阅读说明：本技术 一种双馈异步电动机控制系统的起动方法和装置 (Starting method and device of double-fed asynchronous motor control system ) 是由 倪锴 彭国嘉 甘醇 曲荣海 胡义华 于 2021-06-11 设计创作，主要内容包括：本发明公开了一种双馈异步电动机控制系统的起动方法和装置,属于电机技术领域。本方法首先通过开环给定转子d、q轴电压给定值采集并计算电机接近起动时该转子位置对应的d、q轴电流反馈值i-(rdq),并将其作为闭环控制的参考电流限幅或给定值,不需要安装原动机拖动电机起动或采取开关切换运行模式,有效简化双馈异步电动机的起动过程,实现双馈异步电动机直接起动。(The invention discloses a starting method and a starting device of a control system of a double-fed asynchronous motor, and belongs to the technical field of motors. The method firstly gives the given values of d-axis and q-axis voltages of the rotor through open loop Collecting and calculating d and q axis current feedback values i corresponding to the rotor position when the motor is close to starting rdq And the reference current amplitude limit or the given value of the closed-loop control is used as the reference current amplitude limit or the given value, and a prime motor does not need to be installed to drag a motor to start or adopt a switch to operateAnd the mode effectively simplifies the starting process of the double-fed asynchronous motor and realizes the direct starting of the double-fed asynchronous motor.)

1. A method for starting a doubly-fed asynchronous motor control system, comprising the steps of:

(1) increasing the voltage of a direct current bus to a preset working value, giving d-axis and q-axis voltage reference values of a rotor, and calculating d-axis and q-axis currents of the rotor under an open loop when the three-phase voltage of the stator is at the critical starting voltage of the motor;

(2) setting the d-axis current and the q-axis current under the open loop as the amplitude limit value of a d-axis current reference value and the q-axis current reference value during the closed loop double-fed operation control respectively;

(3) and the motor increases the stator side voltage of the motor under the setting in a closed-loop double-fed control operation mode until the motor is started.

2. The starting method according to claim 1, wherein said raising the dc bus voltage to a preset operating value comprises in particular:

(A1) collecting three-phase voltage at the stator side of the motor, and calculating to obtain a stator voltage vector angle theta₁；

(A2) According to the given value of the DC bus voltageAnd the collected DC bus voltage u_dcAnd calculating to obtain the d-axis current set value of the grid-side converterPresetting set value of q-axis current of network side converterIs zero;

(A3) collected three-phase current i of grid-side converter_gabcAccording to the stator voltage vector angle theta₁Carrying out coordinate transformation to obtain a d-axis current feedback value i of the grid-side converter_gdQ-axis current feedback value i_gqCollected three-phase voltage u of grid-side converter_gabcAccording to the stator voltage vector angle theta₁Carrying out coordinate transformation to obtain a d-axis voltage feedback value u of the grid-side converter_gdQ-axis voltage feedback value u_gq；

(A4) According to the d-axis current set value of the network side converterq-axis current set pointAnd d-axis current feedback value i_gdQ-axis current feedback value i_gqAnd d-axis voltage feedback value u_gdQ-axis voltage feedback value u_gqAnd calculating to obtain the d-axis voltage set value of the grid-side converterGiven value of q-axis voltage

(A5) Given value of d-axis voltage of grid-side converterGiven value of q-axis voltageAccording to stator voltage vector angle theta₁Coordinate transformation is carried out to obtain the three-phase voltage given value of the grid-side converter

(A6) Setting three-phase voltage of grid-side converter to be given value by adopting SPWM (sinusoidal pulse Width modulation) algorithmAnd generating a trigger pulse as a reference voltage to drive each switching tube in the grid-side converter, and controlling the voltage of the direct-current bus to rise to a preset working value.

3. A starting method according to claim 1, characterized in that the closed-loop doubly-fed control operation comprises in particular:

(B1) collecting three-phase voltage at the stator side of the motor, and calculating to obtain a stator voltage vector angle theta₁；

(B2) According to given value of motor speedAnd the collected motor rotation speed omega_rAnd calculating to obtain the d-axis current set value of the rotor side converter

(B3) The stator voltage vector angle θ₁And the collected rotor position angle theta_rAre subtracted to obtainSlip angle theta_sCollected three-phase current i of rotor-side converter_rabcAccording to the slip angle theta_sCoordinate transformation is carried out to obtain a d-axis current feedback value i of the rotor side converter_rdQ-axis current feedback value i_rq；

(B4) According to the d-axis current set value of the rotor side converterq-axis current set pointAnd d-axis current feedback value i_rdQ-axis current feedback value i_rqAnd calculating to obtain the d-axis voltage set value of the rotor side converterGiven value of q-axis voltage

(B5) D-axis voltage set value of rotor side converterGiven value of q-axis voltageAccording to the slip angle theta_sCoordinate transformation is carried out to obtain the three-phase voltage given value of the rotor side converter

(B6) Rotor side converter three-phase voltage set value by adopting SPWM (sinusoidal pulse Width modulation) algorithmGenerating trigger pulse as reference voltage to drive each switching tube in rotor-side converter, outputting three-phase voltage of motor stator, and controllingThe doubly-fed asynchronous motor operates.

4. The starting method of claim 1, wherein the calculation of the d and q axis currents of the rotor in the open loop comprises:

given value of d-axis and q-axis voltages of rotorObtaining the given voltage value of each phase winding through coordinate transformationComparing the voltage with a preset triangular wave, controlling the driving signals of each switching tube in the power converter at the rotor side to generate three-phase current i of the motor rotor_rabc；

When the three-phase voltage of the stator is critical starting voltage, the three-phase current i of the motor rotor is converted into the three-phase current i_rabcCoordinate transformation is carried out to obtain d and q axis current feedback values i of the rotor_rd、i_rq。

5. Starting method according to claim 4, characterized in that the d and q axis voltages of the rotor are given valuesObtaining the given voltage value of each phase winding through coordinate transformationThe method specifically comprises the following steps:

collecting three-phase voltage u of stator_sabcObtaining stator voltage vector angle theta according to phase-locked loop algorithm₁And is related to the rotor speed omega_rCalculated rotor position angle theta_rSubtracting to calculate the slip angle theta_s(ii) a Given value of d-axis and q-axis voltages of rotorAccording to the slip angle theta_sObtaining the given voltage value of each phase winding

6. The starting method according to claim 4, wherein the driving signals for the switching tubes in the rotor-side converter are controlled by:

when the given value of the winding voltage is greater than the triangular carrier, the corresponding upper switching tube driving signal is at a high level, and the lower switching tube driving signal is at a low level; when the given value of the winding voltage is less than or equal to the triangular carrier, the corresponding upper switching tube driving signal is at a low level, and the lower switching tube driving signal is at a high level.

7. A starting method according to claim 6, characterized in that the frequency of said triangular wave is 10kHz and the maximum value is the bus voltage u_dcMinimum value is negative bus voltage-u_dc。

8. A starting device for a doubly-fed asynchronous motor control system, comprising:

a computer-readable storage medium and a processor;

the computer-readable storage medium is used for storing executable instructions;

the processor is configured to read executable instructions stored in the computer readable storage medium and execute the startup method of the doubly-fed asynchronous motor control system of any of claims 1 to 7.

Technical Field

The invention belongs to the technical field of motors, and particularly relates to a starting method and a starting device of a control system of a double-fed asynchronous motor.

Background

Energy development in China adheres to strategic routes of conservation development, clean development and safety development, a power system for ship propulsion at the present stage has remarkable development on energy conversion and distribution, and electrification becomes a development trend of a ship propulsion system. The development of the ship industry has important influence on global transportation and world economy, and the related technology of large ships is also considerably emphasized in the military field, which is an important embodiment of national military strength. In order to meet the increasing demand for electric power of ships, all-electric ships based on electric propulsion systems have gradually become the ship production standard of each large shipyard in the world, which is also the development direction of ships in the future.

Compared with a squirrel-cage asynchronous motor, the double-fed asynchronous motor has the advantages that slip power can be fed back, the capacity of a power converter can be adjusted, and the like. However, the doubly-fed asynchronous motor also has the defects of large starting current, limited speed regulation range, complex structure and the like. At present, there are many researches on starting methods of a double-fed asynchronous motor, and a conventional starting method of the double-fed asynchronous motor adopts a prime motor to drive or adopts an induction motor connection mode to start, wherein the prime motor needs to be additionally provided with an electric motor or other equipment to drive the double-fed asynchronous motor to start; the latter usually requires additional switching devices or algorithms for software controlled switching, both of which present the problem of relatively complex software and hardware for starting the doubly fed asynchronous motor.

Disclosure of Invention

The invention aims to provide a starting method and a starting device of a control system of a double-fed asynchronous motor, aiming at solving the problems that the starting of the existing double-fed asynchronous motor needs additional motors or switching equipment and the starting control is more complicated.

In order to achieve the above object, the present invention provides, in one aspect, a starting method for a doubly-fed asynchronous motor control system,

the doubly-fed asynchronous motor control system comprises: the system comprises a three-phase alternating current voltage regulator, a back-to-back power converter, a controller and a double-fed asynchronous motor. The input end of the three-phase alternating current voltage regulator is connected with a power grid, and the output end of the three-phase alternating current voltage regulator is connected with a grid-side converter. The grid-side converter outputs direct current voltage to be connected with a capacitor and a direct current bus in parallel. The stator of the double-fed asynchronous motor is connected with a three-phase alternating-current voltage regulator in a side mode, and the rotor of the double-fed asynchronous motor is connected with a rotor-side power converter in a side mode, so that the control of rotor current is achieved. Furthermore, the back-to-back power converter comprises a plurality of bridge arms and a direct-current bus capacitor, wherein each bridge arm comprises an upper switch tube and a lower switch tube; the emitter of the upper switch tube of the grid-side converter and the collector of the lower switch tube are connected as the input ends of bridge arms, and the input ends of the bridge arms are respectively connected with the output end of the three-phase voltage regulator; the emitter of an upper switch tube and the collector of a lower switch tube of the rotor-side power converter are connected to serve as the output ends of bridge arms, and the output ends of the bridge arms are respectively connected with one end of a rotor winding of the doubly-fed asynchronous motor; one end of the direct current bus capacitor is connected with the collector electrode of the switch tube on each bridge arm; and the other end of the direct current bus capacitor is connected with the emitting electrode of each bridge arm lower switch tube.

The starting method comprises the following steps:

(1) increasing the voltage of a direct current bus to a preset working value, giving d-axis and q-axis voltage reference values of a rotor, and calculating d-axis and q-axis currents of the rotor under an open loop when the three-phase voltage of the stator is at the critical starting voltage of the motor;

(2) setting the d-axis current and the q-axis current under the open loop as the amplitude limit value of a d-axis current reference value and the q-axis current reference value during the closed loop double-fed operation control respectively;

(3) and the motor increases the stator side voltage of the motor under the preset set value in a closed-loop double-fed control operation mode until the motor is started.

Further, raising the dc bus voltage to the preset operating value specifically includes:

(A1) collecting three-phase voltage at the stator side of the motor, and calculating to obtain a stator voltage vector angle theta₁；

(A2) According to the given value of the DC bus voltageAnd the collected DC bus voltage u_dcAnd calculating to obtain the d-axis current set value of the grid-side converterPresetting set value of q-axis current of network side converterIs zero;

(A3) collected three-phase current of grid-side converterAccording to the stator voltage vector angle theta₁Carrying out coordinate transformation to obtain a d-axis current feedback value i of the grid-side converter_gdQ-axis current feedback value i_gqCollected three-phase voltage u of grid-side converter_gabcAccording to the stator voltage vector angle theta₁Carrying out coordinate transformation to obtain a d-axis voltage feedback value u of the grid-side converter_gdQ-axis voltage feedback value u_gq；

(A4) According to the d-axis current set value of the network side converterq-axis current set pointAnd d-axis current feedback value i_gdQ-axis current feedback value i_gqAnd d-axis voltage feedback value u_gdQ-axis voltage feedback value u_gqAnd calculating to obtain the d-axis voltage set value of the grid-side converterGiven value of q-axis voltage

(A5) Given value of d-axis voltage of grid-side converterGiven value of q-axis voltageAccording to stator voltage vector angle theta₁Coordinate transformation is carried out to obtain the three-phase voltage given value of the grid-side converter

(A6) Setting three-phase voltage of grid-side converter to be given value by adopting SPWM (sinusoidal pulse Width modulation) algorithmAnd generating a trigger pulse as a reference voltage to drive each switching tube in the grid-side converter, and controlling the voltage of the direct-current bus to rise to a preset working value.

Further, the operation of the closed-loop doubly-fed control specifically includes:

(B1) collecting three-phase voltage at the stator side of the motor, and calculating to obtain a stator voltage vector angle theta₁；

(B2) According to given value of motor speedAnd the collected motor rotation speed omega_rAnd calculating to obtain the d-axis current set value of the rotor side converter

(B3) The stator voltage vector angle θ₁And the collected rotor position angle theta_rSubtracting to obtain slip angle theta_sCollected three-phase current i of rotor-side converter_rabcAccording to the slip angle theta_sCoordinate transformation is carried out to obtain a d-axis current feedback value i of the rotor side converter_rdQ-axis current feedback value i_rq；

(B4) According to the d-axis current set value of the rotor side converterq-axis current set pointAnd d-axis current feedback value i_rdQ-axis current feedback value i_rqAnd calculating to obtain the d-axis voltage set value of the rotor side converterGiven value of q-axis voltage

(B5) D-axis voltage set value of rotor side converterGiven value of q-axis voltageAccording to the slip angle theta_sCoordinate transformation is carried out to obtain the three-phase voltage given value of the rotor side converter

(B6) Rotor side converter three-phase voltage set value by adopting SPWM (sinusoidal pulse Width modulation) algorithmAnd generating trigger pulses as reference voltage to drive each switching tube in the rotor-side converter, outputting three-phase voltage of a motor stator, and controlling the operation of the doubly-fed asynchronous motor.

Further, the calculation of the d-axis and q-axis currents of the rotor under the open loop comprises the following steps:

given value of d-axis and q-axis voltages of rotorObtaining the given voltage value of each phase winding through coordinate transformationComparing the power with a preset triangular wave and then carrying out power comparison on the side of the rotorThe driving signals of the switching tubes in the converter are controlled to generate three-phase current i of the motor rotor_rabc；

When the three-phase voltage of the stator is critical starting voltage, the three-phase current i of the motor rotor is converted into the three-phase current i_rabcCoordinate transformation is carried out to obtain d and q axis current feedback values i of the rotor_rd、i_rq。

Further, d-axis and q-axis voltage set values of rotorObtaining the given voltage value of each phase winding through coordinate transformationThe method specifically comprises the following steps:

collecting three-phase voltage u of stator_sabcObtaining stator voltage vector angle theta according to phase-locked loop algorithm₁And is related to the rotor speed omega_rCalculated rotor position angle theta_rSubtracting to calculate the slip angle theta_s(ii) a Given value of d-axis and q-axis voltages of rotorAccording to the slip angle theta_sObtaining the given voltage value of each phase winding

Further, the method for controlling the driving signal of each switching tube in the rotor-side converter specifically comprises the following steps:

when the given value of the winding voltage is greater than the triangular carrier, the corresponding upper switching tube driving signal is at a high level, and the lower switching tube driving signal is at a low level; when the given value of the winding voltage is less than or equal to the triangular carrier, the corresponding upper switching tube driving signal is at a low level, and the lower switching tube driving signal is at a high level.

Furthermore, the frequency of the triangular wave is 10kHz, and the maximum value is bus voltage u_dcMinimum value is negative bus voltage-u_dc。

In another aspect, the present invention provides a starting apparatus for a doubly-fed asynchronous motor control system, including:

a computer-readable storage medium and a processor;

the computer-readable storage medium is used for storing executable instructions;

the processor is configured to read executable instructions stored in the computer readable storage medium and execute the starting method of the doubly-fed asynchronous motor control system according to the first aspect of the present invention.

Through the technical scheme of the invention, compared with the prior art, the method firstly gives the given values of the d and q shaft voltages of the rotor through the open loopCollecting and calculating d and q axis current feedback values i corresponding to the rotor position when the motor is close to starting_rdqAnd the reference current amplitude limit or the given value of the closed-loop control is used, a prime motor does not need to be installed to drag a motor to start or a switch operation mode is adopted, the starting process of the double-fed asynchronous motor is effectively simplified, and the direct starting of the double-fed asynchronous motor is realized.

Drawings

FIG. 1 is a schematic diagram of a doubly-fed asynchronous motor control system;

FIG. 2 is a schematic diagram of a double-fed asynchronous motor control system grid-side converter current double closed loop control;

FIG. 3 is a schematic diagram of open loop control of a doubly fed asynchronous motor control system;

fig. 4 is a schematic diagram of rotor-side current double closed-loop control of a doubly-fed asynchronous motor control system.

Detailed Description

In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention is described in further detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention. In addition, the technical features involved in the embodiments of the present invention described below may be combined with each other as long as they do not conflict with each other.

The invention provides a control system of a double-fed asynchronous motor, which comprises a three-phase alternating-current voltage regulator, the double-fed asynchronous motor, a back-to-back power conversion module, a pulse generation module, a driving module, a position sensor and a controller. As shown in fig. 1, one end of the grid-side power converter is connected to the output of the three-phase ac voltage regulator through an inductor, and the other end of the grid-side power converter is connected to the dc bus capacitor, and is configured to convert the three-phase ac voltage into a dc voltage. One end of the rotor side power converter is connected with the direct current bus, and the other end of the rotor side power converter is connected with the three-phase winding of the rotor of the double-fed asynchronous motor to provide three-phase alternating current for the rotor winding. The stator winding of the double-fed asynchronous motor is also directly connected with the output of the three-phase alternating current voltage regulator.

The starting method comprises the following steps:

(1) increasing the voltage of a direct current bus to a preset working value, giving d-axis and q-axis voltage reference values of a rotor, and calculating d-axis and q-axis currents of the rotor under an open loop when the three-phase voltage of the stator is at the critical starting voltage of the motor;

(2) setting the d-axis current and the q-axis current under the open loop as the amplitude limit value of a d-axis current reference value and the q-axis current reference value during the closed loop double-fed operation control respectively;

(3) and the motor increases the stator side voltage of the motor under the preset set value in a closed-loop double-fed control operation mode until the motor is started.

Specifically, the network-side power converter control block diagram is shown in fig. 2, and includes:

(1) the DC voltage regulator is based on the given value of DC bus voltageAnd the DC voltage u collected by the bus voltage sensor_dcCalculating to obtain a given value of d-axis component of the current on the network side by using a proportional-integral algorithmGiven value of q-axis component of current of grid-side converterNormally set to 0; therefore, given values of d and q axis components of the current of the grid-side converter can be obtained;

(2) the three-phase alternating voltage collected by the output voltage sensor of the three-phase alternating voltage regulator is processed by a three-phase-locked loop algorithm to obtain a stator voltage angle theta₁(ii) a The second rotating coordinate conversion module of the grid-side converter is used for converting three-phase alternating current i acquired by a three-phase current sensor of the grid-side converter_gabcAnd stator voltage angle theta calculated by phase-locked loop₁Obtaining feedback values i of d and q axis components of current of the network side converter through coordinate transformation calculation_gdq；

(3) The current regulator is based on d and q axis component set values of the current of the network side converterAnd a feedback value i_gdqObtaining the given values of d and q axis voltages of the network side converter by using a proportional-integral algorithm and adding a cross coupling term

Specifically, the grid-side converter d and q-axis voltage given value calculation function is as follows:

wherein, the resistance term can be ignored in practice; in the formula, R_gIs a net side resistance, i_gdqIs the grid side converter current dq axis component, L_gIs a series inductance, omega₁For grid voltage angular frequency, u_gdFor the calculated d-axis voltage feedback value of the grid-side converter,setting values of d and q axis voltages of the grid side converter;

(4) a first rotating coordinate transformation module of the grid-side converter is used for transforming the given value of the voltage of d and q axes of the grid-side converterAnd stator voltage angle theta₁Obtaining the three-phase voltage given value of the grid-side converter through coordinate transformation calculation

(5) The three-phase voltage set value is compared with a preset triangular wave through a carrier comparison pulse width modulation module, a PWM driving signal is input into a network side converter to control the action of a switching tube, and a direct-current bus voltage u is generated_dc。

The starting method of the double-fed asynchronous motor control system comprises an open loop link, and a control block diagram is shown in FIG. 3; and a closed-loop control link, a control block diagram of which is shown in fig. 4.

The starting process comprises the following steps:

open loop measurement of rotor current feedback value:

(1) open-loop direct given rotor d, q shaft voltage given valueThe rotor side first coordinate transformation module calculates a stator voltage angle theta according to a phase-locked loop₁And the collected rotor position angle theta_rSubtracting the difference to be used as a coordinate transformation angle, and setting the d-axis voltage and the q-axis voltage of the rotor to be given valuesConversion to three-phase rotor voltage in three-phase stationary frame

(2) The three-phase rotor voltage set value is compared with a preset triangular wave through a carrier comparison pulse width modulation module, a PWM driving signal is input into a rotor side power converter to control the action of a switching tube, and a three-phase alternating current voltage u is generated at the rotor side_rabc；

(3) The rotor side second rotating coordinate transformation module is used for transforming the rotor side three-phase alternating current i according to the rotor side three-phase current sensor_rabcAnd the stator voltage angle theta calculated by the phase-locked loop₁And the collected rotor position angle theta_rThe slip angle θ resulting from the subtraction_sAs a coordinate transformation angle, a feedback value i of the d and q axis components of the rotor current is obtained through coordinate transformation calculation_rdq(ii) a Wherein, the rotor speed before starting in the open loop stage is zero, and the collected rotor position angle theta_rIs always zero;

then starting is carried out under the closed loop of the rotating speed:

(5) the speed regulator setting the value according to the rotating speedAnd the rotor speed omega acquired by the position sensor_rCalculating to obtain a given value of a d-axis component of the side current of the rotor by using a proportional-integral algorithm

(6) The rotor side second rotating coordinate transformation module is used for transforming the rotor three-phase alternating current i acquired by the rotor three-phase current sensor_rabcAnd angle of slip theta_sObtaining feedback values i of d and q axis components of rotor current through coordinate transformation calculation_rdq；

(7) The current regulator is based on the d and q axis components of rotor currentAnd a feedback value i_rdqThe given values of the d and q axis voltages of the rotor are obtained by using a proportional-integral algorithm and adding a cross coupling term

Specifically, the rotor d and q axis voltage given value calculation function is as follows:

wherein, the rotor resistance term is in actual calculationCan be ignored; in the formula (I), the compound is shown in the specification,is the leakage coefficient of the motor, L_mThe motor is mutual inductance, L_sThe motor being a stator inductor, L_rThe motor is a rotor inductor; r_rIs rotor resistance, i_rdqIs the rotor side current dq axis component, ω_sIs the slip speed, omega₁For grid voltage angular frequency, u_sIs the voltage of the stator and is,setting values of d and q axis voltages at the rotor side;

(8) a first rotating coordinate transformation module at the rotor side gives a value according to the d and q axis voltages of the rotorSum and slip angle θ_sCoordinate transformation to obtain three-phase voltage set value of rotor

(9) The three-phase rotor voltage set value is compared with a preset triangular wave through a carrier comparison pulse width modulation module, a PWM driving signal is input into a rotor side power converter to control the action of a switching tube, and a three-phase alternating current voltage u is generated at the rotor side_rabc；

(10) Outputting the rotating speed regulator when startingThe clipping is set to be small, and can be set to 0.5; rotor current q-axis component setpointSet to 0;

(11) firstly, regulating the output of a three-phase alternating current voltage regulator to be a smaller value, and setting the voltage of an output line to be 10V;

(12) running a power converter algorithm on the network side to enable the voltage of the direct current bus to rise to a value that the motor can be started, and setting the voltage to be 70V;

(13) the output line voltage of the three-phase alternating current voltage regulator is regulated to be increased to be close to the starting stator voltage, and the output line voltage can be regulated to 40V;

(14) the feedback value i of the d-axis component of the rotor current obtained by calculation in the open loop stage_rdAs the reference value of the output amplitude limit of the rotating speed regulator;

(15) the feedback value i of the q-axis component of the rotor current obtained by calculation in the open loop stage_rqGiven value as rotor current q-axis component

(16) Gradually adjusting the output line voltage of the three-phase alternating current voltage regulator to rise until the motor is started;

(17) after the motor starts, it will operate in a doubly-fed manner according to the rotor-side power converter control method.

It will be understood by those skilled in the art that the foregoing is only a preferred embodiment of the present invention, and is not intended to limit the invention, and that any modification, equivalent replacement, or improvement made within the spirit and principle of the present invention should be included in the scope of the present invention.