Resonant Power Inverter Galvanic Isolation Startup Currents
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Solution Overview
Problem
Existing power inverters for feeding electric energy from small to medium-sized photovoltaic modules into AC power grids face challenges such as high power losses, safety concerns due to initial high currents during startup and potential hazards from buffer capacitors, and the need for galvanic isolation, while also struggling to efficiently shape AC currents and maintain low costs.
Innovation Solution
A power inverter design featuring a resonant converter with a high frequency transformer, a resonant series circuit, and a controller for sine-modulating AC currents, along with an electrical isolation barrier and EMC-filter components like combi mode chokes and varistors, which enables efficient AC current shaping and safety through zero current switching and galvanic isolation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a DC/DC converter with high frequency transformer and buffer capacitors is used, then galvanic isolation and voltage matching are achieved, but high startup currents and safety hazards occur
Solution Approach 1:
The patent applies resonant oscillation principles to the DC/DC converter circuit, using a resonant circuit composed of inductors and capacitors to create controlled oscillations that enable zero-current switching. This resonant approach allows the converter to operate without dangerous startup currents while maintaining galvanic isolation through the high-frequency transformer.
Solution Approach 2:
The patent changes the operating parameters of the DC/DC converter by implementing frequency-modulated pulse width modulation (FM-PWM) control. This allows the converter to adjust its switching frequency dynamically, enabling soft startup and avoiding high current peaks while maintaining the required galvanic isolation performance.
2Power
If conventional DC/DC converters are used, then voltage matching is achieved, but power losses increase
Solution Approach 1:
The patent utilizes resonant oscillation in the DC/DC converter to achieve soft switching conditions. By operating at or near the resonant frequency of the circuit, the converter minimizes switching losses and improves overall efficiency while maintaining the required voltage matching capability.
Solution Approach 2:
The patent replaces conventional hard-switching DC/DC converter topology with a resonant-switching approach. This substitution eliminates the need for complex commutation circuits and reduces switching losses by utilizing the natural resonant behavior of the circuit components.
3Reliability
If AC current shaping is implemented, then grid compatibility is improved, but device complexity increases
Solution Approach 1:
The patent integrates multiple functions into the DC/DC converter stage. The same resonant circuit that provides galvanic isolation and voltage matching also performs AC current shaping for grid compatibility. This multi-functionality approach avoids the need for separate current shaping circuits, reducing overall device complexity.
Solution Approach 2:
The patent merges the DC/DC conversion function with the AC current shaping function in a single integrated circuit stage. By combining these functions, the patent eliminates the need for additional complex circuitry while achieving both voltage matching and grid compatibility requirements.
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
The solution achieves low power losses, enhanced safety by minimizing startup currents and preventing hazards, and meets regulatory requirements for galvanic isolation while maintaining a high level of performance and low cost.
Implementation Method 1
a high frequency transformer comprising a primary winding and a secondary winding
Implementation Method 2
a resonant series circuit comprising an inductance and a capacity
Implementation Method 3
a high frequency rectifier rectifying a current through the secondary winding of the high frequency transformer
Data Source
Figure 1
Figure 2
Figure 3~12
AI summary
A power inverter (1) for feeding electric energy from a DC power generator into an AC grid with two-power lines comprises: two input terminals (2, 3) for connecting the power generator; two output terminals (4, 5) for connecting the two power lines of the AC grid; a resonant converter (51) including a high frequency transformer (17) comprising a primary winding (16) and a secondary winding (18), at least one high frequency switched semiconductor power switch (9-12) that connects one end of the primary winding (16) of the high frequency transformer (17) to one of the input terminals (2, 3) for providing a current path through the primary winding (16) to the other one of the input terminals (3, 2), a resonant series circuit (19) comprising an inductance and a capacity, and a high frequency rectifier (22) rectifying a current through the secondary winding (18) of the high frequency transformer (17) and having two output lines (26, 27); and an output converter (31) connected between the output lines (26, 27) of the high frequency rectifier (22) and the two output terminals (4, 5).