Multilevel inverters are receiving more
attentions nowadays as one of preferred solutions for medium and high power
applications. As one of the most popular hybrid multilevel inverter topologies,
the Five-Level Active-Neutral-Point-Clamped inverter (5L-ANPC) combines the
features of the conventional Flying-Capacitor (FC) type and
Neutral-Point-Clamped (NPC) type inverter and was commercially used for
industrial applications. In order to further decrease the number of active
switches, this paper proposes a Seven-Switch 5L-ANPC (7S-5L-ANPC) topology,
which employs only seven active switches and two discrete diodes. The analysis
has shown a lower current rating can be selected for the seventh switch under
high power factor condition, which is verified by simulation results. The
modulation strategy for 7S-5L-ANPC inverter is discussed. A 1KVA single-phase
experimental prototype is built to verify the validity and flexibility of the
proposed topology and modulation method.
KEYWORDS:
1. Multilevel inverter
2. Active-Neutral-Point-Clamped (ANPC) inverter
3. Flying-Capacitor
4. Pulse-Width-Modulation (PWM)
SOFTWARE: MATLAB/SIMULINK
Fig. 2. Simulation results under unity power factor condition. (a)
Output voltage and FC voltage. (b) T7 current in case 1. (c) T7 current in case
2. (d) T7 current in case 3. (e) T7 current in case 4.
Fig. 3. Simulation results under reactive power condition (PF = 0.9,
capacitive). (a) Output voltage and FC voltage. (b) T7 current in case 1. (c)
T7 current in case 2. (d) T7 current in case 3. (e) T7 current in case 4
Fig. 4. Simulation results under reactive power condition (PF = 0). (a)
Output voltage and FC voltage. (b) T7 current in case 1. (c) T7 current in case
2. (d) T7 current in case 3. (e) T7 current in case 4.
Fig. 5. Experimental results under unity power factor condition:
waveforms of inverter output voltage, grid voltage, FC voltage and output
current.
CONCLUSION:
In this paper, a novel 7S-5L-ANPC inverter topology
has been proposed. As compared with the conventional 5L-ANPC inverter, it
requires seven active switches for single phase and a low current rating switch
can be selected for the seventh switch under high power factor situation. The
operating principles and switching states are presented. The detailed
comparison between the proposed topology and the conventional 5L-ANPC
topologies in terms of voltage stress and efficiency is made. The specific
modulation strategy of 7S-5L-ANPC inverter under reactive power operation has
been proposed. Computer simulation and experimental prototype based on a single
phase 1KVA prototype have been carried out in unity power factor condition and
reactive power condition. The validity and advantages of the proposed topology
and modulation method are demonstrated.
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