DC-to-AC Converter System for Bumpless Grid Reconnection
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Solution Overview
Problem
Existing power conversion systems fail to maintain uninterrupted power supply to critical loads during grid disruptions and efficiently reconnect to the grid without causing operational disruptions when power is restored, and they lack efficient methods for converting, isolating, and storing DC power.
Innovation Solution
A DC-to-AC converter system that manages the connection between an electric utility grid and alternate AC power sources, using a common DC bus with DC-to-DC converters and AC-to-DC converters, enabling islanding mode operation and bumpless reconnection to the grid, along with DC-to-DC power converters for voltage transformation, isolation, and storage using inductive filters and LCL filters for high efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional power conversion systems are used during grid disruptions, then the system structure is simple, but the power supply to critical loads is interrupted and reconnection causes operational disruptions
Solution Approach 1:
The power conversion system is divided into multiple independent DC-to-DC converter modules, each capable of operating autonomously. This segmentation allows the system to maintain power supply to critical loads through parallel operation of multiple converters, improving reliability while keeping individual module complexity manageable
Solution Approach 2:
The patent employs a common DC bus as an intermediary component that decouples the DC-to-DC converters from direct AC grid connection. This intermediary structure enables the converters to operate independently during grid disruptions and facilitates bumpless reconnection by mediating the power transfer between the converters and the grid through controlled switching of AC contactors
2Loss of energy
If DC-to-DC converters are used for voltage transformation and isolation, then power conversion efficiency is improved, but voltage and current ripple increase
Solution Approach 1:
Multiple DC-to-DC converter outputs are merged into a common DC bus, where their combined output smooths individual voltage and current ripples. The merging of multiple converter outputs reduces the overall ripple amplitude while maintaining high conversion efficiency, as the ripples from different converters tend to cancel each other out
Solution Approach 2:
The system changes operating parameters by adjusting the switching frequencies and duty cycles of individual DC-to-DC converters to achieve harmonic cancellation of voltage and current ripples. By carefully selecting and coordinating converter parameters, the system minimizes ripple while maintaining efficient power conversion
3Ease of operation
If bumpless reconnection to the grid is implemented, then operational disruption during reconnection is eliminated, but synchronization control complexity increases
Solution Approach 1:
The system performs preliminary synchronization of the DC-to-DC converter outputs with the grid voltage before actual reconnection occurs. By pre-synchronizing the phase and frequency of the converter outputs and using controlled closing of AC contactors, the system eliminates operational disruptions during reconnection while managing control complexity through staged activation
Solution Approach 2:
The synchronization control system uses feedback from grid voltage measurements to continuously adjust the phase and frequency of the DC-to-DC converter outputs. This feedback mechanism enables automatic synchronization that achieves bumpless reconnection while the control system manages complexity through closed-loop regulation rather than complex open-loop timing sequences
4Adaptability or versatility
If multiple DC power sources are connected to a common DC bus, then system versatility is improved, but managing interaction between sources becomes complex
Solution Approach 1:
The common DC bus architecture provides a universal interface that can accept multiple types of DC power sources (photovoltaic panels, battery banks, DC generators) with different characteristics. This universal bus design enables versatile power source integration while simplifying management through a standardized connection protocol that handles interaction automatically
Solution Approach 2:
Each DC-to-DC converter on the common DC bus operates with autonomous control that automatically adjusts its power output based on bus voltage conditions. This self-service operation of individual converters eliminates the need for complex centralized coordination, as each converter independently manages its interaction with other sources through voltage-based power sharing
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 ensures uninterrupted power supply to critical loads during grid disruptions, synchronizes with the grid for seamless reconnection, and efficiently converts, isolates, and stores DC power, reducing voltage and current ripple for higher efficiency and safety.
Implementation Method 1
using inductive filters and LCL filters for high efficiency
Implementation Method 2
using inductive filters and LCL filters for high efficiency
Data Source
AI summary
Systems and methods for managing interaction between inverter-based DC and other power systems are disclosed. In one embodiment, a 3-phase isolation transformer is fluxed to create a 3-phase rotating field from the output of a source inverter. An inductive filter turns that output into three sine waves. A secondary inverter regenerates the system, sometimes after the isolation transformer is fluxed, and by advancing or retarding the secondary inverter's phase, current (and, thus, the DC voltage and power direction) is controlled. In another embodiment, an inverter is supplied by a DC source. The inverter is controlled to match its output voltage, current, and phase to a live AC grid, then the two are connected. The inverter frequency is then driven to advance the phase of the inverter in relation to the grid. Alternatively, the inverter voltage is then driven at a level greater than that of the grid.