JPS5850519B2 - Starting device for current source inverter - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a starting device for a current source inverter to which a motor load is connected.

Current source inverters are advantageous for reversible conversion of electric power, such as in regenerative braking of electric motors, and have various advantages over voltage type inverters, such as not requiring a feedback rectifier.

However, at the time of starting, since the impedance of the load motor is low, the voltage drop of the load motor is low, and the charging voltage of the commutating capacitor affected by this voltage drop is insufficient, which may cause commutation failure.

A conventional example of such a current source inverter is shown in FIG.

This figure will be explained below. 1 is an AC power supply, 2 is a converter that converts AC to DC, and 4 is an inverter that converts DC to AC.

A load motor 5 is connected to output terminals U, V, and W of the inverter 4, and the inverter 4 is connected to the converter 2 via a DC reactor 3.

P and N are DC power supply buses.

5CR1-5CR2゜5CR3,...-5CRe is the main thyristor, C1s C2tC3p...pc6 is the commutating capacitor, Dl p D2 tD3 e...s D
6 is a series diode.

Series diode D1 s D2 p D3 s...s
D6 is a commutating capacitor C1s C2s C3p...
Prevents the charge stored in tc6 from discharging through the load.

In the conventional inverter 4 configured in this way, the main thyristors 5CRt, 5CR2, 5CR3-...5CR6 are fired in sequence at 120 electrical degrees as shown in FIG. 2, and the main thyristors 5CR1=5CR2°5CR3,・・・
・Commuting capacitor CUs C2t between 95CR6
The arc is sequentially extinguished and commutated by C3m...tc6, and AC power is supplied to the load motor 5.

The commutation operation is as follows.

Now, considering the state in which the main thyristor SCR□s 5CR5 is fired, the load current flows through the path of the main thyristor SCR, - series diode D0 - load motor 5 - series diode D, - main thyristor SCRs, and the Current capacitor C5 is charged to the polarity shown.

Next, when main thyristor SCR is fired, main thyristor 5CR6 - main thyristor SCR, - commutation capacitor C6
When the circuit is closed, the charging voltage of the commutating capacitor C6 is applied to the main thyristor SCR5 in the opposite direction, that is, it is reverse biased and the arc is extinguished.

Then, the load current flows through the series diode D, the commutating capacitor C6, and the main thyristor 5CRa, and the commutating capacitor C3 is charged to the opposite polarity as shown.
The load current flows through the series diode D and the raw thyristor SCRa, and commutation is completed.

Thereafter, similar operations are repeated to sequentially perform commutation operations.

Now, such a current source inverter fails at the initial stage of startup, and the commutating capacitors C1# C2s C3#...
sC5 has no charge and the main thyristor SCR,.

Charge is accumulated only when 5CR2, 5CRs-..., 5CR6 are fired.

That is, at the initial stage of starting, the main thyristor 5CR
Assuming that I-5CRs is ignited, each commutating capacitor C1t C2e C3t...pC6 is charged to the polarity shown in the diagram along the path shown by the dashed line.

This charging voltage is determined by the load voltage of the load motor 5.

However, the load motor 5 has a characteristic that its winding impedance is small at the time of starting.

Therefore, since the load voltage is low, the charging voltage of the commutation capacitor C1s C2p C3m ""t C6 is low, making it impossible to provide sufficient commutation capacity, and there is a risk of commutation failure. .

Conventionally, this problem was dealt with by increasing the capacitance of the commutating capacitor, but as is well known, in current source inverters, increasing the capacitance of the commutating capacitor causes instability during high frequency operation. .

The present invention has been made in view of the above points, and its purpose is to provide a starting device for a current source inverter that can prevent commutation failures at the time of starting the current source inverter, which occur due to the characteristics of the load motor. It's about getting.

In order to achieve the above object, the present invention is characterized in that a series diode connected in series with the main thyristor, which is predetermined to be conductive at the initial stage of startup, is controlled to be non-conductive at the time of startup, and after a certain period of time has elapsed since startup. The present invention relates to a starting device for a current source inverter that is comprised of a thyristor that is subsequently controlled to conduct continuously.

An embodiment of the present invention shown in FIG. 3 will be described below.

That is, according to the present invention, the series diodes D1 . . . are connected in series with the main thyristors SCR, . D, the thyristor 5CR
It consists of a, 5CRb.

The thyristors 5CRa and 5CRb are controlled to be non-conductive at the initial stage of startup, and are continuously controlled to be conductive after a certain period of time has elapsed.

Such control can be easily configured using a timer or the like that is activated by a start signal.

Figure 4 is a time chart showing the operating status of each part.
The operation will be explained below with reference to this figure.

- That is, t at the initial stage of startup.

At this point, the main thyristors 5CR4-5CR5 are turned on.

Then, thyristors 5CRa and 5CRb are controlled to be non-conductive.

Then, the current does not pass through the load motor 5, but always passes through the commutating capacitor C□p C2e C3e...pc6,
Regardless of the load voltage generated by the load motor 5, it is charged by the maximum voltage E generated by the converter 2, and each commutating capacitor C1s C2p C3m ``''pc6 is charged to the illustrated voltage with the illustrated polarity.

In this case, the current is commutated capacitor C1m C2eC
3,...Since the current flows only to tc6 and does not pass through the load motor 5, each commutating capacitor C1e C2pc3p...
- p C6 charges extremely quickly.

At the time point 11 when this charging is completed, thyristors 5CRa and 5
The conduction of CRb is controlled and thereafter it is kept in a conductive state continuously.

Therefore, from this point in time t0, thyristors 5CRa, 5
CRb acts as a series diode and is equivalent to a conventional one.

The time from the start of the button to the ignition of the thyristors 5CRa and 5CRb can be arbitrarily determined as long as it is at least the time required for the commutation capacitor C6 to have sufficient commutation capability.

When the main thyristor 5CR6 is turned on at time 12, the commutating capacitor C6 is already connected to the main thyristor S at this point.
Since the main thyristor 5CR5 is charged to a voltage sufficient to make it non-conductive, the main thyristor 5CR5 to the main thyristor 5CR6
The transfer to is carried out without failure.

After that, the inverter 4 operates normally, but the commutating capacitors C1s, C2s, C3t, which were charged in advance at the initial stage,
... The sc6 is gradually charged to a predetermined voltage due to the increase in the load voltage due to the increase in the impedance of the load motor 5, and continues normal operation.

That is, the commutation capacitor (4p C2
The commutation ability of m Cs a...pc6 improves as the commutation operation is performed.

By doing the above, commutation capacitor C1 is
e C2p C3e ”... PC6 can be charged rapidly, so commutating capacitor C1s C2# C3m at startup
...e The commutation capability of the C6 can be improved, and commutation failures caused by the characteristics of the load motor 5 at the time of starting the current source inverter can be prevented.

As is clear from the above description, according to the present invention, it is possible to improve the commutation capability of the commutating capacitor at the time of starting, and it is possible to prevent commutation failure at the time of starting the current source inverter caused by the characteristics of the load motor.

Furthermore, there is no need to increase the capacity of the commutating capacitor, and the capacitance of the commutating capacitor can be appropriately selected, making it possible to obtain a current source inverter that operates stably even at higher frequencies.

[Brief explanation of the drawing]

Fig. 1 is a wiring diagram showing a conventional current source inverter, Fig. 2 is a time chart of the firing signal of the main thyristor, Fig. 3 is a wiring diagram showing an embodiment of the present invention, and Fig. 4 is Fig. 3. 3 is a time chart showing firing signals of each thyristor in FIG. 4; Current source inverter, 5CR1, 5CR2. 5CR3m ""98CR6: Main thyristor, Dl
t D2*D3 e ”'s D6 p series diode, 5CRasSCRb; thyristor.

Claims (1)

[Claims] 1 A current consisting of a series diode connected in series with a main thyristor that is predetermined to be conductive at the initial stage of startup, and a thyristor that is controlled to be non-conductive at the time of startup, and then continuously controlled to be conductive after a certain period of time has elapsed from startup. Starting device for type inverter.