KR20220131678A - Apparatus for controlling inverter - Google Patents

Abstract

The present invention provides an inverter control apparatus, which comprises: a first estimation unit for estimating the rotational speed of a motor; a first determination unit for determining a slip frequency command by using the energy of a DC link capacitor of an inverter and a DC link energy command when a DC link voltage of the inverter providing an output voltage to the motor is below a predetermined level; a second determination unit for determining a frequency command by adding the rotational speed of the motor and the slip frequency command; a third determination unit for determining the slip frequency of the motor using the frequency command; and a fourth determination unit for determining the torque of the motor using the slip frequency, wherein the fourth determination unit determines the torque so that a time delay is suppressed when the motor torque is generated using a time delay suppression element. According to the present invention, continuous operation is possible without the inverter being stopped.

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). Inverters used in the industry receive power supplied from commercial power, change voltage and frequency by itself, and supply the motor to the motor. It is defined as a set of devices that control the speed to be used with high efficiency. Such an inverter is controlled by a variable voltage variable frequency (VVVF) method, and the voltage and frequency input to the motor may be varied according to a pulse width modulation (PWM) output.

1 is a block diagram of a general inverter.

In general, the inverter 100 receives three-phase AC power, the rectifying unit 110 rectifies it, and the smoothing unit 120 smoothes and stores the DC voltage rectified by the rectifying unit 110 . The inverter unit 130 outputs an AC voltage having a predetermined voltage and frequency according to the PWM control signal from the DC voltage stored in the DC link capacitor, which is the smoothing unit 120 , to the motor.

Usually, the rectifying unit 110 is composed of a diode, which is a passive element. Such a diode cannot be controlled on/off, and it is impossible to control the DC link voltage stored in the smoothing unit 120, so that the The DC link voltage is determined by the AC input voltage. In addition, since the flow of power is made in one direction of the DC link voltage of the inverter 100 from the AC power of the system, the regenerative operation is impossible. Therefore, in the case of the conventional inverter 100, it is difficult to actively operate according to power and load conditions.

As such, the inverter 100 using the rectifier 110 composed of a diode cannot stably maintain the DC link voltage due to a voltage drop or a power outage of the AC power, so that the continuous operation of the inverter is impossible, and the continuous operation of the inverter is not possible. When the operation is difficult, there is a problem that a considerable amount of time is required for restarting the inverter 100 .

The technical problem to be solved by the present invention is to provide an inverter control device and a method for enabling continuous inverter operation even when the power supply of the inverter is not normal.

Another object of the present invention is to provide an inverter control device and method capable of preventing a problem in which a DC link voltage fluctuates greatly or a low voltage failure occurs due to a change in slip frequency and a change in torque of an electric motor. .

Another object of the present invention is to provide an inverter control apparatus and method capable of stabilizing the system by preventing the system from dissipating even when a proportional control gain is increased due to a sudden change in load or the like.

In order to solve the above technical problem, the present invention provides a first estimator for estimating the rotational speed of a motor, and a DC link capacitor of the inverter when the DC link voltage of the inverter providing the output voltage to the motor is below a certain level. A first determination unit that determines the slip frequency command by using the energy of the DC link energy and a DC link energy command, a second determination unit that determines the frequency command by adding the rotation speed of the motor and the slip frequency command, and the frequency command of the motor An inverter comprising a third determining unit for determining the slip frequency, and a fourth determining unit for determining the torque of the motor using the slip frequency, but determining the torque so that the time delay is suppressed when generating the torque of the motor using the delay suppression element control is provided.

In addition, the inverter control apparatus of the present invention further includes a second estimator for estimating the slip frequency using the torque of the electric motor, and a gain control unit for applying a damping control gain to the estimated slip frequency and providing the damping control gain to the second determination unit. do.

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

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

In addition, the first estimator estimates the rotation speed of the motor by using the inverter output voltage, the output current, and the nominal value of the motor.

In addition, the first estimator includes a fifth determining unit that determines output power using the output voltage and output current of the inverter, and a sixth determining unit that determines the load torque using the output power and the output frequency of the inverter; A third estimator for estimating the slip frequency using torque, the rated slip frequency of the inverter, and the rated torque, and the third estimator for estimating the rotation speed of the motor using the difference between the slip frequency and the output frequency of the inverter including a fourth estimator that

In addition, the first estimator further includes a low-pass filter (LPF) that performs low-pass filtering of the slip frequency estimated by the third estimator.

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

In addition, the eighth determination unit includes a proportional controller.

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

In addition, the generator determines the voltage command from the frequency command and provides it to the inverter.

In addition, the inverter control apparatus of the present invention further includes a control unit that provides an operation flag to the first determining unit when the DC link voltage of the inverter is below a predetermined level.

According to the present invention as described above, when a failure of the input power source occurs, a regenerative operation for converting the mechanical energy of the motor into the electrical energy of the inverter is performed, thereby maintaining the DC link voltage constant, without stopping the inverter It has the effect of enabling continuous operation.

In addition, the present invention compensates for the difference between the change in slip frequency and the change speed of the torque of the motor, thereby preventing the problem that the DC link voltage is greatly shaken or a low voltage failure occurs due to the slow change of the motor.

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

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

In order to fully understand the configuration and effect of the present invention, preferred embodiments of the present invention will be described with reference to the accompanying drawings. However, the present invention is not limited to the embodiments disclosed below, and may be embodied in various forms and various modifications may be made. However, the description of the present embodiment is provided so that the disclosure of the present invention is complete, and to fully inform those of ordinary skill in the art to which the present invention pertains the scope of the invention. In the accompanying drawings, components are enlarged in size than actual for convenience of description, and ratios of each component may be exaggerated or reduced.

Terms such as 'first' and 'second' may be used to describe various elements, but the elements should not be limited by the above terms. The above term may be used only for the purpose of distinguishing one component from another. For example, without departing from the scope of the present invention, a 'first component' may be termed a 'second component', and similarly, a 'second component' may also be termed a 'first component'. can Also, the singular expression includes the plural expression 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 of ordinary skill in the art.

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

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 may 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 . 4 is a graph for explaining 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-up, and a voltage having a magnitude proportional to the frequency is output as the frequency increases. When the output frequency reaches the target frequency, the command frequency ω _ref , the frequency does not increase any more and constant speed operation is performed.

That is, the voltage determining unit 210 determines the magnitude of the output voltage V _{V /f} from the inverter operating frequency ω _{V /f} from the relationship of 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 AC sine wave by the trigonometric function output unit 230 . The AC sine wave and the output voltage are multiplied by the output unit 240 to output the command voltages V _{as_ref} , V _{bs _ref} , and V _{cs _ref} .

That is, the inverter control unit 200 outputs a final command voltage V _{abc _PWM} by synthesizing three-phase pulse width modulation (PWM) voltages corresponding to the three-phase command voltages. In FIG. 2 , the inverter unit 130 of the inverter 100 supplies power to the induction motor 400 by outputting three-phase AC output voltages V _an , V _bn , and V _cn from the DC link voltage of the smoothing unit 120 . 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 is configured by connecting two switches 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 from each other.

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

The smoothing unit 120 is composed of a capacitor or a battery, and maintains a constant voltage. The three-phase switch of the inverter unit 130 converts a DC voltage into an AC voltage, and controls the output voltage of the inverter 100 by turning the switch on/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, when the rectifier 110 is composed of a diode, which is a passive element, it is difficult to control the DC link voltage, and when the three-phase power supply performs abnormal operations such as instantaneous power failure or voltage drop, continuous operation of the inverter 100 This is impossible, and there is a problem in that the DC link voltage is not controlled to a certain extent, causing a failure in the inverter 100 . In addition, in this case, a considerable amount of time is required for restarting the inverter 100 in some cases, so there is a problem in that a large loss occurs.

Therefore, a sustainable ride through operation is required regardless of the power supply state.

In order to solve the above problems, the present invention is an inverter control device that receives the electric energy of the inverter from the kinetic energy of the motor through regenerative operation and continuously operates the inverter and the motor even when the power supply is not normal. is to provide

That is, the control device of the present invention maintains the DC link power of the inverter by using the kinetic energy of the load inertia during a power failure, and performs a regenerative operation by adjusting an appropriate operating frequency. Therefore, as the inertia is large and the load is small, the DC link power supply can be stably maintained for a long time.

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

As shown in the figure, the inverter control device according to an embodiment of the present invention includes a command voltage generator 10 for supplying a command voltage to the inverter 1 and a speed estimator 20 for estimating the speed of the electric motor 2 . ), a sleep frequency generator 30 and a controller 40 may be included.

The control unit 40 may check the DC link voltage of the inverter 1 , and when it is below a predetermined level, transmit a flag for turning on the operation of the sleep frequency generator 30 to the sleep frequency generator 30 .

)를 추정할 수 있다. The speed estimation unit 20 may estimate the speed of the rotor of the electric motor (2). 6 is a detailed configuration diagram of an embodiment of the speed estimation unit 20 of FIG. 5 . In the case of general voltage/frequency operation, since open loop control is performed, it is difficult to use speed information through a speed measuring device such as an encoder. Therefore, the speed estimating unit 20 of an embodiment of the present invention is the rotational speed (

) can be estimated.

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

The output power determining unit 21 includes the output voltage (V _{V /f} ) of the inverter 1 , the 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 taken into consideration to determine the output power of the inverter (1).

Also, the load torque determining 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 determining unit 21 and the load torque determining unit 22 is as follows.

)를 추정할 수 있다. 슬립주파수 추정부(24)에 의해 추정되는 슬립주파수(

)는 아래 수학식과 같다.The slip frequency estimation unit 23 uses the load torque (T _load ) and the rated slip frequency (ω _{sl_rated} ) and the rated torque (T _rated ) of the inverter 1 to the slip frequency (

) can be estimated. The slip frequency estimated by the slip frequency estimation unit 24 (

) is the same as the formula below.

)와 인버터(1)의 출력주파수(ω_{V /f})의 차를 이용하여 전동기(1)의 속도(

)를 추정할 수 있다. 추정된 전동기(1)의 속도는 아래 수학식과 같다. The speed determination unit 24 is the estimated slip frequency (

) and the difference between the output frequency (ω _{V /f} ) of the inverter (1), the speed of the motor (1) (

) can be estimated. The estimated speed of the electric motor 1 is as follows.

At this time, the LPF 25 may be disposed between the output terminal of the slip frequency estimator 23 and the input terminal of the speed determiner 24 to perform low-pass filtering, and the filtered band may be determined in consideration of the stability of the system. will be.

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

On the other hand, the output of the actual motor 2 does not immediately respond to a change in the slip frequency ω _sl , and as the capacity of the motor 2 increases, the response may be delayed. Accordingly, despite the slip frequency (ω _sl ) that can generate the energy required to maintain the DC link voltage (V _dc ), due to the slow change of the motor (2), the DC link voltage (V _dc ) is greatly shaken or stabilized before Undervoltage faults may occur. In order to solve this problem, the inverter control device of the present invention introduces a delay suppression element F(S). A detailed description of this will be given later.

7 is a detailed configuration diagram of an embodiment of the slip frequency generator of FIG. 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 the frequency command determiner 35 may be included, and the regenerative operation may be performed using the slip frequency command ω _sl ^* .

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

The energy E of the DC link capacitor is defined as in Equation 4 below, and the energy E _cap of the capacitor required for the regenerative operation may be determined by the energy determination unit 31 by 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 in Equation 6 below.

The power command determiner 32 may receive the energy (E _cap ) of the capacitor required for the regenerative operation, and determine the power command (P _cap ^* ). For example, the power command determiner 32 may be a proportional controller having a proportional control gain K _p .

In general, a proportional controller measures the output of an object to be controlled, compares it with a desired reference value or a set value, calculates an error, and uses this error value to calculate a control value required for control. It is to perform a control action proportional to the magnitude of the error value. However, this is an example, and it will be apparent to those of ordinary skill in the art that the power command determination unit 32 may be composed of another controller.

)를 이용하여 토크지령(T_e ^*)을 결정할 수 있다.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 ), the rated speed (ω _rated ) and the rated power (P _rated ) of the motor 2 is defined as in Equation 7 below.

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

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

)를 이용하여 슬립주파수 지령(ω_sl ^*)을 계산할 수 있다. The slip frequency command determination unit 34 is a torque constant (

) can be used to calculate the slip frequency reference (ω _sl ^* ).

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

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

)를 더하여 주파수지령(ω_e ^*)을 결정한다. 그리고, 결정된 주파수지령(ω_e ^*)은 지령전압 발생부(10)로 입력된다. In FIG. 5 , the frequency command determination unit 35 includes the slip frequency command (ω _sl ^* ) output from the slip frequency generation unit 30 and the estimated speed (

) to determine the frequency command (ω _e ^* ). And, 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, and from the frequency command ω _e ^* , determines the output voltage and the operating frequency of the inverter 1 and synthesizes them in the inverter 1 . voltage can be provided.

The command voltage generator 10 performs the same function as the inverter controller 200 of FIG. 2 , and the operation of the command voltage generator 10 and the operation of the inverter 1 are as described with reference to FIG. 2 . Therefore, a detailed description thereof 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 of the electric motor 2 is approximated through Equations (7) and (8).

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

The slip frequency determining 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 ) may be calculated by the difference between the frequency command (ω _e ^* ) and the rotational speed (ω _r ) of the electric motor (2).

The torque determining unit 52, by the above equation (8), using the torque constant (K _t ) and the slip frequency (ω _sl ) to determine the torque (T _e ) of the electric motor (2), the delay suppression element ( The torque (T _e ) is determined so that the time delay is suppressed when generating the torque (T _e ) of the electric motor (2) using F(s)).

A transfer function in the control configuration of FIG. 8 is as shown in Equation 9 below.

과

는 각각 추정된 전동기(2)의 회전속도와 토크상수이다. 이때

는 도 5의 속도추정부(20)로부터 결정된다. At this time, K _P is the control gain of the proportional controller, which is the power command determination unit 32,

class

are the rotational speed and torque constant of the motor 2 estimated respectively. At this time

is determined from the speed estimator 20 of FIG. 5 .

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

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

)와 토크상수(

)의 추정이 정확하면, 수학식 11과 같이 나타낼 수 있다.Equation 9 is the rotational speed of the electric motor 2 (

) and the torque constant (

) is accurate, it can be expressed as Equation (11).

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

Here, ω _n is the cut-off 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.

As such, the inverter control device according to the embodiment of the present invention compensates for the difference in the change speed of the change in the slip frequency (ω _sl ) and the change in the torque (T _e ) of the electric motor (2), so that the slow change of the electric motor (2) Due to this, it is possible to prevent a problem in which the DC link voltage fluctuates greatly or a low voltage failure occurs.

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

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

)를 추정한다.The slip frequency estimating unit 53 uses the torque (T _e ) of the electric motor (2) to determine the slip frequency (

) is estimated.

)에 댐핑 제어이득(K_D)을 적용하여 주파수지령 결정부(35)에 제공한다.The gain control unit 54 controls the estimated slip frequency (

) by applying a damping control gain (K _D ) to the frequency command determination unit 35 .

)를 더하고 댐핑 제어이득(K_D)을 적용된 추정 슬립주파수(

)를 차감하여 주파수지령(ω_e ^*)을 결정한다. 그리고, 결정된 주파수지령(ω_e ^*)은 토크 결정부(52)에 제공된다.The frequency command determination unit 35 receives the slip frequency command (ω _sl ^* ) as the estimated speed (

) and applied the damping control gain (K _D ) to the estimated slip frequency (

) to determine the frequency command (ω _e ^* ). Then, the determined frequency command ω _e ^* is provided to the torque determination unit 52 .

)는 주파수지령(ω_e ^*)에서 슬립 주파수 추정부(53)가 추정한 추정 슬립주파수(

)를 차감하여 결정되어 주파수지령 결정부(35)에 제공된다.Estimated speed of electric motor (2) (

) is the estimated slip frequency ( ) estimated by the slip frequency estimator 53 from the frequency command (ω _e ^* )

) is determined by subtracting it and provided to the frequency command determination unit 35 .

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

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

The attenuation coefficient ζ of Equation 16 is obtained by adding the damping control gain K _D to the attenuation coefficient ζ of Equation 14, so that 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 divergence.

The control unit 40 according to an embodiment of the present invention continuously checks the DC link voltage, and provides a flag that turns on the sleep frequency generator 30 when the DC link voltage is less than or equal to a predetermined level, as shown in FIG. 8 and As shown in FIG. 9 , it is possible to control the kinetic energy of the electric motor 2 to be backed up.

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

As shown in the figure, in the control method of an embodiment of the present invention, the control unit 40 continuously checks the DC link voltage of the inverter 1 ( S90 ), and the DC link voltage of the inverter 1 is set to a predetermined value ( S90 ). It can be checked whether the level is below the level (S91). If there is a failure in the input power, the DC link voltage is reduced due to the influence of the input power.

The level of the DC link voltage for the controller 40 of the present invention to transmit the operation flag to the sleep frequency generator 30 may be determined by the driver's setting.

When the control unit 40 determines that the DC link voltage of the inverter 1 is below a predetermined level, the control unit 40 may transmit an operation flag for turning on the operation of the sleep frequency generator 30 . In FIG. 10 , when the input power is normal and the DC link voltage is below a predetermined reference level 10A while the DC link voltage is maintained at a constant level, the control unit 40 controls the operation of the sleep frequency generator 30 . An operation flag for turning on may be transmitted to the sleep frequency generator 30 . In this case, the reference level 10A may be, for example, 200V when a commercial power of 220V is used.

Even in this case, the speed estimation unit 20 may be estimating the rotational speed of the rotor of the electric motor 2 by continuously performing the operation.

Thereafter, when the speed estimator 20 estimates the speed of the motor 2 ( S93 ), the slip frequency generator 30 may generate a slip frequency command using the energy of the DC link voltage.

Thereafter, a frequency command may be generated by adding the slip frequency to the estimated speed (S95), and the command voltage generator 10 may generate an output voltage of the inverter corresponding thereto and provide it to the inverter 1 (S96). .

Referring to FIG. 11 , when the DC link voltage is less than the reference level 10A, the frequency command is generated by adding the slip frequency command to the estimated speed of the motor 2 , in which case the inverter output frequency is lower than the motor speed. It operates at speed, and the magnitude of the output voltage can be determined from the relationship between voltage and frequency. That is, the output frequency of the inverter 1 may be output at a speed lower than the speed of the electric motor 2 , and the DC link voltage of the inverter 1 may be maintained at a constant level.

Then, when the DC link voltage is restored to a predetermined level (T _recovery ) (S97), the controller 40 transmits an operation flag for turning off the sleep frequency generator 30 to the sleep frequency generator 30, It will be possible to control the operation to be normal (S98). At this time, referring to FIG. 10 , the controller 40 may control the inverter output frequency to rise from the inverter output frequency during recovery to recover the speed before the failure.

As described above, according to the present invention, when a failure of the input power source occurs, a regenerative operation for converting the mechanical energy of the motor into the electric energy of the inverter is performed, thereby maintaining the DC link voltage constant, and the inverter is stopped Continuous operation is possible without

Although the embodiments according to the present invention have been described above, these are merely exemplary, and those of ordinary skill in the art will understand that various modifications and equivalent ranges of embodiments are possible therefrom. Accordingly, the true technical protection scope of the present invention should be defined by the following claims.

1: Inverter 2: Motor
10: command voltage generation unit 20: speed estimation unit
30: sleep frequency generation unit 40: control unit

Claims (12)

a first estimator for estimating the rotational speed of the electric motor;
a first determination unit for determining a sleep frequency command using energy of the DC link capacitor of the inverter and a DC link energy command when the DC link voltage of the inverter providing the output voltage to the motor is below a certain level;
a second determination unit for determining a frequency command by adding the rotation speed of the motor and the slip frequency command;
a third determining unit for determining a slip frequency of the electric motor using the frequency command; and
A fourth determining unit that determines the torque of the electric motor using the slip frequency, and determines the torque of the electric motor so that the delay is suppressed when the torque of the electric motor is generated using a delay suppression element
Inverter control device comprising a.
According to claim 1,
a second estimator for estimating 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 determiner
Inverter control device further comprising a.
3. The method of claim 2,
the generating unit
An inverter control device for determining the frequency command by using the slip frequency to which the damping control gain is applied.
4. The method of claim 3,
A transfer function of the DC link energy command with respect to the energy of the DC link capacitor of the inverter is in the form of a second-order low-pass filter.
According to claim 1,
The first estimation unit,
An inverter control device for estimating the rotation speed of the motor by using the inverter output voltage, the output current, and the nominal value of the motor.
According to claim 1,
The first estimation unit,
a fifth determination unit for determining output power using the output voltage and output current of the inverter;
a sixth determination unit for determining a load torque using the output power and an output frequency of the inverter;
a third estimator for estimating a slip frequency using the load torque, the rated slip frequency and the rated torque of the inverter; and
and a fourth estimator for estimating the rotational speed of the motor using the difference between the slip frequency estimated by the third estimator and the output frequency of the inverter
inverter control unit.
7. The method of claim 6,
The first estimation unit,
A low-pass filter (LPF) that performs low-pass filtering of the slip frequency estimated by the third estimator
Inverter control device further comprising a.
According to claim 1,
The first determination unit,
a seventh determination unit for determining the required energy from the energy of the DC link capacitor of the inverter and the DC link energy command;
an eighth determination unit for determining a power command from the required energy;
a ninth determination unit for determining a torque command using the power command and the rotation speed of the electric motor; and
A tenth determination unit that determines a slip frequency command by using a torque constant from the torque command
Inverter control device comprising a.
9. The method of claim 8,
The eighth determination unit, including a proportional controller
inverter control unit.
9. The method of claim 8,
The torque constant is an inverter control device that is determined using the rated torque of the motor and the rated slip frequency of the motor.
According to claim 1,
The generating unit,
An inverter control device for determining a voltage command from the frequency command and providing it to the inverter.
According to claim 1,
When the DC link voltage of the inverter is below a predetermined level, a control unit providing an operation flag to the first determining unit
Inverter control device further comprising a.

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