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Abstract—This paper proposes a triangle carrier based
discontinuous PWM (TCB-DPWM) implement method for three-
level neutral-point-clamped (3L-NPC) inverters. The function
equivalent relationship of proposed TCB-DPWM and space vector
based discontinuous PWM (SVB-DPWM) is mathematically
analyzed in this paper. The proposed TCB-DPWM method
effectively simplified the implementation of the SVB-DPWM by
injecting twice common mode voltages (CMVs) to original
modulation signals, where different DPWM methods can be easily
obtained in a unified scheme by setting different values of
proportional allocation factor for small vectors in different sectors.
In addition, a TCB-DPWM based neutral point voltage balancing
method is investigated to demonstrate its application. The polarity
of the CMV injection is regulated according to the polarity of the
proportional allocation factor to realize the neutral point voltage
balancing. Finally, the proposed TCB-DPWM and neutral point
voltage balancing method are both verified by simulation and
experimental results. The results show that the proposed TCB-
DPWM can effectively simplify the implementation of modulation
and improve system efficiency.
Index Terms—Three-level neutral-point-clamped inverter,
voltage source inverter, discontinuous PWM, neutral point voltage
balancing.
I. INTRODUCTION
hree-level neutral-point-clamped (3L-NPC) voltage source
inverters are widely used in many medium- and high-power
applications. Compared with traditional two-level inverters, the
3L-NPC inverter is with better performances of efficiency,
harmonics and power capability [1-3]. Recently, the T-type 3L-
NPC is proposed to alternate the traditional NPC to improve the
efficiency [4] [5]. The topology diagram of a T-type 3L-NPC
inverter is shown in Fig.1. The main advantage of the T-type
3L-NPC inverter is the lower voltage rating of the employed
devices, as the two switches of neutral point have a peak inverse
voltage of half of that required in the conventional 3L-NPC
inverter. Furthermore, the structure of T-TYPE 3L-NPC
inverter provides lower conduction losses, compared to
conventional 3L-NPC of the same ratings [6].
This work was supported in part by the National Natural Science Foundation
of China (No.51707030), the Sichuan Science and technology support program
(No. 2016GZ0027) and the Fundamental Research Funds for the Central
Universities of China (No. ZYGX2015J075). A part of work in this paper was
exhibited in the conference of APEC 2017, March 26th – 30th, Tampa, FL,
USA.
K. Li, M. Wei, C. Xie are with School of Automation Engineering,
University of Electronic Science and Technology of China, Chengdu, 611731,
It is well-known that the performance of inverter depends on
the modulation strategy. In terms of modulation signal forms,
modulation strategies can be classified into two categories
including continuous PWM (CPWM) and discontinuous PWM
(DPWM). In CPWM, the modulating signals are never clamped
during the period of the fundamental voltage, whereas in
DPWM, the modulating signals could be clamped to constant
voltage levels [7]. Sinusoidal triangle pulse width modulation
(SPWM) and space vector pulse width modulation (SVPWM)
are two typical CPWMs which are widely used in many
applications because of its low output voltage/current harmonic
distortion. For three-phase inverters with DPWM, each phase is
clamped to one constant voltage level for one-third of the
fundamental period. Thus, compared with the losses of the
inverter with CPWM, the switching losses of the inverter with
DPWM are significantly reduced at the average of 33.3% [7-8].
The DPWM is successfully used in conventional two-level
inverters [7-14]. If different phases are clamped to different
voltage levels at different angles of the reference vector,
different types of DPWM will be obtained. Generally speaking,
there is four basic space vector based DPWMs for two-level
inverters: DPWM I [10], DPWM II [11], DPWM III [12],
DPWM IV [7]. Different DPWM methods performances
difference. With different objectives of optimization, different
optimized DPWMs are investigated in literature [7, 13-14]. In
order to minimize the switching losses, a direct digital
China (e-mail:autolikai@gmail.com; 403188925@qq.com; c.xie@uestc.edu.
cn ).
F. Deng is with the Department of Electrical Engineering, Southeast
University, Nanjing, 210096, China (dfjqfa@163.com)
J. M. Guerrero and J. C. Vasquez are with the Department of Energy
Technology, Aalborg University, 9220 Aalborg East, Denmark (e-mail:
joz@et.aau.dk; juq@et.aau.dk).
Triangle Carrier based Discontinuous PWM for
Three-Level NPC Inverters
Kai Li, Member, IEEE, Min Wei, Chuan Xie, Member, IEEE, Fujin Deng, Member, IEEE,
Josep M. Guerrero, Fellow, IEEE and Juan C. Vasquez, Senior Member, IEEE.
T
Fig.1. The topology of the T-type 3L-NPC inverter.