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Operation and Control Scheme of a Five-Level Hybrid Inverter for Medium-Voltage Motor Drives
Dao, Ngoc Dat,Lee, Dong-Choon Institute of Electrical and Electronics Engineers 2018 IEEE transactions on power electronics Vol.33 No.12
<P>This paper proposes a control method for a five-level hybrid flying-capacitor (5L-HFC) inverter, of which structure stems from the conventional five-level active neutral-point-clamped (5L-ANPC) topology by dividing the dc-link stage into three series-connected capacitors. In this inverter, the voltage stress on the power switches connected to the dc link is reduced by a half compared with that of the 5L-ANPC topology, thus the lower number of equally voltage-rated power devices can be employed. Also, the power losses in the 5L-HFC inverter are more evenly distributed than in the 5L-ANPC. In order to balance the dc-link capacitor voltages, a third-order harmonic offset injection is applied. When a diode rectifier is used to supply the dc bus voltage, the balancing method is not effective if the modulation index is higher than 0.64. Thus, an auxiliary circuit is needed to support the balancing of the dc-link capacitor voltages. However, the unbalancing problem can be overcome in a full-range operation without the auxiliary circuit if the back-to-back configuration is utilized. Finally, simulation and experiment results have verified the performance of the 5L-HFC inverter with the proposed control method.</P>
Modulation and Control of Single-Stage Bidirectional Isolated Direct-Matrix-based AC-DC Converters
Ngoc Dat Dao,Dong-Choon Lee 전력전자학회 2019 ICPE(ISPE)논문집 Vol.2019 No.5
In this paper, a single-stage bidirectional isolated direct-matrix-based AC-DC converter with a power factor correction is proposed. This AC-DC converter can control not only the DC output voltage or current, but also the AC grid current with a single conversion stage, which helps to achieve a higher power density with a lower complexity. A modulation scheme that can achieve a zero voltage switching (ZVS) or zero current switching (ZCS) operation in all switches is developed. Hence, the switching frequency of the converter can be increased higher, leading to the smaller passive components. The proportionalresonant (PR) controller is utilized to achieve the unity power factor and low total harmonic distortion (THD) current. The proposed topology has been verified by simulation results for a 3.3 kW system.
Common-Mode Voltage Reduction Based on Space Vector Modulation for Five-Level Hybrid Inverters
Jonathan Pribadi,Ngoc Dat Dao,Dong-Choon Lee 전력전자학회 2019 ICPE(ISPE)논문집 Vol.2019 No.5
This paper proposes a common-mode voltage (CMV) reduction scheme based on a space vector modulation for a five-level hybrid flying-capacitor inverter (5L-HFCI). In the 5L-HFC inverter, the switching states are modified for solving the sequence issue while keeping the flying-capacitor voltage ripple below 4% of the reference value. The CMV can be controlled at the specified limit by eliminating a certain number of voltage vectors. In comparison with the in-phase disposition carrier-based modulation, the CMV peak value of the proposed method is reduced by 50%. The effectiveness of the proposed technique has been verified by simulation results.
Carrier Phase-Shift PWM to Reduce Common-Mode Voltage for Three-Level T-Type NPC Inverters
Tuyen D. Nguyen,Dzung Quoc Phan,Dat Ngoc Dao,Hong-Hee Lee 전력전자학회 2014 JOURNAL OF POWER ELECTRONICS Vol.14 No.6
Common-mode voltage (CMV) causes overvoltage stress to winding insulation and damages AC motors. CMV with high dv/dt causes leakage currents, which create noise problems for equipment installed near the converter. This study proposes a new pulse-width modulation (PWM) strategy for three-level T-type NPC inverters. This strategy substantially eliminates CMV. The principle for selecting suitable triangle carrier signals for the three-level T-type NPC is described. The proposed method can mitigate the peak value of CMV by 50% compared with the phase disposition pulse-width modulation method. Furthermore, the proposed method exhibits better harmonic spectrum and lower root mean square value for the CMV than those of the reduced-CMV method on the basis of the phase opposition disposition PWM scheme with modulation index higher than 0.5. The proposed modulation can easily be implemented using software without any additional hardware modifications. Both simulation and experimental results demonstrate that the proposed carrier phase-shift PWM method has good output waveform performance and reduces CMV.
Carrier Phase-Shift PWM to Reduce Common-Mode Voltage for Three-Level T-Type NPC Inverters
Nguyen, Tuyen D.,Phan, Dzung Quoc,Dao, Dat Ngoc,Lee, Hong-Hee The Korean Institute of Power Electronics 2014 JOURNAL OF POWER ELECTRONICS Vol.14 No.6
Common-mode voltage (CMV) causes overvoltage stress to winding insulation and damages AC motors. CMV with high dv/dt causes leakage currents, which create noise problems for equipment installed near the converter. This study proposes a new pulse-width modulation (PWM) strategy for three-level T-type NPC inverters. This strategy substantially eliminates CMV. The principle for selecting suitable triangle carrier signals for the three-level T-type NPC is described. The proposed method can mitigate the peak value of CMV by 50% compared with the phase disposition pulse-width modulation method. Furthermore, the proposed method exhibits better harmonic spectrum and lower root mean square value for the CMV than those of the reduced-CMV method on the basis of the phase opposition disposition PWM scheme with modulation index higher than 0.5. The proposed modulation can easily be implemented using software without any additional hardware modifications. Both simulation and experimental results demonstrate that the proposed carrier phase-shift PWM method has good output waveform performance and reduces CMV.