Part Number: C2000-DIGITAL-CONTROL-LIBRARY
Tool/software: Code Composer Studio
Hi,
We are designing an IPM motor controller and have a problem. I would like to get your suggestions about it. In abstract, when driving IPM with zero d-axis current (id=0), there is a phase delay between rotor d-axis and phase current (Ia). However, i expect d-axis of rotor should be synchronized with zero crossing of phase A current. I have to note that, software libraries for motor control (like Clarke, Park, PID, SVPWM etc.) imported from TMS570 Motorware (which is mainly ported from c2000 libraries)
Firstly, we make offset calibration of rotor position sensor. We are using an absolute position sensor which also has A,B,Z pulse outputs. For measuring d-axis offset, we spin IPM (with another motor) and observe back-EMF of phase A (Van, line to neutral) and Z-pulse (zero position pulse). After calibration process, we make sure position sensor generates zero pulse at zero corssing of Van. Here is the scope screen:
CH2 : Van (back-EMF voltage of phase A to neutral) CH4: Encoder zero pulse (Z pulse)
Then we apply q-axis current from inverter (keeping d-axis current at zero, id=0) and observe Z-pulse and phase current:
CH3 : Ia (phase A current) CH4: Encoder zero pulse (Z pulse)
Here is the problem. There is a phase delay (approximately 45 electrical degrees) between phase A current and rotor zero position. I expect zero crossing of phase A current and zero position of rotor should coincides (zero phase delay). I repeated the process for differenct speed and load conditions and phase delay is always near 45 degrees. I seems, from scope, some d-axis current injected to motor but inverter measures zero d-axis current.
I simulate my control system design (build the Simulink model of all coordinate transformation, SVPWM libraries and others) on Simulink. Phase A current and d-axis is synchronized as i expected (Shown figure below). So i think there is no problem about axis transformation equations (Clarke,Park, Inverse Park etc. ).
I would appreciate it if you have an opinion and forward your suggestions about the problem.