higdig
Electrical
- Jul 19, 2008
- 4
- 0
- 0
Good day,
We wish to get into electric car drives. Actually, we want to have a brushless DC machine for each of the car wheels.
(so that's 4 DC machines per car)
We know this is a knew way of doing it, that no-one's ever tried before, and so it'll be risky. -but it will make for smaller size since the motors are in the wheels.
We'll use a battery for power.
We will have coils around the stator of each wheel and simply switch current in and out of them as the wheel turns. We will have to sense the rotary position of the wheel so that we know when to switch current through which coil.
We will also need to know the actual and demanded rotary speed of the wheel so that we know whether to pulse the coils with a greater or lesser duty cycle.
We will also have to sense coil current so that we don't run the iron into saturation and so that we don't melt the coils.
Also, we'll switch current into each of the coils using a four transistor H-bridge...the reason for this being that it will allow "regen"...where during braking the wheel acts like a generator and puts power back into the battery.
We know that we need four quadrant operation since we want to be able to go... 1. forwards,... 2. backwards, and be able to do... regen going both.... 3. forwards, -and.... 4. backwards...making for 4 quadrant operation.
...It all sounds deceptively simple.
We believe that just to check that our theory works.....we should start with just a little model car, with very small wheels, probably just 4 inch diameter wheels to start with.
We will need to control the coil currents well because what if one wheel hits a skid patch?....or when the car turns a corner and the inner wheels are supposed to go slower than the outer but with the same torque?
If we get this small model working, -will it be straightforward to scale up to the full car size?
....people tell me that with higher power power-systems, all sorts of transient electrical effects come into play and things start going wrong badly and unpredictably.
Is this true?
Also, what kind of power would we need for the four motors for an electric car that could up to do say 80 miles per hour? (one motor for each of the four wheels)
We wish to get into electric car drives. Actually, we want to have a brushless DC machine for each of the car wheels.
(so that's 4 DC machines per car)
We know this is a knew way of doing it, that no-one's ever tried before, and so it'll be risky. -but it will make for smaller size since the motors are in the wheels.
We'll use a battery for power.
We will have coils around the stator of each wheel and simply switch current in and out of them as the wheel turns. We will have to sense the rotary position of the wheel so that we know when to switch current through which coil.
We will also need to know the actual and demanded rotary speed of the wheel so that we know whether to pulse the coils with a greater or lesser duty cycle.
We will also have to sense coil current so that we don't run the iron into saturation and so that we don't melt the coils.
Also, we'll switch current into each of the coils using a four transistor H-bridge...the reason for this being that it will allow "regen"...where during braking the wheel acts like a generator and puts power back into the battery.
We know that we need four quadrant operation since we want to be able to go... 1. forwards,... 2. backwards, and be able to do... regen going both.... 3. forwards, -and.... 4. backwards...making for 4 quadrant operation.
...It all sounds deceptively simple.
We believe that just to check that our theory works.....we should start with just a little model car, with very small wheels, probably just 4 inch diameter wheels to start with.
We will need to control the coil currents well because what if one wheel hits a skid patch?....or when the car turns a corner and the inner wheels are supposed to go slower than the outer but with the same torque?
If we get this small model working, -will it be straightforward to scale up to the full car size?
....people tell me that with higher power power-systems, all sorts of transient electrical effects come into play and things start going wrong badly and unpredictably.
Is this true?
Also, what kind of power would we need for the four motors for an electric car that could up to do say 80 miles per hour? (one motor for each of the four wheels)
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