JPH0779550B2 - Power converter control method - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a power converter using a self-extinguishing element, and more particularly to a control method suitable for a high-frequency switching power converter.

[Conventional technology]

A method of controlling a power converter that performs switching control using a self-extinguishing element is described, for example, in JP-A-59-204470. In such power conversion, it is possible to increase the carrier frequency in order to improve the waveform.
As a result, no particular consideration has been given to the fact that the number of times the self-extinguishing element is switched increases.

[Problems to be Solved by the Invention] Waveform improvement is a very important issue, and therefore the switching frequency must be increased. However, on the other hand,
It was found that the loss of the self-extinguishing element increases as the frequency of the switching increases, and the element may be destroyed by the increase of heat generated during the switching.

An object of the present invention is to provide a power converter control method capable of reducing the loss of the self-extinguishing element and reducing the harmonic components of the AC waveform.

[Means for solving problems]

The purpose is to connect a plurality of self-extinguishing elements to a three-phase bridge, and to make the self-extinguishing elements conductive and non-conductive by a control signal of a switching pulse train obtained by pulse width modulation control, thereby inputting to the bridge. In a method of controlling a power converter that converts direct current into alternating current or converts alternating current input into direct current, in a plurality of self-extinguishing element groups connected to the positive electrode side or the negative electrode side of the bridge, the The distribution order of the switching pulses is changed such that the distribution order is reversed between a certain cycle and a subsequent cycle for each of the predetermined cycles, and even immediately after the change, the self-extinguishing element in the conductive state immediately before the change is changed. This is achieved by maintaining continuity.

[Action]

For example, in the distribution circuit, normally, a cycle of commutation from the first self-extinguishing element to the second self-extinguishing element and then from the second self-extinguishing element to the third self-extinguishing element is distributed as one cycle. (1,2,3-1,2,3 ---). On the other hand, in the present invention, first, the distribution of the first cycle is (1,2,3) as described above, and in the second cycle, the third self-extinguishing element moves to the second self-extinguishing element, and then the second self-extinguishing element. The distribution order is switched so that commutation (3,2,1) is made from the arc element to the first self-extinguishing element. The 3rd cycle is the same as the 1st cycle, and when the commutation occurs, the distribution (1,2,3-3,2,1-1,2,3 −...) is controlled. If the numbers are equal,
Since the number of times of switching can be saved and the switching pulse train is macroscopically the same as the normal switching pulse train, it is possible to perform control with the same low-order harmonics without malfunction.

〔Example〕

An embodiment of the present invention will be described below with reference to FIG. FIG. 1 is a configuration diagram of a power converter embodying the present invention. In this case, the elevator control is targeted. This device is a bridge that is composed of a power source 1 that gives a DC power corresponding to a load change generated in a hoisting device 6 due to a change in a load of a car 8, a DC reactor 2, and self-extinguishing elements G _{1 to} G _6. The circuit 3, the capacitor 4 that absorbs the overvoltage generated when the self-extinguishing elements G _{1 to} G ₆ are switched, and the hoist 6
It is composed of an induction motor 5 for driving. Further, a control circuit 15 of the present apparatus, an elevator control circuit 11 that outputs a speed command V *, a frequency command circuit 12 that generates a frequency command * corresponding to the speed command V * while managing the state of the induction motor 5, and a frequency. A pulse distribution circuit 13 that generates and distributes the switching pulses P _{1 to} P ₆ of the self-extinguishing elements G _{1 to} G ₆ based on the command *, and controls the firing and extinction of the self-extinguishing elements G _{1 to} G _6. And a gate circuit 14 for switching.

Next, the generation principle of the switching pulse trains P _{1 to} P ₆ in the pulse distribution circuit 13 will be described with reference to FIG. Figure 2 (d) is in generation principle diagram in the period T of a 60 electrical degrees, the modulation wave e _m1, e _m2, e _m3 is the sine wave amplitude Wo each a phase difference of 120 degrees. This cycle is determined by the frequency command *. Here, by setting an arbitrary period T _c , e _m1 , e _m2 ,
A pulse train having a sinusoidal pulse width distribution can be obtained by dividing the period T _c using the size of e _m3 . This period T _c
Is equivalent to the carrier cycle in pulse width control.

If now using the instantaneous value of the modulating wave e _m1, e _m2, e _m3 at the midpoint t ₁ of the period T _c, the instantaneous value of the modulating wave e _m1, e _m2, e _m3 becomes A, B, and C . Of these, the reference value W ₁ used to obtain C is determined by the relationship such as the modulation rate. Here, in the period T, the self-extinguishing element
Suppose G ₅ is continuously firing. The period T corresponds to 60 degrees of inverter operation. As shown in FIG. 2 (b), a pulse having a width corresponding to B / (A + B + C) is distributed to P ₁ , a width corresponding to C / (A + B + C) is distributed to P ₂ , and
A pulse having a width corresponding to A / (A + B + C) is distributed to P ₃ .

In this figure, pulse every period T _c, it is distributed in the order of P ₂ -P ₃ -P _1, this operation is repeated.

Therefore, in the present invention, this pulse distribution method is reviewed and pulses are distributed as shown in FIG. Here, the same 60 degree period as in FIG. 2 (b) is selected. The pulse distribution method of the present invention, P ₁ -P ₂ in period T _c1 as shown in FIG. 3 (a)
The pulses are distributed in the order of −P ₃ , and in the next period T _c2 , the period T _c1
Distributing the pulses in the order of P ₃ -P ₂ -P ₁ contrary to the case of. In the next cycle T _c3 , distribution is performed in the same order as in the cycle T _c1, and this is repeated.

Incidentally, when the pulse distribution order of the cycle T _c1 is the same as that in FIG. 2 (b), the pulse train in the case of implementing the present invention is shown in FIG. 3 (b).
Shown in. In this case, the symmetry of the pulse train is slightly inferior to that in FIG. 2 (a).

When the pulse distribution shown in FIG. 3A is used for the fundamental wave-period, the switching pulse trains P _{1 to} P ₆ as shown in FIG. 4 are obtained.
Is obtained, the self-extinguishing elements G _{1 to} G ₆ operate, and pulse width control currents I _U , I _V , and I _W are obtained.

Here, looking at the number of pulse trains per self-extinguishing element, when T / T _c = 5 shown in FIGS. 3 and 4, the electrical angle is
There are 12 in 360 degrees. In the conventional distribution shown in FIG. 2 (c), the number is 15. When T / T _c = 20, the number is 60 in the conventional distribution, whereas it is 41 in the present invention. Therefore, the number of times the self-extinguishing element is switched is reduced, and the loss generated during the switching of the self-extinguishing element is reduced.
This effect becomes greater as the ratio of T _c to T becomes smaller, that is, the carrier frequency becomes higher, as described above.

Also, since the present invention is for pulse distribution as has been seen so far, the amount of the pulse width control currents I _U , I _V , and I _W of the low-order harmonics hardly changes. Therefore, if the number of times of switching of the self-extinguishing element is made the same as that of the conventional method, the carrier frequency is increased and the content of harmonics can be reduced.

As described above, according to the present embodiment, the harmonics can be reduced without increasing the heat generation amount of the self-extinguishing element, so that the resonance point of the mechanical system of the elevator constituted by the counterweight 7 and the car 8 overlaps. Subharmonic torque ripple is suppressed and comfortable elevator control is obtained.

In the case of the embodiment shown in FIG. 3 and FIG.
P ₁ and the order of the _{-P 2 -P 3, P 3 -P} 2 -P 1, P 2 -P 3 -P 1, P 1 -P 3 -
Although the method of distribution in the order of P ₂ was shown, P ₃ −P ₁ −P ₂ and P ₂ −P ₁
-P ₃ may be distributed in this order.

In the present embodiment, in each cycle of period T _c, there is shown how to change the order of the pulse distribution, to control to change every several cycles of such two cycles or three cycles, the period T _c Good. However, the effect of the present invention decreases as the number of change cycles increases.

Although the present embodiment has described the DC-to-AC power converter, the present invention can be applied to an AC-to-DC power converter by adding means such as periodic processing with AC power and control of the duty factor. Needless to say, can be implemented.

〔The invention's effect〕

According to the present invention, even if the frequency of the carrier wave is increased, the number of times of switching of the self-arc-extinguishing element can be suppressed to a low value, so that heat generation of the self-arc-extinguishing element is reduced and power conversion efficiency is increased. On the other hand, if the number of times of switching is the same as in the conventional case, harmonics can be suppressed, so that there is an effect that a low distortion waveform can be easily obtained with a simple filter circuit.

[Brief description of drawings]

FIG. 1 is a configuration diagram of an elevator power converter according to an embodiment of the present invention, FIG. 2 is a principle diagram of generating a switching pulse of a self-extinguishing element of the power converter of FIG. 1, and FIG. FIG. 4 is an explanatory diagram of a switching pulse train for the power converter shown in FIG. 4, and FIG. 4 is an operation waveform diagram of each part of the power converter shown in FIG. 1 ... Power supply, 2 ... DC reactor, 3 ... Bridge circuit, 5
… Induction motor, 6… Hoist, 7… Fishing weight, 8
… Car, 9,10… floor, 11… elevator control circuit,
12 ... frequency command circuit, 13 ... pulse distributing circuit, 14 ... gate circuit, 15 ... control circuit, G ₁ ~G ₆ ... self-turn-off devices.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Shigeta Ueda 4026 Kuji Town, Hitachi City, Hitachi, Ibaraki Prefecture Hitachi Research Institute, Ltd. (72) Hiromi Inaba 4026 Kuji Town, Hitachi City, Ibaraki Prefecture Hitachi, Ltd. Hitachi Research Laboratory (72) Inventor Hideaki Takahashi 1070 Ma, Katsuta City, Ibaraki Prefecture Hitachi Co., Ltd. Mito Factory

Claims (2)

[Claims] 1. A plurality of self-extinguishing elements are connected in a three-phase bridge, and the self-extinguishing elements are input to the bridge by conducting and non-conducting by a control signal of a switching pulse train obtained by pulse width modulation control. In the method of controlling a power converter for converting direct current to alternating current or converting alternating current input to direct current, in a plurality of self-extinguishing element groups connected to the positive electrode side or the negative electrode side of the bridge, within a predetermined cycle The distribution order of the switching pulses is changed such that the distribution order is reversed between a certain cycle and a subsequent cycle for each of the predetermined cycles, and the self-extinguishing element that is in a conductive state immediately before the change is changed. A method for controlling a power converter, which is characterized in that it maintains continuity immediately after that. 2. The power converter control method according to claim 1, wherein the predetermined period is a period of a carrier wave used for the pulse width modulation control.