KR20210126917A - Power transforming apparatus for driving motor and method for controlling same - Google Patents

Abstract

The present invention relates to a power conversion device, and more particularly, to a power conversion device for driving a motor having a three-phase input power source and a control method thereof. The power conversion device for driving a motor comprises: a rectifying unit which rectifies an AC input from an AC power source; an inverter which includes a plurality of switching elements and converts a DC voltage output from the rectifying unit into an AC voltage to drive the motor; a current sensing unit which detects an output current flowing between the inverter and the motor; and a control unit which controls the inverter so that a voltage output from the inverter and input to the motor is smaller than an output voltage of the rectifying unit.

Description

Power transforming apparatus for driving motor and controlling method thereof

The present invention relates to a power conversion device, and more particularly, to a power conversion device for driving a motor having a three-phase input power source and a method for controlling the same.

In general, an inverter, which is a power conversion device that generates AC power from DC power, is used to drive and control the motor, and a three-phase inverter may be used to drive and control the motor.

The three-phase inverter includes three pairs of switching elements capable of operating independently of each other, and may control an output voltage, an output line voltage, a load voltage of a load, and the like of the inverter according to a switching state of each switching element.

In order to drive such a power converter, it is required to store and smooth a DC link voltage, and a current terminal (DC-link) capacitor plays this role.

However, these capacitors have a relatively short lifespan, and a decrease in capacitance due to deterioration of the capacitor causes a decrease in filter performance, and consequently a decrease in control performance and secondary failure of the system due to phase current imbalance and DC voltage pulsation increase. can cause Moreover, as such a capacitor, an electrolytic capacitor with a large size is usually used, which increases the size of a product having such a power conversion device.

Accordingly, attempts have been made to eliminate such electrolytic capacitors. Prior art document 1 shows an inverter system that does not include such an electrolytic capacitor.

However, the inverter system disclosed in this prior art document 1 requires an additional auxiliary diode circuit for generating a gate signal for on/off of the system-side active element switch. In addition, since the prior art document 1 does not require fast dynamic characteristics as an inverter system for driving an elevator, there is no problem even using a low DC link voltage. However, this prior art document 1 cannot be used for driving a servo motor requiring fast dynamic characteristics.

Moreover, a torque control mode exists in a servo motor, and torque precision is an important factor in such torque control. However, according to the inverter system disclosed in Prior Art Document 1, there is a problem that a steady-state error may occur in the current when the voltage is insufficient, and thus a steady-state error may occur during torque control.

Therefore, it is required to develop a power conversion device that does not use an electrolytic capacitor and does not have such a problem.

1. Publication No. 10-2009-0043913 (published on May 7, 2009)

An object of the technical problem to be solved is to provide a power conversion device for driving a motor that does not include an electrolytic capacitor and a method for controlling the same.

Another object of the present invention is to provide a power conversion device for driving a motor and a method for controlling the same, in which dynamic characteristics are not deteriorated due to a voltage shortage phenomenon even with a rapid torque command change.

Another object of the present invention is to provide a power conversion device and a method for controlling the same in which a steady-state error does not occur during torque control because a voltage shortage phenomenon does not occur.

According to the present invention, it is possible to provide a power conversion device capable of reducing the product size by removing a DC link (DC-link) smoothing electrolytic capacitor from the power conversion device for a servo motor.

Accordingly, the failure rate of the power conversion device may be reduced, and thus, advantages such as increase in system reliability, reduction in size of the power conversion device, circuit simplification through removal of the initial charging circuit, and improvement of input current harmonic characteristics may be realized.

In addition, as described above, by designing a servo motor and a control process to prevent a voltage shortage caused by the removal of the electrolytic capacitor of the power conversion device, the peak value of the voltage between the terminals of the motor at the maximum load at the base speed is the line of the input voltage. It can be designed to be less than 86% of the voltage peak.

Accordingly, it is possible to secure fast dynamic characteristics without insufficient voltage at the base speed of the motor and the maximum load condition.

As a specific example, the present invention provides a power conversion device for driving a motor, comprising: a rectifying unit for rectifying an AC input from an AC power source; an inverter including a plurality of switching elements to convert the DC voltage output from the rectifier into an AC voltage to drive the motor; a current sensing unit detecting an output current flowing between the inverter and the motor; and a controller configured to control the inverter so that a voltage output from the inverter and input to the motor is smaller than an output voltage of the rectifier.

Also, the controller may control the inverter so that the voltage input to the motor is equal to or less than a value obtained by subtracting a voltage change of the output voltage of the rectifier from the output voltage of the rectifier.

Also, the controller may control the inverter such that a voltage input to the motor is equal to or less than a maximum value of a pure DC component of the rectifier.

Also, the controller may control the inverter such that a voltage input to the motor is equal to or less than a minimum value of a change in an output voltage of the rectifier.

배 이하일 수 있다.In addition, the voltage input to the motor is the output voltage of the rectifier

It can be less than double.

In addition, a snubber capacitor disposed between the rectifier and the inverter to suppress a switching voltage variation of the DC voltage may be further included.

In addition, the snubber capacitor may be directly connected to the rectifying unit.

Also, the snubber capacitor may be directly connected between the inverters.

The control unit may include: a speed control unit configured to generate a target current based on a target speed and the speed of the motor sensed through the current sensing unit; and a current controller to generate a target voltage based on the target current, but to make the target voltage less than an output voltage of the rectifier.

The control unit may further include a driving signal generating unit configured to generate a driving signal based on the generated target voltage and the position of the motor sensed by the current sensing unit.

As another specific example, the present invention provides a method for controlling a power conversion device including an inverter for driving a motor by converting a DC voltage output from a rectifier into an AC voltage including a plurality of switching elements, a target speed and current generating a target current based on the speed of the motor sensed through a sensing unit; generating a target voltage based on the target current so that the target voltage is smaller than an output voltage of the rectifier; and generating a driving signal based on the generated target voltage and the sensed position of the motor.

In addition, the target voltage may be generated such that the voltage input to the motor is equal to or less than a value obtained by subtracting a voltage change of the output voltage of the rectifier from the output voltage of the rectifier.

Also, the target voltage may be generated such that a voltage input to the motor is equal to or less than a maximum value of a pure DC component of the rectifier.

In addition, the target voltage may be generated such that a voltage input to the motor is equal to or less than a minimum value of an output voltage variation of the rectifier.

According to the present invention, there are the following effects.

First, according to the present invention, in the power conversion device not including the electrolytic capacitor, the dynamic characteristics may not be deteriorated due to the voltage shortage phenomenon even with a rapid torque command change due to the optimal control design accordingly.

In addition, since a voltage shortage phenomenon does not occur, a steady-state error may not occur during torque control.

Accordingly, the failure rate of the power conversion device may be reduced, and thus system reliability may be increased, and the size of the power conversion device may be reduced.

In addition, since the initial charging circuit can be removed, the circuit can be simplified, and the input current harmonic characteristics can be improved.

1 is a block diagram illustrating a power conversion device according to an embodiment of the present invention.
2 is a circuit diagram illustrating a power conversion device according to an embodiment of the present invention.
3 is a signal diagram illustrating a system voltage signal.
4 is a signal diagram illustrating a DC link voltage signal passing through a rectifier of a power conversion device according to an embodiment of the present invention.
5 is a signal diagram for explaining a control voltage of a power conversion device according to an embodiment of the present invention.
6 is a block diagram showing details of a control unit according to an embodiment of the present invention.
7 is a signal diagram illustrating torque control characteristics in a steady state in a power conversion device without a general electrolytic capacitor.
8 is a signal diagram illustrating torque control characteristics in a steady state in a power conversion device according to an embodiment of the present invention.
9 is a signal diagram showing an example of a position control characteristic in a power conversion device without a general electrolytic capacitor.
10 is a signal diagram showing an example of the position control characteristics in the power conversion device according to an embodiment of the present invention.
11 is a signal diagram showing another example of position control characteristics in a power conversion device without a general electrolytic capacitor.
12 is a signal diagram illustrating another example of a position control characteristic in a power conversion device according to an embodiment of the present invention.

Hereinafter, the embodiments disclosed in the present specification will be described in detail with reference to the accompanying drawings, but the same or similar components are assigned the same reference numerals regardless of reference numerals, and overlapping descriptions thereof will be omitted. The suffixes "module" and "part" for the components used in the following description are given or mixed in consideration of only the ease of writing the specification, and do not have a meaning or role distinct from each other by themselves. In addition, in describing the embodiments disclosed in the present specification, if it is determined that detailed descriptions of related known technologies may obscure the gist of the embodiments disclosed in the present specification, the detailed description thereof will be omitted. In addition, it should be noted that the accompanying drawings are only for easy understanding of the embodiments disclosed in the present specification, and should not be construed as limiting the technical spirit disclosed herein by the accompanying drawings.

Furthermore, although each drawing is described for convenience of description, it is also within the scope of the present invention that those skilled in the art implement other embodiments by combining at least two or more drawings.

It is also understood that when an element, such as a layer, region, or module, is referred to as being “on” another element, it may be directly on the other element or intervening elements may exist in between. There will be.

1 is a block diagram illustrating a power conversion apparatus according to an embodiment of the present invention, and FIG. 2 is a circuit diagram illustrating a power conversion apparatus according to an embodiment of the present invention.

1 and 2, the power conversion device 100 is a rectifier 110 for rectifying the three-phase system power 10, an inverter that outputs a three-phase alternating current using the DC voltage rectified by the rectifier 110 ( 140 ), an inverter controller 150 for controlling the inverter 140 , and a DC-link capacitor C1 positioned between the rectifier 110 and the inverter 140 .

The inverter 140 outputs a three-phase alternating current, and this output current is supplied to the motor 200 . Here, the motor 200 may be a compressor motor driving the air conditioner. Hereinafter, the motor 200 may be a servo motor for driving an industrial or commercial robot, and the power conversion device 100 will be described as a motor driving device for driving such a servo motor as an example. That is, the power conversion device 100 may be the same component as the motor driving device.

However, the motor 200 is not limited to a servo motor, and may be used in various application products using a frequency-variable AC voltage, for example, AC motors such as air conditioners, refrigerators, washing machines, electric vehicles, automobiles, and vacuum cleaners.

On the other hand, the motor driving device 100, the DC-link voltage (Vp) for detecting the DC terminal voltage detection unit (F), the input voltage detection unit (E), the input current detection unit (D), the output current detection unit ( G) may be further included.

The motor driving device 100 may receive AC power from the three-phase system 10 , convert power, and supply the converted power to the motor 200 . Hereinafter, the three-phase system 10 may have the same meaning as the three-phase AC power source. Accordingly, the three-phase system and the AC power supply will be described using the same reference numerals.

The rectifier 110 receives and rectifies the AC power supply 10 , and outputs the rectified power to the converter 120 side. To this end, the rectifier 110 may use a full-wave rectification circuit using a bridge diode.

The input voltage sensing unit E may detect an input voltage Vs from the input AC power supply 10 . For example, it may be located in front of the rectifying unit 110 .

The input voltage sensing unit E may include a resistance element, an OP AMP, and the like for voltage detection. The detected input voltage Vs is a discrete signal in the form of a pulse, and may be applied to the controller 150 to generate the inverter control signal Si.

Next, the input current sensing unit D may detect the input current Is from the input AC power supply 10 . Specifically, it may be located in front of the rectifying unit 110 .

The input current sensing unit D may include a current sensor, a current transformer (CT), a shunt resistor, and the like for current detection. The detected input voltage Is is a discrete signal in the form of a pulse and may be applied to the controller 150 to generate the inverter control signal Si.

The DC voltage sensing unit F detects the pulsating voltage Vp of the DC-link capacitor C1. For this power detection, a resistive element, an OP AMP, etc. may be used. The detected voltage Vp of the DC-link capacitor C1 is a discrete signal in the form of a pulse, and may be applied to the inverter control unit 150, and the DC voltage Vp of the DC-link capacitor C1 ) based on the inverter control signal Si may be generated.

Here, the DC-link capacitor C1 is located between the rectifying unit 110 and the inverter 140, and may be a snubber capacitor for suppressing a switching voltage variation of the DC voltage rectified by the rectifying unit 110. have. Hereinafter, the DC-link capacitor C1 will be described using the same reference numerals as the snubber capacitor.

The snubber capacitor C1 may be directly connected between the rectifier 110 and the inverter 140 . That is, the snubber capacitor C1 may be directly connected to the rectifier 110 when viewed from the input side of the power and may be directly connected to the inverter 140 from the output side of the power.

That is, the snubber capacitor C1 is configured to prevent the switching element from being destroyed due to a voltage increase across the switching element due to the switching of the switching elements included in the inverter 140, and has a capacity of several uF or less. can be Such a capacitor C1 can be distinguished from an electrolytic capacitor for a general DC-link.

Typically, the power conversion device includes an electrolytic capacitor in which the DC-link capacitor is a smoothing capacitor and a film capacitor in which the snubber capacitor is used.

Here, in the present invention, the DC-link capacitor (C1) may be a film capacitor for the snubber capacitor described above. That is, a separate large-capacity electrolytic capacitor may not be included. Hereinafter, the DC-link capacitor C1 may refer to a film capacitor rather than an electrolytic capacitor as the snubber capacitor C1. This will be described in detail later.

On the other hand, the inverter 140 is provided with a plurality of inverter switching elements (Qa, Qb, Qc, Qa', Qb', Qc'), the DC power supply (Vp) rectified by the rectifier 110 at a predetermined frequency. It can be converted into three-phase AC power and output to the three-phase servo motor 200 .

Specifically, the inverter 140 has a pair of upper switching elements Qa, Qb, Qc and lower switching elements Qa', Qb', Qc' connected in series with each other, and a total of three pairs of upper and lower switching The elements may be connected in parallel with each other.

The switching elements Qa, Qb, Qc, Qa', Qb', and Qc' of the inverter 140 may use a power transistor, for example, an insulated gate bipolar mode transistor (IGBT). Available.

The controller 150 may output the inverter control signal Si to the inverter 140 to control the switching operation of the inverter 140 . The inverter control signal Si is a pulse width modulation (PWM) switching control signal, based on the output current io flowing through the motor 200 and the DC-link voltage Vp across the DC-link capacitor C1. can be generated and output. At this time, the output current io may be detected from the output current sensing unit G, and the DC-link voltage Vp may be detected from the DC-link voltage sensing unit F.

The controller 150 includes a gate driver (not shown) that transmits a PWM signal to the gate terminals of the switching elements Qa, Qb, Qc, Qa', Qb', Qc' included in the inverter 140 . It may include a configuration. Here, the gate driver may be included in the inverter 140 . That is, the inverter 140 may use an integrated power module (IPM) including a gate driver.

The output current sensing unit G may detect the output current io flowing between the inverter 140 and the motor 200 . That is, the output current sensing unit G detects a current flowing through the motor 200 . The output current sensing unit G may detect all of the output currents ia, ib, and ic of each phase, or may detect the output currents of the two phases using three-phase balance.

The output current sensing unit G may be positioned between the inverter 140 and the motor 200 , and a current transformer (CT), a shunt resistor, or the like may be used to detect the current.

As such, the output current sensing unit (or current sensing unit) G may detect an output current flowing between the inverter 140 and the motor 200 . In this case, the controller 150 may control the inverter 140 so that the voltage output from the inverter 140 and input to the motor 200 is smaller than the output voltage of the rectifier 110 .

3 is a signal diagram illustrating a grid voltage signal, and FIG. 4 is a signal diagram illustrating a DC link voltage signal passing through a rectifier of a power conversion device according to an embodiment of the present invention. 5 is a signal diagram for explaining a control voltage of a power conversion device according to an embodiment of the present invention.

Referring to FIG. 3 , the system voltage 10 represents the line voltage. It can be seen that the system voltage 10 is generated by repeating a three-phase AC voltage signal with a predetermined phase difference.

When this line voltage passes through the rectifier 110 , it may be in a full-wave rectified state as shown in FIG. 4 . That is, the three-phase system voltage may be full-wave rectified and changed into a DC voltage signal as shown in FIG. 4 . In this case, the maximum output voltage of the rectifier 110 corresponds to Vp, and a certain pulsation (ripple; voltage fluctuation) may occur.

Referring to FIG. 5 , the maximum value of the pure DC component excluding the pulsation (voltage fluctuation) among the output voltages of the rectifier 110 may be defined _{as V R . The maximum value (V R} ) of the pure DC component of the rectifier 110 is a value obtained by subtracting the voltage fluctuation of the maximum output voltage (Vp) of the rectifier 110 from the maximum output voltage (Vp) of the rectifier 110 (V _R ) may correspond to Also, at this time, the minimum value of the pulsation (ripple) may be defined _{as r min .} Meanwhile, V _R may correspond to the minimum value of the output voltage fluctuation of the rectifier 110 .

According to one embodiment of the present invention, the control unit 150, the voltage input to the motor 200 is a voltage change of the maximum output voltage (Vp) of the rectifier 110 from the maximum output voltage (Vp) of the rectifier 110 The inverter 140 may be controlled to be less than or equal to the value V _{R obtained by subtracting V R .}

That is, the controller 150 may control the inverter 140 so that the voltage input to the motor 200 is equal to or less than _{the maximum value V R of the pure DC component of the rectifier 110 .}

In other words, the controller 150 may control the inverter 140 so that the voltage input to the motor 200 is equal to or less than _{the minimum value r min of the output voltage variation of the rectifier 110 .}

배에 해당할 수 있다. 따라서, 제어부(150)는, 모터(200)에 입력되는 전압이 정류부(110)의 최대 출력 전압(Vp)의

배가 되도록 인버터(140)를 제어할 수 있다. _{The maximum value (V R} ) of the pure DC component of the rectifier 110 or the minimum value (r _min ) of the output voltage fluctuation of the rectifier 110 is the maximum output voltage Vp of the rectifier 110 .

It could be a ship. Accordingly, the controller 150 determines that the voltage input to the motor 200 is equal to the maximum output voltage Vp of the rectifier 110 .

The inverter 140 may be controlled to double.

The power conversion device control process of the controller 150 may be implemented by a semiconductor IC such as a micro computer.

That is, the control process performed by the control unit 150 includes: generating a target current based on the target speed and the speed of the motor 200 sensed through the current sensing unit G; generating a target voltage based on the target current, but making the target voltage smaller than the output voltage of the rectifier 110, and generating a driving signal based on the generated target voltage and the detected position of the motor 200 It may be configured including the step of

6 is a block diagram showing details of a control unit according to an embodiment of the present invention.

Referring to FIG. 6 , the detailed configuration of the control unit 150 described above is shown, and the inverter 140 and the motor 200 are expressed together here.

For example, the controller 150 may mainly use a motor control method of a proportional integral control method.

That is, the control unit 150 of the proportional integral control method includes a speed control unit 152 , a current control unit 154 , a driving signal (PWM) generation unit 155 , a current sensing unit 156 , and a position estimation unit 157 . may include.

Here, the current sensing unit 156 may be the same as the current sensing unit G described above.

The speed and position of the motor 200 may be implemented in a sensorless manner through the current sensing unit 156 . _{That is, the position estimator 157 may estimate the rotor position θ M} of the motor using the current sensed by the current sensing unit 156 , and the speed and position of the motor 200 are determined using this. can be detected. _{The rotor position θ M} estimated by the position estimator 157 may be fed back through the low-pass filter 158 .

That is, when the speed and position of the motor 200 are sensed in a sensorless manner that does not include a sensor, the speed and position may be estimated using the current sensed using the current sensing unit 156 .

The speed controller 152 may generate a target current based on the target speed (speed command value: W _r ^* _{) and the speed W M} of the motor 200 sensed through the current sensor 156 . The current sensed by the current sensing unit 156 may be fed back to the current controlling unit 154 .

A torque control unit 153 is provided between the speed control unit 152 and the current control unit 154 to separate the current command value (I ^* ) into a d-axis current command value (I _d ^* ) and a q-axis current command value (I _q ^* ). can do.

In addition, the current control unit 154 may generate a target voltage (V _dq ^* : voltage command ^{value) based on the target current (I *: current command value) output from the speed control unit 152 .}

The drive signal generator 155 generates _{a drive signal (PWM signal) based on the target voltage V dq} ^* generated by the current controller 154 and the position of the motor 200 sensed by the current detector 156 . can do.

A driving voltage may be generated in the inverter 140 by the driving signal (PWM signal), and the motor 200 may be driven by the driving voltage.

In some cases, a frequency variable unit (not shown) may be positioned at the front end of the speed controller 152 to vary the switching frequency according to the efficiency of the inverter for each speed.

As such, the control unit 150 determines the target voltage based on the target current and the speed control unit 152 for generating a target current based on the target speed and the speed of the motor 200 sensed through the current sensing unit 156 . However, it may include a current controller 154 for generating the target voltage to be less than the output voltage of the rectifier 110 .

That is, as described above, the current controller 154 of the controller 150 controls the voltage input to the motor 200 from the maximum output voltage Vp of the rectifier 110 to the maximum output voltage Vp of the rectifier 110 . A target voltage for controlling the inverter 140 may be generated to be less than or _{equal to a value (V R} ) obtained by subtracting a voltage change of .

As described above, the current controller 154 controls the inverter 140 so that the voltage input to the motor 200 is less than or equal to _{the maximum value (V R ) of the pure DC component of the rectifier 110 to generate the target voltage.} Also, a target voltage for controlling the inverter 140 may be generated such that the voltage input to the motor 200 is _{equal to or less than the minimum value r min of the output voltage variation of the rectifier 110 .}

배가 되도록 인버터(140)를 제어하기 위한 목표 전압을 생성할 수 있다. 최대 출력 전압(Vp)의

배는 정류부(110)의 출력 선간 전압 피크의 대략 86%에 해당할 수 있다.In other words, the current controller 154 determines that the voltage input to the motor 200 is the maximum output voltage Vp of the rectifier 110 .

A target voltage for controlling the inverter 140 to be doubled may be generated. of the maximum output voltage (Vp)

The double may correspond to approximately 86% of the output line voltage peak of the rectifier 110 .

In addition, the control unit further includes a driving signal (PWM) generating unit 155 for generating a PWM driving signal based on the position of the motor 200 sensed by the generated target voltage and current sensing unit 156, can be configured.

Hereinafter, details of driving the motor 200 using the controller 150 of the proportional integral control method and the circuit shown in FIG. 2 will be described.

7 is a signal diagram illustrating torque control characteristics in a steady state in a power conversion device without a general electrolytic capacitor.

In FIG. 7( a ), V _dc represents the magnitude of the DC link (DC-link) voltage, and 0.5V _dc , -0.5V _dc represents the pole voltage zero potential reference DC link voltage limit. Also, v ^* _an , v ^* _bn , v ^* _cn Each represents the three-phase, for example, a-phase, b-phase, c-phase pole voltage reference.

Referring to FIG. 7( a ), when driving without an electrolytic capacitor in a general power conversion device, the voltage command is limited by the DC link voltage, and thus a desired voltage command may not be synthesized.

FIG. 7( b ) shows the current command and current in the case of driving without an electrolytic capacitor in a general power conversion device.

In FIG. 7(b) , the superscript '*' means a command, and the subscripts 'd' and 'q' indicate the d and q axes in the synchronous coordinate system, respectively.

Referring to FIG. 7(b) , it can be seen that, due to the influence of the voltage limit shown and described in FIG. 7(a), the current command cannot be followed, and a harmonic current component of the synchronous speed is generated.

For this reason, the torque of the motor cannot be controlled to a desired value, and a steady-state error may occur during torque control. Also, the harmonic components of the current can create harmonic pulsations in the torque. Such torque harmonics can cause velocity pulsations in the steady state.

8 is a signal diagram illustrating torque control characteristics in a steady state in a power conversion device according to an embodiment of the present invention.

In general, the magnetic flux linkage of the magnet is defined as in Equation 1 below.

Here, a means phase a. Thus, _a λ _{_PM} defines a phase flux linkage of the magnets. R _stator is the radius of the stator, l _axis is the axial length of the motor, N _a is the winding function expressing the winding shape of the winding, and B _rad is the magnetic flux density in the radial direction.

In order to reduce the magnetic flux linkage of these magnets, these variables can be modified and designed.

_{For example, suppose that N a} is changed by changing the number of turns of the winding. In this case, if the number of turns _{is defined as N t} , the magnetic flux linkage (λ _PM ) and the inductance (L _ds , L _qs ) have the same relationship as in Equation 2 below.

Using this relationship, the current control characteristics in the case where the design satisfies the above-mentioned conditions are as shown in FIG. 8 .

As shown in FIG. 8 , it can be seen that the voltage commands are not applied to the voltage limit, and the current also follows the commands well. Therefore, a steady-state error of torque may not occur, and current/torque/speed pulsation due to insufficient voltage may not occur.

9 is a signal diagram showing an example of a position control characteristic in a power conversion device without a general electrolytic capacitor.

In order to directly see the phenomenon caused by the lack of voltage described above with reference to FIG. 7 , a case in which the speed is limited during position control without controlling the weak magnetic flux is shown.

Referring to FIG. 9 , it can be seen that the speed limit is applied as the position increases, and the current is not controlled due to the voltage limit.

The steady-state error of current control occurs as a steady-state error of torque. Therefore, it can be confirmed that the speed control unit increases the torque command to maintain the speed.

Due to this action, the position control may not be significantly affected (compare with FIG. 10 below).

On the other hand, the responsiveness of speed control can be confirmed in area A. Referring to FIG. 9 , the time taken to reach the speed command is 8.6 ms.

In addition, the steady-state characteristics during speed control can be confirmed in the B area. In region B, it can be seen that the current pulsation of the harmonic component of the synchronous speed creates a pulsation of torque and pulsation of speed.

10 is a signal diagram showing an example of the position control characteristics in the power conversion device according to an embodiment of the present invention.

10 shows a result of performing a simulation by applying the proposed method under the same conditions as the method described above.

Referring to FIG. 10 , it can be seen that the current follows the command value without a steady-state error because the speed limit is applied as the position increases, but the voltage is not insufficient.

In this case, the responsiveness of the speed control can be confirmed in the A area. Referring to FIG. 10 , the time taken to reach the speed command is 7.3 ms. That is, it can be confirmed that the time taken to reach the speed command is increased by comparing the results of the general case described above.

In addition, the steady-state characteristic in speed control can be confirmed in the B area. It can be seen that there is no current pulsation due to lack of voltage in region B, and therefore no torque/speed pulsation.

11 is a signal diagram showing another example of position control characteristics in a power conversion device without a general electrolytic capacitor.

The case of FIG. 11 is the same as the conditions described in FIG. 9, and the speed limit is further increased to show the fastest possible position control dynamic characteristics under the limited condition.

At this time, the maximum speed that can be operated by the general control process under the condition that the speed pulsation is allowed is at the level of 5100r/min, and the time to reach 95% of the command is 109.211ms.

12 is a signal diagram illustrating another example of a position control characteristic in a power conversion device according to an embodiment of the present invention.

The case of FIG. 12 is the same as the conditions described with reference to FIG. 10, and by increasing the speed limit further, the fastest position control dynamic characteristics can be seen under the limited conditions.

In this case, under the condition that the speed pulsation is allowed, the maximum operating speed by the control process proposed in the present invention is 5900r/min. In addition, the time when 95% of the command is reached is 94.8 ms.

Therefore, according to an embodiment of the present invention, it can be seen that the dynamic characteristics are improved compared to the general control process of the conventional power conversion device without an electrolytic capacitor.

11 and 12 are not generally considered to be in a normal control state. However, through these results, it can be seen that the control process of the power conversion device proposed in the embodiment of the present invention can secure faster dynamic characteristics at the DC link voltage than in the conventional general case.

As described above, according to the present invention, in a power conversion device not including an electrolytic capacitor, a decrease in dynamic characteristics due to a voltage shortage may not occur even with a rapid torque command change due to an optimal control design accordingly.

In addition, since a voltage shortage phenomenon does not occur, a steady-state error may not occur during torque control.

Accordingly, the failure rate of the power conversion device may be reduced, and thus system reliability may be increased, and the size of the power conversion device may be reduced.

In addition, since the initial charging circuit can be removed, the circuit can be simplified, and the input current harmonic characteristics can be improved.

The above description is merely illustrative of the technical spirit of the present invention, and various modifications and variations will be possible without departing from the essential characteristics of the present invention by those skilled in the art to which the present invention pertains.

Therefore, the embodiments disclosed in the present invention are not intended to limit the technical spirit of the present invention, but to explain, and the scope of the technical spirit of the present invention is not limited by these embodiments.

The protection scope of the present invention should be construed by the following claims, and all technical ideas within the equivalent range should be construed as being included in the scope of the present invention.

10: three-phase grid 100: power converter
110: rectifier 140: inverter
150: control unit 200: motor

Claims (15)

A power conversion device for driving a motor, comprising:
a rectifying unit for rectifying the AC input from the AC power source;
an inverter including a plurality of switching elements to convert the DC voltage output from the rectifier into an AC voltage to drive the motor;
a current sensing unit detecting an output current flowing between the inverter and the motor; and
and a controller configured to control the inverter so that a voltage output from the inverter and input to the motor is smaller than an output voltage of the rectifier. The power for driving a motor according to claim 1, wherein the controller controls the inverter so that the voltage input to the motor is equal to or less than a value obtained by subtracting a voltage change of the output voltage of the rectifier from the output voltage of the rectifier. conversion device. The power conversion device for driving a motor according to claim 1, wherein the control unit controls the inverter such that a voltage input to the motor is equal to or less than a maximum value of a pure DC component of the rectifier. The power conversion device for driving a motor according to claim 1, wherein the control unit controls the inverter such that a voltage input to the motor is equal to or less than a minimum value of an output voltage variation of the rectifier. 5. The method of claim 4, wherein the voltage input to the motor is the output voltage of the rectifier.

Power conversion device for motor driving, characterized in that less than twice. The power conversion device for driving a motor according to claim 1, further comprising a snubber capacitor positioned between the rectifier and the inverter to suppress a switching voltage variation of the DC voltage. The power conversion device for driving a motor according to claim 6, wherein the snubber capacitor is directly connected to the rectifier. The power conversion device for driving a motor according to claim 7, wherein the snubber capacitor is directly connected between the inverters. According to claim 1, wherein the control unit,
a speed control unit configured to generate a target current based on a target speed and the speed of the motor sensed through the current sensing unit; and
and a current controller configured to generate a target voltage based on the target current, and to make the target voltage smaller than an output voltage of the rectifier. 10. The motor driving of claim 9, wherein the control unit further comprises a driving signal generating unit configured to generate a driving signal based on the generated target voltage and the position of the motor sensed by the current sensing unit. for power converters. A method for controlling a power conversion device including an inverter for driving a motor by converting a DC voltage output from a rectifier into an AC voltage including a plurality of switching elements, the method comprising:
generating a target current based on the target speed and the speed of the motor sensed through a current sensing unit;
generating a target voltage based on the target current so that the target voltage is smaller than an output voltage of the rectifier; and
and generating a driving signal based on the generated target voltage and the sensed position of the motor. The method of claim 11 , wherein the target voltage is generated so that the voltage input to the motor is equal to or less than a value obtained by subtracting a voltage change of the output voltage of the rectifier from the output voltage of the rectifier. The method of claim 11 , wherein the target voltage is generated such that a voltage input to the motor is equal to or less than a maximum value of a pure DC component of the rectifier. The method of claim 11 , wherein the target voltage is generated so that a voltage input to the motor is equal to or less than a minimum value of an output voltage variation of the rectifier. 12. The method of claim 11, wherein the voltage input to the motor is the output voltage of the rectifier.

Control method of the power conversion device, characterized in that less than twice.

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