Showing papers on "Stationary Reference Frame published in 2013"

Modeling, Analysis, and Design of Stationary-Reference-Frame Droop-Controlled Parallel Three-Phase Voltage Source Inverters

Abstract: Power-electronics-based microgrids (MGs) consist of a number of voltage source inverters (VSIs) operating in parallel. In this paper, the modeling, control design, and stability analysis of parallel-connected three-phase VSIs are derived. The proposed voltage and current inner control loops and the mathematical models of the VSIs are based on the stationary reference frame. A hierarchical control scheme for the paralleled VSI system is developed comprising two levels. The primary control includes the droop method and the virtual impedance loops, in order to share active and reactive powers. The secondary control restores the frequency and amplitude deviations produced by the primary control. Also, a synchronization algorithm is presented in order to connect the MG to the grid. Experimental results are provided to validate the performance and robustness of the parallel VSI system control architecture.

A New Hybrid PLL for Interconnecting Renewable Energy Systems to the Grid

Abstract: There is a need to develop new control strategies for interconnecting renewable energy systems (RESs) to the power grid due to the continuously increasing penetration of RES and, in particular, of wind power systems. The control strategies are typically based on a fast and accurate detection of the phase angle of the grid voltage which may be estimated by using a phase-locked loop (PLL) control circuit. The performance of the PLL under normal and abnormal operational conditions is a crucial aspect, since the RES is desired to operate accurately to support the power system under grid fault conditions. This paper investigates the performance of three different PLLs: a synchronous reference frame (SRF) PLL, a stationary reference frame PLL, and a decoupled double SRF PLL. The results of this investigation motivate the development of a new hybrid PLL which is a combination of the aforementioned PLLs and uses the advantages of each PLL. The proposed decoupled stationary reference frame PLL (dαβPLL) may be an appropriate solution to use in an interconnected RES with fault ride through (FRT) capability, since it prevails the other PLLs with regard to its accuracy under unbalanced faults. Furthermore, it has a lower deviation of the estimated phase after the fault occurs. This could be depicted as a faster response of the dαβPLL within the same frequency limits. The performance of the new hybrid dαβPLL is verified through simulations and experiments. Furthermore, the new PLL is used in an interconnected RES through experiments under normal and FRT operations.

Discontinuous Decoupled PWMs for Reduced Current Ripple in a Dual Two-Level Inverter Fed Open-End Winding Induction Motor Drive

Abstract: This paper presents investigations on current ripple in a dual 2-level inverter feeding an open-end winding induction motor drive. Pulsewidth modulations (PWMs) for the independently controlled inverters are implemented using a simple effective time placement affected by offset-time concept, thus, eliminating the use of sector identification and lookup tables. Analytical expressions for ripple content in the motor phase current are developed and a current trajectory is theoretically obtained directly from the switching states of the dual inverter in a stationary reference frame. In addition, this paper also describes a current ripple trajectory in the motor by exploring the freedom of independently operating the individual inverters with different PWMs. Based on the analysis, discontinuous PWMs are employed for the individually inverters that not only offer the advantage of reducing the total switching commutations in the inverters but also reduces the current ripple. Analytical expression for the RMS ripple current and variation in RMS ripple current in one cycle of operation for different PWMs are also presented for the entire speed range of the dual-inverter drive. The performance of the dual-inverter drive with the proposed PWM variants is first studied analytically and then verified by performing suitable experiments on a 1-kW open-end winding induction motor drive.

MRAS Speed Observer for High-Performance Linear Induction Motor Drives Based on Linear Neural Networks

Abstract: This paper proposes a neural network (NN) model reference adaptive system (MRAS) speed observer suited for linear induction motor (LIM) drives. The voltage and current flux models of the LIM in the stationary reference frame, taking into consideration the end effects, have been first deduced. Then, the induced part equations have been discretized and rearranged so as to be represented by a linear NN (ADALINE). On this basis, the transport layer security EXIN neuron has been used to compute online, in recursive form, the machine linear speed. The proposed NN MRAS observer has been tested experimentally on suitably developed test set-up. Its performance has been further compared to the classic MRAS and the sliding-mode MRAS speed observers developed for the rotating machines.

Speed Sensorless Vector Controlled Induction Motor Drive Using Single Current Sensor

Abstract: New speed and current estimation techniques are proposed in this paper. These are used to formulate a single current sensor-based vector controlled drive. The speed sensorless control is formulated by developing a new model reference adaptive system (MRAS) using the outer product of →vs* and →is as the functional candidate. Contrary to the method available that depends on stator resistance, the proposed approach is immune to the variation of stator resistance. This is possible by using reference quantities (i.e., voltage and currents) in reference model and actual quantities (i.e., currents) in adjustable model. The current estimation on the other side extracts the information of the phase currents in two-phase stationary reference frame by using the corresponding synchronous reference frame variables and the vector rotator. The current estimation also does not depend on stator resistance and hence the complete system can perform very well at low speed. The proposed speed and current estimation techniques are simulated in MATLAB/Simulink and experimentally validated through a dSPACE-1104-based laboratory prototype.

A novel design method for SOGI-PLL for minimum settling time and low unit vector distortion

Abstract: Phase-locked loops (PLLs) are necessary in grid connected systems to obtain information about the frequency, amplitude and phase of the grid voltage. In stationary reference frame control, the unit vectors of PLLs are used for reference generation. It is important that the PLL performance is not affected significantly when grid voltage undergoes amplitude and frequency variations. In this paper, a novel design for the popular single-phase PLL topology, namely the second-order generalized integrator (SOGI) based PLL is proposed which achieves minimum settling time during grid voltage amplitude and frequency variations. The proposed design achieves a settling time of less than 27.7ms. This design also ensures that the unit vectors generated by this PLL have a steady state THD of less than 1% during frequency variations of the grid voltage. The design of the SOGI-PLL based on the theoretical analysis is validated by experimental results.

A Control Technique for Integration of DG Units to the Electrical Networks

Abstract: This paper deals with a multiobjective control technique for integration of distributed generation (DG) resources to the electrical power network. The proposed strategy provides compensation for active, reactive, and harmonic load current components during connection of DG link to the grid. The dynamic model of the proposed system is first elaborated in the stationary reference frame and then transformed into the synchronous orthogonal reference frame. The transformed variables are used in control of the voltage source converter as the heart of the interfacing system between DG resources and utility grid. By setting an appropriate compensation current references from the sensed load currents in control circuit loop of DG, the active, reactive, and harmonic load current components will be compensated with fast dynamic response, thereby achieving sinusoidal grid currents in phase with load voltages, while required power of the load is more than the maximum injected power of the DG to the grid. In addition, the proposed control method of this paper does not need a phase-locked loop in control circuit and has fast dynamic response in providing active and reactive power components of the grid-connected loads. The effectiveness of the proposed control technique in DG application is demonstrated with injection of maximum available power from the DG to the grid, increased power factor of the utility grid, and reduced total harmonic distortion of grid current through simulation and experimental results under steady-state and dynamic operating conditions.

An Adaptive Digital Control Technique for Improved Performance of Grid Connected Inverters

Abstract: Grid connected voltage source inverters may be controlled in the stationary reference frame by means of the infinite impulse response (IIR) P+Resonat regulator. This regulator is able to correctly track fixed frequency sinusoidal references, but does not perform well if the frequency of the electric grid voltage is varied. In order to avoid the lack of precision to track variable frequency sinusoidal references, an adaptive IIR filter structure is proposed which offers good tracking properties even if the frequency of the grid voltage varies. This filter adapts its coefficients in real time and is inherently stable no matter the adaptation process, thus overcoming one of the most important drawbacks of the IIR filter structure. Furthermore, this structure is perfectly suited to be programmed in fixed point digital signal processors (DSPs) because of some important numeric properties, i.e., it has a high mapping precision and a low round-off accumulation, and it avoids quantization limit cycle oscillations. The proposed adaptive controller has been tested by means of the TI TMS320F2812 DSP. The obtained experimental results show up that this controller allows the correct tracking of a sinusoidal reference, even if this reference is time variant.

Study and Control of Three-Phase PWM Rectifier Based on Dual Single-Input Single-Output Model

Abstract: A novel dual single-input single-output (DSISO) model for a three-phase two-level PWM rectifier is proposed, in order to simplify the complicated structure of multiple input variables and multiple control objectives. In the proposed model, the three-phase PWM rectifier is equivalent to two single-phase PWM rectifiers in the α-β stationary reference frame, which is easier to analyze than a three-phase PWM rectifier. Based on the DSISO model, the small-signal model is derived, the control-to-output transfer function is deduced, and the design principle of the voltage controller is given. The control strategy is analyzed to determine switching control signals in a switching period. Experimental results confirm the validity of the DSISO model and the feasibility of the control strategy based on DSISO model.

Methods of determining initial position of a rotor and systems thereof

Abstract: At least one example embodiment discloses a drive system including a motor including a rotor, the motor configured to receive a measured current, a controller configured to generate a voltage for the motor at a stationary reference frame, the voltage having a frequency and the measured current being based on the voltage, a filter configured to obtain position information of the rotor based on the measured current and a nonlinear observer configured to estimate a rotor position of the motor during the stationary reference frame based on the position information. The controller is configured to control the motor based at least in part on the estimated rotor position.

Park's vector approach for online fault diagnosis of induction motor

Abstract: In this paper, the induction motor is modelled in stationary reference frame using the equations derived from the equivalent circuit model of the stationary reference frame. After implementing the model, it is analysed under healthy and faulty condition. The considered faulty conditions of the induction motor include the stator and rotor fault. Any single phasing situation creates the stator fault that may result in opening and shorting of one or more phase winding. In this work the modelled induction motor is modified for analysing the open circuit fault of the stator phase windings and the result are compared using the using the voltage pattern and the current pattern obtained using Park's vector approach. The results are compared to give the best solution in stator fault diagnosis. The broken bar fault is introduced in the rotor by making some modifications in the model and the current pattern obtained using Park's vector approach is analysed with the difference in the pattern produced during the healthy condition. Finally, both the faults are introduced in the model and the result is analysed using Park's vector approach.

Sensorless control method for PMSM based on frequency-adaptive disturbance observer

Abstract: The rotor angle can be estimated from the stator flux in permanent magnet synchronous motor (PMSM). Although integrations are essential to estimate the stator flux from the voltages and currents in the stationary reference frame, disturbances can arise in the process of integrations due to practical reasons. In this paper, a frequency-adaptive disturbance observer has been proposed to remove the disturbances in estimating the stator flux and to enhance the accuracy of the rotor angle estimation. The design and utilization of the proposed observer are detailed under the consideration of its application to the practical system driving PMSM. The performance of the proposed sensorless method has been mainly assessed through experiments at low speed operations, where the sensorless drive of PMSM is regarded as being extremely difficult without the signal injection.

A real-time observer for UAV's brushless motors

Abstract: Vector control has been widely used in control of permanent magnet synchronous motors (PMSM). This technique requires an accurate knowledge of the rotor position. In many applications, such as mini-UAV, it is not possible to install any mechanical sensor. Therefore, a sensorless technique using position observer has to be implemented in order to estimate the rotor position. In this paper, we propose a new observer for PMSM sensorless control: the position estimate is generated upon electromagnetic relations (dynamics of magnetic flux in the motor) in the two-phase stationary reference frame. The implementation of the proposed observer is not a real burden; its validity is experimentally tested and satisfactory results are obtained regarding real position (and speed set-point) tracking in different operating situations.

A new sensorless control strategy by high-frequency pulsating signal injection into stationary reference frame

Abstract: In this paper, a new sensorless control strategy by injecting a high frequency pulsating signal into the stationary reference frame is proposed. Differing from the two most popular conventional high frequency injection methods, i.e. pulsating voltage into estimated rotor synchronous rotating reference frame and rotating voltage into stator stationary reference frame, the new proposed strategy injects a pulsating high frequency carrier voltage into stator stationary reference frame. Then, the rotor position information can be retrieved from the rotor position dependent response current. The algorithm of the proposed strategy, compensation of cross-saturation effect and magnetic polarity detection are discussed and analyzed in this paper. The new proposed strategy has the advantage of fixed and simpler voltage signal injection, also the simpler and quicker demodulation from the response current comparing with the conventional high frequency injection methods. Furthermore, the experimental results based on an interior permanent magnet synchronous machine (IPMSM) demonstrate that the new proposed strategy has robust magnetic polarity detection, and can achieve accurate rotor position estimation with outstanding steady and dynamic performances.

Sensorless control of surface-mounted permanent-magnet synchronous machines for low-speed operation based on high-frequency square-wave voltage injection

Abstract: This paper proposes a high-frequency signal injection-based position estimation scheme for surface-mounted permanent-magnet synchronous machines (SPMSM) operating in the low-speed range. A square-wave voltage vector is injected in the estimated rotating reference frame. The rotor position information is then extracted from the envelopes of the resulting induced high-frequency currents in the stationary reference frame. The proposed position estimation method has almost no dependence on machine asymmetric properties and, therefore, is well suited for SPMSM applications. Simulation results are provided to verify the effectiveness of the proposed method from 1 Hz to 50 Hz electric fundamental frequency under all load conditions. Experimental results on a 2.4-kW SPMSM in both sensorless speed and torque controls are also provided to validate the proposed method. The sensorless speed control can be achieved as low as 0.3 Hz electric fundamental frequency.

Optimalization of SOGI PLL for single-phase converter control systems: Second order generalized integrator (SOGI)

Abstract: A precise and robust synchronization of a control system of single-phase converters connected to ac power grid is a key factor for proper function of these devices. This paper presents optimization of Second Order General Integrator Phase Locked Loop (SOGI PLL) and its implementation. The SOGI makes it possible to identify the position of either the power grid voltage or current vector in a stationary reference frame. The presented method is able to secure fast response on amplitude steps of input signal and hence track precisely the fundamental harmonic of the input signal.

Particle filter based grid synchronization with voltage unbalance and frequency variation in smart grid

Abstract: Computing the phase angle of a three-phase voltage signal in utility grid is critical for the synchronization of smart grid. Only if the phase angle is accurately estimated, the energy transfer between the distributed power generators and the utility grid can be properly controlled. In this paper, we propose a particle filter (PF) based scheme to estimate the phase angle of the utility grid in the presence of voltage unbalance and frequency variation in the αβ stationary reference frame where the positive and negative sequences of the input three-phase signal are separated by Clarke transformation. For the filter algorithm, the traditional SIR filter is customized for the grid synchronization problem by exploiting the feature of the grid state system dynamics and incorporating the deterministic resampling. Extensive simulations have been conducted to verify the effectiveness and efficiency of the proposed PF-based synchronization scheme. It is shown that the proposed PF-based scheme outperforms the traditional EKF-based scheme in terms of both estimation accuracy and convergence time, when both the voltage imbalance and frequency variation are exerted.

Sensorless vector control of linear permanent magnet synchronous motor

Abstract: A practical vector control algorithm for speed control of linear permanent magnet motor without a position sensor is presented. The vector control algorithm is based on decoupled control of d and q-axes currents. The errors in the d and q-axes currents are used as inputs to the two PI controllers to generate the orthogonal d and q-axes components of the reference voltage in rotor flux vector frame of reference. Decoupling of both the d-axis and q-axis currents control loops is achieved by adding the decoupling terms to the command voltages in the rotor flux vector reference frame generated by the PI controllers. These decoupled voltages are further transformed to the stationary frame of reference by using the electrical position of the mover, in order to generate the reference voltage vector by using space vector modulation. A fixed switching frequency is achieved because of space vector modulation which results in a smooth response of both the d and q-axes current control loops. Sensorless estimation of the mover's position is determined from the orthogonal components of the stator flux vector in stationary reference frame and the load angle. The load angle is calculated from the electromagnetic thrust force using a linearized relation between the load angle and the thrust force. The presented control scheme is experimentally validated by its practical application to a prototype linear permanent magnet synchronous motor drive system in the laboratory. Practical results prove the excellent response of both the d-axis and q-axis current control loops. These practical results also imply the effectiveness of proposed sensorless speed estimation algorithm under both the loaded and unloaded operating conditions for the prototype linear permanent magnet synchronous motor.

Development of a proportional + resonant (PR) controller for a three-phase AC micro-grid system

Abstract: This document presents a Proportional + Resonant (PR) controller design for regulating the active and reactive power output of a three-phase AC Micro-Grid inverter system The system employs a Voltage Sourced Inverter (VSI) The VSI is configured to operate as a current source through an interface L-filter The power is controlled indirectly by controlling the inverter’s output current The stationary reference frame strategy is adopted for the design of the PR controller A model of a grid connected AC inverter and a detailed design of the inverter’s PR based control scheme are presented The control scheme is developed and simulated in MATLAB/Simulink software environment The control algorithm code is generated for a target device Using Processor In-the Loop (PIL) simulation, functional equivalence testing is performed between the simulated control algorithm and the compiled algorithm code on the target device Results in both normal and PIL simulations are discussed from the viewpoint of steady state and dynamic performance of the controller

Current control of six phase induction motor under open phase fault condition

Abstract: In this paper, the analysis and design of current controller of a multiphase induction motor with open phase are proposed. The current controller is designed in the stationary reference frame where the multiphase machine is represented in two orthogonal subspaces called dq and xy. In fault conditions, the controller will be able to control the same dq reference current vector as normal operation and additional unbalanced xy reference current vector. To compensate this unbalancing, the current control scheme based on positive and negative-sequence controllers is used. A discussion and simulation of the strategies are presented.

An extended flux model-based rotor position estimator for sensorless control of interior permanent magnet synchronous machines

Abstract: Starting from the classical dynamic model of interior permanent magnet synchronous machines (IPMSMs) expressed in the stationary reference frame, this paper presents a mathematical model reconstruction process for IPMSMs, from which an extended flux-based IPMSM model is derived. Compared with the commonly used extended electromotive force-based model, the extended flux-based model has notable advantages of simpler model structure and less sensitive to machine parameter and speed variations. An extended flux model-based position estimator is then proposed for sensorless control of an IPMSM by utilizing a sliding-mode observer with a dynamic position compensator. The latter improves the dynamic performance and low-speed operating capability of the sensorless controller. Both simulation and experimental results are provided to validate the proposed position estimator and sensorless IPMSM drive system.

Predictive power control of grid-connected four-level inverters in stationary reference frame

Abstract: This paper proposes a four-level diode-clamped inverter for the grid connection of high power, medium voltage wind energy conversion systems. A predictive control scheme is presented in stationary reference frame to regulate the active and reactive powers along with the DC-link capacitor voltages. The proposed method doesn't require any PI controller, phased lock loop and the complex modulation. The discrete-time model of the inverter is used to predict the future behavior of the control variables for all possible switching states generated by the inverter. These predictions are evaluated using a cost function, and then, the switching state which minimizes the cost function is chosen and applied to the inverter. The feasibility of the proposed method is verified by MATLAB/Simulink software.

Investigating characteristics of a concentrated-winding interior permanent magnet synchronous machine for sensorless direct torque control

Abstract: This paper investigates characteristics of a fractional-slot, concentrated-winding (FSCW) Interior Permanent Magnet Synchronous Machines (IPMSM) under sensorless Direct Torque Control (DTC). The FSCW IPMSM is being developed vigorously in recent years because of its high-power density, high efficiency, wide field-weakening capability, and high fault tolerance compared to the distributed-wound IPMSMs. The major disadvantage of concentrated winding is often cited to be its non-sinusoidal stator MMF. However, using appropriate combination of slots and poles, nearly sinusoidal EMF and very low cogging torque can be achieved. Although steady-state performance such as efficiency and constant power speed range of this type of PM machines have recently been published, dynamic performances have yet not been reported. The sensorless DTC schemes, which rely on the machine model, were applied to a prototype a 14-pole/ 18-slot, double layer concentrated-wound IPM machine. The model for distributed wound IPMSM was used for the control. This paper investigates the appropriate stationary reference frame of the FSCW IPMSM motors which should be appropriately shifted because of the harmonic and sub-harmonic components in the stator mmf of the concentrated winding machine compared with the distributed windings (DW) machine. The experimental results on the concentrated winding IPM machine confirmed the effectiveness of the proposed adjustment of the stationary reference frame according to the investigation of the difference between concentrated and distributed windings of an IPMSM.

Fault Detection and Diagnosis in Induction Machines: A Case Study

Abstract: Nowadays in industry there many processes where human intervention is replaced by electrical machines, especially induction machines due to his robustness and performance. Although, induction machines are a high reliable device, they are also susceptible to faults. Therefore, the study of induction machine state is essential to reduce human and financial costs. It is presented in this paper an on-line system for detection and diagnosis of electrical faults in induction machines based on computer-aided monitoring of the supply currents. The main objective is to detect and identify the presence of broken rotor bars and stator short-circuits in the induction motor. The presence of faults in the machine causes different disturbances in the supply currents. Through a stationary reference frame, such as αβ-vector transform it is possible to extract and manipulate the results obtained from the supply currents using Principal Component Analysis (PCA).

Improved direct torque control of induction motors using adaptive observer and sliding mode control

Abstract: This paper presents the synthesis of an adaptive observer which is used for the improvement of the direct torque control of induction motor drives. The observer detects stator flux components in two-phase stationary reference frame, rotor speed and stator resistance by measure of the stator terminal voltages and currents. The observer is adapted using a simple algorithm which does not imply a high computational load. Stability analysis based on Lyapunov theory is performed in order to guarantee the closed loop stability. Simulation tests under load disturbance and stator resistance variation are provided to evaluate the consistency and performance of the proposed control technique in the low and high speeds.

Predictive Current Control for Grid-Connected Inverters Under Unbalanced Grid Voltage

Abstract: Based on the mathematic models of grid-connected inverter under unbalanced grid voltage,the control strategy were proposed to implement the balance of three-phase current,eliminate the ripple in active and reactive power,in which the current reference of the positive sequence and the negative sequence for the different control targets was deduced.And then,based on the two-phase stationary reference frame,a predictive current control scheme was proposed to implement the accurate control of the positive sequence and the negative sequence current,which can eliminate the bad effects to the operation performance of grid-connected inverter,caused by the current sampling delay and the sequence decomposition.The feasibility of the proposed algorithms and control strategy were validated by experimental studies on a 3 kVA grid side converter system.

Performance analysis of PV fed single phase T-source inverter

Abstract: This paper deals with performance analysis of PV fed single phase T-source inverter for a standalone system. The T-source inverter has an ability to perform DC to AC conversion and buck boost operation in a single stage. Compared to Z-source inverter the number of passive elements are reduced in T-network. The traditional voltage and current source inverters cannot provide such feature. Normally, the proportional integral (PI) control is commonly used in the stationary reference frame for current controlled inverters. However, it has two main drawbacks: inability to track a sinusoidal reference without steady state error and poor disturbance rejection capability. These problems are overcome by using proportional resonant (PR) controller. The performance analysis of T-source inverter is carried out with PI and PR controller. A simulation of Single phase T-source inverter is done using MATLAB/ Simulink.

An adaptive phase-locked loop algorithm for single-phase utility connected system

Abstract: This paper proposes a novel algorithm employed to detect both the phase-angle and the frequency of the single-phase utility grid voltage. The proposed algorithm uses an adaptive notch filter (ANF) operating in conjunction with a Phase-Locked Loop (PLL) system, yielding an algorithm called ANF-αβ-pPLL. The αβ-pPLL structure is based on the instantaneous active power theory for three-phase power systems. Thus, for single-phase systems, the proposed PLL algorithm can be analyzed into a fictitious two-phase stationary reference frame (αβ-coordinates), in which a normalized fictitious quadrature voltage (νβ) is obtained from the estimated PLL phase-angle. On the other hand, an adaptive filter is used to extract the fundamental component of the utility voltage, allowing the rejection of voltage harmonic disturbance. In order to validate the theoretical development, the performance of the single-phase ANF-αβ-pPLL algorithm is evaluated by means of both simulation and experimental tests under utility grid disturbances, such as voltage harmonics, voltage sags/swells, phase-angle jumps and frequency variations.