SYSTEM

TECHNICAL FIELD

The present invention relates to a drive system that includes a power supply, a control unit, a shifting device, an inverter and at least two motors. The present invention further relates to a method for controlling a drive system.

BACKGROUND

In the industrial field, drive systems usually use multiple motors in parallel to drive, for example, multiple pumps, fans and other operating devices. This is because in case only one high-power motor is used and the motor fails, the entire drive system may not fail to work. Therefore, it is common to apply a redundant structure provided with multiple motors in parallel to ensure normal operation of a system. A drive system provided with multiple motors in parallel could operate more stably and more efficiently. Even if one motor fails, the drive system could still continue to operate.

Usually for the drive system provided with multiple motors, each motor is equipped with a motor controller to achieve control over each motor. The motor controller may be a contactor, a soft starter or an inverter. The contactor is economical, and can be directly switched between two states, i.e., be connected or disconnected. However, if a motor is directly connected to a power supply by using a contactor, the motor is quickly accelerated to max power when it is started, which is not suitable for most applications, and the motor may be damaged by a large impulse current. The soft starter is similar to the contactor, but with an additional function of limiting starting acceleration. However the cost of the soft starter is several times that of a contactor. The inverter is able to precisely control the motor, and can continuously change the speed of the motor, but the cost is high. Nowadays, in the drive system provided with multiple motors, to make the output of the motors fully meet the demand on the drive system, it may be necessary to equip each motor with an inverter, so as to precisely control the drive system. Therefore, the use of multiple inverters may multiply the cost. SUMMARY To solve the above mentioned one or more problems, one aspect of the present invention provides a drive system that includes a power supply, a control unit, a shifting device, an inverter and at least two motors, where the power input of the inverter is connected to the power supply, a power output of the inverter is connected to the shifting device,, the shifting device is connected to the power supply and the at least two motors, and the shifting device is capable of connecting the power output of the inverter to the power input of one first motor of the at least two motors, according to control signal of the control unit. The control unit could receive system demand signal and provide control signals to the shifting device and the inverter. Through the drive system according to the embodiment of the present invention, multiple motors in the drive system can be controlled by using only one inverter.

According to an advantageous embodiment, the shifting device is capable of directly connecting the power input of the at least one motor other than the first motor to the power supply or disconnecting the power input of the at least one other motor from the power supply, according to control signal of the control unit. In this way, when a certain motor is operating at full capacity, the motor can be directly connected to the power supply by the shifting device, so that one of the other motors can be controlled by the inverter. If all the motors operate at full capacity or at max power, all the motors can be directly connected to the power supply by the shifting device.

According to an advantageous embodiment, the shifting device includes at least two switch units with the same number as the at least two motors, where each switch unit is connected to one of the at least two motors, and each switch unit is capable of controlling the motor to be connected to or disconnected to the inverter or the power supply according to a control signal of the control unit. By the switch units, the motor can be connected to or disconnected from the inverter or the power supply in a simple and low-cost manner. The control unit may be, for example, a programmable logic controller (PLC), a function integrated in the inverter or the shifting device, a custom module, a micro-processor, a field programmable gate array (FPGA), a computer, an input/output (10) module connected to a network, or the like.

According to an advantageous embodiment, the at least two switch units each include two switch members, where the two switch members are both connected to corresponding motors, wherein one switch member is connected to the power output of the inverter, and the other switch member is directly connected to the power supply. In addition to such a simple and low-cost connection manner, other connection manners can also be used. The switch members may be contactors. In addition, other devices having an on/off function or a switch function, for example, relays such as solid state relays, a custom module built from silicon-controlled rectifiers (SCRs), triodes for alternating current (TRIACs), insulated gate bipolar transistor (IGBTs), metal-oxide-semiconductor field-effect transistors (MOSFETs), and multi-pole devices, also can be used to achieve a similar on/off function under the control of the control unit.

According to an advantageous embodiment, the drive system comprises three motors, and the shifting device comprises three switch units, each switch unit being capable of controlling the motor to be connected to or disconnected to the inverter or the power supply according to a control signal of the control unit, wherein the three switch units each comprise two switch members, for each switch unit the two switch members are both connected to the corresponding motor, wherein one switch member is connected to the power output of the inverter, and the other switch member is directly connected to the power supply .

According to an advantageous embodiment, the drive system further comprises one or more second inverters, wherein a power input of the second inverters are connected to the power supply, the power output of the second inverters are connected to the shifting device, and the shifting device is capable of connecting the power outputs of the second inverters to the power input of a motor respectively By setting the second inverter, redundancy control over the drive system can be achieved, thereby enhancing reliability of the drive system. Certainly, more inverters also may be set according to actual situations.

According to another aspect of the present invention, a method for controlling a drive system is further provided, wherein the drive system comprises a power supply, a control unit, a shifting device, an inverter and at least two motors, wherein the method comprising: connecting the power output of the inverter to the power input of one first motor in the at least two motors by the shifting device, according to control signal of the control unit . Through the method according to the embodiment of the present invention, multiple motors in the drive system can be controlled by using only one inverter.

According to an advantageous embodiment, the method further includes: directly connecting the power input of at least one motor other than the first motor to the power supply or disconnecting the power input of at least one other motor from the power supply by the shifting device, according to control signal of the control unit. In this way, when a certain motor is operating at full capacity, the motor can be directly connected to the power supply by the shifting device, so that one of the other motors can be controlled by the inverter. If all the motors operate at full capacity or at max power, all the motors are directly connected to the power supply by the shifting device.

According to an advantageous embodiment, the method further includes: when output power demand on the drive system is increased and therefore the first motor operates at max power, directly connecting the power input of the first motor to the power supply by the shifting device, and connecting the power output of the inverter to a second motor that is not directly connected to the power supply, according to control signal of the control unit. Thus, the inverter previously used for one motor can be released and used for another motor. The previous motor operates at full capacity under the control of the inverter, and then is connected to the power supply; therefore, a non-operating motor will not be directly connected to the power supply, which prevents the motor from being damaged by an inrush current.

According to an advantageous embodiment, the method further includes: when the output power demand on the drive system is decreased such that the output power of the first motor is decreased to zero, by the shifting device, connecting the power output of the inverter to a motor that is directly connected to the power supply, and disconnecting the motor from the power supply. Thus, the inverter previously used for one inverter can be released and used for controlling another motor.

According to an advantageous embodiment, the method further includes: when output power demand on the drive system is such that the at least two motors all operate at max power, directly connecting the at least two motors to the power supply. Certainly, when the output power demand on the drive system is zero, the at least two motors are disconnected from the inverter and the power supply. BRIEF DESCRIPTION OF THE DRAWINGS

To make the technical features, objectives and effects of the present invention more comprehensible, specific embodiments of present invention are described below with reference to the accompanying drawings.

The following accompanying drawings are only intended to exemplarily describe and explain the present invention, and do not limit the scope of the present invention, where:

FIG. 1A is a schematic view of a drive system according to the prior art;

FIG. IB shows the output schematically, which is based on system demand, of the drive system according to the prior art in FIG. 1A;

FIG. 2A is a schematic view of another drive system according to the prior art;

FIG. 2B shows the output schematically, which is based on system demand, of the drive system according to the prior art in FIG. 2A;

FIG. 3 is a schematic view of a drive system according to an embodiment of the present invention;

FIG. 4 is a schematic view of a shifting device according to an embodiment of the present invention;

FIG. 5 is a schematic view of an embodiment in which a drive system according to an embodiment of the present invention is used for driving a pump; and

FIG. 6 shows the output schematically according to system demand based on the embodiment of FIG. 5.

List of reference signs:

1 Power supply

2 Inverter

3 Shifting device

4 Control unit

11, 12, 13 Motor

21 Power input of the inverter

22 Power output of the inverter

100 Drive system

Ci, C2, C3 Contactor

Ii, h, I ₃ Inverter

Mi, M ₂ , M ₃ Motor

Si, S ₂ , S3 Switch unit

Pi, P ₂ , P ₃ Pump

C11, C12; C21, C22; C ₃ l, C ₃ 2 Switch member or contactor DETAILED DESCRIPTION

FIG. 1A is a schematic view of a drive system according to the prior art. The drive system includes three motors Mi, M2 and M ₃ . In the drive system according to the prior art, the motors are used for driving pumps Pi, P ₂ and P ₃ , and thus are integrated in the pumps. The pumps equipped with the motors Mi, M ₂ and M ₃ are connected in a hydraulic circuit. The motors Mi, M ₂ and M ₃ in the pumps are connected in parallel to a power supply 1 through contactors Ci, C ₂ or C3. A state in which the one, two or all of the motors Mi, M ₂ and M ₃ in the pumps are connected to the power supply and a state in which one, two or all of the motors Mi, M ₂ and M ₃ in the pumps are disconnected from the power supply can be achieved through the contactors Ci, C ₂ and C3.

FIG. IB schematically shows the output based on system demand, of the drive system in FIG. 1 A. A curve Ld indicates the output demand on the drive system which varies with time T. As the motors Mi, M ₂ and M ₃ are used for driving pumps Pi, P ₂ and P ₃ in this embodiment, the output demand on the drive system can be converted to a fluid velocity, flow, pressure, and so on. Herein, the curve Ld, for example, indicates total flow output by the pumps. Curves Lei, Lc ₂ and Lc ₃ are control signals of contactors Ci, C ₂ and C ₃ . According to the control signals, the motors Mi, M ₂ and M ₃ either do not operate, or operate at full capacity. A curve L _r indicates an actual output that is pumped by the pumps, which varies with time. It can be seen that, if the contactors Ci, C ₂ and C ₃ are used to control the three motors Mi, M ₂ and M ₃ , respectively, there is a great deviation between the actual output and the output demand on the drive system.

FIG. 2A is a schematic view of another drive system driving pumps according to the prior art. What is different from the drive system shown in FIG. 1 is that, motors Mi, M ₂ and M3 in this drive system are connected to the power supply 1 through inverters Ii, I ₂ and I3, where each inverter can precisely control the motor connected thereto. FIG. 2B shows the output based on system demand, of the drive system in FIG. 2A. It can be seen that, a system output curve Lr' can precisely meet the system demand through precise control by the three inverters over the motors. Although such a drive system achieves precise control, the cost of the system is significantly increased due to use of multiple inverters.

In each drive system, a control signal may be generated by varies kinds of signal sources, for example, a PLC, or a micro-processor or a dedicated unit in an inverter or the shifting device

FIG. 3 is a schematic view of a drive system 100 according to an embodiment of the present invention. In the embodiment, the drive system 100 includes a power supply 1, a control unit 4, a shifting device 3, an inverter 2 and two motors 11 and 12. Though not shown, three, four or more motors can be used. As shown in FIG. 3, according to this embodiment, a power input 21 of the invert 2 is connected to the power supply 1, and a power output 22 of the inverter 2 is connected to the shifting device 3. The shifting device 3 is also connected to the power supply 1, and is also connected to the motors 11 and 12. The shifting device 3 is able to connect the power output of the inverter to the power input of either of the two motors, for example, a first motor 11, according to control signal of the control unit 4. Thus, the first motor 11 is controlled by the inverter 2.

It should be noted that, the motors in the drive system 100 can drive any electric devices known to those skilled in the art, such as pumps, fans and wheels. As the driven devices are different, output requirements on the drive system 100 are different. For example, when pumps are driven, output requirements on the drive system 100 driving the pumps may be needs for the total flow or pressure of a fluid pumped by the pumps. Therefore, if the driven electric devices are not taken into account, these specific needs could correspond to output power demand on the drive system 100.

When the output power demand on the drive system 100 is lower than the max power of the motor controlled by the inverter 2, output of the motor, for example, the first motor 11, precisely meets the output demand on the drive system 100, and at this time, the second motor 12 does not operate. When the output power demand on the drive system 100 is continuously increased to be greater than the max power of the first motor 11 , the shifting device 3 disconnects the inverter 2 from the first motor 11 , and directly connects the first motor 11 to the power supply 1 , and thus the first motor 11 continues to operate at the max power, for example the rated power. The shifting device 3 connects the power output of the inverter 2 to the power input of the second motor 12, according to control signal of the control unit and precisely controls the second motor 12 by using the inverter 2. Hence, output of the drive system 100 always precisely meets the output demand on the drive system. On the contrary, when the system demand is reduced such that the output of the second motor 12 directly controlled by the inverter control signal is zero, or is reduced to the max power of the motor 11 that is directly connected to the power supply 1 and operates at the max power, the shifting device 3 cuts off the connection between the motor 11 and the power supply 1 , and connects the power output of the inverter 2 to the power input of the motor 11. Thus, the second motor 12 no longer operates, and the first motor 11 continues to operate under the control of the inverter 2. In this way, control over two motors is achieved by using only one inverter, and output of the drive system can precisely meet the output demand on the drive system. Of course, in case there are three motors or even more, the inverter 2 could also be used to control the motors in a similar way under control of the shifting device 3.

FIG. 4 is a schematic view of a shifting device 3 according to an embodiment of the present invention. Although the shifting device 3 according to this embodiment is used for controlling a drive system provided with two motors, a shifting device controlling three, four or even more motors may also be provided according to the present invention. As shown in FIG. 4, the shifting device 3 includes two switch units Si and S ₂ . In the case where more than two motors are provided, the shifting device 3 may include multiple switch units with the same number as the motors. In this embodiment, the control unit 4 outputs control signal to the shifting device 3. Each of the two switch units Si and S ₂ , is connected to one of the motors 11 and 12, and the switch unit is capable of connecting the motor connected thereto to or disconnecting the motor connected thereto from the inverter 2 or the power supply 1 according to the control signal of the control unit 4. Although the control unit 4 as shown in FIG. 3 is a separate control unit, which receives system demand signal and provide control signals to the inverter 2 and the shifting device 3, it is conceivable that the control unit may be, for example, a PLC, a function integrated in the inverter 2 or the shifting device 3, a custom module, a micro-processor, an FPGA, a computer, an 10 module connected to a network, or the like.

Specifically, according to this embodiment, each switch unit Si, S ₂ include two contactors. A first contactor Cn of the first switch unit Si and a first contactor C ₂₁ of the second switch unit S ₂ are connected to the inverter 2, and a second contactor C ₁₂ of the first switch unit Si and a second contactor C ₂₂ of the second switch unit S ₂ are connected to the power supply 1. As the contactor has an on/off function, and can achieve a connected state and a disconnected state, each contactor can simply control the corresponding motor to be connected to or disconnected from the inverter 2 or the power supply 1. Certainly, in addition to the contactor, other devices having an on/off function or a switch function, for example, relays such as solid state relays, a custom module built from SCRs, TRIACs, IGBTs, MOSFETs, multi-pole devices, and the like, can also be used to achieve a similar on/off function under the control of the control unit 31.

FIG. 5 is a drive system according to an embodiment of the present invention. Similar to the drive system 100 as shown in FIG. 3, the drive system includes a power supply 1 and an inverter 2. The difference lies in that, this drive system is provided with three motors 11, 12 and 13. Accordingly, a shifting device 3' is also provided with three switch units Si,

5 ₂ and S3 respectively for the three motors 11, 12 and 13. Certainly, a greater number of motors also can be used according to actual situations, for example, N motors, where N is a natural number greater than or equal to 2, and in the meantime, each motor is provided with a switch unit. According to the technical solution of the present invention, through a shifting device having N switch units, output of the drive system can precisely meet the demand for drive output by using one inverter. Certainly, multiple inverters also may be used. For example, in the drive system according to an embodiment of the present invention shown in FIG. 5, three motors 11, 12 and 13 are controlled by the shifting device 3'. In this embodiment, the shifting device 3' is simply designed to control the switch units by one control unit 4. Although the control unit 4 shown in this embodiment is a separate control unit, it is conceivable that the control unit may be, for example, a PLC, a function integrated in the inverter 2 or the shifting device 3', a custom module, a micro-processor, an FPGA, a computer, an 10 module connected to a network, or the like.

Specifically, according to this embodiment, the switch units Si, S ₂ and S3 each include two contactors. Similar to the control unit 31 shown in FIG. 4, each switch unit has one contactor connected to the inverter 2, and the other contactor to the power supply. In this way, connection or disconnection between the motor and the inverter 2 or the power supply 1 can be simply controlled through the contactor. Certainly, in addition to the contactor, other devices having an on/off function or a switch function, for example, relays such as solid state relays, a custom module built from SCRs, TRIACs, IGBTs, MOSFETs, multi-pole devices, and the like, also can be used to achieve a similar switch function.

The embodiment in FIG. 5 further exemplarily shows an application where a drive system according to an embodiment of the present invention is used for driving multiple pumps.

FIG. 6 shows output, which is based on system demand, in the case of the application in FIG. 5. A curve Ld indicates that output flow demand of pumps driven by the drive system that varies with time T. A curve Li indicates how the inverter output signal varies with time. Curves Lcn, Lc2i and Lc ₃ i are control signals of contactors Cn, C ₂₁ and C31 through which switch units Si, S ₂ and S3 are connected to an inverter; curves Lci ₂ , Lc ₂₂ and Lc ₃₂ are control signals of the contactors C ₁₂ , C22 and C ₃ 2 through which the switch units Si, S ₂ and

53 are directly connected to power supply. Peaks of the curves Lcn, Lc2i and Lc3i mean that the contactors connect the inverter 2 to the motors, so that the power output of the inverter 2 can be connected to respective motors, and precisely controls the motors. Troughs of the curves mean that the inverter 2 is disconnected from the motors, and cannot control the motors. Peaks of the curves Lci ₂ , Lc22 and Lc ₃ 2 mean that the contactors directly connect the power supply 1 to the motors, so that the motors rotate at full capacity at this time. Curves Ln, L ₁₂ and L ₁₃ show output of pumps Pi, P2 and P ₃ driven by the motors 11, 12 and 13. A curve L _r indicates that actual total output of the pumps driven by the drive system that varies with time T.

As regards to drive system, when demand for output of the drive system, for example, output power, is greater than zero, the power output of the inverter 2 is connected to one of the multiple motors, for example, the first motor 11, by the shifting device 3' under the control of the control unit 4, in other words, the shifting device 3' connects the inverter 2 to one motor, and controls the motor by using the inverter. In the meantime, other motors are separately directly connected to the power supply 1 or are disconnected from the power supply 1 by the shifting device 3', that is, other motors operate at full capacity or do not operate. For example, when output demand on the drive system is lower than the motor controlled by the inverter 2 (for example, the first motor 11), output of the motor precisely meets the output demand on the drive system, and at this time, the second motor 12 and the third motor 13 do not operate, that is, the shifting device 3' disconnects the second motor 12 and the third motor 13 from the inverter 2 and the power supply 1. When the output demand on the drive system is continuously increased such that the first motor 11 operates at max power or at full capacity, the shifting device 3' disconnects the inverter 2 from the first motor 11 , and directly connects the first motor 11 to the power supply 1 , according to control signal of the control unit 4; thus, the first motor 11 continues to operate at the max power. Through such switching, a large impulse current is avoided. At this time, the shifting device 3' connects the power output of the inverter 2 to another motor, for example, the second motor 12, and precisely controls output of the second motor 12 by using the inverter 2. Similarly, when the output demand on the drive system is continuously increased such that the second motor 12 also operates at max power or at full capacity, the shifting device 3' disconnects the inverter 2 from the second motor 12, and directly connects the second motor 12 to the power supply 1; thus, the second motor 12 continues to operate at the max power, and the shifting device 3' again connects the power output of the inverter 2 to the third motor 13, and precisely controls output of the third motor 13 by using the inverter 2. Of course, motors are not mandated to be selected in the foregoing sequence. A motor which has the shortest service time could be selected to be connected to the power output of the inverter 2. It is conceivable that, in a drive system provided with N motors (N is a natural number greater than or equal to 2), operations can be performed in the same way, until N-l motors are directly connected to the power supply and operate at full capacity, and the remaining one motor is precisely controlled by the inverter.

According to the embodiment in FIG. 5, with reduction of the system demand, when output of the third motor 13 controlled by the inverter control signal is decreased to 0, the shifting device 3 cuts off a direct connection between the power supply 1 and either of the first motor 11 and the second motor 12, and connects the power output of the inverter 2 to this motor. At this time, the third motor 13 no longer operates, one of the first motor 11 and the second motor 12 is precisely controlled by the inverter 2, and the other is connected to the power supply and continues to operate at full capacity. When the system demand is continuously decreased such that the output of the motor controlled by the inverter control signal is 0, the motor still directly connected to the power supply is disconnected, and the power output of the inverter 2 is connected to this said motor. It should be noted herein that, according to the present invention, when a motor is selected to be connected to the inverter or the power supply, selection of the motor is not necessarily made in sequence, and any motor not currently connected to the inverter may be selected. Such a selection may be made randomly or by using an algorithm, and following the total operating time of each motor, a motor with the shortest operating time is selected to be connected to the inverter. Similarly, in selecting a motor to be disconnected from the power supply, a motor with the longest operating time may be selected. According to the embodiment of the present invention, output of the drive system always precisely meets the output demand on the drive system. Thus, control over multiple motors is achieved by using only one inverter, and output of the drive system can be precisely controlled.

Though not shown, one or more inverters also can be set in a drive system provided with three or more than three motors, and thus one or more motors can be controlled by the inverter through a shifting device, and the rest motors are connected to the power supply and operate at full capacity or are disconnected from the power supply. Therefore, low-cost, precise and flexible control over motors is achieved and reliability of the drive system is increased.

It should be understood that, although the specification is described according to each embodiment, it does not mean that each embodiment only includes one separate technical solution, and such a description manner of the specification is merely for clarity. Persons skilled in the art should regard the specification as a whole, and technical solutions in the embodiments also can be properly combined to form other embodiments that persons skilled in the art can understand.

Described above are merely specific embodiments of the present invention, which are not intended to limit the scope of the present invention. Any equivalent variation, modification and combination made by persons skilled in the art without departing from the idea and principle of the present invention should fall within the protection scope of the present invention.