JPH036743B2 - - Google Patents

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention relates to a power conversion device that converts AC power at a commercial frequency to AC power at a higher frequency, and particularly relates to a current source inverter among so-called high frequency inverters. It is.

[Conventional technology]

FIG. 7 is a circuit diagram showing a conventional current source inverter. In the figure, 1 is a forward conversion circuit composed of a bridge connection of thyristors 11 to 16, 2 is a DC reactor, and 3 is a bridge connection of thyristors 31 to 34. 4 is a gate control circuit that receives a load voltage detection signal and outputs a signal to fire the thyristors 11 to 16 and 31 to 34 at a timing to secure the reverse voltage time; 5 is a capacitor 51 and a coil; This is a parallel resonant circuit consisting of 52.

Next, the operation will be explained. The thyristors 11 to 16 of the forward converter 1 conduct electricity at a phase angle such that the load voltage reaches a predetermined value according to the gate signal of the gate control circuit 4, and transfer power from the three-phase AC side of the terminal RST to the terminals P ₁ ,
Convert it to DC voltage and output it to N. The DC reactor 2 functions to smooth the current in the closed circuit passing through the next inverse conversion circuit 3 and the parallel resonant circuit 5 to such an extent that it can be regarded as a substantially constant current. Since the thyristors 31 to 34 of the inverse conversion circuit 3 do not have a self-extinguishing ability, they are always operated at a leading power factor as shown in the voltage and current waveforms of each part shown in Fig. 8, and the thyristors are turned off at _T1 shown in Fig. 8b. The gate control circuit 4 controls to provide a reverse voltage period longer than the time. 35 is a voltage detector for detecting the zero point of the load voltage, which is the reference point for determining the timing. Thyristor 3
1 and 34 and the thyristors 32 and 33 alternately repeat conduction, the parallel resonant circuit 5 has a state shown in FIG.
A sinusoidal voltage v and a square wave current i as shown in are given.

[Problem that the invention seeks to solve]

As described above, in the conventional current source inverter, in order to operate the thyristor normally without commutation failure, it is necessary to provide a reverse voltage time longer than the turn-off time of the thyristor. Therefore, even if the frequency becomes high and the period of one cycle becomes short, a certain amount of time (approximately 30 μsec) of reverse voltage time, that is, phase difference time of voltage and current, is always required, resulting in a very poor power factor. However, there was a problem in that it was not possible to economically send power to the load. In this case, it may be possible to use a thyristor with a short turn-off time, but if the rated voltage is the same, it would be difficult to manufacture and therefore expensive.

The present invention was made to solve the above-mentioned problems, and an object of the present invention is to provide a current source inverter that is inexpensive and can economically send power to a load even in a high frequency range.

[Means for solving problems]

A current source inverter according to the present invention includes an inverse conversion circuit formed of a series configuration of a diode and a transistor, and a base drive circuit for the transistor.

[Effect]

In this invention, since the inverse conversion circuit is configured by driving the base of a transistor, the time required before the voltage reaches zero point is reduced compared to the inverse voltage time of the thyristor type.

〔Example〕

An embodiment of the present invention will be described below with reference to the drawings. In FIG. 1, 1 is a forward conversion circuit composed of thyristor power modules 17 to 19;
6 is a DC reactor, 6 is an inverse conversion circuit composed of transistor power modules 61 and 62 and diode power modules 65 to 68, 5 is a parallel resonant circuit composed of a capacitor 51 and a coil 52, and 35 is a voltage detection circuit. 69 is a current detector, 7
is a transistor base drive circuit composed of a base drive signal generation circuit 70, base drive amplifiers 71 to 74, and the like.

Next, the operation of the current source inverter configured as described above will be explained. However, since the operation of the forward conversion side circuit is the same as the conventional one, the explanation will be omitted.
In the base drive signal generation circuit 70, from the signal of the voltage detector 35 regarding the load voltage during steady state,
A timing signal for switching the transistor power modules 61 and 62 is generated using the voltage zero point as a reference. That signal is the base drive amplifier 71
~74, power modules 61,62
internal transistors 61a, 62b and 61
b and 62a are alternately driven to switch the output current path. During this switching operation, there is a moment when all the transistors are in communication, and the overlapping period varies depending on the load conditions. Therefore, the zero point of the load current is confirmed by the signal of the current detector 69, and the timing of the base drive signals 70a and 70b is controlled by a feedback loop so that the voltage zero point and the current zero point are within a certain range. FIG. 3A is a detailed diagram of the base drive amplifier 71 and a pair of transistors 61a. While the base drive amplifier 71 is driving the transistor 61a, the drive base current I of the transistor shown in the current waveform of FIG. 3B flows from terminals 71a to 71b. _{The B1} sink three-stage Darlington connection type transistor 61a is driven into the saturation region. In the next half cycle, a voltage is applied from terminal 71b to terminal 71a to flow a current for releasing the accumulated carriers of I _B2 shown in the current waveform to quickly cut off the current in transistor 61a, and after that, weak disturbances etc. A bias voltage is applied to prevent malfunction. Note that when the drive base current I _B1 of the transistor is applied, the current I _C flows from the collector to the emitter with a delay of about 1 _μsec . During the time when _B2 continues to flow, the transistor's current blocking ability is not recovered, and it takes quite a long time (5~5~
20μsec) Since the current I _C continues to flow from the collector to the emitter, even if the signals at terminals 70a and 70b of the base drive signal generation circuit 70 are mutually inverted at the same timing, the period of conduction of all transistors is automatically maintained. can be secured. However, if the overlapping period is longer than the natural commutation period, a discharge circuit is formed for the load capacitor 51 and a large current flows, which increases the duty of the transistor and there is a risk that it may eventually be destroyed.
5-68 is required.

Conversely, if there is a blank period in which both the signals at the terminals 70a and 70b are at rest, the transistors 61a and 61
A situation occurs in which all of b, 62a, and 62b are blocked. At this time, the DC reactor 2 acts to continue the current and generates a high voltage, resulting in dielectric breakdown of the transistor that acts to block current flow. Therefore, in order to prevent this phenomenon, it is necessary to commutate the current and alternately switch it while ensuring a circuit in which the current of the DC reactor 2 continues.

This circuit basically requires no reverse voltage time, so unlike the thyristor type, it is possible to operate with a lagging power factor, but in the case of a lagging power factor, the reverse voltage is increasing in the circuit to be commutated, resulting in a leading power factor. Since the driving force for commutation is weak compared to the state of , there is a great risk of destroying the transistor.

Therefore, in order to ensure stability and safety, Figure 2 a~
Operation is performed under control with a slight leading power factor as shown in i.

Therefore, the timing of the base drive signal is controlled in such a manner that the commutation time can be secured, taking into account the transistor's cut-off operation time (the time from when I _B2 flows until it becomes completely OFF). Normally, the commutation overlap time is about 5μsec, so 5 to 5 seconds before the voltage zero point
A timing of 20 μsec is obtained, which is much shorter than the reverse voltage time of the thyristor type (30 μsec or more), and operation with a high power factor is possible even at high frequencies.

Figure 4 shows the commutation part in Figure 2 and Figure 3B.
This is an enlarged view of the relationship between the base drive currents on the time axis.

In this figure, the collector-emitter current I _C decreases regardless of whether it is absorbed by the carrier or not, and the commutation is completed because the direction of the voltage in the load circuit assists the commutation since the pair of transistors has started conducting.
In this case, the transistor is different from the case where the carrier absorption current I _B2 is caused to flow when the current I _C is flowing, and the current is blocked from flowing from a much deeper saturated state, and the current is blocked from the collector to the emitter. When there is no voltage applied and the carrier moving force is weak, when the time from the start of commutation to the voltage zero point (T ₁ to _{T 3} ) is short, the current I _C flows again after commutation as shown at T ₄ . A blocking condition occurs, and this current interruption generates an overvoltage proportional to the circuit inductance of the bridge to which the transistor is connected. That is, during operation, the time corresponding to the leading power factor of about 20 μs from T ₁ to _{T 3} is allowed, or the current is operated so that the overvoltage falls within the permissible value.

In the embodiment of the present invention, as shown in FIG. 5, the base drive circuit 7 for the transistor 61a includes a first circuit unit 71 connected to the base and emitter.
and a second circuit unit 91 connected to the collector and base.

Figure 6 explains the operation in this case.
The same time points as in the figure are shown. Here the current I _B1 ,
The flow of I _B2 is the same as in Figure 4, but the difference is that a current of I _X is flowed from the collector to the base in synchronization with the current I _B2 . Since a voltage is applied between the collector and base while flowing I _B2 , the carrier between the collector and base becomes I _X and is quickly absorbed. Therefore, the current flow ends in less than 50% (about 10 μsec) of the flow time of the current I _B2 shown in FIG. 4, and the current flow is blocked. Therefore, the power factor can be improved significantly and it can be used even in a high frequency range.

In the above embodiment, the configuration of the inverse conversion circuit 6 is shown as power modules 61 and 62 of transistors with built-in two elements and power modules 65 to 68 of diodes with one element. 4 power modules on the DC side, 2
A configuration may also be adopted in which two power modules of diodes with built-in elements are connected to the high frequency output side.

〔Effect of the invention〕

As described above, according to the present invention, the thyristor is replaced with a general-purpose power module transistor and diode, so the device can be made inexpensively.
Another advantage is that it can be used at a higher frequency than the thyristor type.

[Brief explanation of the drawing]

FIG. 1 is a circuit conceptual diagram showing a current source inverter according to an embodiment of the present invention, FIG. 2 is a waveform diagram explaining the circuit operation, and FIG. 3 is a connection detail and drive current of the base drive circuit shown in FIG. 1. Figure 4 is a waveform diagram explaining the operation at the time of commutation in Figure 3, Figure 5 is a diagram showing waveforms.
The figure is a connection diagram of a base drive circuit showing an embodiment of the present invention, Figure 6 is a waveform diagram explaining the operation at the time of commutation in Figure 5, and Figure 7 is a circuit conceptual diagram of a conventional thyristor type current source inverter. , FIG. 8 is a waveform diagram illustrating the circuit operation of FIG. 7. In the figure, 5 is a parallel resonant circuit, 6 is an inverse conversion circuit, 7 is a base drive circuit, and 6 is a parallel resonant circuit.
1 and 62 are transistors, and 65 to 68 are diodes. Note that the same reference numerals in each figure indicate the same or corresponding parts.

Claims (1)

[Claims] 1. In a current source inverter in which each side of a bridge-connected inverse conversion circuit is composed of a series-connected circuit of a transistor and a diode, and the load is a parallel resonant circuit, the base drive circuit of each transistor is connected to the base and emitter of the transistor. A first base current is passed from the base of the transistor to the emitter, and a second base current is then passed from the emitter to the base to cut off the current of the transistor, and a predetermined bias voltage is applied. a first circuit unit that is connected between the transistor and the base, and a second circuit unit that is connected between the transistor and the base and causes an accumulated carrier discharge current between the collector and the base to flow from the collector to the base in synchronization with the second base current. A current source inverter characterized by comprising a circuit unit.