JPH07177784A - Voltage-type inverter device - Google Patents

Abstract

PURPOSE:To limit the output voltage of an inverter for avoiding a case where voltage current cannot be controlled when a DC power supply voltage decreased rapidly by reducing the generation torque of an induction motor to a level which is lower than the maximum torque which an inverter device can output when the DC power supply voltage is reduced to a specific value or less. CONSTITUTION:When a DC power supply voltage DCV decreases rapidly, a DC power supply voltage DCV is detected by a DC voltage detection circuit 1 and us compared with a set value DCV1* of a DC voltage reduction detection value setting circuit 14 by a comparator 13 and then a torque limit compensation signal TL is output by a torque limit value compensation circuit 17. A torque limit circuit 18 limits a torque reference T* to a torque limit compensation signal TL or less, thus reducing the torque of an induction motor 4 and hence rapidly reducing the terminal voltage of the induction motor 4 for preventing the output voltage of the inverter from reaching the limit.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a voltage type inverter for variable speed control of an induction motor, and more particularly to a voltage type inverter device capable of continuing operation when a DC power supply voltage drops.

[0002]

2. Description of the Related Art Normally, in a voltage type PWM inverter, DC
An SR converter or thyristor converter is used as a power source. FIG. 9 is a circuit diagram of a conventional voltage source inverter. In the figure, 1 is a converter, 2 is a filter capacitor, 3 is an inverter circuit, and 4 is an induction motor.
Although the converter 1 is shown as an SR converter here, it may be a voltage controllable converter such as a thyristor converter. Further, the output of the converter 1 becomes a DC power source of a constant voltage due to the action of the filter capacitor 2,
The inverter circuit 3 converts this into AC power of variable frequency variable voltage to control the induction motor 4. Although the inverter circuit 3 is illustrated here as an IGBT inverter, it may be one using a self-turn-off element such as GTO or GTR.

FIG. 10 shows a conventional protection circuit diagram when the DC voltage drops. In the figure, the circuit constituent elements 1, 2, 3, 4 are the same constituent elements as in FIG. 9, and therefore their explanations are omitted. 5 is a speed sensor of the induction motor 4, 6 is a speed reference setting circuit, 7 is a speed control circuit, 8 is a magnetic flux control circuit, 9 is a vector control circuit, 10 is a current control circuit, 11
Is a PWM control circuit, 12 is a DC voltage detection circuit, 13 is a comparator circuit, 14 is a DC voltage drop detection value setting circuit,
Reference numeral 15 is an induction motor voltage correction circuit, and 16 is a current sensor.

Next, an outline of the operation of the inverter protection circuit shown in FIG. 10 will be described. In the figure, the speed control circuit 7 so that the speed S _p of the induction motor 4 detected by the set speed S _p ^* and the speed sensor 5 of the speed reference setting circuit 6 becomes equal to output the reference T ^* of torque . Also,
The magnetic flux control circuit 8 outputs the excitation current reference _If ^* of the induction motor. The vector control circuit 9 receives the torque reference T ^* and the excitation current reference _If ^* as inputs, calculates the primary current of the induction motor as a vector, and outputs the primary current reference I ^* . The current control circuit 10 controls the primary current reference I ^* to be equal to the primary current I of the induction motor 4 detected by the current sensor 16 and outputs the voltage reference V ^* . The PWM control circuit 11 PWM-controls the inverter circuit 3 based on this voltage reference V ^* .

In the inverter device configured as described above, if the DC voltage DCV drops due to a power supply voltage fluctuation or a rapid change in the induction motor load, the DC voltage DCV is detected by the DC voltage detection circuit 12, and the DC voltage DCV is detected. The set value DCV ₁ ^* of the drop detection value setting circuit 14 is compared by the comparator circuit 13, and the induction motor voltage correction circuit 15
The exciting current correction signal I _fc is output by the
The difference from _f ^* is input to the vector control circuit 9 to lower the induction motor voltage. Thus, if for some reason D
When the C voltage drops, the output voltage of the inverter is lowered to prevent the primary current control failure of the induction motor 4.

FIG. 10 shows an example in which the induction motor is vector-controlled. Similarly, the induction motor 4 is detected by detecting the DC voltage.
There is also a method of controlling to reduce the magnetic flux of. Also,
In the case of performing open loop control without detecting the speed of the induction motor, there is also a method of reducing and controlling the output frequency or output voltage of the inverter.

[0007]

The DC voltage drop protection circuit configured as described above functions without any problem when the DC voltage drops slowly. However, when the DC voltage sharply drops, such as when the induction motor load sharply increases or the power supply voltage sharply decreases, the magnetic flux and voltage of the induction motor 4 have a large time constant and do not suddenly decrease. Is not in time, the output voltage of the inverter circuit 3 is limited, and various problems occur. For example, if the output voltage is limited, the current flowing through the induction motor 4 becomes uncontrollable, and an overcurrent may flow through the inverter to stop it or damage the equipment. Further, since the inverter cannot pass the sine wave current, the torque ripple generated by the induction motor 4 becomes large, which may damage the motor and the load.

Further, if the frequency of the inverter is suddenly lowered due to the inertia of the motor, the regenerative state becomes impossible to control the regenerative current, and there is a possibility that an overcurrent may flow. Regarding such a sudden drop in DC voltage, conventionally, there is no way to prevent the output voltage of the inverter circuit from being limited, except to take measures so that the DC voltage does not drop on the DC power supply side.

However, the SR converter 1 cannot control the DC voltage, and even when the thyristor converter is used, the control of the PWM inverter is fast, while the control of the DC voltage by the thyristor converter is slow. The measures on the DC power supply side were difficult. In the end, there is no effective measure to protect against a situation where the DC voltage drops sharply.

The present invention has been made in view of the above circumstances, and an object thereof is to prevent a situation in which the output voltage of the inverter is limited and the voltage and current cannot be controlled when the voltage of the DC power supply sharply decreases. To provide a device.

[0011]

In order to achieve the above object, the first aspect of the present invention is a voltage type inverter device for variable speed control of an induction motor, wherein a sensor for detecting a DC power supply voltage and the DC power supply voltage are provided. When the DC power supply voltage drops below a predetermined value, a comparator circuit that operates when the value of the DC power supply voltage drops below a predetermined value, and a torque limit circuit that limits the torque of the induction motor to a certain value or less by the output of the comparator circuit The torque generated by the induction motor is smaller than the maximum torque that the inverter device can output.

According to a second aspect of the present invention, the reference value of the torque of the induction motor is 1 or 1 by the output of the comparator circuit.
A torque limit circuit for limiting the reference value of the torque component of the next current to a certain value or less is provided.

Further, a third comparator circuit which operates when the DC power supply voltage drops below a first predetermined value and a second comparator circuit which operates when the DC power supply voltage rises above a second predetermined value. A hysteresis is provided at the operating point of the torque limit circuit by making the second predetermined value larger than the first predetermined value.

Further, according to a fourth aspect of the present invention, when the DC power supply voltage becomes equal to or lower than a predetermined value, an operation circuit which outputs an operation result which is proportional to the difference between the predetermined value and the DC power supply voltage or is proportionally integrated. , A torque limit circuit that limits the reference value of the torque of the induction motor or the torque component of the primary current to a certain value or less based on the calculation result, and the amount of decrease when the DC power supply voltage decreases to the predetermined value or less Is increased, the reference value of the torque of the induction motor or the torque component of the primary current is decreased.

[0015]

According to the voltage source inverter device of the present invention, it is possible to prevent the output voltage of the inverter from reaching the limit by rapidly reducing the motor terminal voltage by reducing the motor torque.

[0016]

Embodiments of the present invention will be described below with reference to the drawings. [Arrangement of Embodiment] FIG. 1 is a circuit diagram of an embodiment of the present invention. In the figure, 1 is a converter, 2 is a filter capacitor, 3 is an inverter circuit, 4 is an induction motor, 5
Is a speed sensor of the induction motor 4, 6 is a speed reference setting circuit,
7 is a speed control circuit, 8 is a magnetic flux control circuit, 9 is a vector control circuit, 10 is a current control circuit, 11 is a PWM control circuit,
12 is a DC voltage detection circuit, 13 is a comparator circuit, 1
4 is a DC voltage drop detection value setting circuit, 16 is a current sensor,
Reference numeral 17 is a torque limit value correction circuit, and 18 is a torque limit circuit.

[Operation of the Embodiment] The operation of this embodiment will be described below with reference to the circuit configuration diagram of FIG. 1, the operation explanatory diagram of FIG. 2, and the current / voltage vector diagram of the induction motor.

In FIG. 1, the circuit components 1 to 11 operate in the same manner as the conventional example described in FIG. For example, if the DC voltage DCV suddenly drops for some reason, the DC voltage detection circuit 12
DC voltage drop detection value setting circuit 14 that detects the voltage DCV
The set value DCV ₁ ^* of the
3, the torque limit value correction circuit 17 outputs the torque limit correction signal T _L. The torque limit circuit 18 limits the torque reference T ^* to the torque limit correction signal T _L or less. As a result, the torque of the motor decreases and the terminal voltage of the motor also decreases.

FIG. 3 shows a simplified current / voltage vector diagram of the induction motor. FIG. 3A shows the case where the induction motor torque is small, and FIG. 3B shows the case where the induction motor torque is large. Figure 3
Where I ₁ is the primary current vector of the induction motor, I _t
Is the torque component of I ₁ , I _f is the excitation component of I ₁ , V ₁ is the terminal voltage vector of the induction motor, V ₂ is the secondary voltage vector of the induction motor, I ₁ R is the resistance drop of the induction motor voltage,
I ₁ L is the leakage reactance drop of the induction motor voltage.

As can be seen by comparing FIGS. 3 (a) and 3 (b), the magnitude of the induction motor terminal voltage V ₁ is ₁ (under the same conditions of the secondary voltage V ₂ and the exciting current _If ). Next current I ₁
Generally becomes larger as becomes larger. Therefore, the induction motor terminal voltage V ₁ can be reduced by reducing the induction motor torque. Moreover, the difference from the conventional example described in FIG. 9 is that the secondary voltage V ₂ of the induction motor and the amount having a large time constant such as the magnetic flux are not changed and the torque component I _{t of the} primary current and the induction motor voltage are changed. This is because only the rapidly changeable amounts such as the resistance drop amount I ₁ R and the leak reactance drop amount I ₁ L of the induction motor voltage are controlled.

Thus, if for some reason DC
When the voltage decreases, the output voltage of the inverter can be lowered by limiting the internal torque component of the primary current of the induction motor, and the primary current control failure of the induction motor 4 can be prevented. When the DC voltage DCV rises again,
When the comparator circuit 13 exceeds the predetermined value DCV ₁ ^* or more, the torque limit correction signal T _L is returned to the original value to obtain a normal motor torque.

By the way, as shown in the vector diagram of FIG. 3, in this embodiment, when the DC voltage drops below the secondary voltage of the induction motor, the inverter output voltage is limited even if the torque is zero. However, it is unlikely that the DC voltage will drop significantly in this way, and there is no practical problem. Rather, the advantage of being able to reduce the motor terminal voltage with responsiveness is greater.

Further, in this embodiment, even if the torque is reduced to zero and the motor is in the free running state, the magnetic flux of the motor is maintained, so that a simple inverter stop, which has been conventionally performed,
Unlike protection by free run, normal operation can be restored quickly when the DC voltage is restored.

[Effects of the Embodiment] By forming the protection circuit as described above and reducing the motor torque, it is possible to prevent the motor terminal voltage from rapidly decreasing and the output voltage of the inverter from reaching the limit.

[Other Embodiments] FIG. 4 is a circuit diagram of another embodiment of the present invention. The same components as those in FIG. 1 are designated by the same reference numerals, and the description thereof will be omitted. In FIG. 4, 13A and 13B are comparator circuits, and 14A and 14B are DC.
A voltage drop detection value setting circuit, 17A is a torque limit value correction circuit.

The operation of this embodiment will be described below with reference to the circuit configuration diagram of FIG. 4 and the operation explanatory diagram of FIG. In FIG. 4, the circuit components 1 to 11 operate in the same manner as the conventional example described in FIG. For example, if the DC voltage DCV suddenly drops for some reason, D
The DC voltage DCV is detected by the C voltage detection circuit 12, and D
And it outputs a torque limit correction signal T _L by the torque limit value correction circuit 17A setting value DCV ₁ ^* and the DCV of C voltage drop detection value setting circuit 14A compared by a comparator circuit 13A. The torque limit circuit 18 limits the torque reference T ^* to the torque limit correction signal T _L or less. As a result, the torque of the motor decreases and the terminal voltage of the motor also decreases. Even if the DC voltage DCV rises again and exceeds the set value DCV ₁ ^* , the torque limit correction circuit 1
7A continues to hold the torque limit correction signal T _L , and DC
When the set value DCV ₂ ^* of the voltage drop detection value setting circuit 14B is exceeded, comparison is made by the comparator circuit 13B and the output _TL of the torque limit value correction circuit 17A is returned to the original value.

Thus, if for some reason DC
When the voltage decreases, the output voltage of the inverter can be lowered by limiting the internal torque component of the primary current of the induction motor, and the primary current control failure of the induction motor 4 can be prevented. In addition, by providing the voltage drop detection value with hysteresis as described above, the DC voltage DCV becomes a predetermined value DCV ₁ ^*.
Torque limit correction signal T _L
Normal operation is possible without chattering.

FIG. 6 is a diagram for explaining the operation different from that of the embodiment of FIG. 4, and the operation of this embodiment will be described below with reference to the circuit configuration diagram of FIG. 4 and the operation diagram of FIG. In FIG. 6, the circuit components 1 to 11 operate in the same way as the conventional example described in FIG. For example, when the DC voltage DCV suddenly drops for some reason, the DC voltage detection circuit 12 detects the DC voltage DCV, and the set value DCV ₂ ^{* of} the DC voltage drop detection value setting circuit 14B and the D
The CV is compared by the comparator circuit 13B, and the torque limit correction signal T _L is output by the torque limit value correction circuit 17A. DC voltage DCV is DCV ₂ ^* and DC
When it is between V ₁ ^* , the torque limit correction signal T _L drops in proportion to the DC voltage DCV. The torque limit circuit 18 limits the torque reference T ^* to the signal T _L or less. As a result, the torque of the motor decreases and the terminal voltage of the motor also decreases. When the DC voltage DCV rises again and exceeds the set value DCV ₁ ^* and is between DCV ₂ ^* , the torque limit correction signal T _L rises in proportion to the DC voltage DCV. Thus, by providing a certain width in the voltage drop detection value and gradually lowering the torque limit T _L , even when the DC voltage DCV goes up and down in the vicinity of the predetermined value DCV ₁ ^* ,
Normal operation is possible without sudden changes in the torque generated by the motor.

FIG. 7 is a circuit configuration diagram of still another embodiment of the present invention. The same components as those in FIG.
The description is omitted. In FIG. 7, 19 is a PI controller circuit.

The operation of this embodiment will be described below with reference to the circuit configuration diagram of FIG. 7 and the operation explanatory diagram of FIG. In the figure, the circuit components 1 to 11 operate in the same manner as the conventional example described with reference to FIG. For example, if the DC voltage DCV suddenly drops for some reason, D
DC voltage DCV is detected by the C voltage detection circuit 12, and DC
The PI controller circuit 19 compares the set value DCV ₁ ^{* of the} voltage drop detection value setting circuit 14 with the DCV and outputs the torque limit correction signal T _L. The torque limit circuit 18 uses the torque reference T ^* as the torque limit correction signal T _L.
Limited to: As a result, the torque of the induction motor decreases and the terminal voltage of the induction motor also decreases. DC voltage DCV
Rises again and exceeds the set value DCV ₁ ^* , PI
The controller circuit 19 raises the torque limit correction signal T _L again and restores it. In this way, if the DC voltage drops for some reason, the output voltage of the inverter is lowered by limiting the internal torque component of the primary current of the induction motor, and the inability to control the primary current of the induction motor 4 is prevented. be able to. Further, by performing PI control of the voltage drop detection set value DCV ₁ ^* and the DC voltage DCV as described above, it is possible to continue the operation at the induction motor terminal voltage according to the DC voltage drop amount.

In each of the above embodiments, the case where the converter circuit and the inverter circuit correspond to each other by 1: 1 has been taken as an example, but the present invention is not limited to this example, and one converter includes a plurality of inverter circuits. It can also be applied to a common converter system that supplies a DC power supply to.

Further, as the converter, not only the thyristor converter but also the PWM converter using the self-extinguishing element is applicable. Furthermore, in each of the above-mentioned embodiments, the reference of the torque of the induction motor is limited, but the present invention is not limited to this, and even if the reference of the torque component of the primary current is limited. Good.

[0033]

As described above, according to the present invention,
Preventing the output voltage of the inverter from reaching the limit by detecting the DC voltage and configuring the control circuit so as to reduce the motor torque when it falls below a predetermined value. You can Further, it is possible to avoid a situation in which the voltage and current cannot be controlled without taking measures to prevent the DC voltage from decreasing on the DC power supply side, and it is possible to stop the inverter due to an overcurrent, or to stop the equipment. Since it is damaged or the inverter cannot pass the sinusoidal current, the torque ripple generated by the motor is increased, and it is possible to prevent a problem such as damage to the motor or the load device.

[Brief description of drawings]

FIG. 1 is a circuit configuration diagram of an embodiment of the present invention.

FIG. 2 is a diagram for explaining the operation of FIG.

FIG. 3 is a current / voltage vector diagram of the induction motor of FIG.

FIG. 4 is a circuit configuration diagram of another embodiment of the present invention.

FIG. 5 is a diagram for explaining the operation of FIG.

FIG. 6 is a diagram for explaining another different operation from FIG. 4;

FIG. 7 is a circuit configuration diagram of still another embodiment of the present invention.

FIG. 8 is a diagram for explaining the operation of FIG. 7.

FIG. 9 is a circuit diagram of a conventional voltage source inverter.

10 is a configuration diagram of a conventional protection circuit using the inverter of FIG.

[Explanation of symbols]

1 ... Converter, 2 ... Filter capacitor, 3 ... Inverter circuit, 4 ... Induction motor, 5 ... Speed sensor, 6 ... Speed reference setting circuit, 7 ... Speed control circuit, 8 ... Flux control circuit,
9 ... Vector control circuit, 10 ... Current control circuit, 11 ... P
WM control circuit, 12 ... DC voltage detection circuit, 13, 13
A, 13B ... Comparator circuit, 14, 14A, 14B
... DC voltage drop detection value setting circuit, 15 ... Induction motor voltage correction circuit, 16 ... Current sensor, 17, 17A ... Torque limit value correction circuit, 18 ... Torque limit circuit, 19 ...
PI controller circuit.

Claims (4)

[Claims] 1. A voltage source inverter device for variable speed control of an induction motor, a sensor for detecting a DC power supply voltage, a comparator circuit which operates when the DC power supply voltage becomes a predetermined value or less, and an output of the comparator circuit. By including a torque limit circuit for limiting the torque of the induction motor to a certain value or less, when the DC power supply voltage drops to a predetermined value or less, the generated torque of the induction motor than the maximum torque that the inverter device can output. A voltage source inverter device characterized by reduction. 2. A torque limit circuit for limiting the reference value of the torque of the induction motor or the reference value of the torque component of the primary current to a certain value or less by the output of the comparator circuit. 1. The voltage source inverter device according to 1. 3. A first comparator circuit, which operates when the DC power supply voltage drops below a first predetermined value, and a second comparator circuit which operates when the DC power supply voltage rises above a second predetermined value. 2. The voltage type inverter device according to claim 1, wherein a hysteresis is provided at an operating point of the torque limit circuit by making the predetermined value larger than the first predetermined value. 4. When the DC power supply voltage becomes equal to or lower than a predetermined value, a calculation circuit that outputs a calculation result that is proportional to the difference between the predetermined value and the DC power supply voltage or a proportional integral of the difference; A torque limit circuit that limits the reference value of the torque of the induction motor or the torque component of the primary current to a certain value or less is provided, and when the DC power supply voltage decreases to the predetermined value or less, the decrease amount increases as the amount decreases. 2. The voltage type inverter device according to claim 1, wherein the reference value of the torque of the induction motor or the torque component of the primary current is reduced.