In scalar control, the motor is fed with variable frequency signals generated by the PWM control from an inverter using the feature rich PIC microcontroller. Here, the V/f ratio is maintained constant in order to get constant torque over the entire operating range. Since only magnitudes of the input variables – frequency and voltage – are controlled, this is known as “scalar control”. Generally, the drives with such a control are without any feedback devices (open loop control). Hence, a control of this type offers low cost and is an easy to implement solution. In such controls, very little knowledge of the motor is required for frequency control. There are number of ways to implement scalar control. In this project, the popular Pulse Width Modulation technique is used.
In AC grid connected motor drives, a rectifier consists of common diode bridge providing a pulsed DC voltage from the mains is required. Although the basic circuit for an inverter may seem to be simple, accurately switching these devices provides a number of challenges. Voltage source inverter can be classified into two stepped wave inverter and PWMinverter. Stepped wave inverter is also called square wave inverter and which has two operating modes, 180 degree conduction mode and 120 degree conduction mode. In 180 degree conduction mode each switch is operated for 180 degrees and it is 120 degree for the other. Some examples where voltage source inverters are used are: uninterruptible power supply (UPS) units, adjustable speed drives (ASD) for ac motors, electronic frequency changer circuits etc. Commercially available inverter units used in homes and offices to units to power some essential ac loads in case the utility ac supply gets interrupted are also familiar. In such inverter units, battery supply is used as the input dc voltage source and the inverter circuit converts the dc into ac voltage of desired frequency.
The three phase inductionmotors are the frequently encountered machines in industry because of its simple design, rugged and easy maintenance. The frequency of induction motor is proportional to the synchronous speed. The rotating magnetic flux produced by three phase currents rotates with a constant speed where the supply frequency of the drive is proportional to synchronous speed. Hence the rotating flux and rotor current generate a force that drives the motor and accordingly torque will develop. For CHBMLI fedinduction motor drive the inverter setup is based on series connection of single phase inverters with separate dc sources. The level shifted multi-carrier PWM principle is applied to CHBMLI where it uses many triangular carrier signals and one modulating signal. Fig.2 shows the PWM generation. In this the pulse pattern depends on the ratio of modulating Vcontrol to the peak carrier voltage Vtri referred as modulation index (Ma).
Inverter-driven ac motors have become common in variable speed applications due to increased energy conservation. The use of high-frequency PWM methods and also multilevel inverters make the output voltage of the inverters more sinusoidal but also generate high common-mode voltage (CMV). From the studies on PWM-inverter-fed drives in the last few decades, it is found that high-frequency CMV of the inverters causes voltage drop across the bearings and this may cause bearing currents leading to premature bearing failures. Owing to increased cost of maintenance and downtime, attention on protecting the motor bearings has increased . Among the known solutions such as the
The conventional DC to DC type high frequency link inverters consist of three power stages, the HF PWM Bridge, active rectifier and polarity-reversing bridge. In this work DC to DC type HFL inverter with two stage conversion is achieved by using a fly back converter, which is used as a high frequency link. The flyback converter is used in both AC to DC and DC to DC conversion with galvanic isolation between input and any outputs. The fly back converter is a buck- boost converter with a inductor split to form transformer, so that the voltage ratios are multiplied with an additional advantage of isolation. Figure 2 shows the schematic of flyback converter.
Multilevel inverters are gaining popularity in high power applications. This paper proposes a new ladder type structure of cascaded three-phase multilevel inverter with reduced number of power semiconductor devices which is used to drive the induc- tion motor. The ultimate aim of the paper is to produce multiple output levels with minimum number of semiconductor devices. This paper uses only 11 switches along with 3 diodes and 4 asymmetrical sources to produce an output voltage of 21 levels. The modulation technique plays a major role in commutation of the switches. Here we implement the multicarrier level shifting pulse width modulation technique to produce the commutation signals for the inverter. The proposed multilevel inverter is used to drive the three-phase induction motor. The mathematical modeling of three-phase induction motor is done using Simulink. Furthermore the PI and fuzzy logic controllers are also used to produce the reference waveform of the level shifting technique which in turn produces the commutation signals of the proposed multile- vel converter. The controllers are used to control the speed of the induction motor. The effectiveness of the proposed system is proved with the help of simulation. The simulation is performed in MATLAB/Simulink. From the simulation results, it shows that the proposed multilevel inverter works properly to generate the multilevel output waveform with minimum number of semiconductor devices. The PI and fuzzy logic controller performances are evaluated using the results which indicate that with the help of controllers the harmonics has been reduced and the speed con- trol of induction motor is achieved under different loading conditions.
Capacitors are meant for power factor correction, which tends to increase the total harmonic distortion. The second concern is the switching of the power factor correc- tion capacitors. During a capacitor switching, transient over voltages are produced which contain a high frequency component. These transient over voltages, if large enough, can damage sensitive power electronic devices. The impact of the power factor correction circuit on induction motor drive system, in which the power factor correc- tion circuit has a single power device with a forward diode in the boost configuration, has been analyzed . The above approach increases the losses in diode and bridge rec- tifier and consequently decreases the system efficiency. A zero voltage transition iso- lated PWM boost converter for single stage power factor correction has been proposed , which suffers from the problem of existence of low ripple frequency. A canonical switching cell converter has been designed and analyzed with CMOS gate  . The designed topology produces heat problem due to power loss and hence system perfor- mance is affected by poor efficiency. A Boost PFC converter has been analyzed in terms of input voltage and current . The above converters are not suitable to relatively small size power supply due to its lower efficiency.
also helps to improve the overall power factor of the system. The return path of the high frequency current is through this capacitor C as at high frequency C offers negligible capacitive reactance ( X c 1 2 fC ), where f is in KHz range, hence, the capacitor C acts as a short circuit and allows high frequency current to flow. It also acts as higher order harmonic filter at the same cost. IGBT is used as the power semiconductor switch for its superiority for domestic induction cooker operating below the frequency range of 50 kHz (Pal et al., 2011). Figure 2 shows the equivalent circuit of mirror inverter.
ABSTRACT: In this paper, the three phase frequency variable inverter is designed in Matlab/Simulink. The overall two level three phase inverter circuit consisting of six IGBTs is controlled using Pulse width modulation (PWM) signal. PWM signal controls the applied voltage on the gate drive of six IGBTs. Each IGBT is maintained at different phase delay to produce three phase pure sine wave. The frequency of inverter is initially set to 50 Hz, the rotor speed, electromagnetic torque and rotor angle of an asynchronous machine is measured. When the rotor speed increases a particular limit (1450 RPM), the inverter frequency is automatically reduced to 30Hz by the use of feedback.
______________________________________________________________________________________ Abstract— There are different method of speed control of three phase induction motor and to control the speed of three phase induction motor generally using V/F control strategy. Out of the a number of methods of speed control of an induction such as pole changing, frequency variation, variable rotor resistance, variable stator voltage, constant V/f control, slip recovery method etc., the constant V/f speed control method is the majority generally used. In this method, the V/f ratio is kept constant which in turn maintains the magnetizing flux constant so that the maximum torque remains unchanged. Thus, the motor is totally utilized in this method. This paper include with simulation of V/F speed control of three-phase induction motor using PWMinverter strategy. The simulation work proves the idea of V/F control using PWMinverter and the software used for simulation is PSIM (Powersim).The performance of the volt per hertz strategy were evaluated through simulation shown in results. In constant V/F control, by use PWMinverter, we can vary the supply voltage as well as the supply frequency such that the V/F ratio remains constant so that the flux remains constant too. So, we can get different operating zone for various speeds and torques and also we can get different synchronous speed with almost same maximum torque. Thus the motor is fully utilized and also we have a good variety of speed control. It is effortless, cost-effective to easier to design in open loop. But the drawbacks of open loop is it doesn’t correct the change in output also it doesn’t reach the steady state quickly.
PWM technique is extensively used for eliminating harmful low-order harmonics in input and output voltage and current of static power. In PWM control, the inverter switches are turned ON and OFF several times during a half cycle and output voltage is controlled by varying the pulse width. At present, available PWM schemes can be broadly classified as carrier modulated sinusoidal PWM (SPWM) and pre calculated programmed PWM schemes. The inverters of the pulses are varied by charging the amplitude of the sinusoidal wave form. In this method the lower order harmonics are eliminated. As the switching for increases more harmonics can be eliminated. The limiting factors are the switching devices speed, switch losses & power ratings.
Large electric drives and utility applications require advanced power electronics converters to meet high power demand. As a result multilevel power converter structure has been introduced as an alternative in high power and medium voltage situation. Three level voltage-fedPWM inverters are recently showing popularity for multi-megawatt industrial drive application. The output voltage waveforms in multilevel inverter can be generated at low switching frequency with high efficiency and low distortion.
THE rapid development of power and microelectronics in recent years allows the use of the induction machine also in high-performance motor drives. At low- and medium-power levels the variable-speed induction motor drives are usually re-alized using pulsewidth- modulated (PWM) voltage-source in-verters (PWM- VSIs). However, the switched voltages yield high voltage slopes over the stator windings, which stresses the insulations and causes bearing current problems. A possible solution for this problem is the use of a PWM current-source in-verter (PWM-CSI) (Fig. 1). Both the voltages and the currents of the machine are almost sinusoidal and, therefore, the voltage stresses in the machine windings are lower.
This paper presents a new 7-level inverter for induction motor drive. The Inverter presented here gives a seven level output voltage. This configuration required very less number of switches, carrier signals and gate drivers when compared to diode clamped multi-level inverters, flying capacitor multi-level inverter and cascaded multi-level inverter.Software tool used is MATLAB/ SIMULINK is used for simulation of the inverter and the results are presented at the end.
28 In the widely utilized Pulse Width Modulation (PWM) methods, the inverter output voltage approximates the reference value through high frequency switching. In AC motor drive applications, typically a rectifier device converts the AC three phase line voltages to DC voltage. Following the rectifier voltage passive filtering stage, the PWM-VSI interfaces the DC source with the AC motor to control the shaft speed/position/torque. Some industrial applications of inverters are for adjustable-speed ac drives, induction heating, standby aircraft power supplies, UPS (uninterruptible power supplies) for computers, HVDC transmission lines, etc . When utilized in such applications, the device is often termed as converter (opposite of inverter), hence PWM-VSC.
ABSTRACT: The split phase induction motor are fixed speed motor used in most industrial processes due to their reliability, rugged nature, low maintenance and reduced cost. Induction motor use is limited in many industrial applications requiring variables speed due to high costs incurred in methods of speed control and efficiency of the methods used. This paper is implemented to control the speed of split phase induction motor using PWM technique based cycloconverter. The cycloconverter is built on with IGBT due to its improved dynamic performance, efficiency and reduction in the level of audible noise. With the help of PWM minimizes the lower order harmonics i.e. 1 and 3 order. In this paper simulink model of PWM based triggered cycloconverter is developed and the results shows that the output response is 2 & 4 times to input response. The output response of the cycloconverter is applied to the split phase induction motor and various output response of motor have obtained then observed the main & auxiliary winding current and speed-torque characteristics of the split phase induction motor.
To overcome the disadvantage faced by conventional VSI And CSI disadvantages a new concept was developed in year 2002 by Dr. F.Z. Peng. This involves combination of VSI and CSI to form a cross coupled network of Two Inductors and Two Capacitors, known as Impedance Network. Normally, three phase inverters have 8 vector states (6 active states and 2 zero states). But ZSI along with these 8 normal vectors has an additional state known as the Shoot Through State, during which the switches of one leg are short circuited. In this state, energy is stored in the Impedance Network and when the Inverter is in its active state, the stored energy is transferred to the load, thus providing boost operation. Whereas, this shoot through state is prohibited in VSI.
In order to verify the proposed cascaded multilevel inverter topology for induction motor drives. The simulation is based on MATLAB/SIMULINK was carried out. The simulation of nine level inverterfedinduction motor model was done using Simulink. The simulation results of phase voltage, phase currents, stator currents, motor speed and FFT spectrum were presented. The inverter output voltage is shown in Fig.5 and the current is shown in Fig.6.The motor currents are shown in the Fig.7 and the motor speed and Torque is shown in Fig.8 and Fig.9. The FFT analysis for the motor drive system was also done as shown in Fig.10. It is seen that the percentage of harmonics in the multilevel inverterfedinduction motor drive is less compare to classical inverter system.
ABSTRACT: The Z-source inverter is a recent topological invention in the field of power conversion. It has both buck and boost capabilities as they allow the operation of the inverter in the shoot though state. This feature of shoot through state is not permitted in traditional voltage and current source inverters as it would destroy the device. Z-source inverter employs a unique LC network in between the DC source and the inverter. By controlling this shoot through state, it is possible to produce any desired output ac voltage. This paper presents a Z-source network for induction motor drive. The proposed system is developed with the help of PIC microcontroller which generates the PWM pulses to drive the gate. Simple Boost Control PWM technique has been employed in this inverter to supply the motor with ac voltage. The proposed drive system is simulated using Matlab/Simulink.
Abstract:- This paper represent the MATLAB simulation analysis of space vector pulse width modulation (SVPWM) voltage source inverter give the supply to the PMSM drive. The main Aim of this paper supply AC supply to the PMSM through VSI by using SVPWM technique. Number of PWM methods is used to generates gate pulses, but most commonly used PWM method for three phase voltage source inverter (VSI) are sinusoidal PWM (SPWM) and space vector PWM (SVPWM). Now a day SVPWM technique are used because SVPWM technique reduces the voltage and current harmonic content, increase fundamental output voltage by 15% and smooth control of PMSM. So here present modeling simulation of SVPWM inverterfed PMSM drive in MATLAB/ simulation the result of total harmonic distortion(THD) fast Fourier transformation (FFT) of current are obtained in MATLAB Simulation.