Traction Battery Current Feedforward Control for Rail Vehicle Stability
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Solution Overview
Problem
Existing methods for controlling battery current in traction batteries for rail vehicles often result in oscillations and unstable behavior, leading to potential safety shutdowns and inefficiencies in power utilization, especially during start-up processes.
Innovation Solution
The method involves manipulating the battery ideal current to calculate the pilot control torque by adding a zero-dependent constant to the z-transform of the desired ideal battery current, which cancels out unstable poles and zeros, preventing oscillations and ensuring stable current utilization.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the ideal battery current is manipulated by adding a zero-dependent constant to cancel unstable poles and zeros, then the stability and reliability of battery current is improved, but the device complexity and control algorithm complexity increases
Solution Approach 1:
The patent applies parameter changes by modifying the ideal battery current signal through adding a zero-dependent constant in the z-transform domain. This mathematical transformation changes the parameters of the control signal to cancel out unstable poles and zeros, thereby improving system stability without requiring hardware modifications.
Solution Approach 2:
The patent introduces an intermediary mathematical operation (adding zero-dependent constant to the z-transform of ideal battery current) that acts as a mediator between the desired current profile and the actual system response. This intermediary transformation stabilizes the system by canceling unstable dynamics before the current is applied to the battery.
2Productivity
If the battery current is increased to enable rapid build-up of traction torque, then the productivity and response speed is improved, but the risk of exceeding current limits and causing safety shutdowns increases
Solution Approach 1:
The patent applies preliminary anti-action by pre-modifying the ideal battery current signal to account for unstable system dynamics. By adding the zero-dependent constant before the current is applied, the system preemptively counteracts potential oscillations and instabilities that would otherwise cause safety shutdowns, allowing aggressive current profiles to be used safely.
Solution Approach 2:
The patent uses feedback principles by considering the system's transfer function characteristics (poles and zeros) in the design of the ideal battery current. The control algorithm continuously adapts the current profile based on the known system dynamics, ensuring that rapid current build-up does not excite unstable modes that would lead to shutdowns.
3Ease of operation
If conventional feedforward torque calculation is used without manipulating ideal battery current, then the ease of operation is maintained, but oscillations and unstable behavior occur leading to power loss
Solution Approach 1:
The patent modifies the parameters of the ideal battery current in the z-transform domain by adding a zero-dependent constant. This parameter change transforms the conventional feedforward approach into a stabilized version that accounts for system poles and zeros, eliminating oscillations and energy loss while maintaining computational feasibility.
Data Source
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AI summary
The invention relates to a method for controlling the, current output of a battery, wherein the battery is used as a traction battery for driving a rail vehicle. A battery actual current Ibat,ist passes, as a three-phase alternating current, via a converter STR (DCDCW, ZWK, DCACW) to an asynchronous motor (ASM), which is used as the drive for the rail vehicle. The battery actual current Ibat,ist is set with the help of control circuits (Masm controller, Uzk controller, Ibat controller) as a function of a feedforward control torque Mff and a specified torque Mtf . The feedforward control torque Mff is calculated using a transfer function Hsys (z), which maps the torque setpoint value Msoll onto the battery actual current Ibat,ist as follows: Ibat(z) Hsys(z) Msoll(z). According to the invention, a zero point z=znmp, which lies outside the unit circle, is determined by the transfer function Hsys(z). The feedforward control torque Mff is calculated as follows: Μff(z) Ibat,neu(z) / (Hsys(z) z) where: Ibat,neu(z) = Ibat,ideal(z) - Ibat,ideal(z=znmp) where: Ibat,neu[n] = Ibat,ideal[n] for all n > 0, so that pole point/zero point cancellation is reached by z = znmp at the battery ideal current Ibat,ideal.