JPH09140181A - Inverter - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a tough inverter not tripped easily in which stabilized vector control of motor torque can be carried out even when a motor is in regenerative state and the regenerative energy being returned back to the inverter can be lessened while taking account of the heating of motor and thereby advantageous with regard to heating at the inverter section. SOLUTION: A positive/negative discriminating circuit 9-6 discriminates between powering state and regenerative state based on the polarity of torque current iq. At the time of regeneration, a switch circuit 9-5b is closed to make a switching from a voltage setter 7 providing an AVR level setting for powering to a voltage setter 7-1 providing an AVR level setting for regeneration in order to increase the V/f ratio. Consequently, an induction motor 5 is brought into over exciting state and a part of regenerative energy is absorbed by the induction motor 5 itself.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a vector control type inverter device, and more particularly to an inverter device suitable for controlling an induction motor in a regenerative operation state by driving the induction motor at a variable speed.

[0002]

2. Description of the Related Art If a VVVF (variable voltage variable frequency) inverter device is used, AC power whose voltage and frequency can be arbitrarily changed can be supplied to an electric motor, and as a result, the electric motor is driven at a variable speed at an arbitrary rotational speed. can do.

In particular, at this time, by applying vector control to the control of the inverter, the current of the induction motor can be separated into a torque current and an exciting current and independently controlled.
Similar to the DC motor, since the induction motor can provide highly flexible rotation speed control by controlling the actual torque, the vector control type inverter device has been widely used in recent years.

By the way, when the induction motor is operated at a variable speed by the inverter device as described above, the regenerative operation can be easily obtained as it is. Therefore, in many cases, an inverter device in which the electric motor is controlled at a variable speed is used under the control mode including the regenerative operation according to the type of the driven device. Then, the voltage of the DC power section in the inverter main circuit rises due to the energy regenerated from the electric motor, which inevitably causes the electric motor to be in the over-excited state and the exciting current becomes excessive.

Then, in this case, normally, the exciting current of the electric motor cannot be grasped as much as expected in the vector control, so that the torque current is also affected and the actual torque of the electric motor cannot be accurately controlled. There was a problem of being lost.

Further, considering the over-excited state when the regenerative operation state is continuous, the heat generation in the electric motor is also affected, and there is a problem that heating may occur.

Therefore, an inverter device equipped with an AVR (automatic voltage adjustment) function and provided with constant V / f control has been conventionally used. An example of the inverter device will be described with reference to FIG. INV represents an inverter main circuit, and CON represents a control circuit system. Here, the V / f constant control is control for keeping the ratio of the output voltage V to the output frequency f of the inverter constant, and is a well-known control method in the VVVF inverter device.

In FIG. 3, reference numeral 1 denotes a forward conversion unit (converter unit) which rectifies three-phase AC power of R, S, and T into DC power.
Reference numeral 2 is a DC power unit (capacitor), 3 is an inverse conversion unit (inverter unit) for inversely converting DC power into three-phase AC power, and these form an inverter main circuit INV. Next, 4 is a primary current (output current) detector, which functions to detect the three-phase alternating current output from the inverse conversion unit 3. An induction motor 5 is operated at a variable speed by this inverter device.

In the control circuit CON, 7 is A
A voltage setting device for giving a VR level set value may be a device that uses a memory inside the inverter device and reads and gives the AVR level setting voltage stored therein, or a device that gives an AVR level setting voltage from outside the inverter device. good. The AVR level setting value is the above-mentioned V
It is a value for setting the ratio of / f.

Next, 8 is a DC voltage detecting section for detecting the DC voltage V _PN of the DC power section 2. And 9 is a microcomputer
(Microcomputer), which is composed of a one-chip microcomputer including an A / D converter, a counter, a timer, an input / output port, a RAM, a ROM and the like.

Further, inside the microcomputer 9, an A / D converter 9-1 for fetching the value of the DC voltage detector 8 and a PWM signal generation calculator 9-2 for driving the inverse converter 3 are provided. An A / D converter 9-3 for fetching the current value detected by the primary current detector 4 and a two-phase / three-phase conversion calculation unit 9-4, and a vector control calculation unit 9-5 are provided. Here, ωr * is a frequency command, iq is a torque current, and id is an exciting current.

Incidentally, in FIG. 3, a rotation speed detector (encoder) 6 attached to the induction motor 5 is shown so that the feedback type vector control format can be adopted, but in the following description, The case of so-called sensorless system without using the rotation speed detector 6 has been described. Further, in this case, the forward conversion unit 1 may not be provided and a DC power source may be connected to the PN terminal of the DC power unit 2 for use.

Next, the operation will be described with reference to FIG.
The inverter device of No. 2 uses the torque current iq fetched from the A / D converter 9-3 via the two-phase / three-phase conversion calculation unit 9-4 to determine the slip frequency ωs required at that time.
Then, the vector control calculation unit 9-5 determines that the primary frequency command ω1 commanding the inverse conversion unit 3 is the frequency command ω.
This primary frequency command ω is set to a value corresponding to r *.
1 is calculated, and the data is calculated by the PWM signal generation calculation unit 9-2.
Send to

Therefore, the PWM signal generation / calculation unit 9-2 is
Considering the data of the DC voltage V _PN fetched from the DC voltage detector 8 through the A / D converter 9-1, the ratio of the motor terminal voltage V ₁ / output frequency f is set by the voltage setting unit 7 to AVR. The duty of the switching pulse is calculated to reach the level setting value, and the PW corresponding to it is calculated.
The M signal is output to the inverse conversion unit 3.

Therefore, it has such an AVR function,
/ F Inverter device with constant control provided,
For example, according to the conventional inverter device shown in FIG. 3, V ₁ / f is always constant regardless of the power running regenerative state of the induction motor 5, so that the energy regenerated from the induction motor 5 causes the inverter main circuit to operate. The voltage of the DC power unit rises, and as a result, the actual torque of the electric motor cannot be accurately controlled, or the inverter device is apt to trip overvoltage.

[0016]

The above prior art does not take into consideration the trip resistance (tenacity) during operation of the inverter device and the heat generation in the inverse conversion unit, and the electric motor as the load is in the regenerative operation state. In that case, there is a problem that the trip easily occurs and the temperature of the inverse conversion unit rises.

That is, in the conventional inverter device having the AVR function, no distinction is made between the power running operation and the regenerative operation of the electric motor for control. Therefore, when the electric motor is in the regenerative state, the DC side voltage of the inverse converter is changed. Even when it causes a rise, the terminal voltage of the motor is kept at a constant ratio to the output frequency, so the loss of the motor can be suppressed to a small amount, but excess regenerative energy is returned to the inverter side. Then, it becomes an overvoltage condition.

Therefore, in the prior art, the protection function such as the overvoltage protection of the inverter device is easy to work, and therefore,
It lacks so-called trip resistance and lacks tenacity. Further, as a result, in the conventional technology, the primary current of the motor also becomes excessive, and as described above,
This is also disadvantageous in terms of heat, accompanied by an increase in loss in the inverse conversion section of the inverter device.

An object of the present invention is to stably control the electric motor torque by vector control even when the electric motor is in a regenerative state. At this time, the heat generated by the electric motor is also taken into consideration, and the regeneration to the inverter device is performed. An object of the present invention is to provide a tenacious inverter device that can reduce energy, is advantageous in heat generation of the inverse conversion portion, and is hard to trip.

[0020]

The above object is to provide an inverter main circuit having at least an inverse converter for converting DC power into AC power, and switching control of semiconductor elements in the inverter main circuit to achieve AC output frequency. In an inverter device for driving an electric motor, which includes a control circuit system that performs constant V / f control for maintaining a ratio of frequency voltage to a predetermined value, an AC frequency voltage with respect to the AC output frequency depending on a power running operation state and a regenerative operation state. This is achieved by providing means for changing the ratio.

[0021]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, an inverter device according to the present invention will be described in detail with reference to illustrated embodiments. FIG.
Is an embodiment of the inverter device according to the present invention, and the inverter main circuit INV is the same as the conventional example shown in FIG.
Regarding the control circuit system CON, only the configuration of the vector control operation unit 9-5 in the microcomputer 9 is partly different, and the other configurations are the same as those of the conventional example of FIG. I will focus on the points that exist.

In the embodiment of FIG. 1, first, 7-1 is a voltage setter for giving an AVR level set value at the time of regeneration, and V ₁ / V according to the AVR level set value at the time of power running given by the voltage setter 7. It serves to generate the AVR level setpoint necessary to provide a V ₁ / f ratio that is greater than the f ratio.

Next, reference numeral 9-6 is a positive / negative discriminating circuit of the torque current iq. Since the sign of the torque current iq is positive during power running and negative during regeneration, the positive / negative of the induction motor 5 is judged. It functions to generate a switching signal s when the power running state and the regenerative state are discriminated and the operating state of the induction motor 4 becomes the regenerative operation.

By the way, the vector control calculation unit 9-5 is
As in the conventional example shown in FIG. 3, the primary frequency command ω1 is calculated so that the primary frequency command ω1 commanded to the inverse conversion unit 3 has a value corresponding to the frequency command ωr *, and the data is calculated by the PWM signal. Although it is to be sent to the generation calculation unit 9-2,
In the embodiment of FIG. 1, the part for performing the vector control calculation is shown collectively in the block 9-5a, and the vector control calculation part 9-5 further includes the first switch circuit 9 -5b is provided.

The first switch circuit 9-5b is switch-controlled by a switching signal s generated by the positive / negative discriminating circuit 9-6, and at the time of power running, as shown in the figure, a voltage setting device for setting the AVR level at the time of power running. When the switching signal s is supplied during regeneration, the switching signal s is switched to the output side of the voltage setter 7-1 for AVR level setting during regeneration, contrary to the figure.

Therefore, the first switch circuit 9-5b
Causes the AVR level set value for power running to be taken into the block 9-5a for vector control calculation, but at the time of regeneration, the AVR level set value for regeneration is taken into the block 9-5a. So that
The vector control operation is performed with a V ₁ / f ratio larger than the V ₁ / f ratio according to the AVR level set value during power running.

As described above, the other configuration of the embodiment of FIG. 1 is the same as that of the conventional example of FIG.

Next, the operation of the embodiment shown in FIG. 1 will be described. First, when the induction motor 5 is in the power running mode, the switch circuit 9-5b is switched to the output side of the voltage setting device 7 as shown in FIG. The same operation as that of the conventional example is performed, and vector control with high torque control accuracy can be performed.

Now, assuming that the induction motor 5 is now in the regenerative operation state, the AVR function causes V
Since the induction motor 5 is controlled to be constant at ₁ / f, there is no risk of the induction motor 5 being overexcited as described above, but with the V ₁ / f value as it is, the regeneration generated from the induction motor 5 is returned to the inverter side. There is too much energy, the inverter becomes overvoltage, and it is easy to trip, and the temperature rise in the inverse conversion part becomes a problem.

However, in the embodiment of FIG. 1, if the operating state of the induction motor 5 is changed from the power running operation to the regenerative operation state, the switching signal s is generated from the positive / negative discriminating circuit 9-6. -5b is A at the time of regeneration
It is switched to the output side of the voltage setting device 7-1 for VR level setting, and as a result, the V ₁ / f value is made larger than the value up to that time, and the AVR function is activated by this, so that the induction motor 5 is overloaded. Being excited.

As a result, the induction motor 5 is overexcited even under the same regenerative torque value.
Of the regenerated energy, the amount that the induction motor 5 itself absorbs and becomes a loss is increased, and the regenerated energy returned to the inverter side is reduced accordingly.

Therefore, according to this embodiment, even if the regenerative torque of the induction motor 5 in the regenerative operation state increases and the regenerative energy increases, the increase of the energy amount returned to the inverter side is suppressed. Tripped (overvoltage protection)
It is possible to easily give tenacious and tenacious properties.

Next, FIG. 2 shows another embodiment of the inverter device according to the present invention. In the figure, 9-5c is a regenerative AV.
The R level voltage generating circuit, 9-5d is a second switch circuit, and 9-5e is an adding circuit, and other configurations are the same as those of the embodiment of FIG.

First, the regenerative AVR level voltage generation circuit 9-
Reference numeral 5c serves to take in the primary current I ₁ of the induction motor 5 from the primary current detector 4 via the A / D converter 9-3 and generate a voltage E which increases in proportion to it. , The horizontal axis is the primary current I ₁ and the vertical axis is E
If it takes, it is configured to generate the voltage E according to the characteristic shown in the drawing. .

The second switch circuit 9-5d is opened and closed by a switching signal s generated by the positive / negative discrimination circuit 9-6,
It is opened as shown in the figure during power running, but when the switching signal s is supplied during regeneration, it operates to close, contrary to the figure.

When the second switch circuit 9-5d is closed, the adder circuit 9-5e outputs the voltage E from the regenerative AVR level voltage generation circuit 9-5c supplied through the second switch circuit 9-5d.
It functions to add to the output of the voltage setter 7 and supply it to the block 9-5a.

Therefore, according to the embodiment of FIG. 2, when the induction motor 5 is in the regenerative operation state, the switch circuit 9-5 is used.
d is closed, and the voltage E from the regenerative AVR level voltage generation circuit 9-5c is added to the AVR level setting value at the time of powering output from the voltage setting device 7. As a result, the block 9- AVR level setting value input to 5a is increased to AVR level setting value as required to give it up to V ₁ / f larger V ₁ / f ratio than the ratio of, therefore, even the same regenerative torque value However, since the induction motor 5 is overexcited, the amount of regenerated energy that is absorbed and lost by the induction motor 5 itself increases, and the regenerative energy returned to the inverter side is increased accordingly. Will be reduced.

Therefore, according to the embodiment of FIG. 2 as well, similar to the embodiment of FIG. 1, even if the regenerative torque of the induction motor 5 in the regenerative operation state becomes large, the regenerative energy returned to the inverter side is thereby increased. Decreased and also tripped
(Overvoltage protection) It is possible to easily give tenacious characteristics that are difficult to perform.

In the case of the embodiment of FIG. 2, the voltage E from the regenerative AVR level voltage generating circuit 9-5c is
Since the primary current I ₁ of the induction motor 5 increases substantially in proportion to the primary current V _{1, the} primary voltage V ₁ also increases as the regenerative torque of the induction motor 5 increases, and the induction motor 5 is regenerated by the induction motor 5. Since the amount absorbed by itself and increased as a loss increases, the regenerative energy returned to the inverter side can be made substantially constant.

As a result, even if the regenerative torque of the induction motor 5 increases, the temperature rise of the inverter can be suppressed, but the exciting current of the induction motor 5 becomes excessively large by that much.
This time, heat generation in the induction motor 5 becomes a problem. Therefore, in the embodiment of FIG. 2, the regenerative AVR level voltage generating circuit 9
-5c is configured to have the following characteristics.

That is, in the region until the primary current I ₁ of the induction motor 5 reaches the predetermined first current value, the voltage E is kept at the predetermined lower limit value, and the current I ₁ becomes the first lower limit value. In the region from the current value being exceeded to the predetermined second current value, the voltage E increases almost in proportion to the primary current I ₁ .
In the region exceeding the second current value, the regenerative AVR level voltage generating circuit 9-5c is configured so that the voltage E has a characteristic of keeping a predetermined upper limit value.

At this time, the lower limit value is selected so that the inverter is less likely to trip (heat protection, overvoltage protection), and the upper limit value is set to a value that does not cause a problem in heat generation of the induction motor 5. Be sure to select it.

Therefore, according to the embodiment of FIG. 2, the lower limit and the upper limit are given to the characteristic of the voltage E with respect to the primary current I ₁ of the induction motor 5, so that the induction motor 5 can be provided. Both the inverter and the inverter can cooperate in heat generation, and high reliability can be secured.

In the embodiment of the present invention described above, the so-called sensorless system in which the rotation speed detector (encoder) is not used has been described, but it may be implemented by a feedback type vector control system. In this case, as shown in the drawing, the rotation speed detector 6 attached to the induction motor 5 may be used. In this case, the forward conversion unit 1 is not provided, and the P of the DC power unit 2 is
A DC power supply may be connected to the N terminal for use.

[0045]

According to the present invention, since the exciting current and the torque current can be accurately detected during vector control of the electric motor, the actual torque can be accurately controlled. Also,
At this time, it is possible to reduce the regenerative energy to the inverter device in consideration of the heat generated by the electric motor, so that it is possible to suppress the heat generation of the reverse converter with the increase of the regenerative torque. It is possible to easily provide a rich and tenacious inverter device.

[Brief description of the drawings]

FIG. 1 is a block diagram showing an embodiment of an inverter device according to the present invention.

FIG. 2 is a block diagram showing another embodiment of the inverter device according to the present invention.

FIG. 3 is a block diagram showing a conventional example of an inverter device.

[Explanation of symbols]

INV Inverter main circuit CON Inverter control circuit system 1 Forward conversion part (converter part) 2 DC power part (capacitor part) 3 Inverse conversion part (inverter part) 4 Primary current detector 5 Induction motor 6 Rotation speed detector 7 AVR level Voltage setting device that gives a setting value (during power running) 7-1 AVR level Voltage setting device that gives a setting value (during regeneration) 8 DC voltage detection unit 9 Microcomputer (microcomputer) 9-1 A / D converter 9-2 PWM signal Generation calculation unit 9-3 A / D converter 9-4 Two-phase / 3-phase conversion calculation unit 9-5 Vector control calculation unit 9-5a Block (vector control calculation unit) 9-5b First switch circuit 9-5c Regeneration AVR level voltage generation circuit 9-5d Second switch circuit 9-5e Adder circuit 9-6 Positive / negative determination circuit

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification number Internal reference number FI Technical indication location H02P 7/63 302 H02P 5/408 H (72) Inventor Naoki Takada 7-1, Higashi Narashino, Narashino, Chiba No. 1 Industrial Machinery Division, Hitachi, Ltd. (72) Inventor Kazuhiro Ito 7-1-1 Higashi Narashino, Narashino City, Chiba Prefecture In the Industrial Machinery Division, Hitachi, Ltd. (72) Takamichi Ozone, 7 Higashi Narashino, Narashino, Chiba Prefecture 1-1-1, Hitachi Ltd. Industrial Equipment Division (72) Inventor Masayuki Hirota 7-1-1, Higashi-Narashino, Narashino, Chiba Prefecture Hitachi Keiyo Engineering Co., Ltd.

Claims (3)

[Claims] 1. An inverter main circuit having at least an inverse converter for converting DC power into AC power, and switching control of semiconductor elements in the inverter main circuit to set a ratio of an AC frequency voltage to an AC output frequency to a predetermined value. In an inverter device for driving an electric motor, which comprises a control circuit system for performing a constant V / f control, the means for changing the ratio of the AC frequency voltage to the AC output frequency in accordance with the power running operation state and the regenerative operation state is the above control. An inverter device characterized by being provided in a circuit system. 2. The invention according to claim 1, wherein the control of the inverter main circuit by the control circuit system comprises:
It is a vector control method that separates the motor current into an exciting current component and a torque current component, and is configured to determine the power running operation state and the regenerative operation state based on the polarity of the torque current. Characteristic inverter device. 3. The inverter device according to claim 1, wherein an upper limit value and a lower limit value are given to a ratio of the AC frequency voltage to the AC output frequency in the regenerative operation state.