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This paper corroborates three different hybrid modulation strategies suitable for single-phase voltage source inverter. The proposed method is formulated using fundamental switching and carrier based pulse width modulation methods. The main tale of this proposed method is to optimize a specific performance criterion, such as minimization of the total harmonic distortion (THD), lower order harmonics, switching losses, and heat losses. The proposed method is articulated using fundamental switching and carrier based pulse width modulation methods. Thus, the harmonic pollution in the power system will be reduced and the power quality will be augmented with better harmonic profile for a target fundamental output voltage. The proposed modulation strategies are simulated in MATLAB r2010a and implemented in a Xilinx spartan 3E-500 FG 320 FPGA processor. The feasibility of these modulation strategies is authenticated through simulation and experimental results.

Pulse width modulation (PWM) strategies are dedicated for power converters to shape the output profile in a way beneficial to the industrial requirements. There have been several control strategies developed to enhance the fundamental component and minimizing the total harmonics distortion (THD) through elimination of lower order harmonics and to create a wider dead band for a given switching frequency [

This paper corroborates three different hybrid modulation methods suitable for single-phase voltage source inverter derived using concatenation of fundamental switching and carrier based pulse width modulation (PWM) methods like unipolar PWM, inverted sine carrier PWM, and sixty-degree PWM, respectively. Consequently, with better harmonic profile for a target fundamental output voltage, the harmonic pollution in the power system will be moderated and the power quality will be improved.

The PWM schemes developed for single-phase inverters shown in Figure

Single-phase inverter.

Similar to unipolar PWM, the voltage switches between two levels

The inverted sine carrier PWM (ISCPWM) control scheme for single-phase full-bridge inverter eliminates poor output voltage spectral quality and reduced fundamental output voltage. It enhances the fundamental output voltage particularly at lower modulation index ranges while keeping the total harmonic distortion (THD) lower without involving changes in device switching losses.

The 60-degree PWM is similar to the modified pwm. The idea behind 60-degree PWM is to “flat top” the waveform from 60 degrees to 120 degrees and 240 degrees to 300 degrees. The power devices are held on for one-third of the cycle (when at full voltage) and have reduced switching losses. The 60-degree PWM creates a large fundamendal (2/3) and utilizes more of available dc voltage than does sinusoidal PWM. The output waveform can be approximated by the fundamental and the first few terms.

The main philosophy of the PWM modulation emphasizes providing desired fundamental magnitude and reduced THD by pushing the lower order harmonics to higher carrier band thereby minimizing the filter design. In this direction, a new PWM strategy is developed to offer lesser switching loss with improved harmonic profile while offering desired fundamental output voltage. The proposed hybrid pulse width modulation (HPWM) strategies shown in Figure

Proposed hybrid strategies.

Hybrid UPWM (HUPWM)

Hybrid ISCPWM (HISCPWM)

Hybrid 60° PWM (H-60° PWM)

The hybrid switching controller (HSC) basically consists of logic circuits generating gating signal for each device with two different frequencies, quarter cycle being switched at FFS, while the other quarter cycle is modulated at CBPWM. A random switching scheme is embedded with this hybrid modulation in order to swap both FFS and CBPWM for every quarter cycle of the output waveform. A simple base PWM circulation scheme is also introduced here to get resultant hybrid PWM circulation that inherits the characteristics of CBPWM methods. The hybrid modulation scheme consists of base PWM circulation and hybrid switching controller (HSC) to generate new modulation pulses.

The block diagram representation of base PWM circulation design is seen in Figure

In addition to PWM circulation pulses, the HPWM requires three square wave signals that make every power switch operating at carrier based PWM (CBPWM) and square wave randomly per quarter cycle to equalize the power losses within each device. Two signals are random switching pulse (

HSC combines random signals (

In order to evaluate the quality of output voltage waveform acquired from single-phase inverter using the proposed HPWM methods, the simulation study is carried in MATLAB/Simulink platform. The input parameters for simulation study are taken with dc-link voltage

Thorough simulation study has been carried out for single-phase inverter by keeping

Proposed Hybrid UPWM (HUPWM).

Proposed Hybrid ISCPWM (HISCPWM).

Proposed Hybrid 60° PWM (H-60° PWM).

Figure

Fundamental output voltage against modulation depth.

The hardware rig is constituted using MOSFETs (IRF 840), laboratory variable dc-link voltage setup and resistive-inductive load of

HUPWM (a) pulse pattern, (b) output voltage waveform, and (c) harmonic spectrum.

HISCPWM (a) pulse pattern, (b) output voltage waveform, and (c) harmonic spectrum.

HSDPWM (a) pulse pattern, (b) output voltage waveform, and (c) harmonic spectrum.

Various HPWM strategies for single-phase inverter operating at low switching frequency with lesser switching commutations are proposed. The proposed HPWM method can be extended to any carrier based PWM methods. In comparison with conventional PWM methods, the proposed methods offer lesser number of switching commutations and reduced switching loss for the same fundamental voltage. The harmonic performance of the HPWM methods are examined in the entire operating range and its performance is better. The proposed methods facilitate balanced conduction loss with reduced switching loss within each device. Also the hybrid PWM strategy reduces conduction losses to a larger extent so that the THD is better when compared to the conventional PWM methods. The experimental results demonstrate that the proposed methods can be extended to any type of dc-ac/ac-ac power conversion systems.

The authors declare that there is no conflict of interests regarding the publication of this paper.