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Because a modular motor drive is composed of multiple identical pole drive units and controllers, it can be considered as a multi-agent system. This makes modular motor drives particularly interesting during faults, when the remaining healthy agents assure the continuity of operation. Nevertheless, for some crucial information such as the rotor position, these drives still rely on a single sensor which introduces a single point of failure. In this work, this single high-resolution position sensor is replaced by multiple binary, low-resolution position sensors. A vector tracking observer algorithm, implemented in the different controllers, processes this low-resolution sensor data into a position estimate. Subsequently, these position estimates of the different agents are exchanged with other agents using a distributed averaging algorithm. For this latter approach, it is shown in this work that it improves the position estimation under healthy conditions as well as during agent malfunctions. The concept is demonstrated on a modular axial-flux permanent magnet synchronous machine with fifteen pole drive units, each equipped with a low-resolution position sensor, that are assigned to five agents.

There is currently a growing interest in replacing the internal combustion engine with electric motors in transportation applications. However, there are different problems related to electric motors for this application. One of them is the oversizing of the energy decoupling system since to ensure that the decoupling capacitor can store the power fluctuations, the capacitance required by the system is usually oversized. This leads to preference for the use of capacitors with construction technologies that have a lower lifetime than the remaining elements of the propulsion system, directly affecting the reliability of the system. In this article, the energy flow handled by the decoupling capacitor is analyzed considering the critical case of operation of an induction motor to minimize the capacitance required by the propulsion system; emphasizing the conditions that generate a higher energy return, from the motor mode of the electric machine to the decoupling capacitor. From the energy analysis, an equation for the capacitor calculation is obtained, involving proportionality factors that relate to the different operating powers, reducing up to 62.2% of the capacitance value required by the decoupling system, under conditions of maximum energy return in motor mode, compared to existing equations in the literature.

Based on the brushless DC motor system with DC-link small capacitance powered by a single-phase AC power source, a boosting DC-link voltage strategy to reduce the commutation torque ripple of brushless DC motors is proposed in this paper. The control strategy utilizes the special topology of the motor system to boost the DC-link capacitor voltage in a specific zone during the non-commutation period. During the commutation period, the high voltage of the DC-link capacitor is released to meet the voltage requirement of the brushless DC motor during commutation. In order to reduce the commutation torque ripple and ensure the normal operation of the brushless DC motor, each rectifier cycle is divided into three zones according to the characteristics of the periodic change of the rectifier output voltage. Different operation modes are proposed for different zones. In DC-link capacitor boost voltage mode, the DC-link capacitor boosts the voltage to meet the voltage of the motor demand during the commutation period for achieving the purpose of reducing the commutation torque ripple. In this paper, the controller of the brushless DC motor system is designed and the experimental platform is built. The experimental results verified the correctness of the theoretical analysis and the feasibility of the proposed method.

Nowadays, energy storage systems, such as batteries, are spreading in many applications. Among the kinds of batteries, the lithium-ion technology is one of the most promising solutions. Considering the photovoltaic (PV) plants, it is very important to perform a correct sizing of the battery pack to both maximise the self-consumption and minimise the total costs. In general, PV plants need a dc–dc converter to maximise the electric power that can be extracted from PV panels and a dc–ac converter to connect them to the ac grid. The battery pack can be connected in three different ways: dc coupled and ac coupled using a dedicated converter or through a direct connection on the dc-link between the dc–dc and dc–ac converters. In the present study, the last solution, without any dedicated converters, is used and a simple control strategy to both maximise the power extracted from the PV panel and regulate the charging/discharging of the battery is proposed.

The reliability of a motor control based on a variable speed drive is an important issue for industrial applications. Most of these machines are inverter based induction motors and are used in specific and complex industrial installations. Unlike the induction motor, the feeding part is very delicate and sensitive to faults. In order to improve system performance, it is therefore very important for a researcher to know the impact of a fault on the whole of his drive system. This paper discusses the short-circuit fault of the DC-link capacitor of an inverter fed induction motor. The simulation results of this type of faults are presented and its impact on the behavior of the rectifier, the inverter as well as the induction motor analyzed and interpreted.

This research introduces a filtering circuit design integrated with the DC-link of a medium power variable speed drive (VSD) system. The designed filtering circuit employs modern power electronic circuits to improve time response characteristics in both grid and dc-link sides. Depending on the widely used multi-level converters, a conventional three-level H-bridge four-quadrant chopper scheme was developed into a cascade five-level H-bridge four-quadrant chopper scheme. The time response of the proposed system was performed with both choppers, and results showed that voltage drop on cascade chopper transistors was reduced to half in comparison with voltage drop on conventional four-quadrant chopper transistors. Moreover, the sharp fluctuations in system's waves were mitigated; consequently, time response characteristics in both steady and transient states were remarkably improved. The total harmonic distortion factor THD% of the input current and voltage was reduced to 26.2% and 2.43% respectively and the ripple factor RF for DC-link current was reduced to 0.196., Electrical engineering; Energy; Industrial engineering; Applied computing; Information systems; Variable speed drive system VSDS; Four-quadrant chopper; Power quality; Cascade multi-level converters; DC-link; Harmonic mitigation.

This paper proposes a power electronic module that uses a switched capacitor for retaining the integrity of the dc-link voltage of a variable speed drive (VSD) during a 0.2 s short-term power interruption (STPI). Ride-through was achieved through switched capacitor onto the dc bus. However, this technique presents a challenge of the high inrush currents during a ride through compensation. In this work both analytical and experimental investigations were conducted in order to reduce the in-rush currents and its impact on the performance of the VSD during the STPI. Inrush peak currents were reduced by approximately 90%. Experimental results showed torque pulsations of 12.8% and 14.3% at the start and end of dc-link voltage compensation, respectively. A method for sizing the switched capacitor and the inrush limiting resistors is proposed. This methodology is based on the use of readily available nameplate information of the VSD and the electric motor. The proposed module can be retrofitted to existing VSDs that are based on v/f control.

A sensorless stand-alone control scheme of a doubly fed induction generator (DFIG)-DC system is investigated in this paper. In this layout, the stator voltage is rectified by a diode bridge that is directly connected to a dc bus. The rotor-side voltage source inverter is the only controlled converter required in this system and is directly powered by the same dc bus created by the stator-side rectifier. DC voltage and stator frequency are regulated by two independent proportional-integral regulators that give the references for inner current controllers implementing field-oriented control. As it is capable of creating a stable and regulated dc bus, this system can be conveniently adopted to supply dc loads or to form a dc grid. Due to the constraint imposed by the stator diode bridge, the DFIG has to operate under a constant stator voltage, and the conventional stator field-oriented control implemented in stand-alone ac DFIG must be modified. This paper presents the control structure and the theoretical framework for the controller synthesis. Simulation and experimental validations on a small-scale rig are included.

The field-weakening operation of a doubly fed induction generator (DFIG) connected to a dc-link is analyzed in this paper, in order to optimize the efficiency. In the considered DFIG-dc system, the stator feeds a constant-voltage dc link by a diode bridge, and the rotor current is controlled using a voltage-source inverter connected to the same dc link. Since the stator voltage amplitude is imposed by the dc-link, a variation in stator flux magnitude results in a frequency change. However, in this system, a stator frequency variation over a wide range can be accepted, if the rated flux is not exceeded. Thus, the stator flux amplitude can be adjusted through the magnetization current component by the voltage-source inverter and according to the load level, in order to reduce losses in the machine and in the inverter. This paper presents an optimization analysis and simplified formulae determining the optimal reference magnetization current in the control of the system. Conversely to field weakening in conventional drives, in this case, the enabling of field weakening control is not dependent on rotor speed, but depends on the reference torque. The proposed optimal control is validated through simulation and experimental results.

This paper deals with three-level topology of neutral point piloted converters (3L-NPP). These converters can be realized in two variants. The first one is represented by one power semiconductor switch only placed in the top and bottom part of an output leg of a half bridge representing a phase of a three phase converter; the second one is represented by two serial connected semiconductor switches in top and bottom part of the converter leg. These topologies are often compared with neutral point clamped converters but not between themselves. Therefore, the analysis of those topologies is performed in detail in this paper and furthermore, they are compared with a standard two level voltage source converter (2L-VSC) in the point of view of converter losses and output quantities distortion.

This paper presents a self-sensing technique for the field-oriented control and frequency regulation of a doubly fed induction generator connected to a dc-link. In this system, the stator circuits are connected to a dc-link through a diode bridge and the rotor circuits are controlled by a voltage source inverter connected to the same dc-link. As the diode bridge maintains the fundamental harmonics of the stator current and voltage approximately in phase, an almost zero average $d\mbox{-axis}$ stator current results in the stator flux reference frame. This property is used to estimate the slip angle, required to implement the field orientation in the self-sensing technique in loaded conditions. At no load the system is controlled using a different methodology. The analysis and synthesis of the control chains are presented by analytic relations. The sensitivity study shows that the method exhibits reduced sensitivity to the parameter mismatch, resulting in a small orientation error. Experimental results confirm the good performance of the proposed method.

This paper proposes a technique to suppress low-order harmonics for an open-end winding induction motor drive for a full modulation range. One side of the machine is connected to a main inverter with a dc power supply, whereas the other inverter is connected to a capacitor from the other side. Harmonic suppression (with complete elimination of fifth- and seventh-order harmonics) is achieved by realizing dodecagonal space vectors using a combined pulsewidth modulation (PWM) control for the two inverters. The floating capacitor voltage is inherently controlled during the PWM operation. The proposed PWM technique is shown to be valid for the entire modulation range, including overmodulation and six-step mode of operation of the main inverter. Experimental results have been presented to validate the proposed technique.

A DFIG connected to a dc bus by a diode rectifier and a unique reduced-power PWM converter is considered in this paper. With respect to the traditional ac-grid connected DFIG, such a layout avoids the grid-side PWM converter and is an interesting solution to integrate the DFIG in a dc microgrid together with other generating units, loads as well as storages. The peculiarity of the DFIG, which allows the control of the rotor current space vector independently of the mechanical position, offers two important benefits when the stator is connected to a constant voltage dc grid by a diode bridge: it avoids the need to boost the flux amplitude at low speed, and it allows to considerably reduce the torque ripple due to the diode commutation. This last issue is developed in this paper by using a field-oriented control scheme based on proportional-integral and resonant Controllers. The proposed control is validated through simulation and experiments.

This paper deals with a new conversion topology for doubly-fed induction generators (DFIGs) suitable for wind energy conversion systems integrated in microgrids. It consists of a DFIG which is fed by a pulse width modulation converter on the rotor and with the stator connected to a dc grid through a diode rectifier. In this configuration, the stator diode rectifier and the rotor-side inverter share the same dc bus, so that the conventional grid-side inverter is avoided. Since only a diode rectifier designed for the full power and a reduced power inverter are required, this layout allows a cheap and effective integration of the DFIG with other generating and storage systems connected to the same dc bus. A simple control technique suitable to regulate the power delivered to the dc grid is proposed. The scheme is based on the regulation of the amplitude of a suited fraction of the rotor flux linkage: the optimal value of this fraction is theoretically deduced in order to minimize the DFIG derating due to the current harmonics. The effectiveness of the proposed control is proven by simulations and experimental tests.

An unbalanced DC-link voltage regulation strategy is proposed for a three-level voltage source inverter used in the rotor cascade of a double-fed asynchronous motor-generator. The major problem in determining the presence of the unbalanced component is investigated and a solution is proposed using an adaptable filter. This latter is only of a low order and is designed to ensure easy implementation into a (DSP). The regulator is based on the injection of a second order harmonic and its design is presented as well as an investigation of the critical point for correct action of the regulator. Real measurements performed on a low-power test bench after implementation into a DSP validate the accuracy and quality of the filter as well as the control strategy proposed.

This paper reports an investigation to develop a dynamic hybrid power system simulation model to maximize the renewable energy extraction and to analyze disturbances. The investigated model is based on two types of renewable power generation: wind turbine generator and photovoltaic generator, connected to a three-phase isolated grid constituted by a diesel generator. The interconnection between the renewable sources and the AC diesel generator is made by a DC-link with buffer batteries and an inverter. First, the system is sized according to the electric demand and the availability of renewable energy resources. Then, each component of the hybrid power system is dynamically modelled in order to maximize the renewable energy to total energy ratio and to analyze the disturbances that affect the correct operation.