JP2980698B2 - Inverter device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[Object of the Invention]

[0002]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a power converter.

[0003]

2. Description of the Related Art Conventional phase loss detection of an inverter device for driving an induction motor will be described with reference to the block diagram of FIG.

[0004] In the inverter device 1 for converting DC to AC, if the output of the three-phase AC is out of phase, it seriously impairs the load of the motor IM and the like.

[0005] For this reason, output phase loss detection is provided in the inverter device, and a protection operation is performed to prevent an extended failure of the inverter itself as well as the load.

Conventionally, as a method of detecting this open phase, the current of each phase is measured by a current detector 2 and the sum of the instantaneous values (I _U , I _V , I _W ) of each phase of the three-phase output current is zero. There was a way to detect that it was not.

However, this method has the following problems.

[0008]

That is, an open phase due to an abnormality on the load side, for example, an open phase due to a ground fault in the motor can be detected, but an open phase operation due to disconnection of the three-phase output line or failure of the inverter. Has the disadvantage that it cannot be detected.

SUMMARY OF THE INVENTION It is an object of the present invention to solve the above-mentioned problems and to provide an inverter device capable of reliably detecting a phase loss.

[Structure of the Invention]

[0011]

In order to solve this problem, according to the present invention, there are provided means for detecting instantaneous values of three-phase output currents I _U , I _V and I _W , and a three-phase AC based on the three instantaneous values. a means for calculating the effective value of the current and the effective value constantly monitors fluctuations rate (this value and I _RMS), the fluctuation rate at output phase continues more than a predetermined time at a predetermined level or higher From this, we know open phase detection.

[0012]

The instantaneous values of the output currents I _U , I _V and I _W of the inverter device are detected by the current detector 2. Then, the effective value calculating section calculates the three-phase output current effective value I _RMS . The I _RMS value has the following characteristics.

When the three-phase output currents are balanced and the phase difference is normal, I _RMS shows a substantially constant value, but when the phase difference deviates more than 120 degrees due to output loss or the like, I _RMS fluctuates greatly. . That is, the output fluctuates greatly when the output is out of phase.

[0014]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described based on an embodiment shown in FIG.

The three-phase output current of the inverter is measured, its effective value I _RMS is calculated by the effective value calculating section 3, and its fluctuation rate _ID is known through the differentiating circuit section.

[0016] When the variation rate I _D of I _RMS has continued more than a predetermined time at a predetermined value or more in this example, the open phase detection.

This has the following advantages.

Even when the balance of the three-phase output is disturbed or the amplitude of the three-phase output current changes at the start of the inverter or in a transient state such as a load change, the constant C in FIG. It is possible to prevent erroneous phase loss detection in a transient state.

Incidentally, the effective value I _RMS of the three-phase output current is expressed as follows.

That is, under normal conditions, the amplitudes of the three-phase currents are equal. This is I, and the phase is delayed by 120 degrees, so that I _RMS = (I _U ² + I _V ² + I _W ² ) ^1/2 = I [Sin ² ωt + Sin ² (ωt-120 °) + Sin ² (ωt-2
Is revealed by 40 °)] ^1/2.

Sin ² ωt + Sin ² (ωt-120 °) + Sin
^{Since 2} (ωt−240 °) = 3/2, it shows a constant value of I _RMS = (3/2) ^1/2 I.

On the other hand, when the output is out of phase, the operation is as follows.
As an example, when the W phase is out of phase, I _RMS = (I _U ² + I _V ² ) ^1/2 (because I _W = 0) = I [Sin ² ωt + (− Sin ² ωt) ² ] ^1/2 (I _V = −I _U ) = I [Sin ² ωt + Sin ² ωt] ^1/2 = {2I | Sin ωt |, and the value of I _RMS greatly varies. This variation rate is checked by the differential operation unit. This is the same when the U and V phases are lost.

Therefore, in order to detect an open phase,
The rate of change is constantly monitored and the rate of change I_DofLarge values (| I
_D |> C) has continued for a predetermined time or moreInverter
For protection operation.

[0024]

[0025]

The effective value calculator 3 used as a means for detecting an open phase is often used in a control loop even in a conventional inverter device.

Therefore, even when the present invention is applied to the conventional inverter device, it is only necessary to add a portion for monitoring the rate of change of the effective value and a sequence for protecting the inverter based on the value of the rate of change.

[0028]

According to the present invention, an inverter device capable of simply and reliably detecting an open phase can be realized at low cost.

[Brief description of the drawings]

FIG. 1 is a configuration diagram of an open-phase detection of an inverter device according to the present invention.

2 is a phase loss detection configuration diagram of a conventional inverter equipment.

[Explanation of symbols]

1 ... inverter equipment 3 ... effective value calculating section 4 ... open phase detecting unit

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁶ identification code FI H02M 7/48 H02M 7/48 M (58) Investigated field (Int.Cl. ⁶ , DB name) H02H 7/20-7 / 122 H02M 7/48 H02H 3/253-3/44 G01R 29/16 G01R 31/02

Claims (1)

(57) [Claims] 1. A inverter device that outputs three-phase alternating current, comprising means for calculating the effective value from the means and the instantaneous value to detect the instantaneous values of the three-phase output currents, a further fluctuation index of said effective value Means for calculating, and detecting a phase loss when the calculated value continues at a predetermined level or more for a predetermined time or more.