JPS5926192B2 - current source inverter - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a current source inverter, and more particularly to a current source inverter that enables high frequency operation.

Conventionally, when attempting to operate a current-source inverter that drives an induction motor at a high frequency, the commutation capacitor capacity is limited so that the commutation period does not exceed ■cycles in order to avoid chopping operation. Therefore, under the same load conditions, the commutation capacitor voltage is higher than that of an inverter operating at a low frequency, and the main thyristor and diode must have a high withstand voltage. This will be explained with reference to FIGS. 1 to 4. FIG. 1 shows the main circuit configuration of a conventional current source inverter, and FIG. 2 shows its operation sequence. The DC current rectified by the forward converter Rf is passed through the DC reactor LD to supply a constant current Id to the inverse converter. The main thyristors SU, SV, SW, SX, SY, and S2 of the inverse conversion section are arranged in the order of Su-S2-Sv-SX-SW-SY as shown in FIG.
It fires with a phase difference of 600 for each period of 200 to obtain a square wave output current 1u, 1, 1w with a width of 1200. Diodes Du, Dv, Dw, Dx, DY, in series with the main thyristor
D2 is a commutating capacitor Cu, Cv, Cw, Cx, CY,
Used with CZ for interphase commutation.

In such current source inverters, thyristors Su,
When S2 is in conduction state, as shown in Fig. 3,
Motor current is thyristor 511 - diode Du - motor winding Zu - winding Zw - diode D2 - thyristor S
It flows in the order of 2. Note that the constant current source Id is equivalently shown assuming that the reactance of the DC reactor LD is sufficiently large. From this state, the commutation operation from thyristor Su to Sv is carried out by the charging of the commutating capacitor C, which is charged to the polarity shown at the same time as the ignition of thyristor Sv.
u is extinguished, and the output current is thyristor Sv - commutating capacitor C - diode Du - winding Zu - Zw - diode D
2- flows in the path of thyristor S2. This state is indicated by the period 0-tl in FIG. In addition, from thyristor Su to S
At the time of commutation to v, the voltage waveform Vu between the windings Zu and Zv is at voltage vo as shown in FIG. 2, so a reverse voltage is applied to the diode Dv, making it non-conductive. Period from 0 to tl
The commutating capacitor C is charged in the opposite direction to the polarity shown in the third diagram, and when the commutating capacitor voltage Eu becomes equal to the line voltage Vu at time tl, the diode Dv
becomes conductive, the output current Iv begins to accumulate, the output current IIJ begins to decrease, and at time 2, the ammeter u reaches zero and the commutation is completed.

Therefore, the period 0 to 2 is the commutation transient period, and if the above transient period is longer than the inverter output frequency,
The induction motor becomes unstable.

During this transition period, the time TO-t1 is proportional to the capacitance of the commutating capacitor C.

In order to shorten this excessive period, it is possible to reduce the commutating capacitor capacity, but since the commutating capacitor voltage EO is in the relationship, reducing the capacitor capacity will increase the voltage by a factor of 2. .

As a result, the inverter becomes expensive without increasing the reverse breakdown voltage of the main thyristor or diode. SUMMARY OF THE INVENTION An object of the present invention is to provide a current source inverter that can obtain a high frequency output by reducing the capacitance of a commutating capacitor and making it possible to limit the voltage of the capacitor.

FIG. 5 shows a main circuit configuration showing an embodiment of the present invention.

The difference between this figure and FIG. 1 is that there is a bridge circuit consisting of diodes D1 to D6 whose AC input terminals are connected to the inverter output terminals, a constant voltage DC power supply E1 provided between the output terminals of the bridge circuits, and a constant voltage DC power supply E1 provided between the output terminals of the bridge circuits. High-voltage side and low-voltage side GTO thyristors Sl, S2 provided in the forward direction between the output terminals of the circuit and the inverter main circuit DC input terminal, respectively, and reactors Tl, t provided in series with the thyristors Sl, S2, respectively.
2, the thyristors S1 and S2 are the high voltage side main thyristor; they fire simultaneously with the firing of the low voltage side main thyristor, and the DC power source E1 is set to the limiting voltage value of the commutating capacitor. The commutation operation of such a configuration will be explained by taking as an example the flow between thyristors Su to S.

When thyristor S1 is fired at the same time as thyristor Sv is fired, the energy of commutating capacitor C is transferred from diode Du to diode D1 to thyristor S1 to Discharge occurs in the path from reactor t1 to thyristor Sv, and a current 11 shown in FIG. 7 flows. Along with this current, the voltage Eu of the capacitor C increases toward the opposite polarity to that shown in the figure, and at time T in FIG.
When reaching t1 from O, the capacitor voltage Eu becomes zero. This time TO-t1 is connected to the commutation margin time of the thyristor Su, and this time is set from the resonance frequency of the reactor t1 and the capacitor C.

After time t1, at time T2 when the voltage Eu of the capacitor C becomes equal to the output line voltage Vu-v, the diode D
v becomes conductive.

From this point on, the current Iu starts to decrease, and the current 1v starts to increase. Then, the voltage Eu of the capacitor C increases until time T3. During this T2 to T3 time, in the conventional circuit, the energy stored in the motor windings is transferred to the commutating capacitor, and the voltage of capacitor C increases until the current 1u becomes zero. In the circuit of the embodiment, how long does it take for the voltage of commutating capacitor C to become equal to the voltage of DC power supply E1? That is, when the commutation capacitor voltage Eu becomes equal to the voltage of the DC power source E1 at time T3,
The energy stored in the windings Zu and Zw is
It is regenerated to the DC power supply E1 through the path of w - diode D3 - power supply E1 - diode D4, and the voltage of the commutating capacitor C is limited to the DC power supply voltage. Well, when the voltage of capacitor C reaches E1, the frost flow 1V reaches a predetermined value, and the current 1V reaches a predetermined value.
u becomes zero at time T4. In addition, the low pressure side thyristor Sz
For the commutation operation from Sx to Sx, a similar operation can be achieved by firing the thyristor S2 at the same time. In the embodiment, the thyristors Sl and S2 are GTO thyristors, which facilitates the turn-off control of the thyristors Sl and S2. It can have a function.

Concerning the above, the current source inverter according to the present invention has a commutating capacitor capacity that is not limited by its charging voltage.
The capacity can be reduced to a value limited by the thyristor's commutation margin time, and operation at a high frequency determined by the thyristor's commutation margin time becomes possible.

[Brief explanation of drawings]

Figure 1 is the main circuit configuration diagram of a conventional current source inverter, Figure 2
The figure is a commutation time chart of a current source inverter, Figure 3 is an equivalent circuit diagram to explain the commutation operation in Figure 1, Figure 4 is a commutation operation waveform diagram in Figure 3, and Figure 5 is the main 6 is an equivalent circuit diagram for explaining the commutation operation of FIG. 5, and FIG. 7 is a waveform diagram of the commutation operation shown in FIG. 6. . SU, S~', SW, SX, SY, SZ... Main thyristor, CU, CV, CW, CX, CY, CZ,...
...Commuting capacitor, Rf...Forward converter, IM...
...Induction motor.

Claims (1)

[Claims] 1 In a current source inverter with a motor as a load, a diode bridge with an AC input terminal connected to the output terminal of the inverter, a DC power supply connected in parallel between the output terminals of the diode bridge, and the output terminal of the diode bridge. and a high-voltage side terminal and a low-voltage side terminal of the inverter main circuit, respectively, and a thyristor that is fired when the high-voltage side and low-voltage side main thyristors commutate, respectively, and a reactor connected in series with the thyristor, respectively. A current source inverter, characterized in that the charging voltage of the commutating capacitor is limited to the above DC power supply voltage.