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33-429: Reluctance motor subtypes include synchronous, variable, switched and variable stepping. Reluctance motors can deliver high power density at low cost, making them attractive for many applications. Disadvantages include high torque ripple (the difference between maximum and minimum torque during one revolution) when operated at low speed, and noise due to torque ripple. Until the early twenty-first century, their use

66-450: A DC motor for the stator windings. The rotor however has no magnets or coils attached. It is a solid salient-pole rotor (having projecting magnetic poles) made of soft magnetic material, typically laminated steel. When power is applied to a stator winding, the rotor's magnetic reluctance creates a force that attempts to align a rotor pole with the nearest stator pole. In order to maintain rotation, an electronic control system switches on

99-488: A duty cycle of each phase of 1/2, rather than 1/3 as in the simpler sequence. The control system is responsible for giving the required sequential pulses to the power circuitry. It is possible to do this using electro-mechanical means such as commutators or analog or digital timing circuits. Many controllers incorporate programmable logic controllers (PLCs) rather than electromechanical components. A microcontroller can enable precise phase activation timing. It also enables

132-423: A soft start function in software form, in order to reduce the amount of required hardware. A feedback loop enhances the control system. The most common approach to powering an SRM is to use an asymmetric bridge converter. The switching frequency can be 10 times lower than for AC motors. The phases in an asymmetric bridge converter correspond to the motor phases. If both of the power switches on either side of

165-460: A charged particle is not due to the charged particle's movement. This may be appreciated by looking at the units for each. The unit of electric field in the MKS system of units is newtons per coulomb, N/C, while the magnetic field (in teslas) can be written as N/(C⋅m/s). The dividing factor between the two types of field is metres per second (m/s), which is velocity. This relationship immediately highlights

198-446: A dual-phase rotor output 23 kW at 14,000 RPM with a power density of 1.4 kW and 94% peak efficiency, while a comparable conventional rotor produced 3.7 kW. The use of nonpermeable posts and bridges allows them to be larger and stronger, reducing interfence between the flux lines of the rotor and the stator. One limitation is that magnetization is limited to 1.5 T , compared to conventional motors 2 T. The switched reluctance motor (SRM)

231-421: A generator. The load is switched to the coils in sequence to synchronize the current flow with the rotation. Such generators can be run at much higher speeds than conventional types as the armature can be made as one piece of magnetisable material, as a slotted cylinder. In this case the abbreviation SRM is extended to mean Switched Reluctance Machine, (along with SRG, Switched Reluctance Generator). A topology that

264-412: A rotor pole is equidistant from two adjacent stator poles, the rotor pole is said to be in the "fully unaligned position". This is the position of maximum magnetic reluctance for the rotor pole. In the "aligned position", two (or more) rotor poles are fully aligned with two (or more) stator poles, (which means the rotor poles completely face the stator poles) and is a position of minimum reluctance. When

297-441: A stator pole is energized, the rotor torque is in the direction that reduces reluctance. Thus, the nearest rotor pole is pulled from the unaligned position into alignment with the stator field (a position of less reluctance). (This is the same effect used by a solenoid , or when picking up ferromagnetic metal with a magnet .) To sustain rotation, the stator field must rotate in advance of the rotor poles, thus constantly "pulling"

330-451: A wound field brushed DC motor . The rotor consists of soft magnetic material, such as laminated silicon steel , which has multiple projections acting as salient magnetic poles through magnetic reluctance . For switched reluctance motors, the number of rotor poles is typically less than the number of stator poles, which minimizes torque ripple and prevents the poles from all aligning simultaneously—a position that cannot generate torque. When

363-705: Is ampere , kg is kilogram , and s is second . Additional equivalences result from the derivation of coulombs from amperes (A), C = A ⋅ s {\displaystyle \mathrm {C=A{\cdot }s} } : T = N A ⋅ m , {\displaystyle \mathrm {T={\dfrac {N}{A{\cdot }m}}} ,} the relationship between newtons and joules (J), J = N ⋅ m {\displaystyle \mathrm {J=N{\cdot }m} } : T = J A ⋅ m 2 , {\displaystyle \mathrm {T={\dfrac {J}{A{\cdot }m^{2}}}} ,} and

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396-464: Is a type of reluctance motor . Unlike brushed DC motors , power is delivered to windings in the stator (case) rather than the rotor . This simplifies mechanical design because power does not have to be delivered to the moving rotor, which eliminates the need for a commutator . However it complicates the electrical design, because a switching system must deliver power to the different windings and limit torque ripple . Sources disagree on whether it

429-549: Is a type of stepper motor . The simplest SRM has the lowest construction cost of any electric motor. Industrial motors may have some cost reduction due to the lack of rotor windings or permanent magnets. Common uses include applications where the rotor must remain stationary for long periods, and in potentially explosive environments such as mining, because no commutation is involved. The windings in an SRM are electrically isolated from each other, producing higher fault tolerance than induction motors . The optimal drive waveform

462-474: Is a type of stepper motor . The simplest SRM has the lowest construction cost of any electric motor. Industrial motors may have some cost reduction due to the lack of rotor windings or permanent magnets. Common uses include applications where the rotor must remain stationary for long periods, and in potentially explosive environments such as mining, because no commutation is involved. Switched reluctance motor The switched reluctance motor ( SRM )

495-460: Is a type of reluctance motor. Unlike brushed DC motors , power is delivered to windings in the stator (case) rather than the rotor . This simplifies mechanical design because power does not have to be delivered to the moving rotor, which eliminates the need for a commutator . However it complicates the electrical design, because a switching system must deliver power to the different windings and limit torque ripple . Sources disagree on whether it

528-552: Is both motor and generator is useful for starting the prime mover, as it saves a dedicated starter motor. Tesla (unit) The tesla (symbol: T ) is the unit of magnetic flux density (also called magnetic B-field strength) in the International System of Units (SI). One tesla is equal to one weber per square metre . The unit was announced during the General Conference on Weights and Measures in 1960 and

561-738: Is named in honour of Serbian-American electrical and mechanical engineer Nikola Tesla , upon the proposal of the Slovenian electrical engineer France Avčin . A particle, carrying a charge of one coulomb (C), and moving perpendicularly through a magnetic field of one tesla, at a speed of one metre per second (m/s), experiences a force with magnitude one newton (N), according to the Lorentz force law . That is, T = N ⋅ s C ⋅ m . {\displaystyle \mathrm {T={\dfrac {N{\cdot }s}{C{\cdot }m}}} .} As an SI derived unit ,

594-665: Is not a pure sinusoid , due to the non-linear torque relative to rotor displacement, and the windings' highly position-dependent inductance. The first patent was by W. H. Taylor in 1838 in the United States. The principles for SR drives were described around 1970, and enhanced by Peter Lawrenson and others from 1980 onwards. At the time, some experts viewed the technology as unfeasible, and practical application has been limited, partly because of control issues and unsuitable applications, and because low production numbers result in higher cost . The SRM has wound field coils as in

627-414: The apparently similar induction motor which also energizes windings in a rotating phased sequence. In an SRM the rotor magnetization is fixed, meaning the salient 'North' poles remains so as the motor rotates. In contrast, an induction motor has slip, meaning it rotates at slower than the magnetic field in the stator. SRM's absence of slip makes it possible to know the rotor position exactly, allowing

660-614: The circuit performs the same action. This efficient circuit is known as the (n+1) switch and diode configuration. A capacitor , in either configuration, is used for storing BEMF for re-use and to suppress electrical and acoustic noise by limiting fluctuations in the supply voltage. If a phase is disconnected, an SR motor may continue to operate at lower torque, unlike an AC induction motor which turns off. SRMs are used in some appliances, in linear form for wave energy conversion, magnetic levitation trains, or industrial sewing machines. The same electromechanical design can be used in

693-496: The derivation of the weber from volts (V), W b = V ⋅ s {\displaystyle \mathrm {Wb=V{\cdot }s} } : T = V ⋅ s m 2 . {\displaystyle \mathrm {T={\dfrac {V{\cdot }{s}}{m^{2}}}} .} The tesla is named after Nikola Tesla . As with every SI unit named for a person, its symbol starts with an upper case letter (T), but when written in full, it follows

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726-419: The fact that whether a static electromagnetic field is seen as purely magnetic, or purely electric, or some combination of these, is dependent upon one's reference frame (that is, one's velocity relative to the field). In ferromagnets , the movement creating the magnetic field is the electron spin (and to a lesser extent electron orbital angular momentum ). In a current-carrying wire ( electromagnets )

759-510: The motor can operate with sinusoidal voltage. Speed control requires a variable-frequency drive . High-powered SynRMs typically require rare-earth elements such as neodymium and dysprosium . However, a 2023 study reported the use of a dual-phase magnetic laminate to replace them. Magnetizing such a material creates highly magnetized regions, serving as the rotor poles, while leaving other regions non-magnetic (nonpermeable). In one experiment using high-temperature nitriding to increase strength,

792-408: The motor to be stepped slowly, even to the point of being stopping completely. If the poles A0 and A1 are energised then the rotor will align itself with these poles. Once this has occurred it is possible for the stator poles to be de-energised before the stator poles of B0 and B1 are energized. The rotor is now positioned at the stator poles b. This sequence continues through c before arriving back at

825-439: The phase are turned on, then that corresponding phase is actuated. Once the current has risen above the set value, the switch turns off. The energy now stored within the winding maintains the current in the same direction, the so-called back EMF (BEMF). This BEMF is fed back through the diodes to the capacitor for re-use, thus improving efficiency. This basic circuitry may be altered so that fewer components are required although

858-597: The reluctance also varies with position. This presents a control systems challenge. Synchronous reluctance motors (SynRM) have an equal number of stator and rotor poles. The projections on the rotor are arranged to introduce internal flux "barriers", holes that direct the magnetic flux along the so-called direct axis. The number of poles must be even, typically 4 or 6. The rotor operates at synchronous speeds without current-conducting parts. Rotor losses are minimal compared to those of an induction motor , however it normally has less torque . Once started at synchronous speed,

891-399: The rotor along. Some motor variants run on 3-phase AC power (see the synchronous reluctance variant below). Most modern designs are of the switched reluctance type, because electronic commutation gives significant control advantages for motor starting, speed control and smooth operation (low torque ripple). The inductance of each phase winding in the motor varies with position, because

924-501: The rotor so that it is aligned in between A and B. Following this A's stator poles are de-energized and the rotor continues on to be aligned with B. The sequence continues through BC, C and CA to complete a full rotation. This sequence can be reversed to achieve motion in the opposite direction. More steps between positions with identical magnetisation, so the onset of missed steps occurs at higher speeds or loads. [REDACTED] In addition to more stable operation, this approach leads to

957-427: The rules for capitalisation of a common noun ; i.e., tesla becomes capitalised at the beginning of a sentence and in titles but is otherwise in lower case. In the production of the Lorentz force , the difference between electric fields and magnetic fields is that a force from a magnetic field on a charged particle is generally due to the charged particle's movement, while the force imparted by an electric field on

990-530: The start. This sequence can also be reversed to achieve motion in the opposite direction. High loads and/or high de/acceleration can destabilize this sequence, causing a step to be missed, such that the rotor jumps to wrong angle, perhaps going back one step instead of forward three. [REDACTED] A much more stable system can be found by using a "quadrature" sequence in which up to two coils are energised at any time. First, stator poles A0 and A1 are energized. Then stator poles B0 and B1 are energized which, pulls

1023-613: The tesla can also be expressed in terms of other units. For example, a magnetic flux of 1 weber (Wb) through a surface of one square meter is equal to a magnetic flux density of 1 tesla. That is, T = W b m 2 . {\displaystyle \mathrm {T={\dfrac {Wb}{m^{2}}}} .} Expressed only in SI base units , 1 tesla is: T = k g A ⋅ s 2 , {\displaystyle \mathrm {T={\dfrac {kg}{A{\cdot }s^{2}}}} ,} where A

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1056-481: The windings of successive stator poles in sequence so that the magnetic field of the stator "leads" the rotor pole, pulling it forward. Rather than using a mechanical commutator to switch the winding current as in traditional motors, the switched-reluctance motor uses an electronic position sensor to determine the angle of the rotor shaft and solid state electronics to switch the stator windings, which enables dynamic control of pulse timing and shaping. This differs from

1089-528: Was limited by the complexity of designing and controlling them. Advances in theory, computer design tools, and low-cost embedded systems for control overcame these obstacles. Microcontrollers use real-time computing control algorithms to tailor drive waveforms according to rotor position and current/voltage feedback. Before the development of large-scale integrated circuits , the control electronics were prohibitively costly. The stator consists of multiple projecting (salient) electromagnet poles, similar to

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