Power feed-back during controller failure in inverter fed permanent magnet synchronous motor drives with flux weakening

Abstract

When permanent magnet synchronous motors are operated in the flux weakening region, the internal voltage may be much larger than the DC link voltage. If the switching signals are blocked, the freewheeling diodes act as a rectifier and the motor will feed power back into the inverter. This work focuses on the magnitude of the feedback power during such controller failure. Simulations and approximated analysis are used to draw descriptive and comparative curves. Measurements veri ' the computer results but also show that nonlinear effects may have significant influence. INI'HODUC~'IONPermanent magnet excited motors have gained increasingly interest in the last decade due to the discovery of strong and potential low cost permanent magnet materials. Of particular interest are the rugged AC motors. Because of high efficiency, combined with possible compact designs, permanent magnet excited AC motors are well suited for battery fed drives, as in electric traction and remotely operated vehicles [ 1-41. In these applications, the torque requirement is usually high for low speeds, allowing for decreased torque at higher speeds. These requirements are for the high speed region typically met by field weakening in traditional motor drives. In permanent magnet synchronous motors (PMSM), field weakening or more precisely: flux weakening, is obtained by phase advance of the stator currents. The armature reaction then opposes the flux from the magnets and reduces the total stator flux linkages. In inverter fed drives this is obtained by control of the phase of the currents or voltages [ 5 ] . A voltage source inverter (VSI) fed PMsM drive is schematically drawn in Figure 1.The excitation from the magnets alone is constant in flux weakening. The rotational induced voltage from this flux is proportional to speed and may become several times the DC link voltage of the inverter. If for some reason the gate firing signals are blocked or the control is lost, the freewheeling diodes of the inverter behave like a diode rectifier. The motor will act as a generator and feed power back into the DC link. The power can be dissipated in a dumping resistor, or accumulated if the inverter is fed from a battery. If the DC link can not handle the power, the voltage may increase to destructive levels. 42 41, Fax: +47 1 59 42 79 I I I Figwe 1 : A VU fed PMSM drive.In the design of drives with flux weakening, it is essential to predict the magnitude of the power feed-back in failure. It is also necessary to know the influence from motor parameters and the DC link voltage to select the best design. In this work, such failure conditions have been simulated and measured. The results are presented in descriptive curves which show the power during failure vs. speed. Different parameters are compared. An approximate analysis with assumption of continuous currents is perfoxmed. For nonsalient pole motors, this analysis results in a particular simple expression. MODEL DESCRIPTION The motor modelThe state space model for the PMSM is described in synchronous ...

Inverterless High-Power Interior Permanent-Magnet Automotive Alternator

“…It is interesting to observe that they resemble the waveforms in brushless PM motors when driven from a six-step inverter. The waveforms correspond well to those observed earlier by Adnanes [10].…”

“…Uncontrolled generation was described initially by Adnanes [10]. Later, Jahns et al [9], [11] performed a detailed study of this effect.…”

“…The high-power alternator requirement is also indicated. now be calculated using the approach given in [13] for inverter operation and in [9], [10], and [12] for inverterless operation.…”

Uncontrolled generator operation of interior PM synchronous machines following high-speed inverter shutdown

“…), this threshold condition occurs when p.u. Equation (7) can be rewritten using (8) and (9) in a more compact form as follows: (10) which can be readily solved for to yield…”

“…The existence of this special fault mode consisting of high-speed uncontrolled generator (UCG) operation has been known to exist for some time, and some of the characteristics of this operating regime have been investigated in [8]. However, some of the most interesting performance characteristics and machine parameter dependencies associated with the UCG operating mode could not be readily observed using the dynamic simulation tools adopted in this earlier paper.…”