ENGINE DRIVE SYSTEM WITH POWER STORAGE DEVICE

Abstract

Motor drive system (1), comprising: a converter (11) configured to convert power between AC power in a power source (2) and DC power in a DC intermediate circuit (4); a drive inverter (12) configured to convert the power between the DC power in the DC intermediate circuit (4) and the AC power that serves as drive power or regenerative power for a drive servo motor (3); a drive motor control unit (13) configured to control the drive servo motor (3) connected to the drive inverter (12); a power storage device (14) configured to store DC power from the DC intermediate circuit (4) or to supply DC power to the DC intermediate circuit (4); and a base holding energy change unit (15) configured to change a base holding energy, defined as a reference value of a holding energy of the power storage device (14), in accordance with the holding energy of the power storage device (14); i) wherein the basic holding energy change unit (15) is configured to compare a minimum holding energy value of the power storage device (14) in a predetermined period and a predefined energy shortage threshold, and if, as a result of the comparison, the basic holding energy change unit (15) determines that the minimum holding energy value of the power storage device (14) is lower than the energy shortage threshold, the basic holding energy change unit (15) is configured to set as the new basic holding energy a value calculated by adding to the basic holding energy a value equal to or greater than a difference between the energy shortage threshold and the minimum holding energy value of the power storage device (14); or ii) wherein the base holding energy change unit (15) is configured to compare a maximum holding energy value of the power storage device (14) in a predetermined period and a predefined threshold for determining excess energy, and if, as a result of the comparison, the base holding energy change unit (15) determines that the maximum holding energy value of the power storage device (14) is higher than the threshold for determining excess energy, the base holding energy change unit (15) is configured to set as the new base holding energy a value calculated by subtracting from the base holding energy a value equal to or greater than a difference between the maximum holding energy value of the power storage device (14) and the threshold for determining excess energy; or iii) wherein the basic holding energy change unit (15) compares a minimum holding energy value of the power storage device (14) over a predetermined period and a predefined energy allowance threshold, and if, as a result of the comparison, the basic holding energy change unit (15) determines that the minimum holding energy value of the power storage device (14) is higher than the energy allowance threshold, the basic holding energy change unit (15) is configured to set as the new basic holding energy a value calculated by subtracting from the basic holding energy a value equal to or less than a difference between the minimum holding energy value of the power storage device (14) and the energy allowance threshold.

Description

BACKGROUND OF THE INVENTION 1. Scope of the invention

[0001] The present invention relates to a motor drive system with a power storage device. 2. Description of the related technology

[0002] In a motor drive system for driving a servo motor intended for use in machines including machine tools, robots, etc. (hereinafter referred to as the "drive servo motor"), the AC power supplied by an AC power source is converted into DC power by a converter (rectifier). The DC power is then output to a DC link. The DC power in the DC link is further converted back into AC power by another converter, and the AC power is used to drive the drive servo motor for each drive axis. It is common practice to use one converter for multiple inverters to reduce the cost and space requirements of the motor drive system.In other words, an inverter configured to convert the AC power supplied by an AC power source into DC power is used as a power source unit common to a variety of drive inverters (drive servo amplifiers), and these drive inverters generate AC power to drive each drive servo motor using the DC power supplied by the power source unit.

[0003] During acceleration or deceleration control of the drive servo motor by the motor drive system, a power spike occurs because the AC power source is required to deliver or regenerate high AC power. Particularly in a motor drive system with multiple drive inverters connected to a converter, this power spike can be relatively high. Reducing the power spike is desirable because the higher the power spike, the greater the required capacity of the power source and the higher the operating costs of the motor drive system, and the more power problems such as power outages and flickering can occur in the power source.

[0004] To reduce power peaks, a conventional method employs a power storage device that can store DC power in a DC link connecting the converter to the inverters in the motor drive system. Energy consumed or regenerated by the drive servo motor is then exchanged via this DC link. This method reduces power peaks because the regenerative power generated by the drive servo motor during deceleration can be stored in the power storage device, or the stored power can be reused during acceleration.In other words, the use of a power storage device that inputs and outputs power to and from the DC link makes it possible to handle even operation (acceleration and deceleration) of the drive servomotor where the power consumption is higher than the maximum output power of the power source. Examples of power storage devices include capacitor power storage devices and flywheel power storage devices.

[0005] For example, a press machine has a very high maximum power consumption during a pressing operation and often presents a problem related to a shortage of power source capacity. In such circumstances, a motor drive system in a press machine includes a flywheel energy storage device located in an intermediate circuit. This device supplies power from the energy storage device when the press machine draws high power, enabling it to operate even with a low-capacity power source. For instance, when the drive servo motor draws low power, a buffer servo motor coupled to a flywheel rotates at a constant speed. When the drive servo motor draws higher power, for example,Due to acceleration or deceleration, the speed of the buffer servomotor is reduced, power regeneration occurs via a buffer inverter, and the DC power for driving the drive servomotor is fed into the DC link. Thus, even during acceleration and deceleration operations that consume more power than the maximum power conversion rate of the inverter, the drive can be powered by regenerative energy from a buffer servomotor coupled to a flywheel.

[0006] As disclosed, for example, in JP 2013 - 9 524 A, it is known that a motor drive device includes an AC / DC converter that converts AC power from an AC source into DC power, a DC / AC converter that converts DC power into AC power to drive a motor or converts AC power regenerated by the motor into DC power, a DC intermediate unit that connects a DC side of the AC / DC converter to a DC side of the DC / AC converter and exchanges DC power, an energy storage unit comprising at least one capacitor storage unit and at least one flywheel storage unit connected to the DC intermediate unit that stores DC power from the DC intermediate unit or supplies DC power to the DC intermediate unit, and a motor control unit.which performs a control that enables the DC converter to output a desired AC power, based on a motor operating command to issue a command relating to the operation of the motor, and an energy control unit that performs a control that enables the energy storage unit to store the DC power from the DC intermediate unit or to supply the DC power to the intermediate unit.

[0007] As disclosed, for example, in JP 2016-46833A, a system for controlling a servo motor to drive an axis of industrial machinery or a machine tool is known to include a plurality of first servo motors for driving axes, a plurality of converters that convert an AC voltage to a DC voltage, a plurality of first inverters that receive the DC voltage from the converters and convert the DC voltage to an AC voltage to drive the plurality of first servo motors or convert the AC voltage generated by the first servo motors to DC, second servo motors that rotate inertially, a plurality of second inverters that receive the DC voltage from the converters and convert the DC voltage to an AC voltage to drive the second servo motors or convert the AC power regenerated by the second servo motors to DC power,and a servo motor controller that controls the plurality of first servo motors and the plurality of second servo motors, wherein the plurality of second servo motors are fewer than the plurality of second inverters, at least one of the second servo motors includes a plurality of independent windings, and at least some of the plurality of second inverters are connected to a plurality of independent windings provided in a second servo motor.

[0008] JP 2013-153605 A describes a charge and discharge circuit control. This circuit causes the charge and discharge circuit to discharge an energy storage device onto a DC bus and to charge the energy storage device from the DC bus. The control is based on the DC bus power, the energy storage capacity of the energy storage device, a power threshold contained in a charge and discharge command generated by a charge and discharge command generator, a target energy storage capacity, and an additional charge and discharge denial signal. The power threshold serves to define the upper and lower limits of the power supplied and discharged between the DC bus and the energy storage device and is defined as a function of the power supply circuit's capacity. The target energy storage capacity is a target value for controlling the energy storage capacity of the energy storage device.The auxiliary signal to reject charging and discharging is a signal that orders permission / prohibition of charging and discharging of the energy storage device.

[0009] DE 10 2012 011 914 A1 describes a motor control device. This device comprises an AC-DC converter that converts alternating current supplied by a power source into direct current, a DC-AC converter that converts direct current into alternating current and vice versa, a DC connection unit that connects the DC side of the AC-DC converter to the DC side of the DC-AC converter and supplies the direct current from one to the other and vice versa, an energy storage unit comprising at least one capacity storage unit and at least one flywheel storage unit, each of which is connected to the DC connection unit and stores or supplies the direct current, and an energy control unit that performs control so that the energy storage unit stores or supplies the direct current.

[0010] DE 10 2006 033 562 B3 describes a press system with an energy management system. A central control unit monitors the operation of all servo drive devices connected to a DC link and the flywheel energy storage system.

[0011] DE 10 2015 007 913 A1 describes a method for online adaptation of at least one characteristic curve of a hybrid vehicle comprising a hybridized powertrain with an electric drive which can be supplied with current from an electric energy storage device, wherein the at least one characteristic curve is used to select an operating mode and / or to determine an operating point of the powertrain.

[0012] DE 10 2013 207 680 A1 describes a hybrid drive system. This system comprises an internal combustion engine, a generator driven by the internal combustion engine, a battery storage system, and an electric motor. The hybrid drive system can be operated in a load point shifting mode, a recuperation mode, and a boost mode. In load point shifting mode, a power or torque distribution controller specifies the torque outputs of the internal combustion engine and the electric motor to maintain a predetermined setpoint for the state of charge of the battery storage system. In load point shifting mode, the setpoint for the state of charge of the battery storage system is shifted depending on changes in the state of charge of the battery storage system during a previously executed recuperation and / or boost mode.

[0013] DE 10 2015 211 948 A1 describes a method for controlling an energy flow in an energy network and an energy network itself. In this method, the energy input and / or output of at least one participant in the energy network is controlled, at least temporarily, by at least one control device of the energy network, depending on at least one energy tolerance representative of a permissible deviation from the normal energy input and / or output of the at least one participant. SUMMARY OF THE INVENTION

[0014] In a motor drive system where a DC link connecting a converter and a drive inverter is equipped with a power storage device to reduce power surges, if the energy stored in the power storage device becomes depleted, the servo motors will not receive sufficient drive power. This could lead to an inadvertent shutdown of the motor controller and the machine tool, including the motor controller. For example, if an unexpectedly high load is applied to the drive servo motors, they will consume more power than normal. Since the energy stored in the power storage device is consumed in greater quantities than originally planned, subsequent operation of the drive servo motors is very likely to fail due to power outages.If the energy stored in the power storage device is greater than required, it can also accelerate wear and tear on the device. For example, in a flywheel energy storage device, the buffer servomotor used to turn the flywheel rotates at a higher speed when the rotational energy is greater. This increases vibration due to the rotational speed, accelerating the wear of the buffer servomotor and the flywheel coupled to it. Similarly, in a capacitor energy storage device, for instance, the increasing voltage of the capacitor with increasing stored energy puts greater stress on the capacitor and accelerates its wear.Accordingly, in the motor drive system, including the power storage device intended to reduce the power peak of the power source equipment, there is a need for a technique to maintain the energy stored in the power storage device to a reasonable extent.

[0015] To solve the above problem, the present invention relates to a motor drive system according to claim 1. Claims 2 to 4 describe particularly advantageous implementations of the motor drive system according to claim 1.

[0016] According to one aspect of the present disclosure, a motor drive system includes a converter configured to convert power between alternating current in a power source and direct current in a DC link, a drive inverter configured to convert power between the DC power in the DC link and alternating current serving as drive power or regenerative power for a drive servo motor, a drive motor control unit configured to control the drive servo motor connected to the drive inverter, a power storage device configured to store DC power from the DC link or to supply DC power to the DC link, and a base holding energy change unit configured to change a base holding energy.which is defined as the reference value of a holding energy of the power storage device, in accordance with the holding energy of the power storage device. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] The present invention will be better understood by reference to the following accompanying drawings: Fig. 1 is a block diagram representing a motor drive system according to one embodiment; Fig. 2 is a block diagram illustrating the motor drive system according to the embodiment, which includes a flywheel power storage device; Fig. Figure 3 is a block diagram illustrating the motor drive system according to the embodiment, which includes a capacitor power storage device; Fig. Figure 4 is a diagram illustrating an exemplary relationship between the DC power supplied by the power storage device in the motor drive system according to the embodiment and the DC power supplied by a converter; Fig. Figure 5 is a timing diagram that illustrates an example of the control of the power storage device by a power storage device control unit; Fig. Figure 6 is a time diagram illustrating an exemplary relationship between the total power consumption and the holding energy of the power storage device when a basic holding energy change process is performed in the motor drive system according to the embodiment according to a first mode; Fig. Figure 7 is a time diagram illustrating an exemplary relationship between the total power consumption and the holding energy of the power storage device when a basic holding energy change process is performed in the motor drive system according to the embodiment in accordance with a second mode; Fig. Figure 8 is a time diagram illustrating an exemplary relationship between the total power consumption and the holding energy of the power storage device when a basic holding energy change process is performed in the motor drive system according to the embodiment in accordance with a third mode; Fig. 9 is a flowchart that represents a functional sequence of the motor drive system according to the embodiment; and Fig. Figure 10 is a flowchart illustrating the operation of the motor drive system according to the embodiment. DETAILED DESCRIPTION

[0018] A motor drive system with a power storage device is described below with reference to the drawings. The same reference numerals denote the same elements in these drawings. These drawings use different scales as needed to facilitate understanding. The mode shown in each drawing is an example of the implementation of the present invention, and the present invention is not limited to the modes shown in these drawings. The "power of a drive servo motor" includes the "power consumption of the drive servo motor" and the "amount of regenerative power of the drive servo motor," and the "power of a buffer servo motor" includes the "power consumption of the buffer servo motor" and the "amount of regenerative power of the buffer servo motor."The angular velocities of the drive servo motor and the buffer servo motor are referred to simply as "speeds" or "rotational rates" in the following.

[0019] A motor drive system according to an embodiment of the present disclosure is used for a system comprising drive servomotors of drive axes in machines including a machine tool, a robot, etc., drive inverters that supply alternating current to drive the drive servomotors in accordance with the drive servomotors, and a converter.

[0020] Fig. Figure 1 is a block diagram illustrating a motor drive system according to one embodiment. The case where two drive servomotors 3 are controlled by a motor drive system 1 connected to an AC power source 2 is given here as an example. However, the number of drive servomotors 3 does not particularly limit this embodiment and can be one, three, or more. Similarly, the number of phases of the power source 2 and the drive servomotors 3 does not particularly limit this embodiment, and, for example, a three-phase or single-phase configuration can be used. The type of drive servomotor 3 also does not particularly limit this embodiment, and, for example, an induction or synchronous motor can be used.Examples of machines equipped with the drive servomotors 3 include a machine tool, a robot, forging machines, an injection molding machine, industrial machines, various electrical appliances, an electric train, an automobile and an aircraft.

[0021] Each circuit component of the motor drive system 1 is first described.

[0022] As in Fig. As shown in Figure 1, the motor drive system 1 according to the embodiment includes a converter 11, drive inverter 12, a drive motor control unit 13, a power storage device 14, a basic holding energy change unit 15, a power consumption calculation unit 16 and a power storage control unit 17.

[0023] The converter 11 acts as a rectifier configured to convert the power between the AC power in the power source 2 and the DC power in a DC link 4. The converter 11 is implemented in a three-phase bridge circuit when a three-phase AC current is supplied from the power source 2, and in a single-phase bridge circuit when a single-phase AC current is supplied from the power source 2.The converter 11 is implemented as a bidirectional AC / DC converter, such as a 120-degree line rectifier circuit and a PWM switching control rectifier circuit, which converts the AC power received from power source 2 into DC power and outputs the DC power to the DC side, and converts the DC power of the DC intermediate circuit 4 into AC power and outputs the AC power to power source 2 during power regeneration. When the converter 11 is implemented as, for example, a PWM switching control rectifier, it is implemented in a bridge circuit of switching elements and diodes connected antiparallel to the switching elements, and performs bidirectional AC / DC power conversion by switching each switching element on and off according to a drive command received from a host controller (not shown).Examples of the switching element can include a unipolar transistor such as a FET, a bipolar transistor, an IGBT, a thyristor, and a GTO, but the type of switching element itself does not limit this embodiment, and other types of switching elements can be used.

[0024] For converter 11, a "maximum power conversion" is defined as the maximum amount of power that enables the conversion of alternating current (AC) to direct current (DC), and the maximum amount of power that enables the conversion of DC to AC. The maximum power conversion is generally defined as specification data associated with the conversion capacity of converter 11 and is given, for example, in a specification table or operating manual for converter 11.

[0025] The drive inverters 12 are connected to the converter 11 via the DC link 4. The DC link 4 includes a DC link capacitor (also called a smoothing capacitor), which is not shown here. The DC link capacitor's function is to store the DC power in the DC link 4 and to suppress pulsing of the DC output of the converter 11.

[0026] The drive inverter 12 is a servo amplifier configured to convert the DC power in the DC link 4 into AC power and supplies the AC power to the drive servomotor 3 as drive power to operate it. The drive inverter 12 converts the power between the DC power in the DC link 4 and the AC power that serves as drive power or regenerative braking for the drive servomotor 3. The drive servomotor 3 generally includes at least one winding, and one drive inverter 12 can preferably be used per winding in the drive servomotor 3 to drive it. Fig. Figure 1 represents, by way of example, drive servomotors 3 of the single winding type, and accordingly, a drive inverter 12 is connected to each drive servomotor 3.

[0027] The drive inverter 12 is implemented in a bridge circuit of switching elements and diodes connected antiparallel to the switching elements. The ON / OFF control of each switching element is based on PWM switching control, for example, a triangle wave comparison scheme. The drive inverter 12 is implemented in a three-phase bridge circuit when the drive servomotor 3 is used as a three-phase motor and in a single-phase bridge circuit when the drive servomotor 3 is used as a single-phase motor. Examples of the switching element can include a unipolar transistor such as a FET, a bipolar transistor, an IGBT, a thyristor, and a GTO, but the type of switching element itself does not limit this embodiment, and other types of switching elements can be used.

[0028] The drive inverter 12 converts the power between the DC power of the DC link 4 and the AC power, which serves as drive power or feedback for the drive servomotor 3, by ON / OFF control of each switching element based on a drive command received from the drive motor control unit 13 (described later). In particular, the drive inverter 12 performs the switching operation of the internal switching elements, based on a drive command received from the drive motor control unit 13, to convert the DC power supplied by the converter 11 via the DC link 4 into AC power with a desired voltage and frequency to drive the drive servomotor 3 (inverting operation). The drive servomotor 3 thus operates, for example, with AC voltage with variable voltage and variable frequency.During the deceleration of the drive servomotor 3, regenerative power may occur, but the switching operation of the internal switching elements is based on a drive command received from the drive motor control unit 13 in order to convert the AC regenerative power occurring in the drive servomotor 3 into DC power and to feed the DC power back into the DC intermediate circuit 4 (rectifier operation).

[0029] The drive motor control unit 13 controls the drive servomotors 3, which are connected to the drive inverters 12, to operate them (i.e., rotate them) according to a predefined operating pattern. The operating pattern of the drive servomotors 3 results from a combination of acceleration, deceleration, constant rotation, and, if necessary, stopping, according to the operating data of the machine equipped with the drive servomotors 3. A group of operations with the same drive servomotors 3 is defined as "a cycle," and the aforementioned "operating pattern" is created by repeatedly executing this cycle. The operating pattern of the drive servomotors 3 is defined by an operating program for the drive servomotors 3.For example, if the drive servomotors 3 are provided in a machine tool, an operating program for the drive servomotors 3 is defined as one of the machining programs for the machine tool.

[0030] Since the drive servomotors 3 are controlled in speed, torque, or rotor position, based, for example, on variable voltage and frequency AC power supplied by the drive inverters 12, the control of the drive servomotors 3 by the drive motor control unit 13 is ultimately achieved by controlling the power conversion operation of the drive inverters 12. In other words, the drive motor control unit 13 controls the drive servomotors 3 to operate them according to a predefined operating pattern by controlling the power conversion of the drive inverters 12.More precisely, the following process is carried out: The drive motor control unit 13 generates a drive command to control the speeds, torques, or rotor positions of the drive servomotors 3, based, for example, on the (rotor) speeds (speed feedback) of the drive servomotors 3 detected by a speed sensor 51, a current flowing through the windings of the drive servomotors 3 (current feedback), a predefined torque command, and an operating program for the drive servomotors 3. The power conversion operation of the drive inverters 12 is controlled based on the drive command generated by the drive motor control unit 13.The configuration of the drive motor control unit 13 defined herein is for illustrative purposes only, and the configuration of the drive motor control unit 13 can be defined including terms such as a position command generation unit, a torque command generation unit, and a shift command generation unit.

[0031] In order to enable the drive servomotors 3 to be driven with a power that is higher than the maximum power conversion of the converter 11, the motor drive system 1 includes a power storage device 14.

[0032] The power storage device 14 stores direct current from the DC link 4 (power storage) and supplies the DC link 4 with direct current (voltage supply). The energy storage and power supply of the power storage device 14 are controlled by the power storage control unit 17. The base holding energy is defined as a reference value (setpoint) of the energy to be stored by the power storage device 14. By controlling the power storage control unit 17, the power is stored in the power storage device 14 so that the holding energy of the power storage device 14 can return to the base holding energy, which is the setpoint of the holding energy of the power storage device 14.For example, when the drive servomotors 3 are not in operation and the power output / intake by the power storage device 14 is not particularly required, the holding energy of the power storage device 14 is maintained based on the holding energy. When the power supply operation of the power storage device 14 is performed, the holding energy of the power storage device 14 drops to a value lower than the base holding energy. However, when the power storage operation of the power storage device 14 is performed, the holding energy of the power storage device 14 increases and recovers the base holding energy as the setpoint. Depending on the drive condition of the drive servomotors 3 by the motor drive system 1, the power supply of the power storage device 14 can be performed before the holding energy of the power storage device 14 returns to the base holding energy.

[0033] Examples of the power storage device 14 include a flywheel power storage device, as in Fig. 2 shown, and a capacitor power storage device, as shown in Fig. 3 shown.

[0034] Fig. Figure 2 is a block diagram illustrating the motor drive system according to the embodiment, which includes a flywheel power storage device. The flywheel power storage device 14 includes a flywheel 41, a buffer servomotor 42, and a buffer inverter 43.

[0035] The flywheel 41 can store rotational energy, which is also referred to as inertia.

[0036] The buffer servomotor 42 serves to rotate the flywheel 41, which is connected to the axis of rotation of the buffer servomotor 42. The rotational energy can be stored in the flywheel 41 by rotating the buffer servomotor 42. The number of phases of the buffer servomotor 42 does not particularly restrict this embodiment, and, for example, a three-phase or single-phase configuration can be used. A speed detector 52 for the buffer servomotor 42 is provided in the servomotor, and the (rotor) speed of the buffer servomotor 42 detected by the speed detector 52 is used by the power storage control unit 17 to control the power storage device 14.

[0037] The buffer inverter 43 converts the power between the DC power in the DC link 4 and the AC power, which serves as drive power or feedback for the buffer servomotor 42, by switching each switching element ON / OFF based on the power storage and power supply commands received from the power storage control unit 17. The buffer inverter 43 is implemented in a bridge circuit consisting of switching elements and diodes connected antiparallel to the switching elements. The buffer inverter 43 is implemented in a three-phase bridge circuit when the buffer servomotor 42 is used as a three-phase motor and in a single-phase bridge circuit when the buffer servomotor 42 is used as a single-phase motor.Examples of the switching element can include a unipolar transistor such as a FET, a bipolar transistor, an IGBT, a thyristor, and a GTO, but the type of switching element itself does not limit this embodiment, and other types of switching elements can be used. For example, the ON / OFF control of each switching element in the buffer inverter 43 is performed based on a PWM switching signal obtained by comparing the received drive command with a triangular carrier.

[0038] By controlling the power conversion of the buffer inverter 43 by the power storage control unit 17, the buffer servomotor 42 connected to the flywheel 41 rotates with acceleration or deceleration or rotates at a constant speed, so that the amount of DC power to be stored or supplied by the power storage device 14 (the amount of DC power to be supplied to or released from the DC intermediate circuit 4 by the power storage device 14) is set. More precisely, the following process is carried out.

[0039] In the power storage device 14, the buffer inverter 43 performs an inversion operation to convert the DC voltage in the DC link 4 into AC voltage, based on a power storage command received by the power storage control unit 17. Thus, electrical energy from the DC link 4 is supplied to the buffer servomotor 42 and used to rotate the servomotor for the buffer servomotor 42 connected to the flywheel 41. In this way, electrical energy flowing from the DC link 4 into the power storage device 14 is converted into rotational energy of the flywheel 41 and stored.

[0040] In the power supply of the power storage device 14, the buffer inverter 43 performs rectification operation to convert AC regenerative power into DC power by executing the AC regenerative power generation during braking of the servo motor for the buffer servomotor 42 connected to the flywheel 41, based on a power supply command received from the power storage control unit 17. Thus, the rotational energy stored in the flywheel 41 is converted into electrical energy and supplied to the DC intermediate circuit 4.

[0041] In the Fig. In the flywheel power storage device 14 shown in Figure 2, the power of the buffer servomotor 42 corresponds, for example, to the holding energy of the power storage device 14. The holding energy of the power storage device 14, i.e., the power of the buffer servomotor 42, can be calculated, for example, according to the following equation (1): Holding energy of the power storage device 14=(1 / 2)×J×ω2 where ω is the rotational speed (angular velocity) of the buffer servomotor 42, which is detected by the velocity detector 52, and J is the moment of inertia of the buffer servomotor 42.

[0042] As can be seen from equation (1), since the holding energy of the power storage device 14 is proportional to the square of the rotational speed of the buffer servomotor 42, the rotational speed (or its square) of the buffer servomotor 42 can be used as a parameter representing the holding energy of the power storage device 14.

[0043] Fig. Figure 3 is a block diagram illustrating the motor drive system according to the embodiment, which includes a capacitor power storage device. The capacitor power storage device 14 includes a capacitor 44 and a DC / DC converter 45, which are configured to convert power between the DC voltage in the DC link 4 and the DC voltage stored in the capacitor 44.

[0044] Examples of the DC / DC converter 45 are a DC / DC boost and buck chopper circuit.

[0045] The amount of DC power to be stored or provided by the power storage device 14 (the amount of DC power fed into or delivered from the intermediate circuit 4 by the power storage device 14) is set by controlling the boost and buck chopper operations of the DC / DC converter 45 by the power storage control unit 17. More precisely, the following operation is performed.

[0046] In the power storage device 14, the DC / DC converter 45 is controlled to set the DC voltage at the capacitor 44 lower than the DC voltage at the intermediate circuit 4 by the power storage control unit 17, based on a power storage command received by the power storage control unit 17. Thus, electrical energy flows from the intermediate circuit 4 into the capacitor 44, and the power storage of the power storage device 14 is carried out.

[0047] In the power supply of the power storage device 14, the DC / DC converter 45 is controlled to adjust the DC voltage at the capacitor 44 to be higher than the DC voltage at the DC intermediate circuit 4 by the power storage control unit 17, based on a power supply command received from the power storage control unit 17. Thus, electrical energy flows from the capacitor 44 into the DC intermediate circuit 4, and the power supply to the power storage device 14 is carried out.

[0048] In the Fig. For example, the amount of DC power stored in capacitor 44 corresponds to the holding energy of the power storage device 14 shown in Figure 3. The holding energy of the power storage device 14 can be calculated, for example, according to the following equation (2): Holding energy of the power storage device 14=(1 / 2)×C×V2 where C is the capacitance of capacitor 44 and V is the voltage of capacitor 44.

[0049] As can be seen from equation (2), since the holding energy of the power storage device 14 is proportional to the square of the voltage of the capacitor 44, the voltage (or its square) of the capacitor 44 can be used as a parameter representing the holding energy of the power storage device 14.

[0050] Since the motor drive system 1 includes the power storage device 14, which performs the above-mentioned operations, the energy stored in the power storage device 14 is supplied to the drive servomotors 3 as well as the energy supplied by the converter 11 and is used as power to accelerate the drive servomotors 3 during the acceleration of the drive servomotors 3. Fig. Figure 4 is a diagram illustrating an exemplary relationship between the DC power supplied by the power storage device in the motor drive system according to the embodiment and the DC power supplied by the converter. The power supplied by the converter 11 to the DC intermediate circuit 4 is included not only as drive power for the drive servomotors 3 (i.e., the outputs of the drive servomotors 3 correspond to the drive power), but also as winding losses in the drive servomotors 3, a loss in the converter 11, and losses in the drive inverter 12. The sum of the power consumed by the drive servomotors 3, the drive inverters 12, and the converter 11 is referred to below as the "total power consumption" and is represented by a solid line in Figure 4. Fig. Figure 4 shows the maximum power conversion in rectifier mode of converter 11. An alternating long and short dashed line indicates the maximum power conversion value. Fig. As shown in section 4, the amount (a hatched area in Fig. 4), by which the maximum supplied power of the converter 11 is exceeded in the total power consumption, is compensated by DC power supplied by the power storage device 14 to the DC intermediate circuit 4.

[0051] In the motor drive system 1, the energy recovered by the drive servomotors 3 during deceleration is stored in the power storage device 14. Since the energy stored in the power storage device 14 is used to drive the drive servomotors 3 in conjunction with the power supplied by the converter 11, the drive servomotors 3 can be driven with a power output exceeding the maximum power conversion of the converter 11, thereby reducing the power peak. Reducing the power peak can decrease the capacity of the power source and the operating costs of the motor drive system 1, and may even prevent power outages and flickering in the power source 2.

[0052] To get to the description of Fig. Returning to section 1, the power consumption calculation unit 16 calculates a total power consumption, which results from the sum of the outputs of the drive servomotors 3, the winding losses in the drive servomotors 3, the losses in the converter 11, and the losses in the drive inverters 12. The power of the drive servomotor 3 is obtained by multiplying the rotational speed of the drive servomotor 3, which is detected by the speed sensor 51, by the torque of the drive servomotor 3. When the drive servomotor 3 accelerates, it consumes alternating current supplied by the drive inverter 12, and the power of the drive servomotor 3 during this power consumption is defined as "positive." This means that when power is regenerated during the deceleration of the drive servomotor 3, the power of the drive servomotor 3 is "negative."Since the winding losses in the drive servomotor 3, the losses in the converter 11, and the losses in the drive inverter 12 are generally lower than the absolute value of the power of the drive servomotor 3, the power of the drive servomotor 3 has a dominant influence on the total power consumption. Accordingly, the positive or negative sign (consumption or regeneration) of the output of the drive servomotor 3 corresponds almost exactly to the positive or negative sign of the total power consumption.

[0053] Since the buffer inverter 43 and the DC / DC converter 45 also have losses, the power calculation unit 16 can calculate a total power consumption sum obtained by further adding the losses in the buffer inverter 43 or the DC / DC converter 45 to the sum of the outputs of the drive servomotors 3, the winding losses in the drive servomotors 3, the losses in the converter 11 and the losses in the drive inverters 12.

[0054] The power storage control unit 17 controls the power storage and supply of the power storage device 14 by controlling the power conversion process of the buffer inverter 43 in the power storage device 14, which is referred to as the in Fig. The flywheel power storage device 14 is designed as shown in Figure 2. The power storage control unit 17 controls the power storage and supply of the power storage device 14 by controlling the charging and boosting processes of the DC / DC converter 45 in the power storage device 14, which is designed as a capacitor power storage device 14, as shown in Figure 2. Fig. 3 shown.

[0055] The power storage control unit 17 compares the total power consumption and a supply threshold, and if, as a result of the comparison, the power storage control unit 17 determines that the total power consumption is higher than the supply threshold, the power storage control unit 17 controls the power storage device 14 to supply DC power to the DC intermediate circuit 4.Furthermore, the power storage control unit 17 compares the total power consumption and a power storage threshold, and if, as a result of the comparison, the power storage control unit 17 determines that the total power consumption is lower than the power storage threshold, the power storage control unit 17 controls the power storage device 14 to store direct current from the DC intermediate circuit 4, so that the holding energy of the power storage device 14 returns to the base holding energy.

[0056] The supply threshold can be set based on the maximum amount of power conversion for the rectifier operation of the converter 11. For example, if the difference between the maximum power conversion and the total power consumption calculated by the power consumption calculation unit 16 for the rectifier operation of the converter 11 is negative because the total power consumption is greater than the maximum power supplied during the rectifier operation of the converter 11, i.e., the energy supplied by the converter 11 from the power source 2 to the DC link 4 is insufficient to cover the total power consumption, the power gap can preferably be compensated by direct current supplied to the DC link 4 by the power storage device 14.The supply threshold is set as a reference value for assessing whether the current state is one in which DC power should be supplied from the power storage device 14 to the DC intermediate circuit 4, since the total power consumption is higher than the maximum power supplied for rectification of the converter 11.

[0057] The threshold for power storage can be set based on the maximum amount of power conversion for the reverse operation of the converter 11. For example, if the difference between the absolute value of the maximum power conversion and the absolute value of the total power consumption calculated by the power consumption calculation unit 16 for the reverse operation of the converter 11 is negative, because the total power consumption is greater than the maximum regenerative power when the converter 11 is reversed, the excess power can preferably be stored in the power storage device 14.The power storage threshold is set as a reference value for assessing whether the current state is one in which the DC voltage from the DC intermediate circuit 4 should be stored in the power storage device 14, since the total power consumption is higher than the maximum power supplied when the converter 11 is inverted.

[0058] The functionality of the power storage control unit 17 is described in more detail below.

[0059] The power storage control unit 17 compares the total power input calculated by the power calculation unit 16 with the supply threshold. If the power storage control unit 17 determines that the total power input is higher than the supply threshold, it calculates, for example, the difference between the total power input and the supply threshold as the "power quantity," i.e., the amount of DC power to be delivered by the power storage device 14 to the DC intermediate circuit 4. The power storage control unit 17 then issues a power supply command to the power storage device 14 to execute the control to deliver DC power to the DC intermediate circuit 4 in accordance with the supply power.

[0060] The power storage control unit 17 compares the total power input calculated by the power calculation unit 16 and the power storage threshold, and if the power storage control unit 17 determines that the total power input is lower than the power storage threshold, the power storage control unit 17 calculates, for example, the difference between the power storage threshold and the total power input as the "power storage quantity", which is the quantity of direct current to be stored in the power storage device 14 from the DC intermediate circuit 4.The power storage control unit 17 issues a power storage command to the power storage device 14 to execute the control for storing DC power according to the power storage quantity from the DC intermediate circuit 4, so that the holding energy of the power storage device 14 returns to the base holding energy. Depending on the drive condition of the drive servomotors 3 by the motor drive system 1, the power supply command can be issued by the power storage control unit 17 to the power storage device 14 before the holding energy of the power storage device 14 returns to the base holding energy.

[0061] The power storage device 14 performs the power supply upon receiving the power supply command from the power storage control unit 17 and performs the power storage upon receiving the power storage command from the power storage control unit 17.

[0062] Fig. Figure 5 is a timing diagram illustrating an example of the control of the power storage device by the power storage control unit. As an example, in an operating pattern of a cycle of the drive servomotors 3, which are driven by the motor drive system 1, time t1 to time t3 is defined as acceleration, time t3 to time t5 as deceleration, time t5 to time t7 as acceleration, and time t7 to time t9 as deceleration. As the drive servomotors 3 are accelerated by the motor drive system 1 during time t1 to t3, the total power consumption gradually increases. When the total power consumption exceeds the supply threshold at time t2, the power storage control unit 17 controls the power storage device 14 to supply DC power to the DC link 4.When the drive servomotors 3 are decelerated by the motor drive system 1 between t3 and t5, the drive servomotors 3 undergo regeneration and the total power consumption becomes negative. During t3 to t4, since the total power consumption is lower than the power storage threshold, the power storage control unit 17 controls the power storage device 14 to store DC power from the DC link 4. When the drive servomotors 3 are accelerated by the motor drive system 1 between t5 and t7, the total power consumption gradually increases. When the total power consumption exceeds the supply threshold at t6, the power storage control unit 17 controls the power storage device 14 to supply DC power to the DC link 4.When the drive servomotors 3 are decelerated by the motor drive system 1 during time t7 to t9, the drive servomotors 3 undergo regeneration and the total power consumption becomes negative. During time t7 to time t8, since the total power consumption is lower than the power storage threshold, the power storage control unit 17 controls the power storage device 14 to store DC power via the DC link 4.

[0063] The selection of the power storage device 14 will now be described using an example. For example, if in Fig. 5. If the maximum power conversion (maximum output power) for rectification of the converter 11 is 1000 kW, the maximum power conversion (maximum regeneration) for inversion of the converter 11 is 1000 kW, the supply threshold is 600 kW, and the power storage threshold is -600 kW, the basic holding energy is set, for example, as follows. Fig. 5 are the time t2 to time t3 in which the total power consumption is higher than the threshold for supply, for example 300[ms] and the time t3 to time t4 in which the total power consumption is lower than the threshold for power storage, for example 100[ms].

[0064] The amount of energy to be supplied by the power storage device 14 during the time t2 to t3 is expressed by the following equation (3): Supply energy quantity=(1000−600)[kW]×0.3[s]÷2=60[kJ]

[0065] The amount of energy to be stored in the power storage device 14 during the time t3 to t4 is expressed by the following equation: (4) Energy storage amount=(1000−600)[kW]×0.1[s]÷2=20[kJ]

[0066] Equation (3) shows that the power storage device 14 can preferably supply a maximum energy of 60 kJ, but the base holding energy of the power storage device 14 is set to 70 kJ (= 60 kJ + 10 kJ) with a tolerance of, for example, 10 kJ for safety reasons. The power storage device 14 with the base holding energy of 70 kJ must store a maximum of 20 kJ of energy, as shown in equation (4). Thus, taking into account, for example, 10 kJ for safety reasons, the power storage device 14 with a maximum storage capacity of 100 kJ (= 70 kJ + 20 kJ + 10 kJ) can be selected.

[0067] For example, if in the case of the flywheel power storage device 14 the inertia of the buffer servomotor 42 is 1 [kg·m2], the rotational speed of the buffer servomotor 42 to obtain the basic holding energy of 70 [kH] is expressed by the following equation (5): √(70[kJ]÷1[kg⋅m2]÷2)=187.1[rad / s]=1786.7[min−1]

[0068] The rotational speed required of the buffer servomotor 42 to construct the flywheel power storage device 14 with a maximum storage capacity of 100 [kJ] is expressed by the following equation (6): √(100[kJ]÷1[kg⋅m2]÷2)=223.6[rad / s]=2135.2[min−1]

[0069] From equation (5) and equation (6) the buffer servomotor 42, which has a basic speed (corresponding to the basic holding energy) of 2000 [min], can be determined. -1 ] and the maximum speed of 3000 [min -1] exhibits, for example, the flywheel power storage device 14, which has a basic holding energy of 70[kJ] and a maximum storage capacity of 100[kJ].

[0070] The numerical values ​​mentioned in the description for the selection of the power storage device 14 described above are only examples, and the numerical values ​​are correctly set according to the purpose to which the motor drive system 1 is applied.

[0071] Back to the description of Fig. 1, the basic holding energy change unit 15 changes the basic holding energy, which is defined as the reference value of the holding energy of the power storage device 14, according to the holding energy of the power storage device 14.

[0072] The holding energy of the power storage device 14 can, for example, be determined according to equation (1) for the in Fig. 2 flywheel power storage device 14 shown and according to equation (2) for the in Fig. The holding energy of the power storage device 14 shown in Figure 3 can be calculated. In this case, the calculation process for the holding energy of the power storage device 14 can be performed by the basic holding energy change unit 15, by the power storage control unit 17, or by a calculation unit (not shown) that is provided separately.Since, for example, the power storage control unit 17 calculates the "power storage quantity" from the DC intermediate circuit 4, which is the amount of DC power to be stored in the power storage device 14, or the "power supply quantity," which is the amount of DC power to be supplied to the DC intermediate circuit 4 by the power storage device 14, the power storage control unit 17 can calculate the holding energy of the power storage device 14 based on the amount of energy gained by integrating the "power storage quantity" or the "power supply quantity." In this case, the power storage control unit 17 performs the calculation process for the holding energy of the power storage device 14 and sends the calculation result to the basic holding energy change unit 15.

[0073] For example, a basic holding energy change process by the basic holding energy change unit 15 is performed in three modes, as described below.

[0074] A base holding energy change process through a first mode increases the base holding energy when the holding energy of the power storage device 14 becomes short.According to the first mode, the base holding energy change unit 15 compares a minimum value of the holding energy of the power storage device 14 in a predetermined period and a predefined threshold for determining energy deficiency, and if, as a result of the comparison, the base holding energy change unit 15 determines that the minimum value of the holding energy of the power storage device 14 is less than the threshold for determining energy deficiency, the base holding energy change unit 15 sets as the new base holding energy after a change a value which is calculated by adding to the base holding energy before the change a value which is equal to or greater than a difference between the threshold for determining energy deficiency and the minimum value of the holding energy of the power storage device 14.A group of operations with the same drive servomotor details 3 is defined as "a cycle," and a single cycle is defined as the "predetermined time period" described above. Two or more cycles can be defined as a "predetermined period." The energy shortage threshold can be set to a value greater than zero. For example, the energy shortage threshold is set to approximately 10% of the maximum storage capacity of the power storage device 14. The numerical value of the energy shortage threshold mentioned here is only an example, and the numerical value of the energy shortage threshold can be set to an optionally chosen value, for example, according to the intended use of the motor drive system.

[0075] Fig. Figure 6 is a time diagram illustrating an exemplary relationship between the total power consumption and the holding energy of the power storage device when the basic holding energy change process is performed according to the first mode in the motor drive system according to the embodiment. Fig. Figure 6 shows an upper part representing the total power consumption calculated by the power consumption calculation unit 16, and a lower part representing the holding energy of the power storage device 14. It is based on an example where the holding energy of the power storage device 14 may be momentary during time t7 to time t9, when the drive servomotors 3 are accelerated and decelerated by the motor drive system 1, and the total power consumption varies, as shown in the upper part of Figure 6. Fig. Figure 6 illustrates the "acceleration, deceleration, acceleration, deceleration" of the drive servomotors 3, which is defined as one cycle. Fig. 6 is, for example, the "acceleration, deceleration, acceleration, deceleration" from time t1 to time t 10 a cycle and the "acceleration, deceleration, acceleration, deceleration" of time t 12 at time t 20 is a cycle. Since each cycle has the same operating pattern, each cycle typically has essentially the same total power consumption. A standby process period is provided between a preceding cycle and a subsequent cycle to recover the holding energy of the power storage device 14 to its base holding energy. During the standby process period, DC power is stored in the power storage device 14, into which the AC power from the power source 2 is converted by the converter 11, and the holding energy of the power storage device 14 gradually increases. In the example of Fig. 6. The standby process period ends at time t. 11, since the holding energy of the power storage device 14 returns to the base holding energy and the next cycle begins at time t 12 is started. Although the operation of the drive servomotor 3 in a cycle is defined by way of example as "acceleration, deceleration, acceleration, deceleration", a cycle can be defined including a constant speed, a stop or the like.

[0076] Until time t1, the holding energy of the power storage device 14 is maintained at the base holding energy. During time t1 to t3, as the drive servomotors 3 are accelerated by the motor drive system 1, the total power consumption gradually increases. When the total power consumption exceeds the supply threshold at time t2, the power storage control unit 17 controls the power storage device 14 to supply DC power to the DC link 4, and as a result, the holding energy of the power storage device 14 gradually decreases.

[0077] When the drive servomotors 3 are decelerated by the motor drive system 1 during time t3 to t5, the drive servomotors 3 undergo regeneration and the total power consumption becomes negative. During time t3 to t4, since the total power consumption is lower than the power storage threshold, the power storage control unit 17 controls the power storage device 14 to store DC power from the DC link 4. This gradually increases the holding energy of the power storage device 14.

[0078] When the drive servomotors 3 are accelerated again by the motor drive system 1 at time t5, the total power consumption gradually increases. During the period t5 to t6, as DC power is converted into AC power from the power source 2 by the converter 11 and stored in the power storage device 14, the holding energy of the power storage device 14 gradually increases. When the total power consumption exceeds the supply threshold at time t6, as the power storage control unit 17 controls the power storage device 14 to supply DC power to the DC link 4, the holding energy of the power storage device 14 gradually decreases. At time t7, the holding energy of the power storage device 14 becomes lower than the energy shortage threshold.

[0079] When the drive servomotors 3 are decelerated by the motor drive system 1 at time t8, the drive servomotors 3 undergo regeneration, and since the total power consumption is lower than the power storage threshold from time t8 to time t9, the power storage control unit 17 controls the power storage device 14 to store DC current from the DC link 4. As a result, the holding energy of the power storage device 14 gradually increases. At time t 10 A cycle ends.

[0080] In a cycle from time t1 to time t 10 The holding energy of the power storage device 14 assumes a minimum value at time t8. The basic holding energy change unit 15 records the minimum value of the holding energy in one cycle and compares the minimum value of the holding energy with the threshold for energy deficiency detection. In the example of Fig. 6. The basic holding energy change unit 15 determines that the minimum holding energy value of the power storage device 14 at time t8 is lower than the energy deficit threshold. The basic holding energy change unit 15 calculates the "energy deficit amount" as a difference between the energy deficit threshold and the minimum holding energy value of the power storage device 14 in one cycle and sets a new basic holding energy value obtained by adding at least one value of the energy deficit amount to the current basic holding energy. Since the minimum holding energy value is below the energy deficit threshold, the basic holding energy is changed to increase it.Although the new base holding energy can be set at any time after the minimum holding energy value of the power storage device 14 is detected (time t8), it is desirable that the new base holding energy be set as early as possible. In the example of . Fig. 6 will be the new base holding energy before the start time t 10 The standby process period is set. The newly set base holding energy is greater than the previously set base holding energy by at least the energy deficit or more. From time t 10A standby process begins to recover the holding energy of the power storage device 14 up to the base holding energy. During the standby process period, DC power is stored in the power storage device 14, into which the AC power from the power source 2 is converted by the converter 11, and the holding energy of the power storage device 14 gradually increases. In a subsequent period, which includes the standby process period, the power storage device 14 performs a power storage cycle, setting the new base holding energy as the reference value (setpoint). Since the holding energy of the power storage device 14 at time t 11 When the standby process returns to the new base holding energy, the standby process is terminated and the next cycle begins at time t. 12 started.

[0081] For example, the holding energy of the power storage device 14 decreases in the cycle from time t12 until time t 20 a minimum value at time t 18 Since each cycle has the same operating pattern, each cycle typically has essentially the same total power consumption. In other words, the total power consumption in the cycle from time t 12 until time t 20 is equal to the total power consumption in the cycle from time t1 to time t 10 . At the latest from time t 11 , i.e., after the standby process period, since the power storage device 14 performs power storage with the newly set “increased base holding energy” as a reference value (setpoint), no energy shortage occurs even if in the cycle from time t 12 until time t 20 the same total power consumption as in the cycle from time t1 to time t 10is consumed. In other words, the minimum value of the holding energy of the power storage device 14 in the cycle from time t 12 until time t 20 will not fall below the threshold for determining energy deficiency. Also within the cycle of time t. 12 until time t 20The basic holding energy change unit 15 detects the minimum holding energy value and compares it to the energy deficiency threshold. Based on this comparison, the basic holding energy change unit 15 determines that the minimum holding energy value is not below the energy deficiency threshold and, consequently, the current basic holding energy remains unchanged and is maintained.If, in a subsequent cycle, the minimum holding energy value is below the energy deficit threshold by a factor, the basic holding energy change unit 15 calculates as "energy deficit amount" a difference between the energy deficit threshold and the minimum holding energy value of the power storage device 14 and sets as the new basic holding energy a value obtained by adding at least one value of the energy deficit amount or more to the basic holding energy at that time.

[0082] In conventional technology, to which the present embodiment is not applicable, because the next duty cycle of the drive servomotors begins at a time when the holding energy of the power storage device has not recovered (increased) to the base holding energy, the minimum value of the holding energy of the power storage device gradually decreases as the duty cycle of the drive servomotors is repeated. The holding energy of the power storage device eventually becomes zero, the holding energy of the power storage device becomes scarce, insufficient drive power is supplied to the drive servomotors, and a motor control system and a machine tool, including the motor control system, will inadvertently trigger an alarm stop.In contrast, according to the present embodiment, if the minimum holding energy falls below the threshold for determining the energy deficit, the base holding energy is increased by adding at least the amount of energy deficit, or more, to the current base holding energy. Since the power storage control unit 17 controls the power storage of the power storage device 14 by setting the increased base holding energy as the setpoint, and the power storage device 14 performs power storage with the new base holding energy as the reference value (setpoint), the holding energy of the power storage device 14 can be maintained at a suitable level, thus avoiding energy deficits.

[0083] A base holding energy change process through a second mode reduces the base holding energy when the holding energy of the power storage device 14 is too high.According to the second mode, the base holding energy change unit 15 compares a maximum value of the holding energy of the power storage device 14 in a predetermined period and a predefined threshold for determining excess energy. If, as a result of the comparison, the base holding energy change unit 15 determines that the maximum value of the holding energy of the power storage device 14 is higher than the threshold for determining excess energy, the base holding energy change unit 15 sets as the new base holding energy after a change a value calculated by subtracting a value equal to or greater than a difference between the maximum value of the holding energy of the power storage device 14 and the threshold for determining excess energy from the base holding energy before the change.A group of operations with the same drive servomotor details 3 is defined as "a cycle," and a single cycle is defined as the "predetermined time period" described above. Two or more cycles can be defined as a "predetermined period." The threshold for determining excess energy can, for example, be set to a value smaller than the storage capacity of the power storage device 14. Thus, for example, the threshold for determining excess energy is set to approximately 90% of the maximum storage capacity of the power storage device 14.The numerical value of the threshold for determining excess energy mentioned here is only an example, and the numerical value of the threshold for determining excess energy can be set to an optionally chosen value, for example according to the intended use of the motor drive system.

[0084] Fig. Figure 7 is a time diagram illustrating an exemplary relationship between the total power consumption and the holding energy of the power storage device when the basic holding energy change process is performed according to the second mode in the motor drive system according to the embodiment. Fig. Figure 7 shows an upper part representing the total power consumption calculated by the power consumption calculation unit 16, and a lower part representing the holding energy of the power storage device 14. An example is now assumed in which the holding energy of the power storage device 14 is stored during the time t8 to t 10 is too high when the drive servomotors 3 are accelerated and decelerated by the motor drive system 1 and the total power consumption varies, as in the upper part of Fig. Figure 7 illustrates the "acceleration, deceleration, acceleration, deceleration" of the drive servomotors 3, which is defined as one cycle. Fig. 7, for example, is the "acceleration, deceleration, acceleration, deceleration" from t1 to t 10 a cycle and the "acceleration, deceleration, acceleration, deceleration" of t 12 to t 20a cycle. Since each cycle has the same operating pattern, each cycle typically has essentially the same total power consumption. A standby process period is provided between a preceding cycle and a subsequent cycle to recover the holding energy of the power storage device 14 to its base holding energy. During the standby process period, the converter 11 converts the DC power supplied (discharged) to the DC intermediate circuit 4 from the power storage device 14 into AC power and feeds the AC power back to the power source 2, and the holding energy of the power storage device 14 gradually decreases. In the example of Fig. 7. The standby process period ends at time t. 11 , since the holding energy of the power storage device 14 returns (decreases) to the base holding energy and the next cycle begins at time t 12is started. Although the operation of the drive servomotor 3 in a cycle is defined by way of example as "acceleration, deceleration, acceleration, acceleration, deceleration", a cycle can be defined including a constant speed, a stop or the like.

[0085] Until time t1, the holding energy of the power storage device 14 is maintained at the base holding energy. During time t1 to t3, as the drive servomotors 3 are accelerated by the motor drive system 1, the total power consumption gradually increases. When the total power consumption exceeds the supply threshold at time t2, the power storage control unit 17 controls the power storage device 14 to supply DC current to the DC link 4. This gradually decreases the holding energy of the power storage device 14.

[0086] When the drive servomotors 3 are decelerated by the motor drive system 1 during time t3 to t5, the drive servomotors 3 undergo regeneration and the total power consumption becomes negative. During time t3 to t4, since the total power consumption is lower than the power storage threshold, the power storage control unit 17 controls the power storage device 14 to store DC power via the DC link 4. This gradually increases the holding energy of the power storage device 14.

[0087] When the drive servomotors 3 are accelerated again by the motor drive system 1 at time t5, the total power consumption gradually increases. If the total power consumption exceeds the supply threshold at time t6, as the power storage control unit 17 controls the power storage device 14 to supply DC power to the DC intermediate circuit 4, the holding energy of the power storage device 14 decreases further with the current base holding energy as the setpoint.

[0088] When the drive servomotors 3 are decelerated by the motor drive system 1 at time t7, the drive servomotors 3 undergo a regeneration. Since the total power consumption is lower than the power storage threshold during time t7 to t9, the power storage control unit 17 controls the power storage device 14 to store DC current from the DC link 4. This gradually increases the holding energy of the power storage device 14. At time t8, the holding energy of the power storage device 14 exceeds the threshold for determining excess energy.

[0089] If the drive servomotors 3 are at time t 10When the motor drive system 1 is stopped and one cycle ends, the total power consumption becomes zero. Since the drive servomotors 3 do not perform regeneration, the holding energy of the power storage device 14 decreases. At time t 10 A cycle ends.

[0090] In a cycle from time t1 to time t 10 The holding energy of the power storage device 14 reaches a maximum value at time t9. The basic holding energy change unit 15 records the maximum holding energy value in one cycle and compares it to the threshold for determining excess energy. In the example of Fig. 7. The baseline holding energy change unit 15 determines that the maximum holding energy of the power storage device 14 at time t9 is higher than the threshold for determining excess energy. The baseline holding energy change unit 15 calculates the "excess energy" as the difference between the maximum holding energy of the power storage device 14 in one cycle and the threshold for determining excess energy, and sets a new baseline holding energy value obtained by subtracting at least one value of the excess energy from the current baseline holding energy. Since the maximum holding energy becomes higher than the threshold for determining excess energy, the baseline holding energy is changed so that it decreases.Although the new base holding energy can be set at any time after the maximum holding energy value of the power storage device 14 is detected (time t9), it is desirable that the new base holding energy be set as early as possible. In the example of . Fig. 7 will be the new base holding energy after the start time t 10 The standby process period is set. The newly set base holding energy is at least the excess energy amount or more lower than the previously set base holding energy. From time t 10A standby process begins to recover (reduce) the holding energy of the power storage device 14 to the base holding energy. During the standby process period, the converter 11 converts DC power, which is supplied (discharged) from the power storage device 14 to the DC intermediate circuit 4, into AC power and feeds the AC power back to the power source 2, and the holding energy of the power storage device 14 gradually decreases. In a subsequent period, which includes the standby process period, the power storage device 14 performs a power storage operation, setting the new base holding energy as the reference value (setpoint). Since the holding energy of the power storage device 14 at time t 11 When the base holding energy returns to (decreases) the previous level, the standby process is terminated and the next cycle begins at time t. 12 started.

[0091] For example, in the cycle from time t 12 until time t 20 The holding energy of the power storage device 14 reaches a maximum value at time t 20 Since each cycle has the same operating pattern, each cycle typically has essentially the same total power consumption. In other words, the total power consumption in the cycle from time t 12 until time t 20 is equal to the total power consumption in the cycle from time t1 to time t 10 . At the latest from time t 11 , i.e., after the standby process period, since the power storage device 14 performs power storage with the newly set “reduced base holding energy” as a reference value (setpoint), no energy surplus occurs even if in the cycle from time t 12 until time t 20 the same total power consumption as in the cycle from time t1 to time t 10is consumed. In other words, the maximum value of the holding energy of the power storage device 14 in the cycle from time t 12 until time t 20 will not exceed the threshold for determining excess energy. Also within the cycle of time t. 12 until time t 20The basic holding energy change unit 15 detects the maximum holding energy value in this cycle and compares it to the threshold for determining excess energy. As a result of this comparison, the basic holding energy change unit 15 determines that the maximum holding energy value is not higher than the threshold for determining excess energy, and therefore the current basic holding energy is not changed and is maintained.If, in a subsequent cycle, the maximum holding energy value exceeds the threshold for determining excess energy by a factor, the basic holding energy change unit 15 calculates as "excess energy" a difference between the maximum holding energy value of the power storage device 14 and the threshold for determining excess energy and sets as the new basic holding energy a value obtained by subtracting at least one value of excess energy or more from the current basic holding energy.

[0092] In conventional technology, to which the present embodiment is not applicable, since the next duty cycle of the drive servomotors begins at a point in time when the holding energy of the power storage device has not yet recovered (decreased) to the base holding energy, the maximum value of the holding energy of the power storage device gradually increases as the duty cycle of the drive servomotors is repeated. This increases the load on the power storage device, and eventually the power storage device is destroyed. In contrast, according to the present embodiment, if the maximum value of the holding energy becomes higher than the threshold for determining excess energy, the base holding energy is reduced by subtracting at least the excess energy, or more, from the current base holding energy.Since the power storage control unit 17 controls the power storage of the power storage device 14 for the next cycle by setting the reduced base holding energy as the setpoint, and the power storage device 14 performs the power storage so that the holding energy returns to the new base holding energy, the holding energy of the power storage device 14 can be maintained to a reasonable extent and excess energy can be avoided.

[0093] A base holding energy change process by a third mode reduces the base holding energy when the holding energy of the power storage device 14 has an allowance.According to the third mode, the base holding energy change unit 15 compares a minimum value of the holding energy of the power storage device 14 in a predetermined period and a predefined threshold for energy allowance determination, and if, as a result of the comparison, the base holding energy change unit 15 determines that the minimum value of the holding energy of the power storage device 14 is higher than the threshold for energy allowance determination, the base holding energy change unit 15 sets as the new base holding energy after a change a value calculated by subtracting a value equal to or less than a difference between the minimum value of the holding energy of the power storage device 14 and the threshold for energy allowance determination from the base holding energy before the change.A group of operations with the same drive servomotor details 3 is defined as "a cycle," and a single cycle is defined as the "predetermined time period" described above. Two or more cycles can be defined as a "predetermined period." The energy allowance threshold can be set to a value greater than zero, but must be set to a value greater than the energy shortfall threshold. For example, the energy allowance threshold is set to approximately 20% of the maximum storage capacity of the power storage device 14. The numerical value given here for the energy allowance threshold is only an example, and the energy allowance threshold can be set to an optionally chosen value, e.g.,However, depending on the intended use for which the motor drive system is applied, it must be set to a value greater than the numerical value (e.g. 10%) that is set for the threshold for determining energy deficiency.

[0094] Fig. Figure 8 is a time diagram illustrating an exemplary relationship between the total power consumption and the holding energy of the power storage device when the basic holding energy change process is performed according to the third mode in the motor drive system according to the embodiment. Fig. Figure 8 shows an upper part representing the total power consumption calculated by the power consumption calculation unit 16, and a lower part representing the holding energy of the power storage device 14. An example is now assumed in which the holding energy of the power storage device 14 reaches a minimum value at time t7 when the drive servomotors 3 are accelerated and decelerated by the motor drive system 1, and the total power consumption varies as shown in the upper part of Figure 8. Fig. Figure 8 illustrates the "acceleration, deceleration, acceleration, deceleration" of the drive servomotors 3, which is defined as one cycle. Fig. For example, 8 is the “acceleration, deceleration, acceleration, deceleration” from t1 to t9 one cycle and the “acceleration, deceleration, acceleration, deceleration” from t 11 to t 19a cycle. Since each cycle has the same operating pattern, each cycle typically has essentially the same total power consumption. A standby process period is provided between a preceding cycle and a subsequent cycle to recover the holding energy of the power storage device 14 to its base holding energy. During the standby process period, DC power is stored in the power storage device 14, into which the AC power from the power source 2 is converted by the converter 11, and the holding energy of the power storage device 14 gradually increases. In the example of Fig. 8. The standby process period ends at time t. 10 , since the holding energy of the power storage device 14 returns to the base holding energy and the next cycle begins at time t 11is started. Although the operation of the drive servomotor 3 in a cycle is defined by way of example as "acceleration, deceleration, acceleration, deceleration", a cycle can be defined including a constant speed, a stop or the like.

[0095] Until time t1, the holding energy of the power storage device 14 is maintained at the base holding energy. During time t1 to t3, as the drive servomotors 3 are accelerated by the motor drive system 1, the total power consumption gradually increases. When the total power consumption exceeds the supply threshold at time t2, the power storage control unit 17 controls the power storage device 14 to supply DC current to the DC link 4. This gradually decreases the holding energy of the power storage device 14.

[0096] When the drive servomotors 3 are decelerated by the motor drive system 1 during time t3 to t5, the drive servomotors 3 undergo regeneration and the total power consumption becomes negative. During time t3 to t4, since the total power consumption is lower than the power storage threshold, the power storage control unit 17 controls the power storage device 14 to store the DC power from the DC link 4. This gradually increases the holding energy of the power storage device 14.

[0097] When the drive servomotors 3 are accelerated again by the motor drive system 1 between time t5 and time t7, the total power consumption gradually increases. Since direct current, which is converted into alternating current from the power source 2 by the converter 11, is also stored in the power storage device 14 between time t4 and t6, the holding energy of the power storage device 14 gradually increases. When the total power consumption exceeds the supply threshold at time t6, the power storage control unit 17 controls the power storage device 14 to supply direct current to the DC link 4, and as a result, the holding energy of the power storage device 14 gradually decreases.

[0098] When the deceleration of the drive servomotors 3 by the motor drive system 1 is initiated at time t7, the drive servomotors 3 undergo a regeneration cycle. Since the total power consumption is lower than the power storage threshold during time t7 to t8, the power storage control unit 17 controls the power storage device 14 to store the DC power from the DC link 4. This gradually increases the holding energy of the power storage device 14. A cycle ends at time t9.

[0099] In a cycle from time t1 to time t9, the holding energy of the power storage device 14 reaches a minimum value at time t7. The basic holding energy change unit 15 detects the minimum holding energy value in a cycle and compares it to the energy allowance threshold. The basic holding energy change unit 15 determines that the minimum holding energy value of the power storage device 14 is higher than the energy allowance threshold. The basic holding energy change unit 15 calculates the difference between the minimum holding energy value of the power storage device 14 in a cycle and the energy allowance threshold as the "energy allowance amount" and sets the new basic holding energy value by subtracting at least one value of the energy allowance amount from the current basic holding energy.Since the minimum holding energy value has not fallen below the threshold for determining the energy allowance, the base holding energy is adjusted to decrease. Although the new base holding energy can be set at any time after (time t7) the minimum holding energy value of the power storage device 14 is detected, it is desirable to set the new base holding energy as early as possible. In the example of . Fig. 8. The new base holding energy is set before the start time t9 of the standby process period. The newly set base holding energy is at least the energy allowance amount or more lower than the previously set base holding energy. From time t9, a standby process begins to recover the holding energy of the power storage device 14 into the base holding energy. During the standby process period, DC power is stored in the power storage device 14, into which the AC power from the power source 2 is converted by the converter 11, and the holding energy of the power storage device 14 gradually increases. In a subsequent period, which includes the standby process period, the power storage device 14 performs power storage, setting the new base holding energy as the reference value (setpoint). Since the holding energy of the power storage device 14 at time t 10When the new base holding energy is restored, the standby process is terminated and the next cycle begins at time t. 11 started.

[0100] For example, the holding energy of the power storage device 14 decreases in the cycle from time t 11 until time t 19 a minimum value at time t 17 Since each cycle has the same operating pattern, each cycle typically has essentially the same total power consumption. In other words, the total power consumption in the cycle from time t 11 until time t 19is equal to the total power consumption in the cycle from time t1 to time t9. At the latest from time t9, i.e. after the standby process period, since the power storage device 14 performs power storage with the newly set "reduced base holding energy" as the reference value (setpoint), the power storage device 14 performs power storage so that the holding energy returns to the new base holding energy and thus the load on the power storage device 14 is reduced and the holding energy of the power storage device 14 can be maintained to a reasonable extent.To prevent the occurrence of energy shortage in the next cycle by performing the baseline energy change process according to the third mode, the energy allowance threshold used in the baseline energy change process according to the third mode must be set to a value higher than the energy shortage detection threshold used in the baseline energy change process according to the first mode.

[0101] The basic holding energy change processes according to the above first mode, second mode and third mode can be carried out independently as a basic holding energy change process in the motor drive system 1 according to the present embodiment or carried out in combination.

[0102] Next, the functionality of the motor drive system 1 will be described. Fig. Figure 9 is a flowchart illustrating the operational sequence of the motor drive system according to the embodiment. An example is described in which the basic holding energy change processes of the first and second modes are executed. The drive motor control unit 13 controls the drive servomotors 3 so that they operate according to a predetermined operating pattern (S101). During this time, the power storage control unit 17, using the calculation result of the power consumption calculation unit 16, controls the power storage and supply of the power storage device 14.

[0103] In step S102, the basic holding energy change unit 15 calculates the holding energy of the power storage device 14. As described above, the calculation process for the holding energy of the power storage device 14 can be performed by the power storage control unit 17 or the separately supplied calculation unit.

[0104] In step S103, the basic holding energy change unit 15 compares the minimum holding energy value of the power storage device 14 within the specified time interval and the predefined energy shortage threshold to determine whether the minimum holding energy value is lower than the energy shortage threshold. If the minimum holding energy is found to be lower than the energy shortage threshold, the process proceeds to step S104. If the minimum holding energy is found to be higher than the energy shortage threshold, the process continues to step S105.

[0105] In step S104, the base holding energy change unit 15 sets a new base holding energy value obtained by adding at least one value equal to or greater than the difference between the energy deficit threshold and the minimum holding energy value of the power storage device 14 to the base holding energy. The process then returns to step S101.

[0106] In step S105, the basic holding energy change unit 15 compares the maximum holding energy value of the power storage device 14 within the specified time period and the predefined threshold for determining peak energy, and determines whether the maximum holding energy value of the power storage device 14 is higher than the threshold for determining excess energy. As a result of the comparison, if it is determined that the maximum holding energy value is higher than the threshold for determining excess energy, the operation proceeds to step S106. If it is determined that the maximum holding energy value is not higher than the threshold for determining excess energy, the operating sequence returns to step S101.

[0107] In step S106, the base holding energy change unit 15 sets a new base holding energy value calculated by subtracting from the base holding energy a value equal to or greater than the difference between the maximum holding energy value of the power storage device 14 and the threshold for determining excess energy. The work sequence then returns to step S101.

[0108] Although the diagram is omitted, the basic holding energy change unit 15 determines whether a predetermined time has elapsed before the execution of step S103, and if the predetermined time has elapsed, the operation sequence proceeds to step S103. The basic holding energy change process of steps S103 and S104 by the first mode and the basic holding energy change process of steps S105 and S106 by the second mode can be executed in reverse order. In this case, the basic holding energy change unit 15 determines whether a predetermined time has elapsed before the execution of step S105, and if the predetermined time has elapsed, the operation sequence proceeds to step S105. Furthermore, the process of steps S103 and S105 can be executed before steps S104 and S106.

[0109] Fig. Figure 10 is a flowchart illustrating an alternative operating sequence of the motor drive system according to the embodiment. Fig. 10. The basic holding energy change process will be carried out according to the third mode in which, with reference to Fig. The example described in section 9 is further elaborated upon, in which the basic holding energy change processes are carried out according to the first mode and the second mode. Fig. 10 is the process of steps S101 to S106 as with reference to Fig. 9 described.

[0110] In step S107, the basic holding energy change unit 15 determines whether a predetermined time has elapsed or not. After the predetermined time has expired, the operating sequence continues with step S108.

[0111] In step S108, the basic holding energy change unit 15 compares the minimum holding energy value of the power storage device 14 within the specified time period and the predefined energy allowance threshold to determine whether the minimum holding energy value of the power storage device 14 is higher than the energy allowance threshold. As a result of the comparison, if the basic holding energy change unit 15 determines that the minimum holding energy value is higher than the energy allowance threshold, the operating sequence proceeds to step S109. If the basic holding energy change unit 15 does not determine that the minimum holding energy value is higher than the energy allowance threshold, the operating sequence returns to step S101.

[0112] In step S108, the basic holding energy change unit 15 calculates a new basic holding energy from the basic holding energy, which is equal to or less than the difference between the minimum value of the holding energy of the power storage device 14 and the threshold for determining the energy allowance.

[0113] The basic holding energy change process of steps S103 and S104 by the first mode, the basic holding energy change process of steps S105 and S106 by the second mode, and the basic holding energy change process of steps S107 and S108 by the third mode can be performed in a modified order.

[0114] The basic holding energy change processes according to the first mode and the second mode were compared with reference to Fig. 9 and the basic holding energy change processes according to the first mode, the second mode and the third mode with reference to Fig.As described in section 10, but as described above, the basic holding energy change processes according to the first mode, the second mode, and the third mode can be executed independently of one another as a basic holding energy change process in the motor drive system 1 according to the present embodiment. Furthermore, the basic holding energy change processes according to the first mode and the third mode can be executed in combination, or the basic holding energy change processes according to the second mode and the third mode can be executed in combination.

[0115] The drive motor control unit 13, the basic holding energy change unit 15, the power consumption calculation unit 16, and the power storage control unit 17 described above can, for example, consist of a single software program or a combination of various electronic circuits and software programs. In this case, for example, an arithmetic processing device, such as a CPU or an MPUDSP, can be used to execute the software programs in order to implement the functions of the respective components.Alternatively, the drive motor control unit 13, basic holding energy change unit 15, power consumption calculation unit 16 and power storage control unit 17 can be implemented by an integrated semiconductor circuit in which software programs for implementing the functions of the drive motor control unit 13, basic holding energy change unit 15, power consumption calculation unit 16 and power storage control unit 17 are stored.

[0116] The drive motor control unit 13, the base mounting energy conversion unit 15, the power consumption calculation unit 16, and the power storage control unit 17 are, for example, provided in a main control device (not shown) in the motor drive system 1. If, for example, the motor drive system 1 is configured to control the drive of the drive servomotors 3 in a machine tool, the drive motor control unit 13, the base mounting energy conversion unit 15, the power consumption calculation unit 16, and the power storage control unit 17 can be provided in a numerical control device in the machine tool.If the drive motor control unit 13, the basic holding energy change unit 15, the power consumption calculation unit 16 and the power storage control unit 17 are formed in the form of a software program, an arithmetic processing unit in the numerical control device can be caused to execute the software program, and thereby the functions of the respective components can be realized.

[0117] According to the embodiment of the present disclosure, in the motor drive system with the power storage device, which is provided to reduce the power peak of the energy source equipment, the energy stored in the power storage device can be kept in the correct amount.

Claims

Motor drive system (1), comprising: a converter (11) configured to convert power between AC power in a power source (2) and DC power in a DC link (4); a drive inverter (12) configured to convert power between the DC power in the DC link (4) and the AC power serving as drive power or regenerative power for a drive servo motor (3); a drive motor control unit (13) configured to control the drive servo motor (3) connected to the drive inverter (12); a power storage device (14) configured to store DC power from the DC link (4) or to supply DC power to the DC link (4);and a basic holding energy change unit (15) configured to change a basic holding energy, defined as a reference value of a holding energy of the power storage device (14), in accordance with the holding energy of the power storage device (14);i) wherein the basic holding energy change unit (15) is configured to compare a minimum holding energy value of the power storage device (14) in a predetermined period and a predefined energy shortage threshold, and if, as a result of the comparison, the basic holding energy change unit (15) determines that the minimum holding energy value of the power storage device (14) is lower than the energy shortage threshold, the basic holding energy change unit (15) is configured to set as the new basic holding energy a value calculated by adding to the basic holding energy a value equal to or greater than a difference between the energy shortage threshold and the minimum holding energy value of the power storage device (14);orii) wherein the basic holding energy change unit (15) is configured to compare a maximum holding energy value of the power storage device (14) in a predetermined period and a predefined excess energy threshold, and if, as a result of the comparison, the basic holding energy change unit (15) determines that the maximum holding energy value of the power storage device (14) is higher than the excess energy threshold, the basic holding energy change unit (15) is configured to set as the new basic holding energy a value calculated by subtracting from the basic holding energy a value equal to or greater than a difference between the maximum holding energy value of the power storage device (14) and the excess energy threshold;oriii) wherein the basic holding energy change unit (15) compares a minimum holding energy value of the power storage device (14) over a predetermined period and a predefined energy allowance threshold, and if, as a result of the comparison, the basic holding energy change unit (15) determines that the minimum holding energy value of the power storage device (14) is higher than the energy allowance threshold, the basic holding energy change unit (15) is configured to set as the new basic holding energy a value calculated by subtracting from the basic holding energy a value equal to or less than a difference between the minimum holding energy value of the power storage device (14) and the energy allowance threshold. The motor drive system (1) according to claim 1, further comprising: a power consumption calculation unit (16) configured to calculate a total power consumption calculated as the sum of a power of the drive servomotor (3), a winding loss in the drive servomotor (3), a loss in the converter (11) and a loss in the drive inverter (12);and a power storage control unit (17) configured to compare the total power consumption and a supply threshold that is predefined, and a power storage threshold that is predefined, configured to control the power storage device (14) to supply DC current to the DC intermediate circuit (4) when the power storage control unit (17) determines, as a result of the comparison, that the total power consumption is higher than the supply threshold, and configured to control the power storage device (14) to store DC current from the DC intermediate circuit (4) when the power storage control unit (17) determines that the total power consumption is lower than the power storage threshold, so that the holding energy of the power storage device (14) is restored to the base holding energy. Motor drive system (1) according to claim 1 or 2, wherein the power storage device (14) comprises: a flywheel (41) configured to store rotational energy; a buffer servomotor (42) comprising a rotary axis coupled to the flywheel (41); and a buffer inverter (43) configured to convert power between the DC power in the DC intermediate circuit (4) and the AC power serving as drive power or regenerative power for the buffer servomotor (42). Motor drive system (1) according to claim 1 or 2, wherein the power storage device (14) comprises: a capacitor (44); and a DC / DC converter (45) configured to convert the power between the DC power in the DC intermediate circuit (4) and the DC power stored in the capacitor (44).

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