adaptive observer

In this paper, an alternative approach for extracting the angular position estimation error for an Interior Permanent Magnet Synchronous Machine (IPMSM) is introduced.The originality of this work consists on obtaining the angular position estimation error by the measurable currents, in the αβ stationary reference frame, without considering the high frequency signal injection. Then, using the obtained angular position estimation error, an Adaptive High Order Sliding Mode Observer (AHOSMO) is proposed for estimating the position, speed and acceleration of the IPMSM. The observer is used for a parameter-free virtual dynamical system to avoid impact of the parameter variations on the estimation. The convergence analysis of the proposed observer is established using a Lyapunov stability theory. Furthermore, simulation and experimental results are presented to illustrate the efficiency of the proposed approach against disturbances and noises. The proposed approach is compared with high frequency (HF) and back electromotive force (BEMF) approaches.

Power and Voltage Control for Single-Phase Cascaded H-Bridge Multilevel Converters under Unbalanced Loads

The conventional control method for a single-phase cascaded H-bridge (CHB) multilevel converter is vector (dq) control; however, dq control requires complicated calculations and additional time delays. This paper presents a novel power control strategy for the CHB multilevel converter. A power-based dc-link voltage balance control is also proposed for unbalanced load conditions. The new control method is designed in a virtual αβ stationary reference frame without coordinate transformation or phase-locked loop (PLL) to avoid the potential issues related to computational complexity. Because only imaginary voltage construction is needed in the proposed control method, the time delay from conventional imaginary current construction can be eliminated. The proposed method can obtain a sinusoidal grid current waveform with unity power factor. Compared with the conventional dq control method, the power control strategy possesses the advantage of a fast dynamic response. The stability of the closed-loop system with the dc-link voltage balance controller is evaluated. Simulation and experimental results are presented to verify the accuracy of the proposed power and voltage control method.

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.

Direct Torque and Flux Control of a Four-Switch Three-Phase Inverter-Fed Synchronous Reluctance Motor Drives

This paper presents an application of direct torque and flux control (DTFC) for a four-switch three-phase inverter (FSTPI)-fed synchronous reluctance motor (SynRM) in which the saturation and iron losses' effects are involved in the machine control modeling. The DTFC switching technique for the SynRM fed by FSTPI in low-power and low-cost applications is implemented by imitating the six-switch three-phase inverter (SSTPI). By considering equal effective vectors depicted in SSTPI, the αβ stationary reference frame is represented by using six sectors. Similarly, the voltage space vector formation is constructed in FSTPI. Accordingly the SynRM performance under DTFC is precisely analyzed by considering the saturation and iron losses' effects. The DTFC behavior based on SSTPI- and FSTPI-fed SynRM is evaluated using Simulink benchmark. At different operating conditions, further simulation and experimental results of DTFC based on FSTPI dynamically confirm the effectiveness of the proposed control application on the SynRM.

Control of a cascaded STATCOM with battery energy storage system under unbalanced and distorted grid voltage conditions

This paper proposes a novel control strategy of a star-connected cascaded static synchronous compensator with a battery energy storage system (STATCOM/BESS) under unbalanced and distorted grid voltage conditions. Cascaded second-order generalized integrators are utilized to effectively extract the fundamental positive- and negative-sequence components from the adverse grid voltage. Moreover, proportional multi-complex integral current controllers are adopted to improve the harmonic characteristic of the grid-connected current with zero steady-state error and rapid dynamic response in the stationary αβ reference frame. However, unbalanced grid voltage along with the control target of obtaining the fundamental positive-sequence grid-connected current leads to unbalanced active powers among the three phase clusters. This issue will result in an unbalanced clustered state of charge of battery units and seriously affect the battery life and system performance. Accordingly, clustered active-power-balancing control is presented to solve this issue by injecting an appropriate zero-sequence voltage. Simulation results show the good operational performance of the cascaded STATCOM/BESS and verify the validity and effectiveness of the proposed control strategy.

Study on Control Scheme for the Inverters in Low Voltage Microgrid with Nonlinear Loads

There are a lot of nonlinear loads in real low voltage microgrid system. It will cause serious output voltage and grid current harmonic distortions problems in island and grid-connected modes, respectively. To solve this problem, this paper proposes a droop control scheme with quasi-proportion and resonant (quasi-PR) controller based on αβ stationary reference frame to make microgrid smoothly switch between grid-connected and island modes without changing control method. Moreover, in island mode, not only stable output voltage and frequency, but also reduced output voltage harmonics with added nonlinear loads can be achieved; In grid-connected mode, not only constant power, but also reduced grid current harmonics can be achieved. Simulation results verify the effectiveness of the proposed control scheme.

An Inductance Voltage Vector Control Strategy and Stability Study Based on Proportional Resonant Regulators under the Stationary αβ Frame for PWM Converters

The mathematical model of a three phase PWM converter under the stationary αβ reference frame is deduced and constructed based on a Proportional-Resonant (PR) regulator, which can replace trigonometric function calculation, Park transformation, real-time detection of a Phase Locked Loop and feed-forward decoupling with the proposed accurate calculation of the inductance voltage vector. To avoid the parallel resonance of the LCL topology, the active damping method of the proportional capacitor-current feedback is employed. As to current vector error elimination, an optimized PR controller of the inner current loop is proposed with the zero-pole matching (ZPM) and cancellation method to configure the regulator. The impacts on system's characteristics and stability margin caused by the PR controller and control parameter variations in the inner-current loop are analyzed, and the correlations among active damping feedback coefficient, sampling and transport delay, and system robustness have been established. An equivalent model of the inner current loop is studied via the pole-zero locus along with the pole placement method and frequency response characteristics. Then, the parameter values of the control system are chosen according to their decisive roles and performance indicators. Finally, simulation and experimental results obtained while adopting the proposed method illustrated its feasibility and effectiveness, and the inner current loop achieved zero static error tracking with a good dynamic response and steady-state performance.

The SVFT-Based Control

In this paper, a controller based on the space vector Fourier transform (SVFT) is proposed. The vector controller is implemented in the stationary αβ reference frame and can be designed to track unbalanced and distorted three-phase reference signals containing specific positive-sequence, negative-sequence, and harmonic components. In order to evaluate the proposed controller closed-loop response, three-phase unbalanced and distorted reference currents are imposed in a grid-connected voltage source converter. The ability of the controller to follow the references with zero steady-state error is proved through frequency response plots and stability analysis. Experimental results are obtained to confirm the properties of the proposed scheme.

Study on the Output Performance of DFIG under Unbalanced Grid Voltage

This paper uses dynamic equivalent circuits to study the impact of the unbalanced grid voltage on a Doubly Fed Induction Generator (DFIG) and draws the curves between the voltage unbalance factor (VUF) and the output characteristics of DFIG. A mathematical model of the grid and rotor side converters (GSC and RSC, respectively) is given in the stationary αβ reference frame under unbalanced network voltage conditions, which could be used in the coordinated control of the GSC and RSC. Finally, simulation studies on a 1.5MW DFIG can verify the feasibility of the proposed coordinated control strategy which can be used to improve the performance and stability of the whole wind power generation system.

A Stationary Reference Frame Grid Synchronization System for Three-Phase Grid-Connected Power Converters Under Adverse Grid Conditions

Grid synchronization algorithms are of great importance in the control of grid-connected power converters, as fast and accurate detection of the grid voltage parameters is crucial in order to implement stable control strategies under generic grid conditions. This paper presents a new grid synchronization method for three-phase three-wire networks, namely dual second-order generalized integrator (SOGI) frequency-locked loop. The method is based on two adaptive filters, implemented by using a SOGI on the stationary αβ reference frame, and it is able to perform an excellent estimation of the instantaneous symmetrical components of the grid voltage under unbalanced and distorted grid conditions. This paper analyzes the performance of the proposed synchronization method including different design issues. Moreover, the behavior of the method for synchronizing with highly unbalanced grid is proven by means of simulation and experimental results, demonstrating its excellent performance.