Inverter control device and control method

Abstract

To set a count value of an overload accumulation counter when an inverter is restarted to a correct count value reflecting the amount of decrease in the count during a power-off period.SOLUTION: When inverter power is shut down, a motor frequency value (or rotation value) and an overload cumulative counter value are recorded in an EEPROM (Step S10), when the power is restored and picked up, the frequency value of a motor is obtained (Step S21), the difference between the obtained frequency value of the motor and the frequency value recorded in the EEPROM is divided by a preset reduction coefficient to estimate an elapsed time from the power shutdown to the power restoration (Step S22), a count decrement of an overload accumulation counter that has decreased within the elapsed time is calculated (Step S23), and a value obtained by subtracting the count value of the overload accumulation counter from the count decrease amount is set as the count value of the overload accumulation counter at the time of picking up the power recovery (Steps S24 to S27).SELECTED DRAWING: Figure 2

Description

[Technical field]

[0001] The present invention relates to a method for determining an abnormality in an overload operation of a motor in an industrial inverter. [Background technology]

[0002] In inverter equipment that performs operation and stopping operations by combining an inverter and a motor, abnormality determination for overload operation has been performed, for example, based on the count value (accumulated load value) of an accumulated overload counter prepared inside the inverter control mechanism.

[0003] FIG. 7 shows an example of the motor speed, transition of the current value, behavior of the overload accumulation counter, etc. when an abnormality is determined during motor overload operation.

[0004] In Figure 7, (a) shows the motor speed, (b) shows the “operating status” signal, the sequence output of the inverter control device, (c) shows the motor current value, (d) shows the “abnormal output” signal, the sequence output of the inverter control device, (e) shows the count value of the overload accumulation counter, and (f) shows the “reset operation” signal, the sequence input of the inverter control device.

[0005] When the motor is operated by the inverter, if the motor current value (Figure 7(c)) exceeds the motor overload occurrence reference value defined in the inverter, as shown at time t1, the overload accumulation counter adds a fixed number per hour as the load accumulation value, and if the motor current value continues to be overloaded relative to the reference value, the count value of the overload accumulation counter (Figure 7(e)) increases from time t1 to t2.

[0006] When the motor current value changes (load reduction or stop) and falls below the motor overload occurrence reference value, the cumulative overload count value is decreased. When the decreased count value of the cumulative overload counter falls below 0, it is limited to 0.

[0007] Next, as at time t2, when the count value of the overload cumulative counter exceeds a predetermined overload abnormality judgment level (for example, 100, ranging from 0 to 100), it is deemed to be an abnormality, and an alarm or abnormality output signal is issued to notify the abnormality, and the motor is stopped.

[0008] That is, at time t2, the sequence output “abnormal output” signal goes to high level, the sequence output “operating status” signal goes to low level, the motor current value becomes 0 between times t2 and t3, the motor speed gradually decreases, and the count value of the overload accumulation counter decreases after time t3.

[0009] Next, at time t4, when the sequence input "reset operation" signal (FIG. 7(f)) is input, the sequence output "abnormal output" signal in FIG. 7(d) goes to low level.

[0010] Incidentally, a conventional method for protecting an inverter from overload has been proposed, for example, as described in Patent Document 1. In Patent Document 1, the counter counts up during overload operation, stops counting during normal operation, and counts down under conditions where the semiconductor temperature drops, thereby storing the relationship between overload operation and semiconductor temperature, and stops operation when the counter exceeds a certain value, thereby protecting the inverter from failure.

[0011] As a method for detecting an overload state of a motor, for example, Patent Document 2 has been proposed, in which a timer is operated during the conduction time to monitor the load state of the motor. [Prior art documents] [Patent documents]

[0012] [Patent Document 1] JP 2005-39882 A [Patent Document 2] JP 2004-23802 A Summary of the Invention [Problem to be solved by the invention]

[0013] Fig. 8 shows the counting operation when the inverter is stopped and restarted in a control device that judges abnormalities based on the count value of an overload accumulation counter in response to an overload operation of a motor.

[0014] In Figure 8, (a) shows the motor speed, (b) shows the “operating status” signal, which is the sequence output of the inverter control device, (c) shows the motor current value, (d) shows the “abnormal output” signal, which is the sequence output of the inverter control device, (e) shows the count value of the overload accumulation counter, and (f) shows the inverter power supply status (on, off) signal.

[0015] In FIG. 8, in the period before time t1 is reached, the sequence output “operating status” signal (FIG. 8(b)) and the inverter power supply status signal (FIG. 8(f)) are both at high level, and the motor current value has already exceeded the motor overload occurrence reference value (FIG. 8(c)), but the count value of the overload accumulation counter is increasing below the overload abnormality judgment level.

[0016] Next, at time t1, when the count value of the overload accumulation counter exceeds the overload abnormality judgment level, the sequence output "abnormality output" signal goes to high level, the sequence output "operating status" signal goes to low level, the motor current value becomes 0 between times t1 and t2, the motor speed gradually decreases, and the count value of the overload accumulation counter decreases after time t2.

[0017] Next, if the inverter power supply is cut off (or a CPU reset operation, etc. occurs) at time t3 when the count value of the overload cumulative counter is other than 0, the inverter power supply status signal and the sequence output “abnormal output” signal both go to low level.

[0018] Furthermore, if the count value of the overload accumulation counter is stored in a volatile storage device (recording device) such as RAM inside the inverter control mechanism, the count value will be erased (a value other than 0 will become 0, as shown in Figure 8(e)).

[0019] Next, at time t4, when the power supply to the inverter is restored, the inverter power supply status signal goes to high level, and immediately thereafter at time t5, the sequence output “operating status” signal goes to high level, the motor current value begins to increase, and the motor speed gradually increases.

[0020] Next, when the motor current value exceeds the motor overload occurrence reference value at time t6, the overload accumulation counter starts counting up from the count value 0 as shown in FIG. 8(e) regardless of the actual state of the motor.

[0021] For this reason, the load state becomes different from the actual state of the motor, and even if the motor itself is in a state where it should be considered abnormal, the inverter judges that this has not yet occurred, and the abnormal output is delayed, which raises concerns that the motor may be damaged.To solve this problem, we would like to propose an improvement such as the operation shown in Figure 9.

[0022] That is, the amount of count decrement in the overload accumulation counter during the inverter power supply cut-off period shown at times t3 to t4 in Figure 9 is compensated for as shown by the dashed line in Figure 9(e) and reflected in the count value when the inverter power supply is restored.

[0023] In FIG. 9, the operations other than the overload accumulation counter in (e) are the same as those in FIG.

[0024] In addition, in the technologies of Patent Documents 1 and 2, if a power outage occurs while a counter or timer is operating, the measurement means cannot measure time. In a state where measurement is not possible, no current is passed through the inverter or motor, so the temperatures of the semiconductors and motor drop, but there is no way to correct this.

[0025] For this reason, if operation is continued after power is restored, the relationship between the counter or timer and the semiconductor temperature is lost, and the inverter cannot continue to operate to its maximum extent even in an overload state.

[0026] In view of the above problems, the present invention aims to improve the operation of the load accumulation amount during overload operation of a motor in an industrial inverter and to comply with current standards. It is an object of the present invention to provide an inverter control device and control method that can set the count value of an overload accumulation counter when the inverter is restarted to a correct count value that reflects the amount of count decrement during a power supply cut-off period. [Means for solving the problem]

[0027] In order to solve the above problems of The inverter control device is A control device for an inverter that drives a motor, an overload accumulation counter that increases a count value when a current value of the motor exceeds a preset reference value during operation of the inverter, and decreases the count value when the current value of the motor is equal to or less than the preset reference value; a non-volatile memory for recording an elapsed time acquisition parameter for acquiring an elapsed time from when the inverter is powered off to when the inverter is restarted; an elapsed time acquisition unit that determines an elapsed time from when the inverter is powered off to when the inverter is restarted, based on an elapsed time acquisition parameter recorded in the nonvolatile memory when the inverter is powered off and an elapsed time acquisition parameter acquired when the inverter is restarted after the power is cut off; a count decrement calculation unit that calculates a count decrement of the overload cumulative counter within the elapsed time calculated by the elapsed time acquisition unit; and a count value setting unit that determines and sets a count value of the overload accumulation counter at the time of restarting the inverter from the count decrement determined by the count decrement calculation unit.

[0028] In one preferred embodiment, the elapsed time acquisition parameters include a drive frequency or a rotation speed of the motor and a count value of the overload accumulation counter, The elapsed time acquisition unit is characterized in that it calculates the elapsed time by dividing the difference between the motor drive frequency or rotation speed at the time when the inverter is powered off, which is recorded in the non-volatile memory, and the motor drive frequency or rotation speed acquired at the time of restart after the power is cut off, by a set frequency or rotation speed reduction coefficient.

[0029] In one preferred embodiment, The inverter is provided with a clock function capable of continuing counting even if a main power supply is cut off. the elapsed time acquisition parameters include a clock count value counted by a clock function inside the inverter and a count value of the overload accumulation counter, The elapsed time acquisition unit is characterized in that it calculates the elapsed time from the difference between the clock count value recorded in the non-volatile memory at the time when power is cut off from the inverter and the clock count value acquired when the inverter is restarted after the power is cut off.

[0030] In one preferred embodiment, the elapsed time acquisition parameters include a heat sink temperature inside the inverter obtained by measurement or estimation and a count value of the overload accumulation counter, The elapsed time acquisition unit is characterized in that it obtains the elapsed time by dividing the difference between the heat sink temperature inside the inverter when the inverter is powered off, which is recorded in the non-volatile memory, and the heat sink temperature inside the inverter acquired when the inverter is restarted after the power is cut off, by a set temperature reduction coefficient.

[0031] In order to solve the above problems The inverter control method is as follows: an overload accumulation counter that, when an inverter that drives a motor is in operation, increases a count value when a current value of the motor exceeds a preset reference value, and decreases the count value when the current value is equal to or less than the preset reference value; A non-volatile memory in which an elapsed time acquisition parameter for acquiring an elapsed time from when the power supply of the inverter is cut off to when the inverter is restarted is recorded, a step of recording an elapsed time acquisition parameter in the non-volatile memory when the inverter is powered off; acquiring a parameter for acquiring an elapsed time when the inverter is restarted after the power supply is cut off; an elapsed time acquisition step of determining an elapsed time from when the inverter is powered off to when the inverter is restarted, based on an elapsed time acquisition parameter recorded in the nonvolatile memory when the inverter is powered off and an elapsed time acquisition parameter acquired when the inverter is restarted after the power is cut off; a count decrement calculation step for calculating a count decrement of the overload cumulative counter that has decreased within the elapsed time calculated in the elapsed time acquisition step; and a count value setting step of determining and setting a count value of the overload accumulation counter at the time of restarting the inverter from the count decrement determined in the count decrement calculation step.

[0032] In one preferred embodiment, the elapsed time acquisition parameters include a drive frequency or a rotation speed of the motor and a count value of the overload accumulation counter, The elapsed time acquisition step includes a step of obtaining the elapsed time by dividing a difference between the motor drive frequency or rotation speed at the time of power-off of the inverter, which is recorded in the non-volatile memory, and the motor drive frequency or rotation speed acquired at the time of restart after the power-off, by a set frequency or rotation speed reduction coefficient.

[0033] In one preferred embodiment, The inverter is provided with a clock function capable of continuing counting even if a main power supply is cut off. the elapsed time acquisition parameters include a clock count value counted by a clock function inside the inverter and a count value of the overload accumulation counter, The elapsed time acquisition step includes a step of calculating the elapsed time from the difference between a clock count value recorded in the non-volatile memory at the time when the inverter is powered off and a clock count value acquired when the inverter is restarted after the power is powered off.

[0034] In one preferred embodiment, the elapsed time acquisition parameters include a heat sink temperature inside the inverter obtained by measurement or estimation and a count value of the overload accumulation counter, The elapsed time acquisition step includes a step of obtaining the elapsed time by dividing the difference between the heat sink temperature inside the inverter when the inverter is powered off, which is recorded in the non-volatile memory, and the heat sink temperature inside the inverter acquired when the inverter is restarted after the power is cut off, by a set temperature reduction coefficient. Effect of the Invention

[0035] the above According to the present invention, the count value of the cumulative overload counter when the inverter is restarted can be set to a correct count value that reflects the amount of count decrement during the power supply cutoff period, so that the actual motor overload state can be maintained and the overload function can operate in accordance with the actual operation. [Brief description of the drawings]

[0036] [Figure 1] 3 is a time chart of the operation according to the first embodiment of the present invention. [Diagram 2] 3 is a flowchart of an operation according to the first embodiment of the present invention. [Diagram 3] 5 is a time chart of the operation according to the second embodiment of the present invention. [Figure 4] 11 is a flowchart of an operation according to a second embodiment of the present invention. [Diagram 5] 11 is a time chart of an operation according to a third embodiment of the present invention. [Figure 6] 11 is a flowchart of an operation according to a third embodiment of the present invention. [Figure 7]4 is a time chart of a conventional motor overload operation. [Figure 8] 4 is a time chart showing a conventional counting operation when an inverter is stopped and restarted. [Figure 9] 4 is a time chart of an operation plan that the present invention aims to improve. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0037] Hereinafter, the embodiments of the present invention will be described with reference to the drawings, but the present invention is not limited to the following embodiment. In this embodiment, a control device for an inverter that drives a motor includes a non-volatile memory that records elapsed time acquisition parameters for acquiring the elapsed time from when the inverter is powered off to when it is restarted, such as the count value of an overload accumulation counter, the driving frequency or rotation speed of the motor, the clock count value counted by a clock function inside the inverter, and the heat sink temperature inside the inverter obtained by measurement or estimation calculation, an elapsed time acquisition unit that acquires the elapsed time from when the inverter is powered off to when it is restarted based on the elapsed time acquisition parameters recorded in the non-volatile memory when the inverter is powered off and the elapsed time acquisition parameters acquired when the inverter is restarted after the power off, a count decrement calculation unit that acquires the amount of count decrement of the overload accumulation counter that has decreased within the elapsed time acquired by the elapsed time acquisition unit, and a count value setting unit that acquires and sets the count value of the overload accumulation counter at the time of restarting the inverter from the count decrement acquired by the count decrement calculation unit. EXAMPLES

[0038] In this embodiment 1, the count value of the overload cumulative counter and the drive frequency or rotation speed of the motor are used as parameters for acquiring the elapsed time, and if the cut-off time of the inverter power supply is relatively short and the motor is still rotating at the time of restart, the elapsed time is estimated from the difference in the picked-up frequency or rotation speed (frequency / rotation speed), and the amount of count reduction of the overload cumulative counter is estimated from that and expanded to the count amount recorded before cut-off.

[0039] FIG. 1 is a time chart of the compensation operation by picking up in the first embodiment, and FIG. 2 is an operation flowchart of the process performed by the control device of the inverter in the first embodiment.

[0040] FIG. 2(a) is a flow chart for when the inverter is powered off. In step S10, the motor drive frequency or rotation speed at the time of power off and the count value of the overload accumulation counter are stored (recorded) in a non-volatile memory, EEPROM, or the like.

[0041] FIG. 2(b) is a flowchart for picking up the recovery of the inverter power supply. In step S21, the motor drive frequency or rotation speed is acquired by the picking operation. In step S22, the difference between the motor drive frequency or rotation speed at the time of power interruption recorded in the non-volatile memory in step S10 and the motor drive frequency or rotation speed acquired when the motor is restarted after the power interruption is divided by a preset frequency or rotation speed reduction coefficient to estimate the elapsed time from the power interruption to the restart.

[0042] Next, in step S23, the amount of count decrement of the overload accumulation counter is calculated from the estimated elapsed time, and in step S24, the calculated amount of count decrement is subtracted from the count value of the overload accumulation counter.

[0043] Then, in step S25, it is determined whether the count value resulting from the subtraction is below 0. If it is below 0, the count value is limited to 0 in step S26, and then in step S27, it is expanded to the count value of the overload accumulation counter at the time of restarting the inverter (at the time of recovery pick-up) (expanded as the current count value).

[0044] Here, an example of a method for setting the reduction coefficient of the frequency or rotation speed used in the elapsed time estimation calculation in step S22 will be described. Here, it is assumed that an opportunity is provided for free-run stop operation in the event of a fault during test operation such as pre-adjustment operation or automatic adjustment operation (auto-tuning operation). In this measurement, the reduction amount from the motor frequency / rotation speed after a certain time has elapsed from the start of measurement (for example, after 10 seconds or 1 minute) is measured using an encoder or the like, and a coefficient value (reduction coefficient) is calculated based on the calculation formula in <Example 1> below and recorded.

[0045] This coefficient value (reduction coefficient) is obtained during test operations such as pre-adjustment operation and automatic adjustment operation (auto-tuning operation), and can also be set by manually inputting parameters. This coefficient value (reduction coefficient) is protected by recording it in EEPROM, and is retained even when the power is shut off.

[0046] <Example 1> Let's say that during a test run or similar, the device is operating at 50Hz, then goes into free-running mode and after 10 seconds has reduced to 25Hz. The coefficient value (reduction coefficient) is considered to be (measurement start value - value after time has elapsed) / time, and in this example, the coefficient is (50-25) / 10=2.5. This 2.5 is stored in the EEPROM.

[0047] Next, we will explain the details of the compensation operation by picking up in this embodiment 1. In Fig. 1, (a) shows the motor speed, (b) shows the sequence output "operating state" signal of the inverter control device, (c) shows the motor current value, (d) shows the sequence output "abnormal output" signal of the inverter control device, (e) shows the count value of the overload accumulation counter, and (f) shows the inverter power supply state (on, off) signal.

[0048] In FIG. 1, in the period before time t1 is reached, the sequence output “operating status” signal (FIG. 1(b)) and the inverter power supply status signal (FIG. 1(f)) are both at high level, and the motor current value has already exceeded the motor overload occurrence reference value (FIG. 1(c)), but the count value of the overload accumulation counter is increasing below the overload abnormality judgment level.

[0049] Next, at time t1, when the count value of the overload accumulation counter exceeds the overload abnormality judgment level, the sequence output "abnormality output" signal goes to high level, the sequence output "operating status" signal goes to low level, the motor current value becomes 0 between times t1 and t2, the motor speed gradually decreases, and the count value of the overload accumulation counter decreases after time t2.

[0050] A-(1) At time t3, the inverter power supply status signal and the sequence output "abnormal output" signal go to low level. The control device determines this as a power cut or restart occurring during operation, free-running due to a stop, or deceleration.

[0051] A-(2) Before the CPU is stopped due to a power cut, the motor frequency / rpm value and the count value of the cumulative overload counter are recorded in a recording device such as an EEPROM that retains the data even when the power is cut off (step S10).

[0052] When the voltage value drops below a certain level due to a power cut or other reason, the frequency / rpm value at that point is measured using an encoder or other device and the measured value is stored in a non-volatile memory such as an EEPROM.The count value of the cumulative overload counter at that point is also recorded in the same way and stored in a non-volatile memory such as an EEPROM.

[0053] Even if the power interruption continues and the main power supply to the control circuit is turned off and the count value of the cumulative overload counter inside the control circuit is erased as shown by the dashed line in Figure 1(e), the recorded value in the EEPROM is maintained.

[0054] A-(3) Next, at time t4, the power is turned back on and the CPU restarts. At this stage, the motor is still rotating.

[0055] A-(4) When the power supply is restored and the control function has completed starting up again at time t5, if the pick-up restart function is enabled, the pick-up operation is performed and operation is resumed in accordance with the motor frequency / rpm during rotation (the sequence output "operating status" signal becomes high level).

[0056] At the time of picking up, the frequency value / rotation value at that time is obtained using an encoder or the like (step S21 in FIG. 2(b)).

[0057] A-(5) Inside the inverter, the frequency / rpm value at the time of the voltage drop recorded in the EEPROM is compared with the frequency / rpm value acquired at the time of the pick-up operation, and the elapsed time is estimated from the difference (step S22 in Figure 2(b)).

[0058] A-(6) The decrement of the overload cumulative counter is calculated from the estimated elapsed time (step S23 in FIG. 2(b)), and the count value of the overload cumulative counter recorded immediately before the tripping is decremented by the calculated elapsed time to calculate the count value at the current point in time (time t5) (step S24 in FIG. 2(b)). When picking up is completed, this is expanded as the current count value (steps S25 to S27 in FIG. 2(b)).

[0059] A-(7) As long as the current value does not exceed the overload standard again due to operation, the count value of the cumulative overload counter continues to decrease and is limited to 0.

[0060] If the count value recorded in the EEPROM is less than the calculated decrement of the cumulative overload counter, the count value is limited to 0 and then expanded.

[0061] Specific numerical examples of the estimated elapsed time and the decrement of the cumulative overload counter obtained by calculation are shown below. As for the decrement coefficient, as mentioned above, assume that the system is operated at 50Hz during a test run, goes into free-running mode, and decrements to 25Hz after 10 seconds. The coefficient value (decrement coefficient) is considered to be (measurement start value - value after time has elapsed) / hour, and in this example, the coefficient is (50-25) / 10=2.5.

[0062] The count value of the cumulative overload counter is calculated to decrease from 100 to 0 in 1 minute. When the power supply drops (A-(2): time t3), the motor 40 Hz: cumulative overload counter count value of 75 is acquired and recorded in the EEPROM.

[0063] Then, when the process advances to A-(4): time t5, the motor frequency value after power recovery drops to the equivalent of 20 Hz, and pick-up restart is initiated at this point.

[0064] Inside the inverter, calculations are performed based on the coefficient value (reduction coefficient) obtained above, and the elapsed time is estimated, which in this example can be considered to be 40-20 / 2.5=8 (sec).

[0065] The count value of the cumulative overload counter equivalent to 8 seconds is thought to be 8*100 / 60 ≒ 13. By subtracting this from the count value of the cumulative overload counter obtained when the power supply dropped, 75, the count value at the time of picking up can be estimated. In other words, 75-13=62.

[0066] 62 is expanded to the count value of the cumulative overload counter at the time of picking up (time t5). After that, it is increased or decreased depending on the operating situation. EXAMPLES

[0067] In this embodiment 2, the clock count value counted by the clock function inside the inverter and the count value of the overload accumulation counter are used as parameters for acquiring the elapsed time, the time when the power is cut off and the time when the power is turned back on are compared, the amount of decrease in the overload accumulation counter is estimated from the difference value, and the amount of decrease is expanded into the count value of the overload accumulation counter recorded before the cutoff.

[0068] FIG. 3 is a time chart of the compensation operation using the internal clock function in the second embodiment, and FIG. 4 is an operation flowchart of the process performed by the inverter control device in the second embodiment.

[0069] FIG. 4(a) is a flow chart for when the power supply to the inverter is cut off. In step S30, the current time when the power supply is cut off and the count value of the overload accumulation counter are stored (recorded) in a non-volatile memory, an EEPROM or the like.

[0070] FIG. 4(b) is a flowchart for restarting the inverter. In step S41, the elapsed time from power cut to restart is estimated based on the difference between the clock count value at the time of power cut of the inverter recorded in the non-volatile memory and the clock count value obtained at the time of restart after the power cut.

[0071] Next, in step S42, the amount of count decrement of the overload accumulation counter is calculated from the estimated elapsed time, and in step S43, the calculated amount of count decrement is subtracted from the count value of the overload accumulation counter.

[0072] Then, in step S44, it is determined whether the count value resulting from the subtraction is less than 0. If it is less than 0, the count value is limited to 0 in step S45, and then in step S46, it is expanded to the count value of the overload accumulation counter at the time of restarting the inverter (expanded as the current count value).

[0073] Next, a detailed description will be given of the operation of the present embodiment 2. In Fig. 3, (a) indicates the motor speed, (b) indicates the "operating state" signal, which is the sequence output of the inverter control device, (c) indicates the motor current value, (d) indicates the "abnormal output" signal, which is the sequence output of the inverter control device, (e) indicates the count value of the cumulative overload counter, and (f) indicates the inverter power supply state (on, off) signal.

[0074] In FIG. 3, in the period before time t1 is reached, the sequence output “operating status” signal (FIG. 3(b)) and the inverter power supply status signal (FIG. 3(f)) are both at high level, and the motor current value has already exceeded the motor overload occurrence reference value (FIG. 3(c)), but the count value of the overload accumulation counter is increasing below the overload abnormality judgment level.

[0075] Next, at time t1, when the count value of the overload accumulation counter exceeds the overload abnormality judgment level, the sequence output "abnormality output" signal goes to high level, the sequence output "operating status" signal goes to low level, the motor current value becomes 0 between times t1 and t2, the motor speed gradually decreases, and the count value of the overload accumulation counter decreases after time t2.

[0076] B-(1) At time t3, the inverter power supply status signal and the sequence output "abnormal output" signal go to low level. The control device determines that a power interruption has occurred during operation, free-running due to stopping, or deceleration.

[0077] B-(2) Before the CPU stops due to a power cut, the motor frequency / rpm value, the count value of the cumulative overload counter, and the time of power cut are recorded in a recording device such as an EEPROM that retains data even when the power is cut off (step S30). When the power is cut off, the values ​​of the RAM and other data in the control circuit are set to 0.

[0078] B-(3) Next, at time t4, the power is turned back on and the CPU is restarted.

[0079] B-(4) At the time of restart, the time at the time of restart is compared with the time value at the time of power off, and the elapsed time is estimated from the difference (step S41).

[0080] B-(5) The count value of the overload cumulative counter recorded immediately before the tripping is decremented by the amount of the elapsed time calculated above to calculate the count value at the present time (time t4) (step S43), and is expanded as the current count value (steps S44 to S46).

[0081] B-(6) For example, at time t5, while the motor current value is stopped or restarted and does not again exceed the overload abnormality determination level, the count value of the overload cumulative counter continues to decrease and is limited to the value 0.

[0082] B-(7) When the motor current value exceeds the overload abnormality determination level again at time t6, the overload accumulation counter begins to increase.

[0083] Next, specific examples of time measurement methods, estimated elapsed time, and decrements in the overload accumulation counter are shown below. As a method of time measurement, consider using an IC with real-time function (real-time clock: RTC) or a microcomputer with built-in real-time function. The counting method and acquisition method depend on each IC or microcomputer. In this embodiment, as a general example of operation, it is assumed that +1 is counted every 0.1 seconds. This count value is called the clock count value. The clock count value is considered to be data values ​​sent from the IC or CPU at any time and stored in RAM.

[0084] Real-time function ICs (RTC) and microcontrollers with built-in real-time functions are powered by a separate power source from the control device, such as an internal battery, and it is believed that the clock can continue counting even when the main power is cut off.

[0085] When the voltage drops below a certain level due to a power outage or other reason, the clock count value is acquired and recorded in the EEPROM. For example, the acquired value is 300 (B-(2) in Figure 3).

[0086] At the same time, the count value of the cumulative overload counter is recorded in the EEPROM as 75. When the power is restored and the control function has restarted, if the pick-up restart function is enabled, the pick-up operation will be performed and operation will be resumed according to the motor frequency / rpm during rotation (B-(6) in Figure 3).

[0087] For example, the clock count value at this time is 350. Then, take the difference between this and the clock count value recorded in the EEPROM in B-(2) of Figure 3. In this example, 350-300=50 is the clock count value equivalent to the elapsed time.

[0088] The amount of decrease is estimated from this clock count value in proportion to the amount of decrease in the count value of the cumulative overload counter. The count value of the cumulative overload counter is calculated to decrease from 100 to 0 in one minute.

[0089] From the above, if we assume that the clock count value is 0.1 sec = 1 count, then it is equivalent to 50 counts = 5 sec. The count value of the overload accumulation counter equivalent to 5 sec is (5 * 100) / 60 ≒ 8.

[0090] The amount of decrease is subtracted from the count value 75 of the overload accumulation counter recorded in the EEPROM, resulting in 75-8=67.

[0091] This 67 is expanded as the current count value when the picking is completed. If the EEPROM recorded count value is less than the amount of decrease, it is expanded after being limited to 0. EXAMPLES

[0092] In this embodiment 3, the heat sink temperature inside the inverter obtained by measurement or estimated calculation and the count value of the overload accumulation counter are used as parameters for acquiring the elapsed time, and the elapsed time is estimated from the temperature difference of the heat sink when the power is cut off and when it is turned on again. From this, the amount of decrement in the overload accumulation counter is estimated, and the amount of decrement is expanded into the count value recorded before the cutoff.

[0093] In other words, the temperature rise of the motor is estimated from the heat sink temperature inside the inverter. The temperature rise of the motor can be estimated from the output current and the time that current is applied (the time that current is applied can be calculated backwards from the value of the first cumulative overload counter). The elapsed time is then estimated from the difference in the heat sink temperature when the power is cut off and when it is turned back on, from which the amount of count decrement is estimated, and this decrement is expanded into the count value recorded before the cutoff.

[0094] Whether or not to measure the temperature reduction coefficient taking into account the thermal time constant of the motor is determined and set in advance using parameters, etc.

[0095] FIG. 5 is a time chart of the compensation operation based on temperature acquisition in the third embodiment, and FIG. 6 is an operation flowchart of the process performed by the inverter control device in the third embodiment.

[0096] FIG. 6(a) is a flow chart for when the inverter is powered off. In step S50, the heat sink temperature inside the inverter and the count value of the cumulative overload counter at the time of power off are stored (recorded) in a non-volatile memory, EEPROM, or the like.

[0097] FIG. 6(b) is a flowchart for picking up recovery after restart. In step S61, the motor drive frequency or rotation speed is obtained by the picking operation. In step S62, the difference between the heat sink temperature value at the time of power cut recorded in the non-volatile memory in step S50 and the heat sink temperature obtained at the time of restart after power cut is divided by a preset temperature reduction coefficient to estimate the elapsed time from power cut to restart.

[0098] Next, in step S63, the amount of count decrement of the overload accumulation counter is calculated from the estimated elapsed time, and in step S64, the calculated amount of count decrement is subtracted from the count value of the overload accumulation counter.

[0099] Then, in step S65, it is determined whether the count value resulting from the subtraction is less than 0. If it is less than 0, the count value is limited to 0 in step S66, and then in step S67, it is expanded to the count value of the overload accumulation counter at the time of restarting the inverter (expanded as the current count value).

[0100] Next, the operation of the third embodiment will be described in detail. In Fig. 5, (a) indicates the motor speed, (b) indicates the "operating state" signal, which is the sequence output of the inverter control device, (c) indicates the motor current value, (d) indicates the "abnormal output" signal, which is the sequence output of the inverter control device, (e) indicates the count value of the cumulative overload counter, and (f) indicates the inverter power supply state (on, off) signal.

[0101] In FIG. 5, in the period before time t1 is reached, the sequence output “operating status” signal (FIG. 5(b)) and the inverter power supply status signal (FIG. 5(f)) are both at a high level, and the motor current value has already exceeded the motor overload occurrence reference value (FIG. 5(c)), but the count value of the overload accumulation counter is increasing and is below the overload abnormality judgment level.

[0102] Next, at time t1, when the count value of the overload accumulation counter exceeds the overload abnormality judgment level, the sequence output "abnormality output" signal goes to high level, the sequence output "operating status" signal goes to low level, the motor current value becomes 0 between times t1 and t2, the motor speed gradually decreases, and the count value of the overload accumulation counter decreases after time t2.

[0103] C-(1) At time t3, the inverter power supply status signal and the sequence output "abnormal output" signal go to low level. The control device determines that a power interruption has occurred during operation, free-running due to stopping, or deceleration.

[0104] C-(2) Before the CPU is stopped due to a power cut, the inverter heat sink temperature value and the count value of the cumulative overload counter are recorded in a recording device such as an EEPROM that retains data even when the power is cut off (step S50). When the power is cut off, the recorded values ​​in the control circuit become 0.

[0105] C-(3) Next, at time t4, the power is turned back on and the CPU is restarted.

[0106] C-(4) At the time of restart, the heat sink temperature at the time of restart is obtained (step S61), and this is compared with the heat sink temperature value at the time of power off. The elapsed time and the counter decrement amount are estimated from the difference and the temperature decrement coefficient (steps S62, S63).

[0107] C-(5) The count value of the overload cumulative counter recorded immediately before the power is cut off is subtracted from the count decrement corresponding to the calculated elapsed time to calculate the current count value of the overload cumulative counter (step S65), and is expanded as the current count value (steps S65 to S67).

[0108] C-(6) For example, at time t5, while the motor current value is stopped or restarted and does not again exceed the overload abnormality judgment level, the count value of the overload cumulative counter continues to decrease and is limited to the value 0.

[0109] C-(7) At time t6, when the motor current value again exceeds the overload abnormality determination level, the overload accumulation counter begins to increase.

[0110] Next, specific examples of a method for acquiring the heat sink temperature, an estimated elapsed time, a decrement amount of the overload accumulation counter, etc. will be described below.

[0111] The heat sink temperature rises in conjunction with the inverter's gate output command, which causes the semiconductor switching elements that make up the inverter, such as IGBTs, to generate heat and operate. When the power is cut off, the gate command turns OFF, the IGBTs stop, the source of heat is eliminated, and the heat sink temperature drops.

[0112] Here, it is assumed that there is an opportunity to coast or stop if a fault occurs during test operation, pre-adjustment operation, etc. In this measurement, the heat sink temperature is measured after a certain time has elapsed from the start of measurement, for example, after 10 seconds or 1 minute, and the temperature count value is obtained.

[0113] Calculate the temperature reduction coefficient value based on the formula in Example 2 below and record it. This temperature reduction coefficient value is obtained during test operation such as automatic adjustment operation (auto-tuning operation), and can also be set by manually entering parameters. The temperature reduction coefficient value is protected by recording it in EEPROM, and is retained even when the power is shut off.

[0114] When the voltage value drops below a certain level due to a power cut or the like, the temperature count value at that time is recorded and the recorded value is stored in a non-volatile memory such as an EEPROM (step S50). The count value of the cumulative overload counter at that time is also recorded and stored in a non-volatile memory such as an EEPROM.

[0115] Even if the power supply remains cut off and the main power supply to the control circuit is turned off, the recorded values ​​in the EEPROM are retained (C-(2) in Figure 5).

[0116] When the power is restored and the control function has completed starting up again, if the pick-up restart function is enabled, a pick-up operation will be performed and operation will be resumed according to the motor frequency / rpm that was currently rotating.

[0117] At the time of picking up, the heat sink temperature value at that time is obtained (C-(4) in Figure 5).

[0118] Inside the inverter, the heat sink temperature value recorded in the EEPROM at the time of the voltage drop is compared with the heat sink temperature value obtained at the time of the pick-up operation, the elapsed time is estimated from the difference, and the amount of count decrement is calculated from the elapsed time (see Example 2 below).

[0119] The amount of count decrement is subtracted from the count value of the cumulative overload counter recorded in the EEPROM, and is expanded as the current count value when picking up is completed.

[0120] At this time, if the EEPROM recorded count value is less than the amount of decrease, it is limited to 0 and then expanded.

[0121] <Example 2> Let's say that during a test run or similar operation, the heat sink temperature value is 50°C, and then the device enters free-running mode, decreasing to 48°C after 10 seconds. The temperature decrease coefficient value is considered to be (measurement start value - value after time has elapsed) / time, and in this example, the coefficient is (50-48) / 10=0.2. This 0.2 is stored in the EEPROM.

[0122] The count value of the cumulative overload counter is calculated to decrease from 100 to 0 in 1 minute. When the power supply drops (C-(2)), the heat sink temperature is 50°C: the count value of the cumulative overload counter is 60, which is acquired and recorded in the EEPROM.

[0123] Then, when we proceed to C-(4) in Figure 5, the heat sink temperature value after power recovery has dropped to the equivalent of 46°C, and at this point pick-up restart is initiated.

[0124] Inside the inverter, the elapsed time is estimated based on the temperature reduction coefficient value obtained above, and in this example, it can be considered as 50-46 / 0.2=20 (sec). The count value of the overload accumulation counter equivalent to 20 sec is thought to be 20*100 / 60 ≒ 33.

[0125] By subtracting this from the count value of the cumulative overload counter obtained when the power supply dropped, the count value at the time of picking up can be estimated, 60-33=27. 27 is expanded into the count value of the cumulative overload counter at the time of picking up. After that, it is increased or decreased depending on the operating conditions.

[0126] As described above, according to the first to third embodiments, by estimating the overload cumulative counter amount from when the power is turned off to when it is turned on again in the operation of the overload cumulative counter used to determine an overload abnormality during overload operation, the actual motor overload state is maintained, and the overload function can be operated in accordance with the actual operation. [Explanation of symbols]

[0127] S10, S21 to S27: Processing steps of Example 1 S30, S41 to S46: Processing steps of the second embodiment S50, S61 to S67: Processing steps of Example 3

Claims

1. A control device for an inverter that drives a motor, an overload accumulation counter that increases a count value when a current value of the motor exceeds a preset reference value during operation of the inverter, and decreases the count value when the current value of the motor is equal to or less than the preset reference value; a non-volatile memory for recording a count value of the overload accumulation counter and an elapsed time acquisition parameter for acquiring an elapsed time from when the power supply of the inverter is cut off to when the inverter is restarted; an elapsed time acquisition unit that determines an elapsed time from when the inverter is powered off to when the inverter is restarted, based on an elapsed time acquisition parameter recorded in the nonvolatile memory when the inverter is powered off and an elapsed time acquisition parameter acquired when the inverter is restarted after the power is cut off; a count decrement calculation unit that calculates a count decrement of the overload cumulative counter within the elapsed time calculated by the elapsed time acquisition unit; a count value setting unit that determines and sets a count value of an overload accumulation counter at the time of restarting the inverter from the count decrement amount determined by the count decrement amount calculation unit, 2. An inverter control device, wherein the elapsed time acquisition parameters include a drive frequency or a rotation speed of a motor.

2. an overload accumulation counter that increases a count value when a current value of the motor exceeds a preset reference value during operation of an inverter that drives the motor, and decreases the count value when the current value of the motor is equal to or less than the preset reference value; a non-volatile memory for recording a count value of the overload accumulation counter and an elapsed time acquisition parameter for acquiring an elapsed time from when the power supply of the inverter is cut off to when the inverter is restarted, a step of recording an elapsed time acquisition parameter in the non-volatile memory when the inverter is powered off; acquiring a parameter for acquiring an elapsed time when the inverter is restarted after the power supply is cut off; an elapsed time acquisition step of determining an elapsed time from when the inverter is powered off to when the inverter is restarted, based on an elapsed time acquisition parameter recorded in the nonvolatile memory when the inverter is powered off and an elapsed time acquisition parameter acquired when the inverter is restarted after the power is cut off; a count decrement calculation step for calculating a count decrement of the overload cumulative counter that has decreased within the elapsed time calculated in the elapsed time acquisition step; a count value setting step of determining and setting a count value of an overload accumulation counter at the time of restarting the inverter from the count decrement amount determined in the count decrement calculation step, 2. A method for controlling an inverter, comprising the steps of: (a) determining whether or not a drive frequency of a motor is to be exceeded;

Images