Power Inverter Duty Cycle Control for Low-THD Load Response
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Solution Overview
Problem
Existing power inverters generate AC output voltage with high total harmonic distortion (THD) due to high bus voltage and low duty cycle, which increases stress on the inverter architecture and output loads, and are not effective in responding to variations in battery voltage and load changes.
Innovation Solution
A power inverter system that includes primary switches, a transformer, a rectifier, an H-bridge, a detector, and a feedback controller, which adjusts the switching duty cycle of the primary switches to minimize THD and temporarily sets the duty cycle to a maximum allowable level in response to step-up load changes, using a sensing node and AC duty cycle feedback controller to regulate the AC output voltage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If the bus voltage is increased to meet high power output requirements, then the power output capability is improved, but the total harmonic distortion (THD) of AC output voltage increases
Solution Approach 1:
The patent implements dynamic duty cycle adjustment based on real-time detection of load changes. When a step-up load change is detected, the controller temporarily increases the duty cycle to a maximum allowable level to quickly respond to the load variation, then gradually reduces it back to the regulated level. This dynamic adjustment mechanism allows the system to maintain low THD under varying load conditions while meeting high power output requirements.
Solution Approach 2:
The patent changes the duty cycle parameter dynamically in response to detected load changes. By adjusting the duty cycle from a regulated level to a maximum allowable level and then gradually reducing it, the system optimizes the AC output voltage quality. This parameter change strategy resolves the contradiction by allowing high power output through appropriate duty cycle settings while maintaining low THD through controlled adjustments.
2Loss of energy
If the duty cycle is kept low to reduce switching losses, then the efficiency is improved, but the total harmonic distortion (THD) of AC output voltage increases
Solution Approach 1:
The system dynamically adjusts the duty cycle based on real-time load detection rather than maintaining a fixed low duty cycle. When load changes are detected, the duty cycle is temporarily increased to the maximum allowable level to maintain voltage quality, then gradually reduced. This dynamic approach balances switching loss reduction with THD control, allowing the system to operate efficiently while maintaining low harmonic distortion.
Solution Approach 2:
The patent employs a feedback mechanism where the controller detects load changes and adjusts the duty cycle accordingly. The controller monitors the system state and provides feedback control by regulating the duty cycle to maintain low THD while minimizing switching losses. This closed-loop feedback approach resolves the contradiction by optimizing the duty cycle setting based on actual system conditions rather than using a fixed low value.
3Speed
If the switching duty cycle is rapidly adjusted to respond to load changes, then the response speed is improved, but the stability of AC output voltage deteriorates
Solution Approach 1:
The patent implements a two-stage duty cycle adjustment strategy. First, the duty cycle is temporarily set to the maximum allowable level to quickly respond to step-up load changes. Second, the duty cycle is gradually reduced from the maximum level back to the regulated level. This preliminary rapid adjustment followed by gradual stabilization resolves the contradiction by providing fast initial response while ensuring subsequent voltage stability through controlled reduction.
Solution Approach 2:
The system employs periodic adjustment of the duty cycle in response to detected load changes. The duty cycle is temporarily increased to maximum level, then gradually reduced over time in a controlled periodic manner. This periodic action pattern allows rapid initial response to load changes while maintaining stability through the gradual reduction phase, balancing response speed with voltage stability.
Data Source
AI summary
A power inverter includes primary switches, a transformer, a rectifier, a high voltage (HV) bus, an H-bridge, a detector, and a feedback controller. The transformer receives a switched direct current (DC) signal from a battery. The H-bridge outputs an AC signal to a stepped load. The detector detects a step-up load change by monitoring the stepped load. The feedback controller regulates a duty cycle of the AC signal, thereby reducing total harmonic distortion (THD) affecting the power inverter and the stepped load. The feedback controller further regulates the duty cycle of the AC signal by temporarily setting the primary switching duty cycle at a maximum allowable level in response to the step-up load change.