Active Front-end Rectifier Research Articles

Detection and Isolation of Interturn Faults in Inductors of LCL Filter for Marine Electric Propulsion System

This paper presents an online technique to detect and isolate the interturn fault in the inductors of the LCL filter integrated with the active front-end rectifier used for electric propulsion of marine vessels. The proposed online technique is based on the fundamental component of the core-leakage flux measured at the yoke center of the inductor. A comparative study of the grid currents and the core-leakage fluxes under interturn faults is carried out using the proposed analytical models which reveal high sensitivity of the core-leakage flux at the yoke center when compared to the grid currents. The theoretical analysis is validated experimentally on a laboratory-based 11.3-kW marine propulsion system test rig for 1-turn, 2-turn, and 4-turn faults under various loading and supply voltage unbalance conditions. An online fault notification and isolation framework has also been proposed and validated experimentally with two different techniques to increase the reliability for 1-turn fault detection. The methodology requires just a single, low-bandwidth, and inexpensive magnetic flux sensor in addition to the existing current sensors to detect as low as 1-turn fault out of 63 turns.

Degradation Detection and Diagnosis of Inductors in LCL Filter Integrated With Active Front End Rectifier

This paper presents an online methodology to detect and diagnose the inductor degradation in LCL filter integrated with Active Front End Rectifier (AFER) for electric drives in marine propulsion system (MPS). The proposed methodology monitors the leakage fluxes of converter-side inductor and compares it with the same under healthy condition to detect and diagnose the inductance degradation. The magnitude of leakage flux's fundamental component is extracted using the Fast Fourier Transform (FFT) and is used for detection of inductance degradation. Hence, inexpensive and low bandwidth magnetic flux sensors along with a simple FFT algorithm are used to detect and diagnose the inductance degradation. The leakage fluxes of the inductor during degradation are analyzed using the developed analytical model and validated on a laboratory prototype of 11.3-kW MPS test-rig. The validation was carried out for different degrees of converter-side inductor degradation from 3% to 19% under 33%, 73%, and 100% of full-load capacity of the MPS test-rig. Both estimated results using the analytical model and experimental results obtained are found to be in good agreement. The proposed online technique can detect and estimate the degraded inductance as low as 3% and is superior to the technique using grid currents in detecting the inductor abnormality.

Model Predictive Virtual Flux Control to Improve Performance Under Distorted Input Voltage Conditions

This paper proposes a model predictive virtual flux control (MPVFC) method that can mitigate the degradation of the total harmonic distortion of rectifier input currents experienced by active front-end (AFE) rectifiers when input voltages are distorted by harmonics. The proposed method utilizes a cost function based on virtual fluxes, which are robust to input voltage distortions, to control the rectifiers. For the calculation of the proposed cost function which consists of a predictive value of the rectifier virtual flux and a reference of the rectifier virtual flux, the dynamics of AFE rectifiers and the definition of the integration in the discrete time domain are used. Also, the phase of the reference current which is needed when calculating the reference of the rectifier virtual flux is obtained by the input virtual flux. The proposed MPVFC method shows better input current waveforms with lower total harmonic distortion than those obtained with the conventional model predictive control method under input voltage distortion conditions, which was proved via simulations and experiments.

Performance Comparison of Model Predictive Control Methods for Active Front End Rectifiers

Active front-end rectifiers are tasked with generating high-quality, low-distortion sinusoidal line currents in the presence of adverse circuit conditions. When suitable control methods are applied to such rectifiers, significant performance improvements can be realized, especially under abnormal utility conditions. Although several control methods based on model predictive control platforms have been recently developed, there is a lack of comparative studies of these methods in the literature. In this paper, the details and theoretical background of four model predictive control methods, namely, current control, virtual flux control, direct power control, and virtual flux direct power control, are presented. Then, the performance of these methods was compared by the way of experiments to determine the respective quality of the line current under various conditions, such as unbalanced input voltages, input voltage distortion, uncertainty in the parameters, and dc voltage fluctuation. In summary, based on the results of the experiments, the virtual flux control scheme was found to be distinctly superior to the other three schemes for distorted and unbalanced line voltages.

Reactive Power Compensation Using Induction Motor Driven by Nine Switch AC-DC-AC Converter

Induction motors (IM) used for various industrial applications operate with lagging power factor. Electrical distribution agency insists high power factor operation and it gives incentives on operating a system closer to unity. This paper presents a novel reactive power compensation using IM driven by nine switch ac–dc–ac converter for a high power factor operation at the point of common coupling (PCC). The nine switch converter (NSC) with leading power factor operation delivers reactive power to the PCC. Thus, reactive power required for another load at PCC is compensated. Modified sinusoidal pulse width modulation is developed for NSC to operate the active front end rectifier and an inverter simultaneously to feed three-phase IM. A closed loop proportional integral control technique is developed to achieve desired VAR compensation. As per the required VAR compensation, front end rectifier voltage is modified. This is achieved by phase shifting of front end rectifier modulation reference by an angle $\delta$ with respect to utility phase voltage. The PCC phase voltage is continuously sensed to track instantaneous phase angle $\theta$ using synchronous reference frame phase lock loop. The analysis of VAR compensator is presented in the d-q reference frame. The proposed system is simulated in MATLAB for VAR compensation at PCC with 5.4 hp induction motor drive to test the performance of VAR control loop. To validate the feasibility of the proposed system an experimental prototype is developed with 1 hp induction motor drive. Gate pulses are generated using digital signal controller dsPIC33EP256MU810. The simulation and experimental results proved the feasibility of the proposed VAR compensation system.

A power quality enhanced grid voltage sensorless predictive direct power control for active front end rectifiers

In this research work, a power quality enhanced grid voltage sensorless deadbeat predictive direct power control (DB-DPC) approach for AC/DC power converters based on latest virtual flux (VF) estimation, DB-DPC and space vector pulse width modulation (SVPWM) is proposed. At first, the grid voltage sensorless technique with switching table based DPC, which is a conventional approach, is discussed and its performance is analyzed under both increase of load as well as decrease of load conditions. Further, the proposed technique performance is also analyzed under the same circumstance and its performance is compared with the traditional method. The proposed technique has numerous advantages over the conventional method such as constant switching frequency, better active and reactive power control, good regulation of dc bus voltage, and enhanced power quality performance. As the proposed approach utilizes VF, DB-PC, and SVPWM techniques, this ensure line voltage sensorless approach, excellent control dynamics and constant switching frequency, respectively. At the end, experimental validation is done to confirm the supremacy of the proposed technique under load varying conditions and has a phenomenal performance under these circumstances.

A Novel High Bandwidth Current Control Strategy for SiC mosfet Based Active Front-End Rectifiers Under Unbalanced Input Voltage Conditions

SiC mosfet based converters are capable of high switching frequency operation. In this paper, the converter is operated with 50-kHz switching frequency for an active front-end rectifier application. Due to high switching frequency, the grid-side filter size is reduced, and the possibility of a high bandwidth current control loop is utilized in this paper. A current control loop with bandwidth of 5 kHz is designed using a proportional–integral controller in synchronously rotating dq -reference frame. In addition, the performance of the controller is tested under unbalanced input supply conditions. During this condition, new feed-forward signals, which are added to the controller output, are proposed. The gain of the feed-forward signal can be modified to achieve balanced sinusoidal grid currents, constant dc-link voltage, or a controlled negative-sequence input current, which are typical application-depending requirements. A closed-form formula to calculate the gain of the feed-forward signal to achieve the above-mentioned requirements is also proposed in this paper. To verify the proposed method, the simulation and experimental results are presented in this paper.

Balancing distribution systems with three‐phase active front end rectifiers: field experiment results

This study describes field tests of alternative methods to control three-phase active rectifiers to reduce voltage unbalance in low-voltage (LV) distribution systems. The tests show that per-phase control of active power of two residential loads can significantly reduce unbalance throughout an LV feeder shared by 25 homes. Different algorithms, designed to either reduce negative sequence voltage, or phase–neutral (P–N) voltage unbalance using active or reactive power (four algorithms in all), were tested. The algorithm designed to reduce P–N voltage unbalance using active power showed the greatest reduction in median P–N voltage unbalance at the prototypes terminals (up to 87%), the greatest reduction in median current unbalance at the feeder's substation (38%), and was also effective at reducing negative sequence voltage in the feeder. The algorithms controlling reactive power reduced negative sequence voltage, but did not show significant effects on P–N voltage unbalance. Two prototypes were tested at different locations on the same feeder, and the average combined effect of the two prototypes was well predicted by the sum of their individual effects. Some of the results are inconsistent with earlier simulations and laboratory tests which used simple constant impedance load models, highlighting the importance of field trials to validate controller designs.

Аналіз енергоефективності активного випрямляча з покращеною гістерезисною системою керування

The article describes the active three-phase boost rectifier with power factor correction, as known as active front-end rectifiers, with hysteretic control system in conditions of the ideal voltage and distorted voltage. In many industrial applications active front-end rectifiers (AFEs) have emerged as an attractive topology. When compared to traditional diode-based rectifiers, AFEs allow one to obtain sinusoidal input currents with low harmonic distortion, whilst at the same time providing an accurate rectifier voltage. Moreover, the amount of reactive power drawn from the source can be manipulated in order to reach a unity power factor in the input, or also to compensate a lack of reactive power in the source grid. Another area where AFEs play an important role is when a reduction of harmonic distortion is sought. In fact, this converter is widely used as an active filter in which case the AFE is connected in parallel to the nonlinear load thereby generating the harmonic currents necessary to reduce the pollution in the source. The research of the active rectifier was made in the Matlab R2011. Presented an improved hysteresis control system that allows improve the harmonic content generated by the phase currents and thus improve power factor in implementing the conditions of distortion of mains voltages.

Improved finite-control-set model predictive control for active front-end rectifiers with simplified computational approach and on-line parameter identification

In this paper, an improved finite-control-set model predictive control method is proposed for active front-end rectifiers where the computational effort and parameter mismatch problems are taken into account simultaneously. Specifically, a desired voltage vector which only requires one exploration is directly selected by using a single cost function, and the process of selection of the desired voltage vector is optimized by using a sector distribution method. Meanwhile, a model reference adaptive system-based online parameter identification approach is presented to alleviate the parameter mismatch problem. The advantages of the proposed method summarized as follows: First, the proposed algorithm reduces the eight possible voltage vectors to one. The exhaustive exploration can be avoided while the control performance is not deteriorated. Second, the proposed controller can mitigate performance degradation caused by the model parameter mismatch. Simulation results under various parameters operating conditions are presented to demonstrate the efficacy of the proposed method.

Three-Level Inverter-Fed Direct Torque Control of the Synchronous Motor

Synchronous motors and back-to-back converters with IGCT three-level NPC active front end (AFE) rectifiers are widely used in up-to-date large adjustable speed drives. Thanks to the development of the microprocessor technology and power electronics, Direct Torque Control (DTC) became possible and available. The structure and the formation of the switching table for switching devices of the inverter are of a great importance for the DTC system. The quality of the transient, particularly, fast response and precision of the motor variables control, depends largely on the table structure and formation. The paper describes the main principles of the inverter control. Twenty-four voltage vectors were divided into seven different variants. These variants can be represented in the form of two adjacent groups; each group contains two variants of short vectors, one variant of long ones and middle vectors are common for the both groups. As a result of the conducted research, a switching table was formed where the switchover from one variant of voltage vectors to the other one is provided by the switching of one switching device only. The simulation results obtained in the Matlab Simulink environment confirmed the efficiency and acceptable characteristics of the transients quality of the formed switching table. During the steady state operation the main control variables, such as torque and stator flux, are maintained with an error which does not exceed 5 %.

Power Quality Analysis of HP Electric Drive based on 3L NPC AFE Rectifiers with SHE Modulation Method

This paper presents power quality analysis of high power (HP) electric drive based on three level neutral point clamped active front end (3L NPC AFE) rectifiers with selective harmonic elimination (SHE) modulation method. As an object of the study has been chosen a power circuit of main electric drive of rolling stand plate mill 5000 JSC "MMK". The main drive is a system in which each 12 MW motor is connected to the grid via 18-pulse connection circuit based on three 3L NPC AFE rectifiers and transformers connected in parallel. The rectifiers operate on the basis of SHE modulation method with elimination: 5, 7, 11 and 13; 5, 7, 17 and 19; 17, 19, 35 and 37 harmonics. The research results has been obtained on the primary and secondary side of the transformers by mathematical modeling and calculated voltage and current harmonic spectrums and total harmonic distortion (THD) at consumption of the rated current. A mathematical model was developed in Matlab/Simulink program. It was determined that SHE modulation method with elimination of 5, 7, 17 and 19 harmonics is the most appropriate for the considered object.

Control Design for PMM-Based Generator Fed by Active Front-End Rectifier in More-Electric Aircraft

The future aircraft electrical power system is expected to be more efficient, safer, simpler in servicing and easier in maintenance. As a result, many existing hydraulic and pneumatic power driven systems are being replaced by their electrical counterparts. This trend is known as a move towards the More-Electric Aircraft (MEA). As a result, a large number of new electrical loads have been introduced in order to power many primary functions including actuation, de-icing, cabin airconditioning, and engine start. Therefore electric power generation systems have a key role in supporting this technological trend. Advances in modern power electronics allow the concept of starter/generator (S/G) which enables electrical engine start and power generation using the same electrical machine. This results in substantial improvements in power density and reduced overall weight. One of the potential S/G solutions is to employ a permanent magnet machine (PMM) controlled by active front-end rectifier (AFE). Operation of the PMM as a generator at wide range of speed that is dictated by the engine and electrical loads connected to the aircraft bus require careful design of the controllers. Corresponding plant models are derived and verified with simulations using developed models in Matlab/Simulink. The relevant controllers are designed based on the derived plants and operating points. The controllers are tested with Simulink models and experimentally using a scaled prototype of the investigated generator system.

Cascaded Dual-Model-Predictive Control of an Active Front-End Rectifier

Model-predictive control (MPC) is an advanced model-based control technique. It allows flexible control schemes with fast time responses. However, like most optimization-based control strategies, MPCs are usually computationally intensive and suffer from a lack of robustness toward parametric variations. The computational burden of these controllers is nowadays being relieved thanks to the progress of digital devices; however, the robustness is still a major issue that prevents the use of MPC controllers in some applications. Systems presenting slow and fast dynamics at the same time are usually controlled by cascaded control loops. MPC techniques are restricted to the control of inner loops, while outer loops use more robust control techniques. The aim of this paper is to provide MPC techniques for both the inner and outer loops of an active front-end rectifier. A first dual-MPC cascaded control shows the drawbacks of usual MPC techniques for outer loops. It is thereafter modified to achieve a robust cascaded dual-MPC that eliminates the variable resistive load parameter from the system dynamical model and formulates a new prediction model containing only known parameters and measurable quantities. Finally, a third method based on the previous one is also presented in order to reduce switching losses. Experimental results for the three methods are presented and compared with double precision offline software simulation results to validate the feasibility of the proposed techniques.

Математическое описание трехуровневого преобразователя частоты с фиксированной нейтралью на базе активного выпрямителя и автономного инвертора напряжения

This paper presents a mathematical description of a three-level neutral point clamped (3L NPC) back-to-back converter based on active front-end rectifier (AFE) and voltage source inverter (VSI). This description allows investigation of electromagnetic processes and analysis of the electromagnetic compatibility (EMC) of the grid – 3L NPC back-to-back converter – load system taking into account the switching functions of AFE and VSI and voltage unbalance in the DC link. The known mathematical models of the 3L NPC back-to-back converter do not provide a block diagram for development of a control system because they use the principle of electrical system separation into subsystems. The developed mathematical model provides a convenient block diagram for the synthesis of a control system neglecting the voltage unbalance in the DC link, a perfect synchronization and switching function linearization. The model is identical to the well-known two-level block diagram of the frequency converter. Linearization at the rated value of the DC voltage was considered.

Анализ электромагнитной совместимости 18-пульсной схемы соединения трехуровневых АВН при использовании метода ШИМ с удалением выделенных гармоник

The article is devoted to electromagnetic compatibility (EMC) analysis of 18-pulse connection circuit based on three level active front-end ( 3L-AFE ) rectifiers with a pulse width modulation selective harmonic elimination (PWMSHE) method. The considered 18-pulse connection circuit includes a parallel connection of three power transformers which have the secondary winding voltages phase shift 20°, 0°, and -20. The each 3L- AFE rectifier has neutral point clamped topology and consists of power semiconductor modules, snubbers and direct current (DC) capacitors. Research of EMC has been carried out by simulation using Matlab/Simulink program. The obtained results presented total harmonic distortional (THD) dependences and harmonic spectrums of grid current and voltage. To sum up, the main conclusions and prospects of the further research have been formulated.

Active front‐end rectifier modelling using dynamic phasors for more‐electric aircraft applications

The more-electric aircraft (MEA) has become a dominant trend for next-generation aircraft. The electrical power system (EPS) on-board may take many forms: AC, DC, hybrid, frequency-wild, variable voltage, together with the possibility of novel connectivity topologies. To address the stability, availability and capability issues as well as to assess the performance of the power quality and transient behaviour, extensive simulation work is required to develop the EPS architectures. The study develops a fast-simulation model of active front-end rectifiers based on the dynamic phasor concept. The model is suitable for accelerated simulation studies of EPS under normal, unbalanced and line fault conditions. The performance and effectiveness of the developed model have been demonstrated by comparison against time-domain models in three-phase and synchronous space-vector representations. The experimental verification of the dynamic phasor model is also reported. The prime purpose of the model is for the simulation studies of MEA power architectures at system level; however it can be directly applied for simulation study of any other EPS interfacing with active front-end rectifiers.

Active Rectifier Based Harmonic Compensator for a Direct Torque Controlled Induction Motor Drive

ABSTRACTHarmonic mitigation is a key issue in industrial as well as commercial drive applications. The wide use of non-linear loads causes significant power quality degradation in power distribution networks. The main objective of this work is to design an active front end rectifier for harmonic compensation. Active filter is used as drive front end so that it can act as a harmonic compensator and also AC to DC converter. This work proposes a dual purpose drive that can be used as a conventional drive and also to cancel out harmonics in line. Inverter in the drive is controlled by using conventional switching table based direct torque controller for induction motor control. Induction motor based on direct torque control (DTC) was implemented by connecting the inverter to the DC link of the active rectifier in order to transfer the power to induction motor through active rectifier DC link. DTC with five-level torque controller was used to minimize torque ripples. A complete simulation model is developed using MATLAB/Simulink in order to test the performance of the proposed harmonic compensator. Results shows effective harmonic compensation at front end and the current THD is 3.2% which is well below IEEE-519 Standard. The active rectifier based harmonic compensator for a DTC drive with the five-level torque controller was simulated and it was found that the torque ripples are comparably reduced with a switching table based DTC of induction motor drive.

Coupling Inductor Fault Detection and Estimation in Three-Phase Adjustable-Speed Drives With Direct Power Control-Based Active Front-End Rectifiers

Coupling inductors are the most commonly utilized filtering option in grid-connected direct power control (DPC)-based active front-end rectifiers integrated into three-phase adjustable-speed drives (ASDs). Inductor faults, e.g., common interturn short circuits, can drive the whole system to failure. In this paper, a novel strategy is proposed for the early detection of incipient faults in the coupling inductors of the aforementioned ASDs. The proposed method enables a fast identification of the defective phase. The strategy also provides an accurate estimation of the inductance value of the coupling inductors that improves the performance of the DPC method. Simulations and experimental tests demonstrate the validity of this detection and estimation strategy.

Stability and Performance Investigations of Model Predictive Controlled Active-Front-End (AFE) Rectifiers for Energy Storage Systems

This paper investigates the stability and performance of model predictive controlled active-front-end (AFE) rectifiers for energy storage systems, which has been increasingly applied in power distribution sectors and in renewable energy sources to ensure an uninterruptable power supply. The model predictive control (MPC) algorithm utilizes the discrete behavior of power converters to determine appropriate switching states by defining a cost function. The stability of the MPC algorithm is analyzed with the discrete z-domain response and the nonlinear simulation model. The results confirms that the control method of the active-front-end (AFE) rectifier is stable, and that is operates with an infinite gain margin and a very fast dynamic response. Moreover, the performance of the MPC controlled AFE rectifier is verified with a 3.0 kW experimental system. This shows that the MPC controlled AFE rectifier operates with a unity power factor, an acceptable THD (4.0 %) level for the input current and a very low DC voltage ripple. Finally, an efficiency comparison is performed between the MPC and the VOC-based PWM controllers for AFE rectifiers. This comparison demonstrates the effectiveness of the MPC controller.