CN110011592B - Method for expanding constant-torque variable-frequency speed regulation range of alternating-current motor by adopting Y/YY conversion - Google Patents
Method for expanding constant-torque variable-frequency speed regulation range of alternating-current motor by adopting Y/YY conversion Download PDFInfo
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02P—CONTROL OR REGULATION OF ELECTRIC MOTORS, ELECTRIC GENERATORS OR DYNAMO-ELECTRIC CONVERTERS; CONTROLLING TRANSFORMERS, REACTORS OR CHOKE COILS
- H02P25/00—Arrangements or methods for the control of AC motors characterised by the kind of AC motor or by structural details
- H02P25/16—Arrangements or methods for the control of AC motors characterised by the kind of AC motor or by structural details characterised by the circuit arrangement or by the kind of wiring
- H02P25/18—Arrangements or methods for the control of AC motors characterised by the kind of AC motor or by structural details characterised by the circuit arrangement or by the kind of wiring with arrangements for switching the windings, e.g. with mechanical switches or relays
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02P—CONTROL OR REGULATION OF ELECTRIC MOTORS, ELECTRIC GENERATORS OR DYNAMO-ELECTRIC CONVERTERS; CONTROLLING TRANSFORMERS, REACTORS OR CHOKE COILS
- H02P27/00—Arrangements or methods for the control of AC motors characterised by the kind of supply voltage
- H02P27/04—Arrangements or methods for the control of AC motors characterised by the kind of supply voltage using variable-frequency supply voltage, e.g. inverter or converter supply voltage
- H02P27/06—Arrangements or methods for the control of AC motors characterised by the kind of supply voltage using variable-frequency supply voltage, e.g. inverter or converter supply voltage using dc to ac converters or inverters
- H02P27/08—Arrangements or methods for the control of AC motors characterised by the kind of supply voltage using variable-frequency supply voltage, e.g. inverter or converter supply voltage using dc to ac converters or inverters with pulse width modulation
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Abstract
The invention relates to a method for expanding the constant-torque variable-frequency speed regulation range of an alternating-current motor by adopting Y/YY conversion. When the voltage of the motor rises to a rated value along with the frequency, Y/YY conversion is carried out on the stator winding of the alternating current motor, so that the number of turns of each phase of winding in series is reduced to half of the number of turns of the original phase of winding, and half of the power supply voltage of the winding is reduced, so that the winding obtains a lifting space equivalent to one time of voltage again, and the constant torque speed regulation range of the system can be doubled under a new winding connection mode. The invention realizes the purpose of expanding the constant torque speed regulation range of the motor under the conditions of not increasing the power supply voltage and not increasing the number of semiconductor switching devices of the inverter circuit, and the phase of the winding voltage before and after Y/YY conversion is still unchanged, thereby bringing convenience to the control.
Description
Technical Field
The invention relates to the fields of power electronics, DSP technology, motors and electric appliances, in particular to a method for expanding the constant-torque variable-frequency speed regulation range of an alternating-current motor by adopting Y/YY conversion.
Background
The constant torque speed regulating range of the existing AC motor frequency-conversion speed regulating system below the fundamental frequency (50HZ) is strongly restricted by the rated voltage of the motor, when the voltage rises to the rated voltage U along with the rotating speed (or frequency)NIn the process, the constant torque speed regulation reaches the limit, although the output frequency can be continuously increased to increase the rotating speed, the excitation must be reduced, so that the torque is reduced along with the increase of the rotating speed, the constant power speed regulation belongs to the constant torque speed regulation, and the driving requirement of keeping constant torque output under the condition of high speed (above fundamental frequency) cannot be met. For example, the air resistance of an electric vehicle or a high-speed train increases with the square of the running speed, and when the running speed increases to a certain value, the air resistance accounts for the main part of the whole running resistance. Therefore, the constant torque speed regulation range of the alternating current motor is expanded, and the high output torque is still achieved under the high-speed condition, so that the method has important significance for realizing high-speed operation under heavy load.
At present, a method for increasing the rated voltage of a motor is mainly adopted for expanding the constant torque speed regulation range of an alternating current motor, so that the power supply voltage and the voltage withstanding grade of a power semiconductor device are correspondingly increased. However, the improvement of the withstand voltage of the power semiconductor device is limited by various factors, and besides the manufacturing technology, the excessively high du/dt in the use has adverse effects on the reliability of the power semiconductor device and the insulation of the motor. At present, the contradiction [1-16] is solved by adopting a three-level inversion technology at home and abroad, so that the withstand voltage value of each power semiconductor device can be halved, the du/dt of the device is effectively reduced, and the advantage of improving the quality of output voltage waveform is brought. But also a problem of fluctuation of neutral point potential (neutral point potential) occurs [4-10 ]. As the inverter output voltage and current increase, or in low power factor operation, the neutral point potential fluctuation increases, even causing low frequency oscillation, resulting in deterioration of the inverter performance. Further, the number of power semiconductor devices used is doubled, and the larger the number of levels, the more the number of devices required, the higher the cost, and the more complicated the control accompanying this, and the reliability becomes a problem [11-15 ].
The use of cell-cascaded multilevel inversion is also an effective approach [16] [17 ]. The method has the advantages of small harmonic pollution, high input power factor, good output waveform and low du/dt, but also has the defects of more series units and complex control, each series unit needs to be supplied with power by an independent transformer secondary winding with a phase staggered by a certain angle, the number of required secondary side windings is the same as that of the series units, and the windings are complex in connection, so that the additional transformer additionally occupies a large cost and space.
Direct reduction of the number of turns of the motor winding can also be regarded as a way to expand the constant torque speed regulation range, but the method tends to make the PWM in an extremely deep regulation state when the motor runs at low speed, namely, the modulation M value is required to be reduced more, so that the negative effects of increased total harmonic distortion THD (total harmonic distortion) 18-21 and more prominent dead zone effect are brought, and the low-speed performance is seriously weakened.
The documents [22] to [26] adopt a method of combining pole changing and frequency conversion to expand the speed regulating range of the constant power of the motor, but the speed regulating range of the constant torque is still unchanged. This method is only applicable to load types where the torque decreases inversely with the rotational speed. In addition, the control adopted for keeping the currents of the two sets of windings in a good balance state is also complex.
Document [27]]The method for expanding the constant-torque frequency-conversion speed-regulation range of the alternating-current motor by adopting the Y/delta winding conversion method has the advantages of low cost, simpler control and the like, but the expansion range of the constant-torque frequency-conversion speed-regulation is only limited to
And the phase shift of the winding phase voltage pi/6 needs to be considered before and after Y/delta conversion, otherwise, larger transient current can be caused, and the safety of the power semiconductor device is threatened.
In summary, the existing technical solutions for expanding the constant torque speed regulation range have the following disadvantages:
1. and a three-level inversion technology is adopted. The technology improves the voltage capability of a direct current bus borne by each bridge arm by increasing the number of power semiconductor switching devices used by each bridge arm, so as to improve the inversion output voltage and achieve the purpose of expanding the constant torque speed regulation range of the motor. However, the number of power semiconductor devices used is doubled, and the larger the number of levels is, the more the number of devices is required, which is accompanied by an increase in cost and control complexity, and reliability is also a big problem.
2. The unit series type multilevel inversion technology is adopted. The technology improves the total inversion output voltage by a method of serially overlapping each inversion unit, thereby achieving the purpose of expanding the constant torque speed regulation range of the motor. The more the number of series connected inversion units is, the larger the output voltage is, but the number of power semiconductor devices and the control complexity are increased, and each inversion unit needs to be supplied with power by an independent secondary winding of an additional transformer with a phase staggered by a certain angle, the number of required secondary windings is the same as the number of series connected units, and the windings are connected in a complex manner, so that the additional transformer additionally occupies a large cost and space.
3. Technique using a Y/Delta winding transformation method [27]]. Although the technology has the advantages of low cost, simpler control and the like, the expansion range of the constant-torque variable-frequency speed regulation is limited
And the phase shift of the winding phase voltage pi/6 needs to be considered before and after Y/delta conversion, thereby adding a corresponding processing link. Otherwise, large transient current can be caused, and the safety of the power semiconductor device is threatened.
Reference documents:
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three-level NPC inverter at high modulation index includingovermodulation region,with neutral point balancing[J].IEEE Transactions onIndustry Applications,2007,43(3):751-760.
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[27] A system and a method [ P ] for expanding the constant-torque variable-frequency speed regulation range of an alternating-current motor based on Y-delta transformation: ZL201510151913.8,2017-09-26.
Disclosure of Invention
The invention aims to provide a method for expanding the constant-torque variable-frequency speed regulation range of an alternating-current motor by adopting Y/YY conversion, which realizes the purpose of expanding the constant-torque speed regulation range of the motor under the conditions of not increasing the power supply voltage and increasing the number of semiconductor switching devices of an inverter circuit, and the phase of winding voltage before and after the Y/YY conversion is kept unchanged, thereby bringing convenience to control.
In order to achieve the purpose, the technical scheme of the invention is as follows: a method for expanding the constant torque frequency-conversion speed-regulation range of an AC motor by adopting Y/YY conversion divides each phase of winding of a three-phase AC motor into two identical parts of winding, and when the three-phase winding is Y-connected, the two parts of winding of each phase are connected in series end to end; when three-phase windings are YY-connected, two parts of windings of each phase are connected in parallel, namely the windings are connected end to end and the windings are connected end to end, so that the number of turns of the windings connected in parallel is half less than that of the windings connected in series, and the area of a conductor is doubled; the Y/YY conversion time is as follows: when the voltage of the three-phase alternating current motor rises to a rated value along with the frequency, Y/YY conversion is applied to the stator winding of the three-phase alternating current motor, so that the number of turns of each phase of winding in series is reduced to half of the number of turns, and the supply voltage applied to the winding is reduced by half at the same time, which is equivalent to that the winding obtains a lifting space of one time of voltage again, and therefore, the constant torque speed regulation range of the three-phase alternating current motor speed regulation system can be doubled.
In one embodiment of the invention, because Y/YY conversion is applied to the stator winding of the three-phase alternating current motor, the number of turns of each phase of winding in series is reduced to half of the original number of turns, and the supply voltage of the winding is reduced by half; for this purpose, the modulation M of PWM is reduced by half, so that the phase voltage is converted from U after Y/YY conversionNReduced to UN/2 to maintain the air gap flux ΦmIs constant.
In an embodiment of the present invention, the method is specifically implemented as follows:
the constant-torque variable-frequency speed regulating system of the alternating-current motor comprises a DSP control unit, a three-phase alternating-current motor, a speed sensor, a Y/YY conversion control circuit and a variable-frequency power supply circuit, wherein the DSP control unit is used for controlling the Y/YY conversion control circuit to enable a three-phase winding of the three-phase alternating-current motor to carry out Y/YY conversion; the variable frequency power supply circuit supplies power to the three-phase alternating current motor through the Y/YY conversion control circuit, and the speed sensor is used for detecting the rotating speed of the three-phase alternating current motor;
is provided with a UYφPhase voltage, U, for windings of three-phase AC motors in Y connectionYYφPhase voltage under YY connection; when the frequency f of the three-phase AC motor supply1Up to the rated value f1NAt this time, the synchronous speed of the corresponding three-phase AC motor is n1NThree-phase AC motor phase voltage U with PWM modulation degree M of 1φUp to the rated value UNThe Y/YY conversion control circuit performs Y/YY conversion operation on the three-phase alternating current motor windings, namely changing Y connection into YY connection, and the number of turns of each phase winding of the three-phase alternating current motor in series connection is reduced by half so as to ensure that air gap flux phi of the three-phase alternating current motor before and after conversionmWithout change, the winding phase voltage should also be reduced by half, i.e. UYYφ＝UYφ/2＝U N2; for this purpose, the modulation factor M of the PWM is reduced by half, i.e. M is 1/2, so that the phase voltage is converted from U after Y/YYNReduced to UN/2 to maintain the air gap flux ΦmIs constant, i.e. phim＝ΦmN(ii) a Then with f1From f1NTo 2f1NThe modulation M value is increased from M to 1/2 to M to 1, corresponding to the three-phase AC motor phase voltage UYYφBy UNPer 2 Up to the rated value UNThe effect is equivalent to that the rated value of the voltage applied to the three-phase alternating current motor is increased to 2 times of the original value, and the constant-torque speed regulation range is enlarged to 2 times of the original value; control is also possible when the rotational speed is changed from high to low in reverse.
In one embodiment of the present invention, to avoid the rotation speed of the three-phase AC motor being n1NThe nearby fluctuation causes frequent Y/YY conversion operation, and the switching rotation speed n of two Y/YY conversions is set1NAnd n'1N，n1NA critical rotation speed for performing a Y → YY conversion operation on the three-phase AC motor winding when the rotation speed is increased and changed; n'1NA critical rotation speed for executing YY → Y inverse transformation operation when the rotation speed is reduced and changed; and Δ n1＝n1N-n′1N。
In an embodiment of the present invention, when the three-phase ac motor winding performs the Y → YY conversion operation, the DSP control unit controls the variable frequency power supply circuit to block the variable frequency output, and after the conversion is completed, the variable frequency output is turned on, or vice versa, when the three-phase ac motor winding performs the YY → Y inverse conversion operation.
In an embodiment of the invention, the Y-YY conversion control circuit includes first to third single-pole double-throw switches, a fourth switch, a fifth switch; the fixed end of the first single-pole double-throw switch is connected with the head end of the second part of the U-phase winding, the first switching end of the first single-pole double-throw switch is connected with the tail end of the first part of the U-phase winding and one end of the fourth switch, and the second switching end of the first single-pole double-throw switch is connected with the head end of the first part of the U-phase winding; the fixed end of the second single-pole double-throw switch is connected with the head end of the second part of the winding of the V-phase winding, the first switching end of the second single-pole double-throw switch is connected with the tail end of the first part of the winding of the V-phase winding, one end of the fifth switch and the other end of the fourth switch at three ends, and the second switching end of the second single-pole double-throw switch is connected with the head end of the first part of the winding of the V-phase winding; the fixed end of a third single-pole double-throw switch is connected with the head end of the second part of winding of the W-phase winding, the first switching end of the third single-pole double-throw switch is connected with the tail end of the first part of winding of the W-phase winding and the other end of a fifth switch, and the second switching end of the third single-pole double-throw switch is connected with the head end of the first part of winding of the W-phase winding; the tail end of the second part winding of the U-phase winding, the tail end of the second part winding of the V-phase winding and the tail end of the second part winding of the W-phase winding are connected with each other.
Compared with the prior art, the invention has the following beneficial effects:
1. the vector control variable-frequency speed regulation method combined with Y/YY conversion can obviously enlarge the constant-torque variable-frequency speed regulation range. Because the number of turns of the windings in series after the Y/YY conversion of the motor is reduced by half, the constant-torque variable-frequency speed regulation range is correspondingly increased to 2 times of the original range, and the energy density of the motor is obviously improved. Although the system is slightly complex due to the addition of the Y/YY conversion control circuit link, the benefit is remarkable due to the fact that the output power is greatly improved.
2. The number of power semiconductor devices of the inverter circuit is not increased, the power supply voltage is not increased, and only the Y/YY conversion control switch is added. Therefore, the total cost is much lower than that of a three-level method and a unit series multi-level method, the control is simpler, and the reliability is improved;
3. if the semiconductor switch is adopted to control Y/YY conversion, the required process is only microsecond order of magnitude, the process can be regarded as a seamless conversion process, the dynamic performance of the speed regulation system is hardly influenced, and the control requirement of high dynamic performance is well met. If the low-voltage switch is used to control the Y/YY conversion, although the time for completing the contact action needs tens of milliseconds, the time is still far lower than the system time constant, and the influence on the dynamic performance is small.
4. The method of the scheme is compared with a method for expanding the constant torque speed regulation range by adopting Y/delta conversion [27]]With a larger extension range, i.e. 2 times of extension, higher than that of Y/delta conversion
And (5) expanding the times. Therefore, the energy density of the motor is improved more remarkably, the phase of the winding voltage before and after Y/YY conversion is kept unchanged (the phase shift of pi/6 is realized by Y/delta conversion), and convenience is brought to control. The disadvantage is that the Y/YY conversion uses a slightly larger number of switches than the Y/Δ conversion. Nevertheless, the comprehensive advantages of the scheme are obviously better than those of the Y/delta conversion method.
Drawings
FIG. 1 is a schematic diagram of the Y/YY connection of the windings of the present invention.
FIG. 2 shows the variable frequency speed control characteristics of the present invention combined with Y/YY conversion.
FIG. 3 is a block diagram of an AC motor speed regulation system incorporating the Y/YY conversion of the present invention.
FIG. 4 is a Y/YY conversion control circuit of the present invention.
FIG. 5 is a block diagram of the Y/YY conversion control logic of the present invention.
Detailed Description
The technical scheme of the invention is specifically explained below with reference to the accompanying drawings.
The invention adopts a new method of combining Y/YY conversion and frequency conversion to solve the problem of expanding the speed regulation range of constant torque. The basic idea is that when the motor voltage rises to a rated value along with the frequency, the Y/YY conversion is applied to the stator winding of the alternating current motor, so as to reduce the number of turns of each phase winding in series to half of the original number of turns, and simultaneously reduce half of the power supply voltage of the winding, which is equivalent to make the winding obtain a lifting space of one time of voltage again, the constant torque speed regulating range of the system can be extended by one time under a new winding connection mode, which is obviously higher than the expansion range of the document [27], and the winding voltage phase before and after the Y/YY conversion is kept unchanged (the phase shift of pi/6 is realized by the Y/delta conversion), thereby bringing convenience to the control. Therefore, the purpose of expanding the constant torque speed regulation range of the motor is achieved under the conditions of not increasing the power supply voltage and not increasing the number of semiconductor switching devices of the inverter circuit.
Specifically, the invention provides a method for expanding the constant torque variable frequency speed regulation range of an alternating current motor by adopting Y/YY conversion, wherein each phase of winding of the three-phase alternating current motor is divided into two identical parts of winding, and when the three-phase winding is Y-connected, the two parts of winding of each phase are connected in series end to end; when three-phase windings are YY-connected, two parts of windings of each phase are connected in parallel, namely, the windings are connected end to end and the windings are connected end to end, so that the number of turns of the windings connected in parallel is reduced by half compared with the number of turns of the windings connected in series, and the area of a conductor is doubled; the Y/YY conversion time is as follows: when the voltage of the three-phase alternating current motor rises to a rated value along with the frequency, Y/YY conversion is carried out on the stator winding of the three-phase alternating current motor, the number of turns of each phase of winding in series is reduced to half of the number of turns of the original winding, and meanwhile, half of the power supply voltage of the winding is reduced, which is equivalent to that the winding obtains a lifting space of one time of voltage again, so that the constant torque speed regulation range of the three-phase alternating current motor speed regulation system is doubled.
The following is a specific implementation of the present invention.
The speed regulating system adopts a three-phase alternating current motor, and each phase winding is divided into two parts, namely two parts of windings with completely the same number of turns, wire diameter, pole number and structure are connected to form one phase winding. When the three-phase winding is Y-connected, the two parts of each phase are connected in series end to end; when the three-phase windings are YY-connected, the three-phase windings are connected in parallel, namely, the three-phase windings are connected end to end and the three-phase windings are connected end to end. The number of turns of the windings after parallel connection is reduced by half compared with the number of turns of the windings in series connection, and the area of the conductor is doubled. As shown in fig. 1.
The continuation mechanism of the constant torque speed regulation range obtained from the change of each phase voltage before and after the Y/YY conversion and the change of the PWM modulation M value associated therewith is shown in fig. 2.
FIG. 2 is a diagram showing the frequency f of power supply to the motor by the abscissa physical quantity1. Is provided with a UYφFor the phase voltage, U, of the stator winding of the motor at the Y connectionYYφThe phase voltage at the YY connection. When the supply frequency f1Up to the rated value f1N(corresponding to a synchronous speed of n1NPWM modulation degree M is 1, motor phase voltage UφUp to the rated value UN) When the motor is started, the stator winding of the motor is subjected to Y/YY conversion operation, namely Y connection is changed into YY connection, and the number of turns of each phase winding of the motor in series connection is reduced by half so as to reduce the air gap flux phi of the motor before and after conversionmWithout change, the winding phase voltage should also be reduced by half, i.e. UYYφ＝UYφ/2＝UN/2. For this purpose, the modulation factor M of the PWM is reduced by half, i.e. M is 1/2, so that the phase voltage is converted from U after Y/YYNReduced to UN/2 to maintain the air gap flux ΦmIs constant, i.e. phim＝ΦmN. If the load is not changed before and after the Y/YY conversion, the output power of the motor is required to be unchanged. Thus, when the phase voltage is reduced by half, the current is doubled accordingly. The area of the winding conductor under YY connection is just 2 times of that of Y connection, and the requirement of multiplied current on the conductor sectional area is just met. Then with f1From f1NTo 2f1NThe modulation degree M value is increased from M to 1/2 to M to 1, and the corresponding motor phase voltage U corresponds toYYφBy UNPer 2 Up to the rated value UNThe effect is equivalent to that the rated value of the phase voltage applied to the motor is increased to 2 times of the original value, and the constant-torque speed regulation range is enlarged by the same factor.
According to the principle, the constant torque speed regulation range can be expanded to 2 times of the original value by combining Y/YY conversion and frequency conversion. The specific implementation is as follows:
the block diagram of the AC motor speed regulating system adopting the combination of Y/YY conversion and frequency conversion is shown in FIG. 3. The ac motor in the figure is an asynchronous motor or a permanent magnet motor. The variable frequency power supply supplies power to the motor through a Y/YY conversion control circuit. The Y/YY conversion control circuit is composed of a semiconductor switch device or a low-voltage electrical appliance switch, and the specific circuit structure is shown in figure 4. The circuit is controlled by the DSP through an I/O interface. When the DSP measures that the rotating speed of the motor is 0 < n1＜n1NControl K of FIG. 41、K2、K3Normally closed contact closure of transfer switch, K4、K5When the motor is switched off, the stator winding of the motor is in Y connection; when the rotating speed n1Rise to n1NWhen the motor is started, the DSP blocks the frequency conversion output, then sends an instruction to the Y/YY conversion control circuit, and performs Y/YY conversion operation on the motor to enable the switch K to be switched on1、K2、K3The normally closed contact of (A) is opened, the normally open contact is closed, and K is enabled4、K5Closed, the winding becomes YY connected. And after the Y/YY conversion is finished, the DSP starts the frequency conversion output. According to the principle that the magnetic flux is not changed before and after the transformation, half of the modulation degree M value of PWM is adjusted downwards to enable U to be adjustedYYφ＝UYφ/2＝UN/2 to keep the motor air gap flux phi before and after Y/YY conversionm＝ΦmNIs constant. Control is also possible when the rotational speed is changed from high to low in reverse. K in FIG. 41、K2、K3、K4、K5Semiconductor switches may also be used.
As mentioned above, since the phase voltage of the winding of the motor is changed before and after the Y/YY conversion, the modulation degree M value, which is a parameter for controlling the output magnitude of the PWM voltage, is required to be automatically adjusted along with the conversion so as to maintain the air gap flux phimIs constant. For this purpose, a variable M representing different connections of the winding is set in the DSP control programY/YYWhen the stator winding of the motor is Y-connected, M Y/YY1 is ═ 1; when the windings are connected for YY,
to MY/YYThe two assignments of (1) are realized by a DSP main program and are also referred to by a PWM interruption subprogram in real time. The interrupt subroutine is preceded by M before calculating the PWM pulsesY/YYWith another variable M*Multiplying (apparent modulation degree) to obtain modulation degree M which actually influences the PWM output voltage, namely M is M*×MY/YYThe program automatically adjusts the M value according to the change of the number of turns of the winding before and after the Y/YY conversion, and the PWM output voltage is calculated in real time according to the M value. Variable M*Representing the variation range of the phase voltage of the motor, and the value range depends on which PWM algorithm is adopted, if SPWM (sinusoidal pulse width modulation) algorithm is adopted, M is*∈[0,2](apparent modulation degree M*By UdcA base value of UdcIs the dc bus voltage, the same applies below); if SVPWM (space vector pulse width modulation) algorithm is adopted, then
In addition, to avoid the rotation speed being at n1NThe nearby fluctuation causes frequent Y/YY conversion operation, and the switching rotation speed n of two Y/YY conversions should be set1NAnd n'1N，n1NThe critical rotating speed of the Y → YY conversion operation is applied to the stator winding of the motor when the rotating speed is increased and changed; n'1NThe critical rotation speed of YY → Y inverse transformation operation is applied when the rotation speed is reduced and changed. With a return difference, i.e. Δ n, between them1＝n1N-n′1N。
Y/YY conversion control and related MY/YYThe assignment is undertaken by the main program of the DSP, and the control logic is shown in FIG. 5. The main program is composed of two cyclic branches, and the positive or negative conversion operation of Y/YY is implemented according to the rotation speed variation condition and is given to MY/YYThe variables have different values. A branch steering logic control variable is set in the main program to control the main program to be steered to different branches for operation. When the synchronous rotating speed of the motor is measured to be 0<n1<n1NThen, the logic value of the logic control variable is set to 0, and the main routine is shifted to a branch for judging the increase and change of the rotation speed. Once the rotational speed n is measured1≥n1NWhen the motor stator winding is subjected to Y → YY conversion controlFront cover
Is assigned (this value is automatically referenced by the PWM interrupt subroutine, the same below). After the conversion is finished, the logic value of the logic control variable is set to 1, and the main program is converted into a branch for judging the decreasing change of the rotating speed. Once n is measured1＜n′1NWhen the motor is subjected to YY → Y reverse conversion control, M is givenY/YYAn assignment of 1. After the conversion is finished, the logic value of the logic control variable is made to be 0 again, and the main program is switched to a branch … for judging the increase and change of the rotating speed; the cycle is repeated, and the organic combination of Y/YY conversion and frequency conversion is realized.
The logic structure is embedded into the existing vector control PWM program, so that the speed regulation function of the vector control AC motor combining Y/YY conversion and frequency conversion can be realized, and the constant torque speed regulation range can be expanded to 2 times.
The above are preferred embodiments of the present invention, and all changes made according to the technical scheme of the present invention that produce functional effects do not exceed the scope of the technical scheme of the present invention belong to the protection scope of the present invention.
Claims (5)
1. A method for expanding the constant torque frequency-conversion speed-regulation range of an alternating current motor by adopting Y/YY conversion is characterized in that each phase of winding of a three-phase alternating current motor is divided into two identical parts of winding, and when the three-phase winding is Y-connected, the two parts of winding of each phase are connected in series end to end; when three-phase windings are YY-connected, two parts of windings of each phase are connected in parallel, namely the windings are connected end to end and the windings are connected end to end, so that the number of turns of the windings connected in parallel is half less than that of the windings connected in series, and the electric conduction area is doubled; the Y/YY conversion time is as follows: when the voltage of the three-phase alternating current motor rises to a rated value along with the frequency, Y/YY conversion is applied to the stator winding of the three-phase alternating current motor, so that the number of turns of each phase of winding in series is reduced to half of the number of turns, and the supply voltage applied to the winding is reduced by half at the same time, which is equivalent to that the winding obtains a lifting space of one time of voltage again, so that the constant torque speed regulating range of the three-phase alternating current motor speed regulating system can be doubled; for three phasesThe stator winding of AC motor is subjected to Y/YY conversion to reduce the number of turns in series of each phase winding to half of the original number of turns and simultaneously reduce the supply voltage applied to the winding by half, so that the modulation M value of PWM is correspondingly reduced by half to make the phase voltage from U after Y/YY conversionNReduced to UN/2 to maintain the air gap flux ΦmIs constant.
2. The method for expanding the constant-torque variable-frequency speed regulation range of the alternating-current motor by adopting Y/YY conversion as claimed in claim 1 is characterized by comprising the following concrete implementation processes:
the constant-torque variable-frequency speed regulating system of the alternating-current motor comprises a DSP control unit, a three-phase alternating-current motor, a speed sensor, a Y/YY conversion control circuit and a variable-frequency power supply circuit, wherein the DSP control unit is used for controlling the Y/YY conversion control circuit to enable a three-phase winding of the three-phase alternating-current motor to carry out Y/YY conversion; the variable frequency power supply circuit supplies power to the three-phase alternating current motor through the Y/YY conversion control circuit, and the speed sensor is used for detecting the rotating speed of the three-phase alternating current motor;
is provided with a UYφPhase voltage, U, for windings of three-phase AC motors in Y connectionYYφPhase voltage under YY connection; when the frequency f of the three-phase AC motor supply1Up to the rated value f1NAt this time, the synchronous speed of the corresponding three-phase AC motor is n1NThree-phase AC motor phase voltage U with PWM modulation degree M of 1φUp to the rated value UNThe Y/YY conversion control circuit performs Y/YY conversion operation on the three-phase alternating current motor windings, namely changing Y connection into YY connection, and the number of turns of each phase winding of the three-phase alternating current motor in series connection is reduced by half so as to ensure that air gap flux phi of the three-phase alternating current motor before and after conversionmWithout change, the winding phase voltage should also be reduced by half, i.e. UYYφ＝UYφ/2＝UN2; for this purpose, the modulation factor M of the PWM is reduced by half, i.e. M is 1/2, so that the phase voltage is converted from U after Y/YYNReduced to UN/2 to maintain the air gap flux ΦmIs constant, i.e. phim＝ΦmN(ii) a Then with f1From f1NTo 2f1NThe modulation M value is increased from M to 1/2 to M to 1, corresponding to the three-phase AC motor phase voltage UYYφBy UNPer 2 Up to the rated value UNThe effect is equivalent to that the rated value of the voltage applied to the three-phase alternating current motor is increased to 2 times of the original value, and the constant-torque speed regulation range is enlarged to 2 times of the original value; control is also possible when the rotational speed is changed from high to low in reverse.
3. The method for extending the range of constant-torque variable-frequency speed control of an AC motor using Y/YY conversion as claimed in claim 2, wherein the speed of the three-phase AC motor is prevented from being n1NThe nearby fluctuation causes frequent Y/YY conversion operation, and the switching rotation speed n of two Y/YY conversions is set1NAnd n'1N，n1NA critical rotation speed for performing a Y → YY conversion operation on the three-phase AC motor winding when the rotation speed is increased and changed; n'1NA critical rotation speed for executing YY → Y inverse transformation operation when the rotation speed is reduced and changed; and Δ n1＝n1N-n'1N。
4. The method as claimed in claim 2, wherein when the three-phase ac motor winding is subjected to Y → YY conversion, the DSP control unit controls the variable frequency power supply circuit to block the variable frequency output, and after the conversion is completed, the variable frequency output is turned on, or vice versa, when the three-phase ac motor winding is subjected to YY → Y inverse conversion.
5. The method for expanding the constant-torque variable-frequency speed regulation range of the alternating-current motor by adopting Y/YY conversion according to any one of claims 2 to 4, wherein the Y/YY conversion control circuit comprises a first single-pole double-throw switch, a third single-pole double-throw switch, a fourth switch and a fifth switch; the fixed end of the first single-pole double-throw switch is connected with the head end of the second part of the U-phase winding, the first switching end of the first single-pole double-throw switch is connected with the tail end of the first part of the U-phase winding and one end of the fourth switch, and the second switching end of the first single-pole double-throw switch is connected with the head end of the first part of the U-phase winding; the fixed end of the second single-pole double-throw switch is connected with the head end of the second part of the winding of the V-phase winding, the first switching end of the second single-pole double-throw switch is connected with the tail end of the first part of the winding of the V-phase winding, one end of the fifth switch and the other end of the fourth switch at three ends, and the second switching end of the second single-pole double-throw switch is connected with the head end of the first part of the winding of the V-phase winding; the fixed end of a third single-pole double-throw switch is connected with the head end of the second part of winding of the W-phase winding, the first switching end of the third single-pole double-throw switch is connected with the tail end of the first part of winding of the W-phase winding and the other end of a fifth switch, and the second switching end of the third single-pole double-throw switch is connected with the head end of the first part of winding of the W-phase winding; the tail end of the second part winding of the U-phase winding, the tail end of the second part winding of the V-phase winding and the tail end of the second part winding of the W-phase winding are connected with each other.
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