In addition to limiting the overall current, the motor circuit may additionally limit the rate of change of the torque demand. This enables the rate of change of current to be limited, using the same model applied for determining the torque value limits. The torque demand generator may set a torque demand gradient limit which is fixed or dynamic and in the latter case will vary over time. It may be varied according to one or more operating parameters of the vehicle or the motor and drive stage. These parameters may include the motor speed, the vehicle speed, the state of charge of a battery of the vehicle electrical supply, the electrical supply voltage and others from a vehicle stability system or braking system.

The drive stage may convert the current demands into as pulse width modulated (PWM) waveform for each phase of the motor with cyclic pulse width modulated (PWM) drive signals having a first state and a second state and a duty ratio indicative of the ratio of the time spent in each state within a cycle, may comprise using the motor current demand signals together with a signal representative of the duty ratio of the PWM signal applied to each phase to determine the estimates of the current drawn from the electrical supply, and limiting the rate of change of current drawn from the electrical supply by the motor by modifying the motor torque demand signals. The current draw estimate can be expressed as:

$i_{\mathrm{batt}}=d_a?i_a+d_b?i_b+$