DC-AC Converter Using Pulse Density Modulation for Low THD
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Solution Overview
Problem
Existing DC-AC inverters have multiple power conversion stages, high voltage active devices, and high Total Harmonic Distortion (THD) greater than 1%, lacking design scalability and modularity.
Innovation Solution
A DC-AC converter design incorporating a step-up transformer, pulse generator, pulse modulator, switching element, and analog low pass filtering stage, utilizing Pulse Density Modulation (PDM) for direct sinusoid conversion with minimal power stages and passive low pass filters to achieve low THD and modular architecture.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If multiple power conversion stages are used in existing DC-AC inverters, then voltage conversion capability is achieved, but device complexity and conversion losses increase
Solution Approach 1:
The patent combines multiple power conversion stages into a single integrated DC-AC converter architecture. The converter directly converts DC voltage to AC voltage using a unified circuit topology that incorporates the transformer, switching elements, and filtering components in one integrated structure, eliminating the need for separate rectification, inversion, and filtering stages that exist in conventional multi-stage systems.
Solution Approach 2:
The DC-AC converter is designed with multi-functional components that perform multiple operations simultaneously. The transformer provides both voltage transformation and isolation functions, while the switching elements and filtering components work together to achieve voltage conversion, waveform generation, and harmonic filtering in a single device, reducing overall system complexity.
2Power
If bridge rectifiers and active components are used on the high voltage side, then power conversion is achieved, but conversion losses and device complexity increase
Solution Approach 1:
The patent extracts and eliminates the bridge rectifier and high-voltage active components from the conversion path. By using a direct DC-AC conversion topology where the switching elements operate at low voltage on the primary side of the transformer, the design removes the high-voltage rectification stage that causes significant conduction losses and requires complex high-voltage switching devices.
Solution Approach 2:
The transformer acts as an intermediary that transfers power from the low-voltage DC side to the high-voltage AC side without requiring high-voltage active components. The magnetic coupling of the transformer enables voltage transformation and isolation, allowing the switching elements to operate at safe low voltages while still achieving high-voltage output through the transformer ratio.
3Power
If conventional filtering stages are used, then AC voltage output is achieved, but Total Harmonic Distortion remains greater than 1%
Solution Approach 1:
The patent applies preliminary filtering action by integrating the low-pass filtering function directly into the converter output stage. The filtering components are positioned to immediately attenuate high-frequency switching harmonics and ripple components as they are generated, preventing these harmonics from propagating to the output before they can cause distortion.
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 results in a high-efficiency DC-AC converter with THD less than 0.1%, eliminating the need for bridge rectifiers and active components on the high voltage side, enabling scalable and efficient power conversion with reduced conversion losses.
Implementation Method 1
stepping up a low DC voltage from a battery to a high DC voltage using a high-frequency transformer
Implementation Method 2
rectifying high-frequency pulses at a secondary side of the HF step-up transformer
Implementation Method 3
configured for generating an AC voltage of the fundamental frequency based on attenuating a plurality of higher frequency components of an unfiltered AC voltage
Data Source
AI summary
Disclosed herein is a DC-AC converter, in accordance with some embodiments. Accordingly, the DC-AC converter comprises a transformer, a pulse generator, a pulse modulator, a switching element, and an analog low pass filtering stage. Further, the pulse generator is configured for generating pulses characterized by a pulse frequency. Further, the pulse modulator is configured for generating a pulse density modulated signal based on modulating the pulses using a sine wave signal of a fundamental frequency. Further, the switching element is connected in series with a primary winding of the transformer. Further, the switching element is configured to be switched between an on state and an off state based on the pulse density modulated signal. Further, the analog low pass filtering stage is configured for generating an AC voltage of the fundamental frequency based on attenuating higher frequency components of an unfiltered AC voltage at a secondary winding of the transformer.