CN111628660A - Compressor variable frequency speed regulating system and control method of direct current bus voltage - Google Patents
Compressor variable frequency speed regulating system and control method of direct current bus voltage Download PDFInfo
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- CN111628660A CN111628660A CN202010507297.6A CN202010507297A CN111628660A CN 111628660 A CN111628660 A CN 111628660A CN 202010507297 A CN202010507297 A CN 202010507297A CN 111628660 A CN111628660 A CN 111628660A
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
- H02M5/00—Conversion of ac power input into ac power output, e.g. for change of voltage, for change of frequency, for change of number of phases
- H02M5/40—Conversion of ac power input into ac power output, e.g. for change of voltage, for change of frequency, for change of number of phases with intermediate conversion into dc
- H02M5/42—Conversion of ac power input into ac power output, e.g. for change of voltage, for change of frequency, for change of number of phases with intermediate conversion into dc by static converters
- H02M5/44—Conversion of ac power input into ac power output, e.g. for change of voltage, for change of frequency, for change of number of phases with intermediate conversion into dc by static converters using discharge tubes or semiconductor devices to convert the intermediate dc into ac
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
- H02J3/00—Circuit arrangements for ac mains or ac distribution networks
- H02J3/01—Arrangements for reducing harmonics or ripples
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
- H02M5/00—Conversion of ac power input into ac power output, e.g. for change of voltage, for change of frequency, for change of number of phases
- H02M5/40—Conversion of ac power input into ac power output, e.g. for change of voltage, for change of frequency, for change of number of phases with intermediate conversion into dc
- H02M5/42—Conversion of ac power input into ac power output, e.g. for change of voltage, for change of frequency, for change of number of phases with intermediate conversion into dc by static converters
- H02M5/44—Conversion of ac power input into ac power output, e.g. for change of voltage, for change of frequency, for change of number of phases with intermediate conversion into dc by static converters using discharge tubes or semiconductor devices to convert the intermediate dc into ac
- H02M5/453—Conversion of ac power input into ac power output, e.g. for change of voltage, for change of frequency, for change of number of phases with intermediate conversion into dc by static converters using discharge tubes or semiconductor devices to convert the intermediate dc into ac using devices of a triode or transistor type requiring continuous application of a control signal
- H02M5/458—Conversion of ac power input into ac power output, e.g. for change of voltage, for change of frequency, for change of number of phases with intermediate conversion into dc by static converters using discharge tubes or semiconductor devices to convert the intermediate dc into ac using devices of a triode or transistor type requiring continuous application of a control signal using semiconductor devices only
- H02M5/4585—Conversion of ac power input into ac power output, e.g. for change of voltage, for change of frequency, for change of number of phases with intermediate conversion into dc by static converters using discharge tubes or semiconductor devices to convert the intermediate dc into ac using devices of a triode or transistor type requiring continuous application of a control signal using semiconductor devices only having a rectifier with controlled elements
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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
- H02P25/02—Arrangements or methods for the control of AC motors characterised by the kind of AC motor or by structural details characterised by the kind of motor
- H02P25/022—Synchronous motors
- H02P25/024—Synchronous motors controlled by supply frequency
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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
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
- Y02E40/00—Technologies for an efficient electrical power generation, transmission or distribution
- Y02E40/40—Arrangements for reducing harmonics
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- Engineering & Computer Science (AREA)
- Power Engineering (AREA)
- Control Of Ac Motors In General (AREA)
Abstract
The invention provides a compressor variable frequency speed control system and a control method of direct current bus voltage, which comprises the following steps: the rectifier module converts the alternating-current input voltage into direct-current bus voltage; the inverter module is used for converting the DC bus voltage into a motor driving voltage; a motor driven by a motor driving voltage; the control module is used for adjusting the direct-current bus voltage output by the rectifying module; when the motor runs below the rated rotating speed, outputting the direct current bus voltage according to the alternating current input voltage; when the motor operates above the rated rotating speed, the direct current bus voltage is output according to the alternating current input voltage and the rotating speed of the motor. The invention greatly reduces the low-order harmonic wave of the power grid, improves the system efficiency, and the variable frequency speed control system is in the highest-efficiency working mode.
Description
Technical Field
The invention relates to the field of frequency conversion, in particular to a compressor frequency conversion speed regulation system and a control method of direct current bus voltage.
Background
In the existing variable frequency speed control system of the compressor, a three-phase alternating current Power supply is generally adopted for supplying Power on an application occasion with Power of more than 8kW, an uncontrolled rectifier bridge is adopted for rectification at a front stage, and an IPM Module (Intelligent Power Module) is adopted for three-phase inversion at a rear stage to provide alternating current input for a motor, as shown in fig. 1. The system has the disadvantages that firstly, diodes in the rectifier bridge belong to uncontrollable devices, and a large amount of low-order harmonic current can be injected into a power grid when the system works; secondly, the direct current bus voltage is uncontrollable, and the fluctuation of the bus voltage is increased along with the increase of the load power.
The speed regulation of the permanent magnet synchronous motor generally takes a rated rotating speed as a boundary point, constant magnetic flux variable frequency speed regulation is adopted below the rated rotating speed, and weak magnetic variable frequency speed regulation is adopted above the rated rotating speed. When the field weakening is accelerated, the exciting current for field weakening only does useless work, so that the loss of the motor is increased, and the efficiency of the motor is lowered. If the rotating speed can be increased by maintaining the magnetic flux unchanged above the rated rotating speed, the back electromotive force of the motor is inevitably increased, and the output voltage of the inverter module of the frequency converter, namely the terminal voltage of the motor, is also increased accordingly. In the prior art, a software overmodulation algorithm is adopted, but the voltage amplitude which can be improved by the method is limited, and the performance of the motor can be only slightly improved.
Therefore, how to reduce the low-order harmonic of the power grid and improve the efficiency of the variable frequency speed control system becomes one of the problems to be solved urgently by the technical personnel in the field.
Disclosure of Invention
In view of the above disadvantages of the prior art, an object of the present invention is to provide a variable frequency speed control system for a compressor and a method for controlling dc bus voltage, which are used to solve the problems of large low order harmonic of a power grid and low system efficiency in the prior art.
In order to achieve the above and other related objects, the present invention provides a method for controlling dc bus voltage in a variable frequency speed control system of a compressor, where the method for controlling dc bus voltage in a variable frequency speed control system of a compressor at least includes:
when the motor runs below the rated rotating speed, outputting the direct current bus voltage according to the alternating current input voltage;
and when the motor operates above the rated rotating speed, outputting the direct current bus voltage according to the alternating current input voltage and the rotating speed of the motor.
Optionally, when the motor is operating below the rated speed,
if the actual alternating current input voltage fluctuates within a first preset proportion range of the rated alternating current input voltage, setting the direct current bus voltage as a fixed value higher than the peak value of the rated alternating current input voltage;
if the actual alternating current input voltage fluctuates within a second preset proportion range of the rated alternating current input voltage, the direct current bus voltage is set to be higher than the peak value of the actual alternating current input voltage, and the direct current bus voltage changes along with the change of the actual alternating current input voltage;
if the actual alternating current input voltage fluctuates outside a first preset proportion range and a second preset proportion range of the rated alternating current input voltage, a power switch tube in the rectification module is turned off, and a fault signal is output;
and the minimum value of the second preset proportion range is greater than or equal to the maximum value of the first preset proportion range.
More optionally, when the actual ac input voltage fluctuates within a first subinterval of a second preset proportional range of the rated ac input voltage, the dc bus voltage is set higher than a peak value of the actual ac input voltage, and the dc bus voltage varies with variation of the actual ac input voltage;
and when the actual alternating current input voltage fluctuates in a second subinterval within a second preset proportion range of the rated alternating current input voltage, turning off a power switch tube in the rectification module, and entering an uncontrolled rectification mode.
More optionally, when the motor operates above the rated rotating speed, calculating a relation curve of the rotating speed of the motor and the voltage of the direct-current bus; obtaining the direct-current bus voltage corresponding to the motor rotating speed from the relation curve; and if the voltage of the direct current bus is lower than the peak value of the actual alternating current input voltage, adjusting the voltage of the direct current bus to be higher than the peak value of the actual alternating current input voltage.
More optionally, the method for calculating the relationship curve between the motor speed and the dc bus voltage includes:
determining a first end point of the relation curve by using the rated rotating speed of the motor and a preset value which is higher than the rated alternating current input voltage peak value as a horizontal coordinate and a vertical coordinate;
determining a second end point of the relation curve according to the maximum value of the direct-current bus voltage and the motor rotating speed corresponding to the maximum value of the direct-current bus voltage;
and connecting the first end point and the second end point to determine the relation curve.
More optionally, the method for calculating the relationship curve between the motor speed and the dc bus voltage further includes: and adding end points of the relation curve based on actual test data, and determining the relation curve after all the end points are connected in sequence.
More optionally, when the dc bus voltage reaches the maximum dc bus voltage, the flux-weakening boost mode is entered.
In order to achieve the above objects and other related objects, the present invention further provides a variable frequency speed control system for a compressor, which performs the method for controlling the dc bus voltage in the variable frequency speed control system for a compressor, wherein the variable frequency speed control system for a compressor at least comprises:
the rectifier module receives an alternating current input voltage and converts the alternating current input voltage into a direct current bus voltage;
the inversion module is connected with the output end of the rectification module and converts the direct-current bus voltage into motor driving voltage;
the motor is connected to the output end of the inversion module and is driven to operate by the driving voltage of the motor;
and the control module is connected with the motor, the rectifying module and the inversion module and is used for generating control signals of the rectifying module and the inversion module.
Optionally, the rectifier module is an active rectifier module; or the rectifying module comprises a passive rectifying unit and a boosting unit, and the boosting unit is connected to the output end of the passive rectifying unit.
More optionally, the active rectifier module is a VIENNA rectifier module.
More optionally, the VIENNA rectifying module includes six diodes, three inductors, six power switching tubes, and two sets of capacitors; the diodes are connected in parallel after being connected in series in the same direction, the connecting nodes of the first group of diodes in series are connected with the first phase of the alternating current input voltage through a first inductor, the connecting nodes of the second group of diodes in series are connected with the second phase of the alternating current input voltage through a second inductor, and the connecting nodes of the third group of diodes in series are connected with the third phase of the alternating current input voltage through a third inductor; two groups of capacitors are connected in series and then are connected in parallel with each group of series-connected diodes; and each power switch tube is connected in series in a pairwise reverse direction and then is respectively connected between the connection node of each group of series diode and the connection node of the two groups of capacitors.
As described above, the compressor variable frequency speed control system and the control method of the dc bus voltage of the present invention have the following beneficial effects:
1. the front stage of the variable frequency speed control system of the compressor adopts the active rectifier module, so that the low-order harmonic of a power grid is greatly reduced.
2. The compressor variable-frequency speed control system and the control method of the direct-current bus voltage consider the influence of the power grid when the speed is below the rated speed, and improve the efficiency of the inversion module by controlling the direct-current bus voltage to change along with the power grid.
3. When the compressor variable frequency speed control system and the control method of the direct current bus voltage are above the rated rotating speed, the direct current bus voltage is increased by controlling the rectifier module, so that the motor is delayed to enter a weak magnetic area, and the efficiency of the motor is improved.
4. The variable-frequency speed control system of the compressor and the control method of the direct-current bus voltage integrate the full-speed range working condition of the permanent magnet synchronous motor and the alternating-current input voltage fluctuation, so that the variable-frequency speed control system is in the highest-efficiency working mode.
Drawings
Fig. 1 is a schematic structural diagram of a compressor variable-frequency speed control system in the prior art.
Fig. 2 is a schematic flow chart of a method for controlling the dc bus voltage in the variable frequency speed control system of the compressor according to the present invention.
Fig. 3 is a schematic structural diagram of the compressor variable frequency speed control system of the present invention.
Description of the element reference numerals
1 compressor variable frequency speed control system
11 rectification module
12 inversion module
13 electric machine
14 control module
Detailed Description
The embodiments of the present invention are described below with reference to specific embodiments, and other advantages and effects of the present invention will be easily understood by those skilled in the art from the disclosure of the present specification. The invention is capable of other and different embodiments and of being practiced or of being carried out in various ways, and its several details are capable of modification in various respects, all without departing from the spirit and scope of the present invention.
Please refer to fig. 2 to fig. 3. It should be noted that the drawings provided in the present embodiment are only for illustrating the basic idea of the present invention, and the components related to the present invention are only shown in the drawings rather than drawn according to the number, shape and size of the components in actual implementation, and the type, quantity and proportion of the components in actual implementation may be changed freely, and the layout of the components may be more complicated.
Example one
As shown in fig. 2, the present embodiment provides a method for controlling a dc bus voltage in a variable frequency speed control system of a compressor, where the method for controlling a dc bus voltage in a variable frequency speed control system of a compressor includes:
when the motor runs below the rated rotating speed, outputting the direct current bus voltage according to the alternating current input voltage;
and when the motor operates above the rated rotating speed, outputting the direct current bus voltage according to the alternating current input voltage and the rotating speed of the motor.
In this embodiment, the method for controlling the dc bus voltage in the compressor variable frequency speed control system specifically includes the following steps:
1. when the motor operates below the rated speed, the dc bus voltage is further set based on the fluctuation range of the actual ac input voltage (by closed loop control, the actual voltage of the dc bus always tracks the dc bus preset voltage) taking into account the influence of the grid.
Specifically, if the actual ac input voltage Vab fluctuates within a first preset proportion range of the rated ac input voltage Vra (in this embodiment, the preset proportion range is set to be 80% to 120%, the preset proportion range may be set as needed in actual use, but not limited to this embodiment), the rectifier module is controlled to set the dc bus voltage Vbus to be higher than the peak value of the rated ac input voltage Vra, and the dc bus voltage Vbus is kept constant (fixed value), and does not become low correspondingly as the actual ac input voltage Vab becomes low or as the load of the motor becomes large, so the efficiency of the subsequent inverter module is also improved. This is because if the dc bus voltage becomes low, the inverter-side modulation factor becomes large, and thus the conduction loss becomes large. In this embodiment, when the rated ac input voltage Vra is set to 380V, the dc bus voltage Vbus satisfies the following relation:
Vbus＝Vra*1.414*1.01＝380*1.414*1.01＝543V
it should be noted that the value of the rated ac input voltage Vra may be set according to actual conditions, and different countries or regions may have different values, for example, the three-phase line voltage of the power grid power supply in china is 380V, which is not described herein in detail. In this embodiment, the dc bus voltage Vbus is set to 101% of the peak value of the rated ac input voltage Vra, and in actual use, the proportional relationship between the dc bus voltage Vbus and the peak value of the rated ac input voltage Vra may be set as needed, and may be set to 100% to 105% (excluding end point 100%, including end point 105%) as an example, without being limited to this embodiment.
Specifically, if the actual ac input voltage Vab fluctuates within a second preset proportion range of the rated ac input voltage Vra (in this embodiment, the preset proportion range is set to 100% to 120%, the preset proportion range may be set as needed in actual use, but not limited to this embodiment), the rectifier module is controlled to set the dc bus voltage Vbus higher than the peak value of the actual ac input voltage Vab, and the dc bus voltage Vbus changes with the change of the actual ac input voltage Vab, so as to ensure that the rectifier module can normally operate. This is because the rectifier module has a boosting function, and thus the rectifier module can normally operate only when the dc bus voltage must be higher than the peak value of the actual ac input voltage.
In this embodiment, the dc bus voltage Vbus is set to 101% of the peak value of the actual ac input voltage Vab, and in actual use, the proportional relationship between the dc bus voltage Vbus and the peak value of the actual ac input voltage Vab may be set as needed, and may be set to 100% to 105% (excluding 0% of the endpoint, including 5% of the endpoint), for example, without being limited to this embodiment.
Specifically, if the actual ac input voltage Vab fluctuates outside the first preset proportion range and the second preset proportion range of the rated ac input voltage Vra (i.e., is less than 80% of the rated ac input voltage Vra or greater than 120% of the rated ac input voltage Vra in this embodiment), the power switch in the rectifier module is turned off, that is, the control module in the system does not output the PWM driving signal, and outputs the fault signal. At the moment, the inversion side can carry out load reduction operation or soft shutdown. The fault signal includes, but is not limited to, an under-voltage protection signal and an over-voltage protection signal, which are not described herein in detail.
It should be noted that each preset proportion range may be set according to actual needs, and the minimum value of the second preset proportion range is greater than or equal to the maximum value of the first preset proportion range, which is not repeated herein.
2. And when the motor operates above the rated rotating speed, controlling the rectifier module to increase the direct current bus voltage Vbus so that the motor postpones entering a weak magnetic region.
Specifically, a relation curve of the motor rotation speed and the direct current bus voltage Vbus is calculated first.
More specifically, the relation curve takes the motor rotation speed as an abscissa and the direct-current bus voltage as an ordinate. More specifically, the first end point of the relation curve is determined by taking the rated rotating speed of the motor and a preset value higher than the peak value of the rated alternating-current input voltage Vra as a horizontal coordinate and a vertical coordinate. In this embodiment, the motor rotation speed corresponds to the rated motor rotation speed, and the dc bus voltage Vbus corresponds to a preset value higher than a peak value of the rated ac input voltage Vra, so as to determine the first end point of the relationship curve. As an example, the rated rotation speed of the motor is 6000rpm, and the preset value (a peak value higher than the rated ac input voltage Vra) is set to 380V (rated ac input voltage) × 1.414 (peak value) × 1.01 ═ 543V.
It should be noted that, in this embodiment, the preset value is set to 101% of the peak value of the rated ac input voltage Vra, and in actual use, the proportional relationship between the dc bus voltage Vbus and the peak value of the rated ac input voltage Vra may be set as needed, and may be set to 100% to 105% (excluding end point 100%, including end point 105%) as an example, without being limited by this embodiment.
More specifically, the second end point of the relation curve is determined according to the maximum value Vbus _ max of the direct current bus voltage and the motor rotation speed corresponding to the maximum value Vbus _ max of the direct current bus voltage. In this embodiment, the dc bus voltage Vbus corresponds to a maximum value Vbus _ max of the dc bus voltage, and the motor rotation speed corresponds to a motor rotation speed at the maximum value Vbus _ max of the dc bus voltage, so as to determine the second end point of the relationship curve. The maximum value Vbus _ max of the direct current bus voltage satisfies the following relational expression: vbus _ max is Vce × k, where Vce is the maximum rated value of the power switching tube, k is a safety factor, and k is 0.6-0.8. As an example, the maximum value Vbus _ max of the dc bus voltage is set to 1200 (maximum rating of the power switching tube, i.e., power switching tube withstand voltage) × 0.6 (safety factor) ═ 720V, and the corresponding motor rotation speed is 720V (maximum dc bus voltage) ÷ 60V/krpm (motor back-emf constant) = 12000 rpm.
The abscissa and ordinate of the relationship curve are interchangeable, and the relationship curve is not limited to this embodiment.
Specifically, the first endpoint and the second endpoint are connected to determine the relationship curve.
More specifically, the first end point and the second end point are connected, and the straight line obtained thereby is the relationship curve.
As another implementation manner of the present invention, further, referring to actual test data, endpoints of the relationship curve are added, and a curve obtained after the endpoints are sequentially connected is the relationship curve. The number of the added endpoints can be set according to the needs, and is not described in detail herein.
Specifically, the direct-current bus voltage Vbus corresponding to the motor rotation speed is obtained from the relationship curve according to a preset motor rotation speed or an actual motor rotation speed (the actual motor rotation speed always tracks the preset motor rotation speed through closed-loop control).
Specifically, it is finally determined whether the dc bus voltage Vbus meets the requirement, that is, if the dc bus voltage Vbus is lower than the peak value of the actual ac input voltage Vab, the dc bus voltage Vbus is adjusted to be higher than the peak value of the actual ac input voltage Vab; otherwise, the adjustment is not carried out, and the value obtained on the relation curve is taken as the standard; thereby determining the dc bus voltage Vbus.
3. In another embodiment of the present invention, when the dc bus voltage Vbus reaches the maximum dc bus voltage Vbus _ max, if it is desired to continue increasing the motor speed at this time, the motor flux can be weakened only by changing the excitation current, that is, the motor enters the field weakening boost mode.
The active rectification module is adopted in the embodiment, so that the low-order harmonic of a power grid is greatly reduced; when the speed is below the rated speed, the influence of a power grid is considered, and the efficiency of the inversion module is improved by controlling the voltage of the direct-current bus to change along with the power grid; when the speed is higher than the rated speed, the direct current bus voltage is increased by controlling the rectifier module, so that the motor is delayed to enter a weak magnetic area, and the efficiency of the motor is improved; the full-speed range working condition of the permanent magnet synchronous motor and the fluctuation of the alternating current input voltage are integrated, so that the variable-frequency speed regulating system is in the working mode with the highest efficiency.
Example two
The embodiment provides a method for controlling a dc bus voltage in a variable-frequency speed control system of a compressor, which is different from the first embodiment in that when the actual ac input voltage Vab fluctuates within a second preset proportion range of the rated ac input voltage Vra, different processing is performed according to different subintervals.
Specifically, when the motor is operating below the rated speed:
if the actual ac input voltage Vab fluctuates between 80% and 100% of the rated ac input voltage Vra, the rectifier module is controlled to set the dc bus voltage Vbus higher than the peak value of the rated ac input voltage Vra, and the dc bus voltage Vbus is kept constant (fixed value).
If the actual ac input voltage Vab fluctuates within a first sub-interval (in this embodiment, the first sub-interval is set to 100% to 110%, in actual use, the range of the first sub-interval may be set as needed, but not limited to this embodiment) of the second preset proportion range of the rated ac input voltage Vra, the rectifier module is controlled to set the dc bus voltage Vbus to be higher than the peak value of the actual ac input voltage Vab, and the dc bus voltage Vbus varies with the variation of the actual ac input voltage Vab.
If the actual ac input voltage Vab fluctuates within a second subinterval (in this embodiment, the first subinterval is set to 110% to 120% in the second preset proportion range of the rated ac input voltage Vra, in actual use, the range of the second subinterval may be set as needed, but not limited to this embodiment), the power switch in the rectification module is turned off, that is, the control module in the system does not output the PWM driving signal, and enters the uncontrolled rectification mode. This can provide two benefits: firstly, the uncontrolled rectification mode can reduce the switching loss of the rectification module; second, when the load of the motor is increased, the dc bus voltage Vbus is low but high enough to meet the terminal voltage requirement of the motor, so that the modulation degree on the inverter side does not need to be maintained too high, and the conduction loss of the rectifier module and the inverter module is reduced.
And if the actual alternating-current input voltage Vab is less than 80% of the rated alternating-current input voltage Vra or more than 120% of the rated alternating-current input voltage Vra, turning off a power switch tube in the rectifier module and outputting a fault signal.
It should be noted that, the working method and principle of the motor when the motor operates above the rated rotation speed and the dc bus voltage reaches the maximum dc bus voltage are the same as those of the first embodiment, and are not described herein again.
EXAMPLE III
As shown in fig. 3, the present embodiment provides a variable frequency speed control system 1 for a compressor, where the variable frequency speed control system 1 for a compressor includes:
the device comprises a rectification module 11, an inversion module 12, a motor 13 and a control module 14.
As shown in fig. 3, the rectifier module 11 receives an ac input voltage and converts the ac input voltage into a dc bus voltage Vbus.
Specifically, in this embodiment, the rectifier module 11 is a VIENNA rectifier module in an active rectifier module, and various modifications of VIENNA topology are applicable to the rectifier module 11 of the present invention. As an example, the rectifier module 11 includes six diodes, three inductors, six power switching tubes, and two sets of capacitors (two sets of capacitors may be a single capacitor or a combination of multiple capacitors connected in series and parallel), and the capacitance values of the upper and lower sets of capacitors are the same. Every two diodes are connected in series in the same direction and then connected in parallel, namely: the cathode of the first diode D1 is connected with the positive pole Vbus + of the direct current bus voltage, and the anode is connected with the cathode of the second diode D2; the anode of the second diode D2 is connected with the cathode Vbus-of the direct current bus voltage; the cathode of the third diode D3 is connected to the positive pole Vbus + of the dc bus voltage, and the anode is connected to the cathode of the fourth diode D4; the anode of the fourth diode D4 is connected with the negative pole Vbus-of the direct current bus voltage; the cathode of the fifth diode D5 is connected to the positive electrode Vbus + of the dc bus voltage, and the anode is connected to the cathode of the sixth diode D6; the anode of the sixth diode D6 is connected to the negative pole Vbus-of the dc bus voltage V. A connection node of the first diode D1 and the second diode D2 is connected to the first phase L1 of the ac input voltage, a connection node of the third diode D3 and the fourth diode D4 is connected to the second phase L2 of the ac input voltage, and a connection node of the fifth diode D5 and the sixth diode D6 is connected to the third phase L3 of the ac input voltage. Each phase of the ac input voltage is input through an inductor (the first inductor L11, the second inductor L12, and the third inductor L13). The first capacitor C1 and the second capacitor C2 are connected in series and then connected between the positive pole Vbus + and the negative pole Vbus-of the DC bus voltage. Each power switch tube is connected between the connection node of each group of series diode and the connection node of two groups of capacitors after being connected in series in a pairwise reverse direction, namely: the collector of the first power switch tube Q11 is connected with the connection node of the first diode D1 and the second diode D2, and the emitter is connected with the emitter of the second power switch tube Q12; the collector of the second power switch Q12 is connected with the connection node of the first group capacitor C1 and the second group capacitor C2; the collector of the third power switch Q13 is connected to the connection node of the third diode D3 and the fourth diode D4, and the emitter is connected to the emitter of the fourth power switch Q14; the collector of the fourth power switch Q14 is connected with the connection node of the first group capacitor C1 and the second group capacitor C2; the collector of the fifth power switch Q15 is connected to the connection node of the fifth diode D5 and the sixth diode D6, and the emitter is connected to the emitter of the sixth power switch Q16; the collector of the sixth power switch Q16 is connected to the node connecting the first capacitor C1 and the second capacitor C2. Each power switch tube in the rectifier module 11 is connected with a control signal.
It should be noted that the power supply of the power grid in this embodiment is a three-phase four-wire system (three live wires and one ground wire), and if the power supply is a three-phase five-wire system (three live wires and one neutral wire and one ground wire), the neutral wire is connected to the connection node of the two sets of capacitors.
In this embodiment, each power switch tube is an insulated gate bipolar transistor, and the type of each power switch tube may be set as needed in actual use. The rectifier module 11 may be any controllable active rectifier module; the power supply also comprises a passive rectifying unit and a boosting unit, wherein the boosting unit is connected to the output end of the passive rectifying unit; therefore, the controllable rectification is realized, and the present embodiment is not limited.
As shown in fig. 3, the inverter module 12 is connected to the output end of the rectifier module 11, and converts the dc bus voltage Vbus into a motor driving voltage.
Specifically, in this embodiment, the inverter module 12 includes six power switching tubes, which form a three-phase inverter bridge, wherein a seventh power switching tube Q21 and an eighth power switching tube Q22 are connected in series between a positive electrode Vbus + of the dc bus voltage and a negative electrode Vbus-of the dc bus voltage (a collector of the seventh power switching tube Q21 is connected to the positive electrode Vbus + of the dc bus voltage, an emitter of the seventh power switching tube Q21 is connected to the collector of the eighth power switching tube Q22, and an emitter of the eighth power switching tube Q22 is connected to the negative electrode Vbus-of the dc bus voltage); a ninth power switch Q23 and a tenth power switch Q24 are connected in series between the positive pole Vbus + of the dc bus voltage and the negative pole Vbus-of the dc bus voltage (the connection port is the same as the seventh power switch Q21 and the eighth power switch Q22, which is not described herein again); an eleventh power switch Q25 and a twelfth power switch Q26 are connected in series between the positive pole Vbus + of the dc bus voltage and the negative pole Vbus-of the dc bus voltage (the connection port is the same as the seventh power switch Q21 and the eighth power switch Q22, which is not described herein again); each power switch tube in the inverter module 12 is connected with a control signal.
In this embodiment, each power switch in the inverter module 12 is an insulated gate bipolar transistor, and the type of each power switch may be set as needed in actual use. The inverter module 12 may select any one of the structures according to the requirement, and is not limited to this embodiment.
As shown in fig. 3, the motor 13 is connected to an output end of the inverter module 12 and driven by the motor driving voltage to operate.
Specifically, in this embodiment, the motor 13 is a permanent magnet synchronous motor, and when three-phase ac power is supplied to a three-phase stator winding of the motor, a rotating magnetic field is generated, and the rotating magnetic field drives the rotor to rotate synchronously. In other embodiments, the motor 13 may also be an ac asynchronous motor or other three-phase motors, which are not described herein.
As shown in fig. 3, the control module 14 is connected to the motor 13, the rectifier module 11 and the inverter module 12, and generates control signals for the rectifier module 11 and the inverter module 12.
Specifically, in this embodiment, the control module 14 collects an ac input voltage and a signal on the motor 13, and controls the rectification module 11 and the inverter module 12 to execute the control method of the dc bus voltage in the variable frequency speed control system of the compressor according to the first embodiment or the second embodiment to realize the speed regulation of the motor 13, and the working principle refers to the first embodiment and the second embodiment, which is not repeated herein.
The compressor variable frequency speed control system of the embodiment greatly reduces low-order harmonic waves of a power grid, improves system efficiency, is always in a highest-efficiency working mode (including a controlled motor), and is suitable for industrial application.
In summary, the present invention provides a variable frequency speed control system for a compressor and a method for controlling dc bus voltage, including: the rectifier module receives an alternating current input voltage and converts the alternating current input voltage into a direct current bus voltage; the inversion module is connected with the output end of the rectification module and converts the direct-current bus voltage into motor driving voltage; the motor is connected to the output end of the inversion module and is driven to operate by the driving voltage of the motor; the control module is connected with the motor, the rectifying module and the inverting module and used for generating control signals of the rectifying module and the inverting module; when the motor runs below the rated rotating speed, outputting the direct current bus voltage according to the alternating current input voltage; and when the motor operates above the rated rotating speed, outputting the direct current bus voltage according to the alternating current input voltage and the rotating speed of the motor. The front stage of the variable frequency speed control system of the compressor adopts the active rectifier module, so that the low-order harmonic of a power grid is greatly reduced; when the speed is below the rated speed, the influence of a power grid is considered, and the efficiency of the inversion module is improved by controlling the voltage of the direct-current bus to change along with the power grid; when the speed is higher than the rated speed, the direct current bus voltage is increased by controlling the rectifier module, so that the motor is delayed to enter a weak magnetic area, and the efficiency of the motor is improved; the full-speed range working condition of the permanent magnet synchronous motor and the fluctuation of the alternating current input voltage are integrated, so that the variable-frequency speed regulating system is in the working mode with the highest efficiency. Therefore, the invention effectively overcomes various defects in the prior art and has high industrial utilization value.
The foregoing embodiments are merely illustrative of the principles and utilities of the present invention and are not intended to limit the invention. Any person skilled in the art can modify or change the above-mentioned embodiments without departing from the spirit and scope of the present invention. Accordingly, it is intended that all equivalent modifications or changes which can be made by those skilled in the art without departing from the spirit and technical spirit of the present invention be covered by the claims of the present invention.
Claims (11)
1. A control method for DC bus voltage in a compressor variable frequency speed control system is characterized in that the control method for DC bus voltage in the compressor variable frequency speed control system at least comprises the following steps:
when the motor runs below the rated rotating speed, outputting the direct current bus voltage according to the alternating current input voltage;
and when the motor operates above the rated rotating speed, outputting the direct current bus voltage according to the alternating current input voltage and the rotating speed of the motor.
2. The method for controlling the direct-current bus voltage in the variable-frequency speed regulating system of the compressor according to claim 1, wherein the method comprises the following steps: when the motor is operating below the rated speed,
if the actual alternating current input voltage fluctuates within a first preset proportion range of the rated alternating current input voltage, setting the direct current bus voltage as a fixed value higher than the peak value of the rated alternating current input voltage;
if the actual alternating current input voltage fluctuates within a second preset proportion range of the rated alternating current input voltage, the direct current bus voltage is set to be higher than the peak value of the actual alternating current input voltage, and the direct current bus voltage changes along with the change of the actual alternating current input voltage;
if the actual alternating current input voltage fluctuates outside a first preset proportion range and a second preset proportion range of the rated alternating current input voltage, a power switch tube in the rectification module is turned off, and a fault signal is output;
and the minimum value of the second preset proportion range is greater than or equal to the maximum value of the first preset proportion range.
3. The method for controlling the direct-current bus voltage in the variable-frequency speed regulating system of the compressor according to claim 2, wherein the method comprises the following steps: when the actual alternating current input voltage fluctuates within a first subinterval of a second preset proportion range of the rated alternating current input voltage, the direct current bus voltage is set to be higher than the peak value of the actual alternating current input voltage, and the direct current bus voltage changes along with the change of the actual alternating current input voltage;
and when the actual alternating current input voltage fluctuates in a second subinterval within a second preset proportion range of the rated alternating current input voltage, turning off a power switch tube in the rectification module, and entering an uncontrolled rectification mode.
4. The method for controlling the DC bus voltage in the variable-frequency speed regulation system of the compressor according to any one of claims 1 to 3, characterized in that: when the motor is operating above the rated speed,
calculating a relation curve of the motor rotating speed and the direct current bus voltage;
obtaining the direct-current bus voltage corresponding to the motor rotating speed from the relation curve;
and if the voltage of the direct current bus is lower than the peak value of the actual alternating current input voltage, adjusting the voltage of the direct current bus to be higher than the peak value of the actual alternating current input voltage.
5. The method for controlling the DC bus voltage in the variable-frequency speed control system of the compressor according to claim 4, wherein the method comprises the following steps: the method for calculating the relation curve of the motor rotating speed and the direct current bus voltage comprises the following steps:
determining a first end point of the relation curve by using the rated rotating speed of the motor and a preset value which is higher than the rated alternating current input voltage peak value as a horizontal coordinate and a vertical coordinate;
determining a second end point of the relation curve according to the maximum value of the direct-current bus voltage and the motor rotating speed corresponding to the maximum value of the direct-current bus voltage;
and connecting the first end point and the second end point to determine the relation curve.
6. The method for controlling the DC bus voltage in the variable-frequency speed control system of the compressor according to claim 5, wherein the method comprises the following steps: the method for calculating the relation curve of the motor speed and the direct current bus voltage further comprises the following steps: and adding end points of the relation curve based on actual test data, and determining the relation curve after all the end points are connected in sequence.
7. The method for controlling the direct-current bus voltage in the variable-frequency speed regulating system of the compressor according to claim 1, wherein the method comprises the following steps: and when the voltage of the direct current bus reaches the maximum value of the voltage of the direct current bus, entering a weak magnetic speed-up mode.
8. A compressor variable frequency speed control system, which executes the control method of the DC bus voltage in the compressor variable frequency speed control system according to any one of claims 1 to 7, characterized in that the compressor variable frequency speed control system at least comprises:
the rectifier module receives an alternating current input voltage and converts the alternating current input voltage into a direct current bus voltage;
the inversion module is connected with the output end of the rectification module and converts the direct-current bus voltage into motor driving voltage;
the motor is connected to the output end of the inversion module and is driven to operate by the driving voltage of the motor;
and the control module is connected with the motor, the rectifying module and the inversion module and is used for generating control signals of the rectifying module and the inversion module.
9. The variable frequency speed control system of the compressor of claim 8, wherein: the rectifying module is an active rectifying module; or the rectifying module comprises a passive rectifying unit and a boosting unit, and the boosting unit is connected to the output end of the passive rectifying unit.
10. The variable frequency speed control system of the compressor of claim 9, wherein: the active rectifier module is a VIENNA rectifier module.
11. The variable frequency speed control system of the compressor of claim 10, wherein: the VIENNA rectifying module comprises six diodes, three inductors, six power switch tubes and two groups of capacitors; the diodes are connected in parallel after being connected in series in the same direction, the connecting nodes of the first group of diodes in series are connected with the first phase of the alternating current input voltage through a first inductor, the connecting nodes of the second group of diodes in series are connected with the second phase of the alternating current input voltage through a second inductor, and the connecting nodes of the third group of diodes in series are connected with the third phase of the alternating current input voltage through a third inductor; two groups of capacitors are connected in series and then are connected in parallel with each group of series-connected diodes; and each power switch tube is connected in series in a pairwise reverse direction and then is respectively connected between the connection node of each group of series diode and the connection node of the two groups of capacitors.
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| PCT/CN2021/107064 WO2021244669A1 (en) | 2020-06-05 | 2021-07-19 | Compressor variable-frequency speed adjusting system and control method for direct-current bus voltage |
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| CN111628660B (en) | 2021-08-27 |
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