KR102600841B1 - Apparatus for controlling inverter - Google Patents

Abstract

The present invention includes a first estimator that estimates the rotation speed of the motor, and when the DC link voltage of the inverter that provides the output voltage to the motor is below a certain level, the energy of the DC link capacitor of the inverter and the DC link energy command are used to A first decision unit that determines the slip frequency command, a second decision unit that determines the frequency command by adding the rotation speed of the motor and the slip frequency command, and a third decision unit that determines the slip frequency of the motor using the frequency command. , An inverter control device is provided that includes a fourth decision unit that determines the torque of an electric motor using a slip frequency, and determines the torque so that the time delay is suppressed when the torque of the electric motor is generated using a time delay suppression element.

Description

Inverter control device {APPARATUS FOR CONTROLLING INVERTER}

The present invention relates to an inverter control device.

In general, an inverter is a reverse conversion device that electrically converts direct current (DC) into alternating current (AC). The inverter used in the industry receives power supplied from a commercial power supply, changes the voltage and frequency on its own, and supplies it to the motor. It is defined as a series of devices that control speed to utilize it with high efficiency. This inverter is controlled by a variable voltage variable frequency (VVVF) method, and can vary the voltage and frequency input to the motor according to pulse width modulation (PWM) output.

1 is a configuration diagram of a general inverter.

Generally, the inverter 100 receives three-phase AC power, the rectifier 110 rectifies it, and the smoothing unit 120 smoothes and stores the DC voltage rectified by the rectifier 110. The inverter unit 130 outputs the direct current voltage stored in the DC link capacitor, which is the smoothing unit 120, as an alternating current voltage having a predetermined voltage and frequency according to the PWM control signal, and provides this to the motor.

Usually, the rectifier 110 is composed of a diode, which is a passive element. Since these diodes cannot be controlled on/off and the DC voltage stored in the smoothing section 120 cannot be controlled, the smoothing section 120 The DC link voltage is determined by the AC input voltage. Additionally, since the flow of power is unidirectional from the AC power of the system to the DC voltage of the inverter 100, regenerative operation is not possible. Therefore, in the case of the conventional inverter 100, it is difficult to actively operate according to power and load conditions.

In this way, the inverter 100 using the rectifier 110 composed of a diode cannot maintain the DC terminal voltage stably due to a voltage drop or power outage of the AC power, making continuous operation of the inverter impossible. When driving is difficult, there is a problem that a considerable amount of time is required to restart the inverter 100.

The technical problem to be solved by the present invention is to provide an inverter control device and method that enable continuous inverter operation even when the power supply to the inverter is abnormal.

In addition, the present invention provides an inverter control device and method that can prevent problems in which the DC link voltage fluctuates significantly or low-voltage failure occurs due to a change in the slip frequency and a difference in the speed of change in the torque of the motor. .

In addition, the present invention provides an inverter control device and method that can stabilize the system by preventing the system from diverging even if the proportional control gain increases due to a sudden change in load.

In order to solve the above technical problem, the present invention includes a first estimator that estimates the rotation speed of the electric motor, and a DC link capacitor of the inverter when the DC link voltage of the inverter that provides the output voltage to the motor is below a certain level. A first decision unit that determines the slip frequency command using the energy and the DC link energy command, a second decision unit that determines the frequency command by adding the rotation speed of the motor and the slip frequency command, and a motor control unit that uses the frequency command to determine the slip frequency command. An inverter including a third decision unit that determines the slip frequency, and a fourth decision unit that determines the torque of the electric motor using the slip frequency to determine the torque so that the time delay is suppressed when the torque of the motor is generated using a time delay suppression element. Provides a control device.

In addition, the inverter control device of the present invention further includes a second estimation unit that estimates the slip frequency using the torque of the electric motor, and a gain control unit that applies a damping control gain to the estimated slip frequency and provides it to the second decision unit. do.

Here, the second determination unit determines the frequency command using the slip frequency to which the damping control gain is applied.

Additionally, the transfer function of the DC link energy command to the energy of the DC link capacitor of the inverter is in the form of a second-order low-pass filter.

Additionally, the first estimation unit estimates the rotation speed of the motor using the inverter output voltage, output current, and nominal value of the motor.

In addition, the first estimation unit includes a fifth determination unit that determines the output power using the output voltage and output current of the inverter, a sixth determination unit that determines the load torque using the output power and the output frequency of the inverter, and a load A third estimation unit that estimates the slip frequency using the torque, the inverter's rated slip frequency, and the rated torque, and the motor rotation speed is estimated using the difference between the slip frequency estimated by the third estimation unit and the inverter's output frequency. It includes the fourth presumption department.

Additionally, the first estimation unit further includes a low-pass filter (LPF) that performs low-pass filtering of the slip frequency estimated by the third estimation unit.

In addition, the first decision unit includes a seventh decision unit that determines the required energy from the energy of the DC link capacitor of the inverter and the DC link energy command, an eighth decision unit that determines the power command from the required energy, and the power command and motor It includes a ninth determination unit that determines a torque command using the rotation speed, and a tenth determination unit that determines a slip frequency command using a torque constant from the torque command.

Additionally, the eighth decision unit includes a proportional controller.

Additionally, the torque constant is determined using the rated torque of the motor and the rated slip frequency of the motor.

Additionally, the generator determines a voltage command from the frequency command and provides it to the inverter.

Additionally, the inverter control device of the present invention further includes a control unit that provides an operation flag to the first decision unit when the DC terminal voltage of the inverter is below a predetermined level.

The present invention as described above, when a failure of the input power occurs, performs a regenerative operation to convert the mechanical energy of the motor into the electrical energy of the inverter, thereby maintaining the DC link voltage constant and preventing the inverter from stopping. It has the effect of enabling continuous operation.

In addition, the present invention can compensate for the difference in the slip frequency change and the speed of change in the torque of the motor, preventing problems in which the DC link voltage fluctuates significantly or low-voltage failure occurs due to slow changes in the motor.

In addition, the present invention can stabilize the system by preventing the system from diverging even if the proportional control gain increases due to a sudden change in load by applying the control gain.

1 is a configuration diagram of a general inverter.
Figure 2 is a configuration diagram for explaining a conventional inverter control system.
FIG. 3 is a detailed configuration diagram of the inverter control unit of FIG. 2.
Figure 4 is a graph to explain the relationship between the inverter operating frequency and the inverter output voltage.
Figure 5 is a configuration diagram of an inverter system according to an embodiment of the present invention.
Figure 6 is a detailed configuration diagram of one embodiment of the speed estimation unit of Figure 5.
Figure 7 is a detailed configuration diagram of one embodiment of the slip frequency generator of Figure 5.
FIG. 8 is a first configuration diagram for explaining the control relationship between the electric motor and the slip frequency generator in FIG. 5.
FIG. 9 is a second configuration diagram for explaining the control relationship between the electric motor and the slip frequency generator in FIG. 5.
Figure 10 is an example diagram for explaining an inverter control method according to an embodiment of the present invention.
Figure 11 is an example diagram for explaining the voltage-current relationship according to the control operation of one embodiment of the present invention.

In order to fully understand the configuration and effects of the present invention, preferred embodiments of the present invention will be described with reference to the attached drawings. However, the present invention is not limited to the embodiments disclosed below, but can be implemented in various forms and various changes can be made. However, the description of this embodiment is provided to ensure that the disclosure of the present invention is complete and to fully inform those skilled in the art of the present invention of the scope of the invention. In the attached drawings, components are shown enlarged in size for convenience of explanation, and the proportions of each component may be exaggerated or reduced.

Terms such as 'first' and 'second' may be used to describe various components, but the components should not be limited by the above terms. The above terms may be used only for the purpose of distinguishing one component from another. For example, the 'first component' may be named 'the second component' without departing from the scope of the present invention, and similarly, the 'second component' may also be named 'the first component'. You can. Additionally, singular expressions include plural expressions, unless the context clearly dictates otherwise. Unless otherwise defined, terms used in the embodiments of the present invention may be interpreted as meanings commonly known to those skilled in the art.

Hereinafter, a conventional inverter control system will be described with reference to FIGS. 2 to 4, and an inverter control device and method of an embodiment of the present invention will be described with reference to FIGS. 5 to 10.

FIG. 2 is a configuration diagram for explaining a conventional inverter control system, and FIG. 3 is a detailed configuration diagram of the inverter control unit 200 of FIG. 2. When the user inputs the command frequency ω _ref , the inverter control unit 200 synthesizes the command voltage corresponding to the command frequency and outputs it to the inverter unit 130.

In FIG. 3, the inverter control unit 200 includes a voltage determination unit 210, an integrator 220, a phase determination unit 230, and an output unit 240.

The voltage determination unit 210 can determine the magnitude of the output voltage V _{V /f} from the inverter operating frequency ω _{V /} f. The inverter operating frequency ω _{V /f} starts from 0 and reaches the command frequency ω _ref . Here, the output voltage V _{V /f} represents the voltage until the inverter operating frequency ω _{V /f} reaches the command frequency ω _ref . Figure 4 is a graph to explain the relationship between the inverter operating frequency and the inverter output voltage.

When the inverter 100 is initially started, the operating frequency ω _{V /f} of the inverter increases from 0, so a small voltage is output at the initial start, and as the frequency increases, a voltage proportional to the frequency is output. When the output frequency reaches the command frequency ω _ref , which is the target frequency, the frequency no longer increases and constant speed operation occurs.

That is, the voltage determination unit 210 determines the magnitude of the output voltage V _{V /f} from the inverter operating frequency ω _{V /} f based on the relationship in FIG. 4.

The integrator 220 integrates the operating frequency ω _{V /f} to determine the phase θ _{V /f} of the output voltage, and outputs a three-phase alternating current sine wave through the trigonometric function output unit 230. The output unit 240 multiplies the AC sine wave and the output voltage, and command voltages V _{as_ref} , V _{bs _ref} , and V _{cs _ref} are output.

That is, the inverter control unit 200 synthesizes the three-phase pulse width modulation (PWM) voltages corresponding to the three-phase command voltages and outputs the final command voltage V _{abc _PWM} . In FIG. 2, the inverter unit 130 of the inverter 100 outputs three-phase AC output voltages V _an , V _bn , and V _cn from the DC terminal voltage of the smoothing unit 120 to supply power to the induction motor 400. And the three-phase AC output voltage is determined according to the on/off state of the switch of the inverter unit 130. In the inverter unit 130, each phase consists of two switches connected in series, and each phase operates independently of each other to generate an output voltage. At this time, the output voltages of each phase are controlled to have a phase difference of 120 degrees.

In a conventional inverter control system, the inverter 100, which receives AC power from a three-phase power source 300 as an energy source, converts the AC power into DC power through the rectifier 110. At this time, the rectifier 110 is composed of a diode, and current always conducts in one direction.

The smoothing part 120 is composed of a capacitor or battery, and maintains a constant voltage. The three-phase switch of the inverter unit 130 converts direct current voltage to alternating current voltage, and controls the output voltage of the inverter 100 by turning the switch on and off.

The electric motor 400 functions as a load of the three-phase inverter 100. The inverter control unit 200 determines the switching state of the inverter unit 130 so that the electric motor 400 rotates at the same speed as the command frequency.

In such a conventional inverter control system, the rectifier 110 is composed of a diode, which is a passive element, so it is difficult to control the DC voltage, and when the 3-phase power supply operates abnormally such as an instantaneous power failure or voltage drop, the continuous operation of the inverter 100 is difficult. This is impossible, and there is a problem in that the DC terminal voltage is not controlled to a certain level, causing a failure in the inverter 100. Additionally, in this case, a considerable amount of time is required in some cases to restart the inverter 100, resulting in a large loss.

Therefore, sustainable ride through operation is required regardless of power status.

The present invention is intended to solve the above problems, and is an inverter control device that receives electric energy of the inverter from the kinetic energy of the electric motor through regenerative operation and continuously operates the inverter and electric motor even when the power supply is abnormal. is to provide.

That is, the control device of the present invention maintains the DC power of the inverter by using the kinetic energy of the load inertia during a power outage, and performs regenerative operation through appropriate operation frequency adjustment. Therefore, the larger the inertia and the smaller the load, the more stable the DC power supply can be maintained for a longer period of time.

Figure 5 is a configuration diagram of an inverter system according to an embodiment of the present invention.

As shown in the figure, the inverter control device of one embodiment of the present invention includes a command voltage generator 10 that supplies a command voltage to the inverter 1, and a speed estimation unit 20 that estimates the speed of the electric motor 2. ), a slip frequency generator 30, and a control unit 40.

The control unit 40 may check the DC terminal voltage of the inverter 1 and, if it is below a predetermined level, transmit a flag to turn on the operation of the slip frequency generator 30 to the slip frequency generator 30.

The speed estimation unit 20 can estimate the speed of the rotor of the electric motor 2. FIG. 6 is a detailed configuration diagram of one embodiment of the speed estimation unit 20 of FIG. 5. In the case of general voltage/frequency operation, open loop control is performed, so it is difficult to use speed information through a speed measurement device such as an encoder. Therefore, the speed estimation unit 20 of one embodiment of the present invention determines the rotation speed of the electric motor 2 through the available inverter output voltage and current and the nominal value of the electric motor 2. ) can be estimated.

As shown in the figure, the speed estimation unit 20 of the present invention includes an output power determination unit 21, a load torque determination unit 22, a slip frequency estimation unit 23, a speed determination unit 24, and a low range. It may include a low pass filter (LPF) (25).

The output power determination unit 21 includes the output voltage (V _{V /f} ) of the inverter (1), the command output current corresponding to the torque of the inverter (1), the synchronous coordinate system q-axis current (I _qse ) and the number of poles (Pole). ) can be considered to determine the output power of the inverter (1).

Additionally, the load torque determination unit 22 may determine the load torque using the output power and the output frequency (ω _V/f ) of the inverter 1.

The load torque (T _load ) output through the output power determination unit 21 and the load torque determination unit 22 is expressed in the equation below.

_The slip frequency estimation unit ₂₃ determines the slip _frequency ( ) can be estimated. The slip frequency estimated by the slip frequency estimation unit 23 ( ) is the same as the equation below.

The speed determination unit 24 determines the estimated slip frequency ( ) and the output frequency (ω _{V /f} ) of the inverter (1), using the difference between the speed of the electric motor (1) ( ) can be estimated. The estimated speed of the electric motor (1) is expressed in the equation below.

At this time, the LPF 25 is disposed between the output terminal of the slip frequency estimation unit 23 and the input terminal of the speed determination unit 24 to perform low-pass filtering, and the band to be filtered can be determined considering the stability of the system. will be.

In FIG. 5, when the DC link voltage is below a predetermined level under the control of the control unit 40, the slip frequency generator 30 compares the DC link voltage command (V _dc ^* ) and the actual DC link voltage (V _dc ). The slip frequency command (ω _sl ^* ) to keep the DC link voltage constant can be determined. Usually, the slip frequency (ω _sl ) is the difference between the inverter output frequency (ω _e ) and the motor speed (ω _r ). In one embodiment of the present invention, when the DC link voltage (V _dc ) is below a predetermined level, the slip frequency ( By determining ω _sl ) to be a negative number, the motor speed (ω _r ) can be determined to be greater than the inverter output frequency (ω _e ).

Meanwhile, the actual output of the electric motor 2 does not immediately respond to changes in the slip frequency (ω _sl ), and as the capacity of the electric motor 2 increases, there may be a delay in the response. Accordingly, despite the slip frequency (ω _sl ) that can generate the energy necessary to maintain the DC link voltage (V _dc ), the DC link voltage (V _dc ) fluctuates significantly due to slow changes in the motor (2) or before it stabilizes. Low voltage failure may occur. To solve this problem, the inverter control device of the present invention introduces a time delay suppression element (F(S)). A detailed explanation of this will be provided later.

Figure 7 is a detailed configuration diagram of one embodiment of the slip frequency generator of Figure 5.

As shown in the figure, the slip frequency generator 30 of an embodiment of the present invention includes an energy determination unit 31, a power command determination unit 32, a torque command determination unit 33, and a slip frequency command determination unit. (34) and a frequency command decision unit 35, and regenerative operation can be performed using the slip frequency command (ω _sl ^* ).

The slip frequency command (ω _sl ^* ) can be calculated from the difference between the electric energy (E ^* ) corresponding to the DC link voltage command (V _dc ^* ) and the electric energy (E) corresponding to the actual DC link voltage (V _dc ). there is.

The energy (E) of the DC link capacitor is defined as Equation 4 below, and the energy (E _cap ) of the capacitor required for regenerative operation can be determined by the energy determination unit 31 using Equation 5 below.

Here, in Equation 5, C _dc is the capacitance of the DC link capacitor, and V _dc ^* is the DC link voltage command.

The power (P _cap ) of the DC link capacitor is defined as Equation 6 below.

The power command determination unit 32 may receive the energy (E _cap ) of the capacitor required for regenerative operation and determine the power command (P _cap ^* ). For example, the power command decision unit 32 may be a proportional controller with a proportional control gain of _Kp .

In general, a proportional controller measures the output of the object to be controlled, calculates the error by comparing it with the desired reference value or set value, and uses this error value to calculate the control value required for control. It performs a control action proportional to the size of the error value. However, this is an example, and it will be obvious to those skilled in the art that the power command determination unit 32 may be configured with another controller.

The torque command determination unit 33 determines the speed estimated by the speed estimation unit 20 ( ) can be used to determine the torque command (T _e ^* ).

The relationship between the rated torque (T _rated ), rated speed (ω _rated ), and rated power (P _rated ) of the electric motor (2) is defined as Equation 7 below.

Here, Pole is the number of poles of the electric motor (2).

The torque command determination unit 33 can determine the torque command (T _e ^* ) using Equation 7 above.

The slip frequency command determination unit 34 determines the torque constant of the electric motor 2 ( ) can be used to calculate the slip frequency command (ω _sl ^* ).

Here, the relationship between the rated torque (T _rated ) and the rated slip frequency (ω _{sl -rated} ) is defined as Equation 8 below.

That is, by Equation 8 above, the slip frequency command determination unit 34 can determine the slip frequency command (ω _sl ^* ) using the torque command (T _e ^* ) and the torque constant (K _t ).

In FIG. 5, the frequency command determination unit 35 determines the slip frequency command (ω _sl ^* ) output from the slip frequency generator 30 and the estimated speed of the electric motor 2 output from the speed estimation unit 20 ( ) is added to determine the frequency command (ω _e ^* ). Then, the determined frequency command (ω _e ^* ) is input to the command voltage generator 10.

The command voltage generator 10 is for controlling the output voltage of the inverter 1. From the frequency command (ω _e ^* ), the command voltage generator 10 determines the output voltage and operating frequency of the inverter 1 and combines them in the inverter 1. voltage can be provided.

The command voltage generator 10 performs the same function as the inverter control unit 200 of FIG. 2. The operation of the command voltage generator 10 and the inverter 1 are as described with reference to FIG. 2. Therefore, the detailed description will be omitted.

FIG. 8 is a first configuration diagram for explaining the control relationship between the electric motor 2 and the slip frequency generator 30 in FIG. 5. At this time, the block diagram for the electric motor 2 is approximated through Equation 7 and Equation 8.

Referring to FIG. 8, the electric motor 2 may be configured to include a slip frequency determination unit 51 and a torque determination unit 52.

The slip frequency determination unit 51 determines the slip frequency (ω _sl ) of the electric motor (2) using the frequency command (ω _e ^* ). Here, the slip frequency (ω _sl ) can be calculated by the difference between the frequency command (ω _e ^* ) and the rotation speed (ω _r ) of the electric motor (2).

The torque determination unit 52 determines the torque (T _e ) of the electric motor 2 using the torque constant (K _t ) and the slip frequency (ω _sl ) according to Equation 8, and includes a time delay suppression element ( Using F(s)), the torque (T _e ) is determined so that time delay is suppressed when generating the torque (T _e ) of the electric motor (2).

The transfer function in the control configuration of FIG. 8 is expressed in Equation 9 below.

At this time, K _P is the control gain of the proportional controller, which is the power command decision unit 32, class are the estimated rotational speed and torque constant of the electric motor 2, respectively. At this time is determined from the speed estimation unit 20 in FIG. 5.

Additionally, F(s) can be expressed in the form of a first-order low-pass filter. Here, F(s) can be expressed as Equation 10 below.

Here, ω _mot is the cutoff frequency of F(S).

The above equation 9 is the rotation speed of the electric motor 2 ( ) and torque constant ( If the estimation of ) is accurate, it can be expressed as Equation 11.

That is, the transfer function of the control configuration in FIG. 8 can be expressed in the form of a second-order low-pass filter as in Equation 12 below, and Equation 12 can be transformed into a general form as in Equation 13.

Here, ω _n is the cutoff frequency of the transfer function of the control configuration of FIG. 8.

In Equation 13, the attenuation coefficient (ζ) can be expressed as Equation 14 below.

In this way, the inverter control device according to the embodiment of the present invention compensates for the difference in the change speed of the change in slip frequency (ω _sl ) and the torque (T _e ) of the electric motor (2), resulting in a slow change of the electric motor (2). This can prevent problems in which the DC voltage fluctuates significantly or low-voltage failure occurs.

FIG. 9 is a second configuration diagram for explaining the control relationship between the electric motor 2 and the slip frequency generator 30 in FIG. 5. At this time, the block diagram for the electric motor 2 is approximated through Equation 7 and Equation 8.

Referring to FIG. 9, the electric motor 2 may be configured to further include a slip frequency estimation unit 53 and a gain control unit 54.

The slip frequency estimation unit 53 uses the torque (T _e ) of the electric motor (2) to determine the slip frequency ( ) is estimated.

The gain control unit 54 controls the estimated slip frequency ( ) is applied to the damping control gain (K _D ) and provided to the frequency command decision unit 35.

The frequency command determination unit 35 determines the estimated speed of the electric motor 2 in the slip frequency command (ω _sl ^* ) ( ) is added and the damping control gain (K _D ) is applied to the estimated slip frequency ( ) is subtracted to determine the frequency command (ω _e ^* ). Then, the determined frequency command (ω _e ^* ) is provided to the torque determination unit 52.

Estimated speed of electric motor (2) ( ) is the estimated slip frequency estimated by the slip frequency estimation unit 53 from the frequency command (ω _e ^* ) ( ) is determined by subtracting and provided to the frequency command determination unit 35.

The transfer function in the control configuration of FIG. 9 is expressed in Equation 15 below.

In Equation 15, the attenuation coefficient (ζ) can be expressed as Equation 16 below.

The attenuation coefficient (ζ) in Equation 16 is calculated by adding the damping control gain (K _D ) to the attenuation coefficient (ζ) in Equation 14, so even if the proportional control gain (K _p ) increases due to a sudden change in load, etc. The system can be stabilized by preventing the system from diverging.

The control unit 40 of one embodiment of the present invention continuously checks the DC link voltage, and provides a flag to turn on the slip frequency generator 30 when the DC link voltage falls below a predetermined level, as shown in Figures 8 and 8. As shown in Figure 9, the kinetic energy of the electric motor 2 can be controlled to back up.

FIG. 10 is an example diagram for explaining an inverter control method according to an embodiment of the present invention, and FIG. 11 is an example diagram for explaining the voltage-current relationship according to a control operation according to an embodiment of the present invention.

As shown in the figure, in the control method of one embodiment of the present invention, the control unit 40 continuously checks the DC end voltage of the inverter 1 (S90), and determines that the DC end voltage of the inverter 1 is set to a predetermined level. You can check whether it is below the level (S91). If there is a fault in the input power, the DC link voltage decreases due to the influence of the input power.

The level of the DC link voltage for the control unit 40 of the present invention to transmit an operation flag to the slip frequency generator 30 may be determined by the driver's settings.

When the control unit 40 determines that the DC terminal voltage of the inverter 1 is below a predetermined level, the control unit 40 may transmit an operation flag that turns on the operation of the slip frequency generator 30. In FIG. 10, while the input power is normal and the DC link voltage is maintained at a certain level, when the DC link voltage falls below a predetermined reference level (10A), the control unit 40 operates the slip frequency generator 30. An operation flag that turns on can be transmitted to the slip frequency generator 30. At this time, the reference level (10A) may be, for example, 200V when using a commercial power of 220V.

Even in this case, the speed estimation unit 20 may continue to operate to estimate the rotational speed of the rotor of the electric motor 2.

Afterwards, when the speed estimation unit 20 estimates the speed of the electric motor 2 (S93), the slip frequency generator 30 can generate a slip frequency command using the energy of the DC link voltage.

Afterwards, the slip frequency is added to the estimated speed to generate a frequency command (S95), and the command voltage generator 10 generates the corresponding output voltage of the inverter and provides it to the inverter 1 (S96). .

Referring to FIG. 11, when the DC link voltage is less than the reference level (10A), the slip frequency command is added to the estimated speed of the motor 2 to generate a frequency command. At this time, the inverter output frequency is lower than the motor speed. It operates at speed, and the size of the output voltage can be determined from the relationship between voltage and frequency. That is, the output frequency of the inverter 1 is output at a lower speed than the speed of the electric motor 2, and the DC terminal voltage of the inverter 1 can be maintained at a constant level.

Afterwards, when the DC link voltage is restored to a predetermined level (T _recovery ) (S97), the control unit 40 transmits an operation flag to turn off the slip frequency generator 30 to the sleep frequency generator 30, It will be possible to control it to ensure normal operation (S98). At this time, referring to FIG. 10, the control unit 40 may control the inverter output frequency to rise from the inverter output frequency when power is restored to recover the speed before the failure.

As such, according to the present invention, when a failure of the input power occurs, a regenerative operation is performed to convert the mechanical energy of the motor into the electrical energy of the inverter, thereby maintaining the DC terminal voltage constant, preventing the inverter from stopping. Continuous operation is possible without

Although embodiments according to the present invention have been described above, they are merely illustrative, and those skilled in the art will understand that various modifications and equivalent scope of embodiments are possible therefrom. Therefore, the true technical protection scope of the present invention should be determined by the following claims.

1: Inverter 2: Motor
10: Command voltage generation unit 20: Speed estimation unit
30: slip frequency generator 40: control unit

Claims (12)

A first estimation unit that estimates the rotation speed of the electric motor;
a second estimation unit that estimates the slip frequency of the electric motor using the torque of the electric motor;
When the DC link voltage of the inverter that provides the output voltage to the motor is below a certain level, a first decision unit that determines a slip frequency command using the energy of the DC link capacitor of the inverter and the DC link energy command;
a second determination unit that determines a frequency command by adding the rotational speed of the electric motor and the slip frequency command;
a third determination unit that determines a slip frequency of the electric motor using the frequency command;
a fourth determination unit that determines the torque of the electric motor using the slip frequency, and determines the torque of the electric motor so that time delay is suppressed when generating torque of the electric motor using a time delay suppression element; and
A gain control unit that applies a damping control gain to the estimated slip frequency and provides it to the second decision unit.
Inverter control device including.
delete According to paragraph 1,
The second decision section
An inverter control device that determines the frequency command using the slip frequency to which the damping control gain is applied.
According to paragraph 3,
An inverter control device in which the transfer function of the DC link energy command to the energy of the DC link capacitor of the inverter is in the form of a second-order low-pass filter.
According to paragraph 1,
The first estimation unit is,
An inverter control device that estimates the rotation speed of the motor using the inverter output voltage, output current, and nominal value of the motor.
According to paragraph 1,
The first estimation unit is,
a fifth decision unit that determines output power using the output voltage and output current of the inverter;
a sixth determination unit that determines load torque using the output power and the output frequency of the inverter;
a third estimation unit that estimates a slip frequency using the load torque, the rated slip frequency, and the rated torque of the inverter; and
Including a fourth estimation unit that estimates the rotation speed of the electric motor using the difference between the slip frequency estimated by the third estimation unit and the output frequency of the inverter.
Inverter control device.
According to clause 6,
The first estimation unit is,
A low-pass filter (LPF) that performs low-pass filtering of the slip frequency estimated by the third estimation unit.
An inverter control device further comprising:
According to paragraph 1,
The first decision section,
a seventh decision unit that determines required energy from the energy of the DC link capacitor of the inverter and the DC link energy command;
an eighth decision unit that determines a power command from the required energy;
a ninth determination unit that determines a torque command using the power command and the rotation speed of the electric motor; and
A 10th determination unit that determines the slip frequency command using the torque constant from the torque command.
Inverter control device including.
According to clause 8,
The eighth decision unit includes a proportional controller
Inverter control device.
According to clause 8,
An inverter control device wherein the torque constant is determined using the rated torque of the electric motor and the rated slip frequency of the electric motor.
According to paragraph 1,
A command voltage generator that determines a voltage command from the frequency command and provides it to the inverter.
An inverter control device further comprising:
According to paragraph 1,
A control unit that provides an operation flag to the first decision unit when the DC terminal voltage of the inverter is below a predetermined level.
An inverter control device further comprising:

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