RU2724603C1 - Synchronous motor control method - Google Patents

Abstract

FIELD: electrical engineering.SUBSTANCE: invention relates to electrical engineering and can be used in systems for frequency control of speed of synchronous motors supplied from autonomous voltage inverter in mode of sensor-free control. Algorithm is realized using only load feedback signal at inverter output. To control speed of synchronous motor by means of autonomous inverter, containing channels of regulation of amplitude and frequency of voltage of stator winding: signal of amplitude adjustment is input signal ΔU; frequency adjustment channel includes a signal in form of a phase shift (by an angle ϕ) with positive sign; for control of autonomous inverter there used are signals of current sensors Dm after their transformations from three-phase (physical) model i, i, iinto equivalent two-phase model. Operation of the device can be performed without using signals of the integration unit and the adder unit.EFFECT: technical result is providing cost-effective (Cosϕ = 1) and stable (without oscillation) mode of engine rotation under conditions of variable moment of load on its shaft.1 cl, 3 dwg

Description

The invention relates to electrical engineering, to frequency control systems for the speed of synchronous motors powered by a stand-alone voltage inverter (AIN), in the "sensorless" control mode. The goal is to develop an algorithm for a stable and economical mode of operation of the engine in conditions of a changing load moment on its shaft.

Known control methods [1, 2], in which the stator windings of synchronous motors are powered by an m-phase inverter with amplitudes and frequencies that are regulated by current and phase voltage signals in the stator windings or other signals and computational procedures that allow to determine the rotor angular position synchronous machine. Their disadvantages are a large number of necessary sensors, signals and calculations that slow down the inverter response to a change in the load moment [1, 3], or the complexity of the rotor design due to a short-circuited winding [2].

EFFECT: using only signals of current sensors of the motor phases in the algorithm (there is no need for signals from other sensors), increasing the speed and maintaining the mode with the maximum power factor of the electric motor, is achieved by using a stand-alone inverter with a calculator containing the amplitude control channel to power the stator windings U _m and the channel for regulating the frequency of the voltage of the stator winding ω _ass , characterized in that in order to ensure stable rotation of the rotor at the most favorable value of the coefficient of power consumed by the motor (Cosϕ = 1):

- a signal ΔU is introduced into the amplitude control channel E _m , which increases the amplitude if a current arises in the stator windings, which is ahead of the stator voltage and, accordingly, decreases it if the stator current becomes lagging;

- a signal in the form of a phase shift (by an angle ϕ) with a positive sign is introduced into the frequency control channel ω _ass if a current is ahead of the voltage in the stator windings and, accordingly, with a negative sign if the current in the windings is lagging;

- to control the autonomous inverter, the functional circuit of the calculator circled in FIG. 1 by a dashed line, in which the signals of the current sensors Дm are used to “isolate” the signals ΔU ≠ 0 and ϕ after they are converted from the three-phase (physical) model i _A , i _B , i _C into the equivalent two-phase model i _a , i _b for input into calculator

i _a = К _ДТ I _m [Sin (ω _back t + ϕ)],

i _a = К _ДТ I _m [Cos (ω _back t + ϕ)]

and repeating for these signals a computational procedure,

(i _a os Cosωt-i _b ⋅ Sinωt) К _u (1 + 1 / Tp) = К _u (1 + 1 / Тр) ⋅ К _ДТ ⋅I _m Sinϕ = ΔU ≠ 0;

(i _a os Cosωt-i _b ⋅ Sinωt) К _ϕ = К _ϕ ⋅К _ДТ ⋅I _m Sinϕ → 0 as ϕ → 0;

where K _DT is the conversion coefficient of current sensors;

I _m - the amplitude value of the currents of the phase windings of the stator, A;

ω _back - the specified angular frequency of the autonomous inverter, rad / s;

ϕ is the angle of shear between current and voltage in the stator winding, in rad;

ΔU is the increment of the stator voltage task for an autonomous inverter, at which ϕ → 0;

Sin and Cos are trigonometric functions of the angle θ _ass = ω _ass ⋅t + ϕ.

Functional diagram of the electric drive consists of a control panel (PU) 1, a computer (2 ÷ 18) that implements the method and circled in FIG. 1 by a dashed line of an autonomous voltage inverter (AIN) 19 and a synchronous motor 20. It allows using the frequency reference signal ω _rear and a feedback signal for the phase currents of the stator windings of the motor i _A , i _B , i _{C to} generate reference signals for AIN U _A , U _B , U _C and ensure stable operation of the engine in Cosϕ = 1 mode in the load range from idle to the moment of rollover

The circuit contains the following signals and elements of mathematical transformations above them:

1 - a control panel of an electric drive (PU), forms a graph of a given angular frequency of rotation of the stator winding voltage vector ω _ass (t);

2 - integrator or multiplication unit ω _ass by time t, which converts a given angular frequency into a given value of the angular displacement of the stator voltage vector ω _ass t in electric radians;

3 - node multiplication ω _ass on the value of flux link Ψ, providing the formation of the amplitude value of the output voltage of the inverter, compensating the EMF of the windings of the equivalent two-phase synchronous motor E _m = ω _ass ⋅Ψ;

4, 6, 7, and 12 are the nodes of the algebraic summation of signals, respectively (E _m + ΔU) = U _m , (1 + 1 / Tr) K _dt ⋅I _m Sinϕ, (ωt + ϕ) = θ _ass and i _a ⋅Cosωt -i _b ⋅Sinωt;

5 and 8 are multiplication nodes that provide correcting signal levels ΔU = K _U ⋅ (1 + 1 / Tr) K _dt ⋅I _m Sinϕ for the amplitude control channel and signal ϕ = K _ϕ ⋅K _dt ⋅I _m Sinϕ for the control channel frequency

9 - integration node with a coefficient of 1 / T in the composition of the correction signal along the channel for setting the amplitude;

10, 11 - nodes of the transformation θ _back into the trigonometric functions of this angle;

13, 14 - multiplication nodes for the formation of specified voltage values in the equivalent two-phase machine U _a = U _m ⋅ Cosθ _back and U _b = U _m ⋅ Sinθ _back ;

15.16 - nodes of multiplication (product formation) i _a ⋅Cosθ _ass , i _b ⋅Sinθ _ass ;

17 is a node for converting a two-phase voltage reference U _a and U _b into a three-phase voltage reference U _A , U _B , U _C for a stand-alone voltage inverter (AIN)

U _A = U _a = U _m ⋅ Cosθ _ass , U _B = U _m ⋅ Cos (θ _ass -2π / 3), U _C = U _m ⋅ Cos ( _ass θ _ass + 2π / 3);

18 - converter of three-phase current signals i _A , i _B , i _C into current signals of an equivalent two-phase machine i _a , i _b [i _a = i _A ,

19 - an autonomous voltage inverter (AIN) supplying the motor and generating signals of current sensors (Dm) i _A , i _B , i _{C of a} 3-phase synchronous machine;

20 - synchronous motor.

In order to simplify the algorithm (reduce mathematical operations, and therefore time for a repeated computational procedure), we allow a less rigorous synthesis, which ensures a stable rotation mode of a synchronous machine in the entire speed range. The regime with Cosϕ = 1 is achieved only at one speed and at the same value of the load moment. As feedback, it also uses a signal along the reactive component of the stator current K _dt ⋅I _m Sinϕ. Through the dimensionless coefficients K _u and K _ϕ it is fed into the control channels of the amplitude ΔU and frequency ϕ. An example of such a “simplified” structure is shown in FIG. 2. Compared to the structure of FIG. 1 in the structure of FIG. 2 excludes integrator 9 with a coefficient of 1 / T and summation element 6.

The computational procedure used in the AIN control algorithm in FIG. 2, repeated every 60 μs. This allowed the AIN to operate in an electric drive, forming a three-phase sinusoidal voltage with an output frequency of up to 150 Hz and an output voltage amplitude of up to U _m = 650 volts.

In FIG. Figure 3 shows the waveform of voltage and current in one of the windings of a three-phase synchronous motor with a power of 150 kW at a rated load moment and at a speed of 3000 rpm. The electric drive was controlled by the “simplified” algorithm of FIG. 2. The waveform was obtained using the measuring system FLUKE - 435.

An experimental check of an electric drive with a “simplified” AIN control algorithm has shown its stable operation in a wide range of speeds and load moments. However, the Cosϕ = 1 mode was maintained only at one steady-state value of the load moment M = M _n . At lower values of M, including at a load moment close to idle, the current in the stator windings decreased, but not proportionally to the magnitude of the moment, which means that a reactive (demagnetizing / magnetizing) component appeared in the stator current. Energy losses compared to the algorithm of FIG. 1 were slightly higher.

The proposed control method of the AIN provides a soft start and stable (without hesitation) operation of the electric drive at a given speed in a wide range of load moments using only a reference signal ω _ass , current feedback i _A , i _B , i _{C of a} synchronous machine (signals of current sensors Dm ) and a sufficiently “short” time procedure in the calculator according to the algorithm of FIG. 1 or FIG. 2.

Note that the proposed method is suitable for controlling synchronous motors and with electromagnetic excitation, including for controlling high-voltage motors, if they are powered by a high-voltage inverter or frequency converter.

Sources of information

1. Mishchenko V.A., Mishchenko N.I., Mishchenko A.V. A vector control method for a permanent magnet synchronous electric motor on a rotor and an electric drive for implementing this method. Patent of the Russian Federation No. 2141719 dated 03.25.1998

2. Donskoy N.V. Adjustable AC drives. Cheboksary. Publishing House of Chuvash State University, 2011.

3. Khachaturov D.V. A method of controlling a synchronous permanent magnet motor. Patent of the Russian Federation No. 2683586 dated 03/20/2018

Claims (16)

1. The method of controlling the speed of a synchronous motor using a stand-alone inverter containing channels for regulating the amplitude and frequency of the voltage of the stator winding, characterized in that for the purpose of stable rotation of the motor rotor at the most favorable value of the coefficient of power consumed by the motor (Cosϕ = 1): - a signal ΔU is introduced into the amplitude control channel, which increases the amplitude if a current arises in the stator windings, ahead of the stator voltage and, accordingly, decreases it if the stator current becomes lagging; - a signal in the form of a phase shift (by an angle ϕ) with a positive sign is introduced into the frequency control channel if a current is ahead of the voltage in the stator windings and, accordingly, with a negative sign if the current in the windings is lagging; - to control an autonomous inverter, the signals of the current sensors Дm are used after they are converted from a three-phase (physical) model i _A , i _B , i _C into an equivalent two-phase model for input into the computer i _a = К _ДТ I _m [Sin (ωt + ϕ)], i _b = K _DT I _m [Cos (ωt + ϕ)] and a repeating computational procedure, (i _a os Cosωt-i _b ⋅ Sinωt) K _u (1 + Tp) = K _u (1 + Tp) ⋅K _DT ⋅I _m Sinϕ = ΔU ≠ 0; (i _a os Cosωt-i _b ⋅ Sinωt) К _ϕ = К _ϕ ⋅К _ДТ ⋅I _m Sinϕ → 0 as ϕ → 0; where K _DT is the conversion coefficient of current sensors; I _m - the amplitude value of the currents of the phase windings of the stator, A; ω _back - the specified angular frequency of the autonomous inverter, rad / s; ϕ is the angle of shear between current and voltage in the stator winding, in rad; ΔU is the increment of the stator voltage task for an autonomous inverter, at which ϕ → 0; Sin and Cos are trigonometric functions of the angle θ _ass = ω _ass ⋅t + ϕ. 2. The method according to p. 1, characterized in that in order to reduce computational operations from the algorithm, integration using block 9 and summation using block 6 are excluded, the device operates without using the signals of these blocks.

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