JP3409327B2 - Inverter device - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an inverter device for converting an alternating current input into a direct current and then converting it into an alternating current, and more particularly to an inverter device capable of preventing a smoothing capacitor from being damaged due to a ripple included in a direct current link voltage. Is.

[0002]

2. Description of the Related Art For example, as disclosed in Japanese Utility Model Laid-Open No. 5-43800, an inverter device is known which detects a disconnection of a fuse and a missing phase of a three-phase AC power supply without using a contact relay. Is. As shown in FIG. 5, in this inverter device, the power of the three-phase AC power supply (51) is applied to the full-wave rectifier circuit (53) through the fuses (52) for each phase for rectification, and the smoothing capacitor It is made direct current by (54).
This DC output is given to a well-known inverter circuit (56) composed of switching elements controlled by a control circuit (not shown), and converted to AC of a predetermined frequency and voltage by the inverter circuit (56). The electric motor (57) is driven. Further, a fuse (58) for preventing burnout in the event of a short circuit is provided in the DC circuit of the inverter device. Anomaly detection device (6
1) Two resistors (62, 63) inserted in the DC main circuit of the inverter device to divide the DC voltage, a voltage detection circuit (64) that reproduces the DC voltage in an electrically isolated state, and a voltage detection circuit (64 ) Output, the AC component detection circuit (65) that extracts only the AC component, and the peak hold circuit (66) that holds the peak value of the output of the AC component detection circuit (65) are provided, and the peak value is compared with the set value. It is provided with two comparators (67, 68) that determine whether the value falls below the set lower limit value or exceeds the set upper limit value, and outputs an abnormal signal when applicable. Voltage detection circuit
(64) is a duty ratio setting circuit (6 that sets the duty ratio proportional to the voltage value divided by the resistors (62, 63).
9), a transistor (70) that switches the voltage divided by the output signal of the duty ratio setting circuit (69), a photocoupler (71) that transmits the signal switched by the transistor (70) to the secondary side, a photo The coupler (71) includes a buffer (72) for shaping the signal on the secondary side and an integrator (73) for integrating the signal shaped by the buffer (72).

The voltage detection circuit 64 reproduces the voltage of the DC main circuit in an electrically insulated state. Voltage detection circuit
From the output signal of (64), the AC component detection circuit (65) detects only the AC component, and the peak hold circuit (66) detects the peak value of the voltage ripple of the DC main circuit. With this,
Resistors (62, 63), voltage detection circuit (64), AC component detection circuit (6
The detection means is composed of 5) and the peak hold circuit (66).

The output value of the peak hold circuit (66) is the comparator
The upper limit value and the lower limit value, which are given to both (67, 68) and are set in advance, are compared with each other. When the output value of the peak hold circuit (66) is out of the range between the upper limit value and the lower limit value, an abnormal signal is output. Further, the comparators (67, 68) operate only when the operation signal of the inverter device is in the operating state. Therefore, the comparators (67, 68) function as abnormality detecting means.

Although not shown, a control circuit or an abnormality detection device
When the abnormal signal is output from (61), the driving of the electric motor (57) can be switched to the operation by another inverter device or the operation by the commercial power source in a predetermined sequence outside the inverter device.

When the inverter device operates normally, a voltage ripple corresponding to 6 times the output frequency of the three-phase AC power source (51) is generated in the DC main circuit due to the transfer of power. The voltage ripple is detected by the voltage detection circuit (64) and the AC component detection circuit (65), but its peak value is small in a normal state and is within the set upper and lower limit values. Therefore, the abnormal fuse blown signal is not output from the comparator (67) or the comparator (68).

When a phase loss occurs, the power input to the inverter device becomes a single-phase component, and the voltage ripple supplied to the DC main circuit increases. Therefore, the voltage ripple detected by the voltage detection circuit (64) also becomes large, and the peak value output from the peak hold circuit (66) exceeds the set upper limit value. The signal is output. In this way, the magnitude of the voltage or current ripple in the DC main circuit is detected to detect the disconnection of the input and internal fuse of the inverter device and the open phase of the three-phase AC power supply without using a contact relay. You can

[0008]

In an inverter device having a three-phase AC power supply as an input as shown in FIG. 5, ripples contained in the DC rectified by the full-wave rectifier circuit (53) are smoothed. Although it is smoothed by the capacitor (54), the ripple contained in the direct current when the power supply situation is bad and the power supply is open-phase or unbalanced (unbalanced) or the inverter device is mistakenly connected to the single-phase power supply. Grows larger. In this case, the ripple causes the smoothing capacitor (5
There was a defect that the life of 4) was shortened and that the internal temperature of the smoothing capacitor (54) was abnormally increased to cause internal electrolyte leakage, explosion-proof valve operation, and damage such as rupture. Further, the abnormality detecting means for providing a dedicated input voltage detecting circuit to detect a missing phase requires an expensive detecting element having a complicated circuit structure. Further, if the smoothing capacitor (54) is continuously used beyond its expected life, the smoothing capacitor (54) will be damaged.

Therefore, an object of the present invention is to provide an inverter device which avoids erroneous detection of ripples contained in the DC link voltage of the inverter device to smoothly operate the inverter device and prevents damage to the smoothing capacitor. And

[0010]

[Means for Solving the Problems] The AC power input from the three-phase AC power supply (1) through the rectifier circuit (2) is converted into DC power, and the DC power smoothed by the smoothing capacitor (4) The inverter device of the present invention for converting the DC link voltage (V _DC ) into AC power by the inverter (5) and feeding the load (6) is a voltage for detecting the DC link voltage (V _DC ) and generating a detection output. DC link voltage (V _DC ) at a small time interval within a fixed time from the detection output of the detection means (3) and the voltage detection means (3)
The maximum voltage value of DC link voltage (V _DC )
(11) and the minimum voltage value (12), then the maximum voltage value (11)
And a minimum voltage value (12), the potential difference (13) is calculated, and the potential difference (13) is used as a voltage ripple (ΔV _DC ) of the DC link voltage (V _DC ). Output voltage ripple (Δ
V _DC ) and a reference value (ΔV *) are compared to generate a comparison output (9), and the comparison output of the comparator (9) is received to stop and control the inverter (5). And a circuit (10). In the false detection prevention circuit (10), the comparator (9) has a reference value (ΔV *)
When a larger voltage ripple (ΔV _DC ) is detected, a counter for counting the number of detections of the voltage ripple (ΔV _DC ) and advancing the count value is provided, and the comparator (9) continuously outputs the reference value (ΔV _DC ).
*) When a larger voltage ripple (ΔV _DC ) is detected and the counter reaches a predetermined count value, the false detection prevention circuit (10) stops the operation of the inverter (5). Further, when the comparator (9) continuously detects a voltage ripple (ΔV _DC ) larger than the reference value (ΔV *) and the counter does not reach the predetermined count value, the erroneous detection prevention circuit (10) operates the inverter ( Continue the operation in 5). In addition, the comparator (9) shows the voltage ripple (ΔV *) below the reference value (ΔV *).
Upon detection of a V _DC), the erroneous-detection prevention circuit (10) clears the voltage ripple ([Delta] V _DC) 0 the count value of the determination to and counter to be a proper value of the DC link voltage (V _DC) Continue operation of the inverter (5). This causes the voltage ripple
By avoiding erroneous detection of (ΔV _DC ), the inverter (5) can be operated smoothly, and by accurately detecting the voltage ripple (ΔV _DC ), damage of the smoothing capacitor (4) can be prevented.

In the embodiment of the present invention, the calculation means (7)
Is a direct-current link voltage (V _DC ) sampled from the detection output of the voltage detection means (3) at a fixed time, for example, within 100 ms, at a minute time interval, for example, every 2 ms, to sample the direct-current link voltage (V _DC ).
The maximum voltage value (11) and the minimum voltage value (12) are obtained, and then the potential difference (13) between the maximum voltage value (11) and the minimum voltage value (12) is calculated as the ripple (ΔV _DC ) of the DC link voltage (V _DC ). ). Therefore,
The presence or absence of ripple (ΔV _DC ) can be accurately detected at minute time intervals. The calculating means (7) is a DC link voltage
(V _DC ) is detected, DC link voltage (V _DC ) and maximum value (V _DC )
_DCMAX ) is compared and the DC link voltage (V _DC ) is the maximum value (V _{DC
When it is} larger than _DCMAX ), the maximum value in the maximum value storage means for storing the maximum value ( _VDCMAX ) is updated, and the DC link voltage (V
_DC ) and minimum value (V _DCMIN ) are compared, and DC link voltage (V
_{When DC} ) is less than the minimum value (V _DCMIN ), the minimum value
The minimum value in the minimum value storage means for storing (V _DCMIN ) is updated, and then it is determined whether a predetermined time has passed since the previous calculation of ripple (ΔV _DC ). When the predetermined time has passed, the ripple (ΔV _DC) ) _Is calculated, and the maximum value (V _DCMAX ) and the minimum value (V _DCMAX )
_DCMIN ) is initialized. Maximum value of ripple (ΔV _DC ) (V
_{Since DCMAX} ) and the minimum value (V _DCMIN ) are constantly updated to the optimum values within a fixed time range, the ripple (ΔV _DC ) can be calculated accurately.

The erroneous detection prevention circuit (10) compares the DC link voltage (V _DC ) with the regenerative brake resistance operation start level (V _SV ) during deceleration when the load factor is less than a certain ratio, and Link voltage (V _DC ) is the regenerative brake resistance operation start level
When (V _SV ) or more or when the load (6) is in steady operation,
The inverter (5) continues to operate when it is not in steady operation, but the erroneous detection prevention circuit (10) determines that the DC link voltage (V _DC ) is at the regenerative brake resistance operation start level when the load factor is above a certain ratio. When it is smaller than (V _SV ), or when the load (6) is in steady operation, the operation of the inverter (5) is stopped.

[0013]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of an inverter device according to the present invention will be described below with reference to FIGS. As shown in FIG. 1, an inverter device according to the present invention includes a rectifier circuit (2) including a diode bridge that converts AC power input from a three-phase AC power supply (1) into DC power,
An inverter (5) for converting DC power of the rectifier circuit (2) into AC power and an electric motor (6) as a load driven by the AC power of the inverter (5) are provided. Between the pair of output lines of the rectifier circuit (2), a smoothing capacitor (4) for smoothing the DC link voltage (V _DC ) of the DC power of the rectifier circuit (2).
Are connected. As the smoothing capacitor (4), an electrolytic capacitor that smoothes pulsation (ripple) included in the DC link voltage (V _DC ) is usually used. In normal use, the smoothing capacitor (4) reduces the ripple contained in the DC link voltage (V _DC ) and therefore the smoothing capacitor (4) is not damaged. However, when one of the three phases of the AC power supply (1) is in the open phase or unbalanced state, the ripple of the DC link voltage (V _DC ) becomes large, and the motor in that state is large.
If (6) is continuously driven, the internal temperature of the smoothing capacitor (4) will rise abnormally, causing electrolyte leakage, explosion-proof valve operation, rupture, etc., which eventually leads to damage. Although detailed illustration is omitted because it is well known, one DC line of the rectifier circuit (2) is
Voltage detection means (3) such as a voltage detection resistor or a coil for detecting the DC link voltage (V _DC ) is connected. Voltage detection means (3)
The DC link voltage (V _DC ) detected by is sent to the calculating means (7), and the calculating means (7) calculates the ripple (ΔV _DC ) included in the DC link voltage (V _DC ).

FIG. 2 is a waveform diagram of the DC link voltage (V _DC ). The calculation means (7) is composed of a microcomputer having a program-controlled maximum value storage means and minimum value storage means (not shown), and 2 ms within a fixed time of 100 ms from the detection output of the voltage detection means (3). The DC link voltage (V _DC ) is sampled at every minute time interval, and the maximum voltage value (11) and the minimum voltage value (12) of the DC link voltage (V _DC ) are obtained. After that, the potential difference between the maximum voltage value (11) and the minimum voltage value (12)
Since (13) is the ripple (ΔV _DC ) of the DC link voltage (V _DC ), the presence or absence of the ripple (ΔV _DC ) can be accurately detected at minute time intervals. The calculated value of the calculating means (7) is converted into a corresponding voltage level and given to one input terminal of the comparator (9). The reference value (ΔV *) of the reference power source (8) is applied to the other input terminal of the comparator (9). Computing means (7)
Detects the DC link voltage (V _DC ) and detects the DC link voltage
(V _DC ) and the maximum value (V _DCMAX ) are compared, and the DC link voltage (V
_DC ) is larger than the maximum value (V _DCMAX ), maximum value
The maximum value in the maximum value storage means for storing (V _DCMAX ) is updated, the DC link voltage (V _DC ) and the minimum value (V _DCMIN ) are compared, and the DC link voltage (V _DC ) is the minimum value (V _DC ). When it is smaller than _DCMIN ), the minimum value in the minimum value storage means for storing the minimum value ( _VDCMIN ) is updated, and then it is determined whether or not a certain time has passed since the previous calculation of ripple (ΔV _DC ). When a certain amount of time has passed, the ripple (ΔV _DC ) is calculated and the maximum value is calculated.
(V _DCMAX ) and the minimum value (V _DCMIN ) are initialized. As a result, the maximum value (V _DCMAX ) and the minimum value (V _DCMAX ) of the ripple (ΔV _DC )
_{Since DCMIN} ) is constantly updated to the optimum value within a fixed time range, the ripple (ΔV _DC ) can be calculated accurately.

The comparator (9) compares the calculated value of the voltage ripple (ΔV _DC ) output from the calculating means (7) with the reference value (ΔV *) and generates a comparison output. False detection prevention circuit (10)
It receives the comparison output from (9) and controls the inverter (5). The erroneous detection prevention circuit (10) has a counter (not shown) for counting the number of ripple (ΔV _DC ) detections, and the comparator (9) has a reference value.
([Delta] V *) upon detection of the following ripple ([Delta] V _DC), the ripple of the DC link voltage (V _DC) and ([Delta] V _DC) determines that the proper value, the detection number counter is cleared to 0 the inverter Continue the operation in (5). Comparator (9) is the reference value (ΔV *)
When a larger ripple (ΔV _DC ) is detected, the erroneous detection prevention circuit (10) counts the number of times the ripple (ΔV _DC ) is detected and advances the count value of the counter, and the comparator (9) continuously sets the reference value. If the ripple (ΔV _DC ) greater than the value (ΔV *) is detected and the counter does not reach the predetermined count value, the inverter
Continue the operation in (5). When the comparator (9) continuously detects a ripple (ΔV _DC ) larger than the reference value (ΔV *) and the counter in the false detection prevention circuit (10) reaches a predetermined count value, the inverter Since the operation of (5) is stopped, ripple
By avoiding erroneous detection of (ΔV _DC ), the inverter (5) can be operated smoothly, and by accurately detecting the ripple (ΔV _DC ), damage of the smoothing capacitor (4) can be prevented.

The erroneous detection prevention circuit (10) is provided with a DC link voltage (V _DC ) when the load factor of the motor (6) does not reach a certain ratio.
And the regenerative brake resistance operation start level (V _SV ) during deceleration are compared, and when the DC link voltage (V _DC ) is equal to or higher than the regenerative brake resistance operation start level (V _SV ) or whether the motor (6) is in steady operation. determining, if it is not operating steadily, but continues the operation of the inverter (5), when the load factor of the motor (6) is above a certain percentage, the DC link voltage (V _DC) is regenerative braking resistance operation start level ( V _SV ) or the motor (6) is in steady operation, the erroneous detection prevention circuit (10) operates the inverter (5).
Stop driving. Here, steady operation means the target frequency (set frequency) and the inverter after the acceleration of the electric motor (6).
Indicates the operating state where the output frequencies of (5) match.

FIG. 3 shows the ripple of the DC link voltage (V _DC ).
7 is a flowchart showing an operation sequence for calculating (ΔV _DC ). The calculation of ripple (ΔV _DC ) is started in step (14), and the DC link voltage (V _DC ) is detected in step (15). Next, in step (16), the DC link voltage (V _DC )
And compares the maximum value (V _DCMAX), when DC link voltage (V _DC) is greater than the maximum value (V _DCMAX), the maximum in the maximum value storing means for storing the maximum value (V _DCMAX) in step (17) Update the value. Next, in step (18), the DC link voltage (V _DC ) and the minimum value (V _DCMIN ) are compared, and when the DC link voltage (V _DC ) is smaller than the minimum value (V _DCMIN ), in step (19) The minimum value in the minimum value storage means for storing the minimum value (V _DCMIN ) is updated. Then, in step (20), the previous ripple (ΔV
_It is determined whether 100ms has passed from the calculation of _DC ) and 100m
When s has elapsed, the ripple (ΔV _DC ) in step (21),
That is, the difference (V _DC ) between the maximum value (V _DCMAX ) in the updated maximum value storage means and the minimum value (V _DCMIN ) in the updated minimum value storage means.
_DCMAX- V _DCMIN ) is calculated, and the maximum value (V
_DCMAX ) and minimum value (V _DCMIN ) are initialized, and step (2
Computation processing ends in 3).

FIG. 4 shows the ripple (ΔV _DC ) and the reference value (ΔV _DC )
4 is a flowchart showing a process of comparing (*) with an operation sequence of an erroneous detection prevention circuit (10). After starting the process in step (24), the ripple (ΔV _DC ) is compared with the reference value (ΔV *) in step (25). Ripple (ΔV _DC ) is the reference value (Δ
V *) in the following cases, erroneous detection prevention circuit (10) is a ripple of the DC link voltage (V _DC) ([Delta] V _DC) travels determines that the proper value in the step (27), a step (27) The counter detection count is cleared to 0, and the operation of the inverter (5) is continued at step (33) to proceed to step (35). If the ripple (ΔV _DC ) is larger than the reference value (ΔV *) in step (25), the process proceeds to step (26). In step (26), for example, 1 is sequentially added to the counter to increment the count value of the counter. After that, proceed to step (28). In step (28), it is determined whether or not the count value of the counter has reached 10 for 10 times in a row, and if the count value reaches 10, the process proceeds to step (29), in which the count value is less than 10. If so, the process proceeds to step (33) to continue the operation of the inverter (5), and then proceeds to step (35).
Here, the reason why the erroneous detection prevention circuit (10) determines whether or not it has detected a predetermined number of times, for example, 10 times in succession, is that erroneous detection due to noise of the voltage detection means (3), instantaneous power failure, load fluctuation, etc. Inverter when ripple increases only for a relatively short time
This is to prevent (5) from being stopped unnecessarily.

Next, in step (29), it is judged whether the electric motor (6) is in steady operation, and when the electric motor (6) is in acceleration / deceleration operation, the operation proceeds to step (33) to operate the inverter (5). keep working on it,
Proceed to step (35). During acceleration / deceleration of the electric motor (6), the inverter (5) generates a large output current, so that the DC link voltage (V _DC ) easily fluctuates. Therefore, in order to avoid erroneous detection in normal use, it is necessary to continuously operate the inverter (5) when the electric motor (6) is not in steady operation. Further, the ripple (ΔV _DC ) is not detected in order to avoid erroneous detection even when the inverter (5) is stopped. Electric motor
If (6) is in steady operation, the process proceeds to step (30), and in step (30), the false detection prevention circuit (10) determines whether the load factor is 50% or more, and the load factor is 50%. When it is less than the above, the process proceeds to step (33), after continuing the operation of the inverter (5), the process proceeds to step (35). Step when load factor is 50% or more
Proceed to (31). Here, the reason why the operation of the inverter (5) is continued when the load factor is less than 50% is that the ripple (ΔV) of the DC link voltage (V _DC ) is generated at light load even if the input power supply is out of phase. _This is because _DC ) is small, so that it is difficult to distinguish it from the normal usage state, and erroneous detection in the normal state due to this is avoided.

Then, in step (31), the false detection prevention circuit (1
0) compares the DC link voltage (V _DC ) with the regenerative brake resistance operation start level (V _SV ) at the time of deceleration, and compares the DC link voltage (V
_{When DC} ) is above the regenerative braking resistance operation start level (V _SV ), the operation of the inverter (5) is continued in step (33) and the process proceeds to step (35). When electrical energy is regenerated from the electric motor (6) to the DC link circuit via the inverter (5) during deceleration, the DC link voltage (V _DC ) rises, so it is difficult to distinguish the voltage fluctuation from the ripple voltage. . Therefore, it is desirable to continue the operation of the inverter (5) when the DC link voltage (V _DC ) is equal to or higher than the regenerative braking resistance operation start level (V _SV ).

In step (31), when the DC link voltage (V _DC ) is lower than the regenerative braking resistance operation start level (V _{S V} ),
Proceed to step (32) to stop the operation of the inverter (5) to protect the smoothing capacitor (4) and
(34) operating an acoustic alarm or optical alarm (not shown) in, to inform that the ripple ([Delta] V _DC) is large the DC link voltage (V _DC), the process proceeds to step (35), all the processes finish.

The above embodiment of the present invention can be modified. For example, in the above-described embodiment, the electric motor is used as the load.
Although (6) is used, the load is not limited to the electric motor, and the present invention can be applied to a power converter including a main circuit similar to that of FIG. Further, in the above embodiment, the purpose is to protect the smoothing capacitor (4), but excessive increase in ripple at the DC link voltage that often occurs due to input voltage abnormality such as open phase and unbalance. Can be detected and an alarm for an abnormal input voltage can be issued. Furthermore, since the ripple increases even when the capacity of the smoothing capacitor (4) is reduced due to deterioration over time, it can be used as a device for detecting and notifying the life of the smoothing capacitor (4).

[0023]

As described above, the erroneous detection of ripples is avoided to operate the inverter smoothly, and the ripples are accurately detected to stop the inverters to prevent the smoothing capacitor from being damaged. You can
This suppresses the internal temperature rise of the smoothing capacitor,
There are advantages that the life of the smoothing capacitor can be shortened and damage such as electrolyte leakage or rupture can be prevented.

[Brief description of drawings]

FIG. 1 is a block circuit diagram of an inverter device for driving an electric motor according to the present invention.

2 is a waveform diagram of a DC link voltage output from the rectifier circuit shown in FIG.

FIG. 3 is a flowchart for calculating a ripple included in a DC link voltage.

FIG. 4 is a flowchart showing an operation sequence of the false detection prevention circuit shown in FIG.

FIG. 5 is a block circuit diagram of a conventional inverter device.

[Explanation of symbols]

(1) ・ ・ Three-phase AC power supply, (2) ・ ・ Rectifier circuit, (3) ・ ・
Voltage detector, (4) ・ ・ Smoothing capacitor, (5) ・ ・
Inverter, (6) ・ ・ Motor, (7) ・ ・ Computing means,
(8) ・ ・ Reference power supply, (9) ・ ・ Comparator, (10) ・ ・ Error detection prevention circuit, (11) ・ ・ Maximum voltage value, (12) ・ ・ Minimum voltage value, (13) ・ ・ Potential difference ,

─────────────────────────────────────────────────── ─── Continuation of the front page (58) Fields surveyed (Int.Cl. ⁷ , DB name) H02M 7/48 H02P 7/63

Claims (5)

(57) [Claims] 1. An AC power input from a three-phase AC power supply via a rectifier circuit is converted into DC power, and a DC link voltage of the DC power smoothed by a smoothing capacitor is converted into AC power by an inverter. In an inverter device for supplying power to a load, voltage detection means for detecting the DC link voltage and generating a detection output, and sampling the DC link voltage at every minute time interval within a fixed time from the detection output of the voltage detection means Then, the maximum voltage value and the minimum voltage value of the DC link voltage is obtained, and then the potential difference between the maximum voltage value and the minimum voltage value is calculated, and the potential difference is a voltage ripple of the DC link voltage, A comparator for comparing the voltage ripple output from the arithmetic means with a reference value to generate a comparison output, and a comparator for receiving the comparison output of the comparator to stop the inverter. An erroneous detection prevention circuit, wherein the erroneous detection prevention circuit, when the comparator detects the voltage ripple larger than the reference value, a counter that counts the number of detections of the voltage ripple and advances the count value. When the comparator continuously detects the voltage ripple larger than the reference value and the counter reaches a predetermined count value, the erroneous detection prevention circuit stops the operation of the inverter, Continuously detects the voltage ripple larger than the reference value and the counter does not reach a predetermined count value, the false detection prevention circuit continues the operation of the inverter, and the comparator is equal to or less than the reference value. When the voltage ripple of the counter is detected, the erroneous detection prevention circuit determines that the voltage ripple of the DC link voltage is a proper value, and counts the counter value. Inverter apparatus characterized by continuing the operation of the inverter is cleared to zero. 2. The maximum value storage that detects the DC link voltage, compares the DC link voltage with a maximum value, and stores the maximum value when the DC link voltage is greater than the maximum value. Updating the maximum value in the means, comparing the DC link voltage and the minimum value, when the DC link voltage is less than the minimum value, update the minimum value in the minimum value storage means for storing the minimum value. The inverter device according to claim 1, wherein after that, it is determined whether a predetermined time has passed since the previous calculation of the voltage ripple, and when the predetermined time has passed, the voltage ripple is calculated and the maximum value and the minimum value are initialized. 3. The erroneous detection prevention circuit continues the operation of the inverter when the load factor is less than a certain ratio,
The inverter device according to claim 1, wherein the operation of the inverter is stopped when the load factor is equal to or higher than a certain ratio. 4. The erroneous detection prevention circuit compares the DC link voltage with a regenerative brake resistance operation start level at the time of deceleration, and when the DC link voltage is equal to or higher than a regenerative brake resistance operation start level, operates the inverter. The inverter device according to any one of claims 1 to 3, wherein when the DC link voltage is lower than the regenerative brake resistance operation start level, the operation of the inverter is stopped. 5. The erroneous detection prevention circuit determines whether the load is in a steady operation, and when the load is not in a steady operation, continues the operation of the inverter, and when the load is in the steady operation, operates the inverter. The inverter device according to claim 1, which is stopped.