KR100866414B1 - Method and apparatus for controlling 3 phase lc filter for driving induction motor - Google Patents

Abstract

An apparatus and a method for controlling 3 phase LC filter for driving an induction motor are provided to minimize the signal detection for control by detecting only the output voltage of the filter. A transfer function of the LC filter is converted into a secondary low pass filter type by defining an LC filter circuit(20) in a synchronous frame. The LC filter is controlled as the secondary low pass filter with various damping ratios by setting up a damping ratio of the LC filter defined in a synchronous frame to a desired value. A voltage variation value is outputted to a PWM inverter(10) as a voltage instruction value for PWM control by calculating the voltage variation value according to the difference between a filter voltage instruction value and a currently detected filter voltage.

Description

Method and apparatus for controlling three-phase sine wave filter for driving induction motors {Method and apparatus for controlling 3 phase LC filter for driving induction motor}

1 is a configuration diagram of an inverter system having a sine wave filter at an output stage

2 is a controller configuration diagram of a sine wave filter

Figure 3a, Figure 3b is a graph of the experimental results for showing the effect of the present invention.

The present invention relates to the control of a three-phase sine wave (LC) filter consisting of an inductor and a capacitor, and more particularly, to a method and apparatus for controlling an instantaneous voltage of a three-phase sine wave filter.

Most power converters use pulse width modulation (PWM) to control the output voltage and frequency, and adopt a low-power power semiconductor device to implement this. Such power converters are applied to industries in various ways, such as inverters for controlling motors, PWM converters for supplying power by unit power factor control, and uninterruptible power supplies.

The PWM waveform is a square wave and contains harmonics of various frequencies.These harmonics cause insulation deterioration or destruction of the windings of the motor, damage to the bearings, harmonics to the power supply, disturbance of peripheral communication devices, and malfunctions of existing protective devices. There are several problems.

Conventionally, various types of filters have been proposed to reduce such harmonics, and one of them, a sine wave filter (LC filter), has an advantage in that the output voltage is close to an ideal sine wave and there is no circuit loss. However, the sine wave filter is difficult to control because it can cause oscillation in the circuit, and to prevent this, an attenuation circuit or an active control circuit must be provided. Active control circuits are complicated to control and sensitive to control signals, so additional circuits must be minimized and robust to parameter variations.

An object of the present invention is to propose a method and a control device for controlling the instantaneous output voltage of a sinusoidal wave filter in a synchronous coordinate system using the output voltage of the PWM inverter and the sinusoidal wave filter characteristics.

In order to achieve the above object, a sine wave for filtering the motor drive signal output from the three-phase PWM inverter for PWM modulation of the three-phase power source for driving the three-phase induction motor according to the present invention before applying to the three-phase induction motor The method for controlling the (LC) filter is configured as follows. (1) transforming the sinusoidal filter transfer function into a second order lowpass filter by defining the sinusoidal filter circuit in a synchronous coordinate system, and (2) a value desired by a user for the attenuation ratio of the sine wave filter defined in the synchronous coordinate system. (3) calculating the voltage change according to the difference between the filter voltage command value and the currently detected filter voltage, and controlling the PWM as a secondary low pass filter having various attenuation characteristics. Outputting as a voltage command value for control.

In addition, the sine wave filter control device according to the present invention is configured as follows. (1) means for modifying the sinusoidal filter circuit in a synchronous coordinate system to transform the transfer function of the sine wave filter into a second order lowpass filter; Means for controlling as a secondary lowpass filter having various attenuation characteristics, and (3) calculating a voltage change depending on a difference between a filter voltage command value and a currently detected filter voltage and converting the PWM into a PWM inverter. Means for outputting as a voltage command value for control.

의 수학식(단, x는 각각 u상, v상, w상의 PWM 인버터 출력전압 v_ix, 커패시터 전류 i_Cx, 인덕터 전류 i_Lx)으로 정의되고, Here, the sine wave filter is an LC filter composed of a three-phase reactor Lf and a three-phase capacitor Cf,

Where x is defined by u-phase, v-phase, and w-phase PWM inverter output voltage v _ix , capacitor current i _Cx , inductor current i _Lx ,

In the step and means (1), the equation of the circuit of the sine wave filter

과 같은 것을 특징으로 한다. (단, V_ix: PWM 인버터 출력 상전압, L_f: 각 상당 필터 리액턴스, i_Lx: 필터 리액터 전류, C_f: 성형 결선에서의 각 상당 필터 커패시턴스, V_cx: 필터 커패시터의 상전압, I_cx: 필터 커패시터의 상전류, i_mx: 유도전동기 상전류, ': 미분기호, ": 2차 미분기호, *: 지령값, A와 B는 상수, v^* _cdq: 전류제어기에서 출력되는 전압의 동기좌표계에서의 값, v_cdq: 커패시터 전압센싱 및 변환부에서 출력되는 전압의 동기좌표계에서의 값, i_mdq: 모터전류 센싱 및 변환부에서 출력되는 전류의 동기좌표계에서의 값, v_idq: PWM제어를 위한 전압지령값으로서 동기좌표계에서의 값)

It is characterized by the same. (V _ix : PWM inverter output phase voltage, L _f : each equivalent filter reactance, i _Lx : filter reactor current, C _f : each equivalent filter capacitance in the molded connection, V _cx : phase voltage of the filter capacitor, I _cx : Phase current of filter capacitor, i _mx : Induction motor phase current, ': Undifferential sign, ": 2nd undifferential sign, *: Command value, A and B are constants, v ^* _cdq : In synchronous coordinate system of voltage output from current controller , V _cdq : value in the synchronous coordinate system of the voltage output from the capacitor voltage sensing and converter, i _mdq : value in the synchronous coordinate system of the current output from the motor current sensing and converter, v _idq : for PWM control Value in the synchronous coordinate system as the voltage command value)

(zeta)를 통해서 이루어지는 것을 특징으로 한다. In the step and means (2), setting the desired value as a variable for determining the attenuation ratio is based on the above equation.

It is characterized by made through (zeta).

Calculating the voltage change according to the difference between the filter voltage command value and the currently detected filter voltage in the step and means (3), calculates the voltage change using the difference between the control command value and the filter voltage detected at this time. Characterized in that. Here, it is preferable to calculate the voltage change using the difference between the control command value and the filter voltage detected at the present time by the following equation.

The above configuration can actually be implemented by a computer program, and can also be configured by pure hardware.

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

1 is a configuration diagram of a power conversion system including a sinusoidal filter composed of an inductor and a capacitor, and in particular, shows a schematic system configuration for driving a three-phase induction motor.

The PWM inverter 10 is a three-phase voltage inverter and may use an Insulated Gate Bipolar Transistor (IGBT) as a switching element, but in fact, an element such as an integrated gate committed thyristor (IGCT) or a MOSFET may be used. The sine wave (LC) filter 20 is composed of a three-phase reactor Lf and a three-phase capacitor Cf. The three-phase capacitor Cf may be configured by a star connection method or a delta connection method. In FIG. 1, the molded connection is assumed for the convenience of analysis, but the triangular connection method may be considered equivalent to the molded connection. The three-phase induction motor 30 is connected to the filter output terminal. Here, the PWM converter that connects the load side to which the induction motor (IM) 30 is connected to the power source has the same structure as in FIG. 1, except that the filter output is connected to the power source. Therefore, the control algorithm of the sine wave filter can be equally applied.

1, V _ix : PWM inverter output phase voltage, L _f : each equivalent filter reactance, i _Lx : filter reactor current, C _f : each equivalent filter capacitance in the molded connection, V _cx : phase voltage of the filter capacitor, I _cx : phase current of the filter capacitor, i _mx : induction motor phase current. In the following description, 'differential sign', 'differential differential sign', * is command value, and suffix is each phase of three-phase system (x = u, v, w) is assumed.

In FIG. 1, the three-phase sine wave filter circuit may be represented by Equation 1 below.

In Equation 1, x represents u-phase, v-phase, and w-phase inverter output voltage v _ix , capacitor current i _Cx , and inductor current i _Lx , respectively.

Equation 1 is converted into a static coordinate system as shown in Equation 2.

Equation 3 below shows the variables of the stationary coordinate system expanded in complex form.

In order to smoothly execute the algorithm of the present invention, Equation 2 is converted to Equation 4 as shown in Equation 4 below.

Equation 5 expands and displays the variable of the synchronous coordinate system in a complex form.

를 정의한다. 이는, 본 발명의 알고리즘 수행을 위해서, 동기좌표계에서 새로운 제어 변수를 정의하고 정현파필터의 전달 함수를 2차 저역통과 필터의 형태로 변형시키기 위한 것이다. 수학식 6에서와 같이 제어 변수를 정의하고 이를 이용하여 출력 전압을 발생시킴으로써 LC 필터를 2차 저역통과 필터와 동일하게 제어할 수 있으며 부하의 급격한 변화나 출력 전압 지령값의 빠른 변화시 발생할 수 있는 LC 회로의 공진을 제어할 수 있다. First consider the state that the load is not connected. In this case, since all terms related to the motor output current are excluded from Equation 4, Equation 6 is obtained. And new control variables

Define. This is to define a new control variable in the synchronous coordinate system and to transform the transfer function of the sinusoidal filter into a second order lowpass filter in order to perform the algorithm of the present invention. By defining a control variable and generating the output voltage using Equation 6, the LC filter can be controlled in the same way as the secondary lowpass filter, which can occur during rapid changes in load or rapid change in output voltage command value. The resonance of the LC circuit can be controlled.

(zeta)는 감쇠비를 결정하는 변수로서 사용자가 원하는 값으로 설정 가능하다. 수학식 6의 전달함수는 수학식 7과 같으며, 2차 저역통과 필터와 동일한 형태를 갖게 됨을 알 수 있다.Equation 6 indicates that the function of enabling the second low pass filter having various attenuation characteristics to be controlled by setting the attenuation ratio of the sinusoidal filter control unit to a desired value. That is, in Equation 6 defining the control variable

(zeta) is a variable that determines the attenuation ratio and can be set to a value desired by the user. The transfer function of Equation 6 is the same as Equation 7, and it can be seen that it has the same form as the second-order lowpass filter.

In Equation 6, the change rate of the capacitor voltage is approximated as in Equation 8.

Equation 8 shows an algorithm for calculating the input voltage (inverter output voltage) of the filter by preliminarily calculating the change in the filter voltage from the detected filter voltage and the filter voltage command value. In Equation 8, when calculating the change in voltage, the control command value and the filter voltage detected at the present time are not used without using the difference between the filter voltage detected at the present time and the filter voltage detected before one control period according to the prior art. The method of calculating the voltage change using the difference is shown. This method reduces the delay by one control period than the method using the detected voltage difference, which is very effective for the stability of the system.

Substituting Equation 8 into Equation 6, the command value v _idq of the inverter output voltage for controlling the filter is obtained.

When the load is connected, the voltage drop caused by the load current is added.

Equation 10 is an equation for compensating for the voltage drop due to the load current.

Therefore, the output voltage command value v _idq of the inverter may be expressed as the sum of the voltage for controlling the filter and the voltage for compensating the load current, which is expressed by Equation (11).

Here, A and B are expressions expressed in parentheses in Equation 9 as constants, respectively.

As described above, it has been explained that the inverter output voltage command value v _idq can be generated from v ^* _cdq , v _cdq , and i _mdq (easily _obtained in relation to v _{idq_ff} in Equation 10).

2 is a structural diagram for actually implementing a sine wave filter control algorithm according to the present invention described by the above-described formula, and may be configured by software or hardware. Here, the output voltage and the output current are values converted into the synchronous coordinate system as described above, and are both vector quantities. VVVF (variable voltage, variable frequency) of the vector controller (main component) or the output v ^* _cdq of the current controller 200, and the voltage v _cdq and the motor current sensing output from the capacitor voltage sensing and conversion unit 300 And a sine wave filter control unit 100 that implements the algorithm described above by using the current i _mdq output from the converter 400 as an input signal.

In FIG. 2, the sine wave filter control unit 100 will be described below. First, the means 130 for multiplying the voltage v ^* _cdq output from the current controller 200 by the constant A derived from Equation 9, and the voltage v _cdq output from the capacitor voltage sensing and conversion unit 300 in Equation 9 Means for multiplying the derived constant B (140), means for implementing equation (10) for the current i _mdq output from the first adder 110, the motor current sensing and conversion unit 400, which adds the value multiplied by A and B ( Means 150 for converting to v _{idq_ff} by 150 and a second adder 120 that adds the value output from the first adder 110 and the value output from the means 150. The voltage command value v _idq for PWM control is output. This v _idq is applied to the PWM converter 500 to be used for PWM control, thereby enabling the instantaneous voltage control of the sine wave filter. Here, v _idq is a value calculated in the synchronous coordinate system and denotes an inverter output implemented by a sine wave.

Although the sine wave filter control unit 100 is implemented by software, it is apparent to those skilled in the art that the sine wave filter control unit 100 may be implemented by hardware. When implemented by software, this software program can be stored in a computer recording medium. Computer recording media includes all types of recording media having programs and data stored thereon for reading by a computer system. Examples include ROM, RAM, CD, DVD-ROM, magnetic tape, floppy disk, optical data storage device, and the like, and those implemented in the form of transmission via the Internet. In other words, the recording medium may be distributed to networked computer systems so that the computer readable code is stored and executed in a distributed fashion.

FIG. 3 shows data of the sine wave filter output waveform X when the control method according to the present invention is not applied and the sine wave filter output waveform Y when the control method according to the present invention is applied. In FIG. 3 (a), the vibration component is included instead of the complete sinusoidal wave, but in (b), the almost perfect sinusoidal wave comes out.

According to the present invention, the following effects can be obtained. First, the present invention detects only the output voltage of the filter to minimize signal detection for control. Second, it is easy and simple to implement because it uses the coordinate transformation theory and transformation program used in the existing control system and adds the term to control the filter resonance. Third, this control algorithm is robust to parameter fluctuations. In other words, even if the inductance or capacitance fluctuates by ± 20% depending on the operating conditions or time, the stability of the control is not broken. Fourth, since the separation between the resonant frequency of the filter and the sampling frequency of the controller does not have to be large, the control range is relatively high, which has the effect of reducing the size of the filter. Fifthly, the present invention has a characteristic that is robust against noise because it does not use the derivative value of the output voltage.

Claims (11)

A method of controlling a sinusoidal wave (LC) filter for driving a three-phase induction motor to filter a motor driving signal output from a three-phase PWM inverter for PWM modulation of a three-phase power source before applying it to the three-phase induction motor, (1) transforming the sinusoidal filter's transfer function into a second order lowpass filter by defining the sinusoidal filter circuit in a synchronous coordinate system; (2) allowing the user to set the attenuation ratio of the sinusoidal filter defined by the synchronous coordinate system to a desired value so as to be controllable as a secondary lowpass filter having various attenuation characteristics; (3) calculating a voltage change according to the difference between the filter voltage command value and the currently detected filter voltage and outputting the voltage change value to the PWM inverter as a voltage command value for PWM control. How to control the filter. The method of claim 1, The sine wave filter is an LC filter composed of a three-phase reactor Lf and a three-phase capacitor Cf.

Where x is defined by u-phase, v-phase, and w-phase PWM inverter output voltage v _ix , capacitor current i _Cx , inductor current i _Lx , Equation in which the circuit of the sine wave filter in the step (1) is defined as a synchronous coordinate system, characterized in that as follows, the control method of the three-phase sine wave filter for driving the induction motor.

However, V _ix : PWM inverter output phase voltage, L _f : each equivalent filter reactance, i _Lx : filter reactor current, C _f : each equivalent filter capacitance in molded connection, V _cx : phase voltage of filter capacitor, I _cx : Phase current of the filter capacitor, i _mx : induction motor phase current, ': undifferentiated _arc , ": second undifferentiated _arc , *: command value, A and B are constants, v ^* _cdq : voltage in the synchronous coordinate system Value, v _cdq : value in the synchronous coordinate system of the voltage output from the capacitor voltage sensing and converter, i _mdq : value in the synchronous coordinate system of the current output from the motor current sensing and converter, v _idq : voltage for PWM control The value in the synchronous coordinate system as the command value. The method of claim 2, wherein the setting of the damping ratio in the step (2) to a value desired by the user is performed by the above equation.

Control method of a three-phase sine wave filter for driving an induction motor, characterized in that through (zeta). The method of claim 2, wherein the step (3) of calculating the voltage change according to the difference between the filter voltage command value and the currently detected filter voltage is based on the difference between the control command value and the filter voltage detected at the present time. A control method of a three-phase sine wave filter for driving an induction motor, characterized in that the change is calculated. 5. The control of a three-phase sine wave filter for driving an induction motor according to claim 4, wherein the calculation of the voltage change using the difference between the control command value and the filter voltage detected at the present time is performed by the following equation. Way.

A computer-readable recording medium having recorded thereon a program for implementing the method of claim 1. An apparatus for controlling a sinusoidal wave (LC) filter for driving a three-phase induction motor to filter a motor driving signal output from a three-phase PWM inverter for PWM modulation of a three-phase power source before applying it to the three-phase induction motor, (1) means for transforming the sinusoidal filter circuit in the form of a second order lowpass filter by defining the sinusoidal filter circuit in a synchronous coordinate system, (2) means for allowing the user to set the attenuation ratio of the sinusoidal filter defined by the synchronous coordinate system to a desired value so as to be controllable as a second order lowpass filter having various attenuation characteristics; (3) a three-phase sine wave for driving an induction motor, comprising means for calculating a voltage change according to a difference between a filter voltage command value and a currently detected filter voltage and outputting the voltage change value to the PWM inverter as a voltage command value for PWM control. Control device of the filter. The method of claim 7, wherein The sine wave filter is an LC filter composed of a three-phase reactor Lf and a three-phase capacitor Cf.

Where x is defined by u-phase, v-phase, and w-phase PWM inverter output voltage v _ix , capacitor current i _Cx , inductor current i _Lx , A control apparatus for driving a three-phase sine wave filter for driving an induction motor, characterized in that the equation in which the circuit of the sine wave filter in the means (1) is defined as a synchronous coordinate system is as follows.

However, V _ix : PWM inverter output phase voltage, L _f : each equivalent filter reactance, i _Lx : filter reactor current, C _f : each equivalent filter capacitance in molded connection, V _cx : phase voltage of filter capacitor, I _cx : Phase current of the filter capacitor, i _mx : induction motor phase current, ': undifferentiated _arc , ": second undifferentiated _arc , *: command value, A and B are constants, v ^* _cdq : voltage in the synchronous coordinate system Value, v _cdq : value in the synchronous coordinate system of the voltage output from the capacitor voltage sensing and converter, i _mdq : value in the synchronous coordinate system of the current output from the motor current sensing and converter, v _idq : voltage for PWM control The value in the synchronous coordinate system as the command value. 9. The method according to claim 8, wherein the setting by the means (2) to a value desired by the user as a variable for determining the attenuation ratio is as follows.

Control device for a three-phase sine wave filter for driving an induction motor, characterized in that through (zeta). 9. The method according to claim 8, wherein the calculation of the voltage change in accordance with the difference between the filter voltage command value and the filter voltage currently detected by the means (3) is performed using the difference between the control command value and the filter voltage detected at the present time. Control device for a three-phase sine wave filter for driving an induction motor, characterized in that for calculating the change. The control of the three-phase sine wave filter for driving an induction motor according to claim 10, wherein the calculation of the voltage change using the difference between the control command value and the filter voltage detected at the present time is performed by the following equation. Device.

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