Fictitious DC-link Research Articles

Fuzzy Fractional-Order PID Control for PMSG Based Wind Energy Conversion System with Sparse Matrix Converter Topology

Sparse matrix converter (SMC) is an indirect AC-to-AC power electronic converter that has a fictitious DC link between rectification and inversion stages in which neither a capacitor nor an inductor, as the storage element, is utilized. Due to this advantage, SMC is used in AC drives, marine thrust systems, aerospace industry, as well as in wind energy applications. On the other hand, permanent magnet synchronous generator (PMSG) is competitive in wind turbine applications due to their prominent features. In this work, a fuzzy fractional-order PID (FFOPID) controller is designed for a PMSG based wind energy conversion system (WECS) which employs a three-phase three-level SMC. The FFOPID controller is chosen to combine the salient features of the fractional-order calculus and fuzzy logic operations to enhance the dynamic response of classical PID controller with fixed gains. The simulation results taken under different case studies are analyzed in detail, which demonstrate the superiority of the designed FFOPID controller over classical PID control approach in tracking d- and q-axis current references of the SMC at the output. With the designed control approach, the smooth control of the real and reactive power injections into the grid from the WECS are ensured with acceptable transient response.

An indirect modulation strategy of matrix converters for unbalanced input supply with reduced commutation losses

ABSTRACT This article is focussed on developing a novel hybrid modulation technique for matrix converter. The concept of singular value decomposition (SVD) is utilised to synthesise the intermediate fictitious DC link voltage whereas generalised scalar pulse width modulation (GSPWM) is utilised to generate the target output voltage. SVD provides the required flexibility in selecting the switch states to improve the input power factor. In contrast, GSPWM helps in reducing the switching losses significantly by clamping the output voltage in synchronisation with the peak of the output currents. This proposed phenomenon reduces the switchings at high current which in turn, reduces the losses and improves the efficiency of the converter. The feedforward compensation used at the input side of the converter helps in achieving the balanced output currents for unbalanced input conditions. The simulation and experimental results with loss analysis render validation of the proposed technique.

Control of Matrix Converter for AC Drives by Proposed Indirect Space Vector Modulation ISVM Strategy

Matrix Converter is considered as a forced commutated AC-to-AC converter, where an array of bidirectional controlled switches produces variable voltage and frequency. This paper presents amodulation approach to MC operation: a fictitious DC link control technique, which is also known as the Indirect Modulation method and is characterized by lack of reactive storage components in the DC link. This method allows the bidirectional power to flow between the source and load, and thus raise the voltage ratio above 86.6%, control the desired magnitude and frequency, and achieve nearly unity power factor at the input side of the converter.

New switching approach for DVR using one cycle control method

Abstract One of the effective devices to eliminate voltage disturbances of sensitive loads in distribution systems is dynamic voltage restorer (DVR). In previous studies, the sinusoidal pulse width modulation (SPWM) method has been used as a switching method for DVR. However, a new switching approach called “one cycle control” (OCC) is presented in this paper for a three-phase DVR which has higher performance in dynamic and steady state operations compared to SPWM and is also simple and fixed in frequency. Moreover, this approach has few uncomplicated steps which make it suitable for practical implementation. In this study, the ability of the proposed approach is evaluated on two different types of DVR. The first DVR has fictitious dc link. In the second DVR, a battery is used in dc link. The proposed method can improve power quality disturbances such as voltage sag, voltage swell, and flicker. The ability of operating under changing parameters of load can show the robustness of the proposed approach. The simulation results obtained by OCC in six case studies were compared to the results obtained using the PWM method, revealing the higher efficiency of OCC than the PWM method.

A New Topology for Interline Dynamic Voltage Restorer Based on Direct Three-Phase Converter

In this paper, a new topology for Interline Dynamic Voltage Restorer (IDVR) is proposed. This topology contains two direct three-phase converters which have been connected together by a common fictitious dc-link. According to the kind of the disturbances, both of the converters can be employed as a rectifier or inverter. The converters receive the required compensation energy from the gird through the direct link which is provided by the dual-proposed switches. Due to the lack of the huge storage elements, the practical prototype of the proposed topology is more economical in comparison with the traditional structure. Moreover, compensating for long time duration is possible due to the unlimited eternal energy which is provided from the grids. The low volume, cost and weight are the additional features of the proposed topology in comparison with traditional types. This topology is capable to compensate both of the balanced and unbalanced disturbances. Furthermore, restoring the deep sags and power outages will be possible with the support from the other grid. Unlike the conventional topologies, the capability of compensation is independent from the power flow and the power factor of each grid. The performance of the proposed IDVR topology is validated by computer simulation with PSCAD/EMTDC software.

Implementation of sensorless DC‐link capacitorless inverter‐based interior permanent magnet synchronous motor drive via measuring switching‐state current ripples

This study proposes a sensorless speed-control system for a DC-link capacitorless inverter-based interior permanent magnet synchronous motor (IPMSM) drive system via measuring switching-state current-ripples. By measuring the current-ripple of each pulse-width modulation switching-state, the rotor position of the IPMSM can be estimated. As a result, the hardware of a high-frequency sinusoidal voltage or current source is not required. In addition, by suitably selecting the different levels of the fictitious DC-link voltage and compensating the duty cycle of the switching interval, the estimated rotor position error can be effectively reduced to nearly 50%. A 32-bit digital signal processor, TMS-320LF-2407A, is used to execute the rotor position estimation algorithm and the speed-controller. Experimental results validate the theoretical analysis. The proposed sensorless IPMSM drive can be operated from 3 to 2000 r/min. This study proposes a method to implement a DC-link capacitorless inverter IPMSM drive system and improve its performance without injecting any high-frequency voltage or current.

Four-Leg-Based Fault-Tolerant Matrix Converter Schemes Based on Switching Function and Space Vector Methods

A four-leg-based fault-tolerant matrix converter topology is proposed, along with switching function and space vector approaches for modulation schemes, to improve the reliability of matrix converter drives. The four-leg-based fault-tolerant structure utilizes an additional redundant phase module. Based on the reconfigured hardware topology, fault-tolerant modulation strategies with both switching function and space vector approaches are developed to provide the matrix converter drives with continuous and disturbance-free operation. Pulsewidth-modulated algorithms with closed-form expressions, based on a switching function matrix, are presented to synthesize redefined output waveforms with reconfigured converter structures. Furthermore, a space-vector-based scheme using the indirect equivalent circuit with the fictitious dc link is also developed for the fault-tolerant topology after failures. Experimental results show the feasibility of the proposed four-leg-based fault-remedial approach, along with the developed modulation techniques.

Voltage quality improvement by a dynamic voltage restorer based on a direct three-phase converter with fictitious DC link

In this study, a new topology for a three-phase dynamic voltage restorer (DVR) has been proposed. The proposed topology uses direct three-phase to three-phase converter with fictitious DC link to compensate for the balanced and unbalanced voltage sags/swells and voltage flickers. The used converter in the structure of the proposed DVR has two inverter and rectifier parts with an intermediate fictitious DC link. The converter is directly connected to the grid and takes the required compensation power from the grid. As a result, the DC link capacitor and energy-storage elements have been eliminated in the proposed topology. Therefore the voltage compensation can be accomplished for any long time interval. This topology has less volume, weight and cost owing to the elimination of the energy storage elements. Unlike other direct AC/AC converter-based topologies, the proposed topology uses unidirectional switches instead of bidirectional switches, which results in the reduction in the number of switching devices. The computer simulation using PSCAD/EMTDC software and a laboratory-scale experimental prototype verify the capabilities of the proposed DVR in voltage disturbances compensation.