Inverter Phase Current Detection with Widened Voltage Pulses
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Solution Overview
Problem
High-frequency switching in inverter circuits complicates phase current detection due to reduced pulse width and waveform distortion, making reliable detection challenging with conventional shunt resistor-based systems, and alternative methods like hall CTs increase costs.
Innovation Solution
A phase current detection device that includes a shunt resistor and a control section to generate a voltage pulse with a larger width during a dedicated detection period, allowing for stable voltage measurement and reliable detection even at high switching frequencies, without the need for increased operational speed or additional components.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If the switching frequency of the inverter circuit is increased to improve responsiveness and control band, then the carrier frequency increases, but the width of the voltage pulse generated at the shunt resistor is reduced, making reliable phase current detection difficult
Solution Approach 1:
The control section performs preliminary action by generating a detection voltage pulse with intentionally widened width before actual current detection. This preliminary widened pulse ensures that even after accounting for ring-off periods and stabilization time, sufficient pulse width remains for accurate detection at high switching frequencies
Solution Approach 2:
The invention changes the parameter of voltage pulse width by controlling the inverter circuit to generate a detection voltage pulse with width larger than the normal operating pulse width. This parameter change compensates for the reduction in pulse width caused by increased switching frequency
2Productivity
If the switching frequency is increased to ten times or higher using wide bandgap semiconductor, then responsiveness improves, but the voltage pulse width becomes too narrow to ensure stable detection after waiting for voltage stabilization
Solution Approach 1:
The control section performs preliminary action by generating a detection voltage pulse with intentionally widened width before actual current detection. This preliminary widened pulse ensures that even after accounting for ring-off periods and stabilization time, sufficient pulse width remains for accurate detection at high switching frequencies
Solution Approach 2:
The invention provides beforehand cushioning by creating a detection voltage pulse with excess width margin. This cushioning accounts for the time needed for voltage stabilization and ring-off, ensuring reliable detection even at ten times or higher switching frequencies
3Measurement precision
If a hall CT is used instead of a shunt resistor to enable phase current detection at high frequencies, then detection reliability improves, but the cost of the phase current detection device increases
Solution Approach 1:
The invention creates a copied or simulated detection condition by generating an artificial detection voltage pulse that replicates the conditions needed for accurate shunt resistor measurement. This copied detection environment allows high-frequency detection to remain compatible with cost-effective shunt resistor-based systems
Solution Approach 2:
The invention changes the parameter of voltage pulse width by controlling the inverter circuit to generate a detection voltage pulse with width larger than the normal operating pulse width. This parameter change compensates for the reduction in pulse width caused by increased switching frequency
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
Ensures reliable phase current measurement at high switching frequencies with the same wiring design as conventional systems, reducing costs and complexity, while allowing for compact and simultaneous detection of phase currents.
Implementation Method 1
a shunt resistor (R) configured to output a voltage pulse of a voltage corresponding the phase current
Data Source
Figure 1~2
Figure 3~4
Figure 5
AI summary
A control section (4) which repeats inverter control in units of an inverter control period (T2) having a predetermined length is provided. In the control section (4), a phase current detection period (T1) in which a phase current is detected is provided between predetermined two inverter control periods (T2), each of switching states of switching elements (Sup, ..., Swn) of a inverter circuit (3) is controlled so that a voltage pulse having a larger width than a width of a voltage pulse in the inverter control period (T2) is output from a shunt resistor (R) in the phase current detection period (T1).