Simulation Details

Description of the System and Circuit Model

The simulation tool on this website uses a simplified model of the drive, filter, cable, and motor system. The model is used to simulate the response at the motor terminals to a voltage pulse from the drive. However, the model does not consider high frequency resonances (in the 10s of megahertz range). Figure 1 shows the system model.

System model
Figure 1 – Simulation model for electric motor and cable system connected to a motor drive.

First, the motor is modeled as a wye-connected parallel RL circuit.

Then, the cable is modeled as a series inductance with a wye-connected capacitance. Since the cable series resistance and shunt conductance typically do not affect the dv/dt and ringing, they are ignored here.

The filter model depends on the type of circuit selected. At a high level, it is a combination of inductors, capacitors, and/or damping resistors.

Finally, the voltage waveform from the drive is assumed to be relatively free of high frequency ringing due to the loop inductance of the DC link. It is modeled as a trapezoidal waveform.

Simulation Method

The simulation uses an ordinary differential equation (ode) solver to solve the system of differential equations defined by the circuit model. The trapezoidal voltage waveform from the drive is an input to the simulation. Then, the simulation performs a numerical integration using the Dormand-Prince RK method with an adaptive step size.

Determining Circuit Model Values

You can determine the parameters of an electric motor by measuring the terminals of the motor with an impedance analyzer. Then, extract the model values from the impedance data. The information may also be available from the motor manufacturer or in the manufacturer’s literature.

Determine the per-unit-length inductance and capacitance of the cable by measuring a known length of cable. An RCL meter or an impedance analyzer is useful.

Determine the rise time of the drive by experimental measurement with a very short cable attached between the drive and motor. It may also be available from the manufacturer.