To operate lighting, electronics and communication devices, both on trains and in control rooms, 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 (such as voltage and frequency) 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 analogue 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 as well as safety settings. These adjustments, and even firmware updates for the unit itself, can be made at any point in the product’s lifecycle, 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.
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 can be installed in cabinets, at level crossings and in other remote structures to facilitate rail-side communications and control systems powered by batteries or solar panels.
Metra is the commuter rail system serving the Greater Chicago metropolitan area in Illinois and Wisconsin, USA. In its system design, the locomotive supplies 480V three- phase AC to power HVAC (heating, ventilation, air-conditioning), lighting, and low voltage electronics. The same power source is used to power the battery charger for 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 32V DC regulated power supply.
Founded in 1976, Analytic Systems is an innovative Canadian manufacturer of battery chargers, voltage converters, inverters, power supplies, and frequency converters and MPPT solar charge controllers.
Although the company still offers analogue converters, the current emphasis is on its new ‘intelligent’ digital offerings. By using the free ‘Power Wizard’ software, companies such as Metra are able to define the output frequency, output voltage, 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 they produce, 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 PE, 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 of 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,” Piotr commented. “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 120V AC to select fluorescent lights. The inverter senses power loss and switches very quickly to the battery bank to seamlessly maintain 120V AC power to select assigned lights as outlined in the regulations.
Jedraszczak says 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 analogue 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,” he said. “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,” Piotr added.
For the rail industry, whether for rolling stock or rail-side communication and control, intelligent power converters with their flexibility and ease of programming will allow engineers to select from a simplified list of models to 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.