Wireless Debug Isolation for High-Voltage Motor Control Applications



 

If you ever developed a motor control system or application, you probably dealt with isolation protection. Hopefully isolation was included as part of the design requirements and not a result of equipment damage, which typically occurs when you introduce test devices (i.e. PC, JTAG emulator) into the high voltage environment. If you are new to motor control, you should know that regardless of the motor type (AC induction, brushed DC, brushless DC, stepper, etc.), these systems can use upwards of 350v and quickly damage your test equipment if not isolated properly. WiFi can provide isolation, both electrically and physically.

What is Isolation?

Isolation is a technique of separating two components of a device electrically and physically. Physical isolation is typically implemented for safety reasons. Electrical Isolation, and the primary focus of this article, refers to the elimination of ground paths between two electrical devices. In motor control applications, providing electrical isolation can prevent ground loops between the motor control system power rail(s) and the debug equipment. Ground loops are the focus of the next section (see figure 1).

 

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Ground Loops

Ground loops are the most common source of noise in a digital system as well as the most common cause of damaged test equipment. Ground loops occur when two devices are connected at different ground potentials.

When this happens, the ground potential will cause current to flow between the two devices. In audio devices, such as a sound system for example, you may have heard a hum coming out of the speakers. In video, this can present itself as bars, bands visible at different brightness. In an electrical environment this can occur by simply by having two devices plugged into a different wall outlet and attached via cable.

 

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In a typical motor control application, motors will be powered by 220 VAC and operate between 350 and 400 VDC. This [high] voltage bus can also reside on the negative power rail, so preventing ground loops and a path to earth ground is extremely important. A ground loop in this environment will trigger unwanted voltage to flow to and through connected test equipment (computer, emulator, scope, meter, etc.). The act of attaching this test equipment is usually the culprit in providing the path to earth ground and the reason why damage occurs to your emulator and computer.

Isolation Solution Comparisons

There are various isolation options, including galvanic implementations (optical, magnetic, capacitive, etc.).

For optical, it is well established and cost effective but lacks high-speed performance, is power hungry and will degrade over time.

There is wide acceptance in the industry for magnetic (inductive) solutions and they use lower power compared to optical, however they have low tolerance for electromagnetic noise and offer no electro-static discharge (ESD) protection.

Capacitive solutions have low voltage requirements and are not susceptible to noise but they do not offer protection in high power applications.

No single approach suits all applications as each solution offers pros and cons. One way or another, you need to make a trade off in performance, power, or cost.

Wireless Debug Solution

A wireless Ethernet implementation (IEEE 802.11) can reduce or eliminate isolation trade-offs. By separating the physical connection of the debug station (i.e. PC) from the emulator, you can maintain performance and remove ground loops in harsh environments (see figure 2). This is based on the fact that the emulator resides in the same power domain as the motor control application hardware and motors.

Wireless Ethernet, with the various interface speeds, is a proven transport under noisy conditions. It does not sacrifice performance and it will allow the developer to be positioned at a safe distance. Please see the Blackhawk USB510W data sheet in this guide for more information.

Contact Information

Blackhawk

123 Gaiher Drive
Mount Laurel, NJ, 08054
USA

tele: 856.234.2629
fax: 856.866.1100
info@blackhawk-dsp.com
http://www.blackhawk-dsp.com

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