Single-Phase DC/AC Inverter Control for Varying Input Voltages
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
DC/AC inverters using pulse width modulation (PWM) techniques struggle with robust output voltage magnitude variations due to changing input DC voltage, leading to unpredictable AC power characteristics and high harmonic distortions, which complicates and expenses systems, especially in photovoltaic energy systems.
Innovation Solution
A single-phase DC/AC inverter with a hybrid control circuit that uses measurements of output voltage and current to control four switches, ensuring stable AC output even with varying input DC power, implemented using a computer-controlled single-phase inverter bridge, low-pass filter, and voltage and current sensors, eliminating harmonic distortion at low frequencies.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If PWM-based control is used in DC/AC inverters, then the inverter can convert DC power to AC power, but the output voltage magnitude becomes sensitive to input DC voltage variations and harmonic distortions increase
Solution Approach 1:
The patent implements a feedback-based control system that continuously monitors the output voltage and adjusts the switching states of the inverter bridges accordingly. The controller compares the actual output voltage with the reference voltage and modifies the PWM duty cycles to minimize voltage deviations and eliminate harmonics, thereby maintaining stable output voltage magnitude despite input variations.
Solution Approach 2:
The patent dynamically adjusts control parameters such as PWM duty cycle, switching frequency, and modulation index based on real-time operating conditions. By changing these parameters adaptively, the system optimizes the output voltage quality and minimizes harmonic distortions while maintaining robustness against input voltage variations.
2Reliability
If a DC voltage regulator is added to address output voltage sensitivity, then output voltage stability improves, but device complexity and expense increase
Solution Approach 1:
The patent designs the inverter control system to perform multiple functions simultaneously: power conversion, voltage regulation, and harmonic elimination. The unified control architecture integrates these functions into a single controller that manages both H-bridge inverters, eliminating the need for separate DC voltage regulators and reducing overall system complexity.
Solution Approach 2:
The patent combines the DC voltage regulation function with the AC output voltage control function in a single integrated control system. By merging these previously separate control loops into one unified controller that manages both inverter bridges, the system reduces component count and simplifies the overall architecture while maintaining both voltage stability and low harmonic distortion.
3Object-generated harmful factors
If circuitry is added to correct harmonic distortions, then harmonic distortion decreases, but device complexity and expense increase
Solution Approach 1:
The patent employs feedback control to actively suppress harmonic distortions by continuously monitoring the output voltage waveform and adjusting the PWM switching signals in real-time. The controller detects harmonic components and applies corrective switching actions to eliminate them, achieving low harmonic distortion without requiring additional passive filter components.
Solution Approach 2:
The patent replaces traditional passive harmonic filtering circuitry (inductors, capacitors) with an active control-based harmonic elimination approach. By using intelligent switching control and PWM modulation strategies, the system achieves harmonic distortion correction through electronic control rather than bulky passive components, reducing device complexity and expense.
Data Source
AI summary
A single-phase DC/AC inverter has a single-phase inverter bridge with binary switches connected to an RLC low-pass filter. Digital control logic in a control circuit (or in a microcontroller) determines and controls a logic state q determining the position of the switches in the inverter bridge from sensed iL, vC values from the RLC filter. The control logic selects one of multiple possible logic states q based on whether the sensed iL, vC values belongs one of multiple boundary regions of a tracking band in an iL, vC state space.