Motor Inverter Charge Balancing for Series Battery Packs
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Solution Overview
Problem
In electric vehicle recharging systems, individual battery packs, modules, and cells within a rechargeable energy storage system may have differing capacities, states of charge, depth of discharge, state of health, and voltages due to factors like load imbalance and discharge history, leading to challenges in recharging and reconfiguring modular systems, especially during DC fast charging.
Innovation Solution
A method involving a power inverter and stator winding configuration that operates as a switched-mode power converter, using synchronous or interleaved pulse width modulation control to shuttle charge between series-connected batteries, balancing their voltages and states of charge by coupling the midpoint of the batteries to the stator winding and controlling the power inverter to achieve equivalent inductances for charge balancing.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If batteries are connected in series for DC fast charging, then charging speed is improved, but voltage imbalance between batteries worsens
Solution Approach 1:
The motor stator winding acts as an intermediary energy storage element. During charge balancing, the power inverter transfers energy from one battery through the stator winding to the other battery, using the winding's inductance to mediate the energy transfer and equalize voltages without requiring direct battery-to-battery connection
Solution Approach 2:
The power inverter serves multiple functions: it acts as both a standard power conversion device for motor control and a charge balancing system. By utilizing the motor stator winding as part of the balancing circuit, the same hardware performs both propulsion and battery equalization tasks
2Stability of the object's composition
If additional balancing circuitry is added, then voltage balance is improved, but system complexity worsens
Solution Approach 1:
The power inverter is designed to perform both motor control and battery charge balancing functions. The same power semiconductor switches and control circuitry are used for both propulsion and equalization, eliminating the need for separate balancing circuitry and reducing overall system complexity
Solution Approach 2:
The motor stator winding, which is already present in the system for propulsion, is utilized as the inductive element for charge balancing. This self-service approach repurposes existing components rather than adding new ones, maintaining simplicity while achieving voltage balance
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach effectively balances the battery packs during and after DC fast charging, preventing overcharging and ensuring balanced voltage, thereby optimizing the total capacity and extending the life of the rechargeable energy storage system.
Implementation Method 1
controlling the power inverter to operate the power inverter and the stator winding as a switched-mode power converter
Data Source
AI summary
A method and apparatus for electrical energy transfer between a pair of series connected batteries coupled between positive and negative DC rails of a power inverter operatively connected to a plurality of stator phase windings of a stator winding of a motor may include coupling a midpoint of the pair of series connected batteries to the stator winding of the motor, and controlling the power inverter to operate the power inverter and the stator winding as a switched-mode power converter to charge at least one of the stator phase windings from one of the pair of series connected batteries and to discharge the at least one of the stator phase windings to the other of the pair of series connected batteries.