Invertek's Optidrive P2 – providing flexible and future proof Motor Control

Invertek Drives' Technical Manager, Kes Beech, explains how the Optidrive P2 has been future-proofed to offer flexible Motor Control across a range of motor types.

"With an ever increasing focus on improved efficiency for electrical equipment and new, more stringent regulations and standards being introduced and adopted, there has been a growing focus on new motor designs and technologies to meet the required efficiency targets. Whilst traditional induction motors are still the main type of motors in use worldwide, and continue to be used in many applications, the use of new types of motors, such as Permanent Magnet or Synchronous Reluctance is increasing.

Optidrive P2 was developed from the outset to take advantage of these new motor technologies and offer maximum efficiency and best performance when operated with standard induction motors, permanent magnet or synchronous reluctance. Whilst these motor types are still relatively new, the control algorithms used within Optidrive P2 have been developed and tested over several years, providing valuable experience and insight into the operation of each motor type, and as a result providing market leading performance with all types of motors.

Induction Motors
Whilst the basic design of induction motors has remained largely unchanged for many years, the characteristics of higher efficiency motors, such as IE2 type are substantially different from older, less efficient designs. In turn, these changes in motor design have led to changes in the control algorithms used, especially for open loop vector control. Optidrive P2 can provide up to 200% torque from zero speed and open loop speed holding accuracy within + / - 0.5% when used with standard induction motors, whilst also maintaining maximum motor efficiency.

Permanent Magnet Motors
Historically, PM motors were used in applications such as servo, where the compact size and low inertia allowed high performance applications to be achieved. In these applications some form of feedback device, such as an encoder or resolver, was used to allow the motor to be controlled by a servo drive.

The PM motor, as its name suggests, uses permanent magnets in the rotor and so has no magnetizing current. This results in a gain in efficiency compared to an induction motor, where a certain proportion of the power supplied is used for magnetization. PM motors are becoming more and more widely used in industry for reasons of improved efficiency rather than high performance. In these applications, dynamic performance is not critical and so the motor must operate without any feedback device. Optidrive P2 has been developed to work with all types of PM motors and to operate them without encoder feedback. It is important to understand that this is not intended as a replacement for servo drives in applications such as positioning, but is intended to take advantage of the high levels of motor and system efficiency possible.

By design, PM motors can provide high starting torque compared to their rated torque. The optimal magnetic field is always present in the motor, which makes them ideally suited to applications which require high starting torque. Also, as the motor itself is synchronous and rotates at the same frequency as the output of the drive, speed holding and regulating accuracy are also excellent. In this respect, PM motors provide performance at least comparable to the best Induction Motors operating in Sensorless Vector mode.

Synchronous Reluctance
Synchronous Reluctance Motors (SynRM), not to be confused with Switched Reluctance Motors, share a similar stator construction to standard induction motors, however the rotor is substantially different in order to improve the overall efficiency of the motor. Again, SynRM motors are synchronous and provide excellent speed holding accuracy.

In contrast to PM motors, SynRM motors typically have lower starting torque and reduced low speed torque, even compared to standard induction motors. This makes them more suited to variable torque applications such as fans and pumps, rather than more demanding constant torque applications.

With all these operating modes possible by simply selecting the required motor type in one parameter, Optidrive P2 provides an excellent all round solution to today’s varying motor control needs. The commissioning is simple, requiring the user to enter only basic motor nameplate information and complete an autotune."

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