A NEW SIX-SWITCH FIVE-LEVEL ACTIVE NEUTRAL POINT CLAMPED INVERTER FOR PV APPLICATIONS
Abstract
Multilevel inverters are one of the preferred solutions for medium-voltage and high-power applications and have found successful industrial applications. Five-level Active Neutral Point Clamped inverter (5L-ANPC) is one of the most popular topologies a five-level inverters. A Six-Switch 5LANPC (6S-5L-ANPC) topology is proposed. Compared to the conventional 5L-ANPC inverters, the 6S-5L-ANPC reduces two active switches and has lower conduction loss. The proposed modulation enables the 6S-5L-ANPC inverter to operate under both active and reactive power conditions. The FC capacitance is designed under both active and reactive power conditions. The analysis shows the proposed topology is suitable for photovoltaic (PV) grid-connected applications. A 1KVA single-phase experimental prototype is built to verify the validity and flexibility of the proposed topology and modulation method.
EXISTING SYSTEM:
another type of classic multilevel inverters, the FC inverter produces the required output voltage levels by summing the FC and DC-link voltages. The increased number of capacitors in higher levels leads to complex control method to balance the voltages of both DC-link capacitors and FCs. The higher switching frequency to keep the capacitors properly balanced and capacitors maintenance costs result in the less industrial penetration of FC type. The CHB multilevel inverters use series-connected Hbridge cells with an isolated dc voltage sources connected to each cell. Similarly, to have more output levels, more cells are needed. This will lead to impracticality of this type of topology since more isolated DC sources are required. A generalized multilevel inverter topology is presented in, which is capable of balancing each voltage level regardless of the inverter control and load characteristics. The aforementioned conventional multilevel inverters can be derived from this generalized inverter topology. Besides, some new multilevel topologies, such as Multilevel Modular Capacitor Clamped (MMCC) and zigzag multilevel inverter can also be derived using the method in. Hybrid multilevel inverters topologies combine some features of NPC and FC that provides the possibilities to take advantages of both topologies. A hybrid topologies, the Five-Level Active Neutral Point Clamped (5LANPC) inverter provides an acceptable compromise between cost and performance . As shown, the 5L-ANPC inverter combines a 3L-ANPC leg with a 3L-FC power cell. The number of levels is increased with the levels introduced by the FC. This topology enables the modularity factor that is lacking in the NPC type inverter by adding the FC to reach higher level without adding series-connected diodes. In addition, the ANPC inverters splits the DC-link into two capacitors, so the complexity of DC-link capacitor voltages balancing is reduced compared to the conventional NPC and FC type inverters which need four DC capacitors in series. Due to the reduced costs, volume and control complexity, the 5L-ANPC inverter is receiving more attention recently and is already commercially used for medium power level industrial applications
PROPOSED SYSTEM:
The redundant switching states in ANPC inverters allow the voltage across FC to be regulated. To generate the switching pulses and simultaneously regulate the FC voltage, a variety of modulation strategies have been presented such as carrier-based Pulse Width Modulation (PWM), modified carrier-based PWM, real time THD minimization and selective harmonic elimination PWM. From Fig. 2, it is observed that for the existing conventional 5L-ANPC inverter topologies, at least eight active switches are required. And from the point view of industrial application, it would be more desirable if the cost of the system can be reduced. The motivation of this paper is to reduce the number of active switches. For PV application, the output current and grid voltage are generally in phase, so some of reactive current paths can be removed. Based on this, a novel Six-Switch Five-Level ANPC (6S-5L-ANPC) inverter topology is proposed. Compared to the conventional 5L- ANPC inverter, the proposed topology requires only six active semiconductor switches, reducing the volume of system. Additionally, The proposed topology requires only six active semiconductor switches, reducing the volume of system. Additionally, with the proposed modulation method applied to the proposed 6S-5L-ANPC inverter, the system is capable of operating under both active and reactive power conditions.
CONCLUSION
In this paper, a novel 6S-5L-ANPC inverter topology has been proposed. As compared with the conventional 5L-ANPC inverter, it requires only 6 switches for single phase, a reduction from 8 switches. The operating principles and switching states are presented. The results of comparison between 6S-5L-ANPC and the conventional 5L-ANPC topologies show that 6S-5L-ANPC topology has lower conduction loss and thus higher efficiency in high power condition. The specific modulation strategy of 6S-5L-ANPC inverter under reactive power operation has been proposed. Issues related to the DC-link capacitors and FC voltages balancing and the maximum reactive power capability are discussed. The equations to calculate the FC capacitance value in active and reactive power conditions are provided. Computer simulation and experimental prototype based on a single phase 1KVA prototype have been carried out in both active and reactive power conditions to demonstrate the reliability of the proposed topology and modulation method.
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