Dear Ataollah,

you can calculate the maximum output voltage (maximum available voltage for the plant) of a common three-phase two-level VSI considering the programming of the space vector in the complex plane (see attached Figure). It is a property of the inverter topology and the modulation method.

For the linear operation (assuming continuous SVPWM) of the inverter the maximum available voltage (amplitude of the rotating voltage vector) is the inner circle of the inverter hexagon (v = Vdc/sqrt(3)). Hence you are correct choosing the DC-link voltage.

Be aware that this does not hold for the overmodulation region and that the voltage linearity depends on the modulator hence the switching sequence. For more information on the influence of the modulator and the voltage linearity read:

Hava: Simple Analytical and Graphical Methods for Carrier-Based PWM-VSI Drives

I hope I could help

Best wishes

Pascal

Thank you Pascal Schirmer for your response. But suppose I am using Direct torque control (DTC) algorithm without modulation. So at each sampling time, based on the algorithm, switches are turned on and off and the whole DC bus voltage is applied on motor terminals. In this case, what should the DC bus voltage be so that the motor runs at nominal performance?

Dear Ataollah,

I am sorry from your initial question I was not aware you are referring to DTC.

Obviously for DTC this question is far more complex as through the hysteresis control there is no well defined harmonic spectrum and voltage vectors are chosen according to keep torque and flux in certain boundaries. Especially for the initially proposed DTC there is no fixed restriction on the DC voltage. If voltage vectors cannot be applied by the converter the torque will simply drop.

However novel DTC consider certain voltage constraint, which it self are functions of flux, torque and speed of the drive you may consider the following article:

Qihuai Chen ; Tianliang Lin ; Haoling Ren: Direct torque control of a permanent magnet synchronous machine for hybrid hydraulic excavator

Best wishes

Pascal

Hi Ataollah Gogani Khiabani

I think you need more info from supplier.

Ask him what is the EMF constant, or u can run the PMSM motor with a primary drive and can find out what is the EMF constant, it relates ur speed and Back emf. when u get Back EMF at 3000 rmp, u can calculate AC voltage out of ur inverter using V=E+Ir.

The other constant u require is torque constant, to relate output of ur motor to input current. for the rated output torque of 0.64NM u can calculate the current required.

the other parameter is Stator resistance, which u can calculate at room temperature. Put all the parameters, u can get a Vpeak for inverter.

give a 1/0.707 factor to it(considering sine PWM inverter) that will be a safe DC to attain the rated parameters of the motor.