DC Bus Voltage Control for Power Inverter Efficiency
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Solution Overview
Problem
Power inverters used for converting DC power from alternative energy sources like photovoltaic cells face efficiency challenges due to variations in power output, with existing methods complicating the improvement of efficiency measurements, especially at lower power levels and light loads.
Innovation Solution
The method involves determining a first amount of power supplied by the DC alternative energy source and disabling the output converter when it's below a predetermined level, estimating and adjusting the DC bus voltage to reduce it to a minimum level, ensuring it remains above the AC grid voltage and the DC source voltage, and enabling energy transfer from the DC bus to the AC grid to maintain optimal voltage levels.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the inverter operates at light loads to maintain continuous power delivery, then the output power coverage is improved, but the efficiency decreases due to lower efficiency at light loads
Solution Approach 1:
The inverter enters a periodic jog mode where the output converter is enabled for brief intervals at strategically selected zero-crossing points of the AC grid voltage. This periodic operation allows the inverter to deliver power at light loads while minimizing the time the converter operates in its low-efficiency region, thus resolving the contradiction between maintaining output coverage and preserving efficiency.
Solution Approach 2:
The control system predicts future DC bus voltage levels based on current operating conditions and grid voltage zero-crossing timing. By anticipating when voltage will rise above the maximum threshold, the system proactively enables the output converter at optimal moments before the threshold is exceeded, preventing inefficient operation while maintaining power delivery capability.
2Productivity
If the output converter is continuously enabled to deliver power, then the power delivery capability is improved, but the DC bus voltage may exceed maximum thresholds causing operational issues
Solution Approach 1:
The output converter operates in periodic bursts synchronized with AC grid voltage zero-crossings rather than continuously. This periodic operation allows the system to deliver power when needed while creating natural intervals where the DC bus voltage can dissipate and return to safe levels, preventing voltage threshold violations and maintaining reliable operation.
Solution Approach 2:
The control system continuously monitors DC bus voltage levels and uses predictive algorithms to anticipate future voltage based on current power delivery rates and grid conditions. This feedback mechanism enables the controller to make informed decisions about when to enable or disable the output converter, maintaining voltage within safe thresholds while preserving power delivery capability.
3Ease of operation
If the inverter operates without disabling the output converter at low power, then the simplicity of operation is maintained, but energy losses increase due to unnecessary converter operation
Solution Approach 1:
The control system implements automatic periodic enabling and disabling of the output converter based on real-time monitoring of DC bus voltage and power delivery conditions. This automated periodic operation eliminates the need for manual intervention while reducing energy losses by keeping the converter disabled during periods when power delivery is not required, thus maintaining both operational simplicity and energy efficiency.
Data Source
AI summary
An apparatus and method for controlling a DC-to-AC inverter is disclosed. The DC-to-AC inverter may be configured to convert DC power received from an alternative energy source to AC power for supplying an AC grid or load. The inverter may determine whether the power presently supplied by the alternative energy source is less than a predetermined amount of power and, if so, disable an output converter of the inverter. Additionally, the inverter may predict the voltage of a DC bus of the inverter at a future point in time and, if the predicted DC bus voltage is greater than a predetermined maximum DC bus voltage, enable the output converter to transfer energy from the DC bus to the AC grid to reduce the DC bus voltage.