Variable Bus Voltage Battery Pack for Motor Drive
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Solution Overview
Problem
Existing motor driving systems using a fixed bus voltage from a battery pack fail to achieve sufficient power saving due to limitations in switching frequency reduction and increased circuit complexity when using DC/DC converters.
Innovation Solution
A motor driving method that dynamically controls the bus voltage by varying the number of cells in parallel between the positive and negative voltage nodes, using a PWM signal to instruct the battery pack, thereby optimizing the bus voltage and reducing switching losses.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If the bus voltage is kept as a fixed value from the battery pack, then the inverter circuit can supply power to the motor using PWM control, but power saving cannot be sufficiently achieved
Solution Approach 1:
The patent applies dynamics by making the bus voltage variable instead of fixed. The battery pack dynamically adjusts the bus voltage based on motor load conditions, switching between different series connections of battery cells (e.g., 6 cells in series for high voltage, 3 cells in series for low voltage) to match the motor's power requirements, thereby reducing energy loss during light loads
Solution Approach 2:
The patent changes the voltage parameter of the bus by adjusting the number of battery cells connected in series. The battery control unit receives voltage instruction signals from the motor control unit and reconfigures the battery cell connections accordingly, changing the bus voltage from a fixed value to a variable parameter that adapts to different operating conditions
2Loss of energy
If the switching frequency of the inverter circuit is reduced to save power, then power consumption decreases, but the output precision of AC voltages deteriorates
Solution Approach 1:
The patent changes the voltage parameter to compensate for reduced switching frequency. By increasing the bus voltage during periods when switching frequency is reduced, the inverter can maintain adequate output voltage precision without excessive switching losses, as the higher input voltage provides more headroom for PWM modulation
3Loss of energy
If a DC/DC converter circuit is added to control bus voltage, then power saving is improved, but the device complexity increases
Solution Approach 1:
The battery pack is given a dual function: it not only provides power storage but also performs voltage regulation through reconfigurable cell connections. The same battery control unit that manages charge/discharge operations also controls the voltage adjustment by switching cell connections, eliminating the need for a separate DC/DC converter circuit
Solution Approach 2:
The patent merges the voltage regulation function into the battery pack's existing control system. The battery control unit integrates both the power management functions and the voltage adjustment functions, combining what would traditionally require separate DC/DC converter circuits into the battery pack's native control capabilities
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 allows for improved power saving by increasing output precision of AC voltages and reducing switching losses, while maintaining efficient motor drive efficiency without the need for additional DC/DC converters, thus enhancing power consumption and reducing circuit complexity.
Implementation Method 1
an inverter unit converting the bus voltage to an AC voltage by switching according to a PWM signal
Data Source
AI summary
The present invention provides a motor driving method, a battery pack, and a semiconductor device capable of variable-controlling a bus voltage from a battery pack. A battery pack outputting a bus voltage to a positive voltage node using a negative voltage node as a reference, an inverter unit converting the bus voltage to AC voltage by switching according to a PWM signal and driving a motor, and a motor control unit generating the PWM signal are used. The motor control unit outputs a voltage instruction signal for instructing the bus voltage toward the battery pack. The battery pack variable-controls the number of cells coupled in parallel between the positive voltage node and the negative voltage node so as to obtain the bus voltage according to the voltage instruction signal.