Inverter Control Method for Reactive Power and Efficiency
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Solution Overview
Problem
The existing inverter control methods have limited reactive power capability, leading to inefficient dimensioning of passive components to comply with current harmonic limits, which negatively impacts the overall efficiency of the converter.
Innovation Solution
A new mode of operation is introduced where the DC converter sets a constant voltage during sections of the sine half-wave where the output voltage is below a threshold, and the bridge regulates the magnitude and sign of the AC output voltage, allowing improved reactive power capability while maintaining efficiency and compliance with current harmonic limits.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If the bridge switches at twice the mains frequency with zero crossing voltage, then switching losses are minimized, but reactive power capability is limited
Solution Approach 1:
The patent applies dynamics by making the switching strategy adaptive rather than fixed. The control method dynamically selects between two operating modes: Mode 1 (zero-crossing switching) for minimum switching losses, and Mode 2 (forced commutation) for reactive power delivery. This dynamic adaptation allows the system to optimize performance based on real-time operational requirements, resolving the contradiction between minimizing switching losses and enabling reactive power capability.
Solution Approach 2:
The patent changes the switching parameter (switching timing and method) based on operational mode. In Mode 1, switching occurs at zero crossing with twice-mains-frequency timing. In Mode 2, switching is forced at controlled moments to enable bidirectional power flow and reactive power delivery. This parameter change allows the system to transition between efficiency optimization and reactive power capability as needed.
2Loss of energy
If the DC converter maintains sinusoidal voltage magnitude, then efficiency is optimized, but reactive power delivery is insufficient
Solution Approach 1:
The patent segments the operational cycle into distinct modes: Mode 1 for active power delivery with sinusoidal voltage control (optimized for efficiency), and Mode 2 for reactive power delivery with constant voltage magnitude (optimized for power factor correction). This segmentation allows each mode to be optimized for its specific function, resolving the contradiction between efficiency and reactive power capability.
Solution Approach 2:
The patent implements periodic switching between Mode 1 and Mode 2 operation within each AC cycle. The control method periodically transitions between sinusoidal voltage magnitude control and constant voltage magnitude control, enabling the system to alternately optimize for efficiency and reactive power delivery, thereby achieving both objectives over time.
3Reliability
If passive components are dimensioned to comply with current harmonic limits, then standards compliance is achieved, but converter efficiency decreases
Solution Approach 1:
The patent employs feedback control to actively manage current harmonics and comply with standards while maintaining efficiency. The control method continuously monitors the operating conditions and adjusts the switching strategy between Mode 1 and Mode 2 to ensure harmonic compliance without requiring oversized passive components. This active feedback control replaces passive component oversizing with intelligent control, resolving the contradiction between standards compliance and efficiency.
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 enhances reactive power capability and reduces switching losses, resulting in improved efficiency and compliance with current harmonic standards, particularly beneficial for regenerative feedback topologies.
Implementation Method 1
a DC converter (DC/DC) 10 generates a voltage U DC with a sinusoidal magnitude
Implementation Method 2
This is converted to a sinusoidal voltage U AC via a bridge (DC/AC) 11
Implementation Method 3
which is also referred to as a pole changer. This is done by inverting every second half-wave of the absolute value sinusoidal voltage
Implementation Method 4
transistors with a low R ds,on can be used for some of the switches in the bridge circuit. This can contribute to reducing the power loss, since these components only have to be designed for the peak value of the output voltage
Implementation Method 5
it is possible for these transistors to also be switched on via a diode in the event of reverse conduction, so that only a minimal voltage drop is generated at the component even in this operating state
Data Source
Figure 1~2
Figure 3
Figure 4
AI summary
The invention describes methods of actuation for a DC-AC inverter arrangement with a feedback capability, particularly a solar cell inverter in a photovoltaic installation, having a direct-current controller (12) for producing half-cycles of an output-side voltage (u') and a bridge circuit (13) that is connected downstream of the direct-current controller (12) and forms a desired AC voltage (u2) from the output-side voltage (u') of the direct-current controller (12). In this case, at least two different methods of actuation are performed for the direct-current controller (12) and/or the bridge circuit (13) which are selected on the basis of the output-side voltage (u'), wherein two ranges of the output-side voltage (u') are defined in which different methods of actuation take place. The methods of actuation can be performed for different topologies of inverter arrangements.