The seven-level flying capacitor based ANPC converter for grid intergration of utility-scale PV systems

Abstract

The installed capacity of grid connected PV plants has increased significantly over the past few years and is expected to continue its growth over the next decade due to the continuous demand for renewable energy and distributed generation systems. This paper presents a seven-level flying capacitor (FC) based active neutral point clamped (ANPC) converter for the connection of utility-scale PV system to the electricity grid. The multilevel voltage output of the topology provides high quality waveforms while maintaining the operational characteristics of NPC based converters for PV systems. The converter topology together with a method to regulate the FC voltages to their reference values and an optimal third harmonic injection for utilization of the DC-link voltage are presented. Simulation results for the operation of the grid connected converter under steady state and transient operation are provided in order to demonstrate the operation and performance of the topology in grid connected applications. © 2012 IEEE. Abstract-The installed capacity of grid connected PV plants has increased significantly over the past few years and is expected to continue its growth over the next decade due to the continuous demand for renewable energy and distributed generation systems. This paper presents a seven-level flying capacitor (FC) based active neutral point clamped (ANPC) converter for the connection of utility-scale PV system to the electricity grid. The multilevel voltage output of the topology provides high quality waveforms while maintaining the operational characteristics of NPC based converters for PV systems. The converter topology together with a method to regulate the FC voltages to their reference values and an optimal third harmonic injection for utilization of the DClink voltage are presented. Simulation results for the operation of the grid connected converter under steady state and transient operation are provided in order to demonstrate the operation and performance of the topology in grid connected applications.

A Survey Report on MultiiLevel-Inverter Topologies

“…Flying-Capacitor Multiilevel-Inverter(FCMLI) or also called Capacitor-Clamped MultiiLevel-Inverter, is analogous in appearance to Diode-Clamped Multi-Level-inverter, but instead of diodes it uses balancing capacitor to keep voltages at the required value [1]. Figure 3, shows a schematics of Flying-Capacitor MultiiLevel-Inverter, in which charging and Dis-charging of the capacitors connected to neutral point determines the level of voltage [31,32].When semi-conductor switches and is Switched-ON, FlyinggCapacitors in link start charging. When the same switches is switched-off, semiconductor switches and charges the flyingccapacitor link, while in switched-off condition of these switches, the same capacitors start dis-charging [31].…”

“…Multi-levels of voltage at the output of MLI is produced due to different timeconstants of each Clamping-Capacitor. The number of Clamping-Capacitors required to obtain -levels is [32]. Similarly the number of capacitors required is ( ) , as like for that of DiodeeClamped MLI.…”

“… Active and reactive power flow is controllable [31].  No need of T/F, to get the desired number-of voltage levels [31,32].  No need of Clamping-Diode [31].…”

Symmetrical three‐phase seven‐level E‐type inverter for PV systems: design and operation

“…For instance, the cascaded H‐bridge converter in [15, 16] is widely used in PV applications, thanks to its ability to be fed by separated DC sources, resulting in individual module maximum power point tracking capability. Recently other multilevel topologies such as neutral point clamped (NPC) converter [17], flying capacitor (FC) converters [18], T‐Type converters [12, 19, 20], modular multilevel converters [10, 21], and hybrid multilevel converters [22, 23] are used in PV applications.…”

“…Over the last few decades, many multilevel and multi-cell topologies have been developed being still under investigation [9,10]. Each one of multilevel topologies has its own pros and cons which gives great flexibility to select the right topology for each application [14][15][16][17][18][19][20][21][22][23]. For instance, the cascaded H-bridge converter in [15,16] is widely used in PV applications, thanks to its ability to be fed by separated DC sources, resulting in individual module maximum power point tracking capability.…”