MATLAB Simulations

Due to its theoretical complexity with many intricate interweaving estimators and controllers, we decided to break down each block and simulate the Indirect Field Oriented Control blocks in MATLAB for a 3 phase AC induction motor.

 

Space Vector Pulse Width Modulation Block:
The main obstacle to producing an accurate simulation of the entire IFOC system was modeling the Space Vector Pulse Width Modulation block. Without a functioning and realistic model of this advanced PWM technique, many of the other blocks (such as the rotor flux angle estimator and the Park Transform) couldn’t be connected due to dependencies on the output of the SVPWM connection to the motor, thus the majority of the simulation time was designed to model this key step.

 

Benefits of SVPWM over Sinusoidal PWM:
-Enhances DC Bus utilization by 15%
-Total Harmonic Distortion and Lower Order Harmonics and decreased

 

Steps for SVPWM:
1) The alpha and beta components of the complex voltage vector for the current sample are input into the SVPWM block.

2) The SVPWM block determines the magnitude of the alpha-beta voltage vector, the angle (and consequently, its sector location in the SVPWM hexagon), and switching times to be applied to the 3 phase inverter.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

3) The switching times are then fed into a 3 phase inverter simulation, which implements symmetric switching techniques for each PWM period based off of the specified sector. The symmetric switching pattern minimizes switching loss by only switching one IGBT between to transition between adjacent vectors in each sector.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

3 Phase Inverter Block:
The symmetric switching pattern is applied to a 3 phase IGBT inverter simulation for the determined times for each specific switching sector for the current PWM time.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

This is a simulation of our MATLAB code generating 3 phases voltages outputted from the inverter using the SVPWM technique.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

This is a comparison of an ideal voltage wave to the SVPWM generated voltage

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Due to the RL load and equivalent motor circuit, the current across the motor from our voltage waveform generated above is:

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Clark Transform Block:
This first coordinate transform block moves from a 3-axis (for each of the 3 phase currents) 2-dimensional coordinate system referenced to the stator to a 2-axis, 2-dimensional coordinate system still referenced to the stator.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Park Transform Block:
The second coordinate transforms from the 2-axis alpha beta coordinate system  that is referenced to the stator to a synchronously rotating reference frame that is aligned with the current time sample rotor flux angle. Under steady state conditions the direct and quadrature components are DC values.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Flux Angle Estimator (Current Model) Block:
In an asynchronous induction motor, the mechanical speed of the rotor is slightly less than the flux field rotation. This difference is called the slip. In order for the Park and Inverse Park transforms to transform between time variant and time invariant conditions, the angular position of the rotor flux vector for the current time sample must be estimated based on stator currents, rotor velocity, and the rotor time constant (which is the rotor inductance divided by the rotor resistance).

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Field Weakening Region:
In many asynchronous AC Induction motor applications, the reference flux has to be carefully selected. In conventional machine drives, the flux reference is made proportional to the inverse of the rotor speed for field-weakening operation.