Inverter Control Apparatus Phase Current Detection Switching Loss
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Solution Overview
Problem
Existing inverter technologies face challenges in achieving high efficiency when calculating and detecting phase currents from a DC input current, leading to inefficiencies in AC motor drive systems.
Innovation Solution
An inverter control apparatus that calculates phase currents using a current sensor, generates three-phase voltage commands, and modulates these commands to reduce switching losses and stabilize current detection by comparing them with carrier waves, allowing for reduced switching frequency and balanced arm usage in the inverter.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If three carrier waves are used to generate PWM signals, then phase current detection can be stably performed, but switching loss increases and inverter efficiency decreases
Solution Approach 1:
The patent extracts one carrier wave from the traditional three-carrier-wave system, using only two carrier waves with a fixed phase difference to generate PWM signals. This reduction in the number of carrier waves directly decreases the switching frequency and switching loss while maintaining sufficient phase current detection capability through the remaining two carrier waves.
Solution Approach 2:
The patent changes the parameter of carrier wave quantity from three to two, and adjusts the phase difference parameter between the two carrier waves to a fixed value. This parameter optimization reduces the overall switching activity in the inverter while preserving the essential function of phase current detection from DC input current.
2Loss of energy
If switching frequency is reduced to improve efficiency, then switching loss decreases, but phase current detection accuracy deteriorates
Solution Approach 1:
The patent applies preliminary action by pre-setting a fixed phase difference between the two carrier waves before PWM signal generation. This predetermined phase relationship ensures that the PWM signals generated from the two carrier waves maintain sufficient pulse width and detection windows, allowing accurate phase current detection even at reduced switching frequencies.
3Loss of energy
If one phase voltage command is set to full-on or full-off voltage, then switching loss is reduced, but voltage fluctuation and ripple increase
Solution Approach 1:
The patent employs periodic action by using two carrier waves with a fixed phase difference to generate PWM signals that periodically switch between full-on and full-off states. This periodic switching pattern, determined by the carrier wave frequency and phase difference, reduces switching loss while the regularity of the periodic action helps suppress voltage ripples and maintain voltage stability through predictable switching behavior.
Data Source
AI summary
In an inverter control apparatus, a phase current calculation section calculates each of phase currents flowing into a motor by using measurement results of a current sensor, and a voltage command generation section calculates three-phase voltage commands by using each of the estimated phase currents. A command modulation section compares the phase voltage commands with each other, to specify a full-on phase or a full-off phase on the basis of the comparison result and then to set the voltage command of the specified phase to a full-on voltage or a full-off voltage, and offsets the voltage commands of the other two phases according to the full-on voltage or the full-off voltage to modulate the voltage commands into voltage commands allowing the line voltage between the other two phases to be kept constant. A PWM signal generation section generates PWM signals by comparing, according to a predetermined rule set in advance, three carrier waves generated by a carrier wave generation section with each of the phase voltage commands modulated by the command modulation section. Accordingly, each of the phase currents can be calculated from a DC input current, so that the efficiency can be improved.