Multiple Synchronous Reference Frames Research Articles

Hybrid Frame-Based Current Control Scheme for LC-Equipped PMSM With Non-Sinusoidal Back-EMF

Permanent-magnet synchronous machine (PMSM) drive with a sine wave <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">LC</i> filter has the features of low insulation stress and current harmonics. However, few studies consider the impact of back-electromotive force (EMF) harmonics on the <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">LC</i> -equipped PMSM drive system. The non-sinusoidal back-EMF can cause current harmonics, meanwhile, it also affects the stability analysis and high-frequency resonance suppression. In order to solve these two problems simultaneously, a hybrid frame-based current control scheme is proposed in this paper. The quantitative effect of back-EMF harmonics on control behaviors is analyzed first. A virtual triple three-phase system with auxiliary currents is developed to decompose the fundamental and harmonic contents, which not only contributes to independent current harmonic regulation in multiple synchronous reference frames, but also simplifies system stability analysis considering non-sinusoidal back-EMF. Then, an active damping method based on stator current feedback is implemented in the stationary frame to suppress the resonance, and no additional passive components or sensors are required. Finally, experimental results are provided to verify the effectiveness and superiority of the proposed method.

Implementation and performance comparison of harmonic mitigation schemes for three-phase grid-connected voltage-source converter under grid voltage distortion: HiL and experimental validation

This paper presents an implementation methodology for a current harmonic compensation technique of three-phase grid-connected voltage-source converter (VSC), which was applied under the grid voltage distortion and frequency variation. The proportional–integral plus multi-resonant controllers (PIMR) were used to mitigate the high-order harmonic current. The harmonic compensators were used in the synchronous reference frame at harmonic orders 6th and 12th for suppression of the grid voltage harmonic orders 5th, 7th, 11th, and 13th with a total harmonic distortion of 4.69%. The PIMR controller was transformed to the discrete-time domain and implemented on a TMS320F28379D digital signal processor. The PIMR controller was compared with the conventional multiple synchronous reference frame (PIMSR) controller. The two control schemes were validated with a hardware-in-the-loop (HiL) and with a 5 kW three-phase LCL-filtered grid-connected VSC. The PIMR and PIMSR controllers exhibited excellent harmonic rejection on the grid current with a total harmonic distortion close to 1%, which complied with the IEEE 1547 standard. The grid current can track the reference command with a fast dynamic response. Moreover, the PIMR controller consumed a computational time of 1.625μs, 35% of the PIMSR controller.

Multiple Synchronous Reference Frame Current Harmonic Regulation of Dual Three Phase PMSM With Enhanced Dynamic Performance and System Stability

This article proposes an improved multiple synchronous reference frame (MSRF) current harmonic regulation strategy for dual three phase permanent magnet synchronous machine drive system. A new vector space decomposition transformation combined with auxiliary currents is designed to decouple the current fundamental with current harmonics, and the auxiliary currents can be established by the π/9 phase shifting of the physical currents in <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">ABC</i> set and the π/18 phase shifting of the physical currents in <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">XYZ</i> set. By employing the proposed current decomposition, it is easy to detect them using low pass filters in MSRFs. A generic complex vector proportional integral regulator is then employed to control the detected current harmonics to track the current harmonic references. Compared with the existing MSRF-based methods, the proposed method provides a new current harmonic detection with reduced delay effect, which contributes to enhancing the dynamic performance of current harmonic regulation, and also stabilizing the control system. Comprehensive experimental results are given to validate the effectiveness of the proposed control strategy.

Deep Learning Based Predictive Compensation of Flicker, Voltage Dips, Harmonics and Interharmonics in Electric Arc Furnaces

In this research work, deep machine learning-based methods together with a novel data augmentation are developed for predicting flicker, voltage dip, harmonics, and interharmonics originating from highly time-varying electric arc furnace (EAF) currents and voltage. The aim with the prediction is to counteract both the response and reaction time delays of active power filters (APFs) specifically designed for electric arc furnaces (EAF). Multiple synchronous reference frame (MSRF) analysis is used to decompose the frequency components of the EAF current and voltage waveforms into dqo components. Then using low-pass filters and prediction of the future values of these dqo components, reference signals for APFs are generated. Three different methods have been developed. In two of them, a low-pass Butterworth filter is used together with a linear finite impulse response (FIR)-based prediction or long short-term memory network (LSTM) for prediction. In the third method, a deep convolutional neural network (CNN) combined with a LSTM network is used to filter and predict at the same time. For a 40-ms prediction horizon, the proposed methods provide 2.06%, 0.31%, 0.99% prediction errors of the dqo components for the Butterworth and linear prediction, Butterworth and LSTM, and CNN with LSTM, respectively. The error of the predicted reconstructed waveforms of flicker, harmonics, and interharmonics resulted in 8.5%, 1.90%, and 3.2% reconstruction errors for the abovementioned methods. Finally, a Simulink and GPU-based implementation of predictive APF using Butterworth filter + LSTM and a trivial APF resulted 96% and 60% efficiency on compensation of EAF current interharmonics.

Loss-Minimization Strategy of Nonsinusoidal Back EMF PMSM in Multiple Synchronous Reference Frames

Traditional loss-minimization strategies of model-based control, copper loss minimization (CLM), and finite-element-based control suffer from respective problems of iron loss mismatch with a physical view, pseudominimization and amounts of efforts when they are applied to permanent magnet synchronous motor with nonsinusoidal back electromotive force (NS-PMSM). This article combines theories of multiple synchronous reference frames and iron loss resistance to develop a new model of NS-PMSM, based on which the stator iron loss is evaluated to match well with the physical view. Then, a current strategy is proposed to minimize the total stator loss under constraints of ripple-free torque and finite dc supply. The optimal current solution is solved in closed form and implemented effortlessly. A good robustness to phase resistance variation is also achieved. Compared to CLM, the proposed strategy realizes a true minimization with the stator loss reduced by 9% and the motor efficiency enhanced by 0.7% at rated operation of a 3.8-kW NS-PMSM. Precision of the iron loss evaluation and performances of the strategy are validated experimentally on the 3.8-kW motor setup.

Real-Time Detection of Interharmonics and Harmonics of AC Electric Arc Furnaces on GPU Framework

In this paper, a method based on the multiple synchronous reference frame analysis is recommended and implemented to detect time-varying harmonics and interharmonics of rapidly fluctuating asymmetrical industrial loads. The experimental work has been carried out on a typical three-phase alternating current arc furnace installation. In the recommended method, the reference frame is rotated in both directions at speeds corresponding to the positive and negative sequences of all harmonics and all interharmonics 5 Hz apart. To extract the direct current components of the transformed d–q quantities, a low-pass filter is employed. In order to keep the delay of the filter at zero frequency less than a few ms, Kalman estimation technique has been used. Back transformation is then applied for each harmonic and interharmonic component to obtain their positive- and negative-sequences of the associated harmonic and interharmonic in the actual line current waveforms. Parallel computing technique has been applied for the real-time detection of both the phase and the amplitude of all harmonics and interharmonics. This is achieved on NVDIA Jetson TX1 graphics processing unit framework for a sample industrial plant. The developed system is shown to be useful for fast and accurate generation of reference signals for the controllers of the advanced technology power conditioning systems which successfully compensates interharmonics, harmonics, and flicker of the rapidly fluctuating nonlinear industrial loads.

Interaction and coordination between reactive compensation and harmonic suppression for three‐phase buck‐type D‐CAP

Dynamic capacitor (D-CAP) could be designed to compensate reactive power and suppress harmonic currents simultaneously by means of regulating DC and harmonic terms in duty-ratio modulation signal. However, the main constraint is that the amplitudes of DC and harmonic terms are always correlative, leading to the interaction between reactive and harmonic currents of D-CAP. To minimise mutual effects between reactive and harmonic currents, this study presents coordinated control between reactive compensation and harmonic suppression for buck-type D-CAP. The major concern of coordinated algorithm is to pre-estimate and select the DC and harmonic terms reasonably according to their inter-constraint relationship. Thus, D-CAP can optimise the generation of reactive and harmonic current references in different scenarios. Meanwhile, selective current control in multiple synchronous reference frames is employed to regulate reactive and harmonic current effectively. A series of experimental results are provided to verify the correctness of proposed coordinated control.

Exponential Smoothing of Multiple Reference Frame Components With GPUs for Real-Time Detection of Time-Varying Harmonics and Interharmonics of EAF Currents

In this research work, a multiple synchronous reference frame (MSRF)-based analysis method, used together with exponential smoothing (ES) to accurately obtain the time-varying harmonics and interharmonics of electric arc furnace (EAF) currents, is proposed. The proposed method has been implemented on NVIDIA Geforce GTX 960 graphics card for the parallel processing of all harmonics and interharmonics so that real-time processing of the EAF currents obtained from a measurement point of the electricity transmission system is possible. To obtain the best possible accuracy for the EAF current harmonics and interharmonics estimation, the ES order has been optimized specific to each harmonic and interharmonic frequency component. It has been shown on field data that the implemented system is capable of successfully estimating all harmonics up to the 50th and all interharmonics at 5-Hz resolution in real time. Moreover, active filtering of certain harmonics and interharmonics has been achieved in the simulation environment and it has been shown that successful real-time filtering of any harmonic and interharmonic component is possible with the proposed MSRF+ES method. Hence, it can be concluded that the proposed system can be used to generate reference signals for the controllers of the new technology compensation systems such as active power filters.

Suppression of the Second Harmonic Subgroup Injected by an AC EAF: Design Considerations and Performance Estimation of a Shunt APF

This paper proposes a design methodology for an active power filter (APF) system to suppress the second harmonic subgroup injected by an AC electric arc furnace (EAF) to the utility grid. The APF system is composed of identical parallel units connected to the utility grid via a specially-designed coupling transformer. Each APF converter is a three-phase three-wire two-level voltage source converter (VSC). The number of parallel APF units, coupling transformer MVA rating, and turns ratio are optimized in the view of the ratings of commercially-available high voltage (HV) IGBTs. In this research work, line current waveforms sampled at 25.6-kS/s on the medium voltage (MV) side of a 65-MVA EAF transformer are then used to extract the second harmonic subgroup, 95-, 100-, and 105-Hz current components, by multiple synchronous reference frame (MSRF) analysis, which was previously proposed to decompose EAF current interharmonics and harmonics in real-time. By summing up this digital data of the second harmonic subgroup, the reference current signal for the APF system is produced in real-time. A detailed model of the APF system is then run on EMTDC/PSCAD to follow the produced reference current signal according to hysteresis band control philosophy. The simulation results show that the proposed APF system can successfully suppress the second harmonic subgroup of an AC EAF.

Sensorless State Control of Stand-Alone Doubly Fed Induction Generator Supplying Nonlinear and Unbalanced Loads

Control methods of a stand-alone doubly fed induction generator mostly use either proportional-integral regulators in multiple synchronous reference frames or proportional-integral-resonant regulators in a stationary reference frame. These control schemes work well when the plant model is not complex and system decoupling is implemented into the control algorithm. However, when the control system contains multiple resonant terms in order to compensate high harmonics of load current, tuning of many regulators in different coordinate systems becomes problematic. The paper presents the application of a linear-quadratic regulator and a rotor position observer in sensorless control of a stand-alone doubly fed induction generator supplying nonlinear and unbalanced loads. Cooperation of the observer and state controller has been validated in the laboratory experiment. An anti-windup mechanism has been implemented into the resonant terms, and it has been shown that the anti-windup structure is crucial for high performance of the state controller with resonant terms. Further, research on observers based on a model reference adaptive system scheme is done in the paper.

Online Characterization of Interharmonics and Harmonics of AC Electric Arc Furnaces by Multiple Synchronous Reference Frame Analysis

In this paper, a multiple synchronous reference frame (MSRF) analysis framework is developed to determine the positive- and negative-sequence components of all interharmonic and harmonic currents produced by alternating current electric arc furnace (AC EAF) installations, which can be considered as balanced but asymmetrical three-phase, three-wire loads on the power system. The aim of developing the MSRF analysis framework is twofold; deep understanding of the EAF characteristics, and fast and accurate generation of reference signals to the controllers of the advanced technology compensation systems such as active power filters (APFs), synchronous static compensators (STATCOMs), and energy storage systems (ESS), which may successfully compensate interharmonics, harmonics, and flicker. Online characterization of interharmonics and harmonics by MSRF analysis utilizes continuously measured line currents and line voltages on the medium-voltage side of the EAF transformer at a sampling rate of 25.6-kHz per data channel. It has been shown by offline computations that compensation of the sequence components of interharmonics and harmonics of the EAF currents obtained by the proposed framework, reduces the short-term flicker values at the point of common coupling by up to 10-fold. The proposed MSRF analysis framework has been successfully verified by comparing the frequency spectrums of the EAF currents with Fourier analysis results based on one-cycle sliding windows of 10-cycle duration.

Suppression of Low-order Current Harmonics in AC Motor Drives via Multiple Reference Frames Based Control Algorithm

A novel control algorithm devoted to remove undesired low-order current harmonics in AC motor drives is presented in this article. The proposed control algorithm combines a suitable multiple reference frame synchronous harmonic estimator and multiple reference frame vector control implementation to suppress the undesired harmonics contained in the motor stator currents. This control technique can handle positive-, negative-, and zero-sequence sets, keeping a satisfying dynamic behavior. The control technique has been evaluated by numerical simulations and experimentally tested on a permanent magnet synchronous motor drive.

Enriching Electric Power Quality by using Bee Algorithm in Shunt Active Filters

The application of soft computing technique is growing fast in the area of power electronics and drives. The Bee optimization technique is considered as a new technique for power-quality (PQ) devices. The main objective of this paper is to present the Bee optimization method and Multiple Synchronous Reference Frame (MSRF) Theory in cascaded multilevel inverter for harmonic elimination. The foremost aim in Selective Harmonic Elimination Pulse Width Modulation (SHEPWM) strategy is eliminating low-order harmonics, while the fundamental component is satisfied. In this paper, the Bee algorithm (BA) and MSRF theory is applied to a 9-level cascaded multilevel inverter using MATLAB software. The BA is based on the food foraging manners of a swarm of honeybees and it performs a neighborhood search joint with a random search. This method has higher accuracy and possibility of convergence. Simulation results prove supremacy of BA over MSRF theory in attaining perfect overall minima and higher convergence rate. Finally their results are compared and verified for a distorted three phase power system utility.

Sensorless speed control of a five‐phase induction machine under open‐phase condition

Recently, multiphase machines have been promoted as competitors to their three-phase counterparts in high-power safety-critical drive applications. Among numerous advantages of multiphase induction machine (IM) drives, self-starting and operation under open phase(s) stand as the most salient features. With open phase(s), optimal current control provides disturbance- free operation given a set of objective functions. Although hysteresis current control was merely employed in the literature as it offers a simple controller structure to control the remaining healthy phases, it is not suitable for high-power applications. In the literature, multiple synchronous reference frame (dq) control can be an alternative; however, it requires back and forth transformations with several calculations and additional sophistication. In this paper, a simple technique employing adaptive proportional resonant (PR) current controllers is presented to control a five-phase IM under open-phase conditions. Results for both volt/hertz (V/f) and field oriented control (FOC) systems are presented. Moreover, sensorless operation under fault condition is also demonstrated by estimating the machine speed using a rotor flux-based model reference adaptive system (MRAS) speed estimator. The proposed controllers are experimentally verified and compared. Although FOC provides better dynamic performance, V/f control offers a simpler control structure and a lower number of PR controllers.

A multi-band shunt hybrid active filter with reduced sensor count

A Shunt Hybrid Active Filter (SHAF) is an attractive option for realizing low-cost harmonic compensation solutions. This paper proposes a SHAF with multiple harmonic compensation capability using a single Voltage Source Inverter and reduced sensor count. This strategy is apt for harmonic filtering solutions where low cost is the exclusive priority. In this paper, a new estimation approach is proposed to obviate requirement of a large number of sensors. Multiple Synchronous Reference Frames (MSRF) and low pass filters are used to measure 5th and 7th harmonic components separately from load as well as filter currents. Individual current controllers are designed for the 5th and 7th harmonic currents. Control is realized in the synchronously rotating, orthogonal (dq) reference frame. Performance of the controller is validated through simulation, using realistic plant and controller models. Experimental results are provided to corroborate the analytical and simulation results.

A Comparative Analysis of Real-Time Algorithms for Power Signal Decomposition in Multiple Synchronous Reference Frames

The monitoring and rejection of voltage and current harmonics in power electronics applications such as power quality conditioners or distributed generation systems require correct estimation algorithms especially if the harmonic amplitudes are time varying. Power signal decomposition in multiple synchronous rotating reference frames (MSRFs) is considered one of the best solutions. The most commonly employed implementations of this signal transformation are based on phase-locked loops (PLLs), recursive discrete Fourier transforms (RDFT), or discrete Kalman filtering (DKF). In this paper, a rigorous analysis of the performance of these implementations has been carried out. Complete tests have been performed to evaluate the computational burden, the frequency domain response, and the tolerance to low frequency amplitude variations. The results make it possible to select the proper method depending on the requirements of each application.