Power conversion apparatus, and air-conditioning apparatus using the same
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Solution Overview
Problem
Existing power conversion systems face challenges in accurately detecting momentary power failures or voltage sags, leading to instability and false detections, which require tuning for each model and increase design complexity.
Innovation Solution
A power conversion apparatus with a converter control unit that calculates a switching command value based on the ratio of rectified voltage to output voltage and reactor current, allowing for precise detection of momentary power failures or voltage sags without additional components, using a switching control unit to manage the switching element and a supply abnormality determination unit to assess the occurrence of such events.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If detection is performed based on current or voltage values, then momentary power failures or voltage sags can be detected, but false detections occur during system activation or stopping when current or voltage changes naturally
Solution Approach 1:
The patent changes the detection parameter from direct current or voltage values to the switching command value (PWM duty ratio) that controls the converter unit. This parameter reflects the state of the power supply voltage indirectly through the control system's response, allowing detection of momentary power failures without being affected by normal operational variations in current and voltage during activation or stopping.
Solution Approach 2:
The switching command value serves as an intermediary parameter that mediates between the power supply voltage and the converter unit operation. Instead of directly monitoring voltage or current, the system monitors the control signal required to maintain proper operation, which changes characteristically during momentary power failures versus normal operational transitions.
2Measurement precision
If detection thresholds are set to accurately detect momentary power failures, then detection precision improves, but the system becomes sensitive to normal operational variations requiring extensive tuning for each model
Solution Approach 1:
By monitoring the switching command value instead of setting thresholds on current or voltage, the system avoids the need for extensive tuning. The switching command value naturally exhibits distinct characteristics during momentary power failures versus normal operation, allowing for simpler, more universal detection logic that does not require model-specific calibration.
3Use of energy by moving object
If a booster circuit controls input current using semiconductor switching elements, then power conversion efficiency improves, but momentary power failures or voltage sags cause overcurrent in the switching elements and output voltage instability
Solution Approach 1:
The system performs preliminary detection of momentary power failures by monitoring the switching command value before overcurrent or voltage instability occurs. This early detection allows the control system to take preventive action, such as adjusting the switching pattern or protecting the semiconductor elements, before the harmful effects manifest.
Solution Approach 2:
The monitoring of the switching command value creates a feedback mechanism that provides information about power supply stability to the control system. This feedback allows the system to adapt its operation in response to detected abnormalities, maintaining stability and protecting components during momentary power failures or voltage sags.
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
Enables accurate and easy detection of momentary power failures or voltage sags, reducing the likelihood of false detections and system instability, while minimizing the need for additional components and tuning, thus improving reliability and usability.
Implementation Method 1
a rectifier configured to rectify an alternating-current voltage supplied from an alternating-current power supply
Implementation Method 2
a converter unit including a reactor connected to an output terminal of the rectifier, a reverse current prevention element connected in series with the reactor, and a switching element connected between the reactor and the reverse current prevention element, and being configured to raise a rectified voltage rectified by the rectifier
Implementation Method 3
a smoothing capacitor configured to smooth the output voltage output from the converter unit
Data Source
AI summary
A power conversion apparatus includes a rectifier, a converter including a reactor, a switching element, and a reverse current prevention element, a smoothing capacitor configured to smooth the output voltage, a current detector configured to detect a reactor current, a voltage detector configured to detect the output voltage, and a converter control unit configured to control operation of the switching element of the converter. The converter-control unit includes a switching command calculation unit configured to calculate a switching command value responsive to a ratio of the rectified voltage to the output voltage in accordance with the output voltage and the reactor current, a switching control unit configured to control operation of the switching element in accordance with the switching command value, and a supply abnormality determination unit configured to determine occurrence of a momentary power failure or voltage sag in accordance with the switching command value.