Control Method of Motor Drive System and Inverter Device

Abstract

A motor driving system according to an embodiment comprises a converter device and an inverter device. The converter device converts a first AC voltage into a DC voltage. The inverter device converts the DC voltage into a second AC voltage and outputs the second AC voltage to a motor. The converter device causes the DC voltage to follow a DC voltage command value. The inverter device causes the speed of the motor to follow a speed command value. The inverter device corrects the speed command value on the basis of the DC voltage command value and the DC voltage. The inverter device applies the corrected speed command value to control the motor.

Description

Technical Field

[0001] Embodiments of the present invention relate to a motor drive system for an elevator motor and a control method for an inverter device that can cope with a short-term voltage drop.

Background Art

[0002] The elevator mentioned here refers to a machine that transports people and objects in the direction of gravity, and includes so-called elevators, mine shaft hoists, inclined hoists, cranes, and the like.

[0003] Conventionally, in an inverter drive device, when an instantaneous power supply voltage drop occurs, a method of suppressing a speed drop by controlling the field component current of vector control according to the operating state is known. In Patent Document 1, without providing an uninterruptible power supply device or performing power supply duplication, the speed drop is suppressed more than the conventional method by controlling the field component current, and the robustness of industrial variable speed drive equipment such as central air conditioners and paper reels is improved. A method is described.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] Regarding the application of the inverter drive device as described above to an elevator, there are the following problems. That is, the elevator raises and lowers an object with the torque generated by the motor. Therefore, when the torque generated by the motor decreases due to an instantaneous power supply voltage drop, the object to be raised and lowered by the elevator accelerates and decelerates under the influence of gravity. In such equipment, since Patent Document 1 does not explicitly show up to what extent the influence of an instantaneous power supply voltage drop becomes large enough to abandon continuous driving and activate an external means such as an emergency brake to take safety measures, it is difficult to apply to an elevator.

[0006] This invention was made to solve the above problems, and an object thereof is to obtain a motor drive system and a motor control method capable of extending the time during which the inverter drive of the motor can be continued even when there is an instantaneous power supply voltage drop.

Means for Solving the Problems

[0007] The motor drive system according to an embodiment of the present invention includes a first power conversion device that converts a first AC voltage supplied from an AC power supply into a DC voltage and outputs it, and a second power conversion device that converts the DC voltage into a second AC voltage and outputs it to a motor. The first power conversion device has DC voltage control means for controlling the DC voltage to follow a preset DC voltage command value. The second power conversion device has first speed control means for controlling the speed of the motor to follow a preset speed command value, and second speed control means for calculating a correction value of the speed command value based on the DC voltage command value and the DC voltage. The second speed control means calculates the correction value based on the difference between the DC voltage command value and the DC voltage.

Effects of the Invention

[0008] According to the embodiment, a motor drive system and a motor control method capable of extending the time during which the inverter drive of the motor can be continued even when there is an instantaneous power supply voltage drop are realized.

Brief Description of the Drawings

[0009]

Figure 1

Figure 2

Figure 3

Figure 4

Embodiments for Carrying Out the Invention

[0010] Hereinafter, each embodiment of the present invention will be described with reference to the drawings. Note that the drawings are schematic or conceptual, and the relationships between the thickness and width of each part, the ratio of the sizes between parts, etc. are not necessarily the same as those in reality. Also, even when representing the same part, the dimensions and ratios may be shown differently in the drawings. In the present specification and each figure, the same reference numerals are given to the same elements as those described above with respect to the previously shown figures, and the detailed description will be omitted as appropriate.

[0011] (First Embodiment) Figure 1 is a schematic block diagram illustrating a motor drive system according to the first embodiment. As shown in FIG. 1, the motor drive system 100 is provided between the AC power supply 1 and the motor 2. The AC power supply 1 is a power supply that supplies, for example, three-phase AC. The motor 2 is an AC motor, for example, an induction motor. The motor 2 is mechanically coupled to the drum 3 via the gear 4. Although not shown in FIG. 1, a rope is wound around the drum 3, and a cage for loading mined materials, workers, etc. is provided at the tip of the rope. The motor drive system 100 speed-controls the motor 2 in both forward and reverse directions according to, for example, a speed command value output from a main control device (not shown). The speed-controlled motor 2 winds and rewinds the rope around the drum 3 to raise and lower the cage in the shaft.

[0012] The motor drive system 100 includes a converter device (first power conversion device) 10 and an inverter device (second power conversion device) 50. The AC power supply 1 is connected to the input of the converter device 10 and supplies an AC voltage (first AC voltage) to the converter device 10. The output of the converter device 10 is connected to the input of the inverter device 50. The motor 2 is connected to the output of the inverter device 50, and the inverter device supplies an AC voltage (second AC voltage) to the motor 2. A capacitor 20 is connected in parallel between the output of the converter device 10 and the input of the inverter device 50. The capacitor 20 smoothes the voltage output by the converter device 10 and supplies a DC voltage to the inverter device 50. The capacitor 20 has a sufficient capacitance to compensate for changes in the drive torque of the motor 2, etc., which are faster than the response speed of the converter device 10, and stably supply a DC voltage to the inverter device 50.

[0013] The motor drive system 100 includes a DC voltage detector 30, and the DC voltage detector 30 monitors the DC voltage Vdc of the capacitor 20. When the AC voltage of the AC power supply 1 drops or the DC voltage Vdc of the capacitor 20 fluctuates due to a power outage, the motor drive system 100 corrects the speed command value vref output from the main control device to suppress the fluctuation of the DC voltage Vdc. By suppressing the fluctuation of the DC voltage Vdc of the capacitor 20, the motor drive system 100 avoids the operation of the motor 2 from stopping and prevents the reduction of the operation efficiency of the elevator.

[0014] The configuration of the motor drive system 100 will be described in detail. First, the configuration of the converter device 10 will be described. As shown in FIG. 1, the converter device 10 includes a power conversion unit 11, a voltage detector 12, a current detector 13, a PWM control unit 14, a voltage control unit 15, and an AC voltage detector 16. The power conversion unit 11, the voltage detector 12, the current detector 13, the PWM control unit 14, and the voltage control unit 15 are controlled so that the DC voltage Vdc detected by the DC voltage detector 30 follows the DC voltage command value Vdcref (DC voltage control means). The converter device 10 is capable of bidirectional power conversion. That is, the converter device 10 converts the AC voltage (first AC voltage) output from the AC power supply 1 into a DC voltage and outputs it to the inverter device 50. The power conversion unit 11 converts the DC voltage generated by the inverter device 50 during the regenerative operation of the motor 2 into an AC voltage (third AC voltage) and outputs it to the AC power supply 1.

[0015] The input of the power conversion unit 11 is connected to the AC power supply 1. The output of the power conversion unit 11 is connected to the input of the inverter device 50 via the capacitor 20. The power conversion unit 11 is composed of a power conversion circuit that converts an AC voltage into a DC voltage, and the power conversion circuit is composed of a three-phase bridge circuit or the like. The specific circuit configuration, circuit elements, etc. of the power conversion circuit are selected by an appropriate method according to the input / output voltage, input / output current, etc.

[0016] The voltage detector 12 is provided to detect the voltage of each phase of the AC power supply 1. The voltage detector 12 detects the voltage of each phase of the AC power supply 1 and outputs the detected voltage value to the PWM control unit 14 and the AC voltage detection unit 16.

[0017] The current detector 13 is provided to detect the line current of each phase of the AC power supply 1. The current detector 13 detects the line current of each phase of the AC power supply 1 and outputs the detected current value to the PWM control unit 14.

[0018] The PWM control unit 14 is connected to the output of the voltage detector 12, the output of the current detector 13, and the output of the AC voltage detection unit 16. The output of the PWM control unit 14 is connected to the power conversion unit 11. The PWM control unit 14 generates a gate signal based on the voltage value, current value of the AC power supply 1, and the output of the voltage control unit 15, and outputs it to the power conversion unit 11. The output of the AC voltage detection unit 16 is connected to the PWM control unit 14. When the AC voltage detection unit 16 outputs a gate block command GB, the PWM control unit 14 stops the output of the gate signal.

[0019] A DC voltage command value Vdcref is input to the voltage control unit 15. The DC voltage command value Vdcref is set in advance. The DC voltage command value Vdcref is supplied from, for example, the main control device. The voltage control unit 15 inputs the DC voltage Vdc of the capacitor 20 from the DC voltage detection unit 30. The voltage control unit 15 generates a current command value so that the DC voltage Vdc follows the DC voltage command value Vdcref, and outputs it to the PWM control unit 14.

[0020] The output of the voltage detector 12 is connected to the AC voltage detection unit 16. The AC voltage detection unit 16 has a low voltage threshold value. The low voltage threshold value is set in advance. The AC voltage detection unit 16, for example, peak-holds the voltage value detected by the voltage detector 12, and when the value is lower than the low voltage threshold value, generates a low voltage detection signal Ddip and outputs it to the low voltage speed control unit 40 of the inverter device 50.

[0021] Next, the configuration of the inverter device 50 will be described. The inverter device 50 includes a low-voltage speed control unit 40, a power conversion unit 51, an arithmetic unit 52, a speed control unit 53, a speed detector 54, a current control unit 55, a current detector 56, a PWM control unit 57, and an emergency stop unit 58. The power conversion unit 51, the speed control unit 53, the speed detector 54, the current control unit 55, the current detector 56, and the PWM control unit 57 control the speed of the motor 2 to follow the speed command value vref (first speed control means). The low-voltage speed control unit 40 and the arithmetic unit 52 calculate a correction value vc of the speed command value vref based on the difference between the DC voltage command value Vdcref and the DC voltage Vdc (second speed control means).

[0022] The low-voltage speed control unit 40 is connected to the output of the AC voltage detection unit 16 of the converter device 10. The low-voltage speed control unit 40 is connected to the output of the DC voltage detection unit 30. A DC voltage command value Vdcref output from, for example, a main control device is input to the low-voltage speed control unit 40. The low-voltage speed control unit 40 waits and stops operating until it receives a low-voltage detection signal Ddip from the AC voltage detection unit 16. The low-voltage speed control unit 40 starts operating when it receives the low-voltage detection signal Ddip. When starting to operate, the low-voltage speed control unit 40 generates a correction value vc of the speed command value vref based on the DC voltage command value Vdcref and the DC voltage Vdc, and outputs it to the arithmetic unit 52.

[0023] More specifically, the low-voltage speed control unit 40 includes an arithmetic unit 41 and a controller 42. The arithmetic unit 41 receives a DC voltage command value Vdcref and a DC voltage Vdc. The arithmetic unit 41 calculates the difference between the DC voltage command value Vdcref and the DC voltage Vdc, and outputs the calculated difference. The controller 42 is, for example, a PI controller, and performs proportional-integral calculation on the difference between the DC voltage command value Vdcref and the DC voltage Vdc and outputs the result. That is, the controller 42 calculates and outputs a correction value vc of the speed command value vref so that the DC voltage Vdc follows the DC voltage command value Vdcref. The low-voltage speed control unit 40 may have a limiter 43 as in the example of FIG. 1. The limiter 43 limits the output of the controller 42 within the range from the maximum value UL to the minimum value LL of the correction value vc of the speed command value.

[0024] For example, when the motor 2 is in power running and the DC voltage Vdc across the capacitor 20 decreases due to a drop in the AC power supply 1, the low-voltage speed control unit 40 outputs a correction value vc to lower the speed command value vref. The inverter device 50 controls the motor 2 to follow the speed command value vr0 lowered by the correction value vc.

[0025] For example, when the motor 2 is in regenerative operation and the DC voltage Vdc across the capacitor 20 increases due to a drop in the AC voltage of the AC power supply 1, the low-voltage speed control unit 40 outputs a correction value vc to raise the speed command value vref. The inverter device 50 controls the motor 2 to follow the speed command value vr0 raised by the correction value vc.

[0026] The input of the power conversion unit 51 is connected to the output of the converter device 10 via the capacitor 20. The output of the power conversion unit 51 is connected to the motor 2. The power conversion unit 51 controls the motor 2 to follow the speed command value vref output from the main control device or the speed command value vr0 corrected by the low-voltage speed control unit 40 based on the gate signal generated by the PWM control unit 57.

[0027] The speed control unit 53 receives the speed command value vref or the corrected speed command value vr0. The output of the speed detector 54 is connected to the speed control unit 53. The speed detector 54 is provided to detect the rotational speed of the motor 2, and outputs the detected motor speed vs to the speed control unit 53. The speed control unit 53 generates an output current command value based on the speed command value vref and the motor speed vs. When the low-voltage speed control unit 40 outputs the correction value vc of the speed command value vref, the speed control unit 53 generates an output current command value based on the corrected speed command value vr0 and the motor speed vs of the motor 2. The generated current command value is output to the current control unit 55.

[0028] The output of the current detector 56 is connected to the current control unit 55. The current detector 56 is provided to detect the output current Idc of each phase of the power conversion unit 51. The current detector 56 detects the output current Idc of the power conversion unit 51 and outputs the detected output current Idc to the current control unit 55. The current control unit 55 calculates a modulation voltage based on the output current command value input from the speed control unit 53 and the output current Idc detected by the current detector 56, and outputs it to the PWM control unit 57.

[0029] The PWM control unit 57 generates a gate signal based on a reference triangular wave (not shown) and the modulation voltage generated by the current control unit 55, and outputs it to the power conversion unit 51.

[0030] The emergency stop unit 58 is connected to the output of the DC voltage detector 30. The emergency stop unit 58 inputs the DC voltage Vdc across the capacitor 20 detected by the DC voltage detector 30. The emergency stop unit 58 has an emergency stop threshold value. The emergency stop threshold value is set in advance. The emergency stop unit 58 monitors the DC voltage Vdc, and when the DC voltage Vdc drops below the emergency stop threshold value, generates an emergency brake start command DB and outputs it to the main control device. The main control device activates an emergency brake (not shown) based on the emergency brake start command DB to stop the motor 2.

[0031] When the emergency stop unit 58 operates under low voltage conditions, even if the elevator operation continues, if the DC voltage Vdc across the capacitor 20 becomes equal to or greater than the threshold value or equal to or less than the threshold value, the elevator operation is forcibly stopped. This prevents unexpected accidents such as the dropping of goods.

[0032] The calculation method of the parameters for the control in the low voltage speed control unit 40 will be described. In the low voltage speed control unit 40, consider the case where the AC power supply 1 drops while a load or the like is loaded on the cage provided at the tip of the rope wound around or unwound from the drum 3. Note that mechanical friction, windage, heat loss in the electric circuit, etc. are to be ignored. The sum of the kinetic energy, potential energy, and electrical energy stored in the capacitor is kept constant, and the relationship of Equation (1) holds.

[0033]

Equation

[0034] In Equation (1), each constant and variable is defined as follows. Note that the specific configuration of the elevator from the drum 3 onward is shown in FIG. 3. FIG. 3 is a specific example of an elevator of the double drum type. M eq : Equivalent mass converted in the lifting and lowering direction of the cage CON [kg] M qa : Mass of the cage CON and the rope ROa under the pulley SHa supporting the cage CON [kg] M qb : Mass of the counterweight COW and the rope ROb under the pulley SHb supporting the counterweight COW [kg] v: Speed of the cage CON [m / s] g: Acceleration due to gravity [m / s 2 h: Height from the lower limit of the operating range of the cage CON [m] C: Capacitance of the capacitor 20 [F] V: DC voltage [V]

[0035] ​ Differentiate Equation (1) with respect to time t to obtain Equation (2).

[0036]

Number

[0037] Arrange Equation (2) to obtain Equation (3).

[0038]

Number

[0039] Integrate the velocity v with respect to time. Since the height is h, dh / dt = v. Therefore, Equation (4) is obtained.

[0040]

Number

[0041] As shown in Figure 1, assuming that the controller 42 is a PI controller, the correction value vc of the speed command value vref can be expressed as in Equation (5). s is the Laplace operator.

[0042]

Number

[0043] The definitions of the constants and variables in Equation (5) are as follows. vc: Correction value of the speed command value of the inverter device 50 [m / s] v top : Maximum speed of the inverter device 50 [m / s] k p : Proportional gain of the controller 42 k i : Integral gain of the controller 42 V0: Rated DC voltage across the capacitor 20 [V]

[0044] Differentiate Equation (5) with respect to time t to obtain Equation (6).

[0045]

number

[0046] FIG. 2 is a schematic block diagram illustrating a control system for the inverter device of FIG. As shown in FIG. 2, the relationship between the kinetic energy, potential energy, and electric energy due to the charge of the capacitor 20 of the cage CON can be expressed as a loop transfer function 101.

[0047] The first transfer function 102 in FIG. 2 is based on the formula (6), and the change value dvc of the correction value vc of the speed command value is obtained by the PI control of the controller 42. The second transfer function 103 in FIG. 2 is a transfer function when the response delay of the inverter device 50 including the delay time of the speed detector 54 is L [s]. The response of the inverter device 50 is ωc [rad / s], T=1 / ωc, and the response delay including the delay time of the speed detection is L [s]. The third transfer function 104 in FIG. 2 is a transfer function related to the kinetic energy and potential energy of the mechanical system including the cage CON, etc., and the DC voltage fluctuation dV of the capacitor 20 is calculated by the energy of the mechanical system. Therefore, according to this open-loop transfer function 101, the DC voltage fluctuation dV of the capacitor 20 is fed back to determine the fluctuation dvc of the correction value vc of the speed command value vref.

[0048] For example, when the above-mentioned system is subjected to fixed-cycle control by a programmable controller (PLC), the change in the DC voltage across the capacitor 20 can be calculated by integrating dvc over a time t that is an integer multiple of the control cycle.

[0049] The loop transfer function 101 in Fig. 2 results in classical control theory that performs PI control on a first-order lag system with a dead time element. Therefore, by setting the gain margin and phase margin of this system and using, for example, the tuning rule of Chien, Hrones and Reswick, each parameter can be determined.

[0050] Even if the control method of the controller is P control, I control, PID control, or a multi-degree-of-freedom control system, the means of reducing the problem to a first-order lag system with a dead time element is well-known. The controller is not limited to PI control and can be applied to these control methods. Even if the control method of the controller is fuzzy control or non-linear control, it is well-known that the controlled object can be similarly transformed into a "first-order lag system with a dead time element", and these control methods can also be easily applied.

[0051] FIG. 3 is a schematic diagram for explaining the operation of the inverter device according to the first embodiment. FIG. 3 schematically shows an example of an elevator using the double-drum method. In Equation (1), the constants of each part for calculating the equivalent mass M eq converted in the lifting direction of the cage CON are shown. In Equation (1), the equivalent mass Meq calculated using the following Equation (8) can also be used, or Equation (1) can be replaced with an equation related to the equivalent inertia moment J of the shaft of the motor 2 and used.

[0052]

Number

[0053]

Number

[0054] In FIG. 3, Equation (7), and Equation (8), the definitions of each constant are as follows. J motor : Inertia moment of the shaft of the motor 2 alone [kgm 2 J gear : Inertia moment of the output shaft of the gear 4 [kgm 2 n: Reduction ratio of the gear 4 J drum : Inertia moment of the drum 3 [kgm 2 J drumrope ​​​: Moment of inertia of the rope wound around the drum [kgm 2 r drum : Radius of the drum 3 [m] (drum diameter D / 2) M rope : Mass per unit length of the rope [kg / m] L2: Length of the rope from the drum 3 to the pulleys SHa, SHb [m] L 1a : Length of the rope ROa from the pulley SHa to the cage CON [m] L 1b : Length of the rope ROb from the pulley SHb to the cage CON [m] m L : Total mass of the cage CON and the load [kg] J sheave : Moment of inertia of the pulleys SHa, SHb [kgm 2 r sheave : Radius of the pulleys SHa, SHb [m] (pulley diameter D sheave / 2)

[0055] In FIG. 3, HB is the maximum lifting height of the cage CON and the counterweight COW. Also, in FIG. 3, P motor [kW] is the rated output power of the motor 2, and N motor [min -1 is the speed of the motor 2. Also, in FIG. 3, m c [kg] is the mass of the counterweight.

[0056] In an elevator, in addition to the double-drum shown in FIG. 3, its mechanical system can be applied with various lifting methods such as a single-drum method and a cable method. In these various lifting methods, according to the configuration of the mechanical system, the constants of each part can be set, and in the same way as the above example, each design parameter can be calculated.

[0057] The effects of the motor drive system 100 according to the present embodiment will be described. ​​The motor drive system 100 according to this embodiment includes an inverter device 50 having a low-voltage speed control unit 40. The low-voltage speed control unit 40 monitors the DC voltage Vdc on the input side of the inverter device 50, and corrects the speed command value vref of the motor 2 supplied from the main control device according to a decrease or increase in the DC voltage Vdc.

[0058] The correction value vc of the speed command value vref is calculated as an appropriate value by a control system of a first-order lag system with a dead time element. More specifically, when the voltage of the AC power supply 1 drops and the motor 2 is in power running operation, the low-voltage speed control unit 40 decreases the speed command value so as to suppress the decrease in the DC voltage Vdc. Also, when the voltage of the AC power supply 1 drops and the motor 2 is in regenerative operation, the low-voltage speed control unit 40 increases the speed command value so as to suppress the increase in the DC voltage Vdc.

[0059] In this way, even when an instantaneous drop or momentary power failure of the AC voltage output from the AC power supply 1 occurs, causing the DC voltage Vdc input to the inverter device 50 to drop, the low-voltage speed control unit 40 operates to suppress fluctuations in the DC voltage Vdc. Therefore, even in an environment where instantaneous drops or momentary power failures of the AC power supply 1 frequently occur, it is possible to continue the operation of the elevator without interrupting the operation. Note that an instantaneous drop or momentary power failure of the AC voltage means a short-time decrease or power failure of the AC voltage. Specifically, an instantaneous drop of the AC voltage is, for example, a case where the period during which the effective value of the AC voltage is lower than the rated value is about 1 to 10 cycles of the AC voltage period. Also, a momentary power failure of the AC voltage is, for example, a case where the period during which the AC voltage becomes 0V is about 1 to 10 cycles of the AC voltage period. The definition of an instantaneous drop or momentary power failure of the AC voltage is determined according to the power supply conditions at the site or plant where the elevator to which the motor control system is applied is installed.

[0060] At mining sites and other locations where mineral resources are mined, power supply conditions are often poor, and it is difficult to avoid instantaneous drops or power outages in the AC power supply. Even in such situations, in the motor drive system 100 according to this embodiment, by having the low-voltage speed control unit 40, continuous operation can be achieved, and high productivity can be realized.

[0061] (Second Embodiment) FIG. 4 is a schematic block diagram illustrating a motor drive system according to the second embodiment. As shown in FIG. 4, the motor drive system 200 according to this embodiment is different from the inverter device 50 according to the first embodiment in that it includes an inverter device 250 having a regenerative power control unit (regenerative power control means) 61. The motor drive system 200 according to this embodiment includes a rectifier device 210 instead of the self-excited converter device 10. In other respects, the motor drive system 200 according to this embodiment is the same as in the first embodiment, and the same reference numerals are assigned to the same components, and detailed descriptions are appropriately omitted.

[0062] The rectifier device 210 of the motor drive system 200 according to this embodiment has a rectifier circuit 211. The rectifier circuit 211 is, for example, a three-phase diode bridge circuit that rectifies a three-phase AC voltage and outputs a pulsating DC voltage. The pulsating DC voltage is smoothed by the capacitor 20 and output as a DC voltage Vdc to the inverter device 250.

[0063] Similar to the inverter device 50 of the first embodiment, in the inverter device 250, the low-voltage speed control unit 40 monitors the DC voltage Vdc across the capacitor 20 and corrects the speed command value to suppress fluctuations in the DC voltage Vdc.

[0064] When the conversion device that converts the AC voltage of the AC power supply 1 into a DC voltage is the rectification device 210, the rectification device 210 does not have a function of converting a DC voltage into an AC voltage. Therefore, in the inverter device 250 according to the present embodiment, when the motor 2 performs a regenerative operation, the regenerative power control unit 61 is operated, and the power generated by the regenerative operation of the motor 2 is consumed by the resistor 62, thereby suppressing an increase in the voltage across the capacitor 20.

[0065] The regenerative power control unit 61 monitors, for example, the current output by the power conversion unit 51, and causes the resistor 62 to consume the regenerative power when the motor 2 enters a regenerative operation.

[0066] Other operations, including the operation of the low-voltage speed control unit 40, are the same as those of the inverter device 50 according to the first embodiment.

[0067] The effects of the motor drive system 200 according to the present embodiment will be described. The motor drive system 200 according to the present embodiment includes an inverter device 250 having a low-voltage speed control unit 40, and thus exhibits the same effects as the inverter device 50 according to the first embodiment. Further, in the present embodiment, the conversion device for converting an AC voltage (first AC voltage) into a DC voltage is the rectification device 210. Therefore, for the case where the motor 2 performs a regenerative operation, the inverter device 250 has a regenerative power control unit 61. When the AC voltage of the AC power supply 1 undergoes an instantaneous drop or an instantaneous power outage, the speed command value is corrected so as to suppress the generation of regenerative power by the operation of the low-voltage speed control unit 40. Therefore, an increase in the power consumption of the resistor 62 can be suppressed, and it is not necessary to use a resistor 62 that is larger than necessary.

[0068] In the above specific examples described in relation to each embodiment, the low-voltage speed control unit is mounted on the inverter device. However, the present invention is not limited to this, and the low-voltage speed control unit may of course be mounted on other control devices such as a main control device.

[0069] In this way, a motor drive system and a motor control method capable of extending the time during which the inverter drive of the motor can be continued even when the instantaneous power supply voltage drops are realized.

[0070] Although some embodiments of the present invention have been described, these embodiments are presented by way of example and are not intended to limit the scope of the invention. These novel embodiments can be implemented in various other forms, and various omissions, replacements, and changes can be made without departing from the gist of the invention. These embodiments and their modifications are included in the scope and gist of the invention, and are also included in the invention described in the claims and its equivalent scope.

Explanation of Reference Numerals

[0071] 1…AC power supply, 2…motor, 3…drum, 10…converter device, 11, 51…power conversion unit, 14, 57…PWM control unit, 15…voltage control unit, 16…AC voltage detection unit, 20…capacitor, 30…DC voltage detection unit, 40…speed control unit at low voltage, 41, 52…calculator, 42…controller, 50…inverter device, 53…speed control unit, 55…current control unit, 58…emergency stop unit, 61…regeneration control unit, 62…resistor, 100, 200…motor drive system, 101…one-round transfer function, 102…first transfer function, 103…second transfer function, 104…third transfer function

Claims

1. A first power conversion device that converts a first AC voltage supplied from an AC power source into a DC voltage and outputs the DC voltage; A second power conversion device that converts the DC voltage into a second AC voltage and outputs the second AC voltage to a motor; comprising: The first power conversion device has DC voltage control means for controlling the DC voltage to follow a preset DC voltage command value; The second power conversion device has first speed control means for controlling the speed of the motor to follow a preset speed command value; second speed control means for calculating a correction value of the speed command value based on the DC voltage command value and the DC voltage; having: The second speed control means calculates the correction value based on the difference between the DC voltage command value and the DC voltage. A motor drive system.

2. The motor drive system according to claim 1, wherein the first power conversion device has a bidirectional power conversion circuit capable of converting the DC voltage into a third AC voltage and outputting the third AC voltage to the AC power source.

3. The motor drive system according to claim 1, wherein the second power conversion device has regenerative power control means for consuming regenerative power generated by the motor when the motor is in regenerative operation.

4. A method for controlling a motor by a motor drive system having a first power conversion device that converts a first AC voltage supplied from an AC power source into a DC voltage and outputs the DC voltage, and a second power conversion device that converts the DC voltage into a second AC voltage and outputs the second AC voltage to the motor, controlling, by the first power conversion device, the DC voltage to follow a preset DC voltage command value; controlling, by the second power conversion device, the speed of the motor to follow a preset speed command value; calculating, by speed control means, a correction value of the speed command value based on the DC voltage command value and the DC voltage; The speed control means is a control method for a motor that is a control means for a first-order lag system with a dead time element.

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