Cuk converter for driving BDC motor?

[mtwieg]

Hello, I've taken on a project in which I have to control the voltage applied to a brushed DC motor, output 10-16V (unidirectional) and 5-15A. Vin can range from 10-24V, so I need a topology capable of having Vout greater than or equal to Vin (though the polarity of Vout can be negative, that's not a problem). Also I have major restrictions on power dissipation; this supply is to be housed in a sealed plastic enclosure (not my call), about 50 cubic inches. At first I was planning on making a fixed output DC-DC to give 24V or so out, then using a DC chopper to drive the motor, but I'm doubting whether such a two stage approach can give low enough losses.

Using a single variable output DC-DC stage seems like it would have better efficiency, but buckboost converters have very high output ripple currents, so I would need huge capacitors. What I keep coming back to it the Cuk topology, which advertises low ripple currents on input and output, but I have no experience designing or using one. In particular I'm wondering if the size of blocking capacitor will be huge in itself... Does anyone with experience in this topology have any thoughts on its merits for this application?

 

[BradtheRad]

To ask for 5 to 15 A output, that is asking a great deal of a single stage converter.

The capacitor(s) will have that amount of current flowing through it continually.

Every 1/10 ohm of resistance will reduce voltage as much as 1.5 V. That can add up.

Have you considered interleaving 2 or more buck-boost type? Similar to adding them together in parallel.

Interleaving should also give you an easier time filtering output ripple.

 

[mtwieg]

Yes, interleaving is another idea that's crossing my mind. But I'm not certain if interleaved PWM signals can be generated by the MCU (again, not really under my control).

 

[BradtheRad]

Just for curiosity I made a simulation to see how feasible the idea is.

It takes triple buck-boost converters to draw enough amperes from the supply, in order to step 10 V up to 15 V, at 15 A.

Screenshot:



The clocks are evenly staggered.

There can not be hardly any resistance in the components.

The supply is always providing at least 30 amps.