Samples for recent work:
inverter operation of asynchronous machines
Starting with a harmonic analysis of the feeding voltage (resp. feeding current) according to the T - equivalent circuit diagram
additional losses and harmonic torques are calculated taking eddy currents into consideration.
Input:
- parameters of the T - equivalent circuit diagram
- dimensions of the rotor-bars
- feeding voltage versus time (resp. feeding current)
top of page
Results:
- current and voltage versus time
- additional losses in rotorbars and iron
- torque versus time
top of page
temperature distribution stationary / dynamic
According to the structure of an electrical machine and the cooling method a lumped circuit
(consisting of loss sources, thermal capacities and resistances) is assembled flexibly.
For this purposes a Modelica-library with simple components for modeling coolant flows was developed.
Special thanks to Martin Otter!
Input:
- parameters of the thermal circuit diagram
- ambient versus time (temperature, mass flow of coolant)
- individual losses versus time
top of page
Results:
- temperatures versus time
- heat flows versus time
top of page
analysis of windings
Distribution of the windings to the stator slots defines the curve of field excitation, which will be analysed.
Additionally winding factor and harmonic stray factor is calculated.
top of page
starting of asynchronous motors
Considering the voltage-drop at the line impedances due to the starting-current of the motor
the motor's torque minus the load torque accelerates inertia of the drive.
Input:
- load- torque (versus speed) and moment of inertia
- motor- torque, current and power factor (versus speed)
- starting transformer- short circuit voltage and copper losses
- base load- apparent power and power factor
- compensation
- main transformer- short circuit voltage and copper losses
- grid- short circuit impedance
top of page
Results:
- voltage drops at the line impedances (variable versus speed)
- curve of motor's torque versus speed
- calculation of starting time
top of page
Losses during operational cycles
Taking the asynchronous machine's T - equivalent circuit diagram the losses are calculated for each time slice of the cycle;
losses and reactances are adapted to the variable saturation due to inverter operation.
Traget is to calculation of an equivalent constant power or to check thermal stress of the choosen motor.
Input:
- equivalent circuit's parameters- may be read from a design's result
- operational cycle: load- torque and speed versus time
top of page
Results:
- losses versus time
- current and power consumption of the motor versus time
top of page
active compensation of voltage drops
Not only active, but also reactive and harmonic currents cause unwanted voltage drops at line impedances.
This tool demonstrates the effect of exact compensating injection of reactive and harmonic currents.
Input:
- choice of current curve
- power factor of fundamental harmonic
- line impedance
- degree of compensation
top of page
Results:
- curve with / without compensation of voltage
- curve with / without compensation of current
top of page
simulation of diode rectifiers
Using a Modelica-simulation
it is possible to identify mains load and DC-voltage of a diode rectifier
at different network conditions and DC burdens.
Input:
- parameters of supply network
- parameters of line reactor and rectifier
- burden of DC-link
top of page
Results:
- mains voltage and DC voltage versus time
- mains currents versus time
top of page
dynamic simulation of asynchronous motors
A Modelica-Library for dynamic simulation of electrical machines
is under permanent further development. This enables flexible simulation of different operation conditions:
start-up, short-circuit, load impulse, ...
Input:
- parameters (reactances) of the motor
- electrical supply
- mechanical load
top of page
Results:
- speed and torque versus time
- currents versus time
Here You get a short summary of space phasor theory.
top of page