Patent Grant
8348020
The present application claims priority under 35 U.S.C. §119 to Japanese Patent Application No. 2009-206603, filed on Sep. 8, 2009. The contents of the application are incorporated herein by reference in their entirety.
1. Field of the Invention
The present invention relates to an elevator control device.
2. Description of Related Art
A related elevator control device adopts such a system that an inverter device is used for driving an alternating-current (AC) motor (hereinafter, also simply referred to as a motor). Herein, the inverter device subjects a switching element, such as a power transistor or an IGBT (Insulated Gate Bipolar Transistor), to PWM (Pulse Width Modulation) control. It is assumed herein that an inverter device is selected from a viewpoint of generating a torque required in normal operation of an elevator. In such a case, the selected inverter device becomes short of capacitance in overloaded test operation to be carried out at the time of completion or performance evaluation of the elevator. When being selected in consideration of such a test, an inverter device disadvantageously increases in cost and size.
JP 06-009165 A discloses a technique for making a carrier frequency variable in accordance with an operating speed of an inverter device. Moreover, JP 2005-162376 A discloses a technique for switching a coil of a motor to be driven and decreasing a carrier frequency. A decreased carrier frequency of an inverter device allows suppression of a loss caused to a switching element. Therefore, it becomes possible to produce higher torque and larger electric current in an inverter device with invariable capacitance.
According to one aspect of the present invention, an elevator control device includes a motor controller that calculates a voltage command required for driving an elevator cage, a carrier frequency switch circuit that outputs a carrier frequency signal, and a power converter that performs PWM control based on the voltage command and the carrier frequency signal and supplies an AC power to an AC motor. Herein, the elevator control device changes the carrier frequency signal in a case where a torque command for driving the AC motor or an output current reaches a limit value during operation of the elevator, or at a timing obtained previously prior to operation of the elevator.
According to another aspect of the present invention, the elevator control device monitors overload information about the timing obtained previously prior to operation of the elevator and the timing that the output current reaches the limit value during operation of the elevator.
A more complete appreciation of the invention and many of the attendant advantages thereof will be readily obtained as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawings, wherein:
Embodiments will now be described with reference to the accompanying drawings, wherein like reference numerals designate corresponding or identical elements throughout the various drawings.
The elevator control device I includes an AC power supply 1, a power converter 2, an AC motor 3, a base drive circuit 4, a host controller 5, a vector controller 6, a carrier frequency switch circuit 8, a current detector 11, an encoder 12, a traction sheave 21, an elevator cage 22, a counter weight 23 and a load sensor 24. Herein, the elevator cage 22 is controlled so as to be located at a target position through the AC motor 3.
The power converter 2 has a function of performing PWM control based on a voltage command and a carrier frequency signal in order to drive the elevator cage 22 and supplying an AC power to the AC motor 3. More specifically, the power converter 2 generates a direct-current (DC) voltage by converting an AC voltage from the AC power supply 1 into the DC voltage by rectification, and performs PWM control by use of a base signal based on a voltage command from the base drive circuit 4. Then, the power converter 2 subjects a plurality of switching elements incorporated therein to base drive, and drives the AC motor 3 by voltage application.
The base drive circuit 4 outputs a base signal to the power converter 2 in accordance with a voltage command (V) from the vector controller 6 and a carrier frequency signal, e.g., a triangular-wave carrier frequency signal (an Fc signal) from the carrier frequency switch circuit 8.
The traction sheave 21 is coupled to the AC motor 3, and each of the elevator cage 22 and the counter weight 23 is suspended by the traction sheave 21. Herein, the elevator cage 22 may include a load sensor 24 if necessary. The load sensor 24 detects a load onto the elevator cage 22, and sends a load signal indicating an amount of the detected load to the host controller 5.
The host controller 5 acquires a target position from destination floor information to be input thereto, converts the target position into a speed command ωr* by use of information such as a position signal θ from the encoder 12, a preset acceleration/deceleration rate, and a diameter of the traction sheave 21, and outputs the speed command ωr*. Further, the host controller 5 also outputs an activation torque compensation Tload, based on a load signal from the load sensor 24.
The carrier frequency switch circuit 8 sets a carrier frequency signal (an Fc signal) and a torque limit value Tlim, based on a torque command Tref to be input thereto. The carrier frequency switch circuit 8 sends the carrier frequency signal (the Fc signal) to the base drive circuit 4, and also sends the torque limit value Tlim to the vector controller 6. The process of setting the respective values will be described later.
The current detector 11 detects as a current signal (I) a three-phase current (iu, iv, iw) which flows through the AC motor 3.
The encoder 12 is connected to the AC motor 3 to detect a position signal θ of the AC motor 3.
The vector controller 6 is a motor controller that includes a speed controller 31, a speed calculator 32, a torque limiter 33, a current command calculator 34, a current controller (q axis) 35, a current controller (d axis) 36, a coordinate converter 37, a coordinate converter 38, subtracters 39 to 41, and an adder 42.
The speed controller 31 controls a difference between a speed command ωr* calculated by the subtracter 39 and a speed detection signal ωr to be described later (a speed deviation Δωr) such that the speed deviation Δωr takes a value of zero. The adder 42 adds an output from the speed controller 31 and an activation torque compensation Tload to prepare a torque command Tref, and outputs the torque command Tref to each of the torque limiter 33 and the carrier frequency switch circuit 8.
The speed calculator 32 calculates as a speed detection signal ωr an amount of change in an output signal from the encoder 12 per unit time.
The torque limiter 33 limits a torque command Tref by use of a smaller one of a preset torque limit value and a torque limit value Tlim from the carrier frequency switch circuit 8. The torque limiter 33 outputs the torque command Tref thus limited to the current command calculator 34. The AC motor 3 is driven by this torque command Tref.
The current command calculator 34 calculates a current command (Idref, Iqref) by use of a torque command Tref to be input thereto.
The current controller (q axis) 35 controls a difference between a current command Iqref calculated by the subtracter 40 and an electric current Iq to be described later (a current deviation Δiq) such that the current deviation ΔIq takes a value of zero, thereby calculating a voltage command Vqref.
Likewise, the current controller (d axis) 36 controls a difference between a current command Idref calculated by the subtracter 41 and an electric current Id to be described later (a current deviation ΔId) such that the current deviation ΔId takes a value of zero, thereby calculating a voltage command Vdref.
The coordinate converter 37 converts a current signal (I) into a two-phase current (Id, Iq) on a rotational coordinate system. The coordinate converter 38 converts a voltage command (Vdref, Vqref) into a three-phase voltage command (Vu*, Vv*, Vw*), and outputs this three-phase voltage command as a voltage command (V).
Thus, the vector controller 6 receives a speed command ωr* from the host controller 5, a torque limit value Tlim from the carrier frequency switch circuit 8, a current signal (I) from the current detector 10, and a position signal θ from the encoder 12, subjects these inputs to vector control, and outputs a voltage command (V).
Next, the carrier frequency switch circuit 8 is described. The carrier frequency switch circuit 8 has a function of outputting a carrier frequency signal (an Fc signal) in accordance with a torque command Tref for driving the AC motor 3.
In
When the carrier frequencies Fc1 and Fc2 are set at a maximum value and a minimum value of a carrier frequency F which can be set by the user, respectively, an elevator is operated within this range even in a status other than an overload status. For example, the carrier frequency Fc1 is set at a value of 15 kHz, the limit torque Tlim1 takes a value of (150%×inverter rated torque), the carrier frequency Fc2 takes a value of 2 kHz, and the limit torque Tlim2 takes a value of (190%×inverter rated torque); however, the present invention is not limited to these values. Herein, a torque generated from the AC motor 3, through which an electric current corresponding to a rated current of an inverter device flows, is defined as a rated torque (100%). The inverter rated torque is set by use of the rated current of the inverter device, a motor constant of the AC motor 3, and the like.
Prior to operation of the elevator, the user sets the carrier frequency F and the torque limit value Tlim of the elevator control device I.
During operation of the elevator, the carrier frequency switch circuit 8 receives a torque command Tref calculated by the speed controller 31. When a value of a carrier frequency set at this time is in the range shown in
Thus, the carrier frequency switch circuit 8 controls the relation between the torque command Tref to be input thereto and the carrier frequency Fc such that this relation falls within the range shown in
As described above, the carrier frequency switch circuit 8 outputs the carrier frequency signal (the Fc signal) and the torque limit value Tlim in accordance with the torque command Tref. Therefore, the carrier frequency Fc automatically decreases as the torque command Tref increases.
In the foregoing description, the increase of the torque limit value is necessary because the decrease of the carrier frequency Fc allows enhancement of the protection level for the switching element that forms the power converter 2. Alternatively, the protection of the switching element may be exerted with flexibility in such a manner that the carrier frequency Fc is changed, but the torque limit value Tlim is fixed.
The elevator control device I according to the first embodiment of the present invention can automatically decrease a carrier frequency such that a torque command for driving an AC motor falls within an allowable range, and can continuously operate an elevator without causing damage to a switching element.
The V/f controller 7 has a function of controlling an output voltage such that the output voltage rises almost in proportional to a frequency, i.e., controlling the output voltage such that a voltage-to-frequency ratio becomes fixed (V/f=a fixed value), and calculating and outputting a voltage command (V) required for driving an elevator cage 22 through an AC motor 3. This voltage command (V) is obtained by coordinate conversion of a voltage command Vqref which is almost proportional to a frequency command and a voltage command Vdref which takes a value of zero. An expression for calculation of the voltage command (V) is publicly known; therefore, description thereof will not be given here.
Next, specific operations of the carrier frequency switch circuit 8′ are described. The carrier frequency switch circuit 8′ has a function of outputting a carrier frequency signal (an Fc signal) in accordance with an electric current which flows through the AC motor 3, i.e., an output current from a power converter 2.
In
Prior to operation of the elevator, the user sets the carrier frequency F of the elevator control device J.
During operation of the elevator, the carrier frequency switch circuit 8′ receives a current signal (I) detected by a current detector 11 and calculates a magnitude of the current signal (I) as an inverter output current Iout. When the carrier frequency F set at this time is in the range shown in
Thus, the carrier frequency switch circuit 8′ controls the relation between the carrier frequency Fc and the inverter output current Iout such that this relation falls within the range which is determined by an allowable function and is shown in
As described above, the carrier frequency switch circuit 8′ outputs the carrier frequency signal (the Fc signal) in accordance with the inverter output current Iout. Therefore, the carrier frequency Fc automatically decreases as the inverter output current Iout increases.
In the foregoing description, the increase of the limit current value is necessary because the decrease of the carrier frequency Fc allows enhancement of the protection level for the switching element that forms the power converter 2. Alternatively, the protection of the switching element may be exerted with flexibility in such a manner that the carrier frequency Fc is changed, but the limit current value Ilim is fixed.
Although not shown in
The elevator control device J according to the second embodiment of the present invention can automatically decrease a carrier frequency in an overload state even when a motor controller thereof is a V/f controller, and can continuously operate an elevator without causing damage to a switching element.
The third embodiment is based on the following considerations. In an elevator, typically, an acceleration/deceleration rate becomes fixed without changing when being set once upon test operation, a load does not change during operation, and a torque becomes maximum upon acceleration/deceleration. In view of these facts, it is possible to grasp a timing that a torque command Tref reaches a torque limit value during operation of an elevator, based on a superimposed load upon start of the operation.
The host controller 5′ stores therein the relation between the torque and the allowable carrier frequency shown in
Specifically,
Although not shown in
Next, when the torque command Tref reaches the value of the activation torque compensation Tload, the elevator is subjected to speed control. Then, the brake command (c) is output for releasing a brake, so that the speed command ωr* (d) gradually increases from a value of zero in accordance with an acceleration rate including a set S-shaped curve. Thus, the torque command Tref (f) increases, and then decreases as the acceleration rate becomes gentle. Herein, a section (5) due to a limit torque is generated at the torque command Tref, depending on a load onto the elevator cage 22 and a set value of the acceleration rate.
When the speed command ωr* becomes fixed, the torque command Tref takes only a value obtained from the load onto the elevator cage 22. As the elevator is gradually decelerated, the torque command Tref approaches the value of zero. In some statuses, the torque command Tref takes a negative value, and further, a section due to a limit torque is generated at the torque command Tref although not shown in
When the elevator cage 22 reaches the target position and the speed command ωr* takes the value of zero, the brake command (c) is output for applying a brake. Thus, the speed control is completed. The respective signals vary as described above during operation of the elevator.
In the foregoing description, the speed command ωr* output from the host controller 5′ varies in accordance with the acceleration rate including the set S-shaped curve. Alternatively, the speed command ωr* may be calculated in such a manner that the acceleration command (e) is set first and then a value thereof is subjected to integration.
It is apparent from the timing chart in
Accordingly, when a destination floor and a load signal upon start of operation are set, it is possible to determine a timing that a torque command Tref reaches a torque limit value Tlim1.
At the timing that the torque command Tref reaches the torque limit value Tlim1, the carrier frequency decreases from a value of Fc1, so that the limit torque increases. In actual operation, therefore, the elevator is subjected to no torque limitation.
A timing that a value obtained by addition of a load signal upon start of operation to an acceleration command set based on a destination floor becomes larger than a limit torque is stored as a time corresponding to a portion (4) in
As described above, the host controller 5′ can previously set the carrier frequency, based on the timing of change of the speed command ωr*. Therefore, the host controller 5′ can previously grasp the timing of overload, so that the elevator can be operated without such an overload status.
During operation of the elevator, moreover, the host controller 5′ sends the carrier frequency signal (the Fc signal), which is set as described above, to the carrier frequency switch circuit 9. The carrier frequency switch circuit 9 calculates the torque limit value Tlim in accordance with the value of the Fc signal and the relation shown in
In the foregoing description, the torque command Tref is set by use of the value obtained by adding the load signal upon start of operation to the acceleration command set based on the destination floor. Alternatively, the torque command Tref can be set more accurately in such a manner that a mechanical efficiency of the elevator is measured previously and then is added to an acceleration command for reference.
Moreover, the process to be carried out prior to operation of the elevator needs to be carried out each time the output from the load sensor 24 varies. For this reason, it is convenient that this process is carried out after the door of the elevator is closed.
Further, the host controller 5′ can previously grasp the fact that the torque command Tref reaches the torque limit value even when the carrier frequency switch circuit 9 changes the carrier frequency Fc within an allowable range. In such a case, an interlock is actuated, e.g., a buzzer attached to the elevator cage 22 is pressed, for stopping the operation of the elevator. Thus, it is possible to provide a safe inverter device for elevators.
In the foregoing description, the vector controller 6 is employed as a motor controller. In the case of the elevator control device J that employs the V/f controller 7, the host controller may store therein the relation between the output current and the allowable carrier frequency shown in
The elevator control device K according to the third embodiment of the present invention can previously predict a fact that a torque command Tref reaches a torque limit value, and further, can automatically decrease a carrier frequency such that the torque command falls within an allowable range.
As described above, according to the foregoing embodiments, it is possible to automatically decrease a carrier frequency only in a required case in accordance with an operation status. As a result, it is possible to keep a good balance between such a request to use an elevator control device in a low-noise environment and such a request to ensure a current capacity of an inverter device.
The carrier frequency switch circuit 10 operates as in the carrier frequency switch circuit 8′ of the elevator control device J. Thus, the carrier frequency switch circuit 10 changes a carrier frequency signal (an Fc signal) when an output current reaches the current value (the limit current value) shown in
The host controller 5″ stores therein the relation between the torque and the allowable carrier frequency shown in
The host controller 5″ can monitor data obtained by comparison between the Fc signal from the carrier frequency switch circuit 10 and the Fc′ signal calculated previously by the host controller 5″ itself. Examples of a difference to be compared herein include a difference of occasions of overload, and a difference of a timing of overload. The host controller 5″ monitors these differences to grasp secular change of the elevator control device L.
The host controller 5″ may display an overload status or send the overload status to a different device. This overload status can be utilized as abnormal data about the elevator control device L.
In a case where a load status of the elevator does not change, the host controller 5″ may count only the Fc′ signal from the carrier frequency switch circuit 10, and then may display or send the Fc′ signal.
The elevator control device L according to the fourth embodiment of the present invention can grasp an abnormal state thereof. This configuration is effective at maintenance such as a periodic inspection.
The present invention is not limited to the foregoing embodiments, and may be modified appropriately. For example, a different type of compensation using a carrier frequency may be performed in such a manner that an Fc signal to be set by the carrier frequency switch circuit 8 or 8′ is sent to the host controller 5. In the foregoing embodiments, the load onto the elevator cage is detected by the load sensor. Alternatively, such a load may be obtained from a torque command value in a case where the elevator is operated at zero speed, and others. In the example of vector control of the inverter device, further, the encoder is used. Alternatively, the speed and the position information may be obtained by use of a magnetic flux observer or the like.
Obviously, numerous modifications and variations of the present invention are possible in light of the above teachings. It is therefore to be understood that within the scope of the appended claims, the invention may be practiced otherwise than as specifically described herein.
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