MATLAB Simulation of Sinusoidal Pulse Width Modulation based Three and Seven Level Current-Source Inverters

Here, a multilevel current-source inverter (MCSI) topology is analyzed. Here, the issue of constructing a novelmodular single-rating inductor MCSI has been explored. The proposed topology isbuilt with identical modules where all inductors carry the sameamount of current, simplifying the construction and operationof industrial applications with higher efficiency. A new state machine approach with a proper implementation of the phase-shifted carrier-sinusoidal pulse width modulation (PSC-SPWM) allows both current balancein all modules and effective switching-frequency minimization. The performance of the MSCI proposed is simulated with MATLAB. As a result of this topology and PSC-SPWM utilization, current balance was achieved in both main and sharing inductors, even under load and operating point changes. The switching frequency was drastically reduced with a new state machine approach, taking the advantage of the three different zero-states of the topology. The topology adopted allows operation with high efficiency by reducing the current through the inductors and the losses in the switches .


Introduction
The Inverter is an electrical device which converts direct current (DC) to alternate current (AC).
The converted AC can be at any required voltage and frequency with the use of appropriate transformers, switching, and control circuits.The inverter is used for emergency backup power in a home.The inverter is used in some aircraft systems to convert a portion of the aircraft DC power to AC. Static inverters have no moving parts and are used in a wide range of applications, from small switching power supplies in computers, to large electric utilityhigh-voltage direct current applications that transport bulk power.
Inverters are commonly used to supply AC power from DC sources such as solar panels or batteries.

Multi-Level Inverter
The Multi-level inverter is used for industrial applications as alternative in high power and medium voltage situations.As the number of levels increases, the synthesized output waveform has more steps, which produces a staircase wave that approaches the desired waveform.In [1,11], design and implementation of power stages of forced commutated current source converter is explained.On state losses and switching losses-based design of devices is presented in [2,13].In [3,12], it is described that Emitter Turnoff Thyristor (ETO) has a very good storage time dispersion of 100ns and can be further reduced through adjustment of the emitter switch gate resistance.It is evaluated in [4,14] that switching devices based on wide bandgap materials such as silicon carbide (SiC) offer a significant performance improvement on the switch level compared with Si devices.In [5,15], it is presented that the design and experimental analysis of a device, self-powered emitter turn-off thyristor (SPETO) which is high powered and different from the conventional high-power devices.References [6,16] to [10,11] explains about different concepts and topologies related to multilevel inverters.

Sinusoidal pulse width modulation (SPWM)
SPWM or sinusoidal pulse width modulation is widely used in power electronics to digitize the power so that a sequence of voltage pulses can be generated by the on and off of the power switches.Here fig. 1 represents a three level CSI in which the number of levels in the output current are three.A single module is arranged in order to obtain the three levels in the output level.To generate this signal, triangle wave as a carrier signal is compared with the sinusoidal wave, whose frequency is the desired frequency.The gating signals are generated by comparing a sinusoidal reference signal with a triangular carrier wave of frequency.The frequency of reference signal determines the inverter output frequency and its peak amplitude controls the modulation index and output voltage.
The number of levels n in the output current can be determined according to the number of modules m as, n=2m+1.The three levels in output current are obtained from the number of modules by using the following formula n=2*m+1 Here n is the number of levels in the output current and m is the number of modules Here m=1; n=2*1+1=2+1=3 Therefore, the number of levels in the output current=3 is obtained by using a single module

Fig.2 Simulation diagram of Seven level Current Source Inverter
Here fig. 2 represents a seven level CSI in which the number of levels in the output current are seven.
In the above figure a three module is arranged in order to obtain the seven levels in the output level.

Fig. 1
Fig.1 Simulation diagram of three level Current Source Inverter

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Here the seven levels in output current are obtained from the number of modules by using the following formula n=2*m+1 with n as the number of levels in the output current and m as the number of modules Here m=3.So, n=2*3+1=6+1 =7.Therefore, number of levels in the output current=7.

Fig. 3
Fig.3 Sinusoidal pulse width modulation used in three and seven level inverters The above fig.3represents the sinusoidal pulse width modulation (SPWM) in which a repeating sequence i.e., a triangular carrier is compared with a sine wave and the comparison is carried out by using a logical operator are a relational operator which compare the two signals and produces the required output.Output currents for three and seven level current source inverters are shown in figures 4 and 5.

Fig. 4
Fig.4 Output current waveform for a three level CSI

Fig. 5
Fig.5 Simulation results of Sinusoidal Pulse Width Modulation (a) Triangular and sinusoidal signals (b) Generated pulses