Variable Speed Drive Interleaved Inverter Ripple Current Reduction
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Solution Overview
Problem
Variable speed drives (VSDs) with active converters and multiple inverter stages connected to a common DC link require large capacitance for filtering, leading to bulky and expensive designs, with capacitor lifetime limited by internal resistance and operating temperature, necessitating a reduction in capacitance or extension of capacitor life.
Innovation Solution
The method involves providing multiple inverters connected in parallel to the DC link stage, with interleaved switching signals generated to reduce RMS ripple current, allowing for a smaller and more cost-effective design while maintaining similar core temperature thresholds and extending the operating lifetime of capacitors.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If large capacitance is used in the DC link stage to provide filtering for the converter stage, then the filtering performance is improved, but the size and cost of the VSD increase
Solution Approach 1:
The patent applies periodic action by interleaving the switching signals of multiple inverters, causing them to switch at different phases. This periodic distribution of switching events reduces the RMS ripple current in the DC link, allowing smaller capacitors to achieve the same filtering performance, thus reducing VSD size while maintaining reliability
Solution Approach 2:
The patent merges multiple inverter stages into a single VSD system with a common DC link. By combining multiple inverters and coordinating their switching through interleaved signals, the system achieves reduced ripple current and improved filtering efficiency, allowing smaller capacitance values to provide adequate filtering performance
2Reliability
If large capacitance is used in the DC link stage to provide filtering for the converter stage, then the filtering performance is improved, but the cost of the VSD increases
Solution Approach 1:
The interleaved switching signals create periodic action that distributes the ripple current burden across different time phases. This reduces the RMS ripple current magnitude, allowing the use of smaller, less expensive capacitors that still provide adequate filtering performance, thereby reducing overall VSD cost while maintaining reliability
Solution Approach 2:
The patent changes the switching parameters of multiple inverters by introducing phase shifts between their switching signals. This parameter modification reduces the RMS ripple current in the DC link, enabling the use of smaller capacitance values and reducing the cost of passive filtering components
3Productivity
If multiple inverter stages are connected to a common DC link, then the system capability is improved, but the ripple current in the capacitor increases
Solution Approach 1:
The patent applies periodic action through interleaved switching signals that distribute the switching events of multiple inverters across different time phases. This periodic distribution causes the ripple currents from different inverters to partially cancel each other, reducing the total RMS ripple current in the DC link capacitor while maintaining enhanced system capability
Solution Approach 2:
The patent converts the harmful effect of multiple inverters adding ripple current into a benefit by using interleaved switching. The phase-shifted switching signals cause ripple current cancellation, transforming what would be additive harmful ripple into reduced total ripple current, thereby extending capacitor life while maintaining multi-inverter system capability
4Duration of action of stationary object
If the internal operating temperature of the capacitor is reduced, then the lifetime of the capacitor is extended, but the filtering capability may be compromised
Solution Approach 1:
The interleaved switching signals create periodic action that reduces the RMS ripple current magnitude in the DC link capacitor. Lower ripple current reduces I²R heating in the capacitor, thereby reducing its internal operating temperature and extending lifetime while maintaining adequate filtering capability through the coordinated switching of multiple inverters
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
This approach reduces the RMS value of ripple current seen by the DC link, enabling a smaller and less expensive VSD design with extended capacitor life and similar thermal performance to larger systems.
Implementation Method 1
generating a switching signal for each inverter of the plurality of inverters and interleaving the switching signals for each inverter of the plurality of inverters to reduce RMS ripple current at the DC link stage
Implementation Method 2
A voltage source type VSD uses multiple capacitors to provide sufficient filtering for the pulsating DC link ripple current that results from the pulsating converter and inverter currents
Implementation Method 3
a converter stage to convert an AC voltage to a DC voltage
Implementation Method 4
an inverter stage to convert the DC voltage to an AC voltage
Data Source
AI summary
A variable speed drive is provided having a converter to convert an AC voltage to a DC voltage, a DC link to filter and store energy from the converter, and a plurality of inverters. Each inverter is configured to convert a DC voltage to an AC voltage and is electrically connected in parallel to the DC link. An interleaved pulse width modulation control technique is used to control the operation of the plurality of inverters and possibly the converter to lower the RMS ripple current in the DC link.