Abstract
This paper deals with the three-phase current reconstruction method under the low modulation index operation of three-phase three-level PWM inverters by using the single-shunt current signal measurement. The shunt is placed in a DC-link. The proposed reconstruction method is based on the combination of collinear vector injection and shifting of Space Vector Modulation (SVM) signals. The method offers a good solution for the area where the small modulation index appears. In this case, a lack of measurement time exists due to the narrow triggering pulses. This approach was studied theoretically and verified by laboratory experiments.
Highlights
This paper deals with the current reconstruction method for three-level inverters by using the single-shunt measurement placed in the inverter DC-bus
Space vector modulation using a shift approach [2] cannot be applied as it causes the increase of the current ripple, which can lead to the current reconstruction errors
The goal of the presented reconstruction method was to develop the Space Vector Modulation (SVM) method for a low modulation index converter operation when the single-shunt current measurement signal was applied to a three-level inverter
Summary
This paper deals with the current reconstruction method for three-level inverters by using the single-shunt measurement placed in the inverter DC-bus. The authors in [25] described the shifting of the SVM signals to ensure enough time for current measurement, which cannot be applied to the low modulation index operating area since the duty cycles for all three phases are similar and around 50%. The three-phase currents’ reconstruction is inaccurate during the low modulation index operation, due to the short time interval between two pulses’ edges To improve this drawback, a method is proposed that generates an arbitrary voltage vector using Basic Voltage Vectors (BVVs) and collinear vectors, which guarantee the minimum time window for current measurement. The described algorithm is presented with the flowchart diagram shown, where the duty cycle decision for SVM for low modulation index values can be seen If both duty cycles are positive, the reference voltage vector is positioned inside Region 2. ~ 6 inside Region 3, and CIBVVs, vectors V5 and V6 are used inside Region 2, vectors V vectors V2 and V3 inside Region 4
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