CN113323873B

CN113323873B - Electric compressor and control method thereof

Info

Publication number: CN113323873B
Application number: CN202110756879.2A
Authority: CN
Inventors: 陈亚丽; 杨伟兵; 孙爱民
Original assignee: Luohe Vocational Technology College
Current assignee: Luohe Vocational Technology College
Priority date: 2021-07-05
Filing date: 2021-07-05
Publication date: 2022-07-22
Anticipated expiration: 2041-07-05
Also published as: CN113323873A

Abstract

The invention discloses an electric compressor, which comprises a plurality of shells arranged in parallel, wherein a bearing group is arranged at the end part of each shell, a male screw and a female screw are arranged in each shell, the male screw and the female screw are connected with the bearing groups, a driving motor is arranged on the outer side of each bearing group, the driving motor is connected with the male screw, an oil tank is arranged in each shell, an air outlet of each shell is connected with an oil separator, the oil separator is connected with the oil tank through a first oil return pipe, an oil level sensor is arranged in each oil tank, the oil tank is connected with an oil supply pump through a first oil supply pipe, a first electric control valve is arranged on the first oil supply pipe, the oil supply pump is connected with an oil storage tank, the oil tank is connected with the oil storage tank through a second oil return pipe, and a second electric control valve is arranged on the second oil return pipe. The invention can improve the defects of the prior art, solves the problem of oil shortage caused by frequent start and stop of the compressor, and improves the control precision of the refrigeration system on the temperature of the controlled object.

Description

Electric compressor and control method thereof

Technical Field

The invention relates to the technical field of refrigeration equipment, in particular to an electric compressor and a control method thereof.

Background

The compressor is the core equipment of refrigerating system, and in the compressor operation process, the refrigerant oil utilizes the pressure that the compressor produced to realize circulation moistening and cooling. Since the refrigerant oil in the compressor is discharged out of the compressor along with the refrigerant, in order to ensure the sufficiency of the refrigerant oil in the compressor, the refrigerant oil in the discharged refrigerant is separated by an oil separator and flows back into the compressor in the prior art. Because the oil separator needs continuous working pressure to normally work, when the compressor is frequently started and stopped, the working pressure cannot be maintained, the oil return rate of the oil separator is reduced, even the oil cannot be returned at all, at the moment, the problem that the compressor is lack of refrigeration oil occurs, and if the situation exists for a long time, moving parts such as bearings in the compressor and the like are excessively abraded due to lack of lubrication and cooling. Therefore, the prior art does not allow the compressor to be started and stopped frequently (generally, the number of times of starting and stopping per hour is required to be not more than 10 times). However, the existing large-scale refrigeration system usually adopts a mode that a plurality of compressor units are arranged in parallel, and the adjustment of the refrigerating capacity is realized by starting and stopping different compressors, and because the compressors cannot be started and stopped frequently, the large-scale refrigeration system cannot accurately adjust the refrigerating capacity, so that the temperature fluctuation of a controlled object is large.

Disclosure of Invention

The technical problem to be solved by the invention is to provide the electric compressor and the control method thereof, which can solve the defects of the prior art, solve the problem of oil shortage caused by frequent start and stop of the compressor, and improve the control precision of the refrigeration system on the temperature of the controlled object.

In order to solve the technical problems, the technical scheme adopted by the invention is as follows.

An electric compressor comprises a plurality of shells which are arranged in parallel, a bearing group is installed at the end part of each shell, a male screw and a female screw are arranged in each shell, the male screw and the female screw are connected with the bearing group, a driving motor is installed on the outer side of each bearing group, the driving motor is connected with the male screw, an oil tank is arranged in each shell, an air outlet of each shell is connected with an oil separator, each oil separator is connected with the oil tank through a first oil return pipe, an oil level sensor is installed in each oil tank, the oil tank is connected with an oil supply pump through a first oil injection pipe, a first electric control valve is installed on each first oil injection pipe, the oil supply pump is connected with an oil storage tank, the oil tank is connected with the oil storage tank through a second oil return pipe, a second electric control valve is installed on each second oil return pipe, each bearing group comprises a base, a refrigeration oil main runner communicated with the oil tank is arranged in each base, two bearing outer rings are fixed on each base, and bearing inner rings are arranged on the inner sides of the bearing outer rings, install the ball between bearing inner race and the bearing inner race, the retaining ring is installed to the both sides of bearing inner race and bearing inner race, be provided with the first outer lane runner with the refrigeration oil sprue intercommunication in the bearing inner race, be provided with the oil return runner with the casing intercommunication on the retaining ring that is located the base inboard, be provided with the auxiliary runner of refrigeration oil in the base, be provided with the second outer lane runner with the auxiliary runner of refrigeration oil intercommunication in the bearing inner race, the auxiliary runner of refrigeration oil is connected with the fuel feeding pump through the second and annotates the oil pipe, install third electric control valve on the second notes oil pipe.

Preferably, the outlet directions of the first outer ring flow channel and the second outer ring flow channel are parallel to the radial direction of the bearing outer ring, and the outlet direction of the oil return flow channel is parallel to the axial direction of the bearing outer ring.

Preferably, a retainer is arranged between the bearing outer ring and the bearing inner ring, a plurality of mounting positions are uniformly arranged on two sides of the retainer respectively, the balls are mounted in the mounting positions on two sides of the retainer, a first annular groove is formed in one side, facing the bearing outer ring, of the retainer, two rows of protrusions are symmetrically arranged in the first annular groove, through holes are formed in two sides of the first annular groove, and extension lines of outlet axes of the first outer ring flow channel and the second outer ring flow channel are intersected with the bottom surface of the first annular groove.

Preferably, the inner surface of the bearing inner ring is symmetrically provided with two second annular grooves, two rows of balls are in sliding contact with the tops of the two second annular grooves respectively, and the contact part of the second annular grooves and the balls is provided with an arc-shaped part.

Preferably, the oil injection flow rate of the second oil injection pipe is 10% -15% of the oil injection flow rate of the first oil injection pipe.

A control method of the above electric compressor includes the steps of:

A. dividing all driving motors into a normally open unit and an abnormal starting unit, wherein the driving motors in the normally open unit are always kept in an operating state, and the driving motors in the non-normally open unit are switched between the operating state and a shutdown state according to the refrigerating capacity requirement and the actual temperature change of a controlled object;

B. the oil level sensor monitors the oil level in the oil tank, and redundant frozen oil is discharged to the oil storage tank through the second oil return pipe for the oil tank with the oil level exceeding the upper limit of the oil level; for an oil tank with the oil level lower than the lower limit of the oil level, if the oil tank belongs to a normally open unit, freezing oil is injected into the oil tank through a first oil filling pipe, if the oil tank belongs to a non-normally open unit, the freezing oil is injected into a corresponding bearing group through a second oil filling pipe before a driving motor corresponding to the oil tank is started to operate, and whether the freezing oil is injected into the oil tank through the first oil filling pipe is determined according to the change of the oil level in the oil tank after the oil tank is started to operate;

C. and periodically rotating the driving motors in the normally open unit and the normally non-open unit.

Preferably, in the step a, the switching between the running state and the shutdown state of the driving motor in the normally-open unit according to the refrigerating capacity demand and the actual temperature change comprises the following steps,

a1, calculating the number of starting units according to the refrigerating capacity requirement, if the calculated number of units is smaller than the number of actually started units, preferentially starting to shut down the units from an abnormally started unit, if the number of actually started units is still larger than the calculated number of units after all the normally opened units are shut down, continuing to shut down the units from the normally opened units, if the continuous shut-down time of the shut-down units exceeds 1 hour, dividing the shut-down units into the normally opened units, if the calculated number of units is larger than the number of actually started units, starting the shut-down units in the normally opened units, and if the continuous start-up time of the started units exceeds 0.5 hour, dividing the started units into the normally opened units;

a2, adjusting the total output power of the starting unit according to the actual temperature change of the controlled object, arranging the ratio of the output power of the driving motor to the rated power in an ascending order, starting to adjust the driving motor with the minimum ratio of the output power to the rated power when the total output power needs to be increased, and starting to adjust the driving motor with the maximum ratio of the output power to the rated power when the total output power needs to be decreased.

Preferably, in the step B, in the case that the oil level of the oil tank belonging to the non-normally open unit is lower than the lower limit of the oil level, the operation of the unit comprises the following steps,

b1, injecting frozen oil into the corresponding bearing group through a second oil injection pipe 30 seconds before starting up;

b2, after the machine is started, monitoring the oil level in the oil tank, and stopping the second oil filling pipe from filling the refrigeration oil into the corresponding bearing group when the oil level rises above the lower limit of the oil level; and if the oil level does not rise after the machine is started for 90 seconds, the first oil filling pipe is used for filling the refrigeration oil into the oil tank, after the oil level rises to be higher than the lower limit of the oil level, the first oil filling pipe is stopped from filling the refrigeration oil into the oil tank, then the second oil filling pipe is continuously kept for filling the refrigeration oil into the corresponding bearing group for 30 seconds, and then the second oil filling pipe is stopped from filling the refrigeration oil into the corresponding bearing group.

Preferably, the step C of periodically rotating the driving motors of the normally open unit and the normally open unit includes the steps of,

c1, setting an upper limit of the starting time, stopping the driving motor which reaches the upper limit of the starting time when the machine is continuously started, dividing the driving motor into an abnormal starting group, starting the driving motor which has the most starting frequency in the non-normally open machine set, and dividing the driving motor into the normally open machine set;

and C2, for the normally-open unit, when the driving motor in the normally-open unit is turned off in the step A1, the driving motor with the longest continuous starting time is turned off preferentially, and when the driving motor in the normally-open unit is turned on in the step A1, the driving motor with the longest continuous stopping time is turned on preferentially.

The beneficial effect that adopts above-mentioned technical scheme to bring lies in: according to the invention, the structure of the bearing set is optimized, and the refrigeration oil is injected into the bearing through the refrigeration oil auxiliary flow passage when the machine is started in an oil-deficient state by arranging the refrigeration oil auxiliary flow passage, so that the good lubrication and cooling of the bearing are maintained. In addition, the directions of the first outer ring flow channel and the second outer ring flow channel are perpendicular to the direction of the oil return flow channel, so that the refrigeration oil in the bearing can be quickly and uniformly distributed in the bearing along with the rotation of the bearing, the circulation uniformity of the refrigeration oil in the bearing is improved, the refrigeration oil is prevented from being discharged from the oil return flow channel without being fully circulated in the bearing after entering the bearing, and therefore the purpose that the lubrication and the cooling of the bearing can be met by injecting a small amount of refrigeration oil into the bearing from the refrigeration oil auxiliary flow channel can be achieved. The probability of excessive refrigerating oil in the normal operation process of the compressor can be effectively reduced by reducing the oil injection amount of the refrigerating oil auxiliary flow passage. The bearing provided by the invention adopts a double-row ball structure, the compression resistance and the abrasion resistance of the bearing can be improved, and the first annular groove on the retainer can guide the injected refrigerant oil in the rotation process of the bearing, so that the refrigerant oil is uniformly distributed to the positions of the balls on two sides, and the lubrication and the cooling are provided for the balls. The second annular groove is used for storing a small amount of refrigeration oil on the one hand, can make the ball keep lubricated effect before the bearing does not rotate, and on the other hand second annular groove provides unobstructed flow path for refrigeration oil, can make the better smooth and easy high efficiency of the inboard refrigeration oil flow circulation of bearing after the bearing rotates. Through the improvement, the start-stop frequency allowed by the compressor can reach more than 30 times per hour, so that a foundation is laid for the control of a subsequent refrigerating system.

On the basis of optimizing the structure of the bearing set, the invention provides a brand-new electric compressor control strategy. Because the optimized compressor can realize more frequent start-stop control, the accurate start-stop control is preferentially carried out according to the requirement of refrigerating capacity, the working time of all units is basically consistent by adopting a regular alternation mode, and the overuse of individual units is avoided. And then the basic stability of real-time temperature is realized by adjusting the output power of a single unit. For the compressor that lacks oil, carry out the oiling to it before the start, can guarantee the abundant lubrication of its bearing position, use first notes oil pipe to mend the refrigeration oil to the oil tank according to the change cooperation of oil level simultaneously, can make the oil level resume normally in the shortest time, avoid the oil level to appear fluctuating by a wide margin.

Drawings

FIG. 1 is a block diagram of one embodiment of the present invention.

Fig. 2 is a block diagram of a bearing set in accordance with an embodiment of the present invention.

Fig. 3 is a sectional view taken along the line a-a in fig. 2.

In the figure: 1. a housing; 2. a bearing set; 3. a male screw; 4. a female screw; 5. a drive motor; 6. an oil tank; 7. an oil separator; 8. a first oil return pipe; 9. an oil level sensor; 10. a first filler pipe; 11. an oil storage tank; 12. a first electrically controlled valve; 13. an oil supply pump; 14. an anti-shake camera; 15. a second electrically controlled valve; 16. a base; 17. a main refrigeration oil flow passage; 18. an outer race of the bearing; 19. a bearing inner race; 20. a ball bearing; 21. a retainer ring; 22. a first outer ring runner; 23. an oil return flow passage; 24. a refrigeration oil auxiliary flow passage; 25. a second outer ring flow channel; 26. a second filler pipe; 27. a third electrically controlled valve; 28. a holder; 29. an installation position; 30. a first annular groove; 31. an annular groove; 32. a through hole; 33. a second annular groove; 34. an arc-shaped portion.

Detailed Description

The standard parts used in the invention can be purchased from the market, the special-shaped parts can be customized according to the description and the description of the attached drawings, and the specific connection mode of each part adopts the conventional means of mature bolts, rivets, welding, sticking and the like in the prior art, and the detailed description is not repeated.

Referring to fig. 1-3, a specific embodiment of the present invention includes a plurality of housings 1 disposed in parallel, a bearing set 2 is installed at an end of each housing 1, a male screw 3 and a female screw 4 are disposed in each housing 1, the male screw 3 and the female screw 4 are connected to the bearing set 2, a driving motor 5 is installed outside the bearing set 2, the driving motor 5 is connected to the male screw 3, an oil tank 6 is disposed in each housing 1, an oil separator 7 is connected to an exhaust port of each housing 1, the oil separator 7 is connected to an oil tank 6 through a first oil return pipe 8, an oil level sensor 9 is installed in each oil tank 6, the oil tank 6 is connected to an oil supply pump 13 through a first oil supply pipe 10, a first electrically controlled valve 12 is installed on the first oil supply pipe 10, the oil supply pump 13 is connected to an oil storage tank 11, the oil tank 6 is connected to the oil storage tank 11 through a second oil return pipe 14, a second electrically controlled valve 15 is installed on the second oil return pipe 14, the bearing group 2 comprises a base 16, a refrigeration oil main flow passage 17 communicated with the oil tank 6 is arranged in the base 16, two bearing outer rings 18 are fixed on the base 16, bearing inner rings 19 are arranged on the inner sides of the bearing outer rings 18, balls 20 are arranged between the bearing outer rings 18 and the bearing inner rings 19, retaining rings 21 are arranged on two sides of the bearing outer rings 18 and two sides of the bearing inner rings 19, a first outer ring flow passage 22 communicated with the refrigeration oil main flow passage 17 is arranged in the bearing outer rings 18, an oil return flow passage 23 communicated with the shell 1 is arranged on the retaining ring 21 on the inner side of the base 16, a refrigeration oil auxiliary flow passage 24 is arranged in the base 16, a second outer ring flow passage 25 communicated with the refrigeration oil auxiliary flow passage 24 is arranged in the bearing outer rings 18, the refrigeration oil auxiliary flow passage 24 is connected with the oil supply pump 13 through a second oil filling pipe 26, and a third electric control valve 27 is arranged on the second oil filling pipe 26. The outlet directions of the first outer ring flow passage 22 and the second outer ring flow passage 25 are parallel to the radial direction of the bearing outer ring 18, and the outlet direction of the oil return flow passage 23 is parallel to the axial direction of the bearing outer ring 18. A retainer 28 is arranged between the bearing outer ring 18 and the bearing inner ring 19, a plurality of mounting positions 29 are uniformly arranged on two sides of the retainer 28 respectively, the balls 20 are mounted in the mounting positions 29 on two sides of the retainer 28, a first annular groove 30 is arranged on one side of the retainer 28 facing the bearing outer ring 18, two rows of protrusions 31 are symmetrically arranged in the first annular groove 30, through holes 32 are arranged on two sides of the first annular groove 30, and extension lines of outlet axes of the first outer ring flow passage 22 and the second outer ring flow passage 25 are intersected with the bottom surface of the first annular groove 30. The inner surface of the bearing inner ring 19 is symmetrically provided with two second annular grooves 33, two rows of balls 20 are respectively in sliding contact with the tops of the two second annular grooves 33, and the contact part of the second annular grooves 33 and the balls 20 is provided with an arc-shaped part 34. The oil injection flow rate of the second oil injection pipe 26 is 10-15% of the oil injection flow rate of the first oil injection pipe 10.

A control method of the above electric compressor includes the steps of:

A. dividing all the driving motors 5 into a normally open unit and an abnormal starting unit, wherein the driving motor 5 in the normally open unit is always kept in an operating state, and the driving motor 5 in the non-normally open unit is switched between the operating state and a stopping state according to the refrigerating capacity requirement and the actual temperature change of a controlled object;

the switching of the running state and the shutdown state of the driving motor 5 in the non-normally open unit according to the refrigerating capacity demand and the actual temperature change comprises the following steps,

a1, calculating the number of starting units according to the refrigerating capacity demand, preferentially shutting down the units from an abnormal starting unit if the calculated number of the units is smaller than the number of the actually started units, continuing shutting down the units from a normally open unit if the number of the actually started units is still larger than the calculated number of the units after shutting down all the normally open units, dividing the shut-down units into the normally open units if the continuous shut-down time of the shut-down units exceeds 1 hour, starting the shut-down units in the normally open units if the calculated number of the units is larger than the number of the actually started units, and dividing the started units into the normally open units if the continuous start-up time of the started units exceeds 0.5 hour;

when starting a shutdown unit in the normally-open unit, firstly enabling the unit to output rated power, if the startup time of the unit is less than 5 minutes, keeping the state to shutdown, dragging the startup time of the unit to exceed 5 minutes, keeping the state for 5 minutes, and then turning to the step A2 to adjust the output power; the starting-up mode can improve the oil return efficiency of the refrigerant oil in the pipeline of the compressor;

a2, adjusting the total output power of the starting unit according to the actual temperature change of the controlled object, arranging the ratio of the output power of the driving motor 5 to the rated power in an ascending order, starting to adjust from the driving motor 5 with the minimum ratio of the output power to the rated power when the total output power needs to be increased, and starting to adjust from the driving motor 5 with the maximum ratio of the output power to the rated power when the total output power needs to be decreased;

the regulation of the total output power comprises the steps of,

firstly, determining the value range of the output total power according to the actual temperature change range of a controlled object in a sampling interval, then extracting the characteristic data of an actual temperature change curve, selecting a corresponding control strategy from a database according to the characteristic data, finally decomposing the selected control strategy, clustering and grouping the decomposed control strategy blocks according to the dual dimensionalities of time sequence and approximation degree, deleting the group of only one control strategy block, fusing the control strategy blocks in the rest groups, recombining the fused control strategy blocks to obtain a final control strategy, and then correcting the final control strategy according to the predetermined value range of the output total power, so that the output total power in the final control strategy does not exceed the predetermined value range of the output total power. And meanwhile, storing the finally calculated control strategy into a database. The invention does not use the common PID adjusting mode in the prior art, realizes the control of the total output power by carrying out targeted optimization on the pre-stored control strategy, and is insensitive to interference and strong in robustness.

Wherein the fusing of the control strategy blocks comprises the following steps,

and giving weight values to the control strategy blocks in the same group according to the height of the similarity with the cluster center, wherein the weight values of the control strategy blocks are in direct proportion to the similarity with the cluster center, directly reserving the same parts in different control strategy blocks in the same group, weighting and combining different parts in different control strategy blocks in the same group according to the weight values of the corresponding control strategy blocks, traversing and adjusting the combined parts according to the reserved parts, and keeping the consistency of the control targets of the control strategy blocks after fusion. The control strategy fusion method not only realizes weighted fusion, improves the effectiveness of the control strategy after recombination, but also can avoid the problem of strategy target deviation which may occur after strategy fusion.

B. The oil level sensor 9 monitors the oil level in the oil tank 6, and for the oil tank 6 with the oil level exceeding the upper limit of the oil level, redundant refrigeration oil is discharged to the oil storage tank 11 through a second oil return pipe 14; for the oil tank 6 with the oil level lower than the lower limit of the oil level, if the oil tank 6 belongs to a normally open unit, the first oil filling pipe 10 is used for filling the freezing oil into the oil tank 6, if the oil tank 6 belongs to a non-normally open unit, the freezing oil is filled into the corresponding bearing group 2 through the second oil filling pipe 26 before the driving motor 5 corresponding to the oil tank 6 is started to operate, and whether the freezing oil is filled into the oil tank 6 through the first oil filling pipe 10 is determined according to the change of the oil level in the oil tank 6 after the starting to operate;

in the case where the oil level of the oil tank 6, which is included in the non-normally open unit, is lower than the lower limit of the oil level, the operation of the unit includes the steps of,

b1, injecting refrigeration oil into the corresponding bearing group 2 through the second oil injection pipe 26 30 seconds before starting up;

b2, after the machine is started, monitoring the oil level in the oil tank 6, and stopping the second oil filling pipe 26 from filling the refrigeration oil into the corresponding bearing group 2 when the oil level rises above the lower limit of the oil level; if the oil level does not rise after 90 seconds of starting, the first oil filling pipe 10 is used for filling the refrigeration oil into the oil tank 6, after the oil level rises to be higher than the lower limit of the oil level, the first oil filling pipe 10 is stopped to fill the refrigeration oil into the oil tank 6, then the second oil filling pipe 26 is continuously kept to fill the refrigeration oil into the corresponding bearing group 2 for 30 seconds, and then the second oil filling pipe 26 is stopped to fill the refrigeration oil into the corresponding bearing group 2.

C. And (3) periodically rotating the driving motors 5 in the normally open unit and the normally non-open unit.

The regular alternation of the driving motors 5 in the normally open unit and the non-normally open unit comprises the following steps,

c1, setting an upper limit of the starting time, stopping the driving motor 5 which reaches the upper limit of the starting time when the machine is continuously started, dividing the driving motor into an abnormal starting group, starting the driving motor 5 which has the most starting frequency in the non-normally open machine set, and dividing the driving motor into the normally open machine set;

and C2, for the normally-open unit, when the driving motor 5 in the normally-open unit is turned off in the step A1, the driving motor 5 with the longest continuous starting time is turned off preferentially, and when the driving motor 5 in the normally-open unit is turned on in the step A1, the driving motor 5 with the longest continuous stopping time is turned on preferentially.

The inventor conducts experimental verification on the technical scheme of the invention in a 1000-ton commercial refrigeration system project cooperating with Dalian iceberg cold and hot science and technology limited company, and finds that a compressor unit designed by the invention can completely meet the start-stop requirement of 30 times per hour, and in the system test operation, after the control method provided by the invention is used, the energy consumption reduction of 5-7% can be realized.

In the description of the present invention, it is to be understood that the terms "longitudinal", "lateral", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", etc., indicate orientations or positional relationships based on those shown in the drawings, and are used merely for convenience in describing the present invention, and do not indicate or imply that the device or element so referred to must have a particular orientation, be constructed and operated in a particular orientation, and thus, are not to be construed as limiting the present invention.

The foregoing shows and describes the general principles and broad features of the present invention and advantages thereof. It will be understood by those skilled in the art that the present invention is not limited to the embodiments described above, which are described in the specification and illustrated only to illustrate the principle of the present invention, but that various changes and modifications may be made therein without departing from the spirit and scope of the present invention, which fall within the scope of the invention as claimed. The scope of the invention is defined by the appended claims and equivalents thereof.

Claims

1. The utility model provides an electric compressor, casing (1) including the parallelly connected setting of a plurality of, bearing group (2) are installed to the tip of casing (1), be provided with positive screw rod (3) and cloudy screw rod (4) in casing (1), positive screw rod (3) and cloudy screw rod (4) are connected with bearing group (2), driving motor (5) are installed in the outside of bearing group (2), driving motor (5) link to each other with positive screw rod (3), be provided with oil tank (6) in casing (1), its characterized in that: an air outlet of the shell (1) is connected with an oil separator (7), the oil separator (7) is connected with an oil tank (6) through a first oil return pipe (8), an oil level sensor (9) is installed in the oil tank (6), the oil tank (6) is connected with an oil supply pump (13) through a first oil return pipe (10), a first electric control valve (12) is installed on the first oil return pipe (10), the oil supply pump (13) is connected with an oil storage tank (11), the oil tank (6) is connected with the oil storage tank (11) through a second oil return pipe (14), a second electric control valve (15) is installed on the second oil return pipe (14), the bearing set (2) comprises a base (16), a refrigeration oil main flow passage (17) communicated with the oil tank (6) is arranged in the base (16), two bearing outer rings (18) are fixed on the base (16), a bearing inner ring (19) is arranged on the inner side of the bearing outer ring (18), and balls (20) are installed between the bearing outer ring (18) and the bearing inner ring (19), retaining rings (21) are installed on two sides of a bearing outer ring (18) and a bearing inner ring (19), a first outer ring runner (22) communicated with a refrigeration oil main runner (17) is arranged in the bearing outer ring (18), an oil return runner (23) communicated with a shell (1) is arranged on the retaining ring (21) located on the inner side of a base (16), a refrigeration oil auxiliary runner (24) is arranged in the base (16), a second outer ring runner (25) communicated with the refrigeration oil auxiliary runner (24) is arranged in the bearing outer ring (18), the refrigeration oil auxiliary runner (24) is connected with an oil supply pump (13) through a second oil filling pipe (26), and a third electric control valve (27) is installed on the second oil filling pipe (26).

2. The motor-driven compressor according to claim 1, characterized in that: the outlet directions of the first outer ring flow passage (22) and the second outer ring flow passage (25) are parallel to the radial direction of the bearing outer ring (18), and the outlet direction of the oil return flow passage (23) is parallel to the axial direction of the bearing outer ring (18).

3. The motor-driven compressor according to claim 2, characterized in that: a retainer (28) is arranged between a bearing outer ring (18) and a bearing inner ring (19), a plurality of mounting positions (29) are uniformly arranged on two sides of the retainer (28) respectively, balls (20) are mounted in the mounting positions (29) on two sides of the retainer (28), a first annular groove (30) is formed in one side, facing the bearing outer ring (18), of the retainer (28), two rows of protrusions (31) are symmetrically arranged in the first annular groove (30), through holes (32) are formed in two sides of the first annular groove (30), and extension lines of outlet axes of a first outer ring flow channel (22) and a second outer ring flow channel (25) are intersected with the bottom surface of the first annular groove (30).

4. The motor-driven compressor according to claim 3, characterized in that: two second annular grooves (33) are symmetrically arranged on the inner surface of the bearing inner ring (19), two rows of balls (20) are in sliding contact with the tops of the two second annular grooves (33) respectively, and arc-shaped portions (34) are arranged at the contact positions of the second annular grooves (33) and the balls (20).

5. The motor-driven compressor according to claim 1, characterized in that: the oil injection flow rate of the second oil injection pipe (26) is 10% -15% of the oil injection flow rate of the first oil injection pipe (10).

6. A control method of an electric compressor according to any one of claims 1 to 5, characterized by comprising the steps of:

A. dividing all the driving motors (5) into a normally open unit and a non-normally open unit, wherein the driving motors (5) in the normally open unit are always kept in an operating state, and the driving motors (5) in the non-normally open unit are switched between the operating state and a shutdown state according to the refrigerating capacity requirement and the actual temperature change of a controlled object;

B. the oil level sensor (9) monitors the oil level in the oil tank (6), and excess refrigerating oil is discharged to the oil storage tank (11) through a second oil return pipe (14) for the oil tank (6) with the oil level exceeding the upper limit of the oil level; for an oil tank (6) with the oil level lower than the lower limit of the oil level, if the oil tank (6) belongs to a normally open unit, freezing oil is injected into the oil tank (6) through a first oil filling pipe (10), if the oil tank (6) belongs to a non-normally open unit, the freezing oil is injected into a corresponding bearing group (2) through a second oil filling pipe (26) before a driving motor (5) corresponding to the oil tank (6) is started to operate, and after the starting to operate, whether the freezing oil is injected into the oil tank (6) through the first oil filling pipe (10) or not is determined according to the change of the oil level in the oil tank (6);

C. and the driving motors (5) in the normally open unit and the normally non-open unit are periodically alternated.

7. The control method of the electric compressor according to claim 6, wherein: in the step A, the switching of the running state and the shutdown state of the driving motor (5) in the normally-open unit according to the refrigerating capacity requirement and the actual temperature change comprises the following steps,

a2, adjusting the total output power of the starting unit according to the actual temperature change of the controlled object, arranging the ratio of the output power of the driving motor (5) to the rated power in an ascending order, starting to adjust from the driving motor (5) with the minimum ratio of the output power to the rated power when the total output power needs to be increased, and starting to adjust from the driving motor (5) with the maximum ratio of the output power to the rated power when the total output power needs to be decreased.

8. The control method of the electric compressor according to claim 7, characterized in that: in the step B, under the condition that the oil level of an oil tank (6) belonging to the non-normally open unit is lower than the lower limit of the oil level, the operation of the unit comprises the following steps,

b1, injecting refrigeration oil into the corresponding bearing group (2) through the second oil injection pipe (26) 30 seconds before starting up;

b2, after starting up, monitoring the oil level in the oil tank (6), and stopping the second oil filling pipe (26) from filling the refrigeration oil into the corresponding bearing group (2) when the oil level rises above the lower limit of the oil level; if the oil level does not rise after 90 seconds of starting, the first oil filling pipe (10) is used for filling the freezing oil into the oil tank (6), after the oil level rises to be higher than the lower limit of the oil level, the first oil filling pipe (10) is stopped to fill the freezing oil into the oil tank (6), then the second oil filling pipe (26) is continuously kept to fill the freezing oil into the corresponding bearing group (2) for 30 seconds, and then the second oil filling pipe (26) is stopped to fill the freezing oil into the corresponding bearing group (2).

9. The control method of the electric compressor according to claim 8, wherein: in the step C, the step of periodically alternating the driving motors (5) in the normally open unit and the non-normally open unit comprises the following steps,

c1, setting an upper limit of the starting time, stopping the driving motor (5) which reaches the upper limit of the starting time after continuous starting, dividing the driving motor into the normally-opened units, and simultaneously starting the driving motor (5) which is started most frequently in the normally-opened units and dividing the driving motor into the normally-opened units;

and C2, for the normally-open unit, when the driving motor (5) in the normally-open unit is turned off in the step A1, the driving motor (5) with the longest continuous starting time is turned off preferentially, and when the driving motor (5) in the normally-open unit is turned on in the step A1, the driving motor (5) with the longest continuous stopping time is turned on preferentially.