JPS591074B2 - Variable speed drive system of synchronous motor - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a variable speed drive system for a synchronous motor, and more particularly to means for preventing the internal phase difference angle of the motor from exceeding 9 (f') in this system. It is.

In recent years, with the advent of thyristor conversion devices with variable frequency and variable voltage output, high-performance variable speed drive technology for AC motors is being developed.

For synchronous motors, a transvector control system has come to be known as a new speed control system that can be used as if it were a DC machine even though the supplied power is AC. The present invention relates to a variable speed drive system for a synchronous motor known as such a transformer vector control system. First, an outline of the transformer vector control system will be explained. FIG. 1 is a vector diagram (one phase, leading power factor) based on AC theory of a synchronous motor. The magnetic flux due to the field winding current is ψF, but the reaction magnetic flux ψa due to the armature current interferes with this, and the effective magnetic flux that substantially exists becomes ψ. If the armature current I is decomposed into an effective magnetic flux ψ, an in-phase component 11, and an orthogonal component 12, the generated torque T of the motor is expressed by the following equation. T=KT・ψ・12・・・・・・・・・・・・
...(c) However, KT is a constant, and E in Figure 1.

is the no-load induced voltage, E is the terminal voltage, and δ is the magnetic pole angle (also referred to as phase difference angle). The subject of transformer vector control is to accurately determine the effective magnetic flux ψ and torque component current 12 in equation (1) above from externally observable quantities such as field winding current and armature winding current through various calculations. This can be said to be particularly true. FIG. 2 is a block diagram showing a configuration example of a transformer vector control system for a synchronous motor.

Refer to the same figure. The armature of the synchronous motor 17 is powered from a three-phase power supply 20 via a converter 15 such as a cycloconverter, and the field is excited from the same three-phase power supply 20 via a converter 16 such as a thyristor rectifier. The position detector 18 is a device that electromagnetically detects the position of the rotating magnetic pole of the synchronous motor 17, and the output of the detector 18 is calculated in the magnetic pole position calculator 14 to output Sinθ and EOsθ (here θ is the deviation angle of the magnetic pole with respect to a certain coordinate axis whose origin is the center of the stator). The magnetic flux calculator 5 calculates the armature current (Ia, ib, i
c) Given the field current 1f and the above Sinθ, COsθ, the effective magnetic flux ψ contributing to torque generation in the synchronous motor 17, Sinρ, COsp and COsδ
(Here, ρ is the deviation angle of the effective magnetic flux with respect to the coordinate axis with the stator center as the origin, and δ is the deviation angle between the magnetic pole position and the effective magnetic flux position, that is, the magnetic pole angle or phase difference angle. be). The tacho generator 19 is a synchronous motor 17
detects and outputs the rotational speed n. Now, assume that a command value ψ (indicates a command value) regarding the effective magnetic flux is input from the command value input terminal 21. Then, the command value ψ and the effective magnetic flux ψ which is the output of the calculator 5 are compared, and the magnetic flux regulator 2 outputs the magnetizing current command value h in the direction in which the deviation becomes zero. Further, if a command value n for commanding the rotational speed of the synchronous motor is input from the command value input terminal 22,
The n value and the output n of the tacho generator 19 are compared, and the speed regulator 1 outputs the necessary torque command value T in the direction in which the difference becomes zero. The divider 3 has the above (1
), the torque command value τ is divided by the effective magnetic flux ψ to calculate the torque component current command value 12. Here, ψ, ψ, Iu*, I2, etc. are all DC amounts, and it can be said that Iu corresponds to the field current in a DC machine, and I2 corresponds to the armature current. The current command calculator 4 converts these DC amounts into AC current command values 1a, Ib, Ic and If that are actually required for the motor and outputs them. Current regulators 6 to 9 are command direct 1a*
An adjustment output is generated in a direction in which the deviation of the result of comparing the armature current (Ia to 1c) and the field current 1f becomes zero. Firing angle regulators 10 to 13 adjust the armature current and field current of synchronous motor 17 to predetermined values by controlling converters 15 and 16 in response to regulator outputs. As described above, in the transvector control system for a synchronous motor, the speed of the synchronous motor can be controlled with high performance by inputting command values in the form of direct current from the terminals 21 and 22. Next, the details of the magnetic flux calculator 5 will be explained, but first, the coordinate relationships of vector quantities will be clarified.

First, two-phase (axis) conversion of the three phases is performed in order to capture the AC three-phase quantity as a spatial rotation vector, and the relationship will be explained with reference to FIGS. 3 and 4. Figure 3 shows the three-phase sinusoidal waveforms ψA, ψ in Figure 4, with the α axis on the winding axis of phase a of the stator's three phases (A, b, c), and the β axis perpendicular to it.
B,ψ.

, let each instantaneous quantity at time A be ψα, ψ on both axes.
It is expressed by converting it into two phases as β, and its calculation formula is given by the following formula. ψα and ψβ are quantities that change over time on the α and β axes, respectively, but in a symmetric and balanced three-phase system, the combined quantity ψ of both does not change in size over time, and is the same as the three-phase quantity. It becomes a rotation vector that rotates at a speed determined by the frequency.

If d-q coordinate axes that are orthogonal to each other are also taken on the rotor, it becomes possible to express both the stator and the rotor using two axes.
FIG. 5 is a vector diagram of various quantities using such spatial rotation coordinates.

In other words, the α-axis coaxial with the a-phase center and the β-axis perpendicular to this are fixed axes, and the d-axis (sometimes called the magnetic pole axis) located on the center line of the magnetic pole and the q-axis perpendicular to this are the rotational axes. The one axis in the direction of the effective magnetic flux ψ and the two axes perpendicular to this are also rotation axes. The angles θ and ρ are values that change as the motor rotates, and the magnetic pole angle or phase difference angle δ is
Since it is a coordinate system that rotates together, and the angle formed between the d-q axes and the 1-2 axes, it does not change over time. The angle θ can be detected as the relative position of the magnetic pole with respect to the armature winding, for example, in a manner similar to that of an ordinary commutatorless motor (magnetic pole position detector 18 and calculator 4 in FIG. 2). With the above as a preliminary explanation, magnetic flux calculation will be explained next. Generally, the magnetic flux ψ is d−
When expressed by q-axis coordinate system components ψD and ψq (not shown), it is given by the following equation.

Gd(P), Gq(P): A term that includes a delay element determined by the equipment constants of the motor. The angle ρ formed by the α axis and the 1st axis, and the d axis and 1
The magnetic pole angle δ with respect to the axis is expressed by the following equation.

FIG. 6 shows a block diagram of a magnetic flux calculator constructed based on the above equations (4) to (9). Please refer to FIG.

The three-phase/α/β-axis coordinate converter 517 converts each phase current 1a, i
b, ic are converted into currents 1d, iβ of α and β axis coordinate components according to the above equation (6) and output. The α/β/d-q axis coordinate converter 520 converts Id, iβ and the magnetic pole position calculator 14
When inputting Sinθ and COsθ, the above (g)
According to the formula, it is converted into a current 1d,i of the d-q axis coordinate components and output. When the ψd calculator 521 receives the sum of Id and If, it calculates ψd according to the above equation (4) and outputs it. Similarly, ψ, arithmetic unit 522 receives I, and ψ,
Calculate and output. d-q/α/β axis coordinate converter 52
3 receives Sinθ and COsθ from the magnetic pole position calculator 14, and calculates the magnetic fluxes ψD and ψ9 of the d-q axis coordinate components as αη
According to the formula, the magnetic flux ψ ($, ψβ) of the α and β axis coordinate components is converted and output. The magnetic flux component calculator 518 performs the calculation according to the above formula (G) and outputs the magnetic flux ψ, Sinρ, COsρ. The magnetic pole angle calculator 519 also performs the calculation shown in equation (9) above and outputs COsδ and Sinδ.Next, details of the current command calculator 4 will be explained.

As shown in FIG. 2, this computing unit includes a magnetic flux computing unit 5,
The current to be supplied to each winding of the armature and field is calculated by inputting various signals given from the magnetic flux regulator 2, the speed regulator 1, etc. The effective magnetic flux ψ is the magnetic flux created by the current 1 of the 1-axis component of the armature current 1, as ψ,
Then, it becomes 4 which is clear from FIG. 5, and since ψF is created by the field winding current 1f, the effective magnetizing current 1u that creates the effective magnetic flux ψ is expressed by the following equation.

I, takes on positive and negative polarities, and the state in FIG. 5 is I,kuO. Therefore, in order to ensure the effective magnetic flux ψ in a state where the current in the field winding is at a value If, that is, a predetermined magnetizing current 1u.
The magnetizing current that should be supplied from the armature side in order to maintain the current value (as mentioned earlier, the value represents the command value) is given by the following formula.

IlJU Todoroki 1VVV▼
Since the command value 12m of the torque component current on the Rwl armature side is calculated from the torque command value Tm using the relationship of equation (1), each command value on the rotating coordinates i1m and I2m is , are converted into command values iα and iβ on the fixed α and β axes according to the following equations.

．． N-. Then, according to the following formula, it is finally converted into the required three-phase amount to become the armature current command value 1a, Ib, and Ic.

) Next, determine the current 1f to be supplied to the field winding.

Referring to Fig. 5, the armature reaction magnetic fluxes ψ1 and ψ2 seen from the 1st and 2nd axis system are created by the currents 11 and i2, and the effective magnetic flux ψ
Since the magnetizing current of is Iu, these currents (magnetomotive force)
There is a relationship between the field winding current 1f and the following equation. Looking at the power factor angle τ with reference to the torque diagram, if the I component of the armature current 1 is made zero, the power factor of the motor in a steady state becomes 1001).

In order to set 1=0, it is sufficient to set I,=0 in the above equation, so the command value of the current to be supplied to the field winding is determined as in the following equation.

FIG. 7 shows a block diagram of a current command calculator constructed based on the above equations 00) to 1.

Please refer to FIG.

Multiplier 524 calculates the field current If and C from magnetic flux calculator 5.
Multiply by Osδ and output the result 1fC0Sδ. By subtracting this output value and the magnetizing current command value 1u and a half according to the above (substitution) formula, the magnetizing current command value 1, 1, is created. The 1/2/α/β axis coordinate converter 525 receives the above-mentioned magnetizing current command value 11, torque component current command value 12m, and Sinρ and COsρ from the magnetic flux calculator 5, and performs the above (self) calculation. I is converted onto the α and β axes by
Outputs d rice and iβ rice.

Next, the α/β/three-phase coordinate converter 527 converts these Id,
According to the above equation 02), the iβ rice is finally converted into the required three-phase amount 1a (, Ib rice, 10 rice) and output.The field current command calculator 526 performs the calculation according to the above a trial. The field current command value is then output.Since the field winding generally has a large inductance, it is difficult to suddenly change the field current.

Therefore, in response to load torque disturbances that cause sudden changes in armature current and voltage fluctuations in the power supply to the thyristor converter,
In order to maintain the effective magnetic flux at a predetermined value, i1 is added to the armature current command value as shown in FIG. 7 (input of coordinate converter 525). This compensates for transient excesses and deficiencies in magnetic flux, and improves the responsiveness of motor control. Having explained the outline above, it is believed that the variable speed drive system for synchronous motors, known as a transvector control system, has been understood. Now, of the armature current of the synchronous motor, the component that contributes to torque generation is I2,
If the component contributing to magnetic flux generation is I, (see Fig. 5), the peak value of the armature phase current is V'7'.

Therefore, conventionally, the maximum permissible amount of phase current in a motor is 11
Then, it was limited.

By the way, in the above-mentioned synchronous motor variable speed drive system,
In order to make the motor power factor 1, the field current 1f is generally adjusted so that the component current 11 contributing to the generation of magnetic flux of the armature current becomes zero. The explanation will be further continued with reference to FIG. 8, which is a vector diagram of related quantities. In Fig. 8, ψF is the magnetic flux component on the d-axis generated by the field current 1f, ψ2 is the magnetic flux component generated by the torque component current 12 of the armature current, ψ is the effective magnetic flux, and δ is the phase difference angle (
magnetic pole angle). Now, assuming that the field current 1f (ψF) is limited by the rated allowable current of the motor, if the torque component current 12 (ψ2) increases in this state, the phase difference angle δ will increase, and in some cases, It will be over 90 degrees. The torque component current 12 is limited by the above formula A4), but due to the nature of the formula, the restriction by formula A4 cannot guarantee that the phase difference angle δ will not exceed 90 degrees. That's not to say there isn't. Phase difference angle δ is 90
It is well known that if the temperature is exceeded, a disturbance phenomenon will occur. This invention was made in order to eliminate the causes of unstable operation in the conventional synchronous motor variable speed drive system as described above, and therefore, an object of the invention is to ensure that the internal phase difference angle δ is It is an object of the present invention to provide a variable speed drive system for a synchronous motor that does not exceed 90 degrees and therefore prevents disturbance phenomena.

The key point of the configuration of the present invention is that the magnitude of the torque component current 12 is limited in relation to the field current 1f and the phase difference angle δ so that the phase difference angle δ does not exceed 90 degrees.

It goes without saying that limiting I2 leads to limiting generated torque. Next, the principle of this invention will be explained.

In FIG. 8, it is clear from the illustrated vector relationship that when If=I2sin δ, the phase difference angle δ becomes 90 degrees. Therefore, it can be seen that I2 should be limited so as to satisfy the condition I2<(If/Sinδ). FIG. 9 is a block diagram showing one embodiment of the present invention.

Refer to the same figure. The difference from FIG. 2 which shows the conventional method is that a current limiter 23 is arranged between the divider 3 and the current command calculator 4, and the current limit value in the limiter 23 is set in the divider 24. The point is that the instructions are given by The divider 24 divides the field current 1f by Sin δ given by the magnetic flux calculator 5, and gives the result to the current limiter 23 as a limit value. Therefore, the command value from divider 3 is 1
2 is always 12〈(If/
The current is input to the current command calculator 4 after being limited so as to satisfy the condition: Sin δ).

As explained above, according to the present invention, in the variable speed drive system of a synchronous motor, the internal phase difference angle (magnetic pole angle) never exceeds 90 degrees under any circumstances, and therefore the disturbance phenomenon does not occur. This has the advantage that stable operation can be achieved.

[Brief explanation of drawings]

Figure 1 is a vector diagram based on AC theory of synchronous motors,
Figure 2 is a block diagram showing a configuration example of a transformer vector control system for a synchronous motor, Figure 3 is an explanatory diagram explaining the conversion relationship of symmetrical three-phase quantities into two-axis components, and Figure 4 is a flowchart of three-phase alternating current. Figure 5 is a vector diagram showing the coordinate relationships of vector quantities, Figure 6 is a block diagram showing the magnetic flux calculator, Figure 7 is a block diagram showing the current command calculator, and Figure 8 is the related quantities. FIG. 9 is a block diagram showing an embodiment of the present invention. In the figure, 1 is a speed regulator, 2 is a magnetic flux regulator, 3 is a divider, 4 is a current command calculator, 5 is a magnetic flux calculator, and 6 to 9
are current regulators, 10 to 13 are firing angle regulators, 14 is a magnetic pole position calculator, 15 is a conversion device (for example, a cycloconverter), 16 is a field conversion device, and 17
is a synchronous motor, 18 is a magnetic pole position detector, 19 is a tacho generator, 20 is a three-phase AC power supply, 21 and 22 are each command value input terminals, 23 is a current limiter, 24 is a divider, 51
7 is a three-phase/α/β axis coordinate converter, 518 is a magnetic flux component calculator, 519 is a magnetic pole angle calculator, 520 is an α/β/d-q axis coordinate converter, 521 is a ψd calculator, and 522 is a ψq Arithmetic unit, 523 is d-q/a/β axis converter, 525 is 1/2/
α/β axis coordinate converter, 526 is field current command calculator, 5
27 indicates an α/β/three-phase coordinate converter.

Claims (1)

[Claims] 1. A magnetic flux calculator that calculates the effective magnetic flux that contributes to the torque generation of the synchronous motor based on the armature current and field current, and the effective magnetic flux calculated by the calculator and the effective magnetic flux command value and torque commanded from the outside. A current command calculator calculates and commands the armature current and field current actually required for operation of the synchronous motor based on the command value of In a variable speed drive system for a synchronous motor comprising adjustment means for controlling a magnetic current, when the torque command value is input as a command to a current command calculator, the torque component current value of the armature current is converted, and the value is limited to the value obtained by dividing the field current by the sine value of the magnetic pole angle, which is the deviation angle between the magnetic pole position and the effective magnetic flux position. A variable speed drive system for synchronous motors characterized by: