JP2638982B2 - Initial charging method - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to an initial charging method of a smoothing capacitor in a voltage type inverter having a smoothing capacitor in a DC intermediate circuit.

[Prior Art] FIG. 2 shows a main circuit of a conventional voltage source inverter, wherein 1 is a three-phase AC power supply of U-phase, V-phase and W-phase, 2 is a fuse, 3 is a main electromagnetic contactor, 4 is an initial charging circuit,
It consists of a series circuit of a magnetic contactor 5 for initial charging and a resistor 6 and is connected in parallel to the main magnetic contactor 3. Reference numeral 7 denotes a three-phase full-wave rectifier, 8 denotes a DC reactor for smoothing, 9 denotes a capacitor for smoothing, and a discharge resistor 10 that works when the operation of the inverter is stopped is connected in parallel. Reference numeral 11 denotes an inverter formed by bridging transistors, and reference numeral 12 denotes an inverter load.

In this configuration, when starting the inverter, a start command is given and the electromagnetic contactor 5 for initial charging of each phase of U, V, and W is turned on. As a result, the three-phase alternating current flows through the resistor 6 and is DC-converted by the full-wave rectifier 7 to charge the capacitor 9 as shown in FIG. When the predetermined time t ₁ is charged to complete the capacitor 9 has passed, i.e., (the charging voltage at this time Vcs) If the initial charging is completed,
The main electromagnetic contactor 3 is turned on. Thus, the three-phase AC is directly converted to DC by the full-wave rectifier 7 and
, The capacitor 9 is charged to a voltage Vc higher than the initial charging voltage Vcs. The electromagnetic contactor 5 is opened a short time after the main electromagnetic contactor 3 is turned on. In FIG. 3, I _DC indicates the charging current.

[Problems to be solved by the invention]

As described above, in the voltage-type power converter having the capacitor in the input circuit, in order to suppress the charging current at the time of startup,
Although an initial charging circuit is provided, the initial charging circuit generally includes the electromagnetic contactor 5 and the resistor 6, so that when the power conversion device is of a wind-cooled type or the like, if the atmosphere of the installation place is poor, If foreign matter such as dust adheres to the contact of the electromagnetic contactor 5 or an oxide film is formed, and if such foreign matter adheres and the oxide film is formed, contact failure of the contact may occur. As shown by the dotted line in FIG. 3, the initial charging of the capacitor 9 becomes insufficient, an excessive charging current I _DC flows when the main electromagnetic contactor 3 is turned on, and a protection device such as an overcurrent protection device operates. The charging fails, and the operation of the power conversion device stops.

Of course, if a closed type is used as the electromagnetic contactor 5 for initial charging, the above problem can be solved.
In the case of a 0 volt system and several thousand amperes, it is difficult to obtain and extremely expensive.

The present invention has been made to solve the above problems,
It is an object of the present invention to provide an initial charging method that can surely prevent a failure in charging, as a conventional hardware configuration of the initial charging circuit.

[Means for solving the problem]

In order to achieve the above object, the present invention is configured to perform at least one inching operation prior to a regular operation when an electromagnetic contactor of an initial charging circuit is turned on.

[Action]

In the present invention, by the inching operation of the electromagnetic contactor for initial charging, dust attached to the surface of the contact is removed or the oxide film is destroyed, so that contact failure of the contact is eliminated, At the time of the subsequent steady-state operation, the desired charging current can flow into the capacitor.

[Embodiment] An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 shows a time chart of the electromagnetic contactor 5, and at the time of initial charging of the capacitor 9 shown in FIG. First, after closing for a short time Δt (for example, 0.1 second), the circuit is turned off for a short time Δt, and at the time of this inching input operation, the operation is shifted to a steady input operation. When the initial charging is completed, the main electromagnetic contactor 3 is turned on as in the case of the conventional method. The inching input operation may be performed twice, three times,.... The inching operation can be easily performed by a sequencer usually provided for instructing the operation sequence of the inverter.

In this way, the contacts of the electromagnetic contactor 5 for initial charging are separated from each other after the contacts are shockedly closed and then temporarily separated, so that the dust adhering to the contacts floats from the contacts due to this close ( Or the oxide film is broken)
The dust separates from the contact and cleans the surface of the contact. After the contact surface is cleaned, the operation shifts to the normal closing operation, so that the desired initial charging current flows into the capacitor 7.

Since the magnetic contactor 5 for initial charging is closed after the inverter is started, dust adheres to the contact and an oxide film is easily formed on the contact before the next closing operation. In the present embodiment, when the main electromagnetic contactor 3 is inserted, the electromagnetic contactor 5 is operated to perform an inching operation to mechanically remove dust and remove an oxide film from the surface of the contactor. When the charging current I _DC flows,
It can be prevented reliably.

〔The invention's effect〕

As described above, the present invention causes the electromagnetic contactor to perform an inching operation when the electromagnetic contactor of the initial charging circuit is applied to the smoothing capacitor provided in the DC intermediate circuit of the voltage type inverter, so that charging failure is reliably prevented. Thus, the reliability of the device can be improved.

[Brief description of the drawings]

FIG. 1 is an operation flowchart of an electromagnetic contactor for explaining an embodiment of the present invention, FIG. 2 is a circuit diagram of a voltage type inverter having an initial charging circuit, and FIG. 3 explains a problem of a conventional method. FIG. 6 is a diagram showing a charging voltage and a charging waveform for the operation. 3 ... Main magnetic contactor, 4 ... Initial charging circuit, 5 ... Electromagnetic contactor, 6 ... Resistance, 9 ... Capacitor.

Claims (1)

(57) [Claims] An AC power supply is connected to an AC input terminal of a voltage type inverter having a smoothing capacitor in a DC intermediate circuit via a main magnetic contactor, and an initial power supply for initial charging is connected in parallel with the main magnetic contactor. In a circuit configuration in which a series circuit of an electromagnetic contactor and a resistor is interposed, at least one inching operation is performed prior to a steady-state operation of the initial charging electromagnetic contactor for the smoothing capacitor. Charging method.