A magnet’s permeability is near that of air. However, in a permanent magnet machine, the magnet reduces the available iron for flux linkage. In an induction machine, the rotor flux linkage will be the same between the d axis and the q axis. The q-axis inductance is the inductance measure when flux passes between the magnetic poles. The d-axis inductance is the inductance measured when flux passes through the magnetic poles. PM motor d-axis and q-axis inductance: The d axis and q axis inductances are the inductances measured as the flux path passes through the rotor in relation to the magnetic pole. One of the most common methods is the d-q motor model. PM motor equivalent circuit: A permanent magnet motor can be represented in a few different motor models. Hence, it is the degree of magnetization that a material obtains in response to an applied magnetic field. Magnetic permeability:In electromagnetism, permeability is the measure of the ability of a material to support the formation of a magnetic field within itself. In simplistic terms, the d axis is the main flux direction, while the q axis is the main torque producing direction. By convention, the quadrature axis always will lead the direct axis electrically by 90 deg. The q axis, or the quadrature axis is the axis on which torque is produced. The d axis, also known as the direct axis, is the axis by which flux is produced by the field winding. The d axis and q axis:In geometric terms, the “d” and “q” axes are the single-phase representations of the flux contributed by the three separate sinusoidal phase quantities at the same angular velocity. Inductance is measured in Henrys (H) or weber-turns per ampere. It must be made clear that inductance is a passive element and is purely a geometric property. In simpler terms, inductance is the flux linkage per unit current. Inductance: Inductance (L) is the constant of proportionality that defines the relationship between the voltages induced by a time rate of change in current that produced a magnetic field. The voltage in the conductor is determined by the following equation: Changing the magnetic field will induce a voltage in a nearby conductor proportional to the rate of change of the current that produced the magnetic field. It can be demonstrated that a magnetic field and the current that produced it are linearly related. A conductor carrying a constant current will generate a constant magnetic field. Inductor: An inductor is a circuit element that consists of a conducting wire usually in the form of a coil. Magnetic flux field is generated by a permanent magnet within or on the surface of a permanent magnet motor. Magnetic flux: Magnetic flux is defined as the rate of a magnetic field flowing through a given conductor’s cross-sectional area. Flux linkage is defined by the following equation: Flux linkage is determined by the number of windings and flux, where ϕ is used to indicate the instantaneous value of a time-varying flux. Flux current is the rate of current flow through a given conductor cross-sectional area.įlux linkage: Flux linkage occurs when a magnetic field interacts with a material such as what would happen when a magnetic field goes through a coil of wire. Flux defines the rate of flow of a property per unit area. To understand the operation of PM motors, it is important to first understand the concepts of magnetic flux, flux linkage, and magnetic flux.įlux: The flow of current through a conductor creates a magnetic field. An LSPM motor incorporates a PM motor’s magnets within the rotor and a squirrel cage motor’s rotor bars to maximize torque and efficiency (see Table 1). A fourth motor known as a line-start PM (LSPM) motor incorporates characteristics of both motors. The magnets are used to generate a constant motor flux instead of requiring the stator field to generate one by linking to the rotor, as is the case with an induction motor. PM motorsĪ PM motor is an ac motor that uses magnets imbedded into or attached to the surface of the motor’s rotor. Therefore, ac induction machines are the predominant motor operated by adjustable speed drives. The interaction between the field and the current produces the driving force. The current generation requires a speed difference between the rotor and the magnetic field. The rotating field induces a current in the rotor bars. A rotating field is generated by the stator winding. An ac induction machine (IM) also is commonly referred to as an ac motor.
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