Inverter Harmonic Control for Power Optimization
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Solution Overview
Problem
Inverters in photovoltaic systems are limited in optimizing power output, particularly in situations requiring increased active or reactive power, and struggle to maintain power output at low DC voltage conditions due to constraints on harmonic content in the AC current.
Innovation Solution
The method involves detecting a need to increase harmonic content beyond predetermined levels, checking if such an increase is allowed, and if permitted, raising the maximum harmonic level to optimize inverter operation, particularly by adjusting the MPPT voltage reference and modulation schemes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the inverter operates with a predetermined maximum harmonic content level to maintain AC current quality, then the output AC current quality is maintained adequate, but the power output cannot be optimized in situations requiring increased active or reactive power
Solution Approach 1:
The patent applies dynamics by making the maximum harmonic content level adjustable rather than fixed. The control unit dynamically raises the predetermined maximum harmonic content level when active or reactive power output needs to be increased, allowing the inverter to adapt its operating parameters based on power delivery requirements. This resolves the contradiction by enabling the system to maintain adequate current quality under normal conditions while allowing higher harmonics when power output optimization is needed.
Solution Approach 2:
The patent changes the parameter of maximum harmonic content level from a static predetermined value to a dynamically adjustable parameter. When increased power output is required, the control unit raises this parameter, allowing the inverter to operate with higher harmonic content temporarily. This parameter change enables the system to prioritize power delivery over current quality when necessary, resolving the contradiction between maintaining adequate current quality and optimizing power output.
2Power
If the inverter maintains power output at low DC voltage conditions, then power delivery is sustained, but the harmonic content of AC current exceeds predetermined maximum levels
Solution Approach 1:
The patent applies dynamics by enabling the maximum harmonic content level to change based on operating conditions. When DC voltage is low and power maintenance is critical, the control unit dynamically raises the predetermined maximum harmonic content level, allowing the inverter to sustain power output despite degraded current quality. This resolves the contradiction by making the system adaptable to low DC voltage conditions where power delivery priority overrides current quality requirements.
Solution Approach 2:
The patent changes the operational parameters by raising the maximum harmonic content level threshold when operating in low DC voltage conditions. This parameter adjustment allows the inverter to maintain power output by permitting higher harmonic content in the AC current, which would normally be restricted. This resolves the contradiction between maintaining power output and maintaining current quality under low DC voltage stress conditions.
Data Source
AI summary
A method for operating an inverter and an inverter configured to convert DC power supplied from a DC power source into AC power supplied to an AC network by applying maximum power point tracking, MPPT, such that a harmonic content of an AC current supplied from the inverter to the AC network is kept within a predetermined maximum level, wherein during the converting the inverter is configured to detect a need to increase the harmonic content of the AC current supplied from the inverter to the AC network beyond the predetermined maximum level, perform a check whether an increase of the harmonic content of the AC current beyond the predetermined maximum level is allowed, and, if an increase of the harmonic content of the AC current beyond the predetermined maximum level is allowed, raise the predetermined maximum level used in the converting.