JPS6350955B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a PWM inverter, which has greater advantages as the capacity increases.

[Prior art and its problems]

The main circuit of a current typical PWM inverter has a circuit configuration in which a chopper element consisting of a transistor, a reverse blocking thyristor, a reverse conducting thyristor, etc. is connected with a feedback diode in antiparallel to a bridge.

Figure 1 shows _an example of the case where reverse _blocking thyristors _{C 1 to} C ₆ are used as stopper elements _. , C ₄ on → C ₃ , C ₄ , C ₅ on → C ₄ , C ₅ ,
C ₆ on → C ₅ , C ₆ , C ₁ on → C ₆ , C ₁ , C ₂ on → C ₁ ,
Turn on C ₂ and C ₃ in sequence, block the others, and supply three-phase AC from the DC power supply E to the three-phase AC motor M. Note that D ₁ to _{D 6} are feedback diodes.

Looking at the circuit surrounded by the dashed line of the current PWM inverter shown in Fig. 1, each phase arm consists of two reverse blocking thyristor chips C ₁ , C ₄ , C ₃ , C ₆ ,
Since the circuit is configured to directly short-circuit the DC power supply E at C ₅ and C ₂ , this is a dangerous circuit system that could result in a short-circuit accident if firing signals are accidentally given to the thyristor chopper at the same time. Furthermore, in the PWM inverter shown in Fig. 1, even if a reactor (not shown) is connected in series with the power supply Eo to provide short-circuit protection, the feedback current from the feedback diodes D ₁ to _{D 6} will not be transmitted to the power supply Eo. cannot be absorbed (the feedback current is D _1
〜D6 and motor M), it is impossible in principle. Therefore, normally a phase (not shown) is inserted in series with the power supply Eo to cut off the short-circuit current, but with this method, once the power supply is short-circuited, it is troublesome to replace the fused phase with a new one. There are drawbacks such as short-circuit accidents due to erroneous firing of the thyristor chopper and fuse blow-outs due to external noise voltage that occur unrelated.

Since the inverter that drives the alternating current machine literally performs frequent forward and reverse changes (alternating current), it is of course necessary to control the two thyristors mentioned above so that they are never fired at the same time. An important issue is how to protect against short circuits.

Regarding this problem, some measures have been taken in the past for small-capacity devices, but the main circuit configuration is basically a circuit configuration that has an inherent risk of short circuit accidents as described above.
When trying to realize a large-capacity PWM inverter of 1000KW or more, extremely reliable control circuits and protection circuits are required, making it expensive and not widely used.

Therefore, the present invention is designed to simplify the configuration of the protection circuit, and therefore provides a large-capacity device at a much lower cost than the conventional method.
The purpose is to provide something that can be used to manufacture PWM inverters.

[Means for solving problems]

The present invention has been made to solve the above problems, and has independent DC voltage positive and negative terminals P ₁ ,
N ₁ and positive and negative output terminals P ₂ that output variable DC current,
N ₂ and from the positive terminal P ₁ to the positive output terminal P ₂
A first chopper Ch ₁ is connected between the terminals P 1 and P ₂ so that the current flows to the terminals P ₁ and P 2 , and the terminals N ₁ and N ₂ are connected in the direction that the current flows from the negative output terminal N ₂ to the negative terminal N ₁ .
a second chopper Ch ₂ connected between them; a diode D 1 whose anode is connected to the negative terminal N ₁ and a cathode connected to the positive output terminal P ₂ ; and a diode D ₁ whose cathode is connected to the positive terminal P ₁ . , the negative output terminal
A controllable power supply with a diode D2 whose anode is connected to _N2 , and a controllable power supply with a diode _D2 whose anode is connected to N2.
It is equipped with a parallel body in which the negative output terminal of one device is connected to the positive output terminal of the other device, and several phases are connected in parallel. This is a PWM inverter in which the operating breakers are connected in series and the connection point of the two controllable power supplies is used as an inverter output terminal.

Further features and embodiments of the present invention will be described below with reference to the drawings.

Fig. 2 shows a circuit diagram of a basic device called a controllable power supply in the present invention, where E is a DC constant voltage power supply, Ch ₁ and Ch ₂ are choppers using reverse blocking thyristors, and D ₁ and D ₂ are choppers using reverse blocking thyristors. It is a feedback diode.

As the DC power source E, a commercial AC power source converted to DC by a rectifier circuit is usually used, as in the embodiments described later.

The features of this controllable power supply are Chiyotupa Ch ₁ ,
Connect Ch ₂ and feedback diodes D ₁ and D _{2 to} the bridge so that _they are connected to the opposite side so that _they are _of the same type. It was connected in the opposite direction.

The control of the choppers Ch ₁ and Ch ₂ is such that a voltage is applied to the load L when they are fired at the same time.

That is, the controllable power supply device shown in FIG. 2 has positive and negative terminals P _{1 and} N ₁ of a DC power source E, and positive and negative output terminals P ₂ and N ₂ that output variable DC current, and the positive terminal
A first chopper Ch _{1 is connected between terminals P 1 and P 1 so that} a current flows from P ₁ to the positive output terminal P ₂ , and a current flows from the negative output terminal N ₂ to the negative terminal N ₁ . A second chopper between terminals N ₁ and N ₂ in the direction
Ch ₂ is connected to the diode D ₁ whose anode is connected to the negative terminal N ₁ and whose cathode is connected to _{the positive output terminal P 2 ; 2} and a diode _D2 whose anode is connected to D2.

FIG. 3 shows the operation of the choppers Ch ₁ and Ch ₂ , both of which are PWM controlled. i.e. ignition period
The width of Ton is controlled from O to Tc. As a result, the output voltage Eout becomes Eout=E.multidot.2Ton-Tc/Tc and is continuously controlled from -E to +E.

The present invention combines the above base (controllable power supply device) into a bridge circuit like a conventional inverter,
A set of protection circuits is provided in a portion corresponding to the DC power source.

〔Example〕

FIG. 4 shows an embodiment of the present invention, in which the bases (controllable power supplies) S ₁ to S ₆ having the above-mentioned configuration are connected to two
Three sets of series connected circuits are connected in parallel, and a circuit breaker Sw operated by a short circuit current and a DC reactor L are connected to DC between both terminals X and Y, and each of the above The common connection points U, V, and W of the set of controllable power supply devices are used as output terminals, and a three-phase AC motor M is connected thereto. In the figure, CT is a current detector, and MC is an electromagnetic device that operates the high-speed DC circuit breaker Sw.

In this embodiment, as shown in Fig. 5, the DC power source _E1 is used to extract AC from a commercial AC power source _E2 through transformers T, respectively insulated, and rectify it in a diode bridge rectifier circuit DB. A structure with a smoothing structure using capacitor C was used.

This PWM inverter connects each controllable power supply S ₁ , S ₄ ,
By controlling S ₃ , S ₆ , S ₅ , and S ₂ to send out variable voltage variable frequency sine wave currents with a 120° phase difference from each other, three-phase variable voltage, variable current sine AC is supplied to load M. It is something to do.

In that case, the current flowing through the load M is rectified and flows through the reactor L.

If a malfunction occurs, S ₁ and S ₄ , S ₃ and S ₆ , or S ₅
If S ₂ turns on at the same time, the short circuit current will flow through the series circuit (protection circuit) of DC reactor L and high-speed circuit breaker Sw.
flows to In that case, the DC reactor L acts to slow down or suppress the rise of the short circuit current, while the current detector CT detects the short circuit current to detect a failure in advance and control _S1 to _S6 . This current is suppressed by However, if this is not possible, the electromagnetic device MC operates the high-speed circuit breaker Sw to interrupt the series circuit and protect the device.

That is, in the device of the present invention, the expensive circuit breaker Sw
It has the advantage that only one set of DC reactor L is required for the entire device, which is very superior to conventional devices.

In the embodiment shown in Fig. 4 explained above, since _E1 is a rectified power supply, power is transferred from the load to the original commercial power supply.
It is not possible to return to _E1 .

When power regeneration is required, use PWM for regeneration.
Another set of converters _C11 may be provided and connected in the same manner as shown in FIG. 4, and the output terminals may be connected to the original power source instead of the motor M.

FIG. 6 shows the circuit of this embodiment, where _E3 is a three-phase commercial power supply. In this case, 6 DC power supplies
_E1 is made as shown in Figure 5, but unlike the case in Figure 4, it does not require back power. It is only necessary to initially charge the capacitor C shown in FIG. 5, and it is just a potential power source.

If you want to create a load or power source other than the 3-phase AC motor M and commercial power source E ₃ in Figure 6, use 6.
This can be achieved by adding a PWM converter _C11 , a DC reactor, and a high-speed circuit breaker, and connecting the system shown in Figure 6 in parallel.

[Structure of the invention]

As described above, according to the present invention, the protection circuit requires only one simple set of circuit devices, so it is suitable for industrial large-capacity variable-speed drive systems that are becoming larger in recent years.
This is an extremely superior PWM inverter structure.

Although the description has been made here for an industrial large-capacity variable speed drive system using an industrial three-phase commercial power supply, it is obvious that it is extremely effective when applied to a one-phase AC power supply for railways.

Also, although only the case where a reverse blocking thyristor is used as a chopper is illustrated here, it goes without saying that a transistor or a reverse conducting thyristor, which has a large capacity, high speed, and excellent voltage resistance, may also be used. .

[Brief explanation of drawings]

Fig. 1 is an electric circuit diagram of a conventional PWM inverter, Fig. 2 is an electric circuit diagram of a controllable power supply used in the present invention, Fig. 3 is a diagram showing the operation of the chopper, and Fig. 4 is a diagram of the controllable power supply device used in the present invention. Block diagram of the embodiment, No. 5
The figure is a detailed view of the controllable power supply device, and FIG. 6 is a block diagram of a different embodiment. S ₁ to _{S 5} ... Controllable power supply, E ₁ ... DC power supply,
C ₁₁ ...PWM converter, M...3-phase AC motor,
L...DC reactor, Sw...High speed circuit breaker, CT
...Current detector, MC...Electromagnetic device.

Claims (1)

[Claims] 1 It has positive and negative terminals P ₁ and N ₁ of an independent DC power supply and positive and negative output terminals P ₂ and N ₂ that output variable DC current, and the current flows from the positive terminal P ₁ to the positive output terminal P ₂ . A first chopper Ch 1 is connected between the terminals P ₁ and P ₂ so that the current flows, and a first chopper _{Ch 1} is connected between the terminals N 1 and _{N 2} in the direction in which the current flows from the negative output terminal N ₂ to the negative terminal N ₁ . the second tipper Ch ₂ and the negative terminal N ₁
a diode D ₁ whose anode is connected to the positive output terminal P ₂ and a cathode connected to the positive output terminal P 2;
Using a controllable power supply device including a diode D2 having a cathode connected to _P1 and a diode _D2 having an anode connected to the negative output terminal _N2 , and two controllable power supply devices, the negative output of one device is It is equipped with a parallel body in which several phases of series bodies are connected in parallel, in which the terminal and the positive output terminal of the other device are connected, and a DC reactor and a circuit breaker operated by short circuit current are connected in series between the output terminals of this parallel body. and a connection point between the two controllable power supplies is an inverter output terminal.
PWM inverter.