Regenerative Drives - Effect of Power Factor

davezawadi (David Stone): 
 

A note to Adrian.

Using an induction motor will generate power, but you need to consider the rotor cage loss and therefore the efficiency. Your equations will need a significant level of “calibration values” to correctly read the true dyno power, and you might find it easier to measure the speed and torque directly, and just use the motor as a brake. You can measure the torque with no moving parts by mounting the motor on load cells and measuring the difference between the two sides under load. Rotation speed is easy!

Hi David,

Thank-you for the constructive comments. Considering the rotor cage loss is something that I hadn't yet thought about.

The rig will measure the ‘mechanical’ power, as the product of speed & torque (speed from an inductive pickup (or shaft encoder, not decided yet) & torque from a loadcell via a torque arm - the motor being trunion mounted). I'm fairly happy with the fuel to mechanical power bit of the equation.

The end user/requester of this rig seems to have a particular fixation with regeneration onto the mains via a VSD. I think he believes that this is how a ‘real’ diesel generator would be connected and he wants to mimic this. I've tried to explain that this isn't how a genset is sync'd onto the mains & exports real power (don't want to even start to discuss reactive power). There are a couple of VSD manufacturers that claim to be able to measure the exported power in regen mode, but I'm struggling to pin them down on accuracy. As others have said, normally regen is just used as a way to increase efficiency by recovering energy when retarding a spinney thing, for the OPs application & mine the system will spend the majority of its time in regen mode.

I think Client just wants to see that the energy is leaving the system by flowing back onto the mains (as opposed to being lost as heat in a eddy brake or water dyno). The VSD/motor is also used to turn the engine over in order to start it (not talking huge engine here, 10HP is the working figure at the moment) so some elements of the control system will need to watch the torque switch signs as the engine fires & begins to drive the motor. It will also need to watch the torque flip back again if the engine runs out of fuel or stops firing for some other reason.

Adrian

davezawadi (David Stone): 
 

A note to Adrian.

Using an induction motor will generate power, but you need to consider the rotor cage loss and therefore the efficiency. Your equations will need a significant level of “calibration values” to correctly read the true dyno power, and you might find it easier to measure the speed and torque directly, and just use the motor as a brake. You can measure the torque with no moving parts by mounting the motor on load cells and measuring the difference between the two sides under load. Rotation speed is easy!

Hi David,

Thank-you for the constructive comments. Considering the rotor cage loss is something that I hadn't yet thought about.

The rig will measure the ‘mechanical’ power, as the product of speed & torque (speed from an inductive pickup (or shaft encoder, not decided yet) & torque from a loadcell via a torque arm - the motor being trunion mounted). I'm fairly happy with the fuel to mechanical power bit of the equation.

The end user/requester of this rig seems to have a particular fixation with regeneration onto the mains via a VSD. I think he believes that this is how a ‘real’ diesel generator would be connected and he wants to mimic this. I've tried to explain that this isn't how a genset is sync'd onto the mains & exports real power (don't want to even start to discuss reactive power). There are a couple of VSD manufacturers that claim to be able to measure the exported power in regen mode, but I'm struggling to pin them down on accuracy. As others have said, normally regen is just used as a way to increase efficiency by recovering energy when retarding a spinney thing, for the OPs application & mine the system will spend the majority of its time in regen mode.

I think Client just wants to see that the energy is leaving the system by flowing back onto the mains (as opposed to being lost as heat in a eddy brake or water dyno). The VSD/motor is also used to turn the engine over in order to start it (not talking huge engine here, 10HP is the working figure at the moment) so some elements of the control system will need to watch the torque switch signs as the engine fires & begins to drive the motor. It will also need to watch the torque flip back again if the engine runs out of fuel or stops firing for some other reason.

Adrian