DC-Coupled Solar PV and Storage Control for Fault and Loss Reduction
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Solution Overview
Problem
Existing power generation and storage systems face challenges such as increased fault currents, control instability, and high operating costs due to complex interconnections and inefficient energy conversion in AC-coupled systems, while DC-coupled systems struggle with inverter efficiency and voltage matching issues, making it difficult to effectively integrate renewable energy sources and manage energy storage.
Innovation Solution
A DC power bus-based system with a photovoltaic system, energy storage system, and a control system that manages real-time power injection and reactive power responses to AC load changes, allowing flexible and efficient use of renewable energy by controlling the power inverter and energy storage system through a common DC power bus, enabling smooth transitions and maximum energy harvesting.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If AC-coupled systems are used to integrate renewable energy sources and energy storage, then the system can operate independently for each energy source, but the system experiences increased fault current, higher operating costs, and slower response to grid commands
Solution Approach 1:
The patent merges multiple energy sources (PV, wind, diesel generators) and energy storage systems onto a common DC bus, eliminating the need for separate AC interconnections. This consolidation reduces the number of transformers and interconnection points, thereby reducing fault current magnitude while maintaining independent operation capability through DC/DC converters for each source.
Solution Approach 2:
The patent introduces a common DC bus as an intermediary between energy sources and the AC grid. This DC bus acts as a mediator that decouples the AC sides of different energy sources, allowing independent control while reducing fault current propagation. The DC/DC converters connected to the DC bus enable independent operation of each energy source without direct AC coupling.
2Adaptability or versatility
If AC-coupled systems are used with multiple independent inverters and transformers, then each energy source can operate independently, but the operating costs increase
Solution Approach 1:
The patent combines multiple energy sources and energy storage systems onto a single DC bus, eliminating the need for separate AC transformers and reducing the number of inverters. Each energy source connects to the DC bus through a DC/DC converter, and a single inverter handles the DC-to-AC conversion for grid interconnection, significantly reducing equipment count and complexity.
Solution Approach 2:
The common DC bus serves as a universal interface for multiple energy sources (PV, wind, diesel generators) and energy storage systems. The DC/DC converters and single inverter perform multiple functions including power conversion, control, and grid interconnection, replacing the need for separate AC-coupled inverters and transformers for each source.
3Device complexity
If DC-coupled architectures use DC/DC devices on the energy storage system input, then control is simplified, but control instability and difficulty in transitioning from day to night operation occur
Solution Approach 1:
The patent implements dynamic control strategies that adapt to different operating conditions (day/night, grid-connected/islanded). The control system dynamically adjusts the operation of DC/DC converters and inverter based on real-time system state, ensuring stable operation during transitions. The unified DC bus architecture enables seamless switching between different energy sources and storage modes without control instability.
4Productivity
If DC-coupled architectures use DC/DC devices on the PV input, then energy management is improved, but inverter efficiency decreases and DC fault currents increase
Solution Approach 1:
The patent segments the power conversion function into separate DC/DC converters for each energy source and a single shared inverter for DC-to-AC conversion. This segmentation allows independent energy management for each source while maintaining high inverter efficiency, as the inverter operates optimally without additional DC/DC conversion stages that would increase losses.
5Adaptability or versatility
If AC-coupled systems are used, then energy can be converted through multiple devices, but system losses increase and renewable energy harvesting is reduced
Solution Approach 1:
The patent extracts the AC conversion stage from the energy path by using a unified DC bus architecture. Energy from PV, wind, and diesel generators is converted to DC and injected onto the common DC bus, then a single inverter converts DC to AC for grid interconnection or load supply. This eliminates redundant AC-to-DC-to-AC conversions, reducing system losses and maximizing renewable energy harvesting.
6Reliability
If the renewable inverter's maximum power is limited, then the inverter operates within its capacity, but excess energy cannot be used to charge batteries
Solution Approach 1:
The patent adds a DC dimension to the energy pathway by introducing a common DC bus and DC/DC converters. When the AC inverter reaches its maximum power capacity, excess DC power from PV or wind sources can still be converted to DC and stored in batteries through the DC/DC converters connected to the DC bus. This DC pathway provides an additional dimension for energy management, allowing battery charging even when the AC inverter is at full capacity.
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 system provides a flexible, cost-effective, and efficient integration of renewable energy sources and energy storage, improving fault handling and compliance with incentive programs by reducing system losses and enhancing the use of renewable energy, while maintaining reliability and efficiency.
Implementation Method 1
a photovoltaic system connected to the DC power bus
Implementation Method 2
a power inverter connected to the DC power bus, the power inverter configured to convert power between the DC power bus and an AC connected load
Data Source
AI summary
An exemplary power system includes a DC power bus and a photovoltaic system connected to the DC power bus. An energy storage system is connected to the DC power bus and stores energy injected to the DC power bus by the photovoltaic system. A power inverter is connected to the DC power bus and converts power between the DC power bus and an AC connected load. The power system also includes a control system that receives power system data from one or more sub-systems and devices connected to the DC power bus, and controls, in real-time, one or more of the power inverter and the energy storage system to act as a load on the DC power bus based on the received power system data.