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Feedforward of Grid Line-to-Line Voltages for Grid-Connected Inverter under the Weak Grid Condition
Alireza Shayestehfard,Hamza Belkamel,Saad Mekhilef,Hazlie Bin Mokhlis,Mutsuo Nakaoka,Koki Ogura 전력전자학회 2015 ICPE(ISPE)논문집 Vol.2015 No.6
Feedforward control is reliable for rejecting fast and dynamic voltage disturbances in the grid. Mainly this scheme is implemented based on phase voltages of the wye connected configuration. Under unbalanced and distorted grid-condition, the online conversion of line-to-line values into the phase values is unworkable. In order to exploit full advantages of feedforward controller, an appropriate modulator is needed. In this paper the feedforward of grid line-to-line voltages is used in lieu of phase voltages. The introduced feedforward method is implemented with implicit zero-sequence discontinuous pulse width modulation (IZDPWM) technique that is compatible for grid-connected inverters. Regardless the grid topology, IZDPWM exactly copies the distorting harmonics of the grid voltage. Hence, a sinusoidal current is injected to the grid. Moreover, for measuring the grid line-to-line voltages two sensors are required; hence overall system cost is reduced and control system reliability is increased.
Design and Implementation of a New Multilevel DC-Link Three-phase Inverter
Ammar Masaoud,Hew Wooi Ping,Saad Mekhilef,Ayoub Taallah,Hamza Belkamel 전력전자학회 2014 JOURNAL OF POWER ELECTRONICS Vol.14 No.2
This paper presents a new configuration for a three-phase multilevel voltage source inverter. The main bridge is built from a classical three-phase two-level inverter and three bidirectional switches. A variable DC-link employing two unequal DC voltage supplies and four switches is connected to the main circuit in such a way that the proposed inverter produces four levels in the output voltage waveform. In order to obtain the desired switching gate signals, the fundamental frequency staircase modulation technique is successfully implemented. Furthermore, the proposed structure is extended and compared with other types of multilevel inverter topologies. The comparison shows that the proposed inverter requires a smaller number of power components. For a given number of voltage steps N, the proposed inverter requires N/2 DC voltage supplies and N+12 switches connected with N+7 gate driver circuits, while diode clamped or flying capacitor inverters require N-1 DC voltage supplies and 6(N-1) switches connected with 6(N-1) gate driver circuits. A prototype of the introduced configuration has been manufactured and the obtained simulation and experimental results ensure the feasibility of the proposed topology and the validity of the implemented modulation technique.
Design and Implementation of a New Multilevel DC-Link Three-phase Inverter
Masaoud, Ammar,Ping, Hew Wooi,Mekhilef, Saad,Taallah, Ayoub,Belkamel, Hamza The Korean Institute of Power Electronics 2014 JOURNAL OF POWER ELECTRONICS Vol.14 No.2
This paper presents a new configuration for a three-phase multilevel voltage source inverter. The main bridge is built from a classical three-phase two-level inverter and three bidirectional switches. A variable DC-link employing two unequal DC voltage supplies and four switches is connected to the main circuit in such a way that the proposed inverter produces four levels in the output voltage waveform. In order to obtain the desired switching gate signals, the fundamental frequency staircase modulation technique is successfully implemented. Furthermore, the proposed structure is extended and compared with other types of multilevel inverter topologies. The comparison shows that the proposed inverter requires a smaller number of power components. For a given number of voltage steps N, the proposed inverter requires N/2 DC voltage supplies and N+12 switches connected with N+7 gate driver circuits, while diode clamped or flying capacitor inverters require N-1 DC voltage supplies and 6(N-1) switches connected with 6(N-1) gate driver circuits. A prototype of the introduced configuration has been manufactured and the obtained simulation and experimental results ensure the feasibility of the proposed topology and the validity of the implemented modulation technique.