CN108468643B

CN108468643B - Capacity control system and method for screw compressor capable of switching speed at fixed frequency

Info

Publication number: CN108468643B
Application number: CN201810483330.9A
Authority: CN
Inventors: 森山昌幸; 徐峰; 张林波; 朱应求
Original assignee: Mcquay Air Conditioning and Refrigeration Wuhan Co Ltd
Current assignee: Mcquay Air Conditioning and Refrigeration Wuhan Co Ltd
Priority date: 2018-05-18
Filing date: 2018-05-18
Publication date: 2025-03-07
Anticipated expiration: 2038-05-18
Also published as: WO2019218796A1; CN108468643A

Abstract

The invention discloses a screw compressor capacity control system and method capable of switching speed at a fixed frequency, comprising a screw compressor with a fixed frequency motor, a bypass slide valve with adjustable capacity installed on the screw compressor, a bypass slide valve action driver, a motor driver, a controller and a load measuring device, the bypass slide valve is connected to the bypass slide valve action driver signal and is controlled by the bypass slide valve action driver, a bypass slide valve position sensor is also provided, the bypass slide valve position sensor is connected to the screw compressor for measuring the slide valve position, the load measuring device is used to detect the compressor operation load state, the motor driver is connected to the fixed frequency compressor; the bypass slide valve position sensor, the bypass slide valve action driver, the load measuring device, the motor driver and the controller are connected by signal. A higher performance coefficient COP is achieved when running at full load and partial load, adapting to the site with frequent starting, and suppressing the starting current peak.

Description

Screw compressor capacity control system and method capable of switching rotation speed in fixed frequency

Technical Field

The invention belongs to the technical field of refrigeration air conditioner power control, and particularly relates to a screw compressor capacity control system and method.

Background

Screw refrigerating air conditioning units are generally classified into air conditioning units using a fixed frequency and a fixed speed driving screw compressor (abbreviated as fixed frequency screw units) and air conditioning units using a variable frequency and variable speed driving screw compressor (abbreviated as variable frequency screw units). The variable-frequency screw unit has high performance when in partial load operation, the full-load performance coefficient is reduced, and the variable-frequency screw unit has high cost and high price compared with the fixed-frequency screw unit.

The constant-frequency screw unit using the constant-frequency and constant-speed screw compressor generally adjusts the capacity of the constant-frequency screw compressor through a bypass device such as a slide valve when the load is reduced from full load to partial load operation, and the coefficient of performance COP of the partial load is lower because the gas unloaded by the bypass is compressed before bypass.

The variable-frequency screw unit using the variable-frequency variable-speed screw compressor realizes capacity adjustment by adjusting the rotational speed of the screw compressor through the frequency converter when the load is reduced from full load to partial load, has no invalid work caused by bypass, has higher partial load performance coefficient, has about 3-5% lower performance coefficient COP compared with the fixed-frequency screw air conditioner unit when the frequency converter runs at full load due to power loss (about 3-5%), but has high cost.

Therefore, the screw refrigerating air conditioner unit with high coefficient of performance COP (coefficient of performance) in full load and partial load operation is realized under the condition of proper speed control of the fixed-frequency screw unit, particularly under the condition of the cost equivalent to that of the fixed-frequency fixed-speed screw unit, and the screw refrigerating air conditioner unit becomes a technical problem to be solved urgently in the technical field of refrigeration at present.

In industrial applications, it is often desirable that a motor be capable of two-speed (multi-speed) operation, both of which refer to a speed change gear such as a high speed, a low speed, or a medium speed distinction. The common means for starting and operating a two-speed (multi-speed) motor are contactor drive, inverter drive, and soft starter drive. The contactor drive realizes the scheme of star delta start and high-low speed switching of the motor, which has the advantages of high cost, complex structure and high failure rate, the frequency converter drive realizes the scheme of starting and high-low speed switching of the motor, which has low starting current and smooth starting although no secondary current impact exists in the starting process, and the scheme has high cost, and the soft starter drive realizes the scheme of soft start and high-low speed switching of the motor, which has low cost, simple structure and no starting impact, so the frequency converter drive is widely applied.

Conventional soft starter driving schemes generally use a soft starter, and then configure two (multiple) contactors, and when the soft starter is started, one contactor is closed first, then the soft starter is started, and when the soft starter is stopped, the contactor is stopped first, and then the contactor is released. Because the soft starter has the requirement on the starting times in unit hour, if the starting times are required frequently on site, the scheme can cause the soft starter to be damaged, the current requirement is large when the soft starter drives at high speed, the current requirement is small when the soft starter drives at low speed, the starting parameters and the starting current limit are different, and the protection parameters are different, therefore, the traditional soft starter driving scheme cannot reliably protect the motor and control the starting curve.

Disclosure of Invention

The invention aims to solve the technical problem of providing a screw compressor capacity control system and a screw compressor capacity control method capable of switching rotation speed operation at fixed frequency, which realize higher coefficient of performance (COP) in full load and partial load operation at the same cost as that of a fixed-frequency fixed-speed screw unit, adapt to sites with frequent starting and have the capability of inhibiting starting current peaks.

Aiming at the technical problems to be solved, the invention provides the following technical scheme:

a capacity control system of screw compressor capable of switching rotation speed at fixed frequency comprises a screw compressor with a fixed frequency motor, a bypass slide valve with adjustable capacity is arranged on the screw compressor, a bypass slide valve action driver, a motor driver, a controller and a load measuring device are further arranged, the bypass slide valve is in signal connection with the bypass slide valve action driver and is controlled by the bypass slide valve action driver, and the capacity control system is characterized in that a bypass slide valve position sensor is further arranged, the bypass slide valve position sensor is connected with the screw compressor and used for measuring the position of the slide valve, the load measuring device is used for detecting the operation load requirement of the compressor, the motor driver is connected with the fixed frequency compressor, and the bypass slide valve position sensor, the bypass slide valve action driver, the load measuring device and the motor driver are in signal connection with the controller.

Further, the motor drive is configured to achieve fixed frequency motor speed two-speed or multi-speed operation and to switch between speed stages.

Further, the fixed frequency motor comprises at least one winding, the pole number and the rotating speed of the winding are switched through a wiring mode, the motor driver comprises at least one soft starter and two/more contactors, and the soft starter is selectively connected with the motor winding through the two/more contactors.

The fixed-frequency motor comprises at least one group of high-speed windings and at least one group of low-speed windings, the motor driver comprises a high-speed soft starter, a low-speed soft starter and at least one circuit breaker, the circuit breaker is respectively connected with the low-speed soft starter and the high-speed soft starter, the high-speed soft starter is connected with the high-speed windings of the fixed-frequency motor, and the low-speed soft starter is connected with the low-speed windings of the fixed-frequency motor.

Furthermore, when the fixed-frequency compressor further comprises at least one group of medium-speed windings with the rotating speed between the high-speed windings and the low-speed windings, a plurality of starting contactors are further arranged in the soft starter electric control cabinet, wherein the output end of the high-speed soft starter is connected with the high-speed windings of the fixed-frequency compressor through one starting contactor, a plurality of parallel starting contactors are arranged on the output end of the low-speed soft starter, and the parallel starting contactors are connected with the low-speed windings and the medium-speed windings in a one-to-one butt joint mode.

Furthermore, a breaker is arranged in front of the high-speed soft starter and one low-speed soft starter respectively, and the two breakers are connected in parallel on the power supply.

Furthermore, a disconnecting switch QS is connected to the front main path of the two circuit breakers, and the two circuit breakers are formed by the disconnecting switch QS to be selectively connected with the respective soft starter.

The control method of the screw compressor capable of switching rotating speed operation at fixed frequency is characterized in that when the motor is in different rotating speeds, the controller obtains a load demand according to the load measuring device, the bypass slide valve position sensor detects slide valve opening position signals, the controller adjusts the motor operating rotating speed according to the load demand and the slide valve position signals to realize multi-speed output and/or switching, and adjusts the bypass slide valve opening position through the bypass slide valve action driver, so that the bypass slide valve opening position is in a set opening range, and the opening range enables the slide valve opening position to always keep running towards the low-speed operation of the motor and the high-opening position trend operation of the slide valve with the motor speed.

Further, the specific flow of realizing three-speed output and/or switching by adjusting the running rotating speed of the motor through the motor driver is as follows:

Detecting the opening position of the slide valve when the fixed-frequency compressor runs at a high speed, and switching the fixed-frequency compressor into a medium-speed running mode when the opening position of the slide valve is less than or equal to H percent and the load shedding requirement exists, or continuing to run in a high-speed running state, wherein H percent is the lower limit of the opening position of the slide valve when the compressor runs at the high speed, which is set in a controller;

Detecting the opening position of the slide valve when the slide valve is in medium-speed running, if the opening position of the slide valve is less than or equal to M percent and the load shedding requirement exists, switching in the fixed-frequency compressor to run at low speed, if the slide valve is in 100 percent and the load enhancement requirement exists, switching in the fixed-frequency compressor to run at high speed, so that the opening position of the slide valve is in H percent to 100 percent, otherwise, continuing to run in a medium-speed running state, and keeping the opening position of the slide valve in medium-speed running to be M percent to 100 percent, wherein M percent is the lower limit of the opening position of the slide valve when the compressor is in medium-speed running;

When running at low speed, detecting the opening position of the slide valve, if the slide valve position is 100% and the load increasing requirement exists, switching to medium-speed running, and keeping the opening position of the slide valve at the medium-speed running to be M% -100%, otherwise, keeping the slide valve at the low speed running, and keeping the opening position of the slide valve at the low speed running to be N% -100%, wherein N% is the lower limit of the opening position of the slide valve when the compressor runs at the low speed.

Furthermore, the specific flow of realizing double-speed output and/or switching by adjusting the running rotating speed of the motor through the motor driver is as follows:

The controller sets the lower limit of the slide valve opening position of the bypass slide valve as H, namely the slide valve opening position range is H-100%, corresponding to the compressor output capacity range of 50-100%, when the slide valve opening position moves to H% and the capacity of the screw compressor needs to be further reduced at high rotation speed, the screw compressor is switched to low rotation speed operation, and when the low rotation speed operation is performed, the slide valve opening position range is 0-100%, corresponding to the compressor output capacity range of 50%.

Further, when the motor driver power supply starts the main loop to be provided with two soft starters, the high-speed soft starter controls the high-speed winding of the motor, the low-speed soft starter controls the low-speed winding of the motor, the output interlocking between the high-speed soft starter and the low-speed soft starter jointly shares the running and starting of the motor, the system controller adjusts the position of the bypass slide valve through the bypass slide valve action driver according to the input signal of the load measuring device and the slide valve position signal, and adjusts the running rotating speed of the motor through the motor driver, and when the motor runs at different rotating speeds, the opening position of the bypass slide valve is adjusted according to the set range.

Further, the upper limit of the current of the high-speed soft starter is determined by the rotating speed N0 of the highest winding, the upper limit of the current of the low-speed soft starter is determined by the rotating speed N1 of the middle rotating speed winding, and the winding matching rule corresponds to that the rotating speed N0 of the highest winding is larger than or equal to the rotating speed of the winding and is larger than or equal to the rotating speed N1 of the middle rotating speed winding, the high-speed soft start driving is carried out, the rotating speeds of the windings are smaller than or equal to the rotating speed N1 of the middle rotating speed winding, and the low-speed soft starter driving is carried out.

Further, the motor is started in a soft start mode, the starting mode is a slope current mode, the peak value of the starting current of the motor is limited, the starting voltage is regulated, the current is smoothly increased to enable the rotating speed of the motor to reach the rated rotating speed to finish the motor starting, the high-speed winding of the motor corresponds to a high-speed soft starter, the protection parameters are limited according to high-speed current protection, the starting current is limited according to high-speed current, the starting current is ensured to be smooth, the low-speed winding of the motor corresponds to a low-speed soft starter, the protection parameters are protected according to low-speed current, the starting current is limited according to low-speed current, and the starting current is ensured to be smooth.

The motor speed switching mode is that when the motor is switched to low speed or medium speed, the high speed soft starter stops outputting, after the motor is freely stopped for a plurality of seconds, the low speed soft starter is started to enable the motor to run at the low speed or medium speed, when the motor is switched to low speed at medium speed, the low speed soft starter stops outputting, after the motor is freely stopped for a plurality of seconds, the motor winding is switched from the medium speed winding to the low speed winding, then the low speed soft starter is started again to enable the motor to run at the low speed, when the motor is switched to high speed at low speed, the low speed soft starter stops outputting, after the motor is freely stopped for a plurality of seconds, the high speed soft starter is started, and the motor is started to enable the motor to run at the high speed.

The beneficial effects of the invention are as follows:

1. The fixed-frequency double-speed or multi-speed driven fixed-frequency screw compressor is used, the bypass slide valve, the slide valve position sensor and the main controller are used, so that when the compressors run at different rotating speeds, the slide valve is controlled in a reasonable travel range, and full-load and partial-load high-efficiency operation is achieved;

2. When the device is used for a fixed-frequency screw air conditioner unit, a frequency conversion cabinet is not required to be configured, and the overall cost of the unit is reduced by more than 10% compared with that of the frequency conversion screw air conditioner unit on the premise that the same full-load COP and partial-load COP are equivalent;

3. when the device is used for the fixed-frequency screw air conditioner unit, the COP of the partial load of 50% or below is 20-30% higher than that of the fixed-frequency fixed-speed screw air conditioner unit, and the energy-saving effect is obvious.

4. The motor controller main loop is provided with two soft starters, one soft starter drives the high-speed winding, the other soft starter drives the low-speed winding, the output of the soft starters is interlocked, the running and starting of the motor are shared together, the frequent starting of the motor can be met, and the service life of a driving system is prolonged.

5. The soft starter is directly connected to the motor binding posts, six binding posts of the double-speed motor, and the soft starter is only connected with 6 groups of power cables in a butt joint mode with the motor respectively, so that the connection is simple.

6. The parameters of the two soft starters configured in the main loop are respectively matched with the windings of the double-speed motor, the high-current soft starter drives the windings of the high-speed motor, the low-current soft starter drives the windings of the low-speed motor, the parameters correspond to the high-speed motor and the low-speed motor, the protection is safer, and the performance is better;

7. The soft starter is used for driving the motor, current is smooth in the starting process, the starting current peak value can be adjusted, and the starting mode adopts a slope current scheme, so that the starting current is smooth, and the starting curves of the high-speed and low-speed motor are more matched. No secondary impact. The soft starter body has comprehensive protection functions (over/under voltage protection, reverse phase protection, unbalanced three-phase current protection, input/output phase failure and the like) and is more comprehensive and safer for motor protection.

Drawings

Fig. 1 is a schematic diagram of a capacity control system of a screw compressor capable of constant frequency switching rotation speed operation according to the present invention.

Fig. 2 is a control logic diagram of an example of the three-speed operation and switching of the capacity control system of the screw compressor according to the present invention.

In fig. 1-2, reference numerals are given to a fixed-frequency compressor 1, a bypass slide valve operation driver 4, a motor driver 5, a load measuring device 6, a system controller 7, a bypass slide valve 8, and a slide valve position sensor 9.

Fig. 3 is a schematic diagram of the motor drive of the present invention based on a two-speed motor drive system.

Fig. 4 is a circuit block diagram of one embodiment of a two-speed motor drive-based system for a motor drive of the present invention.

Fig. 5 is a main loop structure diagram of the motor driver based on the single soft starter driving of the present invention.

Fig. 6 is a main loop structure diagram of a motor driver according to another embodiment of the present invention based on a single soft starter drive.

Fig. 7 is a flow chart of a motor drive two-speed operation and switching control method of the present invention.

The reference numerals in fig. 3-7 are as follows, 1, a fixed frequency compressor (wherein motor windings 1,2,3 are high-speed windings, motor windings 4, 5, 6 are low-speed windings), 2, a soft starter electric control cabinet (QM 1 is a high-speed soft starter, QM2 is a low-speed soft starter, QF is a circuit breaker), 3, and a Controller (CB).

Fig. 8 is a schematic diagram of the structure of the motor driver 5 based on a multi-speed motor drive according to the present invention.

Fig. 9 is a circuit configuration diagram of one embodiment of the motor driver 5 of the present invention based on a multi-speed motor drive.

Fig. 10 is a flowchart of a three-speed operation and switching control method of the motor driver 5 based on a multi-speed motor drive according to the present invention.

Detailed Description

Fig. 1 is a schematic diagram of a capacity control system of a screw compressor capable of constant frequency switching rotation speed operation according to the present invention. The system comprises a fixed-frequency compressor 1, a bypass slide valve action driver 4, a motor driver 5, a load measuring device 6, a system controller 7 and a bypass slide valve 8, wherein the fixed-frequency compressor 1 is a combination of a screw compressor and a fixed-frequency motor, the motor rotating speed is regulated through pole-to-logarithmic switching, the bypass slide valve 8 with adjustable capacity is installed on the screw compressor, the bypass slide valve 8 is connected with the bypass slide valve action driver 4 and controlled by the bypass slide valve action driver, a slide valve position sensor 9 is further arranged, the bypass slide valve position sensor 9 is connected with the screw compressor and used for measuring the slide valve position, the motor driver 5 is functionally connected with the motor to realize double-speed or multi-speed operation, the load measuring device 6 is used for detecting the operation load demand of the compressor, and the bypass slide valve position sensor 9, the bypass slide valve action driver 4, the load measuring device 6 and the motor driver 5 are in signal connection with the system controller 7.

The control method of the screw compressor and the capacity control system capable of switching the rotating speed at fixed frequency is characterized in that a bypass slide valve position sensor 9 detects a slide valve position signal, a system controller 7 adjusts the position of a bypass slide valve 8 through a bypass slide valve action driver 4 according to a load measuring device 6 input signal and the slide valve position signal, and the motor operation rotating speed is adjusted through a motor driver 5 to realize multi-speed output, or when the motor is operated at different rotating speeds, the system controller 7 sets different movable position ranges for the bypass slide valve 8.

The fixed-frequency screw compressor is characterized in that the closer the slide valve position is to the full potential energy efficiency is higher according to the designed pressure ratio. When the compressor is output in small capacity, the compressor is operated in a state of lower speed and higher slide valve position as much as possible, so that higher energy efficiency is obtained.

The rotating speed is controlled and the positions of the sliding valves are matched, so that the compressor is in a state with lowest power (highest energy efficiency), for example, three-speed compressors output 30 percent of capacity, and three output modes are theoretically adopted, namely ① high-speed (3000 r/min) +30 percent of sliding valves, ② medium-speed (1500 r/min) +60 percent of sliding valves) and ③ low-speed (1000 r/min) +90.9 percent of sliding valves, and the ③ th mode is found to output the highest energy efficiency through multiple researches and experiments of the invention.

In order to further implement this control method and implement the most energy-efficient output of the ③ th mode, the present invention adopts a control flow (control logic of the three-speed operation example) as shown in fig. 2:

detecting the position of a slide valve when the fixed-frequency compressor 1 runs at a high speed, if the slide valve position is less than or equal to H percent and the load shedding requirement exists, switching the fixed-frequency compressor 1 into a medium-speed running state, and otherwise, continuing to run in the high-speed running state;

Detecting the position of a slide valve when the slide valve is in a middle speed running state, if the slide valve position is less than or equal to M percent and the load reducing requirement exists, switching in the fixed-frequency compressor 1 to run at a low speed, if the slide valve is in a position of 100 percent and the load increasing requirement exists, switching in the fixed-frequency compressor 1 to run at a high speed to enable the position of the slide valve to be in a position of H-100 percent, otherwise, continuing to run in a middle speed running state, and keeping the position of the slide valve in a middle speed running state to be in a position of M-100 percent, wherein M percent is the lower limit of the movement of the valve position when the compressor runs at the middle speed;

When the compressor runs at low speed, the position of the slide valve is detected, if the slide valve position is 100% and the load increasing requirement exists, the slide valve is switched to the medium-speed running, the position of the slide valve which keeps the medium-speed running is M% -100%, otherwise, the slide valve which keeps the low-speed running is continued to keep the position of the slide valve which keeps the low-speed running to be N% -100%, and N% is the lower limit of the movement of the valve position when the compressor runs at low speed.

The control logic may also be activated at a low or medium speed as shown in fig. 2. Whether high or low speed, is operated, and is adjusted in accordance with the load demand as shown in fig. 2 in conjunction with the spool valve position.

One embodiment of the compressor start-up according to the above method is as follows, according to the high speed motor operation example, the slide valve is positioned at 50%, the output capacity is 50% at this time, and the load measuring device 6 feeds back to the system controller 7, and load shedding is required. The system controller 7 sends an instruction to the motor driver 5 to stop the high-speed motor, start the medium-speed motor, and when the spool valve is started, the spool valve moves to 66%, the load at the moment is 33% higher than the target load, and the load measuring device 6 feeds back to the system controller 7, so that the load shedding needs to be continued. The system controller 7 sends instructions to the motor driver 5, namely, the medium-speed motor is stopped, the low-speed motor is started, the bypass slide valve 8 can send instructions to the slide valve driver 4 according to feedback of the load measuring device 6, so that the bypass slide valve 8 is finally stopped at 90.9% to realize 30% load output. (this process is a process of switching from high speed to low speed in the compressor capacity from high to low speed, and is most common in actual operation.)

Taking the position of the bypass slide valve 8 as 0% of the minimum capacity of the corresponding screw compressor and taking the position of the bypass slide valve 8 as 100% of the maximum capacity of the corresponding screw compressor as an example, the system controller 7 detects the position of the slide valve of the bypass slide valve 8 through the bypass slide valve position sensor 9 and controls the movable position of the slide valve 8 in a certain range at different rotating speeds so as to realize high performance coefficient from full load to minimum load of the screw compressor. The speed of the two-speed, three-speed operation compressor and the recommended slide valve positions are shown in table 1, table 2.

As shown in Table 1, for three-speed drive screw compressors with pole numbers of 2, 4 and 6 in high, medium and low rotational speeds, when the drive screw compressor is operated at a high rotational speed with pole number of 2, the lower limit H% of the slide valve opening position is defined to be 40-60%, preferably H% is about 50% (i.e. the movable position range of the bypass slide valve is H-100% corresponding to the output capacity range of the compressor when the drive screw compressor is operated at a high rotational speed, when the slide valve position is moved to H%, the screw compressor capacity is further reduced, the screw compressor is switched to be operated at a medium rotational speed with pole number of 4, when the drive screw compressor is operated at a medium rotational speed, the lower limit of the slide valve opening position is defined to be M%, generally M% is about 50-75%, preferably 66% (i.e. the movable range of the slide valve opening position is M-100%, corresponding to the output capacity range of the compressor is 33% -50%), when the slide valve position is moved to M%, the screw compressor is further reduced, the screw compressor is switched to be operated at a low rotational speed with pole number of 6, when the slide valve position is defined to be operated at a low rotational speed, the lower limit of the slide valve position is further reduced, the N% is defined to be the motor is moved to be about 0% -100%, the lower limit of N% corresponding to the movable range of N is more than the minimum load, and the compressor is more than the minimum load value is more than the minimum value, and the lower limit of N is more than the movable range is more than 0% -than the minimum load.

Table 1 three speed compressor output capacity and speed, slide valve position relationship table

Compressor output capacity	Rotational speed	Bypass spool valve movable position range
			50%~100%	High (3000 r/min)	(H% is 40-60%) H% to 100%
33%~50%	Middle (1500 r/min)	(M% is 50-75%) M-100%
			min~33%	Low (1000 r/min)	(N% is 0-50%) N% to 100%

Table 1 illustrates that the 100% slide valve position at medium speed corresponds to the compressor capacity corresponding to the H% slide valve position at high speed, and that the 100% slide valve position at low speed corresponds to the compressor capacity corresponding to the M% slide valve position at medium speed.

As shown in Table 2, for a two-speed drive screw compressor with pole numbers of 2 and 4 for high speed and low speed, respectively, when operating at high speed with pole numbers of 1 (pole number of 2), the controller sets the lower limit of the bypass slide valve position movement to H% (i.e., the bypass slide valve position movable range is H% -100%, corresponding to the compressor output capacity range of 50% -100%), typically H% is around 50%, at high speed, when the slide valve position movement is less than or equal to H%, and the screw compressor capacity needs to be further reduced, the screw compressor will switch to low speed operation (the bypass slide valve position movable range is N% -100%, corresponding to the compressor output capacity range: minimum load: 50%).

Table 2 table of output capacity and speed of the two-speed running compressor and slide valve position relationship

Compressor output capacity	Rotational speed	Bypass spool valve movable position range
			50%~100%	High (3000 r/min)	(H% is 40-60%) H% to 100%
min~50%	Low (1500 r/min)	(N% is 0-50%) N% to 100%

Table 2 illustrates that the 100% slide valve position at low speed corresponds to the compressor capacity corresponding to the H% slide valve position at high speed.

The motor driver 5 used in the present invention has various embodiments, and conventional driving methods, such as "one soft starter+two/more contactor driving" may be applied to the present invention, and are also included in the scope of protection. Besides, the invention is further characterized in that the main loop is provided with two soft starters, one soft starter drives a motor high-speed winding, the other soft starter drives a motor medium-speed winding and a motor low-speed winding, the soft starters output interlocking, the running and starting of the motor are shared together, the frequent starting of the motor can be met, the service life of a driving system is prolonged, the two soft starter parameters of the main loop are respectively matched with the two-speed motor winding, the high-current soft starter drives the high-speed motor winding, the low-current soft starter drives the low-speed motor winding, the parameters correspond to the high-speed motor and the low-speed motor, the protection is safer, and the performance is better. When the fixed-frequency compressor 1 runs at different rotating speeds, the slide valve is controlled in a reasonable travel range, so that full-load and partial-load high-efficiency running is achieved.

As shown in fig. 3, a schematic diagram of the motor drive of the present invention based on a two-speed motor drive system is shown. The controller 3 is connected with the soft starter electric control cabinet 2, the soft starter electric control cabinet 2 is connected with the fixed-frequency compressor 1, a breaker QF, a high-speed soft starter QM1 and a low-speed soft starter QM2 are arranged in the soft starter electric control cabinet 2, and the fixed-frequency compressor 1 comprises a group of high-speed windings (motor windings 1, 2 and 3) and a group of low-speed windings (motor windings 4, 5 and 6).

Fig. 4 is a circuit diagram illustrating one embodiment of the two-speed motor drive-based system for the motor drive of the present invention shown in fig. 3. The control ends of the high-speed soft starter QM1 and the low-speed soft starter QM2 are respectively connected in parallel to the controller 3, the input ends (terminals L1, L2 and L3) of the high-speed soft starter QM1 and the low-speed soft starter QM2 are respectively connected in parallel to three-phase wiring ends after the breaker QF breaks, the output ends (terminals L4, L5 and L6) of the high-speed soft starter QM1 are sequentially connected to windings (motor windings 1,2 and 3) of the high-speed winding of the fixed-frequency compressor 1, and the output ends (terminals L4, L5 and L6) of the low-speed soft starter QM2 are sequentially connected to windings (motor windings 4, 5 and 6) of the low-speed winding of the fixed-frequency compressor 1.

Fig. 5 is a main loop structure diagram of the motor driver 5 according to the present invention based on a single soft starter drive. Which is a variation of the embodiment of fig. 4, differs from fig. 4 in that two circuit breakers QF1 and QF2 are used, each of which is connected to one soft starter, and then the two-speed motor is driven by the two soft starters. The high-speed soft starter QM1 and the low-speed soft starter QM2 are started respectively according to the on-off state of the circuit breakers QF1 and QF2, and the double-speed motor is driven based on the single soft starter.

Fig. 6 is a main loop structure diagram of a motor driver 5 according to another embodiment of the present invention based on a single soft starter drive. In fig. 5, a disconnecting switch QS is connected to the front main path of two circuit breakers QF1 and QF2, and the two soft starters are formed by the disconnecting switch QS to selectively drive the double-speed motor based on a single soft starter.

Fig. 7 is a flow chart of the motor controller according to the present invention based on the above-mentioned two-speed operation and switching control method. Wherein:

the motor is started in a soft start mode, the starting mode is a slope current mode, the peak value of the starting current of the motor is limited, the starting voltage is regulated, the current is smoothly increased to enable the rotating speed of the motor to reach the rated rotating speed to finish the motor starting, the high-speed windings 1,2 and 3 of the motor correspond to a soft starter (QM 1) with large current, the protection parameters are protected according to the high-speed current, the starting current is also limited according to the high-speed current, the starting current is ensured to be smooth;

When the high speed is cut to be at a high speed, the low speed soft starter QM2 stops outputting, and after the motor is stopped for a plurality of seconds, the high speed soft starter QM1 starts the motor to operate at a high speed;

the two soft starters share the starting and running of one motor together, and one soft starter stops when the other soft starter runs, so that the requirement of frequent starting can be met, and the service life is prolonged;

In all starting and running processes, the soft starter feeds current signals back to the controller, and the controller protects the starting and running conditions of the motor according to the current values.

Fig. 8 is a schematic diagram of a motor controller of the present invention based on a multi-speed motor drive. It differs from a two-speed start in that a soft starter is followed by a plurality of contactors. The soft starter control device comprises a controller 3, a soft starter electric control cabinet 2, a circuit breaker QF, a high-speed soft starter QM1, a low-speed soft starter QM2 and N starting contactors (KM 1-KMN are starting contactors), wherein the controller 3 is connected with the soft starter electric control cabinet 2, the soft starter electric control cabinet 2 is connected with a fixed-frequency compressor 1, the soft starter electric control cabinet 2 is internally provided with a circuit breaker QF, the high-speed soft starter QM1 and the low-speed soft starter QM2, the fixed-frequency compressor 1 comprises a plurality of groups of windings, at least one group of high-speed windings (motor windings 1,2 and 3) and one group of low-speed windings (motor windings N, N +1 and N+2).

Fig. 9 is a circuit block diagram of one embodiment of the motor controller of the present invention based on a multi-speed motor drive. The control ends of the high-speed soft starter QM1 and the low-speed soft starter QM2 are respectively connected in parallel to the controller 3, the input ends (L1, L2 and L3 terminals) of the high-speed soft starter QM1 and the low-speed soft starter QM2 are respectively connected in parallel to three-phase wiring ends after the breaker QF breaks, the output ends (L4, L5 and L6 terminals) of the high-speed soft starter QM1 are sequentially connected to windings (motor windings 1, 2 and 3) of the high-speed winding of the fixed-frequency compressor 1 through a starting contactor KM1, the output ends (L4, L5 and L6 terminals) of the low-speed soft starter QM2 are respectively connected in parallel to windings (N, N +1 and N+2) of the low-speed winding of the fixed-frequency compressor 1 through a starting contactor KMN, the other ends are sequentially connected to windings (4, 5 and 6) of the windings of the fixed-frequency compressor 1 through a starting contactor KM2, and the like.

Fig. 10 is a flowchart of a three-speed operation and switching control method of the motor driver 5 based on a multi-speed motor drive according to the present invention. The motor speed switching mode is that when the motor is switched to a low speed or a medium speed at a high speed, the output of the high speed soft starter is stopped, the low speed soft starter is started after the motor is freely stopped for a plurality of seconds, the motor is started to operate at the low speed or the medium speed, when the motor is switched to the low speed at the medium speed, the output of the low speed soft starter is stopped, after the motor is freely stopped for a plurality of seconds, the motor winding is switched from the medium speed winding to the low speed winding, then the low speed soft starter is started again, the motor is started to operate at the low speed, when the motor is switched to the high speed at the low speed, the output of the low speed soft starter is stopped, the high speed soft starter is started after the motor is freely stopped for a plurality of seconds, and the motor is started to operate at the high speed.

Before the motor starts, the controller 3 controls the contactor KMN corresponding to the winding to be started to be attracted first, and then controls the soft starter QM to start.

During switching, the controller firstly stops the starter QM which is working, then releases the contactor KM corresponding to the winding, then starts the starter QM which needs to be operated, and then communicates with the contactor KM corresponding to the winding.

The output of the high-speed soft starter QM1 is stopped, the motor is started to run at a low speed by starting the low-speed soft starter QM2 after the motor is stopped freely for a few seconds, the motor is started to run at a medium speed by starting the medium-speed soft starter QM2 when the high speed is switched to the medium speed, and the motor is started to run at a low speed by starting the low-speed soft starter QM2 when the low speed is switched from the medium speed.

The matching rule of the multi-speed (speed gear is greater than 2) motor and the soft starter is that the high-current soft starter drives the high-speed motor winding and the low-current soft starter drives the low-speed motor winding.

The upper limit of the current of the high-speed soft starter is determined by the rotating speed N0 of the highest winding, the upper limit of the current of the low-speed soft starter is determined by the rotating speed N1 of the middle rotating speed winding, and the winding matching rule corresponds to that the rotating speed N0 of the highest winding is equal to or more than the rotating speed of the winding and the rotating speed N1 of the middle rotating speed winding are driven by the high-speed soft starter, and the rotating speeds of the windings are equal to or less than the rotating speed N1 of the middle rotating speed winding and are driven by the low-speed soft starter.

The two-speed and multi-speed motor drive system main circuit configuration is not limited to the above form, and any solution that uses a soft starter to drive a two-speed or multi-speed motor is within the scope of the present invention. .

Therefore, the invention has the following beneficial effects:

Claims

1. The utility model provides a but screw compressor capacity control system of fixed frequency switching rotational speed operation, includes the screw compressor that contains the fixed frequency motor, installs the bypass slide valve of adjustable capacity on the screw compressor, still sets up bypass slide valve action driver, motor driver, controller and load measuring device, bypass slide valve and bypass slide valve action driver signal connection to receive bypass slide valve action driver control, its characterized in that:

the bypass slide valve position sensor is connected with the screw compressor and used for measuring the position of the bypass slide valve, and the load measuring device is used for detecting the running load demand of the screw compressor;

The motor driver comprises at least one soft starter and at least two contactors, wherein the soft starter is selectively connected with the motor winding through the at least two contactors:

the fixed-frequency motor comprises at least one group of high-speed windings and at least one group of low-speed windings, and the motor driver comprises a high-speed soft starter, a low-speed soft starter and at least one circuit breaker, wherein the circuit breaker is respectively connected with the low-speed soft starter and the high-speed soft starter;

The constant-frequency motor comprises at least one group of medium-speed windings with the rotating speed between the high-speed windings and the low-speed windings, a plurality of starting contactors are arranged in the soft starter in addition to the high-speed soft starter and the low-speed soft starter, wherein the output end of the high-speed soft starter is connected with the high-speed windings of the constant-frequency screw compressor through one starting contactor, a plurality of parallel starting contactors are arranged on the output end of the low-speed soft starter, and the parallel starting contactors are connected with the low-speed windings and the medium-speed windings in a one-to-one butt joint mode.

2. The capacity control system of screw compressor capable of being switched in fixed frequency and rotating speed according to claim 1, wherein the motor driver is arranged to realize the speed multi-speed operation of the fixed frequency motor and the switching between speed stages, and the fixed frequency motor comprises at least one winding, and the pole number and the rotating speed of the winding are switched in a wiring mode.

3. The capacity control system of screw compressor capable of being operated in fixed frequency mode and rotating speed mode, as set forth in claim 1, characterized in that one circuit breaker is arranged in front of each of the high speed soft starter and the low speed soft starter, and the two circuit breakers are connected in parallel to the power supply.

4. The capacity control system of screw compressor capable of being operated in fixed frequency switching speed according to claim 3, wherein a disconnecting switch QS is connected to the front main path of the two circuit breakers, and the two circuit breakers are formed by the disconnecting switch QS to be selectively connected with respective soft starters.

5. The capacity control method of the capacity control system of the screw compressor capable of operating at the constant frequency switching rotation speed is characterized in that when the constant frequency motor is operated at different rotation speeds, the controller obtains load demands according to the load measuring device, the bypass slide valve position sensor detects bypass slide valve opening position signals, the controller adjusts the operation rotation speed of the constant frequency motor according to the load demands and the bypass slide valve opening position signals to realize multi-speed output and/or switching, and adjusts the bypass slide valve opening position through the bypass slide valve action driver, so that the bypass slide valve opening position is in a set opening range, and the opening range enables the bypass slide valve opening position to always keep trend operation towards the low-speed operation of the constant frequency motor and the high-opening position of the bypass slide valve position with the constant frequency motor speed.

6. The capacity control method of the screw compressor capacity control system capable of realizing fixed frequency switching rotation speed operation according to claim 5 is characterized in that the motor driver is used for adjusting the rotation speed of the fixed frequency motor to realize three-speed output and/or switching the specific flow is as follows:

Detecting the opening position of a bypass slide valve when the fixed-frequency screw compressor runs at a high speed, if the opening position of the bypass slide valve is less than or equal to H percent and the load shedding requirement exists, switching the fixed-frequency screw compressor into a medium-speed running mode, otherwise, continuing to run in a high-speed running state, wherein H percent is the lower limit of the opening position of the bypass slide valve when the screw compressor is set in a controller to run at the high speed;

detecting the opening position of a bypass slide valve when the bypass slide valve is in medium-speed operation, if the opening position of the bypass slide valve is less than or equal to M percent and the load shedding requirement exists, cutting in a fixed-frequency screw compressor to run at low speed, if the opening position of the bypass slide valve is in 100 percent and the load increasing requirement exists, cutting in a fixed-frequency screw compressor to run at high speed to enable the opening position of the bypass slide valve to be in H percent-100 percent, otherwise, continuing to run in a medium-speed running state, and keeping the opening position of the bypass slide valve in medium-speed operation to be M percent-100 percent, wherein M percent is the lower limit of the opening position of the bypass slide valve when the screw compressor is in medium-speed operation;

When the screw compressor runs at low speed, detecting the opening position of the bypass slide valve, if the bypass slide valve position is 100% and the load increasing requirement exists, switching to medium-speed running, and keeping the opening position of the bypass slide valve in medium-speed running to be M% -100%, otherwise, keeping the opening position of the bypass slide valve in low-speed running to be N% -100%, wherein N% is the lower limit of the opening position of the bypass slide valve when the screw compressor runs at low speed.

7. The capacity control method of the screw compressor capacity control system capable of realizing fixed frequency switching rotation speed operation according to claim 5 is characterized in that the motor driver is used for adjusting the rotation speed of the fixed frequency motor to realize double-speed output and/or switching the specific flow is as follows:

When the fixed-frequency screw compressor runs at high speed, detecting the opening position of the bypass slide valve, if the opening position of the bypass slide valve is less than or equal to H percent and the load shedding requirement exists, switching the fixed-frequency screw compressor into low-speed running, otherwise, continuing to run in a high-speed running state, wherein H percent is the lower limit of the opening position of the bypass slide valve when the screw compressor is set in a controller and runs at high speed, and when the screw compressor runs at low speed, detecting the opening position of the bypass slide valve, if the opening position of the bypass slide valve is 100 percent and the load increasing requirement exists, switching to high-speed running, and keeping the opening position of the bypass slide valve in high-speed running to be H percent to 100 percent, otherwise, continuing to keep the opening position of the bypass slide valve in low-speed running to be N percent to 100 percent, wherein N percent is the lower limit of the opening position of the bypass slide valve when the screw compressor runs at low speed.

8. A capacity control method of a screw compressor capacity control system capable of operating at a constant frequency switching rotation speed is characterized in that when a motor driver power supply starts a main loop to configure two soft starters, a high-speed soft starter controls a high-speed winding of a constant frequency motor, a low-speed soft starter controls a low-speed winding of the constant frequency motor, output interlocking is carried out between the high-speed soft starter and the low-speed soft starter to jointly share operation and starting of the constant frequency motor, a controller adjusts the opening position of a bypass slide valve through a bypass slide valve action driver according to an input signal of a load measuring device and a bypass slide valve opening position signal, and adjusts the operation rotation speed of the constant frequency motor through the motor driver, and the opening position of the bypass slide valve is adjusted according to a set range when the constant frequency motor operates at different rotation speeds.

9. A capacity control method of a screw compressor capacity control system capable of switching rotating speed operation at fixed frequency is characterized in that the upper current limit of a high-speed soft starter is determined by the rotating speed N0 of a high-speed winding, the upper current limit of a low-speed soft starter is determined by the rotating speed N1 of a medium-speed winding, and winding matching rules are that the rotating speed N0 of the high-speed winding is larger than or equal to the rotating speed of the winding and is equal to the rotating speed N1 of the medium-speed winding, the high-speed soft starter drives the rotating speeds of the windings and the rotating speeds N1 of the windings are all driven by the low-speed soft starter.

10. A capacity control method of a screw compressor capacity control system capable of operating at a constant frequency switching rotation speed is characterized in that a constant frequency motor is started in a soft start mode, a starting mode is a slope current mode, a starting current peak value of the constant frequency motor is limited, starting voltage is regulated, the current is smoothly increased to enable the rotation speed of the constant frequency motor to reach a rated rotation speed to finish the starting of the constant frequency motor, a high-speed winding of the constant frequency motor corresponds to a high-speed soft starter, a protection parameter is limited according to high-speed current protection, starting current is limited according to high-speed current, starting current is smooth, a low-speed winding of the constant frequency motor corresponds to a low-speed soft starter, the protection parameter is protected according to low-speed current, and starting current is limited according to low-speed current, so that starting current is smooth.

11. A capacity control method of a screw compressor capacity control system capable of switching rotating speed operation at fixed frequency is characterized in that a fixed frequency motor speed switching mode is that when a high speed is switched to a low speed or a medium speed, a high speed soft starter stops outputting, after the fixed frequency motor stops freely for a few seconds, a low speed soft starter is started, the fixed frequency motor is started to enable the fixed frequency motor to operate at the low speed or the medium speed, when the medium speed is switched to the low speed, the low speed soft starter stops outputting firstly, after the fixed frequency motor stops freely for a few seconds, a winding of the fixed frequency motor is switched from a medium speed winding to a low speed winding, then the low speed soft starter is started again, the fixed frequency motor is started to enable the fixed frequency motor to operate at the low speed, when the low speed is switched to the high speed, the low speed soft starter stops outputting firstly, after the fixed frequency motor stops freely for a few seconds, the high speed soft starter is started, and the fixed frequency motor is started to enable the fixed frequency motor to operate at the high speed.