Three-Phase Bridge Converter Control Under Phase Overcurrent
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Solution Overview
Problem
Three-phase converters face challenges in maintaining dynamic control behavior during overload states, particularly when network voltage errors occur, leading to increased costs due to the need for oversized IGBT power switches.
Innovation Solution
The procedure involves monitoring individual phases for overload states and continuing operation with non-overloaded phases, using modified target voltage values to control the bridge circuit. These modified values are determined by transforming specified target voltage values into a differential voltage pointer and a modified target voltage pointer in the αβ coordinate system, taking into account maximum phase voltages in overloaded phases.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the bridge circuit is completely blocked when overload occurs in one phase, then all power breakers are protected from damage, but the dynamic control behavior deteriorates and the converter cannot respond to grid voltage drops
Solution Approach 1:
The invention divides the protection and control into three independent phases. When overload occurs in one phase, only that specific phase is blocked while the other two phases continue to operate with full control capability. This segmentation allows the system to maintain dynamic control behavior through the healthy phases while still providing protection for the overloaded phase, resolving the contradiction between complete protection and operational responsiveness.
Solution Approach 2:
The invention implements dynamic phase-dependent control where the control behavior adapts based on the overload status of each individual phase. The control unit applies different control strategies to each phase: blocked control for overloaded phases and full dynamic control for healthy phases. This dynamic approach enables the converter to maintain optimal control behavior in healthy phases while protecting overloaded phases, eliminating the need to completely block the entire bridge circuit.
2Reliability
If IGBT power switches are dimensioned for maximum current capacity, then the bridge circuit can handle overload conditions, but the costs increase significantly
Solution Approach 1:
The invention applies partial action by blocking only the specific phase experiencing overload rather than blocking all phases or requiring all phases to be dimensioned for maximum overload capacity. This allows the system to handle overload conditions in individual phases using standard-rated IGBTs, while healthy phases continue normal operation. The cost is reduced because IGBTs don't need to be oversized for all phases, yet reliability is maintained through selective phase blocking.
3Reliability
If the entire bridge circuit is shut down during overload, then all circuit breakers are protected, but the converter cannot provide grid support functions during voltage faults
Solution Approach 1:
The invention segments the bridge circuit into independent controllable phases. When overload occurs, only the affected phase is blocked while the other two phases remain operational and can continue to provide grid support functions such as reactive power compensation and voltage support. This segmentation resolves the contradiction by allowing the converter to maintain productivity in healthy phases while protecting the overloaded phase.
Solution Approach 2:
The control unit acts as an intermediary that selectively manages each phase based on its overload status. It coordinates between the protection requirement (blocking overloaded phases) and the productivity requirement (maintaining grid support in healthy phases). The control unit enables the converter to fulfill grid support obligations during voltage faults by directing healthy phases to provide reactive current while blocking only the overloaded phase.
Data Source
Figure 1~2
Figure 3~4
Figure 5~6
AI summary
The invention relates to a method for operating a three-phase converter on a three-phase load, in particular an electrical network, the three-phase converter comprising a DC link, at least one three-phase bridge circuit (1) and at least one control unit (4) for controlling the bridge circuit (1); in the at least one bridge circuit (1) at least two power switches (sw1, sw2, sw3, sw1', sw2', sw3') which are series-connected are provided for each phase (L1, L2, L3) and are connected in parallel to the DC link (VDC); in the method, depending on predetermined target voltage values (v1, v2, v3) of the three phases of the converter, the power switches (sw1, sw2, sw3, sw1', sw2', sw3') of each individual phase (L1, L2, L3) are controlled via the control unit (4), such that a three-phase AC voltage is generated on the three-phase load via switching operations of the power switch (sw1, sw2, sw3, sw1', sw2', sw3'). The object of the invention, which is to provide a method for operating a three-phase converter on a three-phase load, in particular an electrical network, by means of which a very good dynamic closed-loop control behaviour can be obtained in spite of cost-effective dimensioning of the IGBT power switch, is achieved by a method according to claim 1.