Double Inverter Grid Feed Apparatus for High Voltage AC Output
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Solution Overview
Problem
Existing mains feed devices face inefficiencies and high costs due to limited AC output voltage, high current loads, and harmonic losses when converting DC voltage from photovoltaic sources into AC supply networks, requiring expensive and complex filtering and transformer designs.
Innovation Solution
A grid feed device with a double inverter topology using separate transformer windings and coordinated control of two inverter units to maximize AC output voltage, reduce current loads, and minimize harmonic losses, featuring independent voltage control of output phases and high-frequency PWM modulation to achieve a sinusoidal output voltage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a single inverter unit is used to convert DC voltage to AC voltage, then the device complexity is reduced, but the AC output voltage is limited and cannot reach the required 400V level
Solution Approach 1:
The single inverter unit is segmented into two separate inverter units (first and second inverter units), each handling different aspects of voltage conversion. This segmentation allows the system to achieve higher AC output voltage by combining the outputs of multiple inverters, resolving the contradiction between device simplicity and voltage capability.
Solution Approach 2:
The patent introduces a time dimension by operating the two inverter units with different switching frequencies. The first inverter operates at a lower frequency while the second operates at a higher frequency, creating a multi-level voltage structure that enables the transformer to step up to the required 400V AC output level.
2Power
If the AC output voltage is increased to reduce current and component size, then the efficiency and component cost are improved, but the DC voltage from photovoltaic sources is limited by the MPP voltage
Solution Approach 1:
The patent employs dynamic switching frequency control where the second inverter unit operates at a higher switching frequency than the first. This dynamic frequency differentiation allows the system to fully utilize the available DC voltage range from photovoltaic sources and transform it into higher AC output voltages, resolving the contradiction between output voltage and voltage range adaptability.
3Power
If high current loads are used to achieve required power output, then the power delivery is sufficient, but the component size, cost, and service life are negatively affected
Solution Approach 1:
The patent changes the voltage parameter by using a transformer connected to both inverter units, which steps up the combined inverter output to the required 400V AC level. This parameter change from voltage to current relationship allows the system to deliver the same power with reduced current, thereby extending component service life and reducing costs.
4Device complexity
If simple inverter operation is used, then the control complexity is reduced, but harmonic losses increase and require complex filtering
Solution Approach 1:
The patent employs periodic switching actions at different frequencies in the two inverter units. The first inverter switches at a lower frequency while the second switches at a higher frequency, creating a structured periodic pattern that naturally reduces harmonic content. This periodic multi-frequency operation eliminates the need for complex filtering while maintaining simple control architecture.
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 solution increases AC output voltage, reduces component size and cost, lowers conduction and switching losses, and eliminates the need for complex filters, resulting in improved efficiency and extended service life while providing a more sinusoidal grid feed-in voltage.
Implementation Method 1
the DC voltage of a DC intermediate circuit is converted into an AC or three-phase voltage by means of at least one inverter unit
Implementation Method 2
by means of a transformer device, which includes three mains transformer windings, is fed into an AC utility grid
Data Source
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AI summary
The invention relates to a grid feed apparatus (10) for feeding electrical energy from a DC energy source (12) into a three-phase AC supply grid (32), wherein the DC voltage of a DC intermediate circuit (24) is converted into a three-phase voltage by means of at least one inverter device (14) and is fed into the AC supply grid (24) by means of a transformer device (16) comprising three grid transformer windings (38). The invention is characterized in that a first winding connection of the grid transformer windings (38) is connected to a half-bridge (30) of a first inverter device (14a), and a second winding connection of the grid transformer windings (38) of the transformer device (16) is connected to a half-bridge of a second inverter device (14b). In other aspects, the invention relates to an energy feed system for connecting a photovoltaic source, a fuel cell source, a rechargeable battery source or a mechanically driven DC generator to an AC supply grid or to an AC load, in particular three-phase motor, or to an operating method for energy-efficient voltage feed.