Digital Power Converters Provide Flexibility

Feb. 10, 2017
Advances in digital signal processing lead to more flexible power converters that can be programmed to meet the precise requirements of variable inputs/outputs required.

Chicago, Illinois

Metra: A commuter railroad in the Chicago metropolitan area operating 11 rail lines.

Analytic Systems: A Canadian manufacturer of battery chargers, voltage converters, inverters, power supplies, and frequency converters and MPPT solar charge controllers.  

An emphasis is on "intelligent" digital inverters

To operate rail lighting, electronics and communication devices both in the rail car and in control booths, power converters — such as inverters, battery chargers and power supplies — are often installed to convert available DC or AC to the appropriate power outputs required.

Complicating matters, both the power source (DC in varying voltages from battery banks) and the outputs (voltage, frequency, etc.) can vary for each piece of equipment. So much so, that finding the ideal converter can be difficult and often requires a customized solution.

Fortunately, digital signal processing (DSP) technology has significantly simplified the process. Unlike analog converters, which require board-level component modifications to alter function or features, DSP-based models can be programmed to accommodate a range of input and output parameters.

By doing so, digital converters can be programmed to accommodate varying custom battery voltage input/outputs and a multitude of safety settings. These adjustments, and even firmware updates for the unit itself, can be made at any point in the product’s life cycle, even after installation.

This is allowing system designers and installers to choose from a simplified selection of models that can essentially be customized to meet the precise needs of each application.

Rail Power

In railway operations, power converters are used with battery banks to provide power for emergency lighting and other electronics systems on rolling stock, when AC is not available.

In addition, inverters, voltage converters and battery chargers are often installed in cabinets, at crossing stations and in other remote structures to facilitate rail-side communications and control systems powered by batteries or solar panels.

In Metra’s system design, the locomotive supplies 480, three-phase VAC to power HVAC, lighting, and low voltage electronics. The same power source is used to power the battery charger that charges the bank of batteries located in each rail car.

When AC power is not available, for whatever reason, the system automatically switches to the battery bank for continued operation on battery power.

To accomplish this, Metra utilizes a custom converter unit developed by Analytic Systems that combines a battery charger and 32-volt DC regulated power supply.

Although the Analytic Systems still offers analog converters, the current emphasis is on its new “intelligent” digital offerings. By using the free Power Wizard software, Metra was able to define the output frequency, output voltage, output frequency and low voltage shutdown parameters of any inverter from a laptop with a standard micro-USB interface.

Another appeal of the inverters is the pure sine wave it produces, which provides cleaner power than cheaper, quasi sine wave alternatives. Pure sine wave inverters are ideal when operating sensitive electronic devices that require a high-quality waveform with little harmonic distortion.

According to Electrical Engineer Piotr Jedraszczak P.E., Metra recently began to use new digital inverter units as part of a recent upgrade of the emergency lighting system on passenger rail cars. The project, motivated by new regulations, also required converting the existing DC lights to brighter, AC-powered fluorescent lights.

The configurability of the IPSi Series intelligent inverters allowed Metra engineers to work within the parameters of the existing system design, with the only major change being an increase in battery size.

“Rather than trying to install a proprietary system, we got an inverter that could be configured to run on our specific rail voltages,” said Jedraszczak. “It is a very good application for the intelligent inverter, because we didn’t have to redesign the fluorescent lighting system on the rail car.”

The inverter from Analytic Systems has two inputs, one from the battery banks and another that feeds 120-volt AC to select fluorescent lights. The inverter senses power loss and switches very quickly to the battery bank to seamlessly maintain 120-volt AC power to select, assigned lights as outlined in the regulations.

Jedraszczak said the inverters were an economical solution given Metra operates several hundred rail cars. He also appreciates that in the event of changing requirements being able to reconfigure the inverter electronically and upgrade firmware is ideal.

“If we have to make a change with an analog inverter, that requires going in at the circuit board level and soldering on a resistor, for example, so it’s very invasive to make even the smallest adjustments,” said Jedraszczak. “With a DSP-based unit, it allows for changing some of those settings electronically so we can make adjustments on a case-by-case basis.”

He also appreciates that Analytic Systems controls every step of the process in house, from concept to finished product.

“From an engineering standpoint, I love that because I can talk to their engineers and they understand my concerns and they can go right down to the floor and have it built, tested, right there and then get right back to me,” added Jedraszczak.

For the rail industry, whether for rolling stock or rail-side communication and control, intelligent power converters and the flexibility and ease of programming will allow engineers to select from a simplified list of models and essentially receive a custom solution.

This will not only eliminate the need for application-specific designs, but also enable faster delivery of the power converter at a more economical cost.

Jeff Elliott is a Torrance, California-based technical writer.

Analytic Systems 5887a47bcb7ee
Analytic Systems 5887a47bcb7ee
Analytic Systems 5887a47bcb7ee
Analytic Systems 5887a47bcb7ee
Analytic Systems 5887a47bcb7ee
Rail

Analytic Systems

Jan. 24, 2017