Dual power motor. Speed ​​regulation in dual feed machine

DESCRIPTION OF THE INVENTION TO THE AUTHOR'S CERTIFICATE Union of Soviet and Socialist Republics 773887 (23) Priority 12,10,78 Published on 10/23/80. Bulletin RI 39 in cases of inventions and discoveries Date of publication of the description 10/25/80 A. A, Krugly, N. G. Bo Chkova and B. N. Abramovich (71) Applicant Central Design and Technological Bureau of Large Electrical Machines (54) DOUBLE-POWER MACHINE The invention relates to electrical engineering, namely to an alternating current electric drive controlled by a thyristor frequency converter and can be used to drive high-power industrial installations , for example, ore-enamel mills. A device is known that contains an asynchronous machine with a multiphase armature connected to the supply network through a 30-res switch, and an inductor connected directly to the output of a frequency converter, the input of which is connected to the output of the power source of the specified converter, a control unit 15 of the frequency converter ; the input of which is connected to the steady-state mode controller through a switch, the second input of which is connected to the output of the control unit when starting the engine. However, the known device has an installed power of the frequency converter and its power source greater than that required for regulating the engine in steady-state modes, and also requires the use a complex stator switching circuit in the form of a switch with a short circuit or several switches. The purpose of the invention is to reduce the installed power and simplify it. equipment, The goal is achieved by the fact that one input of the control unit at start-up is connected to the output of the frequency converter, and its second input is connected to the output of the power source of the specified frequency converter. In addition, the control unit, at start-up, is made in the form of a series-connected signal conditioner, the output of which forms the output of the control unit at start-up, a comparison device, the first input of which forms the input of the control unit at start-up, and an AC-to-DC converter, the input of which forms the second input of the control unit at start-up.3 7738The drawing shows a diagram of the device. The device contains an asynchronous machine 1 with a multi-phase armature (stator) and an inductor (rotor). Through switch 5. body 2 with one closing contact per phase (i.e., normal type) stator machine 1 is connected to the supply network, the rotor of machine 1 is blindly connected to the output of frequency converter 3, frequency converter 3 is connected to the output of its power source 4. The converter valves 3 are switched on by the converter control system 5. The output of commutator 6 is supplied to the input of system 5, which sets the phase. The commutator has two inputs connected through diodes. The output of the steady-state mode regulator 7 is connected to the first input of the switch. The outputs of the regulator 7, for example, the tachogenerator 8, current transformers 9 and voltage 10 in the stator circuit of machine 1 are connected to the input of the regulator 7. The output of the control unit 11 at start-up is connected to the second input of the switch 6. The first input 25 of the control unit at start-up is connected by a circuit 12 with the output of the frequency converter 3, and the second by a circuit 13 with the output of the power source 4. The control block 11 at start-up contains a signal shaper 14, connected by the input to the output of the comparison device 15, one input of which is supplied connection 12, and on the second - connection 13, through the AC-to-DC converter 16. The proposed device works as follows. In the initial position before starting 40 machine 1, switch 2 is turned off, and converter 3, source 4 and control elements 5-16 are turned on. At the moment switch 2 is turned on on the rotor of machine 1, and, accordingly, at the output of converter 3 (which is the same with a dead" connection), a voltage appears that increases to a value significantly greater than the output voltage of converter 3 in steady state. The final voltage in amplitude 50 is equal to the amplitude of the output of source 4. This voltage, through converter 16, is continuously compared in device 15 with the rotor voltage, Both at 55 voltages are supplied to devices 15, 16 through circuits 12, 13. When the rotor voltage (circuit 12) is established in magnitude greater than the source voltage (circuit 13). passing through the digital switch 6 and suppressing the output signal of the regulator 7, it sets the pulse phase in system 5 corresponding to the inverter mode of the converter 3. Suppression of the signal of the regulator 7 in the switch 6 occurs due to the fact that the largest value of the output signal of element 7 is less than the value of the signal by output of the shaper 14. And the diode switch passes only the largest signals. As a result, the valves of the converter 3 turn on and limit the rotor voltage to the voltage of source 4. The current in the rotor circuit is determined by the difference between the applied emf and the voltage of source 4. The rotor voltage begins to increase at the moment the current passes through zero, therefore, on the rotor rings the current and voltage coincide in phase, which means that the action of converter 3 is equivalent to the introduction of active resistance. In this case, the current decreases slightly compared to starting with a short-circuited rotor, and the torque increases significantly. Machine 1 accelerates, the voltage induced in the rotor from the stator decreases, the signal from circuit 12 becomes less than the signal from circuit 13, devices 15 and 14 do not produce a signal, and regulator 7 comes into operation. Machine 1 goes into steady state. formula 1, machine double power supply, containing an asynchronous machine with a multi-phase armature connected to the supply network through a switch, and an inductor connected directly to the output of the frequency converter, the input of which is connected to the output of the power source of the specified converter, a frequency converter control unit, the input of which is connected to the steady-state controller through a switch, the second input of which is connected to the output of the control unit at start-up, differing in that, in order to reduce the installed power and simplify the equipment, the input of the control unit at start-up is connected to the output of the frequency converter , and its second input is connected to the output of the power source of the specified frequency converter, 5 773882, The machine according to claim 1, with the exception that the control unit at start-up is made in the form of a series-connected signal conditioner, the output which forms the output of the control unit at start-up, the comparison device, the first input of which forms the input of the control unit at start-up, and the converter 7 of the AC to DC input of which forms the second input of the control unit at start-up. Sources of information taken into account during the examination 1. Author's certificate of the USSR M 411597, class, N 02 R 7/46, 1972.kaz 7527/77 Circulation 783 All-Russian Scientific Research Institute for Inventions and 113035, Moscow, Zh, Rauw

Application

1954690, 17.08.1973

CENTRAL DESIGN AND TECHNOLOGICAL BUREAU OF LARGE ELECTRICAL MACHINES

ROUND ALEXANDER ARONOVICH, BOCHKOVA NINA GRIGORIEVNA, ABRAMOVICH BORIS NIKOLAEVICH

IPC / Tags

Link code

Double Feed Machine

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By design, a dual-fed machine (asynchronized synchronous machine, controlled AC machine) is similar to an asynchronous machine with a wound rotor. As a rule, a three-phase winding is placed on its stator, and a two-phase or three-phase winding is placed on the rotor.

The stator winding receives power from the network at the frequency of the supply voltage f 1 , and to the rotor winding through a controlled valve converter IF voltage is supplied with frequency f 2 (f 2 < f 1 ) . Voltage frequency and amplitude IF regulated according to a given law by the control system. It is advisable to use dual-power machines in high-power installations, where their advantages are most pronounced. They can operate as generators and motors in both synchronous and asynchronous mode.

In a dual power machine driven by a motor, changing f 2 rotation speed can be adjusted. Current frequency in the rotor of an asynchronous machine

f 2 = f 1 s , (1)

s = ( n 1 - n ) / n 1 (2)

n 1 - frequency of rotation of the magnetic field.

Solving (1) and (2) together, we obtain the dependence

rotor speed n from f 1 And f 2 :

n = n1( f 1 ± f 2 ) / f 1 . (3)

The plus sign corresponds to phase rotation IF, in which the rotor and its magnetic field rotate in opposite directions, and minus - when they rotate in the same direction.

From (3) it follows that, depending on the direction of rotation of the rotor magnetic field, one can obtain n < n 1 , or n > n 1 , If during operation you maintain f 2 = const, then the machine will operate in synchronized mode, and when f 2 = var- in asynchronous. When f 2 = 0 (supplying the rotor winding with direct current), then the machine operates like a conventional synchronous motor.

In order to reduce the active power of the frequency converter, which is equal to R p.h = ( f 2 / f 1 ) R EM (Here R EM - electromagnetic power), frequency f 2 change within small limits. In addition to the rotation speed in a dual-fed machine operating as a motor, it is possible to regulate the reactive power and cos φ . The machine can work with both leading and lagging current. If the additional EMF supplied to the rotor winding E D coincides in direction with the EMF induced in it E 2 , then in this case the rotor speed is regulated. When changing phase E D relatively E 2 Simultaneously with the regulation of the rotation speed, the reactive power also changes, i.e. cos φ .

Double-fed machines operating in power systems as generators have certain advantages over conventional synchronous generators: they operate more stably in modes of deep reactive power consumption, have greater dynamic stability, provide compensation for frequency fluctuations, etc.

Dual power machines can be used as an electromechanical frequency converter for flexible communication of power systems, the frequencies of which differ slightly from each other (no more than 0.5 - 1%). An electromechanical frequency converter for flexible communication of power systems consists of two machines connected by a common shaft (see figure). One of these machines is an ordinary synchronous machine CM, and the other is a dual power machine TIR. The stator windings of machines are connected to different power systems. The control system generates a signal such that the voltage frequency in the rotor of the dual-power machine is equal to the difference in frequencies of the connected power systems. One of the machines works as an engine, and the other as a generator. In this case, power from one power system is transferred to another.

A dual power machine can be used as a constant frequency voltage source at variable rotor speed.

Let's express it in (3) n 1 , through f 1 (from formula n 1 = 60f 1 / p ).

After transformation we get

f 1 = рn / 60 ±f 2 (4)

From (4) it follows: that at a variable rotor speed n get f 1 =const, it is necessary to change the frequency accordingly f 2 voltage supplied to the rotor.

Double-feed machines have not yet been widely used. They are manufactured in single units.

At compressor stations of main gas pipelines and other industrial facilities equipped with an electric drive, an intermediate link - a gearbox - is used between the working mechanism and the electric motor. There is a special class of electrical machines, the use of which would eliminate the need for a gearbox. These are dual feed machines (DFM). Study of MIS having double synchronous speed on the shaft, i.e. 6000 rpm at a frequency of 50 Hz and a 2-pole design, is of very great practical importance for industry, as it allows you to create a gearless electric drive for powerful centrifugal compressors and pumps. The use of a reliable and economical electric drive makes it easier to carry out complex automation tasks for industrial facilities.

In the laboratory, MIS was studied in motor mode with parallel connection of windings when powered from an industrial frequency network, and when rotating at double synchronous speed. The studies were carried out using a balancing device. In this installation, the motor under test is rigidly connected through a coupling to a direct current machine, the housing of which, within certain limits, could rotate freely relative to the shaft. A schematic diagram of the installation on which the experimental study was carried out is shown in Fig.1, which indicates:

MDP - tested asynchronous machine in dual-fed motor mode;

MPS and GPS are independent excitation direct current machines.

The direct current machine (DCM) serves as an accelerating motor for the MDP, and is also a dynamometer that allows you to directly measure the torque of the MPM and load it.

A serial asynchronous motor with a wound rotor was used as the tested MIS, which has the following data:

Engine type - AK-52-6;

Power P nom = 2.8 kW;

Connection diagram of stator windings D/Y;

Stator voltage 220/380 V;

Stator current 13.0/7.5 A;

Nominal shaft rotation speed 920 rpm;

Efficiency - 75.5%;

Power factor cosj= 0.74;

Connection of rotor windings Y;

Voltage 91 V;

Current 21.2 A.

MPS and GPS machines are ordinary serial DC machines of the PN-85 type with the data: P nom = 5.6 kW, U = 220 V, I nom = 30 A, n = 1000 rpm.

The R MOS rotor was powered through an adjustable three-phase autotransformer of the RNT type. To synchronize the MDP with the network, ordinary incandescent lamps are used, turned on in dimming mode at the time of synchronization.

Before starting the installation, it is necessary to find the forward rotation of the stator field and the reverse rotation of the MIS rotor field. To do this, the output ends of the rotor winding R are connected to each other and the MIS is started as a regular squirrel-cage electric motor by applying voltage to the stator using the QF1 circuit breaker. At the same time, the direction of rotation of the engine rotor is fixed. Then, the MIS is switched on with a reversed asynchronous motor by applying voltage to the rotor, having previously connected the output ends of the stator winding S to each other. The same direction of rotor rotation in the first and second cases corresponds to the reverse rotation of the rotor field, that is, the reverse alternation of rotor phases. If this condition is not met, then swap the connection to the network phases A, B, C of any two terminals of the stator winding S or rotor R and again check the fulfillment of the specified condition.

The installation is started as follows: the drive asynchronous motor of the GPS generator is started, resistor R3 is used to set the voltage to 220 V at its terminals. By turning on QF 1, voltage is supplied to the stator S of the MIS, and by turning on QF 2, voltage is supplied to the autotransformer RNT. Then, by rotating the autotransformer handle, the required voltage for the machine rotor is set (91 V). At the same time, EL incandescent lamps burn with an even, non-flashing light. Having secured the MPS body with locking screws, the latter is started by turning on the QF4 circuit breaker and decreasing the value of resistor R2. By smoothly reducing the magnetic flux of the MPS with resistor R1, the MPS is accelerated to double synchronous speed (2000 rpm).

As the rotation speed of the MDP increases, the flashing frequency of the EL lamps decreases. At the moment of synchronization (the lamps go out and do not light up), the QF 3 circuit breaker is turned on. After several swings, the MIS is drawn into synchronization with the network and operates as a synchronous machine in motor mode at a synchronous rotation speed of 2000 rpm. This completes the installation start-up.

By changing the magnetic flux of the MPS (resistor R1), you can smoothly regulate the MIS load from idle to nominal and higher. To do this, it is necessary to release the locking screws securing the MPS housing, which makes it possible to directly measure the torque of the MPS using the scale of the balancing machine and the index arrow attached to the housing of the MPS loading machine. The QF 4 switch can be used to instantly switch on and off any preset load. In this case, the MPS housing must be secured with locking screws during a jerky load.

During the tests, measurements were made of current, voltage, active power, rotation speed, torque and load angle and MDP. Measurements in the stator circuit were carried out using a portable measuring set of type K-50, and in the rotor circuit, active power was measured using a circuit of two wattmeters of type D539/4, having measurement limits for voltage of 75 - 600 V, and for current of 5 - 10 A, connected through current transformers.

The current in the rotor circuit was measured with three ammeters with measurement limits of 0 - 25 A, and two voltmeters were used to measure voltage. One ammeter with a scale of 0 - 250 V, connected to the output of the RNT autotransformer, was used to preset the voltage required for the MIS rotor. The second - astatic type ASTV with measurement limits of 0 - 150 V was directly connected to the terminals of the MIS rotor and was used specifically for measurement purposes.

The measurement of the rotation speed of the MDP was carried out using a stroboscopic device of the ST-5 type, and the measurement of the load angle and the study of oscillations (swings) of the MDP were carried out using a special device developed by the author of this article.

To determine the values ​​of no-load current and power, mechanical losses and losses in steel, to measure the magnetization characteristics and determine the degree of MIS saturation, an no-load experiment was carried out. The idle test was carried out according to the diagram shown in Fig.2, with the only change that the windings of the MDP stator and the RNT autotransformer were connected to the network through a common induction regulator. In addition to the recommendations that GOST gives for conducting an idling test, one must keep in mind that at idling at low voltages the MIS operates unstable and falls out of the synchronous operating mode. Stable operation can be achieved if the MDP has a load on the shaft, the magnitude of which may be insignificant compared to the power of the machine.

Methodology for collecting data when conducting an idle test

MDP starts and loads slightly. The induction regulator sets the required voltage on the stator, and the RNT autotransformer sets the required voltage on the rotor (the required voltage points are calculated in advance, taking into account the constancy of the machine’s transformation ratio). Switch QF 4 removes the load from the MIS, then the compliance of the set voltage points on the stator and rotor is checked, if necessary, correction is carried out, after which instrument readings are taken and the machine is loaded again (by turning on QF 4). Similarly, other idle speed characteristic points are obtained. Immediately after the no-load test, the resistance of the stator and rotor windings is measured using a measuring bridge. For the stator circuit, the resistance was 1.153 Ohms, for the rotor circuit - 0.15 Ohms.

The power consumed by the MIS stator at idle speed covers losses in the copper of the stator winding, in steel and part of the mechanical losses, that is:

P 1 = P M1 + P C1 + P MEX1 (1)

Similarly for the MDP rotor

P 2 = P M2 + P C2 + P MEX2 (2)

From these expressions it is clear that MDP has no secondary losses, because The network energy is supplied to both the stator and the rotor. To separate mechanical losses and losses in steel, we isolate losses in copper from the expressions written above.

In this case

P OS = P 1 - P M1 = P C1 + P MEX1, (3)

P OR = P 2 - P M2 = P C2 + P MEX2

where P OS and P OR are no-load losses in the stator and, accordingly, in the rotor.

The division of no-load losses for the stator circuit of the AK-52-6 engine in MIS mode is shown in Fig.3. A similar division of losses is carried out for the rotor circuit.

By dividing the losses, it was found that the mechanical losses covered on the stator side are 270 W, and on the rotor side - 256 W, i.e. we have virtually equal coverage of mechanical losses on both the stator and rotor sides. The total mechanical losses of the MDP are 526 W, which exceeds the mechanical losses of the AK-52-6 in conventional asynchronous mode due to the higher motor speed in this operating mode.

The power factor at no-load MIS for the stator is determined by the formula:

cosj= P 1 / (Ö3U 1 *I 01) (5)

The power factor for the rotor is determined similarly. The inductive components of the no-load currents for the stator and rotor are found from the expressions

I m1 = I O 1 *sinj 1 (6)

I m2 = I O 2 *sinj 2 . (7)

From the idle test data and the results of their processing, the following conclusion follows:

The no-load current of the machine under study in the MIS mode remains the same, therefore, we can talk about a relative decrease in the no-load current by half, because The power of the machine in this mode doubles.

On Fig.3 shows the magnetization curves of the motor under study in the MIS mode, where U Ф is the phase voltage of the motor; E F - phase electromotive force of the motor (EMF); I m - magnetizing current of the motor. On Fig.4 shows the inductive resistance curve of mutual induction X m, reduced to the stator phase, constructed from the results of the no-load experiment.

The experimental determination of the operating characteristics of the MDP was carried out by two methods: direct and indirect. When determining the characteristics by the direct method, the value of the useful torque was directly read from the scale of the balancing machine, taking into account the correction, which was found empirically according to. The amount of useful power was determined by the expression:

h= P 2 / P 1 (9)

When determining the performance characteristics by the indirect method, losses in steel and mechanical losses of the MDP were assumed to be constant. Losses in the copper windings were determined in the usual way, the efficiency of the MOS was determined by the formula:

h= (P 1 - SP) / P 1 (10)

P 1 - power consumed by the stator and rotor of the MIS;

SP is the amount of losses in TIR.

The power factors of the stator and rotor are found from the expressions

cosj 1 = P 1 / (Ö3U 1 *I 1), cosj 2 = P 2 / (Ö3U 2 *I 2) (11)

The MIS load during the experiment was changed using resistor R1 ( see fig.1). At the same time, voltages, stator and rotor currents of the MIS, torque, power supplied to the stator to the rotor and load angle, etc. were recorded. The results of the study by the direct method are presented in Fig.6 in the form of basic performance characteristics

h= f(P 2) and cosj= f (P 2) (11)

For ease of comparison with the usual asynchronous mode on Fig. 5, a The net engine power is given in kilowatts, per Fig. 5, b- in percentages. The rated power of the engine in MIS mode is taken to be 5.6 kW, because at this power, the stator and rotor of the MIS flow around rated currents. From the given main operating characteristics of an asynchronous machine with a wound rotor it follows that a serial asynchronous motor in dual-power motor mode has significantly better energy performance, namely:

1) an asynchronous motor with a wound rotor in MIS mode in the same dimensions doubles its power (from 2.8 kW to 5.6 kW);

2) the efficiency factor (efficiency) of the engine increases significantly (from 75.5% to 84.5%), and the power factor of the engine in MIS mode - from 0.76 to 0.96.

Studies of the MDP for stability of operation have shown that in engine mode it operates stably over the entire load range, starting with a small load and ending with double overloads (P NOM AD = 2.8 kW, P NOM MDP = 5.6 kW, P max MDP = 11.7 kW, and max = 42°). Achieving the calculated overload (P max MDP = 16.8 kW) was limited by the possibility of the braking device.

A jolt of loads, even above the rated load, does not take the MDP out of the synchronous operating mode. The same can be said with a sudden load shedding from the MDP.

Tests on the stability of the MDP operation also revealed that the time of calming down of its oscillations when the load is applied is significantly less than the time of calming down when dumping. This confirms the theoretical conclusions that the MDP during idling operation is closer to an unstable state. A decrease in the voltage of the supply network and operation of the MIS at idle leads to the occurrence of oscillations (swings), so under these conditions their operation should be considered unstable. Obviously, it is precisely this phenomenon that explains the widespread opinion that the MDP is prone to undamped oscillations. A small load (up to 0.1 R NOM for the AK-52-6 type engine under study) completely eliminates oscillations and the MDP operates stably - without oscillations or loss of synchronous operation.

conclusions

1. Conducted experimental studies of a serial asynchronous motor of the AK-52-6 type with a wound rotor when operating in dual power mode at double synchronous speed, i.e. in dual-fed machine (DFM) mode, confirm the high technical and economic indicators of this class of machines. They have a high efficiency, exceeding the efficiency of the normal mode, which is explained by the absence of secondary losses in these machines (losses in the secondary winding of the transformer, losses in the rotor of an asynchronous motor, excitation losses of a synchronous machine). According to the principle of operation, MDP has no secondary losses at all, because The stator and rotor are primary, the windings of which are connected directly to one common network.

2. MIS are characterized by high values ​​of power factor (cosj), which is associated with the joint action of two power systems to create a common magnetic flux of the machine.

3. MDP develops double power compared to an asynchronous machine in the same dimensions and has double synchronous rotation speed at an industrial frequency of 50 Hz, which allows you to obtain one non-standard rotation speed of 2000 rpm.

4. It has been established that MDPs can operate stably under almost any load. This is confirmed by the oscillograms of load dumping and loading during MDP operation.

Transient processes in MIS associated with load changes are periodic and, just like in conventional synchronous machines, they are damped.

When the voltage of the supply network decreases and the MIS operates at idle, oscillations (oscillations) occur, so under these conditions their operation should be considered unstable.

5. The quality of performance characteristics, the possibility of stable operation of conventional serial asynchronous motors with a wound rotor in MIS mode have shown that this class of electrical machines can serve as a compact and economical energy converter. It can be used practically not only as a high-speed drive (n = 6000 rpm) at an industrial frequency of 50 Hz, but also at ordinary standard rotation speeds with an additional speed of 2000 rpm.

Literature:

1. Gervais G.K. Industrial testing of electrical machines. Gosenergoizdat, 1959.

2. Nuremberg V. Testing of electrical machines. Gosenergoizdat, 1959

3. Kolomoytsev K.V. Switching on a synchronous generator for parallel operation with a network and about a dual-power machine // Electrician. - 2004. - No. 10. - P.11-12.

4.Kolomoytsev K.V. Energy capabilities of dual-power machines // Electrician. - 2008. - No. 5. - P.48.

5. Kolomoytsev K.V. A device for measuring the load angle and studying the oscillations of a dual-fed machine at synchronous speed. Elektrik. - 2011. No. 11. - P.37-39.

Unlike valve cascade circuits, where the flow of sliding energy is directed only in one direction - from the motor rotor to the inverter and then to the supply network, in dual-power motor circuits, a converter is included in the rotor circuit (Fig. 6.38), providing two-way energy exchange, like from the motor rotor to the supply network, and from the network to the rotor windings of an asynchronous motor. Such a converter is a direct coupled frequency converter. In this case, the additional EMF introduced into the rotor circuit can be directed either against the EMF of the rotor, in accordance with it, or at a certain angle (l - 8). In general

TJ = TT g)

°ext ^ext^

Rice. 6.38.

UFA, UFB, UFC- frequency converters with continuous communication

The rotor current is determined from the voltage equilibrium equation in the rotor circuit:

Where z 2 - complex resistance of the rotor circuit.

The active and reactive components of the rotor current are equal:

In these formulas: E y E 2n - current and nominal (at 5=1) rotor EMF;

The active component of the rotor current determines the motor torque and the mechanical power of the motor: mech = co (1-5).

The reactive component of the rotor current determines the reactive power circulating in the stator and rotor circuits of the motor:

Equalities (6.67) show that by adjusting the values ​​and phase of the additional voltage add introduced into the rotor circuit, it is possible to control the active and reactive powers of the engine. From this position it also follows that for the corresponding values U 2 and 8 the active component of the rotor current can be negative for positive slips 5 > 0 and positive for negative slips 5

Braking power R in the case under consideration is insufficient to create electromagnetic power R, therefore, the missing power, proportional to the slip s = co 0 5, is taken from the network through the transformer and rotor converter and sent to the motor rotor.

coming from the shaft, and sliding power + = co =

generates electromagnetic power, which is recovered into the supply network. The power supplied to the network is equal to the difference between the recovered power transmitted through the stator circuit and the power taken from the transformer: = -

In motor mode, at speeds above synchronous speed (Fig. 6.39.5), sliding power is added to the rotor circuit of the motor, taken from the network from the transformer side. It is added to the electromagnetic power entering the engine from the stator side. The sum of these powers is converted into mechanical power on the motor shaft, ensuring that the motor operates with torque M at speeds above synchronous:

Rice. 6.39.A- regenerative braking mode at speeds below synchronous; b- motor mode at speed above synchronous

Note that, despite the fact that slip in this case is negative, the engine develops a motor torque.

In both modes under consideration, the frequency converter operates in such a way that energy from the transformer enters the motor rotor, i.e. The motor is powered from both the stator and rotor sides.

Since the frequency / 2 of the EMF and rotor current is determined by the motor slip / 2 = /, then the frequency of the additional EMF introduced into the rotor circuit must coincide with the frequency of the rotor EMF and change when the motor slip changes.

The maximum possible range of speed control down and up from synchronous is determined by two parameters - the possible maximum values ​​of frequency / 2 and voltage ^ dobtah at the output of the frequency converter serving to power the rotor circuit. The maximum speed control range will be = co max /co m =(+ max)/(- max).

The absolute value of the maximum slip is

| Shah | ^doO / 2n "

Since a direct coupled frequency converter typically provides frequency regulation within 20 Hz (with a supply frequency of 50 Hz), which corresponds to a maximum slip | 0max | = 0, then the maximum speed control range of the dual-fed motor is: = , с 0 /0, с 0 ~ 2, : .

Speed ​​control in the dual-power motor circuit is carried out by changing the relative value and sign of the additional EMF 8 = ?/ext/2n, while the frequency at the converter output is automatically maintained equal to the frequency of the rotor current. The mechanical characteristics of the double-fed motor at 8 = 0.2 are shown in Fig. 6.40.

The main advantage of valve cascade circuits and dual-fed motors is their high efficiency, which is maintained when speed is controlled within a given range. Since these controlled asynchronous drive systems have a limited control range, as a rule, no higher than 2:1, these systems are used mainly to drive powerful (above 250 kW) turbo mechanisms: fans, centrifugal pumps, etc.

Electrical complexes and systems 25 ELECTRICAL COMPLEXES AND SYSTEMS UDC 621.3.07 A.V. Grigoriev OPTIMAL CONTROL OF A DOUBLE-POWERED MACHINE The term “double-fed machine” (DMM) refers to an asynchronous motor with a wound rotor, which can receive power from both the stator and the rotor. Let's consider the MIS control problem with the goal J = inf ∫ (M Z − M) 2 dt, where Mz is the specified 0 (required) value of the electromagnetic torque of the motor, M is the instantaneous value of the electromagnetic torque of the motor. To solve the control problem, we present the MIS model in a coordinate system fixed relative to the rotor voltage vector: ⎧ dΨSX ⎛Ψ ⎞ k = U SX − R S ⎜⎜ SX − R Ψ RX ⎟⎟ + ω 2 ΨSY , ⎪ dt L " L " S ⎪ ⎝ S ⎠ ⎪ ⎞ ⎛ ΨSY k R ⎪ dΨSY = U − Ψ RY ⎟⎟ − ω 2 ΨSX , SY − R S ⎜⎜ ⎪ dt ⎝ LS " LS " ⎠ ⎪ ⎪ dΨ RX ⎪ dt = U RX − ⎪ ⎞ ⎛Ψ k ⎪ - R R ⎜⎜ RX − S ΨSX ⎟⎟ + (ω 2 − pω)Ψ RY , ⎨ L " L " R ⎠ ⎝ R ⎪ ⎪ dΨ ⎪ RY = U RY − ⎪ dt ⎪ ⎞ ⎛Ψ k ⎪ - R R ⎜⎜ RY − S ΨSY ⎟⎟ − (ω 2 − pω)Ψ RX , ⎪ ⎠ ⎝ LR " LR " ⎪ ω 1 d ⎪ = (M − M C), ⎪ dt J ⎩ where ΨSX, ΨSY, ΨRX, ΨRY, - components of the stator and rotor flux linkage vectors along the axes of the x-y coordinate system, stationary relative to the rotor voltage vector; USX, USY, URX, URY, - components of the stator and rotor voltage vectors along the axes of the x-y coordinate system; ω 2 = 2πf 2 - circular frequency of the rotor voltage; f2 - rotor voltage frequency; p - number of motor pole pairs; ω - circular speed of the engine rotor; RS , RR , L S " = L Sl + k S Lm , L R " = L RL + k R Lm , kS , kR active resistance of the stator, rotor, transient inductances of the stator and rotor, electromagnetic coupling coefficients of the stator and rotor, respectively; J is the moment of inertia of the motor rotor; M, MC are the electromagnetic torque of the motor and the resistive torque of the mechanism, respectively. Recording the MIS model in the x-y coordinate system allows us to divide the control action from the rotor into two components - the amplitude of the rotor voltage Urm and its circular frequency ω2. The latter makes it possible to eliminate the dependence between these influences and time in the synthesized control system. We take the rotor voltage frequency as the control action. We will seek a solution to the optimal control problem using Pontryagin's maximum principle. The necessary auxiliary function: H(ΨS ,ΨR ,US ,UR ,α) = ⎛ ⎞ ⎛Ψ ⎞ k =ψ1⎜USX − RS ⎜⎜ SX − R ΨRX ⎟⎟ + ω2ΨSY ⎟ + ⎜ ⎟ ⎝ LS" LS" ⎠ ⎝ ⎠ ⎛ ⎞ ⎛ ΨSY kR ⎞ +ψ 2⎜USY − RS ⎜⎜ − ΨRY ⎟⎟ − ω2ΨSX ⎟ ⎜ ⎟ ⎝ LS" LS" ⎠ ⎝ ⎠ ⎛ ⎞ ⎛Ψ ⎞ k +ψ3⎜URX − RR⎜⎜ RX − S ΨSX ⎟⎟ + (ω2 − pω)ΨRY ⎟ ⎜ ⎟ ⎝ LR" LR" ⎠ ⎝ ⎠ ⎛ ⎞ ⎛ ΨRY kS ⎞ +ψ 4⎜URY − RR⎜⎜ − ΨSY ⎟⎟ − (ω2 − pω) ΨRX⎟ ⎜ ⎟ ⎝ LR" LR" ⎠ ⎝ ⎠ 1 +ψ5 ⋅ ⋅ (C ⋅ (ΨSYΨRX − ΨSX ΨRY) − MC) + J +ψ0 ⋅ (MZ − C(ΨSYΨRX − ΨSX ΨRY))2 , where ψ 1 , ψ 2, ψ 3, ψ 4, ψ 5, ψ 0 - components of the non-zero vector function ψ. The transversality conditions additionally provide: ∂f 0 (Ψ S , Ψ R ,U S ,U R) L S " ⎧ = ⎪ψ 1 = ψ 0 ∂Ψ RX RS ⋅ k R ⎪ ⎪ 2CL S " = Ψ SY (M Z − M), ⎪ RS k R ⎪ ⎨ ⎪ψ = ψ ∂f 0 (Ψ S , Ψ R ,U S ,U R) L S " = 0 ⎪ 2 ∂Ψ RY RS ⋅ k R ⎪ 2CL S " ⎪ =− Ψ SX (M Z − M ), ⎪ RS k R ⎩ 26 A.V. Grigoriev Fig.1. Change in the components of the MIS rotor voltage vector Fig. 2. Changes in the electromagnetic torque, rotational speed and resistance torque of the motor Fig.3. Change in motor stator and rotor currents The main condition for the optimality of the control process in relation to the problem under consideration is: ψ × U = max (1) where U = is the vector of control actions. If we take as control actions the frequency of the voltage supplied to Electrical complexes and systems 27 Fig.4. Changing the amplitudes of the flux linkages of the stator and rotor of the motor rotor, then expression (1) will take the form: 2CL S " Ψ SY (M Z − M)ω 2 + RS k R 2CL S " + Ψ SX (M Z − M)ω 2 = max RS k R from which the MDP control algorithm follows: (2) ⎧(M Z − M)(ΨSY + ΨSX)< 0, ω 2 = −ω 2 max , (3) ⎨ ⎩(M Z − M)(ΨSY + ΨSX) > 0, ω 2 = ω 2 max, One of the possible technical implementations of the obtained control method is to change the phase sequence on the rotor. The resulting control method was tested on a computer model compiled using the Delphi 7 programming environment. For modeling, the parameters of the 4AHK355S4Y3 engine with a power of 315 kW were used. The engine start was modeled as unregulated, the load before t = 1 s was fan, after that it was pulsating, varying according to the law MC = 2000 + 1000 sin(62.8t) N×m. The result of the control is to maintain the electromagnetic torque at the level of MZ = 2000 N×m after time t = 1.4 s. Figure 1 shows changes in the components of the voltage vector in the α-β coordinate system, stationary relative to the stator. Figure 2 shows graphs of the electromagnetic torque, the resistive torque and the circular speed of the engine. Figure 3 shows the graphs of the modules of the motor stator and rotor current vectors, and Figure 4 shows the graphs of the modules of the stator and rotor flux linkage vectors. In Fig. 2 - 4 it can be seen that the task set is Fig. 5. Schematic diagram of an MIS with a converter that changes the phase sequence 28 A.V. Grigoriev Fig.6. The circuit diagram of the MIS with a converter that changes the phase sequence and equivalent circuits of a three-phase alternating current circuit is completed, while the stator flux vector is also stabilized at a certain acceptable level. To implement the resulting control method, you can use the converter circuit shown in Fig. 5. The circuit in Fig. 5 includes only 4 fully controllable elements (transistors VT1..VT4) and 16 diodes (VD1..VD16), which distinguishes it favorably from control circuits with frequency converters containing an intermediate DC link and an autonomous voltage inverter , including 6 fully controllable elements. To simplify the circuit diagram, you can replace the three-phase AC circuit with an equivalent two-phase one. If phase voltages are used as line voltages in an equivalent circuit, i.e. It is necessary to have the output of the midpoint of the transformer N, then the phase sequence is changed by switching on the power supply of phase B instead of phase A as shown in Fig. 6. In the case of using a converter of the second type, the cost of installation is reduced, but for its implementation it is necessary to have an output of the middle point of the transformer. REFERENCES 1, Chilikin M. G., Sandler A.S. General electric drive course: Textbook for universities. – 6th ed., add. and processed – M.: Energoizdat, 1981. – 576 p. 2. Eschin E.K. Electromechanical systems of multimotor electric drives. Modeling and control. – Kemerovo: Kuzbass State. tech. univ., 2003. – 247 p. 3. Theory of automated electric drive / Klyuchev V.I., Chilikin M.G., Sandler A.S. – M.: Energy, 1979, 616 p. 4. Pontryagin L.S., Boltyansky V.G., Gamkrelidze R.V., Mishchenko E.F. Mathematical theory of optimal processes. - 4th ed. -M.: Nauka, 1983. -392 c. Author of the article: Grigoriev Alexander Vasilievich - student gr. EA-02