Solar Battery Charger Bootstrap Circuit for Back-Boost Prevention
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Solution Overview
Problem
Existing solar battery chargers face issues with negative current flow from the battery to the PV panels during startup, known as 'back boosting,' which can be harmful and reduce power efficiency.
Innovation Solution
The proposed battery charger incorporates a bootstrap circuit with a diode and capacitor configuration, along with a control circuit that operates the DC-to-DC converter in asynchronous mode initially and switches to synchronous mode when the charging current reaches a certain threshold, preventing reverse current flow.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a diode is connected in series with the high-end switch to prevent back boosting, then reverse current is blocked, but power dissipation increases and efficiency decreases
Solution Approach 1:
The patent changes the electrical parameters (voltage and current) by operating in two distinct modes: asynchronous mode where the low-side switch remains off preventing reverse current, and synchronous mode where both switches operate efficiently. This parameter change eliminates the need for a series diode and its associated power dissipation.
Solution Approach 2:
The patent dynamically switches between asynchronous and synchronous operating modes based on system conditions. The control circuit transitions from asynchronous mode during startup to synchronous mode during normal operation, optimizing performance while preventing back boosting without constant diode conduction losses.
2Loss of energy
If a FET with FET OR-ing controller is used instead of series diode, then power efficiency is improved, but device complexity and cost increase
Solution Approach 1:
The patent extracts and eliminates the need for complex FET OR-ing controllers and bootstrap capacitors by using a simpler asynchronous-synchronous switching approach. The control circuit directly manages the two MOSFETs without requiring additional complex control components.
Solution Approach 2:
The patent uses simple, readily available components (two MOSFETs, basic control circuit) instead of expensive specialized FET OR-ing controllers. The solution prioritizes cost-effective components that can be easily implemented without complex integrated circuits.
3Productivity
If push-pull configuration operates in synchronous mode from startup, then charging efficiency is maximized, but negative current from battery to PV panels occurs during startup
Solution Approach 1:
The patent performs preliminary action by starting in asynchronous mode where the low-side switch is kept off, preventing any possibility of reverse current flow from battery to PV panels. Only after this safe startup phase does the system transition to synchronous mode for efficient charging.
Solution Approach 2:
The patent uses periodic action by transitioning from asynchronous mode during startup to synchronous mode during normal operation. This two-phase approach ensures safe startup without reverse current, then maximizes charging efficiency during the charging phase.
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
This solution effectively prevents back boosting, enhances power efficiency by minimizing power dissipation, and ensures safe operation of the charging circuit by controlling the mode of operation based on the charging current.
Implementation Method 1
charging of energy storage devices using solar photovoltaic power
Implementation Method 2
a bootstrap circuit comprising a bootstrap capacitor and configured to prevent reverse current from the energy storage device to the charging circuit
Data Source
AI summary
A battery charger (300, 400) disclosed herein includes a DC-to-DC converter (154) configured to receive input from a photovoltaic power source (212) and provide a charging current to an energy storage device (206) and a bootstrap circuit (302, 402) comprising a bootstrap capacitor (222) configured to prevent reverse current from the energy storage device (206) to the charging circuit. The battery charger (300, 400) also includes a control circuit (158) coupled to the bootstrap circuit (302, 402) and the DC-to-DC converter (154) and configured to operate the bootstrap circuit to charge the bootstrap capacitor (222) for a first time duration. The control circuit (158) is also configured to operate the push-pull DC-to-DC converter (154) in asynchronous mode after the first time duration to charge the energy storage device (206) and operate the push-pull DC-to-DC converter in synchronous mode when the charging current reaches a first current value.