June 2019

48 n GAMBICA SUPPLEMENT June 2019 www.drivesncontrols.com SUPRESS INTERERENCE AND ENSURE YOUR DRIVES WORK SMOOTHLY, SAFELY AND IN HARMONY I n many industrial environments, ensuring the stability of drive controllers is sometimes overlooked. However, an EMC-compliant (electromagnetic compatibility) drive assembly with an efficient control cabinet and suppression system is the basis for ensuring the safe and reliable operation of machines. It can also extend the lives of certain components. Manufacturers and operators are required to implement the installed drive systems so as to achieve electrical compliance with the limits (for emissions) and requirements (for fault- free operation) set out in the relevant European and International standards and regulations. Utilising some components can lead to additional advantages besides compliance. When selecting a drive, it is sensible to check what range of accessories the drives supplier can offer. Whilst some of these accessories can be sourced from other third-party suppliers, it is often better to deal with a supplier that can provide everything from a single source, so the items are optimised to suit your drives (or even designed in-house for your drives) and therefore more likely to meet the application requirements. The operation of variable-speed drives with intermediate voltage circuits can put stress on the mains and motor, which can be optimised using additional measures, depending on the place of use and the type of application. An EMC-compliant drives assembly may therefore include accessories and interference suppression components for the mains- and motor-related optimisation of operating conditions. The most common suppression components and their functions are: Mains suppression Mains chokes optimise the harmonics to the mains power supply that result from the pulse-shaped charging of uncontrolled rectifiers and reduce the effective input current. This decrease in stress has the direct effect of significantly increasing the service life of the link voltage capacitors in inverters and servodrives, as well as reducing the stress on the input rectifier. By smoothing the input current draw, the lifetime of the drive and its components are enhanced, particularly at constant high utilisation. For mains chokes, ensure there is sufficient installation space to account for the higher heat emissions and strong magnetic field. Mains EMC/Harmonics filters reduce the cable-fed emission to the required limits of IEC 61800-3-C1/C2. Other variants may offer low leakage currents or the operation of special mains networks. Harmonics filters reduce the low-frequency mains distortion on rectifier supplied devices by a further 8- 15%. They allow easy integration into a switchgear layout. Motor-side accessories Motor chokes provide a cost-effective option for reducing the voltage rise rate (dv/dt) to avoid premature ageing of the coil insulation in AC motors, particularly on high-speed applications. They increase total inductance at output and reduce current ripples, as well as reducing the peak value of the current and stress on IGBTs in inverters. Motor chokes are also suitable for applications with long motor cables (>15m and up to 50m). Sinusoidal filters are low-pass filters that filter out the switching frequency from the PWM (pulse width modulation) output signal of the inverter. Sinusoidal voltage with a small ripple occurs at the output, which results in a sinusoidal motor current. This is why the use of sinusoidal filters at the output is not associated with the supplementary losses in the motor’s stator and rotor, which otherwise occur with inverter use. Mains-motor combinations Some suppliers offer combinations of mains-side and motor-side accessories that can be tailored more closely to suit the specific needs of the machine or robot. Combi-filters (EMC/output choke), for example, are space-saving combinations that provide the advantages of both, with the addition of reduced wiring, and adapt and optimise the drive controller consistently. I/O filters integrate the functions of the mains-side HF filter and motor-side dv/dt filter in a compact enclosure. Part of the input filter that is configured with high damping at minimal leakage current, reduces conducted interference to limit value in compliance with EN 61800-3. These can be incorporated inside some drives, saving space. Low- leakage versions are also available. n www.keb.co.uk To ensure the stability and safety of drive assemblies, OEMs and machine-builders can choose from a variety of mains- or motor-side suppression accessories – or combinations of the two – to ensure that their drives comply with the EMC requirements of the application, says Mark Checkley of KEB Automation. Mark Checkley