Dear All,
I am currently working on thesis on Reduced switch count inverter for driving three phase BLDC motor. However I am not clear abut how to calculate the DC link capacitor values so that it works good with load(impedance).
I understand that there is a relationship between the Capacitor reactance (Xc) and the impedance(Xl) reactance that is feeding the DC capacitors mid point. Suppose if I know the impedance, rated speed, DC voltage How d I get the Capaciotrs value?
What abut the Capacitor value calculation when the DC link mid point in unbalanced?
I would be really thankful if anyone of you could guide me or help me through this.
Regards,
SM
Hello
The following publication may help you to find something about your question.
https://www.researchgate.net/publication/237091045_A_Cost-Effective_Position_Sensorless_Control_for_Four-Switch_Three-Phase_Brushless_DC_Motor_Drives_Using_Single_Current_Sensor
Article A Cost-Effective Position Sensorless Control for Four-Switch...
you should consider the switching frequency and the maximum allowable ripple current through the dc link capacitor .
It is necessary to take account the switching frequency and the permissible ripple current at the terminals of the DC bus capacitor
Thank you Salman and Yacine for the inputs.
But I have a query. The ripple current depends on the duty cycle. So which range(percentage of duty cycle) shall I consider for the ripple current in order to do the capacitance calcualtion. Because the Capacitance value shall be fixed once found for the operation where as duty cycle operating the switches may vary. What abt the voltage ripple and the load inductance consideration?
Primarily , the amount of capacitance in the dc link should gives minimum voltage ripple (i.e >5%) to provide stiff voltage (especially if your source is battery) . then you should consider the worst operating point of the drive cycle (which is the speed that yields maximum current ripple) because the ripple contents affected by the motor speed.
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