JP2003088177A - Motor driving method based on multiple pwm inverter - Google Patents

Abstract

PROBLEM TO BE SOLVED: To solve the problem associated with the circulating current of a multiple PWM inverter. SOLUTION: The armature winding of a motor is divided, and the divided windings are separately driven by PWM output produced from individual carrier waves.

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electric motor and its driving system. [0002] PWM inverters are widely used for variable speed driving of electric motors. A method of performing multiplexing by shifting the phase of a PWM carrier to reduce harmonics and increase output of the PWM inverter is known as a multiplexed PWM inverter. There are several methods depending on the method of synthesizing the output of each multiplexed unit inverter. For high current applications, parallel connection of switching elements is advantageous. FIG. 2 shows a configuration of a center tap reactor system which is one of the realizing methods. The operation will be described with reference to FIG. Reference numeral 15 denotes a motor to be driven. 13 is a double PWM inverter. The PWM carrier 30 and the three-phase signal wave 33 are input to the PWM modulator 32 to generate a PWM signal. The PWM modulator 32 performs PWM modulation by comparing a carrier wave and each signal wave. The three-phase inverter outputs 7, 8, and 9 are generated by the semiconductor switch switching the DC power supply based on the PWM signal. The mechanism up to this point is the same as that of the conventional non-multiplexed PWM inverter. Another PWM characterizes the double PWM inverter
Carrier wave 31. As shown in the figure, the PWM carrier 31
Is 180 ° out of phase with the PWM carrier 30. Generally, in the case of n-fold, n carrier waves having a phase shift of (360 / n) ° are prepared, but in this example, n = 2.
Similarly, three-phase inverter outputs 10, 11, and 12 are generated from the PWM carrier 31. [0004] The unit inverter outputs 7 and 10 are generated from the same signal wave, and their fundamental wave components are the same.
On the other hand, the harmonic components are not the same because the phase of the carrier is shifted by 180 °. As a result, the unit inverter outputs 7 and 1
When the average value of 0 is taken, the fundamental wave component does not change and the harmonic component decreases. The same applies to each pair of unit inverter outputs 8 and 11, and 9 and 12, which are outputs of the other phases of the three phases. In order to take the average value of the unit PWM inverter output generated from the same signal wave, center tap reactors 19, 20,.
21 are used. [0005] The center tap reactor has two input terminals and one output terminal. Considering two input signals as frequency components, if an input component that gives the same potential change to the two input terminals is an in-phase component and an input component that gives a potential change in the opposite direction is a negative-phase component, The impedance between the inputs is high for harmonics to be rejected, but low for low frequency components such as DC and fundamentals. Therefore, there is a risk that a large circulating current will flow if there is a difference between the DC offset of the output of the two connected unit inverters or the amplitude of the fundamental wave component. Referring to FIG. 2, a DC power supply, a semiconductor switch, a unit inverter output 7, a center tap reactor 19, a unit inverter output 10, a semiconductor switch,
A circulating current can flow through a path composed of a DC power supply. The same applies to other phases. [0006] Suppression of residual harmonics even after multiplexing can be solved by a filter. Since the amount of harmonics is reduced by multiplexing, the filter can be made smaller than before. However, the problem of circulating current cannot be solved unless its generation is essentially prevented. If a control circuit is added to compensate for this, the safety of the system largely depends on the completeness of the control circuit. Another problem is that the circuit scale increased by the multiplexing further increases. [0007] In a multiple PWM inverter, there is a risk that a large circulating current flows due to an imbalance in the unit inverter output. [0008] In an electric motor that operates by supplying current to an armature winding, a plurality of armature windings that generate one magnetic pole are insulated from each other and have a high degree of magnetic coupling. The winding is divided into a plurality of windings, and the divided windings are sequentially connected to windings that generate other magnetic poles that are similarly divided to form a plurality of winding circuits that are insulated from each other. Each of the winding circuits is capable of operating the motor, and one set of the winding circuits is connected to one set of unit inverter outputs generated from each carrier of the multiplexed PWM inverter. FIG. 1 shows an embodiment of the present invention. FIG. 1 shows a case where each armature winding of a three-phase AC motor is divided into two. In order to compare the present invention with a conventional method, FIG. 2 shows a mode in which a motor without dividing an armature winding is driven by a center tap reactor type multiple PWM inverter. The present invention relates to an armature winding of a motor, but does not depend on a field structure, and thus can be applied to, for example, an induction motor and a synchronous motor. A dual PWM inverter is used to drive the armature winding in response to the division into two. Double PW
One set of outputs 7, 8, 9 of the M inverter 13 is an output corresponding to each phase of the three-phase alternating current. These are the PWM carriers 30
And the three-phase signal wave 33. The other set of outputs 10, 11, and 12, which are also outputs corresponding to each phase of the three-phase alternating current, are generated from the PWM carrier 31 whose phase is shifted by 180 °. Therefore, the phases of the harmonics are 7 and 10, 8
And 11, 9 and 12 are different. The fundamental wave components are 7 and 1 because they are generated from the common three-phase signal wave 33.
It is the same in each pair of 0, 8 and 11, and 9 and 12. 1
Reference numeral 4 denotes an electric motor driven by the inverter. The armature windings 1 and 4 are armature windings corresponding to one phase of a three-phase alternating current and correspond to the armature winding 16 in FIG. That is, the armature winding 16 divided into two is 1 and 4
It is. Similarly, the armature windings 2 and 5 are obtained by dividing the armature winding 17 in FIG. Similarly, armature winding 3
And 6 show the armature winding 18 in FIG. The meaning of the two divisions is not limited to simply cutting one winding in the middle and dividing it into two. This includes a case in which the most suitable magnetic wire diameter and number of turns are selected again so that the magnetic field generated by the current flowing through the divided windings becomes the same as the original. The dot marks on each armature winding indicate the orientation of the magnetic coupling between the windings in adjacent pairs, ie, 1 and 4, 2 and 5, 3 and 6, respectively. That is, it indicates the direction of the induced electromotive force with respect to the change in the magnetic flux that intersects in common. The armature windings 1, 2, and 3 have one end connected to a central point and the other end connected to a driving power source. With such a connection, the three-phase AC power supply can be connected to the winding circuit including the armature windings 1, 2, and 3 to operate the motor. The armature windings 4, 5, and 6 are connected in the same manner. This winding circuit can also operate the motor. The winding circuit composed of the armature windings 1, 2, 3 and the winding circuit composed of the armature windings 4, 5, 6 are insulated from each other. Although the connection method of the armature windings shown here is called a star connection, another connection method capable of operating the electric motor, for example, a delta connection may be adopted. The armature windings 1 and 4 are located at substantially the same location in space, and when a current in the same direction flows in each of them, the magnetic field generated in the motor is as shown in FIG. It is almost similar to the magnetic field of. In-phase components such as fundamental wave components included in the outputs 7 and 10 of the unit inverter cause currents of the same direction and magnitude to flow through 1 and 4. Armature winding 2
And 5, and each pair of the armature windings 3 and 6 is the same.
Therefore, the unit inverter outputs 7 and 10, 8 and 11, 9
And the magnetic field generated by the in-phase component of each pair of FIG.
Is similar to the magnetic field generated in the method in which the armature winding is not divided as shown in FIG. That is, the in-phase component becomes a mechanical force for operating the electric motor in the same manner as the output current of the conventional inverter. Since the armature windings 1 and 4 are located at substantially the same location, the degree of magnetic coupling between the two windings is close to one. For this reason, when currents of the same magnitude flow in opposite directions to 1 and 4, their magnetomotive forces cancel each other, and almost no magnetic field is generated in the motor. The opposite phase components of the harmonics included in the unit inverter outputs 7 and 10 flow currents of the same magnitude in the opposite directions to 1 and 4. Therefore, a magnetic field hardly occurs in the motor due to the antiphase component. The same applies to each pair of the armature windings 2 and 5 and the armature windings 3 and 6. That is, the negative phase component does not become a mechanical force for operating the electric motor. In the center tap reactor system shown in FIG. 2, the negative phase component current disappears before reaching the armature winding, but the negative phase component current is also output from each unit inverter output. The ability to reduce the current of the negative phase component is caused by the inductance of the center tap reactor. On the other hand, in the present invention, the ability to reduce the current of the negative phase component depends on the leakage inductance between the divided armature windings. FIG. 3 schematically shows how a leakage inductance is generated. Although the armature windings 1 and 4 are drawn in one turn, the number of turns can be increased in practice. The arrows above the armature windings 1 and 4 indicate the direction of the current. 4
0 is the armature core. 41 is a field iron core. Arrows in the iron core and on the space indicate magnetic lines of force. The actual shape of the lines of magnetic force greatly depends on the winding structure and the magnetic permeability of the iron core. However, such a magnetic field is generated unless the armature windings 1 and 4 are completely located at the same position. There is some inductance. The negative phase component of the harmonics generates the magnetic field as described above, which causes torque ripple of the motor. Therefore, the smaller the leakage inductance, the better. On the other hand, if the leakage inductance is small, the negative-sequence current may not be sufficiently reduced. If the leakage inductance is small and the reverse-phase current cannot be reduced sufficiently, a filter may be inserted between the inverter and the motor. FIG. 4 shows an example of a configuration in which a filter that works only for the reverse-phase current is inserted.
Reference numerals 50, 51, and 52 denote the filters, which are reactors coupled so that the inductance is large with respect to the antiphase component and the inductance is zero with respect to the inphase component. This effect is the same as that of the center tap reactor, but does not cause circulating current because there is no coupling of the current path between the two coils. As is apparent from FIG. 1, in the present invention, since there is no current path between the unit inverter outputs to be combined, the problem of circulating current does not occur. The present invention solves the problem of the circulating current of the multiple PWM inverter by changing the armature winding structure of the motor. This facilitates wide-range variable-speed driving of the motor.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a circuit configuration diagram of the present invention. FIG. 2 is a configuration diagram of a motor drive circuit using a center tap reactor type multiple PWM inverter according to the related art. FIG. 3 is a schematic diagram illustrating a leakage inductance between divided armature windings. FIG. 4 is a circuit configuration diagram in which an anti-phase current filter is added to the present invention. [Description of Signs] 1, 2, 3, 4, 5, 6 divided armature windings 7, 8, 9, 10, 11, 12 unit inverter output 13 multiplex PWM inverter 14 divided armature windings Motor 15 having ordinary motors 16, 17, 18 ordinary armature windings 19, 20, 21 center tap reactor 30 PWM carrier 31 PWM carrier 32 out of phase by 32 ° PWM modulator 33 three-phase signal wave 40 armature core 41 Field core 50, 51, 52 Negative-phase current filter

   ────────────────────────────────────────────────── ─── Continuation of front page    (72) Inventor Susumu Kimura             2-10-5 Nishisugamo, Toshima-ku, Tokyo F term (reference) 5H007 AA08 BB06 CB05 CC04 CC09                       EA02                 5H576 BB10 CC01 DD02 DD04 DD05                       EE11 HB01 HB05 JJ29

Claims (1)

Claims: 1. An electric motor which operates by supplying a current to an armature winding, comprising: a plurality of armature windings for generating one magnetic pole which are insulated from each other and have a high degree of magnetic coupling; The winding is divided into windings, and the divided windings are sequentially connected to windings that generate other magnetic poles that are similarly divided to form a plurality of winding circuits that are insulated from each other. Each of the wire circuits is capable of operating the motor, and one set of the winding circuit is connected to each set of unit inverter outputs generated from each carrier wave of the multiplex PWM inverter. Its drive system.