Hello,
Please advise if we can feed the ML4425 BLDC Inverter driver with an upstream regulated current source, instead of using the ML4425 to regulate motor speed and current? (as in the attached block diagram)
We are going to use the ML4425 BLDC Inverter driver IC to drive a BLDC in a water pump.
ML4425 datasheet:
https://pdf.datasheetcatalog.com/datasheet/fairchild/ML4425.pdf
The inverter obviously needs a big supply capacitor at its input, and we do not have room for this, therefore, we will instead put a 150KHz buckboost converter upstream of the inverter, and ‘feed’ the inverter from that. We will in fact use the buckboost converter as an output current regulated power source, and so it controls the current that gets fed to the ML4425 based inverter. We will feed whatever current to the Motor/Inverter that makes it spin at 8000rpm.
The ML4425 is capable of regulating the motor current and speed itself, using its current sense pin (pin 1), etc.. however, we will simply ground the ML4425’s current sense pin, so that the ML4425’s internal current sense and current limitation is bypassed. (since we are limiting the current with our upstream buckboost converter)
We have a closed loop on the motor speed, whereby the motor speed is regulated to 8000rpm, however, if in so doing, the motor current goes over 20 Amps, then our current limiter kicks in and keeps the current regulated to no more than 20 Amps. The current limiter function is done by the buckboost converter and its feedback loop.
The Vin to the buckboost is 18-32V
The motor will be ~34V when at 8000rpm, and will draw approx 20 Amps at this speed of 8000rpm.
Do you agree that we are wise to act in this way? We will experience high voltage spikes at the output of our buckboost converter whenever we are in the inverter commutation dead time intervals, but should that worry us too much? We do have an overvoltage clamp there (converter shuts down till Vout falls below 35V).
Or would we be better off making the buckboost SMPS an output voltage regulated SMPS, with output current limitation?
Alternatively, is there a Current Source Inverter version of the ML4425? (ie something like ML4425 which drives an inverter with switch “overlap time” instead of switch “dead time”)?
Anyway, Is there actually such a thing as an inverter fed BLDC motor being supplied by a current source? That current source taking the the form of eg a current output regulated buckboost converter?
Why would this be done?
How do you calculate the buckboost RHPZ frequency given that the load is a BLDC inverter drive and the BLDC?
RHPZ of CCM Buckboost = (D'^2*R)/(D * L)
Please advise if we can feed the ML4425 BLDC Inverter driver with an upstream regulated current source, instead of using the ML4425 to regulate motor speed and current? (as in the attached block diagram)
We are going to use the ML4425 BLDC Inverter driver IC to drive a BLDC in a water pump.
ML4425 datasheet:
https://pdf.datasheetcatalog.com/datasheet/fairchild/ML4425.pdf
The inverter obviously needs a big supply capacitor at its input, and we do not have room for this, therefore, we will instead put a 150KHz buckboost converter upstream of the inverter, and ‘feed’ the inverter from that. We will in fact use the buckboost converter as an output current regulated power source, and so it controls the current that gets fed to the ML4425 based inverter. We will feed whatever current to the Motor/Inverter that makes it spin at 8000rpm.
The ML4425 is capable of regulating the motor current and speed itself, using its current sense pin (pin 1), etc.. however, we will simply ground the ML4425’s current sense pin, so that the ML4425’s internal current sense and current limitation is bypassed. (since we are limiting the current with our upstream buckboost converter)
We have a closed loop on the motor speed, whereby the motor speed is regulated to 8000rpm, however, if in so doing, the motor current goes over 20 Amps, then our current limiter kicks in and keeps the current regulated to no more than 20 Amps. The current limiter function is done by the buckboost converter and its feedback loop.
The Vin to the buckboost is 18-32V
The motor will be ~34V when at 8000rpm, and will draw approx 20 Amps at this speed of 8000rpm.
Do you agree that we are wise to act in this way? We will experience high voltage spikes at the output of our buckboost converter whenever we are in the inverter commutation dead time intervals, but should that worry us too much? We do have an overvoltage clamp there (converter shuts down till Vout falls below 35V).
Or would we be better off making the buckboost SMPS an output voltage regulated SMPS, with output current limitation?
Alternatively, is there a Current Source Inverter version of the ML4425? (ie something like ML4425 which drives an inverter with switch “overlap time” instead of switch “dead time”)?
Anyway, Is there actually such a thing as an inverter fed BLDC motor being supplied by a current source? That current source taking the the form of eg a current output regulated buckboost converter?
Why would this be done?
How do you calculate the buckboost RHPZ frequency given that the load is a BLDC inverter drive and the BLDC?
RHPZ of CCM Buckboost = (D'^2*R)/(D * L)
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