Modular Multilevel Converter Current Distribution Optimization
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Solution Overview
Problem
Modular multilevel converters face challenges in determining optimal switching states in real-time to minimize power consumption and ensure efficient energy storage, particularly in applications like electric vehicle drives and power grids, where energy distribution and loss minimization are critical.
Innovation Solution
A method for controlling modular multilevel converters that calculates target currents based on setpoint voltage levels, phase angles, and state of charge, using a cost function to determine switching states with minimal losses, and dynamically adjusts saturation values to optimize current distribution and reduce ohmic losses.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If real-time optimization of switching states is implemented to minimize power losses, then system efficiency is improved, but computational complexity and control system requirements increase
Solution Approach 1:
The patent pre-calculates and stores optimal switching states in lookup tables during system initialization or offline operation. During real-time operation, the controller simply retrieves pre-determined switching states based on current operating conditions, avoiding complex real-time calculations while maintaining optimization benefits
Solution Approach 2:
The patent implements dynamic adjustment of saturation values and offset currents based on real-time state of charge measurements and operating conditions. This allows the system to adapt pre-calculated switching strategies to actual system state, maintaining optimality across varying operating conditions without requiring full recalculation
2Loss of energy
If switching states are optimized to minimize ohmic losses, then energy efficiency is improved, but the complexity of determining optimal switching states increases
Solution Approach 1:
The patent creates simplified representations of the complex optimization problem by pre-calculating optimal switching states for various operating conditions and storing them in lookup tables. The controller copies appropriate switching states from these tables based on current conditions, avoiding the need to solve complex optimization problems in real-time
Solution Approach 2:
The patent transforms the complex multi-objective optimization problem into a simpler parameter-based lookup approach. By pre-calculating switching states across a range of parameters (voltages, currents, states of charge) and storing them in tables, the system converts a difficult real-time calculation into a simple parameter-matching and retrieval operation
3Reliability
If state of charge balancing is implemented across all modules, then reliability is improved, but additional control complexity and calculation requirements are introduced
Solution Approach 1:
The patent applies different control strategies to different modules based on their individual states of charge. Instead of uniform control, the system calculates module-specific offset currents that create local adjustments in target currents for each module, promoting state of charge balancing while maintaining overall system efficiency
Solution Approach 2:
The patent implements feedback control by continuously monitoring the state of charge of each module and adjusting offset currents accordingly. The state of charge measurements feed back into the control algorithm, which dynamically adjusts target currents to promote equalization across modules while maintaining real-time adaptability
Data Source
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AI summary
The invention relates to a method for controlling a modular multilevel converter for a load, e.g., a vehicle traction motor. Based on target voltage levels (105) provided by a controller for each switching cycle and a phase angle of the motor phase currents (106), an efficiency-optimized ideal current distribution (210) is determined, and, taking into account the charge states of the individual modules, a charge-state-compensating offset current setting (220) is determined. By summing the efficiency-optimized ideal current distribution (210) and the charge-state-compensating offset current setting (220), a target module current distribution (240) is determined, and switching commands (109) for controlling the multilevel converter are determined based on the target module current distribution (240). A system that allows the implementation of the method is also claimed.