RU2115218C1 - Ac drive control process - Google Patents

Abstract

FIELD: adjustable ac drives with frequency changers. SUBSTANCE: in shaping currents at outputs of frequency changer that feeds electric motor and has two inverting rectifiers of which one is built around fully controlled diodes, both interconnected through smoothing reactor, with output current controlled depending on desired amplitude of smooth current components at frequency changer output, diodes of each inverting rectifier are changed over depending on its desired current distribution through ac conductors, and high-frequency components of current are filtered off at output of frequency changer; inverting rectifier diodes are changed over also depending on desired amplitude of smooth components of current in its ac conductors and separately of output current. EFFECT: improved power factor of electric drive and harmonic content of currents at low speed. 7 cl 13 dwg

Description

 The invention relates to electrical engineering, in particular to control systems for AC electric drives with frequency converters (IF), and can be used when operating at reduced speeds of rotation of the executive motor.

 There is a method of controlling an AC electric drive by generating phase currents at the IF outputs with a first controlled rectifier-inverter (VI), a smoothing reactor and a second controlled VI, connected in series, in which it regulates the rectified current at the output of the first VI connected by AC voltage clamps to the source (supply network), and switch the valves of the second VI connected by clamps of alternating voltage to the motor windings, in accordance with the required distribution azine currents (by the spatial position of the imaging current vector) [1].

 The first and second VI are based on conventional semi-controlled thyristors.

 The rectified current at the output of the first VI is regulated in strict relation to the required amplitude of the main harmonic of the stator currents (the module representing the stator current vector). Three-phase bridge VI provides six possible spatial positions of the current vector and switching of the second VI is carried out six times during the period of stator currents. The module and the spatial position of the stator current vector are set in such a way that the necessary moment and the necessary energy state of the electric drive are provided.

 The disadvantage of this known solution is that at a reduced speed of the electric drive, the first VI operates with reduced rectified voltage and an increased control angle. This determines a reduced power factor at the input of the electric drive and an increased content of harmonics in the currents consumed from the network.

 Another disadvantage is that the stator currents have a higher content of higher harmonics, which increases the energy loss in the motor. In addition, at low speeds, the time resolution interval for the second VI control system has been increased, which prevents high-quality speed control.

 Closest to the proposed one is a method of controlling an AC electric drive by generating currents at the IF outputs with a first VI connected in series, a smoothing reactor and a second VI, made on fully controllable valves, in which the rectified current at the output of the first VI connected by AC voltage clamps to the source is regulated (mains supply), and switch the valves of the second VI connected by clamps of alternating voltage to the motor windings, using latitudinal ulsnoy modulation (PWM) and in accordance with a desired distribution of phase currents (current spatial position of the imaging vector). The high-frequency components of the output currents of the second VI are closed through a three-phase capacitor bank connected to the motor windings [2].

 The disadvantages of this known solution include a reduced power factor and a high content of harmonics in the currents consumed from the mains.

 The proposed control method solves the problem of increasing the coefficient at the input of the electric drive from the supply network, as well as improving the harmonic composition of the currents consumed by the electric drive both from the supply network and in the windings of the AC motor at reduced speeds.

 This problem is solved by the fact that with the known method of controlling an AC electric drive by generating currents at the outputs of the inverter supplying the electric motor and made with two VIs, one or two of which are on fully controlled valves connected to each other through a smoothing reactor, in which the rectified current is regulated depending on the required amplitude of the smooth components of the currents at the inverter output, the valves of each VI are switched depending on the distribution of currents set for it in the AC wires filtered and the high frequency components of the currents at the output of the inverter, each switching valves VI to produce fully controllable valves also depending on the preset amplitude components of smooth currents in its conductors of alternating current and separately from the rectified current.

 In accordance with the invention, the VI on fully controllable valves can be used to form currents in the motor windings or to convert currents from the supply network at the input of the inverter, or for both tasks together.

 The possibility of separate regulation of the rectified current and the amplitude of the smooth components in the AC wires of the VI on fully controllable valves provides an increase in the power factor of the electric drive at reduced speeds.

 In accordance with the invention, the control signals for switching the valves of each of the VIs on fully controllable valves can be formed as the ratios of the given instantaneous values of the smooth components of the phase currents in the alternating current wires of the specified VI to the measured value of the rectified current.

 This ensures an increase in the power factor at the input of the electric drive at reduced speeds and further reduces the effect of the ripples of the rectified current on the motor currents.

 In accordance with the proposed method, assignments for currents in the alternating current wires of each of the VIs on fully controllable valves can be formed by comparing the set and actual voltages at its alternating current clamps.

 This ensures an improvement in the quality of regulation of the electric drive by increasing the speed of the control loops of torque and speed.

In accordance with the invention, the control signals for the valves of each of the VIs on fully controlled valves can be generated by comparing the modulating signal in the form of a unipolar signal of a triangular shape with the obtained ratios of the given instantaneous values of the smooth components of the currents in the AC wires to the measured value of the rectified current. At the same time, at each moment of time, the largest, smallest, and intermediate control signals pi are determined that implement the following algorithm:
- when exceeding the largest control signal of the level of the modulating signal in the anode group of the specified VI include the valve of the phase that corresponds to the largest control signal,
- if the maximum control signal of the level of the modulating signal in the anode group of the specified VI is not achieved, the valve of the phase corresponding to the intermediate control signal is turned on,
- when the smallest control signal is exceeded, the level of the modulating signal taken with the opposite sign, in the cathode group of the specified VI include the valve of the phase that corresponds to the intermediate control signal,
- if the smallest control signal of the level of the modulating signal taken with the opposite sign is not achieved, the valve of the phase corresponding to the smallest control signal is turned on in the cathode group of the indicated VI.

 The specified algorithm ensures that the amplitudes of the smooth component currents in the AC wires correspond to the specified values, regardless of the value of the rectified current.

 In accordance with the invention, when using a VI on fully controlled valves to power the motor windings, the rectified current is also regulated depending on the specified output active voltage level of the specified VI, while the ratio of the rectified current to the required amplitude of the smooth components of the phase currents is determined, and the indicated ratio is kept to a minimum zone of small output voltages corresponding to low speeds of the electric drive, and when exceeding a certain boundary level of the output a tive voltage is increased as the ratio of the output voltage of the active boundary ascending above this level.

 This ensures a decrease in the required rectified voltage in the high-speed zone and, consequently, a decrease in the angle of control of the power supply, supplied from the network, in the low-speed zone.

 In accordance with the invention, the boundary level of the output active voltage of the VI on fully controllable valves can be set proportional to the voltage at the input terminals of the AC inverter.

 At the same time, the required margin for rectified voltage is reduced in case of a possible decrease in voltage at the input terminals of the inverter AC voltage, which provides an additional increase in power factor.

 In accordance with the invention, when using a power supply on fully controllable valves at the input of the inverter to convert currents of the supply network, currents in the alternating current wires of the specified power supply can be formed by its active and reactive components. Moreover, the active component is set proportional to the measured rectified current and the specified rectified voltage at the output of the specified VI, and the reactive component is set proportional to the currents of the capacitors connected to the input terminals of the AC voltage of the inverter.

 This provides a power factor close to unity at the input of the inverter and a reduced content of harmonics in the currents consumed from the network.

 In FIG. 1 shows an example of the implementation of the proposed method for controlling an AC electric drive with connecting the motor windings to the outputs of the VI on fully controllable valves; in FIG. 2 - an example of the implementation of the proposed method with the connection of VI on fully controllable valves to the treatments of the electric motor and to the mains; in FIG. 3 is a functional diagram of an automatic control unit for the electric drive of FIG. one; in FIG. 4 is a functional diagram of a logical comparison unit; in FIG. 5 is a functional diagram of a decoder; in FIG. 6 is a functional diagram realizing the dependence of the rectified current on the output active voltage for the electric drive of FIG. one; in FIG. 7 is a functional diagram of the output part of the main controller when generating tasks of the voltage components of the stator of the electric motor; in FIG. 8 is an exemplary embodiment of an automatic control unit for the electric drive of FIG. 2; in FIG. 9 is a timing diagram for the electric drive of FIG. one; in FIG. 10-13 - characteristics of electric drives according to the prototype and implemented by the proposed method.

 The electric drive of FIG. 1, which implements the proposed control method, comprises an electric motor 1 connected to the inverter outputs with two VIs (VI2, VI3) connected between through a smoothing reactor 4. One of the VIs (in the presented example, VI3) is made on fully controlled valves V1-V6, for example on GTO thyristors. A capacitor bank 5 is connected to the outputs of the VIZ (to AC wires A, B, C). Current sensors 6.7 and voltage sensors 8.9 are installed at the inputs and outputs of the inverter. VI2 inputs are intended for connection to an alternating current mains.

 The automatic control unit 10 is connected by inputs to the outputs of the current sensor 6, 7 and voltage 8, 9, and the outputs are connected to the control outputs of the VI3 valves and to the input of the pulse-phase control system (SIFU) as a part of the VI2.

 In the electric drive of FIG. 2, both VI (VI3, VI11) are made on fully controllable valves (valves in VI11 are designated V1'-V6 '). A capacitor bank 12 is connected to the wires A ', B', C 'of the alternating current VI11.

The automatic control unit 10 includes a regulator 13 (Fig. 3), a feedback signal driver 14, a vector module calculation element 15, dividing element block 16, a vector rotation converter 17, a phase number converter 18, a rectified current controller 19, and a pulse-width modulator 20 made with a decoder 21, two relay elements 22, 23, two summing elements 24, 25 and a modulating signal generator 26 of a triangular shape W _mod .

At the same time, the outputs of controller 13 with the _{task of the} current components i _Mgx , i _Mgy in the orthogonal rotating (relative to the stator axis α) coordinate system x, y are connected to the inputs of the calculation element 15 of the i _Mg module of the vector and to the inputs of the dividend block 16 of the dividers connected by the outputs a vector rotation inverter inputs 17, reference inputs the angle of rotation of which are connected to the outputs of the reference wave signals cosγ _m, sinγ _m (the angle of rotation γ _m rotating orthogonal coordinate system x, y) generator 14 feedback signals, and you ode - to the inputs of the phase inverter 18, the outputs connected to the inputs of the pulse width modulator 20.

The feedback input of the rectified current controller 19 is connected to the corresponding output i _{D of the} feedback driver 14, the outputs of the controller 19 and the pulse-width modulator 20 form the outputs of the automatic control unit 10 connected to the control inputs VI2 and VI3, respectively.

 The implementation of the proposed method provides the introduction of two elements 27, 28 highlight the maximum signal with two inputs each, the summing element 29, as well as the introduction of a pulse-width modulator 20 of the block 30 logical comparison.

 Block 30 can be made with elements 31, 32 (Fig. 4) highlighting the maximum and minimum, relay elements 33, 34, 35 and logical elements And 36-44.

 The decoder 21 can be made with logical elements And 45-56 (Fig. 5) and formers 57-62 signals for opening the valves.

Feedback driver 21 is known in the art of controlled electric drive and is described, for example, in [3]. Its inputs are connected to the outputs of current sensors 6, 7 with signals i _1A , i _1C,; i _SA , i _SC, respectively, with the outputs of voltage sensors 8, 9 with signals U _LAB , U _LCB ; U _SAB , U _SCB, respectively. At the outputs of the driver 14, feedback signals are obtained for the components of the currents i _sx , i _sy and voltages U _sx , U _sy , for the rectified current i _D , the mains voltage U _L , the active voltage U _MA , the reference signals cosγ _M , sinγ _M ; cosγ _L , sinγ _{L the} signals of the velocities ν _M , ν _L , ν.
The main controller 13 is made according to the known scheme described for example in [1].

The signals W _max , W _min at the outputs of the logical comparison unit 30 are generated according to the following algorithm:
W _max = max (W _A , W _B , W _C ),
W _min = min (W _A , W _B , W _C ) /
The logical signals L _Amax , L _Amin for phase A at the outputs of block 30 correspond to:
L _Amax = 1 for W _A > W _B , W _A > W _C
L _Amin = 1 for W _A <W _B , W _A <W _C ,
in other cases, L _Amed = 1. In a similar way, logical output signals L _Bmax , L _Bmed , L _Bmin for phase B and signals L _Cmax , L _Cmed , L _Cmin for phase C are _generated .

The output signal L _{1 of the} element 33 (Fig. 4) is 1 when W _A - W _B > 0, the output signal L _{3 of the} element 35 is 1 when W _C > W _A.

The output signal L _{Amax of} element 36 is 1 for L ₁ = 1 and L ₃ = 0, the output signal L _{Amin of} element 37 is 1 for L ₁ = 0 and L ₃ = 1.

In the case when both the signals L _Amax and L _{Amin are} zero, the logic signal 1 takes place at the output of L _Amed element 38.

The input signal of the decoder 21 L _max = 1 under the condition W _max > W _mod , the input signal L _min = 1 under the condition W _min > W _mod .

The signal for opening the valve V1 VI3 (Fig. 1) is generated in one of two cases:
- when the signal W _A is maximum and it exceeds the modulating signal W _mod ,
- when the signal W _A is intermediate, and the maximum of the signals does not exceed the modulating signal.

 Similarly, signals are generated to open other VI3 valves.

The formation of the increased value i _{Eg of the} given rectified current depending on the output active voltage U _MA VI3 is carried out using a dividing element 63 (Fig. 6), a proportional element 64 and a multiplying element 65.

The inputs of the divisible and divisor of the element 63 receive respectively the signals of the measured value of the output active voltage U _MA and the voltage module U _{L of the} supply network with the output of the driver 14.

The output of the element 63 through the proportional element 64 is connected to one of the inputs of the multiplying element 65, the other input of which receives the task of the rectified current i _Mg from the output of the vector module calculation element 15.

When forming in the main controller 13 tasks of the components U _sgx , U _sgy of the stator voltage of the motor in a rotating coordinate system x, y, its output part is performed with a block 66 of voltage regulators (Fig. 7), a block of 67 multiplier elements, a block of 68 rotation of 90 ^o , blocks 69, 70, 71 of the summing elements, block 72 of the proportional elements.

The first inputs of the block 71 of the summing elements are designed to supply the specified components of the stator voltage U _sgx , U _sgy , and the other inputs are for feedback signals U _sx , U _sy from the corresponding outputs of the shaper 14.

The outputs of block 71 are connected through the block 66 of the voltage regulators to the first inputs of block 69 of the summing elements, the other inputs of which are connected to the outputs of block 68. The outputs of block 68 are connected to the outputs of block 67, the inputs of which are connected to the corresponding outputs U _sx , U _sy , γ _{M of the} shaper 14.

 When implementing the electric drive of FIG. 2, i.e. when performing VI11 and VI3 on fully controllable valves, the automatic control unit 10 further comprises a pulse-width modulator 73 (Fig. 3), a phase number converter 74, a vector rotation converter 75, a dividing element block 76, a maximum signal extraction element 77, an element 78 vector module calculations, multiplying elements 79, 80, dividing element 81, proportional element 82.

 The pulse-width modulator 73 is made similarly to the modulator 20 (Fig. 3), its outputs are intended for connection to the control terminals of the VI11 valves.

The inputs of the modulator 73 through the converters 74 and 75 are connected to the outputs of the block 76 of the dividing elements. The reference inputs of the transducer 75 are connected to the corresponding outputs cosγ _L , sinγ _{L of the} feedback driver 14.

 The inputs of the dividend block 76 are combined with the inputs of the vector module calculation element 78. The output of element 78 through element 77 is connected to the input of the divider of block 76.

The output of element 78 with an increased value of a given rectified current i _{Eg is} intended to be connected to element 27 (Fig. 3).

The input of the divisible U _{Dg of the} dividing element 81 is connected to the output of the summing element 29 (Fig. 3), and the input of the divider combined with the input of the proportional element 82 is connected to the corresponding output U _L of the supply voltage of the driver 14.

The outputs of the elements 81 and 82 through the corresponding multiplying elements 79, 80 are connected to the inputs of the element 78. Other inputs of the elements 79, 80 are connected to the outputs i _D , V _{L of the} shaper 14, respectively.

 All blocks and nodes are made on standard semiconductor elements.

 The electric drive of FIG. 1 operates as follows.

The signal ν _g at the input of the control unit 10 or at the input of the controller 13 (Fig. 3) determines the set speed value. In the controller 13 compares the set and the actual ν value of the speeds. Depending on their difference, a given moment M _{g is formed} .

As a function of a given moment, as well as a given (for example, programmatically) magnetic flux ψ _g , currents i _Mgx , i _{Mgy are generated} in the orthogonal coordinate system x, y.

When the actual currents i _Mx , i _My coming from the outputs of the shaper 14 coincide with the set values, i.e.: i _mx = i _Mgx , i _my = i _Mgy , the actual values of the moment and magnetic flux also coincide with the set values, t .е .: M = M _g , ψ = ψ _g .
The signals W _A , W _B , W _C (Fig. 9a) specify the ratio of the smooth component currents in the wires of the alternating current VI3 to the rectified current i _D. The inclusion of fully controllable valves is made by comparing these signals with each other and with the modulating signals W _mod coming from the output of the generator 26.

 Under the diagram of these signals in FIG. 9 shows the intervals of inclusion of each of the valves VI, and the designation of the intervals coincide with the designation of the valves.

In FIG. 9b, 9c are respectively diagrams of changes in current i _A in wire A and through current i _DD .

For example, valve V1 is turned on under the following conditions:
- when the signal W _A is the largest and, in addition,
W _A > W _mod ;
- when the signal W _A is intermediate and, in addition, the conditions are satisfied:
W _B <W _mod and W _C <W _mod
The smaller the amplitude of the signals W _A , W _B , W _C , the longer the time intervals in which only one of the pairs of valves V1, V4 or V3, V6 or V5, V2 is included. In this case, the rectified current closes through such a pair of valves and does not enter the AC wires of this VI. As a result, when the amplitude of these signals decreases, the ratio of the amplitude of the smooth component currents in the AC wires to the rectified current decreases.

The main controller 13 generates tasks of the current components in the wires of the alternating current VI3 i _Mgx , i _Mgy in the system of rotating coordinates x, y.

In the particular case of an asynchronous electric drive, this can be the coordinate system 1, 2, associated with the depicting vector of the rotor flow ψ _r . The tasks are formed in such a way as to ensure the necessary capacitor currents at the output of VI3 and the stator currents of the motor, and the stator currents must at each moment of time provide the necessary moment of the motor and its necessary electromagnetic state. In the case of an asynchronous electric drive, for example, the required value of the magnetic flux of the rotor ψ _r can be provided. The current tasks are formed by the main controller, depending on the room signals and feedback signals received at its inputs. The latter are formed by the shaper feedback signals 14. The input of the specified shaper receives signals from current sensors 6, 7 and voltage 8, 9 in the main circuits of the electric drive. If there are corresponding additional sensors in the drive, speed and position signals can be received at the inputs of the driver.

The signals of the _reference currents i _Mgx , i _Mgy are fed to the input of the element 15, which generates a signal module representing the vector of a given current i _Mg . In addition, the signals of the reference currents in the x, y coordinates pass through the block 16 of the dividing elements, the output signals of which W _Mx , W _My are fed to the input of the rotation Converter 17.

The inputs of the angle of this transducer receive signals cosγ _M , sinγ _M from the former 14, where γ _M is the angle of rotation of the α axis relative to the stator axis. The rotation converter converts the reference signals W _Mx , W _My into the coordinate system α, β of the stator, the conversion results are signals w _Mα , w _Mβ .

Further, these signals pass through a phase number converter 18, the output signals of which W _MA , W _MB , W _MC are input as signals of predetermined current ratios into a pulse-width modulator 20.

 At the inputs of the divider block 16 receives a signal from the output element 28 of the selection of the maximum signal.

One of the inputs of this element receives the vector module of the set currents i _Mg from the output of element 15. If there was no signal at the second input of element 28, its output signals would have unit amplitude and the drive would be controlled as in the prototype, i.e. the current vector in the VI3 AC wires would be controlled only in the direction.

In this drive, a signal i _{D of the} measured value of the rectified current is supplied to the second input of the element 28. If the measured value of the rectified current i _D exceeds the modulus of the vector of predetermined currents i _Mg , then the amplitude of the signals W _Mx , W _My decreases, therefore, also the amplitude of the signals W _MA , W _MB , W _MC . In this case, the ratio of the amplitude of the smooth component currents in the wires of the alternating current VI3 to the rectified current decreases, which is the difference from the known method.

In this case, an element 27 for extracting the maximum signal in the circuit for setting the rectified current is used. The signal at the first input of this element is the module of the vector of given currents i _Mg . When the signal at the second input of this element i _Eg exceeds the value of the signal at the first input, the setting of the rectified current and the measured rectified current are increased compared to the value of i _Mg . As a result, the rectified current is set by the signal i _Eg , and the amplitude of the smooth component currents in the wires of the alternating current VI3 is still set by the signal i _Mg .

Signal generation i _Eg for the case when VI2 is based on conventional, semi-controlled thyristors is shown in FIG. 6.

As follows from the diagram, the specified signal is formed depending on the module of the vector of the set currents i _Mg , as well as the measured values: the output active voltage of the second VI U _Ma and the voltage module of the source (network) U _L , and the ratio
i _Eg = K _Eg (U _Ma / U _L ) • i _Mg .

As the speed of the drive increases, the output active voltage increases. When a certain speed level is exceeded, depending on the software value of the coefficient K _Eg (transfer coefficient of element 64), the value of i _Eg starts to increase compared to the value of i _Mg , the rectified current i _D starts to increase compared to the amplitude of the smooth components of the currents in the wires of the alternating current VI3 and stops the growth of the required rectified voltage U _D.

 Presented in FIG. 10 characteristics correspond to: a) the prototype, b) the proposed electric drive of FIG. one.

It is indicated here: ν relative velocity; U _D is the rectified voltage; i _D is the rectified current; i ₁ - current consumed from the network; cosφ ₁ - power factor according to the main harmonic of the current consumed from the network.

The characteristics correspond to a certain constant moment of the electric drive. The maximum rectified steady-state voltage U _Dxmax for the proposed method is lower than for the known one. The secondary voltage of the isolation transformer, through which the electric drive is connected to the network, is selected proportional to the value of U _Dsmax , therefore, the reduced secondary voltage is selected for the proposed method. The primary current of the isolation transformer i ₁ , ceteris paribus, has the same values for the known and for the proposed methods at the maximum speed of the electric drive. In this mode, the values of the control angle α VI and, as a consequence, the power factor for the fundamental harmonic on the side of the supply network cosφ ₁ , as well as the harmonic composition of the currents consumed from the network, also coincide.

However, as the speed decreases down to the boundary value ν ₁ during control by the proposed method, the current i ₁ decreases, the control angle of the VI2 remains relatively small, the power factor is kept at a high level, the relatively favorable harmonic composition of the currents consumed from the network is maintained. At the same time, when controlling according to the known method, as the speed decreases, the power factor drops and the harmonic composition of the currents consumed from the network deteriorates.

For electric drives with high demands on the quality of regulation, the output signals of the main controller 13 are the stator voltage components U _sgx , U _sgy in a rotating coordinate system x, y. These signals are supplied as tasks to block 66 (Fig. 7) of the regulators. The feedback inputs of these regulators receive the measured values of the components of the stator voltage U _sx , U _sy from the shaper 14 of the feedback signals. Depending on the difference between the set and measured values, the output signals of the regulators U _RUx , U _{RUy are formed} .

где Ω_u - полоса пропускания контура регулирования напряжения.You can use proportional controllers that implement the vector relation

where Ω _u is the bandwidth of the voltage regulation loop.

где J - оператор поворота вектора на 90^o,
C - относительная емкость конденсаторной батареи,
ω_b - базовая угловая частота,
ν_m - относительная скорость системы координат.The signals of the reference currents in the wires of the alternating current VI3 are generated, as follows from FIG. 7, by vector ratio

where J is the operator of rotation of the vector by 90 ^o ,
C is the relative capacitance of the capacitor bank,
ω _b is the base angular frequency,
ν _m is the relative velocity of the coordinate system.

- измеренные токи статора,

- измеренные напряжения статора, u_Ru= (u_Rux,u_Ruy) - выходные сигналы регуляторов напряжения 66.As follows from FIG. 7 and formulas (3), the tasks of currents VI3 include:

- measured stator currents,

are the measured stator voltages, u _Ru = (u _Rux , u _Ruy ) are the output signals of the voltage regulators 66.

 The first term in the ratio for the given currents is the compensating coupling of the stator currents, the second term provides the necessary steady-state currents of the capacitor bank. As indicated, additional voltage regulators are designed for electric drives with increased requirements for regulation quality, therefore, with the requirements of high-speed response of the magnetic flux and torque control loops. The achievement of this goal is facilitated by the independent regulation of the amplitude of the output currents of the VI3 itself. In the presence of voltage regulators, it becomes possible to establish in the circuits the regulation of magnetic flux and torque, which is limited only by the discrete control of the VI (PWM frequency).

 In the electric drive of FIG. 2, i.e. with the execution of both VIs on fully controllable valves, block 10 comprises an additional unit as shown in FIG. eight.

The valves of the VI 11 are controlled by a pulse-width modulator 73, the input signals to which are supplied through a phase number converter 74, and to the latter through a vector rotation converter 75. The reference inputs of the transducer 75 receive signals cosγ _L , sinγ _L , where γ _L is the rotation angle of the image voltage vector of the voltage source of the alternating voltage (network) U _L relative to the phase axis A.

Input signals are fed to the rotation converter 75 from the block 76 of the dividing elements. The inputs of the dividend of these elements receive current assignments in the alternating current wires VI 11 _LUg , i _LVg in the coordinates U, V. Here, the U axis is directed along the vector U _L , the V axis is orthogonal leading. At the input of the divider of the dividing elements 76, a signal is received from the output of the maximum signal isolation element 77. The signal i _{D of the} measured rectified current and the signal i _Lg specify the module representing the vector of currents in the BM11 alternating current wires. In most drive modes, the rectified current exceeds the reference I _Lg , and for VI11, the amplitude of the currents in the AC wires is independently controlled. The active current task is formed by elements 79, 81 in the ratio
i _LUg = (U _Dg / U _L ) • i _D
in function of a given rectified voltage U _Dg . This signal comes from the output of element 29 (Fig. 4). In this way, the necessary power is supplied to the rectified current circuit. The advancing current task is formed by elements 82, 80 in the ratio
i _Lvg = b _CL • ν _L • u _L , (5)
Where
B _CL - the relative conductivity of the capacitor bank 12 at the input of the VI 11.

The drive characteristics of FIG. 2 are shown in FIG. 10-13 curves c). All characteristics correspond to the steady-state modes of the electric drive with a constant load moment. Here, the rectified voltage and current consumed from the network are approximately proportional to the speed of the electric drive, the rectified current is determined by the required stator current and the current of the capacitor bank at the output of VI3, and the power factor of the main harmonics of the currents cosφ ₁ = 1 is maintained on the power supply side of the electric drive from the source (network). .

 The electric drive of FIG. 2 provides high dynamic and energy performance.

Claims (7)

 1. A method for controlling an AC electric drive by generating currents at the outputs of a frequency converter supplying an electric motor and made with two rectifier inverters, one or two of which are on fully controllable valves connected to each other through a smoothing reactor, in which the rectified current is controlled depending on the required amplitude of the smooth component currents at the output of the frequency converter, switch the valves of each of the rectifiers-inverters depending on the job for the distribution eniya currents in the wires AC and filtered high frequency components of the currents at the output of the frequency converter, characterized in that the switching valves rectifier-inverters fully controlled valves are also produced as a function of smooth components currents predetermined amplitude in its AC power conductors and separated from the rectified current.  2. The method according to claim 1, characterized in that the control signals for switching the valves of rectifiers-inverters on fully controlled valves form in the form of the ratio of the given instantaneous values of the smooth components of the phase currents in the AC wires of the specified rectifier-inverter to the measured value of the rectified current.  3. The method according to claim 1, characterized in that the tasks for the distribution of currents in AC wires of rectifier-inverters on fully controllable valves are formed by comparing the set and actual voltages at its AC terminals.  4. The method according to claim 2, characterized in that the control signals for rectifier-inverter valves on fully controlled valves are generated by comparing the modulating signal in the form of a unipolar signal of a triangular shape with the obtained ratios of the given instantaneous values of the smooth components of the currents in the AC wires to the measured the value of the rectified current, while at each moment of time determine the largest, smallest and intermediate control signals and implement the following algorithm: when exceeding the highest control signal of the level of the modulating signal in the anode group of the specified rectifier-inverter include a valve of the phase that corresponds to the largest control signal, if the maximum control signal of the level of the modulating signal in the anode group of the specified rectifier-inverter is not included, turn on the valve of the phase that corresponds to the intermediate control signal, when the smallest control signal is exceeded, the level of the modulating signal taken with the opposite sign in the cathode groups said inverter includes a rectifier valve that phase which corresponds to the intermediate control signal, if not the smallest modulation level control signal of the signal taken with the opposite sign to the cathodic group of said rectifier-inverter is switched phase of the valve, which corresponds to the smallest control signal.  5. The method according to claim 1 or 2, characterized in that when using a rectifier-inverter on fully controllable valves to power the motor windings, the rectified current is also regulated depending on the specified output active voltage level of the specified rectifier-inverter, and the ratio of the rectified current to the required amplitude of the smooth components of the phase currents, maintain the indicated ratio minimum in the zone of low output voltages corresponding to low speeds of the electric drive, and at When a certain boundary level of the output active voltage is increased, the indicated ratio increases as the output active voltage increases above this boundary level.  6. The method according to p. 5, characterized in that the boundary level of the output active voltage of the rectifier-inverter on fully controllable valves is set proportional to the voltage at the AC input terminals of the frequency converter.  7. The method according to claim 1 or 2, or 4, characterized in that when using a rectifier-inverter on fully controllable valves at the input of the frequency converter, to the AC terminals of which the capacitors are connected, tasks for the distribution of currents in the AC wires of the specified rectifier are the inverters are formed by the active and reactive components, and the active component is set proportional to the measured rectified current and the specified rectified voltage at the output of the specified rectifier-invert a, a reactive component is set proportional currents of said capacitors.

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