Power Conversion Apparatus Torque Control Peak Current Protection
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Solution Overview
Problem
Existing power conversion apparatuses struggle to accurately detect peak motor current during torque control due to misalignment of pulsating components of load torque and DC link voltage, leading to potential breakdowns and demagnetization of motor magnets.
Innovation Solution
A power conversion apparatus with a controller that synchronizes the timing of peak load torque and peak power-supply pulsating components, using a peak holder to maintain the maximum current value and a torque control amount adjuster to reduce output torque variation when the peak current exceeds a predetermined limit, ensuring protection of switching devices.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If torque control is performed to synchronize output torque with load torque pulsation, then vibration of the compressor is reduced, but peak motor current increases causing breakdown of switching devices and demagnetization of motor magnets
Solution Approach 1:
The control device performs preliminary detection of the timing when peak current is likely to occur by monitoring the coincidence of pulsating components, and preemptively limits the variation range of output torque before the peak current exceeds the upper limit, preventing switching device breakdown and demagnetization
Solution Approach 2:
The control device continuously monitors motor current and adjusts the torque control in real-time based on feedback signals. When peak current approaches the upper limit, the control device reduces the variation range of output torque to maintain current within safe operating limits
2Device complexity
If detection of peak motor current is performed at arbitrary timing, then current monitoring is simplified, but accurate detection of peak current is missed due to misalignment of pulsating components
Solution Approach 1:
The control device preliminarily determines the timing when peak current is likely to occur by detecting the coincidence of the pulsating component of load torque and the pulsating component of output voltage, and performs current detection at this predetermined timing to ensure accurate peak current measurement
Solution Approach 2:
The control device dynamically adjusts the detection timing based on the varying pulsation characteristics of load torque and output voltage. By synchronizing detection with the coincident timing of pulsating components, the system adapts to changing operating conditions to maintain accurate peak current detection
Data Source
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AI summary
A converting section (20) is provided, which is configured to convert, by switching of a plurality of switching devices (Sr, Ss, St, Su, Sv, Sw, Sx, Sy, Sz), power from an AC power supply (6) into AC power having a predetermined frequency to output the AC power to a motor (5). A controller (40) is provided, which is configured to perform a torque control such that output torque of the motor (5) contains a power-supply pulsating component which is a pulsating component with the integer-fold of the frequency of output voltage of the AC power supply (6) and that the output torque of the motor (5) varies in association with variation in load torque of the motor (5), and which is configured to obtain a peak current value when the timing of the peak of the power-supply pulsating component and the timing of the peak of a load torque pulsating component are coincident or substantially coincident with each other and to reduce the variation range of the output torque such that the peak current value does not exceed a predetermined upper limit.