Right Harmonic Spectrum for the back-electromotive force of a n-phase synchronous motor

This paper deals with a vector control of n-phase permanent magnet synchronous machine. To use control algorithms already developed for sine-wave 3-phase machines, the spectrum of back electromotive force (EMF) must contain only odd 2k+1 harmonics which verify the following inequality, 1≤ 2k +1< n . In an experimental vector control of a 5-phase drive, two usual algorithms of sine-wave 3-phase machine are thus used to supply a machine with trapezoidal waveform back EMF. In this case, the first and third harmonics are used to produce torque: the other harmonics, and particularly the 7th one, induce effects as torque ripples and parasitic currents

Fault-Tolerant Operation of an Open-End Winding Five-Phase PMSM Drive with Short-Circuit Inverter Fault

Multi-phase machines are well-known for their fault tolerant capability. Star-connected multiphase machines have fault tolerance in open-circuit. For inverter switch short-circuit fault, it is possible to keep a smooth torque of Permanent Magnet Synchronous Machine (PMSM) if the currents of faulty phases are determined and their values are acceptable. This paper investigates fault-tolerant operations of an open-end fivephase drive, i.e. a multi-phase machine fed with a dual-inverter supply. Inverter switch short-circuit fault is considered and handled with a simple solution. Original theoretical developments are presented. Simulation and experimental results validate the proposed strategy

Control Strategies for Open-End Winding Drives Operating in the Flux-Weakening Region

This paper presents and compares control strategies for three-phase open-end winding drives operating in the flux-weakening region. A six-leg inverter with a single dc-link is associated with the machine in order to use a single energy source. With this topology, the zero-sequence circuit has to be considered since the zero-sequence current can circulate in the windings. Therefore, conventional over-modulation strategies are not appropriate when the machine enters in the flux-weakening region. A few solutions dealing with the zero-sequence circuit have been proposed in literature. They use a modified space vector modulation or a conventional modulation with additional voltage limitations. The paper describes the aforementioned strategies and then a new strategy is proposed. This new strategy takes into account the magnitudes and phase angles of the voltage harmonic components. This yields better voltage utilization in the dq frame. Furthermore, inverter saturation is avoided in the zero-sequence frame and therefore zero-sequence current control is maintained. Three methods are implemented on a test bed composed of a three-phase permanent-magnet synchronous machine, a six-leg inverter and a hybrid DSP/FPGA controller. Experimental results are presented and compared for all strategies. A performance analysis is conducted as regards the region of operation and the machine parameters.Projet SOFRACI/FU

Analytical Optimal Currents for Multiphase PMSMs Under Fault Conditions and Saturation

An original analytical expression is presented in this paper to obtain optimal currents minimizing the copper losses of a multi-phase Permanent Magnet Synchronous Motor (PMSM) under fault conditions. Based on the existing solutions [i]opt1 (without zero sequence of current constraint) and [i]opt2 (with zero sequence constraint), this new expression of currents [i]opt3 is obtained by means of a geometrical representation and can be applied to open-circuit, defect of current regulation, current saturation and machine phase short-circuit fault. Simulation results are presented to validate the proposed approach

FPGA Implementation of a General Space Vector Approach on a 6-Leg Voltage Source Inverter

A general algorithm of a Space Vector approach is implemented on a 6-leg VSI controlling a PM synchronous machine with three independent phases. In this last case, the necessity of controlling the zero-sequence current motivates the choice of a special family of vectors, different of this one used in Pulse Width Modulation (PWM) intersective strategy and in common Space Vector PWM (SVPWM). To preserve the parallelism of the algorithm and fulfill the execution time constraints, the implementation is made on a Field Programmable Gate Array (FPGA). Comparisons with more classical 2-level and 3-level PWM are provided.Fui8 within the SOFRACI projec

Sensitivity of a 5-phase Brushless DC machine to the 7th harmonic of the back-electromotive force

This paper presents a vector control of a 5-phase drive composed of a 5-leg Pulse Width Modulation (PWM) Voltage Source Inverter (VSI) supplying a permanent-magnet Brushless DC (BLDC) machine with trapezoidal waveform of the back-electromotive force (EMF). To achieve this control a Multi-machine Multi-converter model is used: the 5-phase machine is transformed into a set of two 2-phase fictitious machines which are each one controlled in a (d,q) frame as 3-phase machines with sine waveform back-EMF. In comparison with the 3-phase BLDC drives, the 5-phase ones present one particularity: a high sensitivity to the 7th harmonic of back-EMF. Experimental results show that the 7th harmonic of back-EMF, which represents only 5% of RMS back-EMF, induces high amplitude parasitic currents (29 % percent of RMS current). The model allows to explain the origin of this sensitivity and how to modify simply the control algorithm. Experimental improvements of the drive are presented

Differing spectrum of HIV-associated ophthalmic disease among patients starting antiretroviral therapy in India and South Africa

Differences in the prevalence and spectrum of HIV-associated ophthalmic disease in Africa and Asia are not well documented. We studied two comparable cohorts of patients initiating antiretroviral therapy in Mumbai, India, and Cape Town, South Africa. The prevalence of HIV-associated ophthalmic disease was higher in the Indian population (17.5%) than in the South African population (12.1%). This was largely because of vitreo-retinal opportunistic infections (11.4%vs. 2.6%, respectively), notably cytomegalovirus retinitis. This difference persisted after adjusting for confounding factors (adjusted odds ratio = 11.32, 95% confidence interval: 2.67–48.13), confirming a marked geographical difference in the prevalence of HIV-associated retinal disease