Modern variable speed drives (VSDs) are equipped with a multitude of features to provide programming flexibility, enhance efficiency and increase the accuracy of control. Let’s dissect some of these features, typified in this case by the A1000 series of industrial AC drives from Yaskawa (www.yaskawa.com).
Control methods: the A1000 provides up to seven different control methods to suit specific motors and applications. Methods range from basic scalar (volts/hertz, or V/f) control, which adjusts frequency and voltage output in direct proportion based on command reference, through open-loop vector control, to closed loop vector control. Vector control essentially “splits” the stator current into separate torque and field components, analogous to the separate armature and field components of a DC motor, and controls VSD output by regulating voltage magnitude, angle of displacement, and frequency. In open loop systems, modeling is used to calculate vectors and adjust output based on measured output current, while in closed loop configuration, sensors such as encoders or tachometers directly measure rotor position and speed and are able to control output even more tightly. In the A1000, V/f control can provide a typical speed control range of 40:1, while open-loop vector can achieve 200:1 turn-down. Due to the greater speed of direct measurement, closed-loop vector control can achieve turn-down of 1500:1. Note that all of these ranges are dependent on specific motor conditions and operating parameters and may vary somewhat per application.
Auto-tuning: this provides a means of fine-tuning the drive’s internal motor modeling data based on actual measurements of motor parameters during drive set-up. Auto-tuning can be static or rotational, depending on driven equipment accessibility. Drives such as the A1000 also provide for continuous auto-tuning during motor operation to adjust for changing motor conditions, such as increased resistance after motor heating. Note that auto-tuning is only effective when the drive is controlling a single motor, since measured parameters are skewed if multiple motors are connected to the same drive.
Motor and drive protection: like most drives, the A1000 provides electronic motor overload and over-current protection. Overload is based on a limit of 150% of rated heavy duty amperage for 60 seconds. Over- and under-voltage is monitored to protect the drive’s DC bus; power loss ride-through of up to a two-second duration is available; drive heatsink temperature is monitored via thermistor; and stall prevention during acceleration, deceleration, and run is available. Electronic ground fault monitoring is also provided.
Network communications: the A1000 supports several network protocols through the addition of optional network adapter cards, including Ethernet/IP, Modbus TCP/IP, DeviceNet, Profibus-DP, Profinet, CANopen, and Mechatrolink-II. Modbus RTU RS485 communication capability is standard, to allow 2-wire or 4-wire serial communication with basic network devices. Most industrial drive manufacturers provide similar communication options.
Input/output capability: a number of digital and analog inputs and outputs are provided as standard, with the flexibility of adding I/O with expansion modules. The I/O provide a means of accepting control inputs, for example a remote speed command (typically as a 0-10 volt or 4-20 ma signal), and sending output commands to monitoring and status reporting devices.
Input power conditioning: on ratings of 30 HP and larger, the A1000 is equipped with a DC link reactor as standard to protect the DC bus and reduce harmonics on the supply circuits caused by high-speed electronic switching in the drive. The reactor adds impedance to smooth bus ripple and slow the rate of rise of incoming voltage transients. AC line reactors are also available for additional harmonic reduction and better input electronics protection, at the expense of some voltage drop.
PC-based programming: various manufacturers provide software packages and PC communication interfaces for drive programming. While not required for basic drive set-up and operation, these software packages can enhance programming ease and flexibility, and are often necessary for custom programming. The A1000 includes DriveWizard software for drive configuration, and incorporates monitoring and trending functions.
While there are many more operating features in the A1000 than can be discussed here, I hope this overview has provided some insight into its capabilities. More can be found at www.yaskawa.com. As noted above, similar functionality is provided by other major drive manufacturers as well. Each may differ in terms of performance, controllability, and available options, but the choice often comes down to factors such as equipment standardization, operator familiarity, and price. Joliet Technologies can source drives from several manufacturers, so we’re sure to be able to meet your application’s requirements. Please contact us for additional information at firstname.lastname@example.org, or respond in our Comments section. You can also visit our web site (www.joliettech.com) or call us at 815.725.9696. See you next week!