Capacitorless AC-AC Voltage Booster Using Bidirectional Switches
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Solution Overview
Problem
Existing AC-AC converters inject harmonics into the electrical mains due to a rectifying stage, and they often rely on electrolytic capacitors with short lifespans and require additional power switches for power factor correction.
Innovation Solution
An AC-AC voltage booster is designed without a rectifying stage, utilizing a 'chopping' function applied to the sinusoidal waveform of the primary voltage, employing bidirectional switches driven in phase opposition by a PWM signal, and monodirectional insulated gate switching devices to generate a sinusoidal current waveform, eliminating the need for rectification and reducing harmonic injection.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a rectifying stage is used in AC-AC converters, then AC-DC conversion is achieved, but harmonics are injected into the electrical mains
Solution Approach 1:
The patent removes the rectifying stage from the AC-AC converter circuit, extracting the harmful function of harmonic injection while preserving the essential voltage conversion capability through direct AC-AC switching topology with bidirectional switches
2Reliability
If electrolytic capacitors are used for AC-DC conversion, then voltage stabilization is achieved, but component lifespan is reduced
Solution Approach 1:
The patent eliminates electrolytic capacitors from the circuit topology, replacing them with a capacitorless AC-AC conversion approach using bidirectional switches and inductive energy storage, thereby removing the lifespan limitation while maintaining voltage stabilization through active switching control
3Object-affected harmful factors
If power factor correction stage is added, then mains waveform distortion is reduced, but device complexity increases
Solution Approach 1:
The patent combines the voltage conversion function and power factor correction function into a single integrated AC-AC converter stage, eliminating the need for separate PFC circuitry by using bidirectional switches that simultaneously achieve both objectives through unified PWM control
4Adaptability or versatility
If bidirectional switches are implemented using monodirectional devices with diode bridges, then AC-AC voltage boosting is achieved, but device complexity increases
Solution Approach 1:
The patent uses monodirectional insulated gate switching devices (MOS or IGBT transistors) connected to diode bridges that serve multiple functions: acting as bidirectional switches for AC-AC conversion, providing voltage boosting capability, and enabling both rectification and inversion operations through unified PWM control signals
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 approach provides a stable and versatile AC-AC converter capable of boosting, stepping down, or stabilizing AC voltage, reducing issues from mains surges and drops, while avoiding harmonic injection and extending component lifespan by eliminating the need for electrolytic capacitors.
Implementation Method 1
energy stored in an inductor connected to the primary AC voltage (for example, the mains voltage) during a powering phase (Ton) of the periodic PWM driving signal, is supplied to the electric load through a free-wheeling switch of the inductance discharge current
Implementation Method 2
The voltage booster of this approach obviates the issue of injection on the electrical mains of harmonics of the current, caused by the rectifying stage of the mains voltage that is present in prior art AC-AC converters. This approach is based on the so-called 'chopping' function typical of a switching converter, but applied instant-by-instant to the sinusoidal waveform of the primary voltage
Data Source
AI summary
A device coupled to a primary AC voltage and a load includes an input, an inductive element coupled thereto, and a generator of a PWM control signal. A capacitor is coupled in parallel to the load. A first bidirectional switch couples the load and primary AC voltage during conduction phases. A second bidirectional switch discharges energy from the load during off phases of the first bidirectional switch. A first driving circuit for the second bidirectional switch, input with the PWM control signal, generates a first PWM signal applied between control and conduction terminals of the second bidirectional switch. A second driving circuit for the first bidirectional switch, input with the PWM control signal, generates a second PWM signal, in phase opposition with the first PWM signal, applied between control and conduction terminals of the first bidirectional switch. An electric decoupling circuit is between the generator and the second driving circuit.