Modern EMU stock has moved decisively away from the DC-series-motor, tap-changer design covered earlier in this subject. Today's 3-phase EMUs use IGBT-based traction and auxiliary converters, 3-phase induction traction motors, and a fully computerised Train Control & Management System (TCMS) — a genuinely different architecture, not just an incremental upgrade.
Technical Data (Salient Features)
- Traction motors: 3-phase induction motors. Output: 268 kW. Max voltage: 1171V. Max continuous current: 175A.
- DC Link voltage: 1800V DC. Transformer secondary: 855V/630A continuous. Technology: IGBT traction & auxiliary converters.
- Max service speed: 110 kmph (test speed 120 km/h). Max coaches: 18 cars.
- OHE voltage window: cuts off below 16kV, above 30kV. Supply frequency tolerance: 50 ± 8% (46–54 Hz).
- Regenerative braking effort: 510 kN. Maximum braking force: 773 kN. Gear ratio: 23:103.
Rake Structure — Basic Units
The basic building block is a 3-car unit: one Motor Coach (MC) in the middle, flanked by two Trailer Coaches (TC). At the outer ends of the full rake, one TC is replaced by a Driving Trailer Coach (DTC). 3 to 6 basic units couple together to form 9, 12, 15, or 18-car rakes.
- DTC: a trailer coach with a driving cab at one end, furnished with a Driving Desk, a Driver Display Unit (DDU), and under-slung Main Air Compressor (MAC) and battery box.
- MC: a powered vehicle with a traction motor on each axle, containing a Shunting Desk, an HT compartment (Traction Converter, Auxiliary Converter, electrical cabinet), and roof-mounted pantograph & VCB.
- TC: a non-powered vehicle with only a passenger saloon area — lights, fans, emergency lights, Air Handling Unit, and Passenger Information System.
Line & Traction Converter (LTC)
Each MC has one LTC cubicle, consisting of two Line Converters, a DC Link, and two Traction Inverters. The Line Converter (a single-phase bridge rectifier using IGBTs) connects the transformer's secondary traction winding to the DC Link. The DC Link — with its 100Hz resonant filter, earth-leakage detection, capacitor bank, and brake-chopper circuit — feeds the Traction Inverter, a 3-phase full bridge inverter (again IGBT-based) that finally drives the 3-phase traction motors.
TCMS — Distributed Control Architecture
The Train Control and Management System uses several distributed computers, connected via MVB/WTB/CAN communication buses, each responsible for a different function.
- CCU (Central Control Computer) — the overall control master: reads all motorman commands, performs control calculations, and issues commands like pantograph/VCB control, TE/BE distribution, neutral section handling, and rake-level isolation.
- MCU (Main Control Unit) — control master for each basic unit; handles EP brake control, holding brake, rollback detection, pantograph & VCB control, and wheel slip/slide control for that unit.
- BCU (Brake Control Unit) — backup to MCU specifically for EP brake control, taking over only if MCU is unhealthy.
- PCU (Passenger Comfort Unit) — one per coach; controls lighting, fans, ventilation, change-over contactors for auxiliary supply, main compressor, and parking brake.
- FGU (Frequency Generator Unit) — transmits master control commands via hard-wired train lines, as a redundant backup mode if the communication network fails.
Auxiliary Converter
One 120 kVA Auxiliary Converter per Motor Coach generates three separate output supplies from the DC Link: 415V 3-phase (for the transformer oil pump, radiator blowers, main compressor, coach ventilation units, and converter blowers), 110V single-phase (saloon lights & fans), and 110V DC (battery charging, emergency lights, head/tail lights, control equipment power).
Each basic unit's Auxiliary Converter feeds into a common DC bus (the 'BN bus') shared across the whole rake — so all converters share the load, and each converter is over-sized enough to cover its own unit plus one adjacent unit if that unit's converter fails.
Redundancy Logic
| Failure | Action Taken | Remaining Capability |
|---|---|---|
| 1 Pantograph failed | Open VCB, MC cut-out | 75% Traction / 100% Auxiliary |
| 1 VCB failed | Lower pantograph, MC cut-out | 75% Traction / 100% Auxiliary |
| 1 Traction Transformer failed | Open VCB, lower panto, MC cut-out | 75% Traction / 100% Auxiliary |
| 1 Line Converter failed | Shutdown that converter only | 87.5% Traction / 100% Auxiliary |
| 1 Line Converter (short circuit) | Shutdown Traction Converter, VCB open | 75% Traction / 100% Auxiliary |
| 1 Traction Motor failed | Shutdown IGBTs in that inverter | 87.5% Traction / 100% Auxiliary |
| 1 Auxiliary Converter failed | Shutdown that converter | 100% Traction / 100% Auxiliary |