Self-Powered MOSFET Bypass Circuit for PV Shadowing

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Solution Overview

Problem

Existing by-pass diode solutions in photovoltaic and DC power systems suffer from significant power loss and inefficiency due to on/off switching during shadowing conditions, and require bulky charge pump circuits that are difficult to integrate in compact systems-in-package.

Innovation Solution

A high multiplication factor inductive voltage booster, assisted by a start-up low multiplication factor charge pump, is used to provide a supply voltage to a polarity inversion detecting comparator, enabling a power switching MOSFET to remain conductive during shadowing conditions, reducing power loss and enabling compact integration.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Productivity

If a by-pass diode is used to bypass shadowed PV cell strings, then power delivery is maintained, but significant power loss occurs in the conducting diode and heat generation increases

Engineering Contradiction:

Improvepower deliveryVSAvoidpower loss

Core Design Contradiction:

ProductivityVSLoss of energy

Solution Approach 1:

The patent changes the operating parameters of the switching device by using pulse-width modulation (PWM) to control the duty cycle, maintaining the MOSFET in a controlled conduction state rather than full on/off switching. This allows optimization of the on-resistance and reduction of power loss while maintaining bypass functionality.

Inventive Principle:

Principle #35Parameter changes

Solution Approach 2:

The patent implements dynamic control of the MOSFET switching device through a control circuit that continuously adjusts the gating signal based on the voltage across the PV string. This dynamic adjustment allows the device to adapt to varying shadowing conditions, optimizing power delivery while minimizing losses.

Inventive Principle:

Principle #15Dynamics

2Loss of energy

If a controlled electronic switching device with charge pump circuit is used, then power loss is reduced, but device complexity and integration difficulty increase

Engineering Contradiction:

Improvepower lossVSAvoidcircuit complexity

Core Design Contradiction:

Loss of energyVSDevice complexity

Solution Approach 1:

The patent merges the charge pump circuit, control logic, and MOSFET gating control into a single integrated control circuit that operates autonomously. This integration reduces the number of discrete components and simplifies the overall device structure while maintaining the low power loss benefits.

Inventive Principle:

Principle #5Merging (Combining)

Solution Approach 2:

The control circuit is designed to be self-powered, using the voltage across the PV string to charge an internal capacitor that provides the gating signal for the MOSFET. This eliminates the need for external power supplies or complex control circuits, reducing device complexity while maintaining low power loss operation.

Inventive Principle:

Principle #25Self-service

3Adaptability or versatility

If Schottky diodes are used for by-pass, then alternative current path is provided, but power loss occurs during conducting period

Engineering Contradiction:

Improvecurrent path alternativeVSAvoidpower loss

Core Design Contradiction:

Adaptability or versatilityVSLoss of energy

Solution Approach 1:

The patent replaces the passive Schottky diode with an active MOSFET switching device controlled by an electronic control circuit. This substitution allows for dynamic control of the bypass path, enabling the system to optimize power delivery while minimizing losses through PWM control and duty cycle adjustment.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

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 significantly reduces power loss and heat generation during shadowing phases while allowing for a compact, reliable system-in-package design, maintaining efficient operation and preventing damage from polarity inversion.

Implementation Method 1

a high multiplication factor inductive voltage booster, adapted to step-up a voltage present at its input terminals from a PV cell string

Methodology Applied

Scientific EffectElectromagnetic induction: Electromagnetic Induction

Implementation Method 2

The power switch is an N-channel MOSFET transistor with its source terminal connected to the negative terminal of the PV panel and its drain terminal connected to the positive terminal

Methodology Applied

Scientific EffectField effect:

Data Source

PatentUS8674545B2Low on-resistance MOSFET implemented, by-pass diode or circuit breaker and related self-powering and control circuit

Publication Date: 2014.03.18 STMICROELECTRONICS SRL

AI summary

A MOSFET implemented self-powered current by-pass or circuit breaker device is based on the use of a high multiplication factor (HMF) inductive voltage booster, adapted to boost a voltage as low as few tens of mV up to several Volts, assisted by a start-up low multiplication factor (LMF) charge pump made with low threshold transistors for providing a supply voltage to a polarity inversion detecting comparator of the drain-to-source voltage difference of a power MOSFET connected in parallel to a DC source or string of series connected DC sources or battery, in series to other DC sources during normal operation of the parallel connected DC source or string of series connected DC sources or battery. The inductance for the high multiplication factor, inductive voltage booster for most of the considered power applications is on the order of a few pH and such a relatively send inductor may be included as a discrete component in a compact package or “system-in-package” of monolithically integrated circuits.