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INTRODUCTION
A BLDC motor has three phase windings on the stator and permanent magnets on the rotor . The BLDC motor is also known as an electronically commutated motor because an electronic commutation based on rotor position is used rather than a mechanical commutation which has disadvantages like sparking and wear and tear of brushes and commutator. The use of the brushless direct current (BLDC) motor in these applications is becoming very common due to features of high efficiency, high flux density per unit volume, low maintenance requirements, and low electromagnetic-interference problems. These BLDC motors are not limited to household applications, but these are suitable for other applications such as medical equipment, transportation, HVAC, motion control , and many industrial tools .Efficiency and cost are the major concerns in the development of low-power motor drives targeting household applications such as fans, water pumps, blowers, mixers, etc.
1.1.OBJECTIVES OF THE PROJECT
To increase efficiency of the motor drive.
To control speed with reduced switching losses.
To reduce cost of application.
1.2 LITERATURE SURVEY
Yie-Tone Chen,. [1] A Driver for the Single-Phase Brushless DC Fan
Motor With Hybrid Winding Structure, proposes a novel driver for a single-phase brushless dc fan motor with a hybrid series/parallel winding structure. The winding symbols and directions of the hybrid motor stator structure are defined, and the winding steps for the proposed series/parallel winding are explained. An adequate
inverter driving circuit, which is capable to simultaneously obtain the advantages of the hybrid structure, is also discussed. At last, the overall system of this hybrid brushless dc motor with the proposed driving circuit is then implemented to verify the
performance of the proposed driver and structure.
Bhim Singh [2]Power Quality Improved PMBLDCM Drive for
Adjustable Speed Application with Reduced Sensor
Buck-Boost PFC Converter ,an improved power quality buckboost converter fed permanent magnet brushless DC motor (PMBLDCM) drive is employed for adjustable speed operation of PMBLDCM. A single-phase, single-switch AC-DC converter topology based on non-isolated buck-boost converter is employed for power factor correction (PFC) and operated with voltage follower control in discontinuous conduction mode (DCM) operation for sensor reduction. This PFC controller
ensures near unity power factor in wide speed range of the drive while restricting thetotal harmonic distortion (THD) in AC mains current within the specified limits of the IEC standard. The proposed control scheme with PFC converter based PMBLDCM drive is designed, modeled and simulated in Matlab-Simulink environment for an air conditioner compressor driven through a 2 kW, 5.2 Nm PMBLDC motor.The obtained results are presented to validate the effectiveness
of the proposed control scheme for power quality improvement at AC mains.
Bhim Singh, Sanjeev Singh, Ambrish Chandra [3] Comprehensive Study of Single-Phase AC-DC Power Factor Corrected Converters With High-Frequency Isolation, Solid-state switch mode AC-DC converters havinghigh-frequency transformer isolation are developed in buck, boost, and buck-boost configurations with improved power quality in terms of reduced total harmonic distortion (THD) of input current, power-factor correction (PFC) at AC mains and precisely regulated and isolated DC output voltage feeding to loads from few Watts to several kW. This paper presents a comprehensive study on state of art of power factor corrected single-phase AC-DC converters configurations, control strategies, selection of components and design considerations, performance evaluation, power quality considerations, selection criteria and potential applications, latest trends, and future developments.
Yungtaek Jang Milan M. Jovanovi´c [4] Bridgeless High-Power-Factor Buck Converter ,A bridgeless buck power factor correction rectifier that substantially improves efficiency at low line of the universalline range is introduced. By eliminating input bridge diodes, the proposed rectifier’s efficiency is further improved. Moreover, the rectifier doubles its output voltage,which extends useable energy of the bulk capacitor after a dropout of the line voltage. The operation and performance of the proposed circuit was verified on a 700-W, universal-line experimental prototype operating at 65 kHz. The measured efficiencies at 50% load from 115 and 230 V line are both close to 96.4%. The efficiency difference between low line and high line is less than 0.5% at full load. A second-stage half-bridge converter was also included to showthat the combined power stages easily meet Climate Saver Computing Initiative Gold Standard.
Xiaoyan Huang [5] A Single Sided Matrix Converter Drive for a
Brushless DC Motor in Aerospace Applications, describes a brushless dc (BLDC) drive with a single sided matrix converter (SSMC) for an electrohydrostatic actuation system in aerospace application. The use of an SSMC with a BLDC motor is novel and is used to achieve operation without a microprocessor. A simple hysteresis current control strategy is implemented to control motor torque. The multiphase SSMC provides high reliability and fault tolerance with the penalty of more power devices. A five-phase SSMC prototype is built. The experiment results are presented to verify the drive performance.
1.3 EXISTING SYSTEM:
Power quality problems have become important issues to be considered due to the recommended limits of harmonics in supply current by various international power quality standards such as the International Electrotechnical Commission (IEC) 61000-3-2 . For class-A equipment (< 600 W, 16 A perphase) which includes household equipment, IEC 61000-3-2 restricts the harmonic current of different order such that the total harmonic distortion (THD) of the supply current shouldbe below 19% . A BLDC motor when fed by a diode bridge rectifier (DBR) with a high value of dc link capacitor draws peaky current which can lead to a THD of supply current of the order of 65% and power factor as low as 0.8 . Hence, a DBR followed by a power factor corrected (PFC) converter is utilized for improving the power quality at ac mains. Many topologies of the single-stage PFC converter are reported in the literature which has gained importance because of high efficiency as compared to two-stage PFC converters due to low component count and a single switch for dc link voltage control and PFC operation .The choice of mode of operation of a PFC converter is a critical issue because it directly affects the cost and rating of the components used in the PFC converter. The continuous conduction mode (CCM) and discontinuous conduction mode (DCM) are the two modes of operation in which a PFC converter is designed to operate . In CCM, the current in the inductor or the voltage across the intermediate capacitor remains continuous, but it requires the sensing of two voltages (dc link voltage and supply voltage) and input side current
for PFC operation, which is not cost-effective. On the otherhand, DCM requires a single voltage sensor for dc link voltage control, and inherent PFC is achieved at the ac mains, but at the cost of higher stresses on the PFC converter switch; hence,
DCM is preferred for low-power applications .The conventional PFC scheme of the BLDC motor drive utilizes a pulsewidth-modulated voltage source inverter (PWM-VSI) for speed control with a constant dc link voltage.This offers higher switching losses in VSI as the switching losses increase as a square function of switching frequency. As the speed of the BLDC motor is directly proportional to the applied dc link voltage, hence, the speed control is achieved by the variable dc link voltage of VSI. This allows the fundamental frequency switching of VSI (i.e., electronic commutation) and offers reduced switching losses.
The parameters of the BL flyback converter are designed such that it operates in discontinuous inductor current mode (DICM) to achieve an inherent power factor correction at ac mains. The speed control of BLDC motor is achieved by the dc link voltage control of VSI using a BL flyback converter. This reduces the switching losses in VSI due to the low frequency operation of VSI for the electronic commutation of the BLDC motor.The performance of the proposed drive is evaluated for a wide range of speed control with improved power quality at ac mains.Moreover, the effect of supply voltage variation at universal ac mains is also studied to demonstrate the performance of the drive in practical supply conditions. Voltage and current stresses on the PFC converter switch are also evaluated for determining the switch rating and heat sink design. Finally, a hardware implementation of the proposed BLDC motor drive is carried out to demonstrate the feasibility of the proposed drive over a wide range of speed control with improved power quality
at ac mains.
1.4 PROPOSED SYSTEM:
The control methods based on an a-priori sensitivity analysis of the DN buses in order to calculate the sensitivity co-efficient of the DG units that allow changing voltage values on the BSP by means of reactive (or active) power. This result is achieved by applying a decentralized voltage control up to capability curves limits by means of the reactive power provided by power inverters or through a reduction of the active power (backup solution). On the contrary, in the proposed control, if the local reactive power compensation based on the sensitivity analysis fails (the reactive power reaches the availability limits) then IPP performs a coordinated regulation of the reactive powers among the RES units. The aim is to avoid their disconnections due to voltage limit violation increasing the total power fed into the grid. It is worthy to highlight that only in this second case the proposed coordinated approach involves also the DSO during the control, which provides the power system state in order to develop the coordinated control.
In detail, from an operational point of view, the coordinated regulation of the reactive power can be divided in three steps:
1) DSO sends data of DN state to IPP.
2) IPP Control Centre (IPPCC) processes data estimating the power set points (active and reactive power) of each RES unit in order to control the voltage profiles within the limits taken into account.
3) Each generator changes the actual power set point with the new one received by IPPCC. Therefore, the core of the control described so far is carried out by IPPCC that has to solve a constrained optimization problem to have the regulation set point.
2.1.BLOCK DIAGRAM DESCRIPTION
Fig. 2.1 shows the proposed BL flyback converter-based VSI-fed BLDC motor drive. The parameters of the BL flyback converter are designed such that it operates in discontinuous inductor current mode (DICM) to achieve an inherent power factor correction at ac mains. The speed control of BLDC motor is achieved by the dc link voltage control of VSI using a BL flyback converter. This reduces the switching losses in VSI due to the low frequency operation of VSI for the electronic commutation of the BLDC motor. The performance of the proposed drive is evaluated for a wide range of speed control with improved power quality at ac mains. Moreover, the effect of supply voltage variation at universal ac mains is also studied to demonstrate the performance of the drive in practical supply conditions. Voltage and current stresses on the PFC converter switch are also evaluated for determining the switch rating and heat sink design. Finally, a hardware implementation of the proposed BLDC motor drive is carried out to demonstrate the feasibility of the proposed drive over a wide range of speed control with improved power quality at ac mains.
2.2 BUCK-BOOST CONVERTER:
Two different topologies are called flyback converter. Both of them can produce an output voltage much larger (in absolute magnitude) than the input voltage. Both of them can produce a wide range of output voltage from that maximum output voltage to almost zero.
The inverting topology – The output voltage is of the opposite polarity as the input buck (step-down) converter followed by a boost (step-up) converter – The output voltage is of the same polarity as the input, and can be lower or higher than the input. Such a non-inverting buck-boost converter may use a single inductor that is used as both the buck inductor and the boost inductor.
The flyback converter is a type of DC-to-DC converter that has an output voltage magnitude that is either greater than or less than the input voltage magnitude. It is a switched-mode power supply with a similar circuit topology to the boost converter and the buck converter. The output voltage is adjustable based on the duty cycle of the switching transistor. One possible drawback of this converter is that the switch does not have a terminal at ground; this complicates the driving circuitry. Also, the polarity of the output voltage is opposite the input voltage. Neither drawback is of any consequence if the power supply is isolated from the load circuit (if, for example, the supply is a battery) as the supply and diode polarity can simply be reversed. The switch can be on either the ground side or the supply.
2.3 Principle of operation
The two operating states of a flyback converter: When the switch is turned-on, the input voltage source supplies current to the inductor, and the capacitor supplies current to the resistor (output load). When the switch is opened, the inductor supplies current to the load via the diode D.
The basic principle of the flyback converter is fairly simple
While in the On-state, the input voltage source is directly connected to the inductor (L). This results in accumulating energy in L. In this stage, the capacitor supplies energy to the output load.
While in the Off-state, the inductor is connected to the output load and capacitor, so energy is transferred from L to C and R.
Compared to the buck and boost converters, the characteristics of the flyback converter are mainly, Polarity of the output voltage is opposite to that of the input.
The output voltage can vary continuously (for an ideal converter). The output voltage ranges for a buck and a boost converter are respectively 0 to inf.
POWER INVERTER:
A power inverter, or inverter, is an electronic device or circuitry that changes direct current (DC) to alternating current (AC) .The input voltage, output voltage and frequency, and overall power handling, are dependent on the design of the specific device or circuitry.A power inverter can be entirely electronic or may be a combination of mechanical effects (such as a rotary apparatus) and electronic circuitry. Static inverters do not use moving parts in the conversion process.
Typical applications for power inverters include:
• Portable consumer devices that allow the user to connect a battery, or set of batteries, to the device to produce AC power to run various electrical items such as lights, televisions, kitchen appliances, and power tools.
• Use in power generation systems such as electric utility companies or solar generating systems to convert DC power to AC power.
• Use within any larger electronic system where an engineering need exists for deriving an AC source from a DC source.
2.6.1 Input voltage
A typical power inverter device or circuit will require a relatively stable DC power source capable of supplying enough current for the intended overall power handling of the inverter. Possible DC power sources include: rechargeable batteries, DC power supplies operating off of the power company line, and solar cells. The inverter does not produce any power, the power is provided by the DC source. The inverter translates the form of the power from direct current to an alternating current waveform.
The level of the needed input voltage depends entirely on the design and purpose of the inverter. In many smaller consumer and commercial inverters a 12V DC input is popular because of the wide availability of powerful rechargeable 12V lead acid batteries which can be used as the DC power source.
Output waveform
An inverter can produce square wave, modified sine wave, pulsed sine wave, or sine wave depending on circuit design. The two dominant commercialized waveform types of inverters as of 2007 are modified sine wave and sine wave.
There are two basic designs for producing household plug-in voltage from a lower-voltage DC source, the first of which uses a switching boost converter to produce a higher-voltage DC and then converts to AC. The second method converts DC to AC at battery level and uses a line-frequency transformer to create the output voltage.[2]
Square wave
This is one of the simplest waveforms an inverter design can produce and is useful for some applications.
Sine wave
A power inverter device which produces a smooth sinusoidal AC waveform is referred to as a sine wave inverter. To more clearly distinguish from "modified sine wave" or other creative terminology, the phrase pure sine wave inverter is sometimes used.In situations involving power inverter devices which substitute for standard line power, a sine wave output is extremely desirable because the vast majority of electric plug in products and appliances are engineered to work well with the standard electric utility power which is a true sine wave.At present, sine wave inverters tend to be more complex and have significantly higher cost than a modified sine wave type of the same power handling.[3]
A "modified sine wave", also referred to as a "3-level modified square wave"
Modified sine wave
The terminology "modified sine wave" has come into use and refers to an output waveform that is a useful rough approximation of a sine wave for power translation purposes.The waveform in commercially available modified-sine-wave inverters is a square wave with a pause before the polarity transition, which only needs to cycle through a three-position switch that outputs forward, off, and reverse output at the pre-determined frequency.[2] The peak voltage to RMS voltage do not maintain the same relationship as for a sine wave. The DC bus voltage may be actively regulated or the "on" and "off" times can be modified to maintain the same RMS value output up to the DC bus voltage to compensate for DC bus voltage variation.
The ratio of on to off time can be adjusted to vary the RMS voltage while maintaining a constant frequency with a technique called PWM. Harmonic spectrum in the output depends on the width of the pulses and the modulation frequency. When operating induction motors, voltage harmonics is not of great concern.Numerous electric equipment will operate quite well on modified sine wave power inverter devices, especially any load that is resistive in nature such as a traditional incandescent light bulb.Most AC motors will run on MSW inverters with an efficiency reduction of about 20% due to the harmonic content.[5]
2.6.2.Output frequency
The AC output frequency of a power inverter device is often the same as the standard power line frequency, for example 60 or 50 cycles per second.If the output of the device or circuit is to be further conditioned (say stepped up by a follow on transformer) then the frequency may be much higher for good transformer efficiency.
2.6.3.Output voltage
The AC output voltage of a power inverter device is often the same as the standard power line voltage, such as household 120VAC or 240VAC. This allows the inverter to power numerous types of equipment designed to operate off the standard line power.The designed for output voltage is often provided as a regulated output. That is, changes in the load the inverter is driving will not result in output voltage change from the inverter.In a sophisticated inverter, the output voltage may be selectable or even continuously variable.
2.6.4.Output power
A power inverter will often have an overall power rating expressed in watts or kilowatts. This describes the power that will be available to the device the inverter is driving and, indirectly, the power that will be needed from the DC source. Smaller popular consumer and commercial devices designed to mimic line power typically range from 150 to 3000 watts.Not all inverter applications are primarily concerned with brute power delivery, in some cases the frequency and or waveform properties are used by the follow on circuit or device.
2.7 Applications
DC power source utilization
Inverter designed to provide 115 VAC from the 12 VDC source provided in an automobile. The unit shown provides up to 1.2 amperes of alternating current, or enough to power two sixty watt light bulbs.An inverter converts the DC electricity from sources such as batteries or fuel cells to AC electricity. The electricity can be at any required voltage; in particular it can operate AC equipment designed for mains operation, or rectified to produce DC at any desired voltage.
Uninterruptible power supplies
An uninterruptible power supply (UPS) uses batteries and an inverter to supply AC power when main power is not available. When main power is restored, a rectifier supplies DC power to recharge the batteries.
Power grid
Grid-tied inverters are designed to feed into the electric power distribution system. They transfer synchronously with the line and have as little harmonic content as possible. They also need a means of detecting the presence of utility power for safety reasons, so as not to continue to dangerously feed power to the grid during a power outage.
Solar
A solar inverter can be fed into a commercial electrical grid or used by an off-grid electrical network. Solar inverters have special functions adapted for use with photovoltaic arrays, including maximum power point tracking and anti-islanding protection. Micro-inverters convert direct current from individual solar panels into alternating current for the electric grid. They are grid tie designs by default.
Induction heating
Inverters convert low frequency main AC power to higher frequency for use in induction heating. To do this, AC power is first rectified to provide DC power. The inverter then changes the DC power to high frequency AC power.
2.8 PWM GENERATOR
Generate pulses for a carrier-based pulse width modulator (PWM).The PWM Generator block generates pulses for carrier-based pulse width modulation (PWM) systems. The block can be used to fire the self-commuted devices (FETs, GTOs, or IGBTs) of single-phase, two-phase, three-phase, or a combination of two three-phase bridges.
The number of pulses generated by the PWM Generator block is determined by the number of bridge arms you have to control:
• Two pulses are generated for a one-arm bridge. Pulse 1 fires the upper device and pulse 2 fires the lower device (shown for the IGBT device).