Inverter Frequency Shift for Common Bus Ripple Reduction
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Solution Overview
Problem
In vehicle propulsion systems, the commonality in switching frequencies among multiple inverters connected to a common bus leads to increased root mean square (RMS) current, necessitating larger and more costly DC link filter capacitors to manage the ripple current effectively.
Innovation Solution
A controller circuit applies a frequency shift to the switching cycles of the inverters, using pulse width modulation (PWM) signals to distribute the harmonic current spectrum across the common bus, thereby reducing the RMS current by varying the frequencies of the PWM signals delivered to each inverter.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If multiple inverters operate at a common switching frequency, then the control system is simple and synchronized, but the RMS current on the common bus increases requiring larger capacitors
Solution Approach 1:
The patent changes the switching frequency parameter of individual inverters by applying frequency shifts to spread the harmonic current spectrum. This allows the system to maintain simple synchronized control while reducing the RMS current on the common bus, thereby reducing capacitor size requirements.
Solution Approach 2:
The patent introduces dynamic frequency adjustment where inverters operate at slightly different switching frequencies rather than a fixed common frequency. This dynamic approach spreads the harmonic spectrum over time, reducing peak currents and RMS values while maintaining overall system coordination.
2Ease of operation
If multiple inverters operate at a common switching frequency, then the inverters are synchronized and easy to coordinate, but the harmonic current spectrum concentrates requiring larger DC link filter capacitors
Solution Approach 1:
The patent modifies the switching frequency parameter of individual inverters by applying frequency shifts. This spreads the concentrated harmonic current spectrum into a distributed spectrum across multiple frequency components, reducing the harmful effects of harmonic concentration while maintaining inverters on the same common bus.
Data Source
AI summary
A system that may include, plural inverters connected to a common bus and at least one capacitor, the inverters configured to convert a direct current (DC) through the common bus to an alternating current (AC) by alternating different switches of the inverters between open and closed states in a respective switching cycle for each of the inverters, and a controller circuit configured to reduce a ripple current conducted onto the common bus to the inverters, by controlling the inverters to apply a frequency shift to the respective switching cycle of one or more of the inverters to spread a harmonic current spectrum along the common bus. The controller circuit is configured to apply the frequency shift to at least a first inverter and a second inverter of the plural inverters.