Modelling 3-phase induction motor and filter for inverter output in LTspice - Electrical Engineering Stack Exchange most recent 30 from electronics.stackexchange.com 2019-06-27T03:14:06Z https://electronics.stackexchange.com/feeds/question/410956 http://www.creativecommons.org/licenses/by-sa/3.0/rdf https://electronics.stackexchange.com/q/410956 1 Modelling 3-phase induction motor and filter for inverter output in LTspice scouseydaniel https://electronics.stackexchange.com/users/178209 2018-12-07T12:00:22Z 2018-12-08T17:37:08Z <p>I am designing an inverter in Ltspice and am looking to have a simple circuit to represent the motor load and filter out the PWM harmonics in order to obtain outputs. The motor characteristics are:</p> <p>Synchronous Inductance: 500 uH</p> <p>Resistance (line-neutral): 500 mohms</p> <p>Will a RLC filter circuit similar to the image shown below work? If so what values should I use for the components (the PWM frequency I am trying to remove is 20kHz, will this use f=1/2*pi*RC)</p> <p><a href="https://i.stack.imgur.com/gUYGf.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/gUYGf.png" alt="enter image description here"></a></p> <p>I think I could do it for single phase however I am struggling with a 3 phase motor especially because of both resistor and inductor when calculating the values required for the filter.</p> <p>Here is the overall circuit</p> <p><a href="https://i.stack.imgur.com/rK4yc.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/rK4yc.png" alt="enter image description here"></a></p> https://electronics.stackexchange.com/questions/410956/modelling-3-phase-induction-motor-and-filter-for-inverter-output-in-ltspice/410991#410991 1 Answer by Charles Cowie for Modelling 3-phase induction motor and filter for inverter output in LTspice Charles Cowie https://electronics.stackexchange.com/users/80875 2018-12-07T15:17:50Z 2018-12-07T15:37:59Z <p>The term synchronous inductance (or reactance) is applied to synchronous motors and generally not to induction motors. The equivalent circuit of an induction motor has been the subject of many questions on this site, for example <a href="https://electronics.stackexchange.com/questions/375374/why-does-the-slipring-motor-speed-increase-with-a-decrease-in-resistance"><strong>this one</strong></a> and <a href="https://electronics.stackexchange.com/questions/339520/does-reactive-power-of-induction-motor-vary-with-load"><strong>this one</strong></a>. The motor is usually modeled as the line-to-neutral equivalent circuit of one phase. The capacitance from windings to ground is ignored for motor performance models, but is probably needed for your purpose. You may need that capacitance at the input side of the motor circuit. There is also a high-frequency path from stator to rotor and through the shaft bearings to ground.</p> <p>Any added capacitance must be on the input side of the motor. Filter reactance may be needed on the input side also. You should not need to remove the carrier frequency entirely. You only need to be concerned about voltage stress on the winding insulation due to high dv/dt. Motor bearing currents probably need to be mitigated by other means. EMI probably needs to be mitigated at the controller and by shielding the motor leads.</p> https://electronics.stackexchange.com/questions/410956/modelling-3-phase-induction-motor-and-filter-for-inverter-output-in-ltspice/411182#411182 0 Answer by Charles JOUBERT for Modelling 3-phase induction motor and filter for inverter output in LTspice Charles JOUBERT https://electronics.stackexchange.com/users/30234 2018-12-08T17:37:08Z 2018-12-08T17:37:08Z <p>I agree with Charles Cowie: the term synchronous inductance is for synchronous motors. Maybe, for your simulation, a phase of the motor could be modeled by an inductance <span class="math-container">\$L_{mot} \$</span> in series with a resistance <span class="math-container">\$R_{mot} \$</span> (and also a capacitor in parallel as wrote Charles Cowie). But the values of the elements are not easy to guess. I would say a first approximation of the impedance of this combination could be:</p> <p><span class="math-container">$$Z_{approx} = \frac{V}{I_{starting}}$$</span></p> <p>where <span class="math-container">\${I_{starting}}\$</span> is the starting current of your motor, and V the rated voltage.</p> <p>I think the first schematic you give is a little misleading. I feel like you're mixing the filter with the equivalent circuit of the motor. Maybe the following one is closer to what you want to simulate?</p> <p><img src="https://i.stack.imgur.com/OTCZC.png" alt="schematic"></p> <p><sup><a href="/plugins/schematics?image=http%3a%2f%2fi.stack.imgur.com%2fOTCZC.png">simulate this circuit</a> &ndash; Schematic created using <a href="https://www.circuitlab.com/" rel="nofollow">CircuitLab</a></sup></p> <p>In this schematic, Rmot and Lmot represent the motor (see above). Lfilter, Cfilter and Rfilter belong to the filter. The purpose of Rfilter is to damp the filter. Values are arbitrary. The structure of the filter is close to the one presented in figure 3 of <a href="https://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/20040172495.pdf" rel="nofollow noreferrer">this document</a>.</p>