JP2545510B2 - Cycloconverter control method - Google Patents

Description

The present invention relates to an input of a cycloconverter when a multiphase AC motor is driven at a variable speed by a plurality of cycloconverters (a pair of thyristor converters connected in anti-parallel). The present invention relates to a control method capable of improving a power supply power factor.

[Conventional technology]

As a measure for improving the input power factor of the cycloconverter,
Third harmonic superposition method described in JP-A-59-117466, JP-A-60-
There are various methods such as the asymmetric control method described in 194760,
Although improved effects have been obtained by applying them in combination, means for further improvement are desired.

[Problems to be solved by the invention]

FIG. 3 shows the main circuit of the thyristor converter. The control delay angle α and the power factor angle of this thyristor converter are equal and are given by the following equation (1).

Here, E2; input line voltage of thyristor converter Ed; output DC voltage of thyristor converter If the input line voltage E2 is made smaller according to the equation (1), the power factor is naturally improved. However, if it is made too small, commutation failure phenomenon during regenerative operation or torque ripple becomes large due to output voltage imbalance when the three-phase AC motor 5 is driven by three-set cycloconverters 411, 421, 431 as shown in FIG. Such problems occur. FIG. 4 shows the output voltage waveform of the cycloconverter for explaining the unbalanced voltage, and the dotted line is the voltage to be output in the present invention. When the maximum output voltage is limited to V _L due to the power supply voltage drop, the shaded area is lost and the waveform is no longer sinusoidal.
Further, considering the three phases, voltage imbalance between the three phases occurs and various adverse effects occur.

In determining the input line voltage E2 of the cycloconverter, the above-mentioned problem is not caused even when the power supply side voltage drop is the maximum value. Therefore, in a normal state (when the power supply voltage is not significantly reduced), the power factor is very poor.

[Means for solving problems]

In Fig. 4, the maximum output voltage is
When only V _L can be output, if the voltage of the dotted line that should be originally output is multiplied by k (= V _L / V _P ) to obtain the voltage of the solid line, the waveform can secure a sine wave and the three-phase interphase voltage can be balanced. . This means lowering the voltage of the AC motor to operate. However, the operating condition of the load must be maintained, that is, the generated torque and the rotational speed of the electric motor must not change. The voltage is lowered to weaken the magnetic flux to maintain the speed, and the amount of decrease in torque due to weak magnetic flux is increased to the torque equivalent current,
It is necessary to prevent the torque from decreasing.

To achieve the above, the power supply voltage is detected, and when this detection signal drops below a certain value, the voltage reference value of the AC motor is linked to the detection value and lowered, and the torque current reference signal is set. It can be realized by increasing it.

That is, the present invention is, in a method for controlling a cycloconverter that drives a multiphase AC electric motor at a variable speed, detects the input AC voltage of the cycloconverter, and when the detected value falls below a predetermined value, Under a constant output of the phase alternating current motor, the voltage command signal corresponding to the induced voltage of the alternating current motor is lowered corresponding to the input alternating voltage detected value, and the torque current reference signal is increased. Is.

[Action]

By controlling as described above, as can be seen from the equation (1), the power factor on the input side can be improved and the output fluctuation of the motor due to the voltage drop on the secondary side can be prevented.

〔Example〕

 Next, an embodiment of the present invention will be described with reference to the drawings.

FIG. 1 shows an embodiment of the present invention. FIG. 2 is obtained by removing the portion of the present invention from FIG. 1, and first, FIG. 2 will be described.

The primary winding 123 of the thyristor transformer 1 is connected to a three-phase AC power source (not shown), and the secondary to fourth windings 11, 21, 31 are connected to the cycloconverters 411, 421, 431, respectively. The cycloconverters 411, 421, and 431 are, as shown in FIG. 3, connected in inverse parallel to each other by a Graetz-connected thyrist converter.

The outputs of the cycloconverters 411, 421, 431 are connected to the three-phase induction motor 5.

The speed feedback signal w _r detected by the speed detector 6 is the speed command
It is compared with w _r * by the comparator 9 and becomes the torque current reference I _t * via the control 10 and is given to the vector calculation block 17. The vector operation block 17 is publicly known and is not directly related to the present invention, and therefore its explanation is omitted. Regarding the vector operation block 17, refer to JP-A-59-156184.

The output of the cycloconverter is applied to the electric motor, and the line voltage is detected by the bipolar DC voltage transformers 81, 82, 83.
V _uv , V _uw , V _wu , given to the vector calculator 17,
In the vector calculator 17, the voltage of the electric motor is separated and detected into a voltage component ed parallel to the exciting current component and an orthogonal voltage component eq. The q-axis voltage component command E _q * given by the setter 121 and the detected e _q are compared by the comparator 13, and the compensation calculation is performed by the calculator 14 to obtain the magnetic flux command φ *. Magnetic flux command φ
The * is converted into the excitation current reference I _m * by the calculator 15. The content of the conversion is to compensate for the saturation phenomenon of the current magnetic flux and the delay time constant. Torque current reference I _t * and excitation current reference I _m *
Is calculated by the vector calculation block 17 for the primary current references i _u *, i _v *, i _w * of the three-phase motor 5. The phase current of the electric motor 5 is detected by the bipolar DC transformers 71, 72, 73, and I _u , I _v ,
I _w , and the comparators 181, 182, 183 display the current reference i _u *, i
_v *, compared with i _w *, is compensation calculated by the arithmetic unit 191, 192, 193 and V _cu, V _cv, the V _cw. V _cu , V _cv , V _cw are applied to the gate pulse generators 211,212,213, and the output pulse of the gate pulse generator causes the 3-set cycloconverter 411,42.
1,431 is phase controlled.

Each q-axis voltage component eq corresponding to the induced voltage of the rotational speed w _r and the electric motor of the motor with the torque current I _t and the exciting current I _m of the electric motor are independently controlled command value by more than
Controlled to match w _r *, E _q *.

Next, an embodiment of the present invention will be described with reference to FIG. A three-phase voltage transformer 22 is provided to detect the voltage of a three-phase AC power supply (not shown) applied to the primary winding 123 of the thyristor transformer 1, and the output of the transformer 22 is a three-phase full-wave rectifier 23. Is converted into a DC voltage by. A band eliminator filter and a low-pass filter for reducing the ripple component contained in the DC voltage are provided as needed, and are included in the block 23 in the notation. Block 24 is a saturation element shown in FIG. 5, and when the power supply voltage V _s is a constant value (V _sc ) or less, it deviates from the saturation value, so the variable function described below is effective, and when it is a certain value or more. Becomes a constant saturation value, the variable function described below stops and becomes a constant value.

The output of the saturation element 24 is used at three places, and first of all, it becomes the q-axis voltage component command E _qc * via the setter 122. That is, when the power supply voltage V _s is a constant value V _sc or higher, E _qc * is a constant value.
If E _q * is maintained, but the power supply voltage V _S is below a certain value V _sc ,
As is clear from FIG. 5, E _qc * decreases in proportion to V _s .

The second is added as a divisor to the divider 11, and when the power supply voltage V _s drops below a certain level, the torque current reference I _t * is set to I _tc.
It is increased to *. This increases the amount corresponding torque current I _t having a reduced q-axis voltage component eq, in order to keep the power of the motor constant.

The third is added to the multipliers 201, 202, 203 for gain compensation of the input signals of the gate pulse generators 211, 212, 213. The gate pulse generator generally has a power supply voltage fluctuation compensating circuit, that is, the ratio (gain) between the gate pulse generator input V _cu and the cycloconverter output voltage E _d is constant even if the power supply voltage changes. The control delay angle α is adjusted so that the adjustment is performed, and this adjustment is instantaneously performed. This feature is when the power supply voltage V _s is higher than a certain value V _sc is very effective, the reverse effect when you want to lower the motor voltage becomes a predetermined value or less V _sc. Therefore, in the latter case, the output signal can be lowered by directly lowering the input signal of the gate pulse (V _cu → V _cuc ) by the output to the saturation element 24.

Due to the above, the power supply voltage varies from the minimum V _s- to V _{s +} , while the input line voltage E ₂ of the cycloconverter is
_{Although the} selection was made so as to secure the required voltage at the time of _s- , the specified voltage may be secured at V _sc by applying the present invention. Therefore, E ₂ is V _s− / V _sc (<1.0) times that of the conventional method, and the power factor is improved to V _sc / V _s− times by the formula (1). Generally, it is possible to make V _s− = 0.85 × V _sr and V _sc = 0.95 × V _sr , so an improvement of about 10% is possible.

FIG. 6 shows another embodiment in which two sets of thyristor converters are connected in series for each phase of an electric motor, and the output voltages of the two sets of cycloconverters (411 and 412,421 and 422,431 and 432) are calculated by calculators 251-256. This is an example of a method for controlling the power factor asymmetrically by using. Applying the present invention to this system,
The power factor can be further improved. The function added to FIG. 1 is to lower the saturation voltage of the calculators 251-1 to 6-6 by linking to the reduced value when the power supply voltage lowers below a certain value (V _sc ).

〔The invention's effect〕

As described above, according to the present invention, since the input line voltage (E ₂ ) of the cycloconverter can be selected to be low, it becomes possible to improve the power factor of the power supply and the reduction of the motor output accompanying it. Can be prevented and the power factor can be improved while keeping the output constant. In addition, since the voltage can be lowered, it is possible to use an element having a low withstand voltage of the thyristor converter.

[Brief description of drawings]

1 is a block diagram showing an outline of a main circuit and a control system of a cycloconverter to which the present invention is applied, FIG. 2 is a block diagram of a conventional cycloconverter in which the present invention is removed from FIG. 1, and FIG. Is a circuit diagram showing a thyristor element structure of a cycloconverter, FIG. 4 is a waveform diagram showing an output AC waveform of a cyclocolmverter, FIG. 5 is an explanatory diagram showing characteristics of a saturation element, and FIG. 6 is another embodiment. It is a block diagram showing the case where the present invention is applied to an asymmetrical control system. 1-3 ... cycloconverter power transformer, 5 ... three-phase AC motor, 6 ... speed detector, 11, 12, 21, 22, 31, 32
...... Secondary and tertiary windings of transformer, 71,72,73 …… Bipolar DC current transformer, 81,82,83 …… Bipolar DC voltage transformer, 9,13,1
81-3 ... Comparator, 10,14,15,191-3 ... Calculator, 11 ...
… Divider, 17 …… Vector operation block, 22 …… Voltage transformer, 23 …… Rectifier and filter, 24 …… Saturation element, 201-203 …… Multiplier, 211-216 …… Gate pulse generator, 251 to 6 ... calculator, 411,412,421,422,431,432 ...
… Cyclo converter.

Claims (2)

(57) [Claims] 1. A method of controlling a cycloconverter for driving a multiphase AC motor at a variable speed, wherein the input AC voltage of the cycloconverter is detected, and when the detected value falls below a predetermined value, the polyphase A cycloconverter characterized in that, under a constant output of the AC motor, the voltage command signal corresponding to the induced voltage of the AC motor is decreased corresponding to the input AC voltage detection value, and the torque current reference signal is increased. Control method. 2. A control method for a cycloconverter according to claim 1, wherein an input signal of a gate pulse generator, which is a voltage command signal corresponding to an output voltage of the cycloconverter, is lowered. Method.