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Regen Braking

Introduction

Electric motors, when used in reverse, function as generators. ASI controllers can convert the vehicle's kinetic energy into electrical energy to recharge the batteries and reduce wear on mechanical components (brake pads) while slowing the vehicle down.

Remote control (network) of regen braking is not covered in this section. Please contact ASI support for information if required.

Wiring

Regen brake sources can either be a digital signal (on/off) or an analog signal (0-5V) that can be connected to Brake1/Analog input 2 or Brake2/Analog input 3.

The following example shows an analog signal connected to the Brake1/Analog input 2 pin.

Configuration

  1. Set Regeneration battery current limit percentage of your battery's peak charging/regen current relative to your Rated motor power divided by Rated system voltage.

    Example

    Your Rated motor power is 2880W, regen is 45A peak and your nominal battery voltage (Rated system voltage) is 48V. Your regeneration battery current limit is = 45A/ (2880W/48V) = 0.75 or 75%.

  2. Set Features bit 4 Regen braking enable to 1.

  3. Set Regen brake source to 1 for Brake2, 1 for Brake1 or 2 for Network.

    • If not already, set Features2 bit 6 Brake 1 Pullup enable or Features bit 7 Brake 2 Pullup enable to 1, to pull up your chosen Regen brake source respectively.

  4. Set the Maximum braking torque to the desired percent of Rated motor current. Start out conservatively, ex. 10%, to understand the braking effect and not risk having too much braking torque and skidding, causing a possible crash. See Regen brake tuning below

  5. Set Analog brake off voltage and Analog brake full voltage to the voltages outputted by the brake input at rest and full range respectively

  6. Set the Analog Brake Deadband Range .

    Note

    Firmware 6.020 and below use and apply the Throttle deadband threshold for the brake1 and brake2 inputs.

  7. Verify that the Brake setpoint follows the brake input: e.g. OFF brakes = 0 at Analog brake off voltage - analog brake deadband range and ON brakes = 1.0 at Analog brake full voltage + Analog brake deadband range, if using the voltages at #5 above. Alternatively, observe digital inputs bit 5 to see if brake1 input turns on, and digital inputs bit 6 for brake2 input at the voltages set.

Regen Braking Implementation

In ASI controllers, battery regenerative current (motor current-driven back into the battery) is always present even if regen braking options are not enabled.

Regen current is always monitored. For instance, a direct drive motor moving backwards while enabled, even slightly, will cause regen currents. To protect the battery from being overcharged the controller can limit this current by setting the Regeneration battery current limit parameter.

Note

If a controller's Regeneration battery current limit parameter is set to 0%. Even a slight rollback of a direct drive vehicle will not allow forward motion until the vehicle comes to a complete stop. To avoid this type of behaviour set this parameter to at least 20%.

Regen brake setpoint is determined by the Analog brake off voltage and Analog brake full voltage as shown in the figure below. When the brake setpoint is 0.0, there is no regen braking and when it is 1.0 there is 100% of available regen braking. Note that for digital inputs, the input source is often pulled up and the off voltage is 4V (brake setpoint = 0.0) and 1V (brake setpoint = 1.0) for full brakes since the circuit generally pulls to ground. For analog regen (ex: using a throttle), generally, the source is not pulled up and like a throttle, the off signal voltage is around 0.9V to 1.2V (brake setpoint = 0.0) and full braking signal voltage is around 3.9V to 4.2V (brake setpoint = 1.0**).

The brake setpoint then maps to the Maximum braking torque output as shown in the figure below.

Example

For a brushless DC motor, torque is approximately proportional to the motor phase current. This is why we set Maximum braking torque as a function of the Rated motor current. As an example, if Rated motor current = 50 Amps and Maximum braking torque = 30%. Then when the braking setpoint is equal to 1.0 (per Unit), the braking “torque” will be equal to 15 Amps.

Warning

Regen braking becomes ineffective at low speeds and should not be used as the sole source of braking. It should only be used in addition to a functioning mechanical braking setup.

Brake Input Tuning

Dialling in the regen braking feel is an iterative process. As such, parameter and mechanical adjustments may need to be repeated several times before vehicle behaviour under braking performs to your satisfaction.

Maximum braking torque can be adjusted to change the total torque available for braking as a percentage of rated motor current.

Positive braking torque ramp can be adjusted to change how reactive the braking is to changes at the input. Increasing this will increase the time taken to go from brake setpoint 0 p.u to brake setpoint 1 p.u.

Negative braking torque ramp can be adjusted to change how fast the commanded braking torque goes brake setpont 1 p.u to brake setpoint 0 p.u.

Regen brake speed can be used to set the lower regen braking speed limit.

Warning

As regen braking becomes ineffective at low speeds and can cause the braking feel to be inconsistent.