New controller cracks low speed DC drive problem

Trident's e-motion SCA-B4-70-10 for brushless motors and SCA-SS-70-10 for brushed DC can achieve near resolver like accuracy performance but at a lower cost to customers.

Trident Engineering has introduced to the UK two new speed controllers for small DC motors.

The SCA-B4-70-10 and the SCA-SS-70-10 use revolutionary technology that gives accurate control over a wide speed range, but still allows smooth and accurate control at very low speeds.

Conventional speed control systems with encoder feedback suffer from the fact that it is impossible to change a TTL signal into a tacho signal over a wide speed range.

For example 1:1000 is just not possible.

This is particularly a problem at low speeds where the ripple is high and the tacho signal is not constant.

The new controllers, available exclusively in the UK from Trident and made by German company, e-motion, are designed for both brushed and brushless motors up to 700W output.

They use a new technique where the frequency of the encoder or the Hall Effect sensors is combined with an internally generated system frequency.

Typically, at low speed, the feed back loop is limited by the low frequency response from the encoder or Hall sensors.

This increases the time constant, creating poor dynamic control or, in some cases, instability.

With the new method the generated system frequency is independent of and not limited by encoder or Hall sensor feedback at low speed giving more accurate control.

This system is particularly useful when controlling an electronically commutated motor.

With existing speed controllers, when driving an EC motor at below 300 rpm, there is a considerable degree of speed fluctuation.

The e-motion SCA-B4-70-10 can, with an encoder feedback, achieve a basic speed range of 10rpm to 8000rpm that can be further increased by optimising the controller settings and system components to give an even greater speed range.

With Hall sensor feedback a constant speed of 50rpm can be realised.

The result of this new development is that the e-motion SCA-B4-70-10 for brushless electronically commuted motors and SCA-SS-70-10 for brushed DC can achieve near resolver like accuracy performance but at a lower cost to customers.

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