Electro-magnetic doubly salient motor capable of ensuring fault-tolerant power generation power by improving bus voltage
阅读说明：本技术 通过提高母线电压保证容错发电功率的电励磁双凸极电机 (Electro-magnetic doubly salient motor capable of ensuring fault-tolerant power generation power by improving bus voltage ) 是由 史宏俊 周波 熊磊 蒋思远 王开淼 于 2021-09-28 设计创作，主要内容包括：本发明公开了一种通过提高母线电压保证容错发电功率的电励磁双凸极电机,涉及电励磁双凸极电机领域,该电励磁双凸极电机在励磁故障发生前,以传统不控整流发电方式进行发电,在励磁故障发生后,切换至故障发电模式,通过提高母线电压的方式使得电枢电流快速达到失磁故障容错发电运行所需电流参考值,使得在绕组励磁时可以具有较高的母线电压,从而实现快速励磁,大大的提高输出功率,提升了电机在失磁故障运行时的容错发电功率,提高了电励磁双凸极电机在各种环境下运行的可靠性,适合应用于航空航天、汽车等行业。(The invention discloses an electro-magnetic doubly salient motor capable of ensuring fault-tolerant power generation power by improving bus voltage, and relates to the field of electro-magnetic doubly salient motors.)
1. An electric excitation doubly salient motor for ensuring fault-tolerant power generation power by improving bus voltage is characterized by comprising a controller, a salient pole stator and rotor structure, an excitation circuit, a main power supply, three groups of H-bridge converters, a load R, a load energy storage capacitor C1, a power main switch S13 and a boost capacitor C2;
the excitation circuit is connected with an excitation winding in the salient pole stator and rotor structure, and the middle points of two bridge arms of each group of H-bridge converters are respectively connected with two ends of one-phase armature winding in the salient pole stator and rotor structure;
the positive pole of the main power supply is connected with the collector of the upper switch tube of each bridge arm in the three groups of H-bridge converters through a diode D13, and the negative pole of the main power supply is connected with the emitter of the lower switch tube of each bridge arm in the three groups of H-bridge converters;
the load is connected with the load energy storage capacitor in parallel and connected with a first end of a power main switch S13, a second end of the power main switch S13 is connected with a collector of an upper switch tube of each bridge arm through a diode D14, an emitter of the upper switch tube of each bridge arm in the three groups of H-bridge converters is connected with a second end of the power main switch S13 through a diode respectively, and a lower switch tube of each bridge arm is connected with a diode in parallel in a reverse direction;
the boost capacitor C2 is connected in parallel at the collector of the upper switch tube of each bridge arm and at the two ends of the emitter of the lower switch tube of each bridge arm in the three groups of H-bridge converters;
the controller is connected with and controls the on-off of the excitation circuit, the three groups of H-bridge converters and the power main switch: when the electro-magnetic doubly salient motor works normally, the power main switch S13 is controlled to be conducted, and a three-phase armature winding forms an uncontrolled rectifier bridge through diodes in three groups of H-bridge converters to generate electricity; when detecting that the double-salient electro-magnetic motor has an excitation fault, disconnecting the excitation circuit, and controlling the on-off of a power main switch S13 by adopting hysteresis loop control, so that the voltage of the boost capacitor is greater than the load voltage of the load to boost the bus voltage for carrying out winding excitation.
2. The doubly salient electro-magnetic machine of claim 1, wherein three groups of H-bridge converters are identical in structure, each H-bridge converter comprises a first bridge arm and a second bridge arm which are respectively formed by connecting an upper switch tube and a lower switch tube in series in an opposite direction, collectors of the upper switch tubes in the two bridge arms are connected, an emitter of the upper switch tube in the first bridge arm is connected with the second end of the main power switch S13 through a diode and an electronic switch, and an emitter of the upper switch tube in the second bridge arm is connected with the second end of the main power switch S13 through a diode; two ends of a lower switching tube in the two bridge arms are respectively connected with a diode in parallel in a reverse direction;
when the electro-magnetic doubly salient motor works normally, the controller controls the power main switch S13 to be continuously conducted, all upper switch tubes and lower switch tubes in the three groups of H-bridge converters to be turned off, three electronic switches in the three groups of H-bridge converters to be turned on, and the three-phase armature winding forms an uncontrolled rectifier bridge through diodes in the three groups of H-bridge converters to generate electricity.
3. The doubly salient electro-magnetic machine of claim 2, wherein when an excitation fault occurs in the doubly salient electro-magnetic machine, the controller controls all three electronic switches in the three groups of H-bridge converters to be switched off, controls the power main switch S13 to be switched on and off by hysteresis control, and controls the states of corresponding upper switch tubes and/or lower switch tubes in the three groups of H-bridge converters according to the current electrical angle interval of the machine.
4. The electrically excited doubly salient machine of claim 3, wherein said three-phase armature windings comprise an A-phase winding, a B-phase winding and a C-phase winding, a first H-bridge converter connecting said A-phase winding, a second H-bridge converter connecting said B-phase winding, a third H-bridge converter connecting said C-phase winding;
controlling the states of corresponding upper switching tubes and/or lower switching tubes in the three groups of H-bridge converters according to the current electrical angle interval of the motor, wherein the states comprise:
when the electrical angle of the motor is at 0, thetaoffIn the interval of-120 degrees, an upper switching tube S9 of a first bridge arm and a lower switching tube S12 of a second bridge arm in a third H-bridge converter are switched on, so that a C-phase winding is in an excitation phase;
when the electrical angle of the motor is positioned in [ theta ]off-120°，θon) During interval, all switching tubes in the three H-bridge converters are controlled to be in an off state, so that the C-phase winding starts to generate electricity;
when the electrical angle of the motor is positioned in [ theta ]on，θoff) During interval, an upper switch tube S1 of a first bridge arm and a lower switch tube S4 of a second bridge arm in the first H-bridge converter are conducted, so that an A-phase winding is in an excitation stage, and a C-phase winding is continuously in a power generation stage;
when the electrical angle of the motor is positioned in [ theta ]off，θonIn the interval of +120 degrees, all switching tubes in the three H-bridge converters are controlled to be in an off state, so that the A-phase winding starts to generate electricity;
when the electrical angle of the motor is positioned in [ theta ]on+120°，θoffIn the +120 DEG interval, an upper switch tube S5 of a first bridge arm and a lower switch tube S8 of a second bridge arm in the second H-bridge converter are conducted, so that a B-phase winding is in an excitation stage, and an A-phase winding is continuously in a power generation stage;
when the electrical angle of the motor is positioned in [ theta ]off+120°，θonIn the interval of +240 degrees, all switching tubes in the three H-bridge converters are controlled to be in an off state, so that the B-phase winding starts to generate electricity;
when the electrical angle of the motor is positioned in [ theta ]onIn the interval of +240 degrees and 360 degrees, an upper switching tube S9 of a first bridge arm and a lower switching tube S12 of a second bridge arm in a third H-bridge converter are conducted, so that a C-phase winding is in an excitation phase, and a B-phase winding is continuously in a power generation phase;
wherein, thetaonRepresenting the armature winding field-on angle, θoffRepresenting the excitation off-angle of the armature winding by 0 °<θon<120°，120°<θoff<240°。
5. The electrically excited doubly salient motor of claim 1, wherein the controller PI-regulates an error between an output voltage and a given voltage to obtain a given current in a process of controlling states of switching tubes of three groups of H-bridge converters, PI-regulates the given current and a current of a current excited winding to obtain a corresponding duty ratio, and increases the duty ratios of the switching tubes of the three groups of H-bridge converters according to the obtained corresponding duty ratios if the output voltage is lower than the given voltage; if the output voltage is higher than the given voltage, the controller reduces the duty ratio of the switching tubes of the three groups of H-bridge converters according to the obtained corresponding duty ratio so as to carry out chopping control on the current of the three-phase armature winding and realize closed-loop control on the output voltage.
6. The doubly salient electro-magnetic machine of claim 1, wherein when hysteresis control is used to control the on/off of the main power switch S13, the hysteresis loop width is 0.5V.
7. The doubly salient electro-magnetic machine of claim 1, wherein the voltage U of said boost capacitor is takenc2>1.2U0，U0Is the load voltage of the load.
Technical Field
The invention relates to the field of an electro-magnetic doubly salient motor, in particular to an electro-magnetic doubly salient motor which ensures fault-tolerant power generation by improving bus voltage.
Background
The electrically excited double salient pole motor is one new type of brushless DC motor developed based on switched reluctance motor, and has stator wound armature winding and exciting winding and rotor without winding. The double-salient electro-magnetic motor is mainly different from a switched reluctance motor in that an excitation winding is embedded on a stator, and the double-salient electro-magnetic motor only needs to be externally connected with an uncontrolled rectifier bridge to generate electricity when the double-salient electro-magnetic motor generates electricity due to the existence of an excitation magnetic field, so that the double-salient electro-magnetic motor has the advantages of good fault tolerance and suitability for severe working conditions, can maintain constant output voltage by adjusting the magnitude of excitation current when the load or the rotating speed changes, is very flexible to control, and has wide application prospects in the fields of aviation, wind power generation and the like.
The presence of the field winding on the one hand increases the flexibility of the system control, but on the other hand also brings safety and reliability problems. The aging, the wetting, the heating, the erosion and the like of the excitation winding can all influence the safe operation of the system. In addition, the excitation power circuit for controlling excitation may also be faulty due to overcurrent, reverse voltage impact, etc., and in case of serious conditions, the whole system will lose excitation. If the electrically excited doubly salient generator has a field loss fault in the operation process, the whole system can stop operating.
At present, the research on the fault-tolerant control strategy of the field failure of the doubly salient electro-magnetic motor is less. The prior art includes: the excitation fault-tolerant power generation system of the electro-excitation doubly salient motor and the control method thereof (China, Authority date: 5 and 17 th in 2017, and Authority number: CN104579067B) disclosed by Shiliwei and the like add redundant bridge arms on the basis of a three-phase full bridge to form a three-phase four-bridge arm converter, and realize the fault-tolerant power generation function of the excitation fault of the motor by alternately supplying positive excitation current and negative excitation current to each phase of the three-phase four-bridge arm converter. "a four-phase electro-magnetic doubly salient motor demagnetization fault-tolerant power generation method" (china, published: 5 and 22 in 2017, published: CN107147339A) disclosed by zhongxingwei et al provides a new control method by adding a redundant bridge arm and combining the characteristic that the self-inductance time of a four-phase motor changes along with the position of a rotor, so as to realize the demagnetization fault-tolerant power generation. Meanwhile, the excitation fault-tolerant power generation system of the electro-magnetic doubly salient motor and the control method thereof (China, published: 6 and 5 in 2018, and published: CN108123646A) disclosed by the Wentangxiang and the like also provide a function of generating power by using a three-phase full-bridge converter directly and providing positive and negative alternate current for each phase by controlling a switching tube of the power converter so as to realize loss-of-excitation fault power generation, and the method does not need to add a new bridge arm, and has the advantages of simple main power circuit structure, lower cost, smaller power generation angle and low power generation efficiency. The 'doubly salient electro-magnetic machine field failure fault-tolerant power generation system and the control method thereof' disclosed by Zhao Feng et al (China, published: 917 in 2019, published: CN110247597A) adopt half-bridge control, and the power generation efficiency is low. In addition, the electromagnetic double-salient motor field failure fault-tolerant power generation system and the control method thereof disclosed by Wangkong (281569) and the like (China, published: 3 and 8 in 2019, published: CN109450340A) propose the use of an H-bridge converter, and the method has the advantages that three-phase windings are independently opened through 12 switching tubes, each phase is independently excited and generated, and the efficiency is relatively high.
Although the above-mentioned various loss-of-magnetization fault-tolerant power generation control topologies can realize fault-tolerant control of loss-of-magnetization faults, the problem that the generated power cannot reach the generated power before fault tolerance exists after fault tolerance.
Disclosure of Invention
The invention provides an electro-magnetic doubly salient motor which ensures fault-tolerant power generation by improving bus voltage aiming at the problems and technical requirements, and the power generation power exists after fault tolerance is further improved. The technical scheme of the invention is as follows:
an electro-magnetic doubly salient motor capable of ensuring fault-tolerant power generation power by improving bus voltage comprises a controller, a salient pole stator and rotor structure, an excitation circuit, a main power supply, three groups of H-bridge converters, a load R, a load energy storage capacitor C1, a power main switch S13 and a boost capacitor C2, wherein the controller is connected with the salient pole stator and rotor structure;
the excitation circuit is connected with an excitation winding in the salient pole stator and rotor structure, and the middle points of two bridge arms of each group of H-bridge converters are respectively connected with two ends of one-phase armature winding in the salient pole stator and rotor structure;
the positive pole of the main power supply is connected with the collector of the upper switch tube of each bridge arm in the three groups of H-bridge converters through a diode D13, and the negative pole of the main power supply is connected with the emitter of the lower switch tube of each bridge arm in the three groups of H-bridge converters;
the load is connected with the load energy storage capacitor in parallel and connected with a first end of a power main switch S13, a second end of the power main switch S13 is connected with a collector of an upper switch tube of each bridge arm through a diode D14, an emitter of the upper switch tube of each bridge arm in the three groups of H-bridge converters is connected with a second end of the power main switch S13 through a diode respectively, and a lower switch tube of each bridge arm is connected with a diode in parallel in a reverse direction;
the boost capacitor is connected in parallel with the collector of the upper switch tube of each bridge arm in the three groups of H-bridge converters and the two ends of the emitter of the lower switch tube of each bridge arm;
the controller is connected with and controls the on-off of the excitation circuit, the three groups of H-bridge converters and the power main switch: when the doubly salient electro-magnetic motor works normally, the main power switch S13 is controlled to be conducted, and the three-phase armature winding forms an uncontrolled rectifier bridge through diodes in three groups of H-bridge converters to generate electricity; when detecting that the double-salient electro-magnetic motor has an excitation fault, disconnecting the excitation circuit, and controlling the on-off of the power main switch S13 by adopting hysteresis loop control, so that the voltage of the boost capacitor is greater than the load voltage of the load to promote the bus voltage for carrying out winding excitation.
The beneficial technical effects of the invention are as follows:
the application discloses an electric excitation doubly salient motor capable of guaranteeing fault-tolerant power generation power by improving bus voltage, before excitation fault occurs, the electric excitation doubly salient motor generates power in a traditional uncontrolled rectification power generation mode, after the excitation fault occurs, the electric excitation doubly salient motor is switched to a fault power generation mode, armature current quickly reaches a current reference value required by fault-tolerant power generation operation of the excitation fault by improving the bus voltage, high bus voltage can be achieved when a winding is excited, quick excitation is achieved, output power is greatly improved, fault-tolerant power generation power of the motor during the fault operation of the excitation fault is improved, reliability of operation of the electric excitation doubly salient motor under various environments is improved, and the electric excitation doubly salient motor is suitable for being applied to industries such as aerospace and automobiles.
In addition, the electro-magnetic doubly salient motor adopts three groups of H-bridge converters, which is beneficial to making each phase winding independent, the problem of current gap possibly caused by midpoint potential change does not exist, and the control strategy is more flexible. The motor does not need to be connected in series with power consumption in the power generation process, so that the loss is reduced, the power generation efficiency can be improved, and the possibility of maintaining fault-tolerant operation when the armature winding breaks down exists besides the function of loss of excitation fault tolerance.
Drawings
Fig. 1 is a control structure diagram of an electrically excited doubly salient motor of the present application.
Fig. 2 is a schematic diagram of the control logic of the electrically excited doubly salient machine of the present application.
Detailed Description
The following further describes the embodiments of the present invention with reference to the drawings.
The application discloses an electric excitation doubly salient motor capable of ensuring fault-tolerant power generation power by improving bus voltage, please refer to fig. 1, and the electric excitation doubly salient motor comprises a controller, a salient pole stator and rotor structure, an excitation circuit, a main power supply E, three groups of H-bridge converters, a load R, a load energy storage capacitor C1, a power main switch S13 and a boost capacitor C2. The power main switch S13 in this application is implemented by a switch tube.
The salient pole stator-rotor structure comprises a stator and a rotor, wherein the stator is provided with a three-phase armature winding and an excitation winding Lf. Excitation winding L in structure of connecting salient pole stator and rotor by excitation circuitfSpecifically, the excitation circuit comprises an excitation power supply UfAnd H-bridge excitation converter, excitation side power supply UfThe direct current side of the H-bridge excitation converter is connected, and the middle point of two bridge arms of the H-bridge excitation converter is connected with an excitation winding LfThe outlet end of the transformer.
The middle points of two bridge arms of each group of H-bridge converters are respectively connected with two ends of a one-phase armature winding in the salient pole stator-rotor structure, and specifically, the three-phase armature winding comprises an A-phase winding LaPhase B winding LbAnd a C-phase winding LcFirst, aThe H-bridge converter is connected with the A-phase winding LaThe second H-bridge converter is connected with the phase-B winding LbThe third H-bridge converter is connected with the C-phase winding Lc。
The positive pole of the main power supply E is connected with the collectors of the upper switching tubes of the bridge arms in the three groups of H-bridge converters through a diode D13, and the negative pole of the main power supply E is connected with the emitters of the lower switching tubes of the bridge arms in the three groups of H-bridge converters.
The load R is connected with a load energy storage capacitor C1 in parallel and connected with a first end of a power main switch S13, and a second end of the power main switch S13 is connected with the collector of the upper switch tube of each bridge arm through a diode D14. The emitting electrodes of the upper switch tubes of each bridge arm in the three groups of H-bridge converters are respectively connected to the second end of the power main switch S13 through a diode, and the lower switch tubes of each bridge arm are respectively connected with a diode in an inverse parallel mode.
And the boosting capacitor C2 is connected in parallel to the two ends of the collector of the upper switching tube of each bridge arm and the emitter of the lower switching tube of each bridge arm in the three groups of H-bridge converters.
The three groups of H-bridge converters have the same structure, each H-bridge converter comprises a first bridge arm and a second bridge arm which are respectively formed by connecting an upper switch tube and a lower switch tube in series in a reverse direction, collectors of the upper switch tubes in the two bridge arms are connected, an emitter of the upper switch tube in the first bridge arm is connected with the second end of the power main switch S13 through a diode and an electronic switch, and an emitter of the upper switch tube in the second bridge arm is connected with the second end of the power main switch S13 through a diode; two ends of a lower switch tube in the two bridge arms are respectively connected with a diode in parallel in a reverse direction. As shown in fig. 1, the first H-bridge converter includes an upper switching tube S1 and a lower switching tube S2 in the first arm, and an upper switching tube S3 and a lower switching tube S4 in the second arm, the second H-bridge converter includes an upper switching tube S5 and a lower switching tube S6 in the first arm, and an upper switching tube S7 and a lower switching tube S8 in the second arm, and the third H-bridge converter includes an upper switching tube S9 and a lower switching tube S10 in the first arm, and an upper switching tube S11 and a lower switching tube S12 in the second arm. Diodes D2, D4, D6, D8, D10 and D12 are connected in parallel at two ends of the lower switching tubes S2, S4, S6, S8, S10 and S12 in sequence, the anodes of the diodes are connected with the emitters of the corresponding lower switching tubes, and the cathodes of the diodes are connected with the collectors of the corresponding lower switching tubes. The upper switch tube S1 is connected to S13 through a diode D1 and an electronic switch K1, the upper switch tube S5 is connected to S13 through a diode D5 and an electronic switch K2, and the upper switch tube S9 is connected to S13 through a diode D9 and an electronic switch K3. The upper switching tubes S3, S7 and S11 are connected to S13 in sequence by diodes D3, D7 and D11, respectively.
The controller is connected with and controls the on-off of each switching tube in the excitation circuit, each switching tube in the three groups of H-bridge converters and the power main switch S13. Besides, various sensors are arranged in the electrically excited doubly salient motor and connected to a controller to acquire various parameter values, specifically: the position sensor is arranged in the salient pole stator and rotor structure and is used for acquiring a rotor position signal theta and an excitation winding LfA current sensor is arranged to collect the current i of the excitation windingfThe three-phase armature windings are respectively provided with current sensors to adopt three-phase winding current ia、ib、icA voltage sensor is arranged at the position of the load R to collect the load voltage U0The positive electrode of the boosting capacitor C2 is provided with a voltage sensor for collecting the voltage U of the boosting capacitorc2。
The operation of the electrically excited doubly salient machine is described below with reference to the structure shown in fig. 1:
when the electro-magnetic doubly salient motor works normally: when the current sensor does not detect the excitation fault, the electric excitation double-salient pole motor works in a generator state, the controller controls the power main switch S13 to be conducted, and the three-phase armature winding forms an uncontrolled rectifier bridge through the diodes in the three groups of H-bridge converters to generate electricity. Specifically, in fig. 1, the controller controls the power main switch S13 to be continuously turned on, controls all the upper switch tubes and the lower switch tubes S1 to S12 in the three groups of H-bridge converters to be turned off, controls three electronic switches K1, K2 and K3 in the three groups of H-bridge converters to be turned on, and controls the three-phase armature winding to form an uncontrolled rectifier bridge through the diodes D1 to D12 in the three groups of H-bridge converters to generate power.
When the current sensor detects an excitation fault, the controller controls to disconnect the excitation circuit, switches to a fault-tolerant mode to operate, and controls by adopting hysteresis controlThe power control main switch S13 is switched on and off, so that the voltage U of the boost capacitorc2Greater than the load voltage U of the load0Is removable Uc2>1.2U0Therefore, the bus voltage is improved to carry out winding excitation, so that the winding excitation can have higher bus voltage, the quick excitation is realized, and the output power is increased. Specifically, in fig. 1, a controller controls three electronic switches K1, K2, and K3 in three groups of H-bridge converters to be turned off, hysteresis control is adopted to control the on-off of a power main switch S13, and a corresponding hysteresis loop width is adopted, and the hysteresis loop width is set to be 0.5V in the present application. And then controlling the states of corresponding upper switching tubes and/or lower switching tubes in the three groups of H-bridge converters according to the current electrical angle interval of the motor. The specific control strategy is as follows, please refer to the control law shown in fig. 2:
when the electrical angle of the motor is at 0, thetaoffIn the interval of-120 degrees, an upper switching tube S9 of a first bridge arm and a lower switching tube S12 of a second bridge arm in a third H-bridge converter are switched on, so that a C-phase winding is in an excitation phase;
when the electrical angle of the motor is positioned in [ theta ]off-120°，θon) During interval, all switching tubes in the three H-bridge converters are controlled to be in an off state, so that the C-phase winding starts to generate electricity;
when the electrical angle of the motor is positioned in [ theta ]on，θoff) During interval, an upper switch tube S1 of a first bridge arm and a lower switch tube S4 of a second bridge arm in the first H-bridge converter are conducted, so that an A-phase winding is in an excitation stage, and a C-phase winding is continuously in a power generation stage;
when the electrical angle of the motor is positioned in [ theta ]off，θonIn the interval of +120 degrees, all switching tubes in the three H-bridge converters are controlled to be in an off state, so that the A-phase winding starts to generate electricity;
when the electrical angle of the motor is positioned in [ theta ]on+120°，θoffIn the +120 DEG interval, an upper switch tube S5 of a first bridge arm and a lower switch tube S8 of a second bridge arm in the second H-bridge converter are conducted, so that a B-phase winding is in an excitation stage, and an A-phase winding is continuously in a power generation stage;
when the electrical angle of the motor is positioned in [ theta ]off+120°，θonIn the interval of +240 degrees, all switching tubes in the three H-bridge converters are controlled to be in an off state, so that the B-phase winding starts to generate electricity;
when the electrical angle of the motor is positioned in [ theta ]onIn the interval of +240 degrees and 360 degrees, an upper switching tube S9 of a first bridge arm and a lower switching tube S12 of a second bridge arm in a third H-bridge converter are conducted, so that a C-phase winding is in an excitation phase, and a B-phase winding is continuously in a power generation phase;
wherein, thetaonRepresenting the armature winding field-on angle, θoffRepresenting the excitation off-angle of the armature winding by 0 °<θon<120°，120°<θoff<240°。
The controller performs PI regulation on the error between the output voltage and the given voltage to obtain given current in the process of controlling the states of the switching tubes of the three groups of H-bridge converters, performs PI regulation on the given current and the current of the current excited winding to obtain corresponding duty ratio, and if the output voltage is lower than the given voltage, the controller increases the duty ratios of the switching tubes of the three groups of H-bridge converters according to the obtained corresponding duty ratio; if the output voltage is higher than the given voltage, the controller reduces the duty ratio of the switching tubes of the three groups of H-bridge converters according to the obtained corresponding duty ratio so as to carry out chopping control on the current of the three-phase armature winding and realize closed-loop control on the output voltage.
What has been described above is only a preferred embodiment of the present application, and the present invention is not limited to the above embodiment. It is to be understood that other modifications and variations directly derivable or suggested by those skilled in the art without departing from the spirit and concept of the present invention are to be considered as included within the scope of the present invention.