WO2018229793A1

WO2018229793A1 - Split-phase and tapped stator winding induction machines for lci- and vsi-fed hybrid drive applications

Info

Publication number: WO2018229793A1
Application number: PCT/IN2018/050384
Authority: WO
Inventors: Dr. Kamalesh HATUA; Jose TITUS
Original assignee: Indian Institute of Technology Madras
Current assignee: Indian Institute of Technology Madras
Priority date: 2017-06-12
Filing date: 2018-06-12
Publication date: 2018-12-20
Anticipated expiration: 2019-12-12

Abstract

In one embodiment of the invention, two sets of identical stator windings are placed 30 electrical degrees apart and a third winding rated for lower voltage arbitrarily placed with respect to the former windings. A machine with tapped stator windings is also disclosed with the tapping taken from a low voltage point on the main winding. The third embodiment has two sets of identical windings kept thirty degrees electrically apart with low voltage tapping taken from each winding. The low voltage winding terminals are connected to VSIs controlled to provide reactive power to the machine. The higher voltage rated terminals are connected with LCIs operating in quasi-square wave mode with firing angle controlled to provide its active power requirement. The LCIs connected to the 30 degree shifted windings are operated with their current outputs also phase shifted by 30 degrees resulting in mmf harmonic cancellation and smooth torque output.

Description

FIELD OF THE INVENTION

The present invention relates to field of industrial motor drives in the medium voltage range, more specifically a combination of LCI and VSI fed Induction motor drive and multiple configurations of stator windings .

BACKGROUND OF THE INVENTION

Industrial motor drive applications in the multi- megawatt power ranges mostly use Load Commutated Inverter (LCI) fed drives. This is mainly due to the several advantages offered by thyristors over other switching devices. Thyristors are cheap, rugged and have lower losses. Also, they are available in much larger voltage and current ratings which make the converter topology simpler.

LCI fed induction motor drives offer several advantages over conventional LCI fed synchronous motor drives in high power industrial drive applications, due to the better economy and ruggedness of the induction motor. However, the requirement of a leading terminal power factor for proper LCI operation makes the drive topology complicated as the induction motor has an inherent lagging power factor. To overcome this problem, hybrid solutions using both LCI and VSI connected at the terminals of the machine have been proposed in literature However, in the MV range, a VSI connected at the machine terminals is not a very practical solution, due to limitations on the maximum possible voltage ratings of the switches used in the VSI. The Load Commutated Inverter (LCI) fed synchronous machine drive is quite popular in industrial applications in the high power, Medium Voltage (MV) range However, the use of an induction machine can reduce the cost significantly in these drives. Nevertheless, LCI fed induction machine drives are not used because of the commutation problems caused by the inherent lagging nature of the stator currents. Thus, MV induction machine drives are typically IGBT based VSI fed drives. However, IGBT based drives are not as rugged and efficient as thyristor based drives. Also, the use of thyristor converters would drastically reduce the cost of such converters. Thus, it would be much cheaper and efficient if an LCI fed induction motor drive can be used in MV high power applications. In this context, the Active- Reactive Induction Machine (ARIM) was invented [US Patent: 8,169,181 B2] to utilize the benefits of thyristors in induction machine drives. However, the ARIM has a serious drawback in the form of low frequency torque oscillations.

Advantages over existing topologies: With the present- day semiconductor device technology, the following are the most popular drives used in the MV drives segment, a) LCI fed synchronous motor drive is the oldest and cheapest among all the drive topologies. For very high power (>10MW) applications, the LCI fed synchronous motor drives are still very popular due to simplicity, reliability of the power hardware and availability of higher rating thyristors. In this drive, the field winding of a synchronous machine is overexcited to ensure leading power factor at the machine terminals. Thus, thyristor switches of the LCI are turned-off without the help of any external commutation circuits.

b) Cycloconverter based Induction and Synchronous motor drives find application in high power (>10MW) low speed applications. This drive is widely used in steel rolling mills and ball mills in cement industry. The cycloconverter is a circuit which uses the SCR to convert AC power of one frequency (say 50 Hz) into AC power at another frequency (usually limited to about 1/3 of input frequency) . The main advantage of the cycloconverter is that SCR turn-off is achieved by the process of line commutation. The major drawbacks of cycloconverter based drives are the complex power structure and the complex waveform of the line current on the input side, which may require a filter to be included. This drive has several limitations. The drive is sluggish in response. It has starting issues. Moreover, this drive has significant amount of low frequency torque ripple.

c) PWM CSI fed Induction motor drives use GTO or IGCT as the power switch. These switches can be turned on or off by controlling the gating pulses. The CSI drive is simple in power structure; it has inherent four-quadrant operation capability and reliable fuse less short- circuit protection. It has fairly good dynamic response but the drive is costly as it uses GTO and IGCT switches. d) Multilevel VSI fed Induction motor drive became popular due to the advent of high voltage IGBTs as power handling switch. Multilevel VSI (3-level) technology exhibit good dynamic response and improved quality of voltage and current but it cannot be used for very high voltage of operation due to limitation of voltage rating of the IGBTs. The cost of the drive is also very high, e) Cascaded bridge fed drive can be used for still higher voltages (11 kV) without any output side transformer. In this topology, each phase is powered by several full bridge cells connected in series. But this power topology requires complex input side transformer design, bulky DC bus capacitors for every half bridge module and high switch count. Also, this drive does not have regeneration capability.

From the above overview of the existing MV drives topologies it can be observed that every drive has some advantages and disadvantages LCI fed synchronous motor drive is cheap, but it has operational limitations. Cascaded Multilevel and Multilevel VSI fed drives has superior performance but costs of the drives are very high. Also, there are serious limitations when the motor is operated for very high voltage and power. Cycloconverter based drive has limited speed range of operation. PWM-CSI based drive has superior performance compared to LCI fed synchronous motor drive and cycloconverter fed drive. But the drive is costly too. Nowadays IGBT based multilevel VSI fed drive is popular but the drive cost is very high due to current price of medium voltage IGBTs.

OBJECTS OF THE INVENTION

Therefore, it is an object of the invention to disclose hybrid operation of LCI and VSI as induction motor drive. It is yet another object of the invention to disclose a special winding of induction motor stator to overcome the torque oscillation problems.

It is yet another object of the invention to disclose multiple induction machine configurations of stator windings suitable for hybrid operation of LCI and VSI.

SUMMARY OF THE INVENTION

To meet the objects of the invention and overcome the disadvantages of the prior art it is disclosed here a motor drive system for a machine comprising of three sets of stator windings, one set of winding forming a first winding, other two sets of windings forming a second set of windings operable in the second mode, characterised in the that, the entire reactive power required by the machine is supplied from the first winding, fed from a low voltage IGBT based Voltage Source Inverter (VSI), and the entire active power requirement of the machine is fed from the second set of power windings only by using thyristor based Load Commutated Inverters (LCI) .

It is disclosed herein a motor drive system for a machine comprising of two sets of stator winding terminals; one set being main winding terminals or the power terminals, and the other set being the excitation terminals connected to low voltage tap points on the main winding, characterised in that entire reactive power required by the machine is supplied from the excitation terminals, fed from a low voltage IGBT based Voltage Source Inverter (VSI), the entire active power requirement of the machine is fed from the power windings only by thyristor based Load Commutated Inverters (LCI) . It is herein disclosed a motor drive system for a machine comprising of four sets of stator winding terminals, two sets being the power terminals forming a first set, and two sets being the excitation terminals connected to low voltage tap points of the windings forming the first set, characterised in that, each of the excitation terminals are fed from low voltage IGBT based VSIs, with or without an output LC filter which makes the voltages and currents in the winding sinusoidal, and the total reactive power requirement of the machine is fed from the excitation terminals equally, and the first set of stator windings share the total active power requirement equally from the two power terminals.

It is further disclosed herein a method of driving a motor comprising the steps of: providing three sets of stator windings, one set of winding forming a first winding, other two sets of windings forming a second set of windings operable in the second mode; and supplying the entire reactive power required by the machine from the first winding, fed from a low voltage IGBT based Voltage Source Inverter (VSI), and the entire active power requirement of the machine is fed from the second set of power windings only by using thyristor based Load Commutated Inverters (LCI) . It is disclosed herein a method of driving a motor comprising the steps of: providing two sets of stator winding terminals; one set being main winding terminals or the power terminals, and the other set being the excitation terminals connected to low voltage tap points on the main winding; and supplying the entire reactive power required by the machine from the excitation terminals, fed from a low voltage IGBT based Voltage Source Inverter (VSI), the entire active power requirement of the machine is fed from the power windings only by thyristor based Load Commutated Inverters (LCI) .

Also disclosed herein a method of driving a motor comprising the steps of: providing four sets of stator winding terminals, two sets being the power terminals forming a first set, and two sets being the excitation terminals connected to low voltage tap points of the windings forming the first set; feeding to each of the excitation terminals from low voltage IGBT based VSIs, with or without an output LC filter which makes the voltages and currents in the winding sinusoidal; and supplying the total reactive power requirement of the machine from the excitation terminals equally, and the first set of stator windings share the total active power requirement equally from the two power terminals.

BRIEF DESCRIPTION OF THE DRAWINGS

Fig.l is the schematic representation of the spatial arrangements of the first embodiment of the invention. Fig.2 is the circuit arrangement of the disclosed drive of the first embodiment. Fig.3 is the schematic representation of the winding arrangements of the second embodiment of the invention. Fig. is the circuit arrangement of the disclosed drive of the second embodiment.

Fig.5 is the schematic representation of the winding arrangements of the third embodiment of the invention. Fig.6 is the circuit arrangement of the disclosed drive of the third embodiment DETAILED DESCRIPTION OF THE INVENTION

The invention and its various embodiments is better understood by reading the description along with the accompanying drawings which appear herein for purpose of illustration only and does not limit the invention in any way.

Referring to FIG.l and FIG.2, in one of the embodiments, a triple stator winding drive topology is disclosed which will be a viable alternative for multilevel VSI fed drives with a very low cost as the proposed drive uses low cost thyristors and low voltage IGBTs. For a high voltage (11 kV) drive, this topology will be an excellent alternative to the twelve-pulse LCI fed synchronous machine drive. The disclosed drive will be operationally superior and will be cheaper compared to conventional LCI fed synchronous motor drive. It is expected to be more efficient compared to existing VSI fed drives as there will be huge savings in switching and conduction loss. Interestingly the proposed drive encompasses the benefits of most of the MV drives with lower cost but the topology remains unnoticed till date. In the first embodiment, the machine has three sets of three phase windings. Two of the windings (power windings), hereafter referred to as PI and P2 windings, are rated for a higher voltage while the third winding, hereafter referred to as Fl winding is rated for a lower voltage. The PI and P2 windings are spatially placed such that their axes are displaced from one another by 30 electrical degrees. The axis of the Fl winding can be placed arbitrarily irrespective of the power winding axes.

The entire reactive power required by the machine is supplied from the Fl winding, fed from a low voltage IGBT based Voltage Source Inverter (VSI) . The entire active power requirement of the machine is fed from the two power windings only by using thyristor based Load Commutated Inverters (LCI) . The proper commutation of the switching devices in the LCI requires a leading power factor to be seen at the terminals. This is ensured by supplying additional reactive power from the VSI connected to the flux winding.

Another embodiment of the invention has a single three phase winding with a low voltage tapping, while another embodiment, the third has two tapped stator windings. In both cases, the drive is operated from an LCI connected at the main machine terminals and a VSI connected at the terminals of the tapping. Since the terminal voltage at the tapping is much smaller than the rated voltage of the machine, a direct VSI connection is made possible. The VSI is controlled so as to provide only the required reactive power to the machine. All the active power is supplied from the LCI by controlling the firing angle of the thyristors. The second embodiment may be called the Tapped Stator ARIM (TSARIM) , and the third embodiment may be called as the Split Phase Tapped Stator ARIM (SP-TSARIM) . The machines are built with stator windings having low voltage taps. For e.g. a tapping can be provided at 690 V for a machine with a rated voltage of 6.6 kV. The main winding terminals are hereafter referred to as the power terminals, and the terminals of the low voltage tapping are referred to as the excitation terminals. Referring to FIG.3, here a single three phase stator winding with low voltage taps is used. The rotor structure is a standard squirrel cage. The power topology of the hybrid LCI and VSI fed drive in the second embodiment is as shown in Fig.4. The power terminals are labeled PA, PB and PC. The excitation terminals are labeled FA, FB and FC . The entire reactive power required by the machine is supplied from the excitation terminals, fed from a low voltage IGBT based Voltage Source Inverter (VSI) . The entire active power requirement of the machine is fed from the power windings only by using thyristor based Load Commutated Inverters (LCI) . Speed control is done from the LCI side by controlling the DC link output current of the rectifier. The LCI is operated with a constant commutation margin angle control. Flux control is taken care of, from the VSI side. The LC filter connected at the output of the VSI makes the current and voltage at the excitation terminals sinusoidal. This also results in a sinusoidal voltage at the power terminals. The proper commutation of the switching devices in the LCI requires a leading power factor to be seen at the terminals. This is ensured by supplying additional reactive power from the VSI connected to the flux winding. Further the VSI can also be used to compensate for some of the lower order current harmonics injected from the LCI. The proposed drive topology is presented in Fig.4. Since the VSI is connected to a lower voltage tap on the stator winding, no additional interfacing transformer is required. Also, because the tapping is taken from the same stator winding, no additional insulation space is required within the stator slots.

The SP-TSARIM is an improvised version of the TSARIM with two separate sets of stator windings. Each winding is provided with a tapping at a low voltage point. Further each of the winding is spatially separated with an electrical angle of 30 degrees between their axes. The winding configuration corresponding to this structure is shown in Fig.5. The circuit configuration of the SP-TSARIM drive is shown in Fig.6.

The drive topology using the machine in third embodiment uses two sets of LCIs connected to the power terminals of each of the stator winding. The power terminals are labeled PA1, PBland PCI for the first winding, and PA2, PB2 and PC2 for the second winding. Each of the excitation terminals (FA1, FBI, FC1 and FA2, FB2, FC2) are fed from low voltage IGBT based VSIs via an output LC filter, which makes the voltages and currents in the winding sinusoidal. Since the stator winding is now split in two different sections, the rating of each converter (LCI as well as VSI) needs to be only half that in the second configuration. The individual VSIs are controlled such that the total reactive power requirement of the machine is fed from the excitation terminals equally. The LCIs share the total active power requirement from the two power terminals. The firing angles of the LCIs are controlled such that their output current vectors differ by 30 electrical degrees. This results in a cancellation of the mmfs corresponding to the 5th and 7th harmonic currents of the LCI, within the air gap of the machine.

Thus, though the SP-TSARIM drive requires an additional set of converters compared to the TSARIM drive, the ratings of the individual converters are lower, and it also results in a much smoother torque profile.

It will be obvious to a person skilled in the art that with the advance of technology, the basic idea of the invention can be implemented in a plurality of ways. The invention and its embodiments are thus not restricted to the above examples but may vary within the scope of the claims

Claims

aim:

A motor drive system for a machine comprising of three sets of stator windings, one set of winding forming a first winding, other two sets of windings forming a second set of windings operable in the second mode, characterised in the that, the entire reactive power required by the machine is supplied from the first winding, fed from a low voltage IGBT based Voltage Source Inverter (VSI), and the entire active power requirement of the machine is fed from the second set of power windings only by using thyristor based Load Commutated Inverters (LCI) .

The motor drive system as claimed in claim 1, wherein in the second set of windings, the two windings are spatially placed such that their axes are displaced from one another by 30 electrical degrees .

The motor drive system as claimed in claims 1 or 2, wherein, the first winding is placed with its axis at any arbitrary position relative to the two windings of the second set of windings.

The system as claimed in claim 1, 2, or 3, wherein the LCI are operated in quasi-square wave mode with 30 degree electrical phase shift between their fundamental currents, such that harmonic cancellation of the fifth and seventh harmonics in the machine mmf occurs within the air-gap of the machine .

The system as claimed in claim 1, 2, 3, or 4, wherein the VSI is controlled using field oriented control to supply only reactive power to the machine from the VSI, and the power factor at the LCI terminals appear leading.

A motor drive system for a machine comprising of two sets of stator winding terminals; one set being main winding terminals or the power terminals, and the other set being the excitation terminals connected to low voltage tap points on the main winding, characterised in that entire reactive power required by the machine is supplied from the excitation terminals, fed from a low voltage IGBT based Voltage Source Inverter (VSI), the entire active power requirement of the machine is fed from the power windings only by thyristor based Load Commutated Inverters (LCI) .

The system as claimed in claim 6, wherein the VSI is controlled using field oriented control to supply only reactive power to the machine from the VSI, and the power factor at the LCI terminals appear leading.

A motor drive system for a machine comprising of four sets of stator winding terminals, two sets being the power terminals forming a first set, and two sets being the excitation terminals connected to low voltage tap points of the windings forming the first set, characterised in that, each of the excitation terminals are fed from low voltage IGBT based VSIs, with or without an output LC filter which makes the voltages and currents in the winding sinusoidal, and the total reactive power requirement of the machine is fed from the excitation terminals equally, and the first set of stator windings share the total active power requirement equally from the two power terminals.

The system as claimed in claim 8, wherein the LCI are operated in quasi-square wave mode with 30 degree electrical phase shift between their fundamental currents, such that harmonic cancellation of the fifth and seventh harmonics in the machine mmf occurs within the air-gap of the machine .

The system as claimed in claims 8 or 9, wherein the VSI is controlled using field oriented control to supply only reactive power to the machine from the VSI, and the power factor at the LCI terminals appear leading.

A method of driving a motor comprising the steps of:

providing three sets of stator windings, one set of winding forming a first winding, other two sets of windings forming a second set of windings operable in the second mode; and

supplying the entire reactive power required by the machine from the first winding, fed from a low voltage IGBT based Voltage Source Inverter (VSI), and the entire active power requirement of the machine is fed from the second set of power windings only by using thyristor based Load Commutated Inverters (LCI) .

The method as claimed in claim 11, wherein in the second set of windings, the two windings are spatially placed such that their axes are displaced from one another by 30 electrical degrees.

The method as claimed in claims 11 or 12, wherein, the first winding is placed with its axis at any arbitrary position relative to the two windings of the second set of windings.

The method as claimed in claims 11, 12, or 13, wherein the LCI are operated in quasi-square wave mode with 30 degree electrical phase shift between their fundamental currents, such that harmonic cancellation of the fifth and seventh harmonics in the machine mmf occurs within the air-gap of the machine .

The method as claimed in claim 11, 12, 13, or 14, wherein the VSI is controlled using field oriented control to supply only reactive power to the machine from the VSI, and the power factor at the LCI terminals appear leading.

A method of driving a motor comprising the steps of:

providing two sets of stator winding terminals; one set being main winding terminals or the power terminals, and the other set being the excitation terminals connected to low voltage tap points on the main winding; and

supplying the entire reactive power required by the machine from the excitation terminals, fed from a low voltage IGBT based Voltage Source Inverter (VSI), the entire active power requirement of the machine is fed from the power windings only by thyristor based Load Commutated Inverters (LCI) .

The method as claimed in claim 16, wherein the VSI is controlled using field oriented control to supply only reactive power to the machine from the VSI, and the power factor at the LCI terminals appear leading.

A method of driving a motor comprising the steps of:

providing four sets of stator winding terminals, two sets being the power terminals forming a first set, and two sets being the excitation terminals connected to low voltage tap points of the windings forming the first set; feeding to each of the excitation terminals from low voltage IGBT based VSIs, with or without an output LC filter which makes the voltages and currents in the winding sinusoidal; and

supplying the total reactive power requirement of the machine from the excitation terminals equally, and the first set of stator windings share the total active power requirement equally from the two power terminals .

The method as claimed in claim 18, wherein the LCI are operated in quasi-square wave mode with 30 degree electrical phase shift between their fundamental currents, such that harmonic cancellation of the fifth and seventh harmonics in the machine mmf occurs within the air-gap of the machine .

The method as claimed in claims 18 or 19, wherein the VSI is controlled using field oriented control to supply only reactive power to the machine from the VSI, and the power factor at the LCI terminals appear leading.