Three Level Converter Operation for Partial Load Efficiency
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Solution Overview
Problem
The efficiency of power electronic converters in photovoltaic systems is suboptimal at partial load due to significant power losses in switching devices and passive components, leading to reduced overall energy delivery to the load.
Innovation Solution
A method for operating a three-level neutral point clamped converter that alternately connects the output terminal to the positive, negative, or mid-point of the DC link voltage, depending on the DC link voltage level, to minimize losses by optimizing switching and conduction states of the converter's devices.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If conventional diode clamped converters are used in photovoltaic systems, then the system can transmit electricity from PV modules to the power grid, but significant power losses occur in switching devices and passive components especially at partial load conditions
Solution Approach 1:
The patent applies dynamic operation by switching between two-level and three-level converter modes based on the DC link voltage level. When DC link voltage is below a threshold, the converter operates in two-level mode with reduced switching activity, and when above the threshold, it switches to three-level mode. This dynamic adaptation minimizes conduction and switching losses at partial load while maintaining efficient operation at full load, directly addressing the energy loss problem.
2Adaptability or versatility
If the converter operates at partial load most of the time, then it matches typical photovoltaic system operating conditions, but the overall efficiency becomes less than optimal due to increased relative losses
Solution Approach 1:
The converter dynamically adapts its operating mode based on load conditions and DC link voltage. At partial load, it operates in two-level mode with fewer active switching devices, reducing both conduction and switching losses. This dynamic adaptation allows the system to maintain optimal efficiency across varying load conditions, particularly improving performance at partial load where PV systems typically operate.
Solution Approach 2:
The patent changes operational parameters by switching between two-level and three-level converter configurations. The key parameter change is the number of voltage levels and active switching devices based on DC link voltage threshold. This parameter adaptation optimizes the balance between power delivery capability and loss minimization for different operating conditions.
3Power
If standard three-level converter operation is used, then full voltage utilization is achieved, but conduction losses and switching losses increase significantly
Solution Approach 1:
The system dynamically selects between two-level and three-level operation based on DC link voltage. When voltage is low, two-level mode provides sufficient power with reduced losses. When voltage is high, three-level mode utilizes the full voltage capability. This dynamic selection optimizes the power-loss tradeoff across different operating conditions.
Solution Approach 2:
The patent extracts and removes unnecessary switching activity and device conduction when full three-level operation is not required. By operating in two-level mode during appropriate conditions, it eliminates redundant switching losses and reduces conduction losses in certain devices, thereby reducing overall energy loss while maintaining adequate power output.
Data Source
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AI summary
A method of operating a three level converter (20) includes controlling the output voltage of the converter when a DC link voltage of the three level converter (20) is lower than one-half of a rated DC link voltage of the converter (20) by, for each leg of the converter (112), alternately connecting an output terminal of the leg to the positive terminal or the negative terminal of the DC link (46). When the DC link voltage is at least one-half of the rated DC link voltage, the method includes controlling the output voltage of the converter (20) by, for each leg (112), selectively connecting the output terminal of the converter to the positive terminal, the negative terminal, or a mid-point of the DC link (46).