What Is the Difference Between Direct and Indirect Vector Control of an Induction Motor?

Vector control, also called fieldoriented control (FOC), is a Variable frequency Drive (VFD) control method in which the stator currents of a 3 phase induction motor are identified as two orthogonal components that can be visualized with a vector. The vector control of induction motors is one of the most suitable and popular speed control technique presently used. The vector control technique decouples the two components of stator current space vector: one providing the control of flux and the other providing the control of torque. The two components are defined in the synchronously rotating reference frame. With the help of this control technique the induction motor can replace a separately excited dc motor. The scalar control technique is simple to implement but have the coupling effect ultimately responsible for the sluggish response, which leads to instability due to higher order system effect. The DC motor needs time to time maintenance of commutator, brushes and brush holders. The main effort is to replace DC motor by an induction motor and merge the advantages of both the motors together into variable speed brushless motor drive and eliminate the associated problems. The squirrel cage induction motor being simple, rugged, and cheap and requiring less maintenance, has been widely used motor for fixed speed application. The induction motor is transformed from a non-linear to linear control plant. It is expected that with increasing computational power of the DSP controllers, it will eventually nearly universally displace scalar volts -per-Hertz (V/f) control. In this paper we will come to know the concept of vector control and different types of vector control techniques available. And finally we will be able to compare them. Key words-Induction Motor, Vector Control, Scalar Control, Sluggish, Higher Order System Effect.

• Related Questions

Why are the 737's variable-speed generator drives so unreliable?

@Jpe61 is correct in his comment that it's likely an electronics issue, since indeed a VSCF is mechanically simpler.VSCF is also used on the MD-90, with poor initial reliability$^1$ MDC went back to IDGs for the MD-95 (717).$^1$ It's also used on the 777 (only for backup, also with poor initial reliability$^2$), and on the F/A-18.$^3$The F/A-18 utilizes cycloconverters, while the aforementioned civilian applications utilize DC-links (possibly the voltage-source inverter type based on this patent by Sundstrand, the makers of the 737 unit).$^3$... when electrolytic capacitors are used, in the case of a voltage DC-link, there is potentially a reduced system lifetime (Wikipedia: AC-to-AC converter DC link converters).More here: Wikipedia: Electrolytic capacitor Operational characteristicsYour link says "the failure rate was just over 1 every 2,000 hrs". The 2,000 hours match the lifetime graphs in the article linked above (shown below).Once you lose a generator, say running at 0.35 load, the other needs to pick up the slack and run at 0.7 load. The CAA's imposed limitation despite the redundancy tells us they don't trust the VSCF at high loads.

Source: airliners.netOne feature on the MD-90 is the air scoop for cooling the VSCF components. The more electronics are used, the more intricate cooling is needed (you can't just dip them in engine oil).There's an official Honeywell video on installing the MD-90's VSCF with hints at improper maintenance practices, which would be a headache for an airline since the system is very niche with different tolerances.So whether it's a 737 or an MD-90, the issues seem to be:Note that the technology hasn't become obsolete, at least academically: a 2017 paper proposes a "novel DC-Link VSCF AC-DC-AC" for the Embraer 190/195, from which:Problems existed with the older VSCF systems in the past; however, the switched power electronics and digital controllers have matured and can be now, in our opinion, safely integrated and replace existing constant-speed hydraulic transmissions powering CSCF AC generators.$^1$ Douglas Jetliners, Guy Norris and Mark Wagner, page 85

$^2$ Boeing tackles 777 power problems, 18 August 1999, flightglobal.com

$^3$ Control of Power Electronic Converters and Systems, Volume 2, page 341


What will be the role of electrical engineers in the development of electric vehicles? Which master's specialization suits to establish a career in the electric vehicle sector from EEE branch prospect?

Hi,As you asked in EEE branch perspective let me divide this into Electrical and Electronic Engineer prospect.Electrical engineers design, develop, test, and supervise the manufacture of electrical components. They are responsible for designing the electrical circuitry that allows a gas engine to charge the battery in a hybrid vehicle and distribute the electricity from the battery to the electric motor. Most of this effort is related to the distribution of power throughout the EV where batteries and motors operate at hundreds of volts. This includes the driving of propulsion motors for the EV.Electronics engineers design, develop, and test electronic components and systems for these vehicles. These engineers are primarily focused on the control systems and additional electronic components for the vehicle. They don't usually focus on the generation and distribution of electricity.Electronics engineers also perform a variety of jobs for EV development, such as:Computer engineers configure the processor and memory along with their associated "building blocks. "Thermal-management engineers design climate control inside the EV as well as controls for heat dissipation on electronic components.EMC (electromagnetic control) engineers provide techniques to prevent EMI from affecting internal systems in the EV as well as external systems in other equipment.Lighting engineers design the EV's internal and external lighting, primarily using LEDs. Test engineers checkout the EV's hardware and software to ensure all systems are operating properly.Test instrument engineers design instruments employed to test various functions on an EV. These instruments might be used on the factory floor or at a car dealer's repair facility. So decide whether you want to become Electrical or electronic engineer based on your interest.Note: If you got into EV industry at first is well and good . If not go and join in any Variable frequency drives development Industry and get some knowledge and try to move to EV Industry. All the best. Mohan Krishna Lagadapati


How many types of chiller alarms are there?

Dozens.At a high-level and assuming water-cooled, low and high oil pressure, low and high refrigerant pressure, low and high condenser and evaporator pressures, low water flow (both evaporator and condenser)... that is just on the fluid side and there are even more there.Then there is the compressor and motor/drive assembly: If so equipped, Variable Frequency Drive -VFD faults (another major list, probably larger than the chiller itself), motor winding temperatures, power phase imbalance/loss of phase.The list can be extensive and because there are so many systems and sub-systems on-board that affect each other, they all have to work together in advance of higher calamities. The above does not include normal operating controls such as flow and pressure switches (e.g. to prove flow before starting the chiller, which avoids evaporator freezing), chiller entering and leaving water temperatures and flow rates (evaporator and condenser) as common examples.Where chillers are part of a larger plant, working in parallel with others (and occasionally in-series), there are the "play nicely" controls to stage additional capacity on and off, to "lead-lag" the chillers for more even wear and tear, priority controls, load-shedding based on power monitoring to avoid utility demand charges, etc. When part of a DDC (Direct Digital Control) system or BMS (Building Management System), almost ANY of the above variables can be monitored and assigned alarm status, (soft and hard/critical), up to the facilities manager's ability to monitor and respond to them. Even if not the core safety function items.The above is a general response to the nature of the question and no specifics of application are to be implied or inferred. The response does not constitute legal or professional engineering advice. Seeking the advice of a qualified professional specific to your particular application, is recommended.How many types of chiller alarms are there?The above is a general response to the nature of the question and no specifics of application are to be implied or inferred. The response does not constitute legal or professional engineering advice. Seeking the advice of a qualified professional specific to your particular application, is recommended


Why does a UPS need an isolation transformer?

Most high-power installations require an isolation transformer. Every variable frequency drive manual I've ever seen requires the same thing. So it's not a UPS-specific requirement.In general, the isolation transformer limits your available fault current, and keeps electrical disturbances generated by your load from propagating quite so easily through your entire facility. Limiting the fault current is particularly important, because fuses and breakers are only rated for some maximum current they are able to interrupt. And that, in turn, gets listed in the product's UL file. (I'm assuming this UPS is UL listed.) So it's not necessarily that the UPS won't work without the transformer. It's more that if something goes horribly wrong, they can't guarantee it won't catch fire.I found this resource that explains more about drive isolation transformers, which is pretty consistent with the above: the selected transformer has a Wye configured secondary, then a secondary ground can be gained with the installation of the isolation transformer. This ground is isolated from the primary input and provides a couple of distinct benefits:Grounding prevents the transfer of common-mode noise and transients, both from the primary source to the motor drive, and from the drive to the power system. This can reduce "bearing currents" that often cause fluting.Introducing a grounded, drive isolation transformer localizes the high-frequency induced ground currents and prevents them from extending upstream of the transformer, minimizing "noise" and related problems often associated with drives.Consider an isolation transformer when power quality and fault currents are the primary consideration.Another optional benefit of isolation transformers is that of electrostatic shielding. This provides a shield between the primary and secondary winding, which can provide in the range of 40-60 dB of common mode noise reduction.What you're talking about may not be a VFD, but many of the same concerns apply to a UPS or any other switching power supply.


What is the main reason for using the timer in star delta starter.?

Obviously, the question is relevant to operating the motor at mains frequency, without VFD (Variable frequency drive or inverter drive).For the convenience of answering and ease of understanding, I am splitting the question in two parts:What is the purpose of the star delta starter?Why is it ncessary to use timer with star delta starter?Answers tpo both the parts of the question are given below.What is the purpose of the star delta starter?During starting (from zero to slightly less than rated speed), motor current depends mainly on the supply voltage. More the supply voltage, more is the starting current. When connected in star, starting current is approximately 1/3 of the starting current in delta connection.At speeds near rated speed, motor current depends upon the load. And for a given load, motor current is inversly proportional to the supply voltage. Hence in steady state condition (speed is stabilised), motor current in delta is 1.73 times higher than the current in Delta. Hence, it is advisable to operate the motor in star, till the motor speeds up near the rated speed.2. Why is it necessary to use timer with star delta starter?If changeover from star to delta is done too early (at too low speeds), motor current remains high for larger time duration (from the instant f changeover till the motor speed increases close to rated speed)If changeover from star to delta is done too late,motor current remains high unnecessary after reaching speed close to the ated speed.Hence changeover from delta to star has to be done as soon as the speed increases close to rated speed. This can be done by using timer and setting it to the time equal to time required to reach rated speed.To know more on this subject, refer to answers to this question:Why is star delta starter preferred with an induction motor?Click on above link for answers to the question.What is the main reason for using the timer in star delta starter. ?.

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