DC Bus Voltage Ripple Compensation via Synchronized PWM Phase Shifting
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Solution Overview
Problem
In aerospace and military applications, there is a need for efficient power conversion systems that reduce voltage ripple across DC buses to minimize heating and electromagnetic interference, while also reducing weight, volume, and cost, and improving reliability.
Innovation Solution
Synchronizing the chopping frequency of multiple power converters and implementing phase shifts to reduce voltage ripple across the DC bus, using digital signal processors to control pulse width modulation schemes and minimize capacitance bank size and EMI filter components.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If multiple power converters are operated without synchronization, then each converter can operate independently, but voltage ripple across the DC bus increases causing heating and electromagnetic interference
Solution Approach 1:
The patent applies periodic action by synchronizing the switching frequencies of multiple power converters to a common frequency and introducing phase shifts between their pulse width modulation (PWM) signals. This periodic coordination causes the voltage ripple components from different converters to cancel each other out through constructive and destructive interference, significantly reducing the overall voltage ripple across the DC bus while maintaining independent converter operation
Solution Approach 2:
The patent changes the temporal parameters of the PWM signals by introducing specific phase shifts (e.g., 180 degrees for two converters, or 120 degrees for three converters) while maintaining the same switching frequency. This parameter modification transforms the ripple cancellation mechanism, allowing the system to achieve reduced voltage ripple without altering the power conversion functionality or requiring additional hardware components
2Reliability
If larger capacitance banks are used to reduce voltage ripple, then voltage ripple decreases, but system weight and volume increase
Solution Approach 1:
The patent replaces the mechanical/electrical approach of using larger capacitance banks with a control-theory approach based on synchronized PWM phase shifting. Instead of physically increasing the energy storage capacity to smooth voltage ripple, the system uses coordinated switching patterns to actively cancel ripple components, thereby achieving voltage stabilization without the weight and volume penalty of larger capacitors
3Object-affected harmful factors
If larger EMI filter components are used to reduce electromagnetic interference, then EMI decreases, but system volume and cost increase
Solution Approach 1:
The patent converts the harmful voltage ripple that generates electromagnetic interference into a beneficial cancellation effect. By carefully coordinating the phase relationships between multiple converters, the system transforms the ripple components from harmful disturbances into a mechanism for mutual cancellation, thereby reducing EMI at its source rather than requiring additional filtering components to suppress it
4Reliability
If phase shifting is implemented to reduce voltage ripple, then voltage ripple decreases, but controller complexity increases
Solution Approach 1:
The patent implements a universal synchronization mechanism where a single master controller generates reference signals that are distributed to all slave converters. This multi-functional approach allows the same control architecture to handle frequency synchronization, phase shift generation, and ripple cancellation coordination across any number of converters, thereby managing complexity through standardization rather than requiring unique control logic for each converter pair
Data Source
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AI summary
A power conversion system having a DC power distribution bus includes multiple power converters connected to the DC power distribution bus with modulation frequencies synchronized so that providing phase shifts between the different modulations has the effect of compensating voltage and current ripples, e.g., reducing voltage fluctuations, across the DC bus. Power conversion may be controlled using space vector modulation implemented, for example, by any of a variety of pulse width modulation schemes. Phase shifts in which nulls of the modulation cycles of different converters do not overlap (in the time domain) may be particularly effective for DC bus voltage ripple compensation. The novel method for DC bus voltage ripple compensation may be implemented by programming a digital signal processor to control the power converters.