More widespread use of frequency inverters is bringing them into smaller, niche markets, so inverter design is adapting with user-friendly features that suit these markets. This is illustrated by the Lenze SMV inverters that operate from a wide range of supply voltages and also benefit from functions that previously required a supervisory PLC.
The SMV sensorless vector drives are manufactured by Lenze in North America, using the AC Tech brand name on that continent. They are available in IP31 and IP65 variants that cover a power range of 0.25-37kW (a maximum of 22kW for the IP65 variant). These designs are established and the performance is proven with sensorless vector control, high dynamics and a 200 per cent overload capacity. There are built-in features to save time and cost, such as the pluggable memory chip that can download all the drive parameters in seconds. Now the functionality has been extended with new features that suit particular market areas.
The SMV has a range of supply voltages that is particularly broad. Models for three-phase supply are available for nominal voltages from 240-600V. Of course, a 10 per cent tolerance is available on top of these voltages. When it comes to single-phase supplies, standard models suit 220-240V as is commonplace in Europe. However, an additional model includes a voltage doubler that accepts 120V single-phase input and outputs three-phase phase at 240V. This suits exports of machinery to territories with more unusual supplies and allows the machine manufacturer to make simple inverter changes rather than change the motor or geared motor.
Customers running repetitive cycles can make use of a new sequencer function that is standard in the SMV drives. Up to 16 individual profiles of ramp time, speed target and time at speed can be pre-programmed into sequence. Following a start signal the sequence runs either once or is repeated. Each of the 16 profiles is stepped through either automatically or manually following an external trigger signal. A stop signal interrupts the sequence at any point and a pause signal holds the sequence in the current active profile. The sequencer function can remove the need for an external controller in simple cyclic applications, ideally where the load is steady and there is no requirement to follow a precise path. Examples are industrial gates and doors where limit switches can detect the position for the end of the sequence, also cycling of washing and plating machinery.
Another user-friendly feature available at no extra cost in the SMV inverters is motor flux braking. This suits infrequent stops, as the motor is used as a heat sink. Effectively the inverter drives the motor to stop on a deceleration ramp while over-fluxing the motor. A high magnetisation current causes the braking energy to converted into heat in the motor. The advantage of motor flux braking is the simplicity and reduction in system costs; no external chopper or braking resistors are required. Typical applications are conveyors, saws and fans.
The SMV now has an enhanced PID sleep mode in which the drive can enter the sleep mode triggered by a user-specified feedback value. There is a choice for the motor to coast to stop, ramp to stop or be braked. Recovery from the sleep mode is possible based solely on a feedback value set by the customer. Typical applications are fans in ventilation and HVAC systems, pumps, escalators and rotating doors.
Pump and fan applications can also take advantage of a new pump rinse and purge function. This prevents the build-up of sludge on pump impellers, which reduces wear and increases efficiency. Customers can set a time delay for the rinse/purge to start after entering sleep mode. Then the motor follows a sequence of ramp to speed, hold, then ramp to stop. With ventilation systems this also avoids a build-up of dirt on fan blades, for example when systems are shut down at night. The rinse/purge function improves efficiency and is a particular requirement for smoke detection systems in high-rise buildings.
With a wide power range 0.25-37kW, broad choice of supply voltages and two levels of protection (IP31 and IP65), SMV inverters are adaptable to suit most types of industrial machinery. Now the new functions are built into the drives at no extra cost, giving machine builders the ability to reduce external components and controls. This new functionality is particularly beneficial for pumps, fans and machines that run repetitive cycles.