KR19990015744A - Inverter operation control method - Google Patents

Abstract

The present invention relates to a control method of the inverter operation, in particular, by converting the deceleration time and frequency of the inverter to prevent overcurrent and overvoltage trip during the inverter operation, it is possible to perform stable inverter operation by preventing the operation stop of the inverter due to the overvoltage or overcurrent. The purpose is to make it work. The present invention for this purpose is to compare the deceleration reference frequency of the inverter and the current operating frequency of the inverter, comparing the DC link reference voltage and the current DC link voltage according to the comparison result, and the comparison result Compensating for the rising value of the DC link voltage according to the step of calculating the deceleration time of the inverter, and the step of decelerating the inverter according to the above calculation results.

Description

Inverter operation control method

The present invention relates to an inverter, and more particularly, to an inverter operation control method for properly controlling the deceleration time during inverter operation.

Inverters are frequently used as speed control devices for motors applied to factory automation systems.

Overcurrent or overvoltage may occur during the operation of the inverter used for industrial purposes.The cause of the overcurrent is the overload of the motor, the short acceleration time, the short time of deceleration (regeneration current during deceleration increase) when the capacity of the inverter is insufficient. There are cases of output short circuit and ground fault, etc. The cause of overvoltage is overvoltage of inverter power supply, short deceleration time.

Therefore, a protection circuit is provided to protect the inverter when an overcurrent or overvoltage occurs during operation of the inverter. The protection circuit detects an overcurrent or an overvoltage and the output current of the inverter is too large or the DC link voltage of the inverter. If too large, the output of the inverter is cut off to electrically protect the inverter by separating the inverter from the motor.

However, if unnecessary protection is performed during operation of the inverter and the operation is stopped, the function of the protection circuit is meaningless.

Therefore, in the case of accelerating and decelerating the speed of the motor by the inverter, it is necessary to properly control the acceleration and deceleration time of the inverter so that the protection circuit is not operated unnecessarily.

In the general inverter, as shown in the circuit diagram of FIG. 1, the inverter 120 providing the driving currents iu, iv, and iw to the motor 110 may include the transistors Q11 and Q12 (Q21, Q22) (Q31, Q32) are connected in series and connected in parallel to the capacitor C1, and the reverse diodes D11, D12, D21, D22, D31, D32 are connected to the transistors Q11, Q12, Q21, Q22, Q31, and Q32. ) In parallel to each other.

Referring to the deceleration operation operation for such a general inverter as follows.

In order to prevent overvoltage during operation of the inverter, the operation command speed and the actual operation frequency of the inverter 120 and the speed of the motor 110 are as shown in the waveform diagram of FIG. The change in speed and DC link voltage DC of the inverter 120 is as shown in the waveform diagram of FIG. 2.

First, when the deceleration is started during inverter operation and the operation command speed of the inverter 120 is changed linearly as shown in FIG. 1, the motor 110 starts braking, but the motor 110 immediately follows the command speed according to the load. It will not rotate and will rotate at a speed greater than the command speed.

At this time, the regenerative energy in which the energy accumulated in the motor 110 is fed back to the inverter 120 is generated, and the direction of the current (iu, iv, iw) by the regenerative energy at that time flows as shown in FIG. The current (iu, iv, iw) causes the level of the DC link voltage DC accumulated in the capacitor C1 to rise.

The amount of regeneration at this time is determined by the difference between the output frequency of the inverter 120 and the rotation frequency of the motor 110.

Therefore, if the level of the DC link voltage rises above the DC link voltage suppression level due to the increase of the regenerative amount during the deceleration during inverter operation, as shown in the waveform diagram of FIG. By stopping, the rise of the DC link voltage of the inverter 120 is suppressed to protect the transistors Q11, Q12, Q21, Q22, Q31 and Q32 of the inverter 120 from overvoltage.

However, since the deceleration operation is stopped when the DC link voltage rises above the predetermined level during the deceleration operation, the actual deceleration time of the inverter becomes longer than the deceleration setting time. Also, when the deceleration time is very short, the overvoltage easily occurs. There is a problem that the operation of the inverter can be stopped due to the operation of the protection circuit.

However, if the input voltage rises during inverter operation and overvoltage occurs and the load of the motor driven by the inverter is large, and the protection circuit is operated during operation, the inverter cannot be stopped. In case of acceleration, if the inverter responds appropriately in consideration of the operation method of the inverter, the inverter can operate normally without the protection circuit.

Accordingly, an object of the present invention is to provide an inverter operation control method invented to perform stable operation of an inverter by converting a deceleration time and a frequency of the inverter so that an overcurrent and an overvoltage trip do not occur during inverter operation. There is this.

That is, the present invention controls the deceleration operation time of the inverter in accordance with the deceleration time of the inverter and the level of the DC link voltage in order to prevent overvoltage and overcurrent trip when the inverter is decelerated, and limits the regenerative current of the inverter during deceleration operation. It is to enable the normal operation of the inverter.

1 is a circuit diagram of a typical inverter.

FIG. 2 is a characteristic waveform diagram illustrating a motor speed and a DC link voltage during deceleration operation in FIG. 1. FIG.

3 is a waveform diagram illustrating a method for preventing overvoltage during deceleration in FIG. 1;

4 is a signal flow diagram for one embodiment of the present invention.

5 is a characteristic waveform diagram of FIG. 4.

6 is a signal flow diagram for another embodiment of the present invention.

7 is a characteristic waveform diagram of FIG. 6.

8 is a signal flow diagram for yet another embodiment of the invention.

Explanation of symbols on the main parts of the drawings

110: motor 120: inverter

Q11, Q12, Q21, Q22, Q31, Q32: Transistor

D11, D12, D21, D22, D31, D32: Switching Diode

The present invention provides an overvoltage protection method using an operating frequency and a DC link voltage of an inverter, a second method, an overcurrent protection method using an operating frequency and an output current of an inverter, in order to prevent tripping of an inverter during deceleration in order to achieve the above object. Third, the present invention provides a method of controlling the overvoltage and overcurrent of the inverter by applying the first and second methods in combination.

That is, the present invention provides a means for comparing the deceleration reference frequency and the current operating frequency of the inverter to achieve the above object, and receives the comparison result and compares the DC link reference voltage of the inverter with the current DC link voltage. In the inverter operation control apparatus having a means for calculating the deceleration time of the inverter by calculating the comparison results, comparing the reference deceleration frequency is greater than or equal to the current operation frequency, wherein the reference deceleration frequency is greater than the current operation frequency Comparing the DC link voltage if the DC link voltage is greater than or equal to the DC link reference voltage, and if the reference deceleration frequency is greater than or equal to the current operating frequency, if the DC link voltage is greater than the DC link reference voltage, the deceleration time is increased by the DC link rise. Adjusting greatly, and wherein the reference deceleration frequency is Setting the deceleration time to the reference deceleration time if the DC link voltage is less than the DC link reference voltage if it is greater than or equal to the operating frequency; and if the reference deceleration frequency is less than the current operating frequency, the DC link voltage is the DC link reference voltage. Comparing the greater than; if the reference deceleration frequency is less than the current operating frequency, if the DC link voltage is greater than the DC link reference voltage, adjusting the deceleration time by a DC link rise; and wherein the reference deceleration frequency is the current operation. If the DC link voltage is less than the DC link reference voltage when the frequency is smaller than the frequency, adjusting the deceleration time as short as possible within the range that the DC voltage does not rise, and wherein the DC link voltage is smaller than the DC link reference voltage and the deceleration pattern is referenced. Deceleration paddle if less than or equal to acceleration / deceleration pattern Performing the step of adjusting to be equal to the reference deceleration to be a pattern, characterized in that to prevent shutdown of the inverter due to the overvoltage.

In addition, the present invention has a means for comparing the output current of the inverter and the output current suppression current of the inverter to achieve the above object, and the inverter operation control device having a means for calculating the deceleration time of the inverter according to the comparison result Comparing whether the output current is greater than the reference current, and if the output current is greater than the reference current, adjusting the deceleration operation time in proportion to the magnitude of the output current of the inverter, wherein the output current is greater than the reference current Setting the deceleration time of the inverter to a deceleration operation time when the output current is smaller than the reference current value and the deceleration pattern is equal to or smaller than the reference acceleration / deceleration pattern. It characterized in that to prevent the operation stop by overcurrent by performing a step.

Hereinafter, the present invention will be described in detail with reference to the drawings.

The inverter for an embodiment of the present invention is configured in the same way as the conventional circuit of FIG.

In general, when the deceleration time is short while the inverter is operating, an overvoltage trip due to the rise of the DC link voltage of the inverter and an overcurrent trip due to the regenerative current of the inverter may occur when the deceleration time is short.

Therefore, if the deceleration time is properly controlled, overvoltage trip and overcurrent trip of the inverter can be prevented.

The present invention performs the same process as in FIGS. 4, 6 and 8 to prevent overvoltage trip and overcurrent trip during deceleration.

One embodiment of the present invention performs the same process as the signal flow of Figure 4 during the deceleration operation to prevent the overvoltage.

In addition, another embodiment of the present invention performs the same process as the signal flow of Figure 6 during the deceleration operation to perform the operation to prevent overcurrent.

Further, another embodiment of the present invention performs the same process as the signal flow of Figure 8 during the deceleration operation to perform the operation to prevent overvoltage and overcurrent.

First, an embodiment of the present invention is an overvoltage protection method using an operating frequency and a DC link voltage of an inverter.

That is, one embodiment of the present invention by adjusting the deceleration slope of the inverter in the direction of suppressing the rise of the DC link voltage of the inverter while monitoring the rise of the DC link voltage of the inverter by the regenerative energy when the motor is decelerated by the inverter It is a method to prevent the overvoltage protection operation of the inverter due to the increase of the DC link voltage of the inverter.

4 is a signal flowchart for an overvoltage protection operation according to an embodiment of the present invention, and FIG. 5 is an operation characteristic diagram showing a DC link voltage and a deceleration pattern of an inverter during an overvoltage protection operation.

Referring to the operation of the embodiment of the present invention as follows.

When the deceleration operation is started at the deceleration starting point as shown in Fig. 5 (b) during the inverter operation, the level of the DC link voltage starts to increase according to the slope (deceleration time) of the deceleration command as shown in Fig. 5 (a).

Here, the section of deceleration initial stage is the section (t2) in FIG.

At this time, the DC link voltage VDC and the DC link reference voltage VDC_ref match.

Therefore, since the current operating frequency (controlled acceleration / deceleration pattern; freal) of the inverter 120 matches the reference acceleration / deceleration pattern Fdec, the actual deceleration time (dec_real) of the inverter is as shown in Equation (1) below. Set to (dec_time).

dec_real = dec_time ------ (1)

Subsequently, in the section t3 of FIG. 5, the DC link voltage VDC of the inverter 120 starts to rise above the DC link reference voltage VDC_ref.

At this time, the current operating frequency freal of the inverter 120 coincides with the reference deceleration frequency Fdec.

Therefore, since the DC link voltage VDC of the inverter 120 is greater than the DC link reference voltage VDC_ref, the actual deceleration time dec_real is determined as shown in Equation 2 below to adjust the deceleration time by the DC link rise. This suppresses the increase in the DC link voltage VDC.

dec_real = dec_real + dec_time {(VDC / VDC_ref)-1} ------ (2)

Subsequently, in the section (t4) of FIG. 5, the DC link voltage VDC rises above the DC link reference voltage VDC_ref, which is a case where the current operating frequency freal is greater than the reference acceleration / deceleration frequency Fdec. .

Accordingly, when the deceleration time of the inverter 120 is larger than the reference deceleration time dec_time, the actual deceleration time dec_real may be determined as in Equation 3 below.

dec_real = dec_real + dec_time {(VDC / VDC_ref)-1} -------- (3)

After that, when the DC link voltage VDC is lowered below the DC link reference voltage VDC_ref, the deceleration time of the inverter 120 increases, so that the entire deceleration time does not become long. Adjust it as short as possible within the range that the link voltage (VDC) does not increase.

Therefore, the actual deceleration time dec_real is determined as shown in Equation (4) below and the rise of the DC link voltage VDC is suppressed by adjusting the deceleration time of the inverter 120 less.

dec_real = dec_real-dec_time {1-(VDC / VDC_ref)} ------- (4)

At this time, since the deceleration slope is adjusted to be shorter than the reference deceleration time dec_time, the operation of the inverter 120 is performed in a direction in which the controlled deceleration pattern freal matches the reference deceleration pattern Fdec.

Thereafter, when the output frequency (freal) of the controlled inverter 120 is equal to or less than the reference deceleration frequency (Fdec), it is operated in the section (t6) of FIG.

Accordingly, the deceleration pattern freal of the inverter 120 is operated to be the same as the reference acceleration / deceleration pattern Fdec.

Therefore, when the operation pattern of the inverter 120 is adjusted in the order of the periods t1 to t6 of FIG. 5, the rise of the DC link voltage VDC is suppressed, and the normal deceleration operation is performed without the occurrence of an overvoltage trip. Can be done.

That is, when the inverter is decelerated, when the DC link voltage VDC rises, the deceleration time dec_real is changed by using one of equations (1) to (4) according to the magnitude of the DC link voltage (VDC). The level of the DC link voltage VDC does not rise above a predetermined level as shown in FIG.

In addition, the present invention provides a method for limiting the regenerative current using the output current of the inverter as another embodiment.

During the inverter deceleration operation, an increase in the DC link voltage (VDC) of the inverter and an increase in the regenerative current of the inverter may also occur according to the deceleration slope of the inverter, and an operation stop of the inverter may also occur due to an overcurrent.

Therefore, another embodiment of the present invention to prevent overcurrent generation by the regenerative current by controlling the deceleration time of the inverter in accordance with the magnitude of the output current of the inverter when the motor is decelerated in order to prevent the operation stop of the inverter The present invention provides a method for preventing an operation stop of the inverter.

FIG. 6 is a signal flowchart for preventing overcurrent according to another embodiment of the present invention, and FIG. 7 is a diagram illustrating an operation characteristic of a current flow and a deceleration pattern of an inverter during an overcurrent prevention operation.

Referring to the operation and effect of the other embodiment of the present invention as follows.

Section (t1) of FIG. 7 is a section in which the inverter starts deceleration during the constant speed operation. When the deceleration operation starts, the output current Io increases in proportion to the regenerative energy of the motor 110 from the moment when the deceleration operation starts. .

At this time, it is necessary to reduce the regenerative energy of the motor 110 that causes the overcurrent protection operation of the inverter 120 so that the circuit does not operate.

Subsequently, when the output current Io of the inverter becomes equal to or greater than the current suppression reference current I_limit by the deceleration operation of the inverter by the section (t2) of FIG. 7, the output current Io of the inverter as shown in Equation (5) below. The output current of the inverter can be reduced by adjusting the deceleration operation time in proportion to the size of.

dec_real = dec_real [1 + {(Io-I_limit) / I_rated}] ----- (5)

Meanwhile, in the section (t2) of FIG. 7, the deceleration time of the inverter may be delayed by adjusting the deceleration pattern of the inverter. At this time, if the output current Io of the inverter decreases below the reference value, the inverter deceleration time dec_real is decelerated. By setting the time, the deceleration time is shortened to compensate for the delay value of the deceleration time due to the current rise during deceleration so that the deceleration time does not become long as a whole.

Accordingly, when the inverter decelerates, an overcurrent protection operation of the inverter due to the regenerative current of the motor 110 is prevented to enable stable operation.

Subsequently, the output current Io becomes equal to or less than the current suppression reference current I_limit when the period becomes t3 in FIG. 7, and when the controlled deceleration pattern is less than or equal to the reference interruption pattern, Adjust the standard accel / decel pattern.

Meanwhile, another embodiment of the present invention uses a method of one embodiment of the present invention and another embodiment as shown in the signal flowchart of FIG. 8 as a method for preventing tripping due to overvoltage and overcurrent of the inverter.

Another embodiment of the present invention performs the same process as the signal flow diagram of FIG. 4 when the overvoltage has occurred, and performs the same process as the signal flow diagram of FIG. 6 as the other embodiments when the overcurrent has occurred. This is to prevent unnecessary operation stop by overvoltage or overcurrent during deceleration operation of inverter.

As described in detail above, the present invention has an effect of preventing the unnecessary operation of the protection circuit by preventing the occurrence of overvoltage or overcurrent by appropriately controlling the deceleration time during the inverter deceleration operation so that stable inverter operation is performed.

Claims (5)

In the case of operating the motor by the inverter, the inverter operation control method for detecting the DC link voltage of the inverter during the deceleration operation of the inverter and calculating the deceleration time of the inverter according to the magnitude of the DC link voltage of the inverter. A first step of comparing the current operating frequency of the inverter; a second step of comparing the DC link reference voltage and the current DC link voltage according to the comparison result; and a rising value of the DC link voltage according to the comparison result. And a fourth step of calculating the deceleration time of the inverter by compensating for the voltage loss, and a fourth step of preventing the inverter from being stopped due to overvoltage by decelerating the inverter according to the calculation result. . In the inverter operation control method, a first step of comparing whether the reference deceleration frequency is greater than or equal to the current operation frequency, and the DC link voltage is a DC link reference voltage when the reference deceleration frequency is greater than or equal to the current operation frequency in the first step. A third step of comparing the greater than and the third step of adjusting the deceleration time by the DC link rise by calculating as shown in Equation (1) below when the DC link voltage is greater than the DC link reference voltage in the second step; If the DC link voltage is less than the DC link reference voltage in the second step, setting the deceleration time as the reference deceleration time as shown in Equation (2) below, and in the first step, the reference deceleration frequency is the current operating frequency. Is less than the fifth step of comparing whether the DC link voltage is greater than the DC link reference voltage; and in the fifth step, the DC link voltage is directly If the link reference voltage is greater than the sixth step of adjusting the deceleration time by the DC link rise as shown in Equation (1) below, and if the DC link voltage is less than the DC link reference voltage in the fifth step, the following equation (3) And a seventh step of adjusting the deceleration time as short as possible within the range in which the DC voltage does not rise. dec_real = dec_real + dec_tim e {(VDC / VDC_ref)-1} ------ (1) dec_real = dec_time ------ (2) dec_real = dec_real + dec_time {(VDC / VDC_ref)-1} -------- (3) The inverter of claim 2, further comprising adjusting the deceleration pattern to be equal to the reference acceleration / deceleration pattern when the DC link voltage is smaller than the DC link reference voltage and the deceleration pattern is equal to or smaller than the reference acceleration / deceleration pattern. Driving control method. In the inverter control method of detecting the output current of the inverter when the inverter is decelerated when the motor is operated by the inverter and calculating the deceleration time of the inverter according to the magnitude of the output current of the inverter, the first control to compare whether the output current is greater than the reference current And if the output current is greater than the reference current, adjusting the deceleration operation time in proportion to the magnitude of the output current of the inverter as in the following equation, and if the output current is smaller than the reference current, And a third step of setting the deceleration operation time and a third step of preventing the inverter from being stopped due to overcurrent by decelerating the inverter according to the calculation result. dec_real = dec_real [1 + {(Io-I_limit) / I_rated}] The method of claim 4, wherein the step of adjusting the deceleration pattern to be equal to the reference acceleration / deceleration pattern when the output current is smaller than the reference current value and the deceleration pattern is equal to or smaller than the reference acceleration / deceleration pattern to prevent operation stop due to overcurrent. Inverter operation control method characterized in that.