Multiphase Converter Current Balancing to Prevent Transformer Saturation
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Solution Overview
Problem
Multi-phase multi-stage converters experience transformer saturation due to direct current components, leading to additional losses, overheating, and noise generation, which can result in transformer damage and increased costs for sound insulation.
Innovation Solution
Measure and adjust the intermediate circuit voltages of sub-modules to determine and compensate for direct current outputs, ensuring all phase modules have the same current level, thereby eliminating direct current component differences that flow into the transformer.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If increased measurement accuracy is used to reduce DC outputs, then DC output precision is improved, but sensor cost increases significantly
Solution Approach 1:
The patent uses the AC voltage component as an intermediary parameter to indirectly determine the DC output. Instead of directly measuring DC output with expensive high-precision sensors, the system measures the AC voltage component across the capacitor, which is correlated with the DC output through the relationship Idc = -C/n * dUz/dt. This intermediary measurement approach achieves the desired precision without requiring expensive direct DC measurement sensors.
Solution Approach 2:
The patent replaces direct electrical measurement of DC output with an alternative measurement approach using AC voltage detection. By substituting the direct DC measurement system with an AC voltage-based indirect measurement system, the patent achieves comparable or superior precision while using more affordable sensor technology suitable for medium- and high-voltage applications.
2Reliability
If saturation compensation is implemented in the transformer, then transformer saturation is reduced, but system complexity and error potential increase
Solution Approach 1:
The patent implements preliminary action by proactively detecting and compensating for DC output deviations before they cause transformer saturation. The control system continuously monitors the AC voltage component, calculates the corresponding DC output using the relationship Idc = -C/n * dUz/dt, and adjusts the converter operation in advance to eliminate DC components. This preventive approach avoids the need for complex reactive saturation compensation measures.
Solution Approach 2:
The patent employs feedback control by using the measured AC voltage component to continuously determine the DC output level and adjusting the converter's target currents accordingly. The feedback loop compares the calculated DC output with the desired zero level and modifies the phase module currents to eliminate deviations, thereby preventing transformer saturation through continuous adaptive control rather than complex compensation circuits.
3Ease of operation
If DC output deviations are not compensated, then system operation is simple, but transformer saturation occurs causing losses and overheating
Solution Approach 1:
The patent implements self-service by enabling the converter system to automatically detect and correct its own DC output deviations without external intervention. The control system uses the inherently present AC voltage component across the capacitor to self-diagnose DC output errors and self-correct by adjusting the phase module currents. This self-regulating mechanism maintains simple operation while preventing energy losses, eliminating the need for complex external monitoring or manual adjustment systems.
Data Source
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AI summary
The invention relates to a method for operating a multi-phase multi-stage converter (3), which is connected to an energy supply (7) via a transformer (5a) and has multiple phase modules (210), each formed by a plurality of sub-modules (610) which are electrically connected in series and have respective multiple semiconductor switches (710, 710') and a respective energy accumulator (724), at which there is an intermediate circuit voltage (Uzkn), wherein, for each phase module (210), the phase module current (IP) is regulated based on a predetermined target current (IS). In order to prevent a saturation of the transformer when using a multi-stage converter, according to the invention, for each phase module (210), a) the intermediate circuit voltages (Uzkn) of the sub-modules (610) are measured, b) the amplitudes of the network-frequency alternating component are determined, and c) the DC current output (Idc) is determined based on the amplitudes and the phase module voltage (UP) associated with the phase module (210), and according to the invention, based on the determined DC current outputs (Idc) of the phase modules (210), the associated target currents (IS) are corrected in such a way that the DC current outputs (Idc) for all phase modules (210) are regulated to the same current level.