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Connection of an LC filter to the output of voltage source inverter (VSI) in squirrel cage induction motor (SQIM) drive converts the pulse-width modulated (PWM) voltages into smooth sinusoidal voltages. However, this connection may lead to closed-loop instability in the rotor flux-oriented (RFO) vector-controlled (VC) SQIM system. The closed-loop stability of the combined SQIM + LC filter (SQLC) system is complex and has not been analyzed properly in the literature. In this paper, a detailed closed-loop stability analysis of the SQLC system has been presented based on stability region (SR) and accordingly the PI gains of VC has been designed. The SR method is adopted to derive the common stability regions for the SQIM system and SQLC system. Thereby, the paper proves that connecting an LC filter in-between the VSI and the SQIM system does not always destabilize the closed-loop system. Further, for an SQLC system, the complete range of current controller gains is obtained at various operating points. The frequency-domain specifications have been used to select a proper stabilizing set and the effect of parametric variation of LC filter on the stabilizing set has also been discussed. The experimental results are provided to validate the analysis. [ABSTRACT FROM AUTHOR]

Light-emitting diodes (LEDs) are widely used in street lighting, landscape lighting, liquid crystal display (LCD) backlighting, healthcare, etc. As an important part of LED lighting products, LED driver plays a vital role in maintenance costs reduction, energy saving and lifetime prolongation. In this paper, a single-stage LED driver is proposed, which is integrated by a totem-pole bridgeless power factor correction (PFC) unit and several modular LCL-T resonant rectifiers. The totem-pole bridgeless PFC unit and the LCL-T resonant rectifiers are integrated by sharing switches, which can simplify the circuit and reduce the system cost. The output current can be regulated by applying the variable inductor control. Constant duty cycle and fixed switching frequency operation can be achieved as well. The operating principle and the performance of the proposed converter are analyzed in this paper. In addition, a precise parameter design method is proposed by considering the high-order harmonics. At last, an experimental prototype is established to validate the proposed parameter design and variable inductor control method. [ABSTRACT FROM AUTHOR]

This paper presents a simple pulse width modulation algorithm for control of an ultracapacitor based energy storage system used for source and load support applications. As opposed to dual loop control philosophy that is widely used for backup applications, this paper presents a simple single loop current control that is only useful for controlling the ultracapacitor based DC/DC converters used in source and load support applications. The proposed PWM blocking method necessitates the DC/DC converter to operate in five states and takes into consideration the essential operational limits associated with the ultracapacitors. The performance of the proposed algorithm is verified experimentally using a 24 V laboratory prototype setup. Further, the shortcomings of dual loop control when applied to source and load support applications are demonstrated. [ABSTRACT FROM AUTHOR]

This paper proposes a novel dual input nine-level inverter (DINLI) topology which requires only seven controllable devices. The dual inputs are un-identical DC voltage sources in the ratio 1:3. A simple control scheme is derived by appropriately modifying the phase disposition pulse width modulation technique to generate high-quality 9-level output from the DINLI topology. At any given instant, a maximum of four switches conduct out of which only a maximum of two switches operate at high frequency, bringing down the switching and conduction losses significantly and improving the overall system efficiency. The bidirectional DINLI (BDINLI) topology with reactive power capability can be realized by replacing the unidirectional devices with the controlled switches (i.e., total nine switches). In addition, the proposed DINLI topology does not require extra voltage balancing circuits which further improves the efficiency. The DINLI operation is verified through MATLAB simulations for grid-connected applications and its extension to an n-level, 3-phase application is also investigated. Experiments performed on a 1KVA laboratory prototype to validate the theoretical claims. [ABSTRACT FROM AUTHOR]

The supply-side current of an inverter-fed induction motor (IM) is easily accessible and less affected by noises than the motor stator current. This paper proposes a novel sensorless speed estimation method for an IM using the spectrum of the supply-side current. However, due to the influence of fundamental supply frequency, it is difficult to carry out the speed detection straight from the supply-side current signal. In this paper, an analytic model for characterizing the supply-side current of an inverter-fed IM using the modulation theory and the switching function concept is developed. Then, the Hilbert transform is applied to extract the speed harmonic component from the supply-side current. Finally, an interpolated Goertzel algorithm is put forward to enhance the estimation precision of IM speed. The performance of the proposed sensorless speed estimation method is proved by the speed estimation results obtained from hardware experiments of an IM fed by an inverter under different load conditions. [ABSTRACT FROM AUTHOR]

When the permanent magnet synchronous motor (PMSM) works in the high-speed region with low carrier ratios, the performance of the rotor flux observer has a great influence on the loading capacity and stability of the speed sensorless vector control system. The problem of the adaptive compensation flux observer (ACFO) of the PMSM at low carrier ratios is analyzed in this paper, and an ACFO with a feedback delay component is presented. After retuning the PI regulator parameters, the new expression related to carrier ratio is obtained, which can improve the performance of the flux observer at low carrier ratios and make the torque and current loop response faster. Meanwhile, the stability of different Euler approaches of the integrator for ACFO in the discrete domain is analyzed, and a new Euler with a coefficient is proposed to combine the merits of the backward Euler and the trapezoid Euler. It shows better performance at low carrier ratios. Finally, the effectiveness of the discrete ACFO is verified by experiments. [ABSTRACT FROM AUTHOR]

A power systems of wearable application requires high power conversion efficiency and bidirectional power flows to obtain the compatibility with various power sources and loads. The conventional flyback converter has a simple structure and bidirectional power conversion capability. However, it shows poor power conversion efficiency caused by hard-switching operation, high DC offset current on the transformer, snubber losses, and large peak current. In this paper, a current-fed CLLC resonant converter is proposed to obtain the high power conversion efficiency and the bidirectional power conversion capability. The soft-switching operation, zero DC-offset current, and small peak current can induce high power conversion efficiency. The asymmetric pulse width modulation (APWM) regulates the bidirectional power flows and the output voltage. The design methodology of the proposed converter is analyzed by introducing its operational principles. The performance of the proposed converter is experimentally verified with a 20 W prototype. [ABSTRACT FROM AUTHOR]

An improved two-stage model predictive current control (MPCC) for three-phase three-level converters in the paper, which can simultaneously achieve common-mode voltage (CMV) reduction, effective dc-link capacitor voltage control, and decreased computational burden, is proposed. Compared to the other current control strategies, it has the capability of handling multiple control objectives and possesses a simple structure. Furthermore, it greatly reduces the CMV since the peak CMVs of all the candidate voltage vectors are constrained to be less than one sixth of the dc-link voltage. In addition, an optimal two-stage voltage vector selection mechanism is employed in the proposed method. It helps to significantly reduce the computational complexity. Simulation and experimental results are provided to verify the effectiveness of the proposed method. [ABSTRACT FROM AUTHOR]

This paper presents Space Vector Modulation (SVM) sequences that reduce Common Mode Voltage (CMV) in Dual Three-phase Asymmetrical Induction Motor (DTAIM). At first, two existing SVM techniques such as Reference SVM (RSVM) and CMV1 are studied. Additionally, three new switching sequences are developed as CMV2, CMV3 and DCMV3, which reduce peak magnitude of CMV by 66.8% in comparison with RSVM technique. In SVM techniques, to obtain least CMV, zero vectors are usually replaced by two opposite large Active voltage Vectors (AV) with equal time duration. In such topologies like CMV1, total six AVs are utilized to synthesize the reference vector. The proposed SVM technique CMV2 utilizes only five large AVs to synthesize the reference vector and reduces CMV. Selection of five neighbouring AVs is reflected in reduction of harmonic flux trajectories and stator current ripple in proposed techniques. Additionally, two more switching sequences (CMV3 and DCMV3) are developed related to utilization of specific zero voltage vectors in all sectors (7 and 56) that produce zero CMV. These two switching sequences also provide easy implementation feature during the development of c-code program. In this study, CMV and stator current ripple are considered as performance parameters for different SVM techniques. All SVM techniques are analysed by analytical results, computer simulations, and using prototype test setup of DTAIM fed by Dual Three-phase Voltage Source Inverters (DTVSIs). [ABSTRACT FROM AUTHOR]

The implementation of finite-control-set model predictive control (FCS-MPC) in voltage source inverters (VSIs) can make the system suffer from poor current harmonics performance, which may complicate the design of the required AC filter. To overcome this shortcoming, a carrier-based modulated model predictive control (CB-MMPC) strategy is proposed in this paper. This method enables the utilization of existing PWM modulation techniques with FCS-MPC, where a modulation waveform with zero-sequence signal injection is generated and compared to a triangular carrier wave, while optimizing the selection of the switching states. As it is shown, the studied CB-MMPC strategy not only considerably improves the current total harmonic distortion (THD) but also attains the performance of fast current dynamic response and robustness as the traditional FCS-MPC. Herein, the detailed implementation of the CB-MMPC control strategy is given, while considering its application to the current feedback control loop of a three-phase three-wire two-level VSI modulated at constant switching frequency. Finally, PLECS circuit simulation and a 3-kW VSI prototype are used to verify the superiority and the effectiveness of the presented CB-MMPC strategy. This is also benchmarked to the FCS-MPC and dead-beat based controllers. [ABSTRACT FROM AUTHOR]

This paper presents an investigation into sideband vibro-acoustics suppression of the permanent magnet synchronous motor (PMSM), associated with several periodic signal-based dithering modulations. Mathematical derivations of four typical periodic signal-based schemes are deduced with the power spectral density (PSD) method. The individual modulation parameters, such as bandwidth and modulation ratio, are determined the values to minimize the sideband vibro-acoustics. The frequency distributions of the sideband components are discussed by the analytical derivations. The relationship between the electromagnetic components and mechanical responses is reconstructed by coupling with temporal features. For verification, the experimental tests with a prototype PMSM are introduced under different operational conditions. According to the results and figures, both magnitude suppression and frequency distribution are accurately correlated with sideband harmonic components as well as vibro-acoustic responses. This investigation thus clearly holds promise for the evaluation and optimization in powertrain used by electric vehicles. [ABSTRACT FROM AUTHOR]

A new transformer-less three-level grid-tied inverter is proposed in this article. By employing the switched-capacitor (SC) modules, a new topology is derived. The proposed topology has some features which are high efficiency, the capability of voltage boosting without utilization of any additional boost stage, and suppressing the leakage current by using common grounded strategy. In this article, a peak current control is employed to generate the gate pulses of power semiconductor switches and adjustment of both active and reactive powers. By doing so, the grid injected current is controlled and adjusted to have a proper quality. The operation modes, design consideration, and a comparison with some recently proposed grid-connected topologies are done through this paper. Finally, the performance and feasibility of the proposed inverter are confirmed with a 500 W experimental prototype. [ABSTRACT FROM AUTHOR]

Nowadays, one of the challenges in transport electrification is the reduction of the components’ size and weight in order to improve the power density. This is often achieved by designing electrical machines with higher rotational speeds and excitation frequencies. In addition, the converter needs to control the machine over a wide speed range given by the mission profile. Therefore, copper losses can significantly increase due to the combination of high frequency excitation and the harmonics introduced by the converter. The winding arrangement design plays a key role in the minimization of the copper losses, thus towards a higher efficiency and/or an improved power density. Different winding topologies can be adopted for high speed electrical machines and amongst them random windings are still one of the most widespread types. This paper presents an in depth study on AC losses in random windings for high frequency motor applications. An analytical method is compared against 2-D Finite Element (FE) simulation results. These are then compared to experimental measurements taken on a custom motorette. Importantly, in order to take into account the random positions of each strand within the machine slots, an Experimental Statistic Method (ESM) is proposed. The ESM allows to define the probability distribution which is useful to evaluate the winding copper losses at the design stage. The contribution of the Pulse Width Modulation (PWM) effect is also considered and experimentally evaluated. [ABSTRACT FROM AUTHOR]

This paper presents a quantitative analysis of the losses of the hybrid cascaded modular multilevel converter (HC-MMC). Regulation of full-bridge (FB) submodule-capacitor voltages in an HC-MMC requires dedicated strategies that affect the voltage harmonics generated by the converter's main power stage and hence its switching patterns and losses. This paper uses an electromagnetic transient simulator (PSCAD/EMTDC) to estimate the semiconductor losses using the switches’ turn-on and turn-off characteristics. The paper examines the losses of a 45-MW HC-MMC for two recently introduced voltage-regulation methods based upon the modified sinusoidal pulse width modulation (PWM) and an existing method based upon the trapezoidal PWM. Losses of a conventional FB-MMC that offers dc-fault blocking capability are also investigated and compared with those of HC-MMC. The loss comparison results indicate that: first, the two voltage-regulation methods for HC-MMC based upon the modified sinusoidal PWM result in markedly lower semiconductor losses than the trapezoidal PWM method; second, compared with the original HC-MMC, a mixed submodule HC-MMC may lower the semiconductor losses at certain operating points with proper addition of mixed submodules; and finally, HC-MMC may have up to 9.0% lower semiconductor losses (relative) than the conventional FB-MMC. [ABSTRACT FROM AUTHOR]

This paper presents an intelligent-based fault-tolerant system for a solar photovoltaic (PV) inverter. Artificial neural network based controller is used to monitor, detect, and diagnose the faults in solar PV panels, battery, semiconductor switches, and inverters. The cascaded multilevel inverter is connected across the combination of solar PV panel and battery for dc–ac conversion. The major advantage of the proposed topology is that it can deliver power from source to the load even under fault and partial shaded conditions. The paper also reviews on various faults in the solar PV energy conversion process and provides suitable solutions for each circumstance. Simulations are undertaken in MATLAB 2016a/Simulink and experimental investigation is carried out for a 3 kWp solar PV system. The results have proven that the system is capable to deliver power in spite of faulty environments. The comparison and discussion of the results were made to show the effectiveness of the proposed system. [ABSTRACT FROM AUTHOR]

This paper introduces a new nonlinear voltage-mode controller for a PWM dc-dc buck converter operating in continuous conduction mode. The sliding-mode control technique is used to derive a simplified equivalent control law based on the averaged dc-dc buck converter dynamics. As opposed to the reported design approaches, the proposed control scheme only requires the output voltage in the feedback loop without the need to the capacitor current. Thus, the analogue implementation cost is reduced and the drawback of adding a capacitor current sensor to the power converter is eliminated. The control equation is realized in a simple analogue circuit using few op-amps and resistors, which is suitable for industrial applications. The system modeling and control design procedure along with the derivation of the existence and stability conditions are presented. The control system performance is analyzed using MATLAB and SaberRD simulations. Furthermore, a simple analogue prototype of the simplified nonlinear voltage-mode controlled dc-dc buck converter is developed on a PCB. The simulation and experimental results show that the controller maintains a constant switching frequency, exhibits fast transient response, and provides good tracking performance under large disturbances. [ABSTRACT FROM AUTHOR]

The hard switching operation of the insulated gate bipolar transistor (IGBT)-based multilevel converters (MLCs) in the transformer less direct integration of renewable power plants produces a considerable amount of switching and conduction power loss. This eventually causes higher junction temperature and lower thermal stability. The symmetrically designed MLC using third harmonic sixty-degree bus-clamped pulse width modulation (BCPWM) technique demonstrates reduced switching losses and better harmonic spectra. However, the development of analytical power loss model is a complex and challenging issue due to the discontinuous switching mode of IGBTs for the BCPWM in MLC. In this regard, an analytical model for calculating the average and the rms currents for the hard switching operation of IGBTs and antiparallel diodes (APDs) with BCPWM is proposed. Furthermore, to calculate the device turn-on and turn-off losses, a discrete form of equation is presented to evaluate the transition times of switching more precisely. The numerical power loss values of IGBTs and APDs found from the derived analytical equations for MLC are compared with the simulation and experimental results. The numerical results agree well with the simulated and the experimental outcomes, which validate the proposed analytical loss model. Moreover, an advanced three dimensional thermal impedance model with chip-wise interdependent multilayer thermal coupling effect is also considered in this paper to realize the critical thermal loading condition of the switching devices. [ABSTRACT FROM AUTHOR]

The dual-loop control strategy in a hybrid reference frame (HRF) for single-phase voltage-source inverters in islanded operation mode is studied, which applies a capacitor voltage shaping loop in the synchronous reference frame (SRF) and a capacitor current shaping loop in the stationary reference frame (HRF-based v+ ic control strategy). This strategy is able to achieve the purpose of active damping, fast dynamic response, and zero reference tracking error. However, due to the inherent characteristics of SRF-based voltage loop and the digital control delay, the performance of the system is degraded and the control parameter design of the HRF-based v+ ic control strategy shows great difficulties. To overcome these shortcomings, in this paper, a systematic parameter design guideline for the HRF-based v+ ic control strategy is proposed to ensure the system stability and optimize the performance of the system under control delay condition. The mathematic model of the HRF-based v+ ic control strategy is established with the consideration of control delay in this paper. Based on this model, a satisfactory region of the system stability indexes can be obtained by stability specifications of the system, and the optimal control parameters can be calculated according to the stability indexes selected from the satisfactory region. By using this method, the system stability and robustness can be guaranteed. Finally, the experimental results are presented to validate the effectiveness of the presented optimal control parameter design methodologies. [ABSTRACT FROM AUTHOR]

The efficiency of a proton exchange membrane fuel cell system (PEMFCS), which includes a PEMFC stack and a dc/dc converter, depends on the applied voltage and there exists an efficiency extreme point (EEP) in PEMFCS. Therefore, the EEP of PEMFCS changes with varying load, because the system parameters are also varying. It makes EEP tracking (EEPT) a challenging assignment. In order to achieve the EEP operation of PEMFCS under varying load conditions without oscillation, this paper proposes a novel EEPT method based on a forgetting factor recursive least square (FFRLS) online identification. The FFRLS algorithm is based on data-driven and uses real-time data of the system to improve the estimation accuracy of PEMFCS parameters under the changing load. On the test bench of PEMFCS-battery system consists of 300-W PEMFCS, lithium-ion battery, PEMFC controller, and DSP controller, a multi-index performance test and comparative analysis were carried out. The results showed that the proposed method is not sensitive to load conditions. The performance of the proposed EEPT method for PEMFCS has been successfully validated. In addition, compared with the “perturb and observe” and “incremental conductance” online tracking algorithms, the proposed online identification method can get more satisfactory results. Such as, reducing the tracking time and hydrogen consumption, making the output power of PEMFCS smoother, which means its operation stress is smaller, and thus, it lasts longer. [ABSTRACT FROM AUTHOR]

Three-phase solar inverters can be operated with different modulation strategies such as sinusoidal pulsewidth modulation (SPWM), space vector modulation (SVM), and third-harmonic injection PWM (THIPWM). The selection of the modulation strategy can significantly affect photovoltaic (PV) leakage currents and power losses and compromise the inverter performance. This paper presents a detailed analysis of traditional and modified modulation effects on power semiconductor losses and PV leakage current. The research focuses on a three-phase three-level T-type neutral point clamped (3L-TNPC) solar inverter. A detailed exploration of traditional SPWM and SVM is presented, and a new modified modulation strategy referred to as two-triplen harmonic injection PWM (2THIPWM) is proposed, which can substitute the SVM scheme. Analytical expressions are derived for the proposed 2THIPWM strategy, which can be used for the SVM power-loss approximation. The comparison between 2THIPWM and SPWM shows a conduction-loss difference greater than the 5% normalized range. The modulation strategies are discussed with respect to the PV common mode current signature, and specific design techniques in modulation lead to reduced leakage currents for safety compliance. The theoretical and experimental results obtained using a 3L-TNPC solar inverter are presented to evaluate the modulation strategies and their impact on performance. [ABSTRACT FROM AUTHOR]

In a photovoltaic (PV) system, the appropriate voltage regulation is essential to guarantee the maximum power operation. In this paper, a direct pulse width modulation controller based on a single gain (k) is presented. This controller directly estimates the duty cycle (D) through gain k, and simultaneously its mathematical operation contains the properties of integral controller. Initially, a comprehensive study is presented to evaluate the D values according to reference points on I–V curves with contrasted irradiance levels. This study has been carried out for resistive and battery loads. Based on critical observations, separate tuning expressions of k gain have been designed for resistive and battery loads. It is revealed that with regard to varying weather, k gain is dynamic for resistive load, while static for battery load. Moreover, it is also shown that inappropriate setting of load will limit maximum power point tracker controller to reach the MPP point. Therefore, two more expressions have been presented to configure the resistive and battery loads. Comparative analysis between different D-schemes is presented, which indicates that for both loads, the proposed scheme has the superior performance with less complexity. Finally, numerous experimental tests have been conducted to verify the tuning criteria and working principle of the proposed scheme. [ABSTRACT FROM AUTHOR]

Stand-alone microhydro systems based on the self-exited induction generator (SEIG) are popular in developing countries. However, an electronic based controller is required to maintain the quality (voltage and frequency) of the generated power within an acceptable range. Conventionally, this controller is designed using a phase-controlled thyristor circuit (or more recently using a dc chopper circuit) and a fixed resistance dump load to receive the excess generated power. Generally, in small communities the total dissipated power in the dump load is greater than the consumed power by all the households. This problem of inefficient power usage can be solved by distributing the controller among households. The objective of this paper is to improve the distributed electronic load controller (DELC). As with the original DELC, the proposed improved DELC is used for two purposes: First, consuming the excess generated power individually by each household; and second, operating as a complementary device for voltage and frequency regulation of the SEIG. The detailed design and experimental verifications of the proposed improved DELC including the design of an appropriate input filter to minimize the network current distortion are presented here. Additionally, MATLAB simulations are used to study the interaction between the proposed improved DELC and the powerhouse controller (the ELC). [ABSTRACT FROM AUTHOR]

Hybrid boost converter (HBC) has been proposed to replace a dc/dc boost converter and a dc/ac converter to reduce conversion stages and switching loss. In this paper, control of a three-phase HBC in a Photovoltaic (PV) charging station is designed and tested. This HBC interfaces a PV system, a dc system with a hybrid plug-in electrical vehicles, and a three-phase ac grid. The control of the HBC is designed to realize maximum power point tracking for PV, dc bus voltage regulation, and ac voltage or reactive power regulation. A testbed with power electronics switching details is built in MATLAB/SimPowersystems for validation. Simulation results demonstrate the feasibility of the designed control architecture. Finally, lab experimental testing is conducted to demonstrate HBC's control performance. [ABSTRACT FROM AUTHOR]

This paper presents a unified approach to deal with sliding mode controllers used for induction motor drives. The study digs deep to identify matched and unmatched disturbances and derive conditions to satisfactorily reject the same. The investigation reveals fundamental limitations of hysteresis (first-order sliding mode) controllers those can be overcome by higher order controllers. Second-order sliding mode controllers are investigated to achieve disturbance rejection and chattering free performance. It is shown that the drive with second-order sliding mode controllers maintains constant switching frequency and decoupling between torque and flux simultaneously on the face of sudden speed, load, or parameter variations. Also, it is shown that the dynamic performance can be improved further at higher sampling frequencies keeping the switching frequency constant. Extensive simulations are carried out in MATLAB/SIMULINK. Implementation of such a drive becomes feasible with low cost field programmable gate arrays (FPGAs) due to their inherent parallel processing capability. A vector-controlled induction motor drive is developed and the controller is implemented using FPGA to corroborate the simulation results through experimentations. [ABSTRACT FROM AUTHOR]

An approach for diagnosis and mitigation of sensor malfunctioning in a permanent magnet synchronous generator based direct-drive variable speed wind energy conversion system (WECS) is presented in this paper. Malfunctioning of current sensors causes erroneous grid- and machine-side current measurements, which significantly affect the operation of grid- and machine-side controllers, and in turn, performance of the WECS system degrades. In the proposed approach, the sliding-mode observer-based fault diagnosis theory is used to diagnose (i.e., to detect and estimate) the error induced in the grid- and machine-side current measurements due to sensor malfunctioning. The proposed mitigation action rectifies the measured grid- and machine-side currents using estimated measurement errors, as soon as malfunctioning of sensors is diagnosed, and ensures resilient operation of the WECS against sensor malfunctioning. The accuracy and effectiveness of the proposed approach are verified through rigorous simulation and experimental studies, which clearly demonstrate the effectiveness of the proposed approach. [ABSTRACT FROM AUTHOR]

This paper presents an elaborate scheme, which is different from the traditional parameter identification method, to estimate the parameters precisely for high-speed magnetic suspension motor. It is well known that the inductance and resistance of each winding play an important role in ensuring the stability of the controller for motor. There have been sufficient research works on equivalent circuit model, where the input and output data are assumed to be true value, and unknown circuit parameters are obtained by solving the equivalent circuit equations of motor. However, the output data are often interfered with noises, such as measurement error, the high-frequency components from pulse width modulation signals and sampling errors. The system response output data are reconstructed through applying in stochastic theory, which is different from the traditional filter techniques, to eliminate effectively the above-mentioned noises. Thus, the parameters can be estimated precisely. As an experimental verification, parameters estimated by the proposed method are applied in calculation of switching point between pulse width modulation mode and pulse amplitude modulation mode for magnetic suspension motor. The experimental results validate the effectiveness of the proposed method. [ABSTRACT FROM AUTHOR]

In this paper, a multilevel inverter based on three-phase H-bridge inverters for an open-end winding induction motor drive is presented and its fault-tolerance capability is investigated. The multilevel topology is obtained using three wye-connected three-phase H-bridge inverters to supply open-end winding induction motors. This topology has the ability to extend the maximum voltage applied to the motor windings up to two times the dc supply voltage of the three-phase inverters. For a given induction motor voltage, the topology allows the use of dc sources with a lower voltage rating. Consequently, faster power semiconductors can be used. This multilevel topology can be directly controlled by modifying known modulation concepts, such as sinusoidal pulse width modulation (PWM). In this study, two sinusoidal PWM modulation techniques will be implemented: the level-shifted carriers (phase disposition) and the phase-shifted modulator. Fault-tolerant operation under an open-switch fault without adding any extra components and without changing the modulation strategy is also proposed, adding fault-tolerant capability to the new topology. Experimental results of this multilevel inverter in normal operation and in fault tolerant mode are presented. The obtained results confirm the fault effectiveness of the proposed multilevel topology. [ABSTRACT FROM PUBLISHER]

Performance of conventional digital current controllers is constrained by transport delays within the feedback acquisition chain, as well as by delays inherent to the pulse width modulation. In this paper, we introduce a novel current controller which provides a very high closed-loop bandwidth, improves the robustness and disturbance rejection, and eliminates the noise and sampling errors in the feedback path. In order to achieve these goals, we suppress the transport delays by introducing an improved execution schedule of the control interrupt and by inserting a cascaded multiplier of differential character. With the novel gain setting rule, the closed-loop bandwidth reaches 17% of the sampling frequency, disturbance rejection capability is doubled, the step response has a negligible overshoot, and the robustness is characterized by the vector margin of 0.65. Experimental verification is performed using an experimental setup with a three-phase inverter, digital controller, and a permanent magnet synchronous motor. [ABSTRACT FROM AUTHOR]

Monitoring of the rotor temperature is very important for both control and protection of induction machines. Temperature sensors are usually avoided due to additional wiring. Although the best precision is achieved by test-signal-based methods, they are rarely used due to a high-torque ripple. The ripple is negligible in cases where inherent pulse width modulation (PWM) voltage component is used as the test signal. In this paper, a novel temperature estimation method is devised, robust against the PWM delays, signal acquisition delays, and phase errors in high-frequency voltage and current components. Opposed to previous solutions where temperature is calculated based on the real part of the impedance, the presented method is based on the absolute value of the impedance at the PWM frequencies. The temperature is calculated from the change of the input impedance. Proposed method for temperature estimation was tested on an experimental setup which uses an inverter with sine modulated output voltages and an induction servo motor. [ABSTRACT FROM AUTHOR]

The flying-capacitor-based multilevel converter is one of the well-known breeds of the multilevel power converters. This paper proposes a new flying-capacitor-based multilevel converter to minimize the number of flying capacitors (FCs) and power switches. The advantage of the proposed FC-based multilevel converter in comparison with the conventional flying-capacitor multicell converter is that it needs fewer FCs. Also, in comparison with the stacked multicell converter, the proposed multilevel converter requires fewer semiconductor switches. In order to balance the voltage of the FCs in proposed multilevel converter, a new active voltage balancing method which is fully implemented using logic-form equations is presented. The proposed voltage balancing method measures output current and FC voltages to generate switching states to produce the required output voltage level, as well as balance the FCs voltages at their reference values. The output voltage of the proposed multilevel converter controlled with suggested active voltage balancing method can be modulated with any pulse-width-modulation (PWM) method, such as phase-shifted-carrier PWM or level-shifted-carrier PWM. Simulation results and experimental measurements of proposed FC-based multilevel converter are presented to verify the performance of the proposed converter, and its novel switching and modulation strategy, which is based on the active voltage balancing method. [ABSTRACT FROM PUBLISHER]

Power converters are a key, but vulnerable component in switched reluctance motor (SRM) drives. In this paper, a new fault diagnosis scheme for SRM converters is proposed based on the wavelet packet decomposition (WPD) with a dc-link current sensor. Open- and short-circuit faults of the power switches in an asymmetrical half-bridge converter are analyzed in details. In order to obtain the fault signature from the phase currents, two pulse-width modulation signals with phase shift are injected into the lower-switches of the converter to extract the excitation current, and the WPD algorithm is then applied to the detected currents for fault diagnosis. Moreover, a discrete degree of the wavelet packet node energy is chosen as the fault coefficient. The converter faults can be diagnosed and located directly by determining the changes in the discrete degree from the detected currents. The proposed scheme requires only one current sensor in the dc link, while conventional methods need one sensor for each phase or additional detection circuits. The experimental results on a 750-W three-phase SRM are presented to confirm the effectiveness of the proposed fault diagnosis scheme. [ABSTRACT FROM PUBLISHER]

In this paper, we introduce an improved ac current controller with robustness against the noise in the feedback path. This three-phase current controller is suited for inverter supplied ac machines and grid-connected power converters. Conventional solutions make use of symmetric pulse-width modulation (PWM) techniques with feedback sampling in the middle of the voltage pulses. Single-sample-based feedback acquisition gets affected by the noise and parasitic phenomena. We perform a thorough analytical and experimental study on feedback errors with conventional sampling, and we consider the impact of the lockout time, motor cables, winding capacitance, and anti-aliasing filters. In order to suppress a significant spectral content in the area of low-order harmonics, we apply an improved acquisition technique, which uses a period-average and removes any PWM noise from the feedback signals. Both anti-aliasing filter and proposed period-average filter introduce delays, which impair the control-loop performance. The conventional current controller is then extended to suppress the effects of the delays. Parameter setting procedure is devised to achieve both the bandwidth and the robustness against the parameter changes. Analytical and experimental studies prove that the proposed feedback acquisition technique improves the robustness in the presence of variable delays and switching transients. Experimental tests show that the extended current controller with period-average feedback acquisition reaches the same bandwidth and robustness as the state-of-the-art controller. [ABSTRACT FROM PUBLISHER]

This paper presents a novel modulated series dynamic braking resistor (MSDBR) control strategy for enhancing the fault ride-through (FRT) of doubly fed induction generator-based wind turbines. The proposed cost-effective protection scheme introduces a voltage booster that offers series voltage compensation capability and provides a means of power evacuation to mitigate the power imbalance during grid faults. To attain flexible and robust control solution for handling both balanced and unbalanced grid faults, the proposed scheme employs a modulated pulse width modulation (PWM) switching technique to control the stator phase voltage individually. The proposed transient management scheme allows the MSDBR to mitigate the impact from different types of grid faults and to fulfill with the recent grid code requirement. Also, reactive current injection capability during faults is also investigated with the proposed voltage reference algorithm. For the controller design, small-signal modeling is utilized with consideration of measurement dynamics for the tuning of controller parameters in order to ensure the system robustness and stability. Finally, the simulation results demonstrate the satisfactory performance of the MSDBR with its preferred allocation for enhancing the FRT performance against both balanced and unbalanced faults. [ABSTRACT FROM AUTHOR]

This paper presents the calculation of the electromagnetic losses for a 2.1-MW permanent magnet synchronous generator for wind energy application. The focus is on recognizing the significance of including the analysis of higher harmonics in the electromagnetic loss calculation. The analyzed harmonics include the ones resulting from the use of a pulse width modulation (PWM) of the voltage of the generator. The magnet losses calculated for the PWM current are several times higher than the ones calculated for the sinusoidal current. In addition, frequency-domain and time-domain models for iron loss calculation are compared. The frequency-domain model that assumes a sinusoidal variation and considers only the fundamental component of the magnetic induction in the stator core material underestimates the iron losses in the machine. Especially, when the additional losses resulting from the higher harmonics, rotational fields, and minor loops are taken into account. Finally, it is shown how the composition and thickness of the electrical steel used in the stator core of the generator influences the total core losses. [ABSTRACT FROM AUTHOR]

This paper presents a new 12-step sensorless drive for brushless dc motor based on back-electromotive force (back-EMF) differences, which are estimated from the disturbance observer (DOB) structure. Availability of rotor position information with a resolution of 30° and commutation without phase shift are the advantages of using the back-EMF differences. Unlike the conventional methods that obtain part of the back-EMF signal from the manipulation of three phase voltages, the proposed DOB structure can access the entire back-EMF profile. By designing a proper low-pass filter in the DOB structure, the back-EMF difference can be well detected with lower sensor noise. Compensation of delay commutation introduced by the filter is also discussed. Experiment results showed that the proposed sensorless drive is capable of running the motor in lower speed, and performs better under different speed and load torque as compared with the conventional method. [ABSTRACT FROM AUTHOR]

This paper presents the development of a wind switched-reluctance generator (SRG) with interleaved interface dc–dc converter. First, the power circuit and control scheme of the SRG are properly designed. The hysteresis current-controlled pulse width modulation (PWM) scheme is designed to achieve good winding current tracking control, and the robust voltage control scheme is developed to yield well-regulated dc output voltage under varying prime mover driving speed and load conditions. Moreover, the voltage regulation and the developed power performances of SRG are further enhanced using the proposed commutation shift approach. Next, an interleaved current-fed push–pull interface dc–dc converter with two modules is developed to establish the boosted common dc bus voltage of a dc microgrid from the SRG output having fault-tolerant capability. The rating analysis and circuit component design are conducted in detail. Similarly, well-regulated voltage with lower ripples is also yielded via the properly designed schematic and control scheme. [ABSTRACT FROM AUTHOR]

Presents a closure to the discussion from the following paper, ?Electrical machine PWM loss evaluation basics (Ruderman, A. and Welch,R.) in Proc. Int. Conf. Energy Efficiency Motor Driven Syst.,Sep. 2005, vol. 1, pp. 58?68. [ABSTRACT FROM AUTHOR]

Presents a discussion on the following paper, ?Electrical machine PWM loss evaluation basics (Ruderman, A. and Welch,R.) in Proc. Int. Conf. Energy Efficiency Motor Driven Syst.,Sep. 2005, vol. 1, pp. 58?68. [ABSTRACT FROM AUTHOR]