Parallel Inverter System with Common AC Point for Parasitic Current Reduction
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Solution Overview
Problem
High-power photovoltaic installations require efficient and cost-effective solutions for connecting multiple inverters in parallel to a power grid, while minimizing parasitic currents and ensuring independent operation of each inverter, as existing transformer-based systems are expensive and prone to failures.
Innovation Solution
A power conversion system where all AC terminals of multiple converters are connected to a common AC point without intermediate transformers, with only the first terminals grounded, allowing each converter to operate independently with different DC voltages, and a control method to dynamically adjust voltage arithmetic means to ensure efficient AC voltage conversion.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If transformers are used for galvanic isolation between inverters and power grid, then safety and voltage transformation are improved, but installation cost and system complexity increase
Solution Approach 1:
The patent removes the transformer component from the inverter system, extracting the galvanic isolation function and replacing it with a direct connection architecture. The inverter is connected directly to the power grid without intermediate transformation equipment, eliminating the transformer while maintaining system functionality through modified control strategies.
Solution Approach 2:
The patent introduces a common AC connection point as an intermediary structure that allows multiple inverters to connect in parallel to the power grid. This common connection point enables galvanic isolation to be achieved through the collective arrangement of multiple inverters rather than through individual transformers for each inverter.
2Power
If multiple inverters are connected in parallel to power grid through transformers, then power requirements are met, but parasitic currents increase and reliability decreases
Solution Approach 1:
The patent segments the power conversion system into multiple independent inverter units that can operate autonomously. Each inverter is equipped with independent control that monitors and adjusts its operation to prevent parasitic currents, allowing the system to scale in power capacity while maintaining individual unit reliability.
Solution Approach 2:
The patent implements feedback control mechanisms that continuously monitor the operation of each inverter and adjust control parameters to eliminate parasitic currents. The control system detects current imbalances and automatically corrects them through modulated switching signals, ensuring stable parallel operation without the reliability issues associated with transformer connections.
3Power
If transformers are used for voltage transformation, then AC voltage conversion is improved, but installation cost increases
Solution Approach 1:
The patent extracts the voltage transformation function from the transformer and integrates it directly into the inverter circuitry. The inverter's switching network and control algorithm are designed to produce the required AC voltage output directly, eliminating the need for separate transformer components and reducing installation costs.
Solution Approach 2:
The patent designs the inverter to perform multiple functions simultaneously: DC to AC conversion, voltage transformation, current control, and parasitic current elimination. This multi-functional approach replaces the specialized transformer component, reducing the overall number of parts and lowering installation and maintenance costs.
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 configuration reduces installation costs, enhances efficiency, and ensures that each inverter can operate independently, preventing system failure from individual component malfunctions, while maintaining effective AC voltage conversion and minimizing parasitic currents.
Implementation Method 1
The control device 4 is configured for calculating a value corresponding to the arithmetic mean of the voltages of the AC terminals (9) of each converter (3) with respect to a same reference point
Implementation Method 2
a plurality of converters (3) connected in parallel on an AC side for converting a DC voltage from the sources (200) into an AC voltage for the load (G)
Data Source
Figure 1a~1b
Figure 1c~1d
Figure 2a~2b
AI summary
The invention relates to a power conversion system and an associated control method. The system comprises a plurality of converters (3) connected in parallel on an AC side, each converter (3) comprising an AC side (3A) for being coupled to a power grid (G), a DC side (3C) for coupling to a direct-current source (200), and a first terminal (1) and a second terminal (2) on said DC side (3C). The outputs on the AC side (3A) of all the converters (3A) are connected to a common output point, the first terminals (1) of the various converters (3) of the system (100) being earthed, and the second terminals (2) of said converters (3) being independent from one another. Thus, each source (200) is adapted and configured to operate independently of the rest of the sources (200).