Buck-Boost Motor Drive Control for Wide-Range DC-Link Voltage
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Solution Overview
Problem
Existing motor driving devices face inefficiencies in power conversion across a wide load range, particularly due to large torque and speed ripples at low speeds and high back electromotive force at high speeds, limiting control precision and overall system efficiency.
Innovation Solution
A motor driving device with a buck-boost converter that switches between buck and boost modes based on instantaneous input voltage and desired DC-link voltage, controlled by a controller to optimize power conversion efficiency across varying loads, including the use of a second buck-boost converter in parallel for enhanced control.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a boost converter is used to constantly control DC-link voltage in the entire load region, then system design and control are simple, but large torque ripple and speed ripple appear in low speed section and back electromotive force becomes large in high speed section
Solution Approach 1:
The patent applies dynamics by transitioning from constant DC-link voltage control to variable DC-link voltage control based on load conditions. The system dynamically adjusts the DC-link voltage using a buck-boost converter, switching between buck mode (for light loads) and boost mode (for heavy loads), thereby optimizing motor control precision across the entire load range while managing system complexity.
Solution Approach 2:
The patent implements parameter changes by varying the DC-link voltage level according to the load region. In light load regions, the DC-link voltage is stepped down to reduce back electromotive force and improve low-speed control. In heavy load regions, the DC-link voltage is stepped up to provide sufficient voltage headroom for high-speed operation, thus resolving the control precision issue across different operating conditions.
2Reliability
If a buck-boost converter is used to vary DC-link voltage depending on motor rotation speed, then driving performance is improved in low speed section and control without weak-field operation is enabled in high speed section, but switching loss is increased due to simultaneous switching of two switches
Solution Approach 1:
The patent applies segmentation by dividing the buck-boost converter operation into distinct phases: buck mode for light load regions and boost mode for heavy load regions. Instead of simultaneously switching both switches, the system selectively activates only the necessary switch based on the operating condition, thereby reducing switching losses while maintaining improved driving performance across the full load range.
3Power
If boost control is used to step up input voltage, then DC-link voltage can be maintained in high speed section, but power conversion efficiency is reduced in wide load region
Solution Approach 1:
The patent applies parameter changes by adapting the power conversion mode (buck or boost) and DC-link voltage level according to the load region and motor operating conditions. In light load regions, the system uses buck mode with reduced DC-link voltage to improve power conversion efficiency. In heavy load regions, it switches to boost mode to maintain sufficient DC-link voltage for high-speed operation, thereby optimizing power conversion efficiency across the wide load range while maintaining required power output.
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
Improves power conversion efficiency by dynamically adjusting the power conversion mode based on load conditions, reducing switching losses and enhancing motor and inverter efficiency across a wide load range.
Implementation Method 1
a rectifier rectifying alternating current (AC) power into direct current (DC) power to output an input voltage
Implementation Method 2
a first buck-boost converter including a plurality of switches for converting the input voltage and having a buck mode of stepping down the input voltage and a boost mode of stepping up the input voltage
Implementation Method 3
an inverter converting a DC-link voltage transformed from the first buck-boost converter into an AC voltage and transferring the AC voltage to a motor
Implementation Method 4
a controller receiving motor information related to driving of the motor, comparing magnitudes of a desired DC-link voltage depending on the received motor information and the input voltage with each other
Data Source
AI summary
A motor driving device is disclosed. The motor driving device includes: a rectifier rectifying alternating current (AC) power into direct current (DC) power to output an input voltage; a first buck-boost converter including a plurality of switches for converting the input voltage and having a buck mode of stepping down the input voltage and a boost mode of stepping up the input voltage; an inverter converting a DC-link voltage transformed from the first buck-boost converter into an AC voltage and transferring the AC voltage to a motor; and a controller receiving motor information related to driving of the motor, comparing magnitudes of a desired DC-link voltage depending on the received motor information and the input voltage with each other, and performing a control to switch only any one of the plurality of switches so that the first buck-boost converter is operated in the buck mode or the boost mode.