motor as a generator during a part of operating cycle
motor as a generator during a part of operating cycle
(OP)
Dear All,
I want to ask if it is possible to use electric motor as a motor and generator in the same time according to the attached photo. On other word, When driving torque is required, the motor will work as an actuator. And, when the braking torque is required in braking mode, the motor will work as a generator. Could I use the motor in generator mode to charge a battery? If yes, what is the suitable circuit for that?
I want to ask if it is possible to use electric motor as a motor and generator in the same time according to the attached photo. On other word, When driving torque is required, the motor will work as an actuator. And, when the braking torque is required in braking mode, the motor will work as a generator. Could I use the motor in generator mode to charge a battery? If yes, what is the suitable circuit for that?





RE: motor as a generator during a part of operating cycle
Variations on that theme have been used from dawn of drives. DC motors are the easiest to use and understand, but induction motors can also be used.
Can not give detailed schematics here because do not know what motor and power range. Google "four quadrant" and "regen" for starters.
Gunnar Englund
www.gke.org
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100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...
RE: motor as a generator during a part of operating cycle
RE: motor as a generator during a part of operating cycle
CJC
http://www.vfdriveinfo.com
RE: motor as a generator during a part of operating cycle
What voltage are you using? There is a big difference in technologies available for the 12 - 100 V range and the 200 - 400 V range. Which one are you using?
Gunnar Englund
www.gke.org
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100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...
RE: motor as a generator during a part of operating cycle
RE: motor as a generator during a part of operating cycle
Also, I'm assuming that it is permanent magnet motor, correct? Or is this a shunt motor?
------------------------------------------------------------------------
If it is broken, fix it. If it isn't broken, I'll soon fix that.
RE: motor as a generator during a part of operating cycle
If you slow the motor down, it will act as a motor and the current will increase as the load increases.
If you over drive the machine it will act as a generator. The first few RPM over speed will be supplying the losses. As the speed is increased the current will drop to zero and them increase as energy is returned to the source. Some motors will transition from full motoring to full generating with as little as 5% change in speed.
Your motor is listed as 48V, 165 RPM.
A shunt motor with those ratings may have, as an example, the following characteristics:
1>Field current and rotor voltage fixed; Full load RPM, 165 RPM,/ Full generation, 173 RPM.
2> Field current and speed fixed: 49.2 Volts applied to the rotor, Full generation/46.8 Volts applied to the rotor, full motoring.
3> Voltage applied to the rotor and speed fixed: Field current -2.5%, full motoring/ field current +2.5%, full generation.
These figures are accurate for a shunt motor near rated speed. The accuracy of this model is compromised by losses, magnetic permeability and saturation, and in the case of compound and shunt motors, by interaction between rotor current and field strength.
Yes it can be done. The challenge is to design circuits that will adapt to smooth control over a wide speed range without excessive losses.
Field control is effective but has a limited range.
You may have success using four six volt batteries. You may be able to get efficient regeneration down to 10% to 12% of rated speed with field strengthening. Then transition to 12 Volts, 24 Volts and finally to 48 Volts.
Bill
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"Why not the best?"
Jimmy Carter
RE: motor as a generator during a part of operating cycle
RE: motor as a generator during a part of operating cycle
Bill
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"Why not the best?"
Jimmy Carter
RE: motor as a generator during a part of operating cycle
What do you mean by "Charging a battery is possible but difficult"?
RE: motor as a generator during a part of operating cycle
I may not be the right person to answer this question. (How to control a robotic arm smoothly and charge a battery efficiently when regenerating.)
Bill
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"Why not the best?"
Jimmy Carter
RE: motor as a generator during a part of operating cycle
The real problem is just as Bill explained. If you run a motor freely at 48 volts (no load) and disconnect the battery and measure the voltage at the instant the battery is disconnected, you will read a reduced voltage probably around 44 to 45 volts or so. You'll need around 52 or so to charge the battery. So even at no load you you need to step up the voltage to charge the battery.
Another option would be a higher voltage regenerative winding in the motor. Basically a motor/generator in one. If you can piggy back a higher voltage motor (say 90 volts at 165 rpm) to the end of the motor and connect that to your charging system is mechanically linked to the motor drive, but electrically separate. Thus when the motor runs at 165 rpm at 48 volts, the generator winding produces about 90 volts. When you need the regenerative braking, you begin to draw current from the generator winding. A brushless DC outrunner might be a good option for this.
Just some thoughts.
------------------------------------------------------------------------
If it is broken, fix it. If it isn't broken, I'll soon fix that.
RE: motor as a generator during a part of operating cycle
This happens in servo drives every time the motor is decelerated faster than losses would slow it. Usually servo drives have a pretty sizeable capacitor bank to absorb some of this, as the capacitor bank is needed to smooth out the rectified AC supply (not an issue when working from a battery). Many times, the capacitor bank can store enough energy to supply the next motoring cycle.
It also happens in hybrid/electricl vehicles every time the brake pedal is pressed. An issue in these vehicles is whether a significant capacitor bank is needed or not. Generally, with the NiMH batteries in the present generation, none is needed because the batteries can absorb the current fast enough. The newer Li-ion batteries cannot take in current so fast, and so may employ a bank of "super-capacitors" as a buffer.
Curt Wilson
Delta Tau Data Systems
RE: motor as a generator during a part of operating cycle
If this is a battery powered application then the PM motor drive should re-charge the battery. Curt basically already described this - if you are using battery as the power source then instead of a DC capacitor buss during regen you have a battery being charged.
Overall, you're still only providing sketchy details which won't help you get any specific answers. Try asking a more specific question besides "Could I use the motor in generator mode to charge a battery?" - the answer to this question is YES but YES doesn't help you actually know how at all.
RE: motor as a generator during a part of operating cycle
Bill
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"Why not the best?"
Jimmy Carter
RE: motor as a generator during a part of operating cycle
When someone talks about "applying torque in the opposite direction of speed" and "4-quadrant operation", as medo79 does here, they are invariably talking about such an electronically controlled system. In this braking mode of operation, current flows "upward" through the flyback diodes to charge up the DC bus supplying the motor power stage. During part of the PWM cycle, the voltage of one lead of the motor is higher than the bus voltage due to the inductance of the motor, regardless of the back EMF at the time, permitting this "reverse" current flow to occur.
Curt Wilson
Delta Tau Data Systems
RE: motor as a generator during a part of operating cycle
RE: motor as a generator during a part of operating cycle
It's always good to see you dropping in to share your knowledge.
Yours
Bill
Bill
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"Why not the best?"
Jimmy Carter
RE: motor as a generator during a part of operating cycle