Inverter Neutral Point Potential Stabilization via PWM Correction
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Solution Overview
Problem
Conventional inverter devices face challenges in suppressing common mode noise due to fluctuations in neutral point potential, particularly influenced by dead time, which limits their effectiveness in mass-produced products and requires expensive control devices or limited operating ranges.
Innovation Solution
An inverter device with a control system that includes a phase voltage command calculating unit and a PWM signal generating unit, which corrects three-phase modulation voltage command values using a single carrier signal to cancel changes in phase voltage, thereby stabilizing the neutral point potential and reducing common mode noise.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If conventional PWM control is used without neutral point potential stabilization, then the inverter device can be simplified and mass-produced, but common mode noise is generated due to neutral point potential fluctuations
Solution Approach 1:
The invention applies preliminary action by calculating and applying neutral point potential fluctuation correction values before the PWM switching occurs. The control device calculates the correction values based on the switching patterns of the upper and lower arm switching elements, then applies these corrections to the phase voltage command values to prevent neutral point potential fluctuations and common mode noise generation before they occur.
Solution Approach 2:
The invention changes the parameter of phase voltage command values by adding neutral point potential fluctuation correction values. This parameter modification adjusts the PWM control signals to compensate for the neutral point potential fluctuations caused by dead time, thereby eliminating common mode noise while maintaining the simplicity of the inverter device structure.
2Object-affected harmful factors
If special carrier signals or voltage vector selection methods are used to suppress neutral point potential fluctuation, then common mode noise is reduced, but the device complexity increases and applicability to mass-produced products is limited
Solution Approach 1:
The invention applies self-service by using the inverter device's own PWM signal generating unit to calculate and apply the neutral point potential fluctuation correction values. The control device utilizes the switching information from the upper and lower arm switching elements to generate correction values, eliminating the need for external specialized control devices or complex additional circuits, thus maintaining simplicity while reducing common mode noise.
3Ease of operation
If switching is performed at carrier clearing timing as in conventional methods, then the control is simple, but dead time causes switching timing shifts that prevent effective suppression of neutral point potential fluctuation
Solution Approach 1:
The invention applies feedback by using the actual switching timing information of the upper and lower arm switching elements to calculate the neutral point potential fluctuation correction values. The PWM signal generating unit monitors the switching patterns and uses this feedback to adjust the phase voltage command values, thereby compensating for dead time effects and achieving reliable neutral point potential stabilization while maintaining simple operation.
Data Source
AI summary
An inverter device is provided which is capable of effectively eliminating or suppressing common mode noise in consideration of the influence of a dead time by using the function of a PWM signal generating unit. A control device 21 includes a phase voltage command calculating unit 33 which calculates three-phase modulation voltage command values for generating voltages to be applied to respective phases of a motor 8, and a PWM signal generating unit 36 which, based on the three-phase modulation voltage command values and a single carrier signal, generates a PWM signal to PWM-control an inverter circuit 28. The PWM signal generating unit 36 corrects the three-phase modulation voltage command values output by the phase voltage command calculating unit 33 to thereby cancel a change in the phase voltage applied to the motor 8 by a change in another phase voltage.