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MassTransit_February_2017

IN THE FIELD CASE STUDY 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. Digital Power Converters Provide Flexibility By Jeff Elliott Advances in digital signal processing lead to more fl exible power converters that can be programmed to meet the precise requirements of variable inputs/outputs required. 32 | Mass Transit | MassTransitmag.com | FEBRUARY 2017 iStock O 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 oft en 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 fi nding the ideal converter can be diffi cult. 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. Th ese adjustments, and even fi rmware updates for the unit itself, can be made at any point in the product’s life cycle, even aft er installation. This is allowing system designers and installers to choose from a simplified selection of An emphasis is on “intelligent” digital inverters. 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 oft en installed in cabinets, at crossing stations and in other remote structures to facilitate railside communications and control systems powered by batteries or solar panels. In Metra’s system design, the locomotive supplies 480, threephase VAC to power HVAC, lighting, and low voltage electronics. Th e 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. Th e converter unit combines a battery charger and 32-volt DC regulated power supply. By using the free Power Wizard soft ware, Metra was able to defi ne 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., T


MassTransit_February_2017
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