Parallel Inverter Phase Current Control via Direct Hysteresis
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Solution Overview
Problem
Existing control methods for phase currents of three-phase inverters connected in parallel struggle with circular currents, which reduce overall power and contribute to harmonic loads, and require complex communication and precalculation of pulse patterns.
Innovation Solution
A direct hysteresis current control method where the measured current space vector is maintained within a hysteresis window about a target current space vector, with the selection of phase currents varied to eliminate zero system currents and reduce switching losses, allowing independent control of each inverter without communication.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If indirect current control with pulse width modulation is used, then the pulse patterns can be precalculated, but the system dynamics are reduced and robustness decreases
Solution Approach 1:
The patent replaces the mechanical precalculation approach of indirect PWM control with a direct hysteresis current control mechanism. Instead of precalculating pulse patterns based on mechanical timing, the system directly compares measured current space vectors with target values and generates switching signals in real-time, achieving both simplicity and high dynamics through this substitution of control methodology
Solution Approach 2:
The direct hysteresis current control allows each inverter to independently regulate its own phase currents without requiring coordinated precalculation with other inverters. Each inverter self-adjusts its switching signals based on its own current measurements and hysteresis band, eliminating the need for complex inter-inverter communication and precalculation while maintaining high dynamic response
2Loss of information
If all three phase currents are measured for every inverter, then complete current information is obtained, but circular currents increase and system complexity increases
Solution Approach 1:
The patent applies different measurement strategies to different inverters based on their roles. The first inverter measures all three phase currents to establish a reference, while subsequent inverters measure only two phase currents assuming the third can be derived. This local differentiation reduces overall system complexity and circular currents while maintaining sufficient current information for effective control
Solution Approach 2:
The patent changes the measurement parameters dynamically by varying which two phase currents are measured for space vector formation in subsequent inverters. This parameter variation, combined with the assumption that phase currents sum to zero, allows the system to operate with reduced measurement complexity while maintaining control effectiveness and minimizing circular currents
3Adaptability or versatility
If inverters are controlled independently without communication, then system modularity increases, but coordination between inverters becomes challenging
Solution Approach 1:
The patent creates an equipotential control framework where all inverters operate from a common reference current space vector derived from the first inverter's measurements. This common reference ensures coordinated operation among independently controlled inverters, maintaining reliability and proper current sharing without requiring direct communication between inverters, thus preserving modularity while ensuring coordination
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach enhances dynamics and robustness, reduces circular currents, and minimizes switching losses by allowing all phase currents to approximate their target values, thereby increasing system modularity and reducing effort in system realization.
Implementation Method 1
a measured current space vector for measured values of the phase currents of the inverter is held within a hysteresis window about a target current space vector
Data Source
AI summary
Disclosed is a method for controlling phase currents of a plurality of three-phase inverters connected in parallel. The phase currents of each inverter are controlled by direct hysteresis current control wherein an actual current space vector for actual values of the phase currents of each inverter is maintained about a target current space vector within a hysteresis window. The measured current space vector of a first inverter is formed by all three phase currents of the first inverter. The actual current space vector of each additional inverter is formed from exactly two phase currents of the respective additional inverter under the proviso that all three phase currents of the additional inverters add up to zero. The selection of the two phase currents from which the actual current space vector is formed, is varied.