JP2001320897A - Power factor improvement circuit, induction motor and control method thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To realize the efficient improvement of a motor torque of an induction motor relatively to a power supply voltage easily and at a low cost. SOLUTION: A capacitor 3 is provided in a power supply line between a motor 1 and an inverter 2, It is to be noted that, if the motor 1 in a Fig. 1 (a) is a multiphase induction motor, the capacitors 3 are provided for the respective phases and, in that case, the Fig. 1 (a) shows the circuit structure of each one phase.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a power factor improving circuit for improving a power factor of an induction motor.

[0002]

2. Description of the Related Art The voltage / current characteristics of an induction motor will be briefly described with reference to FIG. 8A, a motor 101 as an induction motor is driven by an inverter 102 (when the motor 101 is a polyphase induction motor, FIG. 8 shows the motor 101 and the inverter 102 per phase. It shows the relationship with.)

In the configuration shown in FIG. 8A, an example of a vector diagram of an inverter output voltage Vinv, an inverter output current Iinv, a motor terminal voltage Vm, and a motor current Im in the dq axis coordinate system of the motor 101 is shown. Is shown in FIG. As shown in FIG.
When the motor 101 and the motor 101 are directly connected, the inverter output voltage Vinv and the motor terminal voltage Vm are the same, and the inverter output current Iinv and the motor current Im are the same, but due to the influence of the reactance of the motor 101,
The phase of the current will lag behind the voltage.

For this reason, various researches and developments have been made to eliminate the phase difference between the current and the voltage and to improve the power factor. For example, Japanese Patent Publication No. 7-40761 discloses a technique in which a power factor improving means including a capacitor and a reactor is connected between AC input terminals of a power converter that feeds an electric motor. In the official gazette,
By connecting a capacitor in parallel with the induction motor,
A technique for improving a power factor when starting an induction motor is disclosed.

Here, the principle of the conventional power factor improving method will be described with reference to FIG. FIG. 9A is a configuration diagram of an induction motor and an inverter according to a conventional power factor improvement method.
In FIG. 9A, a capacitor 203 is connected in parallel between a motor 201 which is an induction motor and an inverter 202. Therefore, the following equation is established.

(Equation 1) Here, Vc and Ic indicate the voltage and current applied to the capacitor 203, and other symbols are the same as those in FIG.

At this time, as shown in FIG. 9B, first, a phase difference exists between the motor terminal voltage Vm and the motor current Im due to the influence of the reactance of the motor 201. Further, the capacitor 203 allows the capacitor current I
The phase of c advances by π / 2 from the capacitor voltage Vc. Therefore, the inverter output current Iin determined from the equation (2)
The phase difference between V and the inverter output voltage Vinv, that is, the power factor is improved.

[0007]

However, according to the above conventional power factor improving method, the inverter output voltage Vi
The motor torque cannot be improved with respect to nv. That is, the above-described conventional power factor improving method is a method for improving the power factor of the inverter output current Iinv and the inverter output voltage Vinv.
Motor terminal voltage Vm and inverter output voltage Vin
There is no change in v. Therefore, to increase the motor torque, the same inverter output voltage Vinv as in the case where the power factor improvement is not performed is required. Therefore, the above-described power factor improving method cannot efficiently improve the motor torque with respect to the inverter output voltage Vinv.

An object of the present invention is to realize an efficient improvement of motor torque with respect to a power supply voltage (supply voltage) in an induction motor by a simple and inexpensive method.

[0009]

In order to solve the above-mentioned problems, a power factor improving circuit according to the present invention is provided in a power supply line of an induction motor (for example, a motor 1 in FIG. 1). A capacitor connected in series with the motor (for example, FIG.
3).

Further, in the control method of the induction motor (for example, the motor 1 in FIG. 1) according to the present invention, the power is supplied via a capacitor (for example, the capacitor 3 in FIG. 1), so that the torque to the supply voltage is obtained. It is characterized by improving the ratio.

According to the first or seventh aspect of the present invention, the power supply voltage (supply voltage; for example, the inverter output voltage Vinv in FIG. 1) applied to the power supply line is applied to the voltage between the capacitors and the induction motor. Since this is the sum of the voltage and the voltage, the power factor between the power supply voltage (supply voltage) and the current of the induction motor can be improved. When a constant voltage is applied to the induction motor, the required power supply voltage (supply voltage) can be reduced. Conversely, for a constant power supply voltage (supply voltage), the voltage applied to the induction motor,
That is, the output torque can be increased. Also,
In the present invention, since only the connection of the capacitor is used, the above effects can be obtained by a simple and inexpensive method.

Further, as in the second aspect of the present invention, the power factor improving circuit according to the first aspect of the present invention provides a power factor improving circuit according to a speed equivalent signal of the induction motor, for inputting the capacitor (for example, FIG. Switch SW).

Here, as the input means, not only a mechanical switch but also a semiconductor element such as a triac, a semiconductor circuit, a control circuit which can be controlled by a microcomputer, or the like can be used to control the input of a capacitor according to a speed equivalent signal. If possible, any circuit or device may be used.

A power factor improving circuit according to a third aspect of the present invention has a plurality of capacitors connected in series with the induction motor in the middle of a power supply line of the induction motor, and responds to a signal corresponding to the speed of the induction motor. It is characterized by switching the capacitor to be supplied.

The means for switching the capacitor may be a circuit or an apparatus capable of controlling the switching of the capacitor according to the speed equivalent signal, such as a semiconductor circuit or a control circuit which can be controlled by a microcomputer, in addition to the switching by a mechanical switch. If so, any of them may be applied.

According to the second or third aspect of the present invention, the induction motor has a reactance that varies according to the speed. However, it is possible to insert a capacitor in a suitable state to cancel the reactance. Become. According to the third aspect of the present invention, it is possible to insert a suitable capacitor according to the speed of the induction motor.

Further, as in the invention according to claim 4, by connecting the capacity of the capacitor in the power factor improvement circuit according to any one of claims 1 to 3 to the induction motor, the capacity of the capacitor is matched with the induction motor. The magnitude of the reactance may be smaller than the magnitude of the reactance of the induction motor alone.

According to the fourth aspect of the invention, since the magnitude of the reactance can be reduced by connecting the capacitor having the capacity, the power factor between the power supply voltage (supply voltage) and the current of the induction motor can be reduced. Can be improved. The reactance can be set to “0” by setting the capacitance as shown in the expression (21) described later.

According to a fifth aspect of the present invention, there is provided an induction motor including the power factor improving circuit according to any one of the first to fourth aspects.

In this case, the induction motor may be used as an electric motor of a train, as in the invention of claim 6.

According to the fifth or sixth aspect of the present invention, it is possible to have the effect of the invention of any one of the first to fourth aspects as an induction motor. Further, not only the effect in the motor mode of the induction motor but also the use in the power generation mode can obtain the above effect. That is, when the induction motor is used as an electric motor of a train as in the invention of claim 6, the amount of regenerative electric power can be increased, and the increase in electric braking force is promoted. The power that we depended on can be supplemented by electric brakes.

[0022]

Embodiments of the present invention will be described below in detail with reference to the drawings. For the sake of simplicity, FIG.
The description will be made using the same symbols as those of the currents and voltages described in FIG.

First, the principle of the present invention will be described with reference to FIG. FIG. 1 is a diagram for explaining the principle of the present invention. FIG. 1A is a diagram showing a circuit configuration, and FIG. 1B is a diagram showing a vector diagram.

As shown in FIG. 1A, in the present invention, a capacitor 3 is provided on a power supply line between a motor 1 which is an induction motor and an inverter 2. FIG.
In FIG. 1A, when the motor 1 is a multi-phase induction motor, it is necessary to provide a capacitor 3 for each phase. In this case, FIG. 1A shows a circuit for one phase. It shows the configuration.

Here, the relationship between the voltage and current relating to the motor 1, the inverter 2, and the capacitor 3 is as follows.

(Equation 2)

The correlation between each current and each voltage in the dq axis coordinate system of the motor 1 is as shown in the vector diagram of FIG. That is, first, a phase difference exists between the motor terminal voltage Vm and the motor current Im due to the influence of the reactance of the motor 1. Further, the capacitor 3 causes the phase of the capacitor voltage Vc to be delayed by π / 2 from the capacitor current Ic. And the inverter output voltage V
inv is the capacitor voltage V as shown in the equation (3).
It is determined by the sum of c and the voltage Vm between the motor terminals.

The point to be noted here is the inverter output voltage Vinv. The conventional inverter output voltage Vinv shown and described in FIGS. 8 and 9 has the same value (= vector length) as the motor terminal voltage Vm.
However, according to the present invention, the value of the inverter output voltage Vinv can be reduced by the capacitor voltage Vc while the motor terminal voltage Vm has the same value. That is, in order to apply a predetermined voltage to the motor 1, a smaller inverter output voltage Vinv (supply voltage) can be supplied. Conversely, when the inverter output voltage Vinv (supply voltage) is set to the same voltage value as the conventional one, the result is that the voltage Vm for the motor 1 is increased. Therefore, according to the present invention, the output torque-to-supply voltage ratio of the motor 1 can be easily improved. The above is the principle of the present invention.

Next, an embodiment in which the present invention is applied to an inverter-controlled train will be described in detail. still,
The application object of the present invention is not limited to trains,
It goes without saying that the present invention can be applied to various devices using an induction motor, such as a servomotor, a fan, and a pump.

FIG. 2 is a diagram showing a main circuit when the present invention is applied to an inverter-controlled train. In FIG.
The DC power input from the overhead wire 15 via the pantograph 14 is stored by the capacitor 16 connected in parallel with the inverter 12, and the DC power is supplied to the inverter 12. A power factor correction circuit 130 is connected for each phase between the motor 11, which is a three-phase induction motor for driving a train, and the inverter 12. The power factor correction circuit 130 is connected to the motor 11. , Three-phase AC power is supplied from the inverter 12.

FIG. 3 is a diagram showing a configuration of an equivalent circuit per phase of the motor 11 and a power factor improving circuit 130 in FIG. In FIG. 3, a power factor improving circuit 130 is connected in series in the power supply line of the motor 11. The power factor improvement circuit 130 is configured by connecting a capacitor C and a switch SW in parallel. The switch SW is opened / closed in response to a speed-equivalent signal (not shown) of the motor 11, and when the switch SW is released, the capacitor C is turned on.
Power is supplied via the capacitor C.

Here, the motor characteristics of the induction motor in the conventional train will be briefly described. FIG. 4 is a diagram illustrating an example of an effective value such as the inverter output voltage Vinv with respect to the speed of the train. The speed range is 55km for train speed
/ H or less, and the speed range is 55 to 80 km / h.
h, and the speed range indicates a speed range of 80 km / h or more. In the speed range, the motor current Im
Is kept constant at 151 A, and the inverter output voltage V
Since only inv is controlled, the inverter output voltage Vi
nv is proportional to the speed of the train. Then, the inverter output voltage Vinv has a maximum value (1 in FIG.
At this point, the motor current Im is controlled with the inverter output voltage Vinv kept constant, so that the motor current Im is proportional to the speed of the train (speed range).

However, in this speed range, the constant torque region where the maximum torque of the motor (F = 21,364N) can be obtained. However, in the speed range, there is no control element, and the torque becomes the square of the speed. This is a region called a characteristic region that is inversely proportional.

On the other hand, as the capacitor C of the power factor improving circuit 130, a capacitor of 820 μF is connected at a speed of 80 k.
FIG. 5 shows motor characteristics when the motor is turned on at m / h. It can be seen that the constant torque region (F = 21,364N) expands to the high speed side and the inverter output voltage Vinv drops below 1300V. FIG. 5 shows the result of turning on the capacitor C at a speed of 80 km / h.
If the voltage drops below 300V, the speed is 80 km / h before,
That is, in the speed range, the inverter output voltage Vinv corresponding to the speed can be reduced by inserting the capacitor C having an appropriate capacity. The capacitance of the capacitor C will be described later in detail.

This corresponds to improving the power factor between the inverter output voltage and the motor current and improving the output torque-to-supply voltage ratio described above with reference to FIG. That is,
In any speed range, if a capacitor C having an appropriate capacity is inserted, the required power supply voltage for a predetermined motor terminal voltage can be reduced, so that there is room for increasing the inverter output voltage Vinv. be able to. For this reason, the train to which the present invention is applied can move the region that was the conventional characteristic region to the high-speed side, and can also increase the output torque in the characteristic region as compared with the related art.

Further, since the output torque of the motor can be said to be the braking force (electric braking force) of the motor, an electric braking force similar to the maximum torque can be obtained in the range from the speed range. However, in the characteristic region (speed range), since the output torque of the motor is inversely proportional to the square of the speed, the electric braking force is lost as the speed increases.
For this reason, in order to secure the same braking force in the high-speed region as in the low-speed region, the amount of supplementation by the mechanical brake must be increased.

By applying the present invention to a train, the output torque of the motor in a high-speed range can be increased, so that the electric braking force can be increased. Therefore, since the load on the mechanical brake can be reduced, it is possible to reduce the material related to the brake such as the brake shoe and the work related to replacement.

Further, the application of the electric brake means that the motor as the induction motor is used in the power generation mode. That is, since the amount of electric power regenerated to the overhead line can be increased by increasing the electric braking force, it is possible to reduce the electric energy required for the overall operation of the train.

Since the reactance of the induction motor varies depending on the speed and the type of the induction motor, it is necessary to use a capacitor C having an appropriate capacity according to the speed and the like in applying the present invention. That is, as described above, since the induction motor includes a reactance component, it is necessary to select a capacitor having a capacity that reduces the total reactance component including the capacitor C and the induction motor. When applying the present invention to an induction motor of a train having a large range of change in reactance, it is particularly necessary to pay attention to this point. FIG. 6 shows the relationship between speed and reactance with respect to the induction motor (motor) of the train in FIGS. 4 and 5. In FIG. 6, 820 μm
The speed is 80km / h when the condenser of F is inserted.
However, when a capacitor of 410 μF is inserted, the speed becomes 1
12 km / h is the optimum value at which the reactance becomes 0Ω, but the reactance fluctuates as the speed increases or decreases.

For this reason, the power factor improving circuit 130 shown in FIG.
By opening and closing the switch SW in response to a signal (not shown) corresponding to the speed of the induction motor, it is possible to perform optimal control of the timing for turning on and off the capacitor C.
The switch SW need not be a mechanical switch, but may be a semiconductor element such as a triac, a control circuit, or the like. Further, the power factor improvement circuit 130 has been described assuming that the switch SW and the capacitor C are connected in parallel. However, the power factor improvement circuit 130 includes a plurality of capacitors having different capacities in the power factor improvement circuit 130, and switches the input capacitor. Is also good. In this case, it is possible to insert a capacitor having an optimum capacity according to the speed equivalent signal. Further, the capacity of the capacitor may be changed using a variable capacitor in accordance with the signal corresponding to the speed so that the reactance is minimized.

Next, the optimum capacity of the capacitor C, that is, the capacity that minimizes the total reactance of the capacitor C and the induction motor will be described.

First, consider the case where only a induction motor is used without connecting a capacitor. The voltage equation described by the instantaneous vector of the induction motor is represented by the following equations (5) to (8).

(Equation 3)

Here, ω ₁ indicates the power supply angular frequency, and ω _S indicates the slip angular frequency. The current vector I ₁ is a primary current vector, the current vector I ₂ is a secondary current vector, the voltage vector V ₁ is a primary voltage vector, the voltage vector V ₂ is a secondary voltage vector, and the magnetic flux vector φ ₁ Denotes a primary interlinkage magnetic flux vector, and magnetic flux vector φ ₂ denotes a secondary interlinkage magnetic flux vector, and is obtained from the values of the d-axis and the q-axis as shown in the following equation (9).

[0043]

(Equation 4) Here, the subscripts _1d , _1q , _2d , and _2q are the primary side d, respectively.
Axis, the primary q-axis, the secondary d-axis, and the secondary q-axis.

In the steady state, there is no change in magnetic flux (no induced voltage is generated), so the following equation (10) holds.

(Equation 5)

Therefore, the following equation (11) is established by the equations (5), (7) and (10).

(Equation 6)

Here, when the secondary flux linkage vector φ ₂ is made to coincide with the d-axis, the secondary flux vector φ ₂ is perpendicular to the secondary current vector I ₂ , so that the secondary flux vector φ ₂ is perpendicular to the secondary flux vector φ _2. The d-axis component of I ₂ becomes “0”. Therefore, the following equation (1)
2) holds.

(Equation 7)

Then, according to the equation (12), (11)
The equation is expressed as the following equations (13) to (15).

(Equation 8)

Next, a case where the present invention is applied, that is, a case where a capacitor is connected in series to an induction motor will be considered. Since the voltage is delayed by π / 2 with respect to the current, the capacitor voltage Vc
Becomes the following equations (16) and (17).

(Equation 9)

The optimum capacity of the capacitor is shown in FIG.
The capacity to achieve a power factor "1" of the primary current vector I ₁ of the induction motor and the primary voltage vector V ₁ as shown in FIG. In order for the power factor of the primary current vector I ₁ and the primary voltage vector V ₁ to be “1”, the following equation (18) should be satisfied.

(Equation 10)

Therefore, from the expressions (17) and (18), the following expressions (19) and (20) are satisfied, and finally, the capacitance of the capacitor C becomes the expression (21).

[Equation 11]

As described above, the equations (5) to (21) are shown by dividing the current and voltage of the induction motor into the primary side and the secondary side.
The current and voltage on the secondary side correspond to the inverter output current Iinv (= motor current Im) and the inverter output voltage Vinv in FIG. Accordingly, the total reactance of the capacitor and the induction motor becomes “0” by the capacitor having the capacity shown in the equation (21), and the power supply voltage (inverter output voltage Vinv) and the current of the induction motor (motor current Im) are obtained. And the power factor is improved.

Also, when the power factor between the primary current vector I ₁ and the primary voltage vector V ₁ is “−1”, (18)
Expressions (21) to (21) hold.

[0053]

According to the present invention, the power supply voltage (power supply voltage)
And the power factor between the induction motor and the current of the induction motor can be improved, and the ratio of the output torque of the induction motor to the supply voltage (power supply voltage) can be easily improved. When a constant voltage is applied to the induction motor, the required supply voltage can be reduced. Conversely, when the supply voltage is constant, the voltage applied to the induction motor, that is, the output torque is increased. It becomes possible. Also, since the present invention is only connection of the capacitor,
The above effects can be obtained by a simple and inexpensive method.

[Brief description of the drawings]

FIG. 1 is a diagram illustrating the principle of the present invention.

FIG. 2 is a diagram showing a main circuit when the present invention is applied to an inverter-controlled train.

FIG. 3 is a diagram showing a configuration of an equivalent circuit per one phase of the motor and a power factor improving circuit in FIG. 2;

FIG. 4 is a diagram showing an example of motor characteristics of an induction motor in a conventional train.

FIG. 5 is a diagram showing an example of motor characteristics of an induction motor in a train to which the present invention is applied at a speed of 80 km / h.

FIG. 6 is a diagram showing the relationship between the speed of an induction motor and reactance.

FIG. 7 is a diagram showing current and voltage on the primary side of the induction motor.

FIG. 8 is a diagram showing voltage-current characteristics of a conventional induction motor.

FIG. 9 is a diagram for explaining the principle of a conventional power factor improving method.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Induction motor (motor) 2 Inverter 3 Capacitor 130 Power factor improvement circuit SW switch C capacitor

 ────────────────────────────────────────────────── ─── Continuing on the front page (72) Inventor Asaki Watanabe 2-8-8 Hikaricho, Kokubunji-shi, Tokyo F-term in the Railway Technical Research Institute 5G066 FA03 FB01 5H576 AA01 BB01 CC01 DD02 DD04 EE01 EE09 EE19 FF08 HB02 LL27 5H740 AA06 BB08 BB10 NN02 NN17

Claims (7)

[Claims] 1. A power factor improving circuit comprising a capacitor connected in series with an induction motor in a power supply line of the induction motor. 2. The power factor improving circuit according to claim 1, further comprising: an input means for inputting the capacitor in response to a signal corresponding to the speed of the induction motor. 3. A power factor, comprising a plurality of capacitors connected in series with the induction motor in the middle of a power supply line of the induction motor, wherein a capacitor to be supplied is switched according to a speed equivalent signal of the induction motor. Improvement circuit. 4. The power factor correction circuit according to claim 1, wherein the capacitor is connected to the induction motor to reduce the magnitude of reactance combined with the induction motor. A power factor improving circuit having a capacity smaller than a reactance of only an electric motor. 5. An induction motor comprising the power factor improvement circuit according to claim 1. Description: 6. The induction motor according to claim 5, wherein said induction motor is a motor used for a train. 7. Power supply through a capacitor,
A method for controlling an induction motor, wherein a torque-to-supply voltage ratio is improved.