Modular Multilevel Converter Control via Observer-Estimator
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Solution Overview
Problem
Current converter regulation methods fail to simultaneously achieve effective current regulation and energy balancing, leading to inefficient use of power semiconductors and increased costs, as well as higher downtime due to network faults.
Innovation Solution
A method that calculates state intermediate circuit energy values using an estimator unit, combined with an observer unit modeling the converter's state space, allowing for periodic, time-variant control to achieve multivariable control and balance energy across the converter's phases, thereby optimizing regulation and reducing the number of required power semiconductors and capacitor capacity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If conventional current regulation methods are used, then current control is achieved, but energy balancing and converter energy regulation cannot be simultaneously achieved
Solution Approach 1:
The patent combines current regulation, energy balancing, and converter energy regulation into a single integrated control structure. The periodic controller with time-variant amplification simultaneously processes all three control objectives, merging previously separate control functions into one unified system that achieves multivariable control.
Solution Approach 2:
The control structure is designed to perform multiple functions simultaneously: it regulates current, balances energy across intermediate circuits, and controls converter energy. This universal controller replaces multiple specialized controllers, achieving adaptability across different control goals while maintaining a unified device architecture.
2Ease of operation
If separate control structures are used for current regulation and energy balancing, then each function can be controlled independently, but the number of power semiconductors and capacitor capacity increase
Solution Approach 1:
The patent merges independent control functions into a single periodic controller that handles current regulation, energy balancing, and converter energy control simultaneously. This integration eliminates the need for separate control structures, reducing the quantity of power semiconductors and capacitor capacity while maintaining independent control capability through multivariable control strategies.
3Reliability
If traditional regulation methods are used, then basic control is achieved, but regulation speed and precision are insufficient
Solution Approach 1:
The patent employs a periodic controller with time-variant amplification that dynamically adjusts control parameters based on the operating state. This dynamic control approach replaces static traditional regulation methods, enabling faster response and higher precision while maintaining stability through periodic optimization of control gains.
Solution Approach 2:
The control structure incorporates feedback mechanisms that continuously monitor system state and adjust control actions accordingly. This feedback-driven periodic control achieves both high regulation speed and precision by real-time optimization, while maintaining reliability through stable closed-loop control.
4Reliability
If higher capacitor capacity is used to handle network faults, then fault tolerance is improved, but converter costs increase
Solution Approach 1:
The periodic controller with time-variant amplification dynamically optimizes energy distribution and balancing during normal and fault conditions. This dynamic control enables the system to handle network faults effectively with reduced capacitor capacity, as the controller efficiently manages energy fluctuations and prevents excessive energy accumulation that would require larger capacitors.
Solution Approach 2:
The control strategy changes parameters such as amplification factors and control gains periodically to optimize system response under different operating conditions including faults. This parameter optimization enables fault tolerance with smaller capacitor capacity by efficiently managing energy dynamics rather than relying on oversized energy storage components.
Data Source
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AI summary
In order to provide a method for controlling a converter (1) having controllable power semiconductors, wherein actual state values x (k), which describe the state of the converter (1), are compared with target state values x target (k) in order to obtain control difference values, which are fed to a control unit (16), which produces setting voltage values u (k) at the output of the control unit, and control electronics (19) provide control signals according to the setting voltage values u (k) and transmit said control signals to the power semiconductors (S1, S2) of the converter (1), wherein the control unit (16) generates such setting voltage values u (k) that the control difference values become as small as possible, wherein the current control and the converter energy control and the energy balancing can be performed jointly by means of said method, the actual state values x (k) are calculated by an observing unit (21) based on the setting voltage values u(k) and taking into consideration measured current values x (k) and actual state intermediate-circuit energy values w (k) are calculated by an estimating unit (21A) taking into consideration measured intermediate-circuit energy values w (k) of the positive-side (2P) and the negative-side (2N) three-phase voltage source of the converter (1), wherein the observing unit (21) and the estimating unit (21A) model the converter (1) so that the calculated actual state current values x (k) and actual state intermediate-circuit energy values w (k) at steady state correspond to the error-free current and intermediate-circuit energy values, and the error-free current and intermediate-circuit energy values x (k), w (k) are fed to a control unit (16) designed as a periodic controller having periodic time-variant gain. The invention further relates to an alternative method and to an arrangement for carrying out the methods.