Dual DC/DC Converter Biasing to Eliminate Startup Transients
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Solution Overview
Problem
Dual DC/DC converters experience transients when starting operation and connecting to battery racks in pole-to-ground photovoltaic systems, leading to potential damage and inefficiencies due to voltage and current mismatches between the solar field and battery racks, which existing solutions fail to fully mitigate.
Innovation Solution
An intrinsic biasing method for dual DC/DC converters that pre-charges and biases both the solar field and battery sides to equal voltages, using a series of transistors and capacitors connected in series, with control means to manage switching and prevent energy transfer during startup, thereby eliminating biasing transients.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a dual DC/DC converter is used to interconnect ungrounded battery racks with grounded photovoltaic solar fields, then the converter can handle large power values and meet electrical safety regulations, but voltage and current transients occur during startup and connection that can damage components
Solution Approach 1:
The patent applies preliminary action by pre-charging the internal capacitor bus to the same voltage as the photovoltaic solar field before connecting the battery rack. This is achieved through a startup sequence where the converter is first connected to the solar field to charge the internal bus, then the battery rack is connected after voltage equalization. This preliminary charging action eliminates voltage transients during battery connection while maintaining compliance with electrical safety regulations for grounded photovoltaic systems.
2Reliability
If component sizes are increased to withstand voltage and current peaks during transients, then reliability improves, but device weight and manufacturing cost increase
Solution Approach 1:
By pre-charging the internal capacitor bus before battery rack connection, the patent eliminates voltage and current peaks that would otherwise require oversized components. The startup sequence ensures the internal bus voltage equals the solar field voltage before battery connection, preventing transient currents. This allows components to be sized for normal operating conditions rather than transient peak values, reducing converter weight while maintaining reliability.
3Object-affected harmful factors
If a resistive-passive soft charge is used to connect the battery rack to the internal capacitor bus, then connection transients are reduced, but an extra current peak occurs when the soft charge contactors close
Solution Approach 1:
The patent eliminates the need for resistive-passive soft charge by pre-charging the internal capacitor bus to match the battery rack voltage before connection. Since both sides are at the same voltage potential, connecting the battery rack directly to the pre-charged internal bus produces no current peak. This preliminary voltage equalization action replaces the soft charge resistor approach and eliminates the extra current peak that occurs when closing soft charge contactors.
Data Source
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AI summary
The present invention refers to a method of intrinsically biasing a dual DC/DC converter by means of an active pre-charging of the internal side of the converter prior to its connection with the batteries and a soft biasing of the batteries after the connection of the converter with the batteries. This has the advantage of having a dual DC/DC converter capable of charging isolated batteries in photovoltaic installations in a pole to ground configuration, eliminating the biasing transient that occurs when connecting the battery by means of passive resistive soft charging to the internal capacitor bus of the DC/DC converter, and also eliminating the biasing transient that occurs when starting the DC/DC converter for its normal operation.