International Research Journal of Engineering and Technology (IRJET)
e-ISSN: 2395-0056
Volume: 12 Issue: 09 | Sep 2025
p-ISSN: 2395-0072
www.irjet.net
Regenerative Braking and Motor Cooling: Theory and Simulation Arush Mukker1 1Heritage International Xperiential School
---------------------------------------------------------------------***--------------------------------------------------------------------harvested electrical energy is sent “backwards” through Abstract - This study investigates the impact of cooling the drive electronics and stored in the vehicle’s battery or ultracapacitor.
strategies on the thermal stability and regenerative braking efficiency of electric motors, with a focus on comparing air cooling and water cooling under simulated conditions. Electric motors operating under regenerative braking are subject to rapid heating, which can limit performance and reduce efficiency. To address this, the performance of motors was analyzed across key parameters, including peak and steady-state temperatures, average temperature drop per event, energy recovered, and time to thermal cut-off. Results demonstrated that water cooling provided substantial improvements over conventional air cooling. Peak motor temperature decreased from 98 °C to 85 °C, while steady-state temperature dropped from 89 °C to 72 °C, representing 13% and 15% reductions, respectively. The average temperature drop per event improved by 45% with water cooling, reaching 17 °C compared to 11.75 °C with air. Energy recovery showed consistent gains of 18%, both cumulatively (955 kJ vs. 808 kJ) and per event (238 kJ vs. 202 kJ). Additionally, the operational time before thermal cut-off was extended by 36%, increasing from 330 s to 450 s. These findings highlight the effectiveness of water cooling in enhancing both thermal management and regenerative energy recovery, offering a viable pathway for improving electric motor efficiency and durability in electric vehicles.
1.2 Energy Conversion Chain In a complete regenerative cycle, energy goes through multiple conversions. Mechanical braking energy → electrical energy in the motor → DC electrical energy in the battery. Each stage has losses. Typical efficiencies might be on the order of 80–95% in the motor, ~96–98% in the inverter, and ~99% in the battery chemistry [1]. Taking all stages into account (mechanical drivetrain, motor, inverter, and storage), only around 70–80% of the kinetic energy can be recovered at best [1]. This means regen extends range but does not recover energy perfectly. 1.3 Motor-Generator Physics A concise way to describe regen operation is: All motors can act as generators if driven [1]. In a PM AC motor, spinning the rotor faster induces higher three-phase voltages (proportional to RPM), which the inverter rectifies into DC. In a synchronous wound-field motor, an external DC field may be needed to generate voltage, but residual magnetism often suffices to “bootstrap” generation. In an induction motor, the stator is first energized (via inverter) to excite a rotating magnetic field; when the rotor spins faster than this field (i.e. under braking), the slip reverses and the motor produces electrical power. The inverter’s role is crucial: it must handle reverse current. When regenerating, the inverter transitions from a “buck” mode (supplying the motor) to a “boost” mode (pumping energy back to the battery) [2]. Effectively, the inverter rectifies the generated AC and increases its voltage to match or exceed the battery voltage, controlling current to prevent overcharging or overcurrent.
Key Words: Regenerative braking, Electric motor cooling, Thermal management, Energy recovery.
1.INTRODUCTION Regenerative braking converts a vehicle’s kinetic energy into electrical energy by turning the traction motor into a generator. When the driver brakes, the vehicle’s wheels drive the motor shaft faster than its normal speed; the motor’s magnetic field then induces AC voltages and currents that flow back through the inverter, effectively generating electricity instead of consuming it [1]. In practice, an inverter is used as a bidirectional power converter: in motoring mode it “buck-converts” (steps down) battery DC to AC, and in regeneration mode it reverses current flow to act as a boost rectifier to charge the battery [1]. A permanent-magnet (PM) motor naturally produces voltage when spun, making it straightforward to use as a generator [1]. An induction motor, however, must first be supplied with a three-phase AC field via the inverter before it can generate; without that field it simply coasts like a spinning metal piece [1]. In either case, the
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1.4 Role of Inverter and Battery. During regen, the inverter’s semiconductor switches conduct current from the motor windings back into the DC bus. The battery or DC link then absorbs this current. Field-weakening control may be applied: if the motor’s generated voltage at high speed would exceed the battery voltage, the inverter shifts its timing to reduce the effective field, preventing damage [1]. The battery chemistry limits how fast it can accept charge; high regenerative currents can produce heat in the battery as well. In summary, the inverter and battery form the
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