PV Inverter Common-Mode Control for Leakage Current Reduction
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Solution Overview
Problem
In photovoltaic systems, increased parasitic capacitance due to environmental factors like rainy weather leads to elevated leakage currents, causing electromagnetic interference and reducing power generation efficiency, as conventional methods either reduce direct current bus voltage or increase it, resulting in fluctuation and loss of power generation capacity.
Innovation Solution
A photovoltaic system with a sampling control unit that detects leakage current and adjusts the common-mode voltage injection in the pulse width modulated signal to reduce leakage current, maintaining modulation ratio and bus utilization while minimizing power generation loss.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If the direct current bus voltage is reduced to reduce power switching transistor loss, then operating efficiency of the inverter is improved, but when parasitic capacitance increases, the leakage current increases and affects normal operation
Solution Approach 1:
The patent changes the parameter of common-mode voltage injection amount in the pulse width modulated signal to control leakage current. By dynamically adjusting this parameter based on detected leakage current values, the system reduces leakage current without changing the direct current bus voltage, thus avoiding the trade-off between reducing transistor loss and maintaining reliable operation.
2Reliability
If the direct current bus voltage is increased to reduce leakage current, then normal operation of the photovoltaic inverter is ensured, but the direct current bus voltage fluctuates greatly and bus utilization is reduced
Solution Approach 1:
Instead of changing the direct current bus voltage to control leakage current, the patent changes the parameter of common-mode voltage injection amount in the pulse width modulated signal. This approach maintains stable direct current bus voltage and high bus utilization while effectively controlling leakage current through modulation parameter adjustment.
3Object-generated harmful factors
If the direct current bus voltage is adjusted to control leakage current, then leakage current is reduced, but a loss of component in the photovoltaic inverter is large and power generation capacity is lost
Solution Approach 1:
The patent replaces the mechanical/electrical approach of adjusting direct current bus voltage with a control theory approach by adjusting the common-mode voltage injection amount in the pulse width modulated signal. This substitution allows leakage current control without the energy losses associated with voltage adjustment and component stress.
4Object-generated harmful factors
If the common-mode voltage injection amount is adjusted to reduce leakage current, then leakage current is reduced, but the modulation ratio of the photovoltaic inverter is affected
Solution Approach 1:
The patent carefully manages parameter changes by adjusting only the common-mode voltage injection amount in the pulse width modulated signal while keeping the modulation ratio constant. This selective parameter adjustment allows leakage current control without affecting the photovoltaic inverter's modulation ratio and operational characteristics.
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 solution effectively reduces leakage current, stabilizes power generation, and ensures high applicability by maintaining bus utilization and power generation efficiency without affecting the modulation ratio of the photovoltaic inverter.
Implementation Method 1
A photovoltaic system is a new-type power generation system that uses a photovoltaic effect of a photovoltaic solar panel to convert solar radiant energy into electrical energy for use by a mains power grid
Implementation Method 2
a parasitic capacitor exists between the photovoltaic array and a grounded metal frame. When the photovoltaic inverter works, a common-mode circuit is formed among the parasitic capacitor-the photovoltaic system-the power grid, and a common-mode voltage forms a common-mode current, namely, a leakage current, on the parasitic capacitor
Data Source
AI summary
A photovoltaic system and a leakage current control method for the photovoltaic system includes at least one photovoltaic module group, at least one photovoltaic inverter, a grounded metal frame, and a sampling control unit. The photovoltaic module group is mounted on the grounded metal frame. An output end of the photovoltaic module group is connected to an input end of the photovoltaic inverter, and an output end of the photovoltaic inverter is connected to a power grid. The sampling control unit is coupled to both the photovoltaic module group and the photovoltaic inverter and is configured to detect a current value of a leakage current formed by a common-mode voltage of the photovoltaic inverter on a parasitic capacitor. Herein, the parasitic capacitor exists between the photovoltaic module group and the grounded metal frame.