Motors current sources

Starter type Motor voltage Motor current Line or source current Motor torque Source voltage dip... 

The inverter may be a current source inverter, rather than a voltage source inverter (.Section 6.9.4) since it will be the rotor current that is required to be vtiried (equation (1.7)) to control the speed of a wound rotor motor, and this can be independently varied through the control of the rotor current. The speed and torque of the motor can be smoothly and steplessly controlled by this method, without any power loss. Figures 6.47 and 6.48 illustrate a typical slip recovery system and its control scheme, respectively. 

Motoring current drawn from the source Generating or braking current fed to the source... 

The inverters are either voltage source or current source (see Figure 7-7a and b). There are other variations, but they apply to drivers smaller than the ones used with compressors. However, pulse-width-modulated (PWM) (see Figure 7-7c), transistorized units are less complicated and are relatively maintenance-free with reliable units available to at least 500 hp. For all but the smaller compressors, the current source inverter is the one typically used. With a six-step voltage source, a rule of thumb has been to size the motor at two-thirds of its rating so as not to exceed the insulation temperature rise. For current source motors, the output torque is not constant with decreased speed, which fortunately is compatible with most compressors, as torque tends to follow speed. For current source drives, one needs to upsize the motor captive transformer by approximately 15% to account for harmonic heating effects. 

In synchronous motors, the excitation is supplied by a separate direct current source, either as a separate motor-generator (M-G) set or as an exciter mounted directly on the motor shaft. The current can be made to lead to various degrees by varying the magnitude of the field strength. 

Table 15.6. Harmonic rms currents and voltages in a star-wound induction motor that is fed from a current source inverter...

As the net current source propagates toward the tendon, an extracellular potential field arises and follows the action potential complex. At a given field point, this phenomenon is observed as a temporal potential waveform (Figure 25.4b) however, a more complete picture of the phenomenon is obtained by considering the spatial distribution of potentials in the cross section of the motor unit. Figure 25.5 shows schematically how the concentric isopotential lines of individual fibers overlap with those of other fibers in the same motor unit. In a typical healthy motor unit (Figure 14.5a), the mean interfiber distance... 

Pulse width modulation at a fixed frequency has no minimum on-time restriction. Therefore, current peaking and torque ripple can be minimized. For analysis, a d.c. motor can be modeled as a RL circuit, resistor and inductor, or in series with a voltage source. If the motor current is assumed continuous, then the minimum and maximum motor current can be represented by the following equation ... 

B. C. Ghosh and S.N. Bhadra. Bond graph simulation of a current source inverter driven induction motor (csi-im) system. Electric Machines and Power Systems, 21(l) 51-67, 1993. B. Umesh Rai and L. Umanand. Bond graph model of doubly fed three phase induction motor using the axis rotator element for frame transformation. Simulation Modelling Practice and... 

FIG. E-10 Motor current of induction motor started at full voltage. (Source Reliance Electric.)... 

Motor current and torque as full operating speed Is approached. (Source Reliance... 

Regenerative braking If the motor be run beyond synchronous speed by some external means it will work as a generator and feed back useful energy to the supply system. It will draw only the necessary excitation current, / , for the generator action from the source of supply. In such a condition, the motor... 

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