LCCL Filter Topology for High Power Microgrid Inverters
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Solution Overview
Problem
Conventional voltage source DC/AC inverters with LCL filters are limited to low power and low voltage applications, and struggle with high voltage and high power scenarios due to excessive fundamental voltage drop and potential for high short-circuit currents, which can damage circuits and fail to adapt to sudden changes in renewable energy sources in microgrids.
Innovation Solution
The development of new LCCL or LCC filter circuit topologies for single-stage and multistage voltage source DC/AC converters, which include series and shunt capacitors and inductors, allowing for wider power handling ranges and improved harmonic voltage and current management, enabling effective operation in high voltage and high power applications, including microgrids with renewable energy sources.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If conventional LCL filter is used in voltage source DC/AC inverter, then the circuit can operate at low power and low voltage, but it cannot handle high voltage and high power applications due to excessive fundamental voltage drop
Solution Approach 1:
The patent changes the filter topology from conventional LCL to LCCL or LCC configurations, modifying the circuit parameters to include series and shunt capacitors alongside inductors. This parameter change enables the filter to handle high voltage and high power applications while maintaining acceptable fundamental voltage drop through optimized component values and configuration
2Loss of energy
If series inductance of LCL filter is kept small to avoid excessive fundamental voltage drop, then voltage drop is reduced, but harmonic components of current into the grid become excessive and short-circuit currents become dangerously high
Solution Approach 1:
The patent modifies the filter parameters by introducing shunt capacitors in parallel with series LC combinations, creating LCCL or LCC topologies. This parameter change allows the use of larger series inductance values that simultaneously reduce fundamental voltage drop while providing harmonic filtering and limiting short-circuit currents through the capacitive elements
Solution Approach 2:
The patent creates a composite filter structure combining inductive and capacitive elements in specific configurations (LCCL or LCC). This composite topology integrates the benefits of both L and C components to achieve multiple functions: voltage drop reduction, harmonic suppression, and short-circuit current limitation, which cannot be achieved with simple LCL filters
3Adaptability or versatility
If conventional circuit topologies are used in microgrid with renewable energy sources, then the system can operate, but it cannot adapt to sudden changes in power generation from transient sources like solar and wind
Solution Approach 1:
The patent employs dynamic control strategies that work in conjunction with the LCCL/LCC filter topology to enable the microgrid system to adapt to sudden changes in renewable energy generation. The filter's capacitive elements provide rapid response to transient conditions, allowing the system to maintain stability while accommodating variable power input from solar and wind sources
4Device complexity
If conventional LCL filter based converters are used, then the circuit topology is simple, but the system cannot maintain constant frequency operation in islanded microgrid mode under varying load conditions
Solution Approach 1:
The patent changes the filter topology to LCCL or LCC configurations with specific arrangements of series and shunt capacitors. These parameter changes provide the necessary electrical characteristics to maintain constant frequency operation in islanded microgrid mode, enabling the system to handle varying load conditions while preserving frequency stability without requiring overly complex additional circuitry
Data Source
Figure 1
Figure 2A~2B
Figure 2C~2D
AI summary
This invention presents a new circuit topology formed by passive filter LCCL or LCC and voltage source DC/AC converter, which is named as fundamental forming unit. Compared with conventional LCL filter based DC/AC converter, the new converter circuits can handle wider range of power without suffering from disturbance by harmonic voltages and currents. For high voltage and high power application, circuits with multiple stages and multiple parallel branches are developed based on multiple fundamental forming units. Such circuits can be for general purpose application. They can also be for microgrid applications. Furthermore a new series of multistage DC/AC converters with LCL filter have also been developed to handle high power conversion at high voltage and high current levels. By applying such circuits to acting as grid-forming, grid-supporting and grid-feeding generators in a microgrid operating at constant frequency, the microgrid system can handle much higher power and can adapt to drastic change of renewable energy generation and load change. Such microgrid is operated using newly invented methods described in this disclosure.