Inverter Common-Mode Voltage Blending During PWM Scheme Switching
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Solution Overview
Problem
Existing three-phase three-level inverter systems face challenges in efficiently switching between continuous and discontinuous pulse width modulation schemes, leading to increased device loss and reduced service life due to abrupt changes in common-mode voltage, which affects both the ripple current through the bus capacitor and the switching device power.
Innovation Solution
A method and apparatus that generate a third common-mode voltage based on a weighted sum of the first and second modulation schemes' injection instructions, using a mode factor to slowly transition between them, thereby reducing device loss and extending service life by avoiding instantaneous switchover during modulation scheme switching.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If CPWM is used, then ripple current through bus capacitor is reduced, but switching device power increases
Solution Approach 1:
The patent dynamically switches between CPWM and DPWM modulation schemes based on real-time detection of leakage current and modulation conditions. The system transitions from static modulation selection to dynamic adaptation, allowing optimal performance across varying operating conditions.
Solution Approach 2:
The patent changes the modulation scheme parameter (from CPWM to DPWM or vice versa) based on detected electrical conditions. This parameter switching allows the system to optimize the trade-off between ripple current and switching power under different operating states.
2Loss of energy
If DPWM is used, then switching device power is reduced, but ripple current through bus capacitor increases
Solution Approach 1:
The system dynamically adjusts the modulation scheme based on real-time electrical conditions, switching from DPWM to CPWM when leakage current and modulation parameters indicate it would be beneficial. This dynamic adaptation optimizes the balance between switching power and ripple current.
Solution Approach 2:
The patent changes the modulation scheme parameter from DPWM to CPWM based on detected electrical conditions, allowing the system to optimize performance by adjusting this key parameter in response to operating state changes.
3Loss of energy
If modulation scheme is switched abruptly, then ripple current and switching device loss are reduced, but device service life decreases
Solution Approach 1:
The patent introduces a common-mode voltage adjustment period before completing the modulation scheme switch. During this preliminary phase, the common-mode voltage is gradually adjusted to match the target value, preventing abrupt changes that would harm device reliability. This preparatory action ensures smooth transition.
Solution Approach 2:
The patent provides cushioning protection during modulation scheme switching by controlling the common-mode voltage to change gradually rather than instantaneously. This cushioning effect absorbs the stress of switching, preventing sudden shocks to the inverter circuit devices and extending their service life.
4Productivity
If common-mode voltage changes abruptly during scheme switching, then modulation scheme switching is efficient, but device reliability decreases
Solution Approach 1:
The patent implements a preliminary adjustment phase where the common-mode voltage is gradually changed to the target value before the modulation scheme switch is completed. This preliminary action ensures that voltage transitions are smooth, maintaining device reliability while enabling efficient switching.
Solution Approach 2:
The patent maintains continuous control of the common-mode voltage throughout the switching process, ensuring it changes smoothly rather than abruptly. This continuous adjustment preserves the useful function of voltage control while enabling efficient modulation scheme transitions without reliability penalties.
Data Source
AI summary
This application discloses a common-mode voltage adjustment method and apparatus, and a control system, and relates to the field of electronic technologies. In an example method, a controller generates an injection instruction of a first common-mode voltage based on a first modulation scheme, generates an injection instruction of a second common-mode voltage based on a second modulation scheme, and generates an injection instruction of a third common-mode voltage based on the injection instruction of the first common-mode voltage and the injection instruction of the second common-mode voltage during a modulation scheme switching period. The injection instruction of the third common-mode voltage may be used to control a inverter circuit to output the third common-mode voltage.