Two-Stage Power Converter LVRT Control
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Solution Overview
Problem
Existing solar power generation systems face challenges in managing low voltage ride through (LVRT) and zero voltage ride through (ZVRT) events, where the electrical grid's capacity to accept power is reduced, leading to inefficiencies and potential damage during transient events.
Innovation Solution
A two-stage power converter system that includes a DC to DC boost converter and a DC to AC inverter, controlled by a system controller to adjust the photovoltaic array DC voltage and DC bus voltage, allowing for reduced power output during LVRT or ZVRT events by either increasing or decreasing the DC voltage, thereby protecting the system and maintaining grid connectivity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the system operates at full power during LVRT/ZVRT events, then maximum energy transfer is achieved, but system damage risk increases and grid stability is compromised
Solution Approach 1:
The system dynamically adjusts the DC voltage level in response to grid voltage sags, transitioning from fixed voltage operation to adaptive voltage control. During LVRT/ZVRT events, the controller modifies the DC bus voltage to reduce power transfer, preventing system damage while maintaining grid connectivity. This dynamic adjustment resolves the contradiction between maintaining reliability during transient events and preserving productivity.
Solution Approach 2:
The invention changes the operating parameters of the power converter by adjusting the DC voltage level based on grid conditions. When grid voltage drops below threshold levels, the system modifies the DC bus voltage parameter to reduce power output, thereby protecting the system during transient events. This parameter change enables the system to balance reliability and productivity by adapting power transfer levels to grid conditions.
2Reliability
If the DC voltage is increased to reduce power output during LVRT events, then power transfer is limited protecting the system, but voltage control complexity increases
Solution Approach 1:
The DC voltage control mechanism serves multiple functions: it regulates power transfer during normal operation and provides protection during LVRT/ZVRT events. By making the voltage control system multi-functional, the invention reduces the need for separate protection mechanisms, thereby limiting the increase in device complexity while achieving reliable protection during low voltage events.
Solution Approach 2:
The system employs feedback control where the controller continuously monitors grid voltage levels and adjusts the DC bus voltage accordingly. When grid voltage drops, the feedback loop triggers voltage adjustment to reduce power transfer. This closed-loop feedback mechanism provides automatic protection during transient events without requiring complex manual intervention or additional hardware complexity.
3Reliability
If independent control of boost converter and inverter is implemented, then power quality is maintained during transient events, but control system complexity increases
Solution Approach 1:
The control system is segmented into independent control loops for the boost converter and the inverter. Each converter stage has its own control algorithm that operates autonomously based on system conditions. During LVRT events, this segmentation allows the inverter to reduce power transfer while the boost converter maintains DC voltage stability, thereby preserving power quality without requiring a monolithic complex control system.
Solution Approach 2:
The independent control architecture prepares each converter stage in advance for transient events by maintaining readiness to adjust its operation. The boost converter is pre-configured to maintain DC voltage, and the inverter is pre-configured to modulate AC power transfer. When LVRT events occur, these preliminary control configurations enable immediate response to maintain power quality without requiring complex real-time coordination during the event itself.
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 efficiently manages power output during grid voltage events, ensuring safe operation and maintaining power quality by independently controlling the boost converter and inverter, reducing the risk of damage and optimizing energy transfer to the electrical grid.
Implementation Method 1
Solar energy in the form of sunlight may be converted to electrical energy by solar cells. A more general term for devices that convert light to electrical energy is 'photovoltaic cells.'
Implementation Method 2
A two-stage power converter system that includes a DC to DC boost converter and a DC to AC inverter, controlled by a system controller to adjust the photovoltaic array DC voltage and DC bus voltage
Implementation Method 3
A two-stage power converter system that includes a DC to DC boost converter and a DC to AC inverter
Data Source
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AI summary
A power conversion system (14) for providing power to an electrical grid (22) is described. The system includes a boost converter (24) coupled to a photovoltaic (PV) array (12) and configured to control a PV array voltage. The system also includes an inverter (26) coupled to the boost converter by at least one conductor (36) and configured to regulate a voltage drop across the at least one conductor. The system also includes a system controller (16) configured to control operation of the boost converter and the inverter.