Multilevel Power Converter Modulation Control for Lower Losses
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Solution Overview
Problem
Modular multilevel power converters experience unnecessarily high electrical losses and reduced service life due to excessive energy storage at operating points other than the worst-case scenario, leading to inefficient operation and component stress.
Innovation Solution
Regulate the maximum degree of modulation of the phase module branch to a setpoint value, adjusting energy storage levels to match the necessary voltage requirements, thereby optimizing energy use and reducing losses.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If energy regulation maintains constant energy setpoint value across all operating points, then reliable operation is ensured at worst-case operating point, but electrical losses increase and service life reduces at other operating points
Solution Approach 1:
The patent applies dynamics by transitioning from static energy regulation to dynamic degree of modulation regulation. The regulation value is no longer fixed but adapts continuously based on the actual operating point, allowing the system to optimize performance across varying conditions rather than being constrained by worst-case scenarios.
Solution Approach 2:
The patent changes the regulated parameter from constant energy setpoint value to variable degree of modulation. By monitoring actual operating conditions and adjusting the degree of modulation accordingly, the system transforms the rigid energy regulation approach into a flexible parameter that adapts to different operating points, reducing losses while maintaining reliability.
2Reliability
If energy stores are charged to high voltage for worst-case operating point, then controllable operation is ensured, but component service life reduces due to excessive voltage stress
Solution Approach 1:
The system dynamically adjusts the degree of modulation based on actual operating conditions rather than maintaining a fixed high voltage charge level. This allows energy stores to be charged to appropriate voltage levels matched to current operating requirements, reducing unnecessary voltage stress on components while ensuring controllability when needed.
Solution Approach 2:
The patent changes the voltage charge level parameter from constant high voltage (dimensioned for worst-case) to variable voltage levels determined by actual operating points. This parameter adaptation reduces voltage stress on components during normal operation while maintaining sufficient voltage for reliable control when required.
3Power
If switching elements operate with high energy store voltage, then sufficient voltage headroom is available, but switching losses increase
Solution Approach 1:
The patent changes the voltage parameter from constant high voltage to variable voltage levels that adapt to operating conditions. By regulating the degree of modulation rather than maintaining fixed high voltage, the system reduces switching losses at operating points where full voltage headroom is not required, while preserving sufficient power capability when needed.
Data Source
AI summary
A method for controlling a modular multilevel power converter which has at least one phase module branch with a series circuit of modules. Each of the modules has an energy storage device and a power semiconductor circuit with electronic switching elements. A duty cycle of the phase module branch is ascertained, wherein the duty cycle describes the ratio between the voltage which is being output by the phase module branch and the voltage which can be maximally output by the phase module branch. The maximum value of the duty cycle during a preselected time period is ascertained, and the maximum value of the duty cycle is controlled to a target value for the maximum value of the duty cycle by a controller.