What to Search for in a DC/DC Converter for Railway Functions

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Railway electrification programs depend on a gentle DC provide to each energy their DC motors and the management/vitality circuits. These DC-traction programs are extra vitality environment friendly than their coal, gasoline,or diesel-based counterparts whereas additionally lowering CO₂ emissions. DC-to-DC converters play an important position in enhancing the vitality effectivity and energy high quality of electrified railways. Digital elements utilized in these functions might be subjected to extremes in temperature, humidity, vibration and mechanical shock. As such, they require a excessive diploma {of electrical} and structural integrity to have the ability to face up to these circumstances and reliably function.

This text explores the necessities for DC-to-DC converters in railway programs, together with a basic description of DC railways, how DC-to-DC converters are utilized in these programs, and the requirements that permit these units to perform no matter working circumstances.

A take a look at DC electrical railway programs

Early railway electrification programs had been primarily based on low-voltage DC the place the provision was offered by diode rectifiers in traction substations (T15, or Ss) alongside the monitor, with energy distributed to the practice’s motors by counting on an influence provide given from the overhead strains and rails. The most typical voltages for DC-traction programs are 600V for older tramways and underground programs, 750V programs in newer metro, and 1500V utilized by extra suburban strains. Giant 3000V programs are additionally utilized in suburban networks.

Tendencies for DC electrical railway programs

There’s a basic pattern for railway programs to steadily improve in voltage and effectivity. The rise in voltage permits for a lower in present the place greater gauge (thinner) cables are ample. The decrease voltage programs would require a excessive present degree, which result in thicker overhead-lines and brief distances between substations. The rise in vitality effectivity reduces each CO2 emissions by lowering the vitality consumption of the set up. Vitality reuse will also be employed by way of regenerative braking the place the kinetic vitality of the rotor is transformed into electrical energy and despatched again to the ability supply.

How DC-to-DC Converters utilized in railway programs

Regenerative braking depends on using a big bidirectional DC-to-DC converter to ship energy again to the battery financial institution or vitality storage system (ESS) from the DC feeder line. Smaller DC conversion is important in trendy railways to distribute a steady provide of energy to all digital units and subsystems inside the coach. These auxiliary programs embrace greater voltage essential programs akin to engine controls, motor drive controls, and braking programs, in addition to decrease voltage secondary programs together with lighting, battery charging, indication lamp, pump, and data shows, and electrical door openers. The traditional resolution usually includes using an enter filter, a 3-phase inverter, and a low frequency transformer as a way to present electrical isolation between the overhead line voltage and the auxiliary energy provide gear. Sometimes, this transformer is massive and hulking, including further mass to an already space- and weight-constrained software. As a substitute, remoted DC-to-DC converters can be utilized to satisfy the dimensions, weight, and energy necessities of contemporary railway functions. The aim is to transform the excessive 750V, 1500V, and/or 3000V enter voltage to a regulated 24, 28, 36, 48, 72, 96, or 110 volt output.

The facility distribution inside the practice from the primary provide additionally requires a sequence of DC-to-DC conversion to the secondary programs. As acknowledged earlier, the nominal enter voltages can fluctuate from as little as 24 volts to as excessive as 110 volts; from there, a regulated 3.3, 5, 12, 15, or 24 volt output is important.  The EN 50155 European customary for railway electrical gear requires that the nominal enter voltage can fluctuate between 0.7 and 1.25 instances the rated voltage. The usual additionally permits short-term deviations between 0.6 and 1.4 instances the nominal enter voltage.

In different phrases, a 110V system would require a steady voltage vary between 67.2 volts and 120 volts as was a fluctuation voltage vary from 66 volts to 154 volts.  DC-to-DC converters can assist broad enter ranges to cowl multiple nominal enter voltage. For instance, a converter for the widespread 72V and 110V railway enter voltages would want an working enter voltage vary from 43.2 volts to 154 volts (see Desk 1). P-DUKE provides the RHKW, RHMW, and RHDW collection of mountable DC-to-DC converters rated for railway and industrial functions. These units all provide 3,000 VAC of strengthened isolation in addition to a large enter vary from 36 volts as much as 160 volts, permitting them for use in 72V, 96V and 110V railway functions.

Desk 1: Normal voltage vary specs from EN 500155 for railway electrical gear. 

Transformer issues in remoted converters

Remoted DC-to-DC converters will leverage a transformer to supply galvanic isolation between the enter and the output of the system. Sometimes, the DC-to-DC conversion is completed by first translating the sign into AC with an inverter, sending the sign by way of a transformer, after which by way of a rectifier for a regulated DC output (so there isn’t a metallic or conductive path between the 2 elements of the circuit). The quantity of isolation depends on the clearance and creepage distances, usually outlined rigorously by the related requirements. Clearance is the gap by way of air between two conductors, whereas creepage is the gap alongside the floor between two conductors. The clearance distance will stop arcing, and the creepage distance mitigates the prospect a brief will happen within the occasion the floor turns into contaminated and conductive.

The transformer and the variety of transformations from DC to AC (and again) will restrict the extent of effectivity the converter can obtain. The isolation barrier stops the output from being straight managed for higher output regulation. The effectivity of the transformer additionally needs to be taken under consideration which may restrict the effectivity of the converter itself.  P-DUKE’s patented transformer design allows operation at efficiencies as much as 90.5% even with their 4.5 mm clearance and creepage distances (Determine 1).

Determine 1: Patented transformer design allows efficiencies as much as 90.5% regardless of the 4.5 mm clearance and creepage distances. 

Assembly the tough circumstances of railway functions

Exterior of the EN 50155 customary, the EN61373 customary lists out the take a look at necessities for gear utilized in railway autos. These units might be subjected to near-constant vibration and, in some cases, mechanical shock. Exams for vibration will embrace the simulated long-life testing the place the system underneath take a look at is subjected to not less than 15 hours of vibrations at a particular amplitude. For shock testing, the system undergoes a sequence of half sine impulses to breed the results of the transport.

The certifications and security approvals for digital gear utilized in railway programs span between EN 50155, EN 61373, and EN 44545-2 to make sure these programs efficiency no matter electrical, environmental, or hearth hazards respectively. Further requirements embrace the IEC/UL/EN 62368-1 customary for the protection necessities {of electrical} and digital gear within the subject of audio, video, info, and communication gear — programs which can be invariably utilized in railway auxiliary programs.

There aren’t any direct EMI requirements for railway functions outdoors of the EN 50121-2 customary for max emission ranges measured on the railway boundary fence; nevertheless, the electromagnetic atmosphere of those programs are demanding with potential sources from the substations, mains provide, overhead strains, and rolling inventory. For each railway and industrial functions, it’s useful to have a converter that has a degree of electromagnetic immunity.

P-DUKE’s Railway DC-to-DC converter providing

P-DUKE’s RHKW (3W/6/10W), RHMW (20W), and RHDW (40W) collection DC-to-DC converters are perfect for 72V, 96V, and 110V railway inputs and meet EN 50155, EN 61373, and EN 445545-2 railway requirements in addition to the IEC/UL/EN 62368-1 customary (with strengthened insulation) for electrical gear (Determine 2). These converters have in-built EMI circuits which can be designed in accordance with IEC/EN 55032 class A in addition to IEC/EN 50121-3-2. This massively simplifies PCB design and saves board real-estate. The transformer design permits for as much as a 90.5% effectivity whereas additionally assembly the protection and isolation necessities of each harsh industrial and railway functions. They’re examined for vibration and shock with a large working temperature from -40°C to +105°C and are operational at 5000 meters for rolling inventory that will run by way of mountainous areas.

Determine 2: RHDW collection of railway DC-to-DC converters.

Conclusion

DC-to-DC converters utilized in railway functions have a variety of issues from primary voltage necessities to isolation and development. This permits these units to function whatever the harsh electrical, mechanical and environmental circumstances. Not solely do these units want to satisfy widespread railway requirements, however must also have a level of immunity in opposition to electromagnetic interference.

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