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System coordination during acceleration and braking

The output from the storage batteries and engine are controlled as follows according to the running conditions

  • Accelerating : The storage batteries alone are used for acceleration at low speeds, and additional power is provided by the engine generator from the mid-speed range.
  • Braking : The engine is shut down and regenerated power is stored in the batteries.
  • Constant-speed braking : Regenerated power is absorbed using engine braking to prevent overcharging on continuous downhill gradients.
  • Stationary : The engine is shut down to reduce noise in stations and improve fuel consumption.

Diagram of System Coordination : 1.Accelerating

Diagram of System Coordination : 2.Braking

Diagram of System Coordination : 3.Constant-speed running

Diagram of System Coordination : 4.Train Stopping

Storage-battery energy management

Stored energy must be available to the full extent possible from the start of acceleration in order to accelerate up to high speeds using storage-battery power. Similarly, reducing stored energy at the start of deceleration from high speeds using the train brakes enables more regenerated energy to be absorbed.
The hybrid propulsion system uses energy management controls to maintain the optimum level of stored energy to suit the speed range. This is achieved by adjusting the engine generator output so as to ensure a constant total of vehicle kinetic energy and battery stored energy.

Constant-power converter control

The hybrid propulsion system utilizes constant-power converter control using electrical power in order to manage the energy balance of the DC section. This is because charge/discharge control is not possible using conventional constant-voltage converter control, as the voltage at the DC section between the converter and inverter varies depending on the storage-battery energy. New constant-power converter control has been developed to manage the energy balance for the DC section using electrical power, allowing optimum charge/discharge control.

Engine brake control

The hybrid propulsion system uses holding-speed engine brake control that augments conventional braking so as to maintain a constant speed (holding speed) on downhill gradients. The series-hybrid system achieves engine braking by using the braking power generated by the traction motors and inverter to drive the converter and generator in reverse and absorb energy with the engine load. This has the advantage of allowing the engine braking power to be set irrespective of the vehicle speed, which enables the hybrid propulsion system to provide stable, constant-speed running under any running conditions.