Abstract
This paper presents three phase current reconstruction methods for a three-level neutral point clamped inverter (NPCI) by measuring the voltage of a shunt resistor placed in the neutral point of the inverter. In order to accurately acquire the phase currents from the shunt resister, the dwell time of the active voltage vectors need to exceed the minimum time. On the other hand, if the time of active voltage is shorter than the minimum time, the current measurement becomes impossible. In this paper, unmeasurable regions for current are classified into three areas. Area 1 is a region in which both phase currents can be measure. Therefore, it is not necessary to restore the current. In Area 2, only one phase current can be measured. Thus, an estimation or restoration method is needed to measure another phase current. In this paper, the current estimation method using an electrical model of the motor is proposed. Area 3 is the region in which both phase currents can not be measured. In this case, it is necessary to move the voltage vector to the current measurable area by injecting the voltage. In this paper, Area 3 is divided into 36 sectors to inject optimal voltage. The proposed methods have the advantages of high current measurement accuracy and low THD (total harmonic distortion). The effectiveness of the proposed methods are verified through experimental results.
Highlights
Two-level inverters are used in most home appliances, such as washing machines, refrigerators, and air conditioners, due to their simple structure, and high reliability and performance.in order to overcome the limitations of the efficiency and harmonics of the two-level inverter, three-level inverters have been recently investigated
The system was composed of the three-level inverter, proposed current reconstruction method
This paper proposed a phase current reconstruction method using a neutral shunt resistor, which lowers both the cost and volume of a three-level inverter system
Summary
Two-level inverters are used in most home appliances, such as washing machines, refrigerators, and air conditioners, due to their simple structure, and high reliability and performance.in order to overcome the limitations of the efficiency and harmonics of the two-level inverter, three-level inverters have been recently investigated. The three-level neutral point clamped inverter (NPCI) has a structure characteristic of having a neutral point in the direct current (DC). The neutral point is connected to each phase output node by the clamp diodes and switches. Due to this structural feature, the three-level NPCI can output either Vdc /2 or −Vdc /2 by turning on the two switches located in the upper or lower side of a phase. When the switches of Sx3 and Sx4 are turned on, the node voltage of Energies 2018, 11, 2616; doi:10.3390/en11102616 www.mdpi.com/journal/energies
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