DELTA MODULATION CONTROL OF NINE PHASE INVERTER DRIVE USING SIMULATION/MATLAB      

Delta modulation control of Nine Phase Inverter

Drive using Simulation/Matlab

1

_{Dr. Manjesh, ,}

_{Nilima Siddhartha Dabhade,}

1_{Associate Professor,} 2_{Research scholar,} 1_{Department of Electronics Science,} 1_{Bangalore University, Bangalore, India}

Abstract— Motor drives used in the industry must have highly efficient and reliable. Multiphase motor drives have predominant over three phase Three phase motor with advantages of more torque density and linear load. Presented topic focus on the modelling of nine phase inverter to drive nine phase induction motor. Most of the loads used in industries has nonlinear characteristics therefore additional parameters like voltage and current induced with fundamental frequency at the output of the load termed as ‘Harmonics’ which increases the rms current and dissipated as a heat at the output of the load. Several new techniques are employed to minimize the effect of harmonics and heat in the load. In this work a new Delta Modulation(DM) technique is employed to suppress the effect of harmonics and to overcome the low performance of a conventional Pulse Width Modulation( PWM) control. Modeling of the inverter carried out by switching of sinusoidal signal to quantized sinusoidal signal. Data analysis has

been done to compare percentage of THD between PWM and DM technique using Simulink/Matlab.

Index Terms— Delta Modulation, Harmonics, Matlab/Simulink, Nine phase inverter, Nine phase motor, PWMTechnique.

I.INTRODUCTION

Three phase drives have limitations of medium torque load. Multiphase motor drives have predominant over three phase Three phase motor with advantages of more torque density low harmonics distortion and linear load etc [1]. Multiphase drives have major applications in high torque motor drives like aircraft, vehicles (electric, hydraulic, battery powered), agriculture etc.

Multiphase drives increase the demand of inverters in industries. The basic fundamental of inverter is to convert DC voltage supply to AC voltage supply with desire frequency and magnitude. There are two types inverter, voltage and current source Inverters, these inverters can be with Half or full bridge constructed using semiconductor devices (MOSFETs or IGBTs).

Most of the loads used in industries has nonlinear characteristics therefore additional parameters like voltage and current induced with fundamental frequency at the output of the load termed as ‘Harmonics’ which increases the rms current and dissipated as a heat at the output of the load. (THD). The Percentage of THD can be control through several hardware and software techniques like “Filters”, “modulation”, “multilevel” techniques to overcome harmonics distortion.

Harmonics deteriorates the power factor and increases electrical losses in the circuit and device, which reduces efficiency of the device and results equipment failure. The percentage of distortion called Total Harmonics Distortion (THD).

Modulation techniques are used for switching operations in the controller converters and inverters to improve overall efficiency with different types of load. Several modulating techniques have been so far proposed to control output voltages and currents with desire amplitude and frequency to achieve wide linear modulation range, minimum switching losses and high quality with different type of load. There are many types of carrier based and carrier less Switching operations available in the modulation techniques. Carrier based modulation carried out with the reference signal and carrier signal while carrier less modulation is carried out by self-quantization of the signal [1-5].

The Reduction of Total Harmonics Distortion is the main objective in this research work, therefore DMT is adopted in this work and Presented with nine phase inverter to drive nine phase induction motor. Control signals are generated with PWM and Delta modulating techniques for the Nine Phase Inverter Drive using Matlab/Simulink.

I.

PWM

T

Pulse Width Modulation (PWM) is the carrier-based technique where switching signals are modulated with constant amplitude and variable duty cycle (pulse width). PWM control carried out by the comparison of reference sinusoidal or square signal with high frequency carrier sawtooth or triangular signal. Types of PWM depends on switching of reference signal with respect to the carrier signal. In single PWM rectangular signal (Vr) compared with the triangular signal (Vc). As shown in Fig.1. the frequency of t he reference and carrier signals is nearly equal. The amplitude of the generated pulse decides the modulation index. As shown in equation (1) modulation Index (Ma) is the ratio of reference to carrier signal [6-8].

Ma =𝑉𝑟

𝑉𝑐 (1)

II.

D

M

T

Pulse Delta modulation (DM) technique is the most advanced carrier-less modulating technique is as illustrated in Fig.2. Delta Modulating technique is carried out by periodical sampling, quantization and integration of the reference sinusoidal signal to form a feedback loop. The operation of DM can be described with basic structure as shown in Fig.2.(a)-(d). The basic operation of the signal based on the comparison of reference signal (VR(t)) with self-sampled signal (VC(t)). The delta modulation is obtained by quantizing and integrating the modulating signal and predetermined magnitude of the feedback signal, the output of the modulator has two possible levels ±Vs whereas time duration between two successive levels is determined by the slope of the reference signal. As shown in section (D), the upper and lower boundary level from ‘A’ to ‘C’ to controls the output voltage of modulated signal Vm(t), the performance of the Vm(t) evaluated on the basis of modulation index(Δm).

Δm =VR

𝑉𝑠 (2)

Where;

‘VR’ is Reference signal

‘Vs’ is hysteresis comparator.

(a) (b)

( c) (d)

Fig.2. (a)Basic Structure (b)Block diagram(c)Reference sampled signal(d) magnified view Of Delta Modulation

Since the inverter output is not strictly periodic in nature harmonics distortion can be obtained by Discrete Fourier Transform (DFT). DM technique is suitable for AC motor controls because of its inherent V/F control feature and attenuation of low order harmonics. However, the inverter output signal is not synchronized with the control signals due to dependency of duty ratio modulation with slope of the control signal [9-13].

IV.

M

O

N

P

I

The inverter energized with DC supply (230v) to drive the nine-phase induction motor. The inverter constructed with the nine legs and eighteen switches using semiconductor devices (MOSFET’s/IGBT’s). Nine legs are 40° out of phase with each other. Semiconductor switches in each leg are complimentary to each other and conduct for the period of 180° [14-20].

4.1. PWM Switching Control

Fig.3. Modeling of Nine Phase Inverter with PWM Technique

The Fig.4. shows control signals applied to 9-Phase inverter drive. All the control signals are arranged in such a way that alternate switching of positive and negative signal are provided to each switch at a regular interval of time.

Fig.4. Nine phase PWM signal generation with square waveform

4.2 Delta Modulation Switching Control

The complete setup of DM switching is as shown in Fig.5. The modeling of the inverter employed with nine DM control signals which are 40° out of phase with each other. These Nine sinusoidal waveforms are sampled, quantized and integrated to form a feedback loop. The sinusoidal sampled reference signals form a triangular carrier signal. The output load consists of sequence different positive and negative pulses which are provided to the Nine RL load.

Fig.5.Construction of Nine Phase Inverter Drive with DM Technique

The Fig.6. shows the control signals for nine phase inverter Introducing DM signals, the switches of the inverter are controlled by sampled sinusoidal modulating reference signal to form a triangular carrier signal. Performance of the modulation and effects of harmonics determined by the selection modulation index(Δm).

V.

R

A

D

Nine Simulink/MATLAB results for the design of inverter drive with PWM and DM switching technique is as shown in Fig.7. (a) and (b). Control signals have been generated to drive RL load. Comparative output to the RL load has been done to study Waveforms for load to load, load to output, load to neutral voltage and load to neutral current using Simulink scope. Nine Phase Inverter Drive is studied and simulated with RL load for rated frequency of 50Hz and dc voltage (Vdc) of 230v. The obtained results are analyzed and compared for Total Harmonics Ditortion (THD).

(a) (b)

Fig.7. Load-Output, Load-Load, Load-neutral Voltage and Load-neutral Current (a)PWM (b)DM

As plotted in Fig.8 and Fig.9.FFT analysis has been done to obtained percentage of THD for PWM and DM techniques respectively. Comparison of percentage in VTHD and ITHD Between PWM and DM switching techniques is as shown in table I.

(a) (b) Fig.8.(a)V-THD(b)I-THD with PWM Switching(50Hz)

(a) (b) Fig.9. (a)V-THD (b)I-THD with DM Switching(50HZ)

Table- I: THD comparison with PWM and DM switching Techniques

Fundamental Frequency= 50Hz, Vdc=230v, Switching Modes V-THD I-THD

PWM 48.06% 13.46%

DM 34.70% 23.37%

VI.

C

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