JPS6115671B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an inverter device in which a method for charging a commutating capacitor of a series diode type inverter is improved.

Series diode type inverter devices are widely used because of their simple operating principle, but as is well known, if the circuit that initially charges the commutation capacitor at startup is not devised, the commutation capacitor voltage will be insufficient and commutation will fail. There are many. For this reason, conventionally, as shown in Figure 1, a thyristor and a current limiting resistor are connected in series in parallel to the reactor on the inverter's DC side, and when the inverter is started, the thyristor is fired to short-circuit the reactor and eliminate ripples on the converter side. The commutating capacitor was charged with voltage.

The configuration of a conventional circuit will be explained with reference to FIG.
The phase of the current is controlled by a thyristor bridge 2 with an AC power source 1 as input, and the current smoothed by a DC reactor 3 is converted into AC through a series diode type inverter bridge 4 and supplied to a load motor 5. In the series diode type inverter 4, one of the upper thyristor groups 11, 12, 13 and one of the lower thyristor groups 14, 15, 16 are always ignited, just as the thyristors 11 and 15 are ignited. The load current has a 120° current waveform. For example, from thyristor 11 to thyristor 13
When commutating the load current, the thyristor 11 side of the capacitor 33 is charged with positive polarity, and when the thyristor 13 is fired, the capacitor 33 cancels the load current of the thyristor 11 and flows in the opposite direction through the thyristor 13. It discharges. In this way, the discharge current of the capacitor extinguishes the thyristor and commutates, so the capacitor must be sufficiently charged before commutation. The equivalent circuit when thyristor 11 and thyristor 15 are on is shown in the second diagram.
Shown in Figure c. The current applied to the DC terminals A and B of the inverter 4 passes through the thyristor 11, the capacitor 31, the diode 22, the diode 25,
The circuit of thyristor 15 charges the capacitor 31, while the capacitors 32 and 33 charge the thyristor 1.
1. Charge with a circuit consisting of capacitor 33, capacitor 32, diode 22, diode 25, and thyristor 15. The windings of the load motor 5 are connected in parallel to the charging circuit of the capacitor 31 via diodes 21 and 22. Further, the capacitor 32 is connected in parallel with the windings of the load motor 5 via diodes 22 and 23, and the capacitor 33 is connected in parallel with the windings of the load motor 5 via diodes 21 and 23.

Since the capacitors 34, 35, and 36 have the same circuit as above, if the voltage drop of the thyristors 11 and 15 is ignored, the equivalent circuit of FIG.
It can be rewritten as shown in Figure a. Capacitors 37a, 37b are capacitors 31, 32, 3
If 3, 34, 35, 36 are C, 37a=37
It is clear from the above explanation that b=C+1/2C.

A further simplified equivalent circuit can be considered as shown in FIG. 2b. In FIG. 2, reactor 5a represents the load motor winding inductance. To charge the capacitor 37 in FIG. 2b, a voltage must be applied between the A and B terminals, but the DC reactor 3 in FIG. 1 is replaced by the reactor 5a in FIG. Therefore, the peak voltage on the output side of the thyristor bridge 2 is hardly applied between the A and B terminals in FIG. 2b, and the charging of the capacitor 37 becomes a very low value.

Therefore, conventionally, as shown in FIG. 1, a thyristor 41 and a current limiting resistor 42 are connected to both ends of the DC reactor 3, and connected to the gate of the thyristor 41 via a contact 43 and a rectifier 44.
3 was closed, the DC reactor 3 and the current limiting resistor 42 were connected in parallel, and the ripple voltage on the output side of the thyristor bridge 2 was applied to the terminals A and B in FIG. However, in such a circuit, there is a loss due to the current limiting resistor 42, so that sufficient commutation energy of the commutating capacitor cannot be obtained, and the current limiting resistor 42 must be changed depending on the capacity of the load motor 5. Furthermore, since the ripple voltage output from the thyristor bridge 2 is applied to the positive section A and B terminals when the thyristor 41 is turned on, an inrush current flows into the capacitor, which may adversely affect the AC power supply. There were flaws.

The present invention has been made to eliminate the above-mentioned drawbacks, and its purpose is to connect a DC reactor in parallel to the DC bus that connects the converter that outputs ripple voltage and the series diode type inverter that excites the load. An electric valve such as a thyristor is connected with the polarity in the direction in which no load current normally flows, and an ignition command is given only when the inverter is started or at low speed. By applying the obtained voltage to the input terminal of a series diode type inverter, the current limiting resistor can be omitted, sufficient commutation energy of the commutating capacitor can be secured, and the adverse effect on the alternating current power supply due to rush current flowing through the capacitor can be eliminated. Our goal is to provide inverter devices that can.

The present invention will be explained below with reference to the drawings. FIG. 3 shows an embodiment of the present invention, and the same parts as in FIG. 1 are denoted by the same numbers and the explanation thereof will be omitted. Thyristors 41 are connected to both ends of the DC reactor 3 in a direction opposite to the direction in which the DC current flows.

Next, the operation of the present invention will be explained with reference to FIGS. 4 and 5. When the series diode type inverter shown in Fig. 3 is started, the load motor 5 is not rotating or is rotating at a very low speed, so the back electromotive force of the motor can be ignored, and the forward voltage drop of the thyristor and diode can also be ignored. When the electromotive current is controlled to be constant, the thyristor bridge 2 can be considered as a load consisting only of inductance and operates near α≒90°. Therefore, the output voltage of the thyristor bridge 2 fires the three-phase thyristor bridge at α≈90° as shown in FIG. 4 V _SCR , and has a well-known waveform. Further, in FIG. 4, the DC current Id is the current when the DC reactor 3 is inserted, and a smooth current flows. The DC current i _d is a current when the DC reactor 3 is short-circuited, and the ripple current component increases significantly. Next, let us consider the charging of the capacitor 37 by considering the equivalent circuit shown in FIG. 2b when charging the capacitor of the inverter bridge 4. Fifth
In the figure, the DC reactor 3 is the thyristor 41
Before the time t ₂ when the short circuit is not established, due to the action of the reactor 3, as I _d shown in FIG.
A constant current with little ripple flows. In this case, a so-called current limiting or current minor loop is provided, which is not shown in FIG. 3, which controls the starting current, that is, the current I _d of the reactor 3, to be approximately constant by the current control loop of the thyristor bridge 2. .

When the firing signal of the thyristor 41 is given at t ₁ , V
In the section where _{the SCR} is positive, the direction in which the current is increased in the reactor 3, that is, the cathode side of the thyristor 41 is more positive than the anode side, and the thyristor 4
1 is not energized, and reactor 3 operates to smooth I _d . In the period from time t ₂ to _{t 3} , V _SCR becomes negative and acts in the direction of decreasing the current in the reactor 3. Therefore, the reactor 3 acts in a direction to prevent this, that is, the anode side of the thyristor 41 is smaller than the cathode side. The voltage is output in the positive direction, the thyristor 41 is turned on, and the current I _d is circulating between the reactor 3 and the thyristor 41. In this section, there is no result of current ripple reduction due to reactor 3, and the inductance 5a on the load side shown in Fig. 2b is considerably smaller than that of reactor 3, so it rapidly decreases as shown in _id in Fig. 5. do.
In this case, the negative voltage of V _SCR causes the AC power supply 1 to
The energy of the load inductance 5a is regenerated.

Next, at time _t3 , when the thyristor bridge 2 commutates and the V _SCR voltage changes from negative to positive, the cathode side of the thyristor 41 becomes more positive than the anode side, and the thyristor 41 is turned off. That is, the turn-off current of the thyristor 41 flows for a short time from the thyristor converter 2, from the cathode of the thyristor 41, through the anode to the circuit of the capacitor 37 in the equivalent circuit of FIG. 2b, and the thyristor 41 is turned off.

When the thyristor 41 is turned off, the reactor 3 retains the current that was flowing at time _t2 , so it generates a voltage to keep the current _IDL flowing. That is, during the time period _t3 to _t4 , the reactor 3 acts to flow a substantially constant current. On the other hand, since current does not rise instantaneously in the load example inductance 5a, I
The difference between _DL and i _d , that is, the shaded parts a, b,
c charges the capacitor 37, the voltage V _C is applied to the load reactor 5a, and the load current i _d increases. In Figure 5, the time when V _SCR and V _C match
t' ₃ , charging of the capacitor 37 continues even after this time, and the load current continues to increase until time _t4 .
After _t4 , when charging is performed until time _t4 when _DL and _id match, the influence of the reactor 3, that is, the inductance of the reactor 3 is larger than the load inductance 5a, so the change in _Id becomes very gradual. In this way, if control is performed to fire the thyristor 41 only at startup or at low speed, there is always a period during which the capacitor is charged between the next commutation timings, so sufficient commutation energy can be secured. .

In FIG. 3, both the inverter bridge and the thyristor bridge are shown for three phases, but the present invention can be practiced regardless of the number of phases. Furthermore, it goes without saying that it can also be applied to a multiplexed inverter system. Furthermore, as shown in Fig. 6, when the thyristor 41 is fired at the inverter commutation timing only during startup or at low speeds, the capacitor voltage Vc is rapidly charged even when combined with intermittent startup in which the DC current _i is zeroed at the same time. A similar effect can be obtained. Furthermore, the fifth
In the figure, the commutation capacitor is charged at the timing of commutation of the thyristor bridge, but as shown in _FIG . 15, or 13 and 16 respectively or simultaneously to short-circuit the DC side, a DC current i _d flows.At time t ₂ , the thyristor bridge 2 is operated with a phase delay so as to operate as an inverter, and at the same time the thyristor bridge 2 is operated as an inverter. When ignition of thyristor 41 causes the current in reactor 3 to be short-circuited by thyristor 41, the DC current i _d rapidly becomes zero.Afterwards, at time _t3 , the ignition pulse of thyristor 41 is stopped and at the same time the inverter bridge is normalized. When started at the timing of , the i _d in Fig. 5 becomes zero due to the same effect as explained in Fig. 5, so the reactor current I _DL becomes a current source and charges the commutating capacitor in a short time. It is possible to obtain the same effect as the above-mentioned embodiment.Although the DC reactor is completely short-circuited by a thyristor in Fig. 3, it is possible to divide the DC reactor into two and short-circuit one of them by a thyristor. However, if you consider the balance between ripple current and capacitor charging voltage, they work equally well.

As described above, in the present invention, a DC reactor is connected to the DC bus connecting the converter that outputs ripple voltage and the series diode type inverter that excites the load, and the polarity is set in the direction in which the load current does not normally flow in parallel to the DC reactor. An electric valve such as a thyristor is connected to the input terminal of the series diode type inverter and the voltage obtained through the DC reactor during the on/off period of the electric valve is connected to the input terminal of the series diode type inverter. Therefore, it is possible to provide an inverter device that can omit a current-limiting resistor, secure sufficient commutation energy of a commutation capacitor, and eliminate adverse effects on an AC power supply due to inrush current flowing through the capacitor. can.

[Brief explanation of the drawing]

Figure 1 is a conventional circuit diagram, Figure 2 is an equivalent circuit diagram of a commutating capacitor section, Figure 3 is a circuit diagram of the present invention, Figures 4 and 5 are explanatory diagrams of the operation of the present invention, and Figure 6 is FIG. 6 is an explanatory diagram of another embodiment of the present invention. 1... AC power supply, 2... Thyristor bridge,
3... DC reactor, 4... Series diode type inverter, 5... Load motor, 41... Thyristor, 42... Current limiting resistor, 43... Contact, 44...
... Rectifier, 11-16 ... Thyristor, 21-2
6... Rectifier, 31-36... Commutation capacitor.

Claims (1)

[Claims] 1 first main thyristor and diode, second
A series circuit consisting of diodes and a main thyristor is connected in parallel for a predetermined number of phases, and a load motor is connected to the midpoint of the first and second diodes of each phase series circuit, and the first diode of each phase series circuit is connected in parallel. In a series diode type inverter in which a commutating capacitor is connected between each anode terminal, an AC power source is connected to the input terminal, and a DC output terminal outputs a ripple voltage connected to the input terminal of the inverter via a DC bus. a converter, a DC reactor that is provided on the DC bus and has a larger inductance than the load motor, and is connected in parallel to the DC reactor with a polarity in a direction in which no load current normally flows, and is ignited only when the inverter is started or at low speed. An inverter device comprising an electric valve such as a thyristor to which a command is given.