The Induction Machines Design Handbook, Second ...

The General Electric Company (GE) began developing three-phase induction motors in 1891.[12] By 1896, General Electric and Westinghouse signed a cross-licensing agreement for the bar-winding-rotor design, later called the squirrel-cage rotor.[12] Arthur E. Kennelly was the first to bring out the full significance of complex numbers (using j to represent the square root of minus one) to designate the 90Âº rotation operator in analysis of AC problems.[24] GE's Charles Proteus Steinmetz greatly developed application of AC complex quantities including an analysis model now commonly known as the induction motor Steinmetz equivalent circuit.[12][25][26][27]

In both induction and synchronous motors, the AC power supplied to the motor's stator creates a magnetic field that rotates in synchronism with the AC oscillations. Whereas a synchronous motor's rotor turns at the same rate as the stator field, an induction motor's rotor rotates at a somewhat slower speed than the stator field. The induction motor stator's magnetic field is therefore changing or rotating relative to the rotor. This induces an opposing current in the rotor, in effect the motor's secondary winding.[28] The rotating magnetic flux induces currents in the rotor windings,[29] in a manner similar to currents induced in a transformer's secondary winding(s).

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The induced currents in the rotor windings in turn create magnetic fields in the rotor that react against the stator field. The direction of the rotor magnetic field opposes the change in current through the rotor windings, following Lenz's Law. The cause of induced current in the rotor windings is the rotating stator magnetic field, so to oppose the change in rotor-winding currents the rotor turns in the direction of the stator magnetic field. The rotor accelerates until the magnitude of induced rotor current and torque balances the load on the rotor. Since rotation at synchronous speed does not induce rotor current, an induction motor always operates slightly slower than synchronous speed. The difference, or "slip," between actual and synchronous speed varies from about 0.5% to 5.0% for standard Design B torque curve induction motors.[30] The induction motor's essential character is that torque is created solely by induction instead of the rotor being separately excited as in synchronous or DC machines or being self-magnetized as in permanent magnet motors.[28]

Larger single phase motors are split-phase motors and have a second stator winding fed with out-of-phase current; such currents may be created by feeding the winding through a capacitor or having it receive different values of inductance and resistance from the main winding. In capacitor-start designs, the second winding is disconnected once the motor is up to speed, usually either by a centrifugal switch acting on weights on the motor shaft or a thermistor which heats up and increases its resistance, reducing the current through the second winding to an insignificant level. The capacitor-run designs keep the second winding on when running, improving torque. A resistance start design uses a starter inserted in series with the startup winding, creating reactance.

The stator of an induction motor consists of poles carrying supply current to induce a magnetic field that penetrates the rotor. To optimize the distribution of the magnetic field, windings are distributed in slots around the stator, with the magnetic field having the same number of north and south poles. Induction motors are most commonly run on single-phase or three-phase power, but two-phase motors exist; in theory, induction motors can have any number of phases. Many single-phase motors having two windings can be viewed as two-phase motors, since a capacitor is used to generate a second power phase 90Â from the single-phase supply and feeds it to the second motor winding. Single-phase motors require some mechanism to produce a rotating field on startup. Induction motors using a squirrel-cage rotor winding may have the rotor bars skewed slightly to smooth out torque in each revolution.

Linear induction motors, which work on the same general principles as rotary induction motors (frequently three-phase), are designed to produce straight line motion. Uses include magnetic levitation, linear propulsion, linear actuators, and liquid metal pumping.[59]

Despite its simple construction, the mathematical model of the single-phase motors, which describes the various motor operating modes, is quite complex due to the existence of the rotating elliptical electromagnetic field in the motor air gap. This air gap electromagnetic field is highly unsymmetrical; the application of the well-known theory and the mathematical models for the three-phase symmetrical induction motors is improper and inaccurate. Therefore, the unsymmetrical magnetomotive force (mmf) currents and voltages corresponding to the two windings of single-phase induction machines may be decomposed in two symmetrical systems (Figure 2) which are the forward and backward components of the two-phase system [15].

Mechanical losses are mainly covering friction and windage losses. These losses can be determined by driving the motor at the rated speed with no-load or excitation. For the machines that operate at constant or nearly constant speed, these losses are constant. For an accurate calculation of motor losses, it is necessary to have an accurate calculation of motor parameters (resistances and reactances) as well as the currents in all motor windings. In addition, the magnetic flux density in the motor cross-section should be calculated, a parameter that is often more or less accurately predicted in motor analytical calculations. This emphasizes the need for an accurate computer-aided design of the motor capable of handling various design modifications, necessary for improving the motor efficiency factor (Î), which can be finally obtained from the ratio of the output power P2 and the input power P1.

There are some general recommendations for the flux density in the specific parts of the machine. For the stator and the rotor teeth, it should be less than 1.8 T, and for the core (yoke) between 1.3 and 1.5 T [15]. Following these general recommendations, the flux density distribution is within recommended ranges for BM and M1. As for the second optimized model M2, bigger values of the flux density can be observed in the rotor teeth due to the motor construction with closed rotor slots. Yet, this value of the flux density is still below the point of the core saturation with respect to the built-in core material as the saturation point is approximately at 2T (Figure 3). FEM models of the motors are verified in terms of their accuracy by calculating the output torque for one fixed speed. It should be noted that presented diagrams of the torque in Figure 12 do not represent the motor transient characteristics usually plotted during motor acceleration from zero up to the rated speed. The presented diagrams are calculating motor torque at one constant speed, i.e., rated speed, for each of the motor models, within the whole interval. Table 6 presents the comparison between the torque values from the parametric analysis and from the FEM models at rated load operating mode. As the torque in the FEM models has pronounced oscillations, it is calculated as an average value within the time interval from 175 to 200 ms. The presented results in Table 6 and their similarity verify that the FEM models are sufficiently accurate. Therefore, the presented results of the flux density distribution are considered reliable and contribute to the overall estimation of the motor design and the performance.

Consumption of electricity by industrial electric motors is increasingly becoming a critical motor design criterion. Many countries have adopted regulations covering smaller AC induction motors (below 375 kW), as they represent, by far, the largest quantity of induction motors in operation and, thus, have the most impact on electricity consumption.

BÃrÃ, D., Diwoky, F. and Schmidt, E. (2022), "Reduced order field-circuit modeling of squirrel cage induction machines for automotive applications", COMPEL - The international journal for computation and mathematics in electrical and electronic engineering, Vol. 41 No. 3, pp. 794-806. -03-2021-0092

N2 - Brushless doubly fed induction machines (BDFIM) have prominent features for variable speed applications. The design and performance analysis of the machine is however complex compared to the conventional induction machines due to its special magnetic fields generated from two stator winding with different pole numbers and frequencies. In this paper, the effective parameters in BDFIM design and their limitations are investigated. In relation with the design objectives, control variables are identified, and an optimal prototype machine design is proposed. The results from experimental tests and finite element simulations of a 3 kW prototype BDFIM are presented to assess the effectiveness of the proposed parameters determination method.

AB - Brushless doubly fed induction machines (BDFIM) have prominent features for variable speed applications. The design and performance analysis of the machine is however complex compared to the conventional induction machines due to its special magnetic fields generated from two stator winding with different pole numbers and frequencies. In this paper, the effective parameters in BDFIM design and their limitations are investigated. In relation with the design objectives, control variables are identified, and an optimal prototype machine design is proposed. The results from experimental tests and finite element simulations of a 3 kW prototype BDFIM are presented to assess the effectiveness of the proposed parameters determination method.

We consider important to stress that it is stated in [204] that their control approach is also valid for many AC-motors; however, an explicit controller is only presented for induction motors. As we show in the present book much simpler controllers are designed for other AC-motors when using our approach than following the steps suggested by the approach in [204].

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