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What is a Range Extender and solution architecture
Range Extender is a standalone generator unit designed to recharge the traction battery while moving (or during stops) to extend the electric vehicle's range. Unlike conventional portable generators, the REX solution integrates:
- synchronous/asynchronous generator (alternator) or inverter topology,
- AC/DC converter (rectifier/charger converter) with current/voltage control and protection (CC/CV, CAN control),
- a control system (GCU) with an interface to the vehicle's BMS and ECU,
- fuel supply, cooling, and exhaust after-treatment systems,
Key architectural idea: The generator works in conjunction with the battery via a DC bus. The battery acts as a buffer, allowing the generator to operate at an optimal efficiency point (minimizing BSFC - brake specific fuel consumption), and power electronics manage energy flow and protection.
Applications and Integration into Electric Vehicle Systems
Application (example use cases):
- Hybrid and PHEV platforms, where extended range is required for long distances;
- Commercial transport (van, light truck) with limited charging infrastructure;
- Professional specialized equipment and agricultural machinery, off-grid operations;
- Mobile service vehicles and units, where an independent power source is needed.
Integration:
REX connects to the high-voltage bus via an AC/DC converter and a DC-DC converter if necessary. The system must include:
- Battery Management System — for SoC/SoH accounting and charging current limitation;
- GCU (generator control unit) — load control algorithms, ICE (internal combustion engine) operating mode optimization, diagnostics;
- HVIL / IMD / Power contactors HV circuit safety;
- sensors pressure/temperature/emissions for after-treatment control;
- Cooling and noise reduction system (NVH package)
Why a gasoline REX? Reasons for choosing it for electric vehicles and hybrids
Advantages of a gasoline unit as REX:
- Quick start in low temperatures - gasoline engines start more easily in cold conditions, which is critical for emergency charging.
- Lower noise and vibration levels compared to similar diesel engines (important for passenger cars and platforms).
- Low CAPEX - gasoline units are cheaper to purchase and simpler in design.
- Flexibility of modification to OEM requirements: compact layout, onboard AC/DC integration, ease of chassis adaptation.
Restrictions
- Higher fuel consumption (in kWh/l) during prolonged operation compared to diesel.;
- tougher after-treatment for achieving strict NOx/CO levels during long-term operation.
Practical recommendations for REX system architecture
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Hybrid control mode: The generator operates at its optimal economic point; the battery smooths out peaks, which increases overall efficiency and reduces ICE wear.
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CAN/BMS Integration: CAN data exchange (J1939/ISO-TP)—a mandatory element—sets the charging current, SoC limits, and emergency scenarios.
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Post-treatment: For diesel, provide SCR+DPF; for gasoline, TWC and variable valve timing to reduce emissions under frequent loads.
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Safety requirements Fuel compartment ventilation, leak detection sensors, automatic HV cutoff on IMD/HVIL failure.
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Maintenance and TCO: Fuel tank size, service intervals, and access to filters and catalytic converters affect operating costs.
Comparison: Gasoline vs. Diesel vs. Gas (CNG/LPG/LNG)
| Diesel | Gasoline | Gas (CNG/LNG/LPG) | |
|---|---|---|---|
| Fuel efficiency (BSFC) and operation | best BSFC at sustained load; beneficial for continuous, long-term operation (note: optimal for stationary or commercial applications). | Worse for consumption during prolonged operation, but better for short starts/switches; beneficial where the unit is used «as needed.». | with proper combustion technology - low emissions and competitive BSFC; however, high storage pressure (CNG ~200-250 bar) or cryogenic infrastructure (LNG) is required. |
| Emissions and after-treatment | Requires DOC + DPF + SCR for PM and NOx reduction; more complex and expensive maintenance | low CO/HC can be achieved after the three-way catalytic converter (TWC); NOx is more difficult to control at high loads | Cleaner concerning CO/PM, but methane slip is possible; after-treatment is simpler, but compression systems and tanks add mass and cost. |
| Total Cost of Ownership and Infrastructure | Higher CAPEX but lower OPEX at constant load | A single purchase is cheaper; fuel infrastructure is ubiquitous | requires CNG/LNG infrastructure; can be commercially beneficial, but a limitation for widespread REX due to fuel availability |
| NVH and dimensions | creates more vibration; requires enhanced noise protection | A gasoline REX is easier to achieve low noise and compact packaging. | Gas installations require volumetric gas cylinders, which affects placement. |
Conclusion: Choice based on operating scenario
For passenger electric vehicles where REX is needed only occasionally, a gasoline REX is often optimal: low NVH, ease of integration, and cold starting.
For commercial vehicles with long-term operation, a diesel REX is preferable in terms of fuel consumption and service life.
For ecological and urban solutions (if infrastructure is available), a gas REX (CNG/LNG/LPG) offers better emissions but requires compromises in cylinder placement and logistics.
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