JPS60118066A - Power converter - Google Patents

Abstract

PURPOSE:To increase the voltage and capacity of a power converter and to generate high frequency by applying a reverse bias voltage to a normal thyristor by the charge charged to a reverse bias voltage applying capacitor when a self-extinguishing thyristor is turned OFF. CONSTITUTION:A thyristor arm in a power converter 3 is connected in a series with self-extinguishing thyristors 9-14 and a normal thyristor. Reverse bias voltage applying capacitors 15-20 are connected between the thryistor arms. When the thyristors 9-14 are turned OFF, reverse bias voltage is applied to the normal thyristor by the charge changed in the capacitors 15-20.

Description

[Detailed Description of the Invention] [Technical Field of the Invention] The present invention relates to a power conversion device configured by bridge-connecting thyristors and converting direct current to alternating current by natural commutation using an alternating current voltage. The present invention relates to a power conversion device with improved operating frequency limit.

[Technical Background of the Invention] FIG. 1 is a block diagram showing a conventional example of a power converter to which the present invention is applied. 1 is a DC power supply, usually its output current I
. It has the ability to control.

3 is a power conversion device to which the present invention is applied, which is configured by connecting thyristor arms UP, VP, WP, UN, VN, and WN in a bridge manner. 2 is DC N with DC licks 1 to 1.
A DC current I is generated by absorbing the ripple voltage of the source 1 and the power converter 3. smooth. 4 is a synchronous motor ■, which has 5 armature windings and 6 field windings. A position detector 7 detects the rotation angle of the synchronous motor 4. 8 is a power conversion bag @3
The ignition control circuit controls the cyrisk arms UP, VP, WP, UN, and VN according to the output signal of the position detector 7.

Performs WN ignition control.

FIG. 2 is a waveform diagram showing the operation in FIG.
EV and EW are the U phase of the synchronous motor 4 in Fig. 1, and ■
Phase, W phase induced voltage, IU, IV.

IW indicates the U-phase, ■-phase, and W-phase currents of the synchronous motor 14, respectively. Next, in Fig. 1, thyristor arms up and W
The operation when commutation is performed from the state where N is energized to the thyristor arm VP will be explained. When a firing pulse is applied to the thyristor arm VP at time t1 in FIG. 2, since EU is larger than EV at this time, the voltage EU-EV is applied to the thyristor arm VP as a forward voltage. Thyristor arm VP turns on. At the same time, a current change as shown in Figure 1 ■ occurs, IU decreases, and I
V increases. At time t2, when ILJ becomes zero,
Thyristor arm UP turns off.

At this time, since EU is larger than EV, ELJ-EV
is applied to the thyristor arm UP as a reverse voltage. At time t3, when EU and EV become equal, the reverse voltage applied to the thyristor arm UP becomes zero, and thereafter the polarity of the voltage applied to the thyristor arm UP is reversed and a forward voltage is applied. Therefore, the thyristor arm UP must be completely turned off and have recovered its forward voltage blocking ability by time t3, and therefore t3-[2
is set so that it is longer than the turn-off time of the thyristor element.

[Problems with Background Art] There is an increasing demand for applying the above-mentioned commutatorless motor to higher capacity, higher speed applications. For example, there is a demand for replacing compressors conventionally driven by gas turbines or steam turbines with commutatorless electric motors, which are easy to handle and maintain, are highly efficient, economical, and have excellent controllability. In such applications, for example, the motor capacity is 30,000 k
W ~ 10,000 kW.

The rotational speed is large capacity, such as e,ooORP M to 9,0OORPM, and high speed rotation is required, and the motor voltage is also high, about 3 kV to 14 kV. Therefore, a power conversion device that can generate high voltage, large capacity, and high frequency is required. In general, thyristor elements tend to have a longer turn-off time as the voltage and current are higher, and high-voltage, large-current, high-speed thyristors suitable for such uses have not been developed. For example, in the case of a thyristor element with a peak repetitive off voltage and a peak repetitive reverse voltage of 4000 V and an average on current of 150 OA, the turn-off time is about 400 μsec. Here, we specifically select
An example will be explained in which a silice element with a turn-off time of 250 μsec g is used. In Figure 2,
It is desirable that the electrical angle from time t2 to t3 be as small as possible in order to improve the power factor of the synchronous electric motor tli4 and reduce the 1-Herb ripple. - As an example, a case where the electrical angle from t2 to t3 is controlled to 15 degrees will be explained.

When the turn-off time of the thyristor element is 250 μsec, the time from t2 to t13 is controlled to a target of 500 μsec or more, taking into account variations in control, etc. = 12.0
00. czsec = 12m5ec - (1) Therefore, the maximum value j1 of the output frequency is, and the rotation speed of the non-commutator motor is 250ORPM in the case of a 4-pole machine, and 5000RPM is the limit even if a 2-pole machine is used, and the necessary A speed increasing gear is required to obtain the desired rotational speed. In particular, it is difficult to manufacture a large-capacity, high-speed speed-up gear, which limits the application of commutatorless motors to such applications.

[Object of the Invention] The present invention has been made in order to eliminate the drawbacks of the above-mentioned conventional system, and an object of the present invention is to obtain a power conversion device that can generate high voltage, large capacity, and high frequency.

[Summary of the Invention] In order to achieve this object, the present invention comprises a thyristor arm configured by connecting a self-extinguishing thyristor and a normal thyristor in series, and further includes a thyristor arm for applying a reverse bias voltage between the thyristor arms. The device is characterized in that when a capacitor is connected and the self-extinguishing thyristor is turned off, a reverse bias voltage is applied to the normal thyristor by the charge charged in the reverse bias voltage applying capacitor. .

[Embodiment of the Invention] FIG. 3 is a block diagram showing an embodiment of the present invention, and 1 to 8 are the same as those in FIG. 1, and the explanation thereof will be omitted. 9-1
4 is a self-extinguishing thyristor (hereinafter referred to as a gate turn-off thyristor, abbreviated as GTO), 15 to 20 are capacitors for applying reverse bias voltage (hereinafter simply referred to as capacitors), and 21 is an instantaneous value of ru, rv, and IW. 22 is a gate control circuit for GTOs 9 to 11; 23 is a current detector for detecting
is the control circuit of GTO12-14.

Next, the operation of the present invention will be explained in detail with reference to FIG. In the figure, EU, EV, and EW are the induced voltages of the U phase, ■ phase, and W phase of the synchronous motor 4 shown in FIG. 3, respectively, and IU, IV,
IW is the U-phase, ■-phase, and W-phase current of the synchronous motor 4, respectively.
cup, cvp, cWP are each capacitor 15.1
6.17 voltage.

Here, as shown in Fig. 5, the thyristor arms UP and WN
The operation when commutation is performed from the state in which the current is energized to the thyrisk arm ■P will be explained.

At time t4 shown in FIG. 4, when an on-pulse signal is applied to the thyristor arm vP, the GTO and thyristor of the arm VP are fired, and the IU is divided into the capacitors 15 and 16 and 17 as shown in FIG. As a result, the reverse bias of GTO9 is turned off. At this time, EU-EV-C
The voltage at UP causes a current change shown by ■, and commutation from the U phase to the V phase begins. Assuming that the on signal is still being given to GTO9, at time t5 in FIG.
When the voltage of capacitor 15 becomes zero, GTO
9 is turned on again, resulting in the state shown in FIG. EU-E
The voltage V causes a current change shown by ■, and the commutation from the U phase to the V phase continues.

At time t5 in FIG. 4, the current detector 21 detects that IU has decreased to a value △I close to zero, and the control circuit 22
When the GTO9 is turned off by giving an off pulse to the GTO9, the IU is shunted from the GTOlo to the capacitor 15 and the capacitor 16.17 as shown in FIG.
The voltage of -EV-CUP causes the current change shown by ■, and commutation continues. At time t7 in FIG. 4, when IU becomes zero, the thyristor arm UP is turned off as shown in FIG. 9, and the commutation from the U phase to the V phase is completed. Similarly, every 60 degrees, commutation from WN to UN, VP
The commutation from WP to WP is performed.

In this way, the voltage waveforms of the capacitors 15, 16, and 17 become the waveforms shown by cup, cvp, and cwP in FIG. 4, respectively. Here, cup, cvp.

The magnitude of the voltage charged to the CWP is determined by the value of Δ1, the commutation inductance on the output side, and the capacitance of the capacitor, and the magnitude of the voltage can be changed by changing the value of Δ1. For example, as shown in Figure 3, each thyristor arm is
If GTO and three normal thyristors are connected in series and the element breakdown voltages of the GTO and normal thyristors are the same, then the GTO can handle the maximum value of the line voltage on the load side. Since it is sufficient to share 1/4 of the voltage, the value of ΔI may be adjusted so that the voltage charged in the capacitor is equal to 1/4 of the maximum value of the line voltage on the load side. The voltage applied to the thyristor arm at this time will be explained with reference to FIG. In the figure, VUP is the voltage applied to the thyristor arm UP, and at time t7, IU becomes zero, and when the thyristor is turned off, the voltage of EV-EU is applied. Also, VSCR
is the voltage applied to a normal thyristor, VUP+CUP
voltage is applied. Thyristor arm WP at time ℃8
When ignited, a voltage of vup-cwp is applied. At time te, the maximum forward voltage is applied to the thyristor arm UP, and at this time, the voltage V1=CWP is applied to the GTO 9, and the normal thyristor voltage V2=VtJP-CWP is applied. If vl is set to 1/4 of VUP, G
'TO and the normal thyristor will share the voltage in a well-balanced manner. Next, a period during which a normal thyristor is exposed to back pressure will be explained. In Fig. 4, at time tlo, when EU and EV become equal, the back pressure applied to the thyristor arm UP becomes zero, but the normal thyristor has a CLI
A back pressure of P is applied, and the time when the normal back pressure of the thyristor becomes zero is extended to tit. If CUP is 1/4 of the maximum line voltage, or 0.25, then tl
.

The electrical angle from to tll is s i n”10.25 =
Since the electrical angle is 14.5°, if the electrical angle from time t7 to tio is controlled to 15° as explained in the conventional embodiment, the electrical angle from t7 to 111 is 15°+
14.5°=29.5°.

[Effects of the Invention] As explained above, according to the present invention, in the same way as explained in the conventional embodiment, even if an element with a turn-off time of 250 μsec or less is used as a normal thyristor, variations in control, etc. are taken into consideration. If the time from t7 to tll is controlled to a target of 500 μ'sec or more, the minimum value T2 of the output side cycle is 360°T2 = 500 μsec x 2g, 5° = 610
2 μSeO = 6, 102 m5ec (3) Therefore, the maximum value f2 of the output frequency is 000! 2'=6102=164Hz ・-・(zL)
Therefore, the rotational speed of a commutatorless motor is 49 in the case of a 4-pole motor.
If you use 20 RPM and a two-pole machine, you will get 9840 RPM. In the conventional system, as mentioned above, a 4-pole machine has two
50 ORPM, 500 ORPM was the limit for a two-pole machine, so a speed-up gear was required to obtain the required rotation speed.In particular, it was difficult to manufacture a speed-up gear for large capacity and high speed rotation, so it was Steam turbines had to be used.

According to the present invention, it is possible to apply a commutatorless motor that is easy to handle and maintain, is highly efficient, economical, and has excellent controllability to such applications, and has industrial effects. is large.

Although the case where the GTO is connected in series with a normal thyristor has been described above, it may be configured using other known forced commutation circuits.

Furthermore, although a case has been described in which a synchronous motor is connected as a load of the power converter of the present invention to form a non-commutator motor, the power converter of the present invention is a high-pressure input capacity motor that can be operated at a higher frequency. It can also be applied to other uses as a device. Further, since the power conversion device of the present invention can reduce the commutation margin angle, it is possible to operate at a higher power factor.

[Brief explanation of the drawing]

Fig. 1 is a block diagram showing a conventional embodiment, Fig. 2 is a waveform diagram showing the operation of the conventional embodiment, Fig. 3 is a block diagram showing an embodiment of the present invention, and Fig. 4 is a block diagram showing an embodiment of the present invention. Waveform diagrams for explaining the present invention in detail, and FIGS. 5 to 9 are main circuit diagrams for explaining the present invention in detail. 1...DC power supply, 2...DC reactor, 3...
Power converter, 4... Synchronous motor, 5... Armature winding, 6... Field winding, 7... Position detector, 8...
Ignition control circuit, 9.10, 11.12, 13.14...
・Self-extinguishing thyristor, 15, 16.17, 18.1
9゜20... Capacitor for applying reverse bias voltage, -2
1... Current detector, 22.23... Gate control circuit. Applicant's agent Patent attorney Takehiko Suzue Figure 5 Figure 6

Claims (1)

[Claims] In a power conversion device that is configured by connecting a small number of thyristor arms in a bridge manner and converts direct current to alternating current through natural commutation due to the alternating current voltage, the thyristor arm is composed of a self-extinguishing thyristor and a normal thyristor. A reverse bias voltage applying capacitor is connected between the thyristor arms, and when the self-extinguishing thyristor is turned off, the charge charged in the reverse bias voltage applying capacitor causes the normal A voltage conversion device characterized in that a reverse bias voltage is applied to the thyristor.