JPH033471B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to a circulating current type cycloconverter device used as a variable voltage variable frequency power source for driving an induction motor, a synchronous motor, etc.

[Technical background of the invention and its problems]

In general, a cycloconverter is a power conversion device that directly converts AC power at a commercial frequency into AC power at a different frequency, and is widely used as a variable voltage variable frequency power source for driving induction motors and synchronous motors.

The methods of this cycloconverter are broadly divided into circulating current type and non-circulating current type. The former operates the positive group converter and negative group converter simultaneously,
The current supplied to the load is controlled by the average value of the output voltages of the two converters. On the other hand, in the latter, the positive group converter or the negative group converter is operated alternately depending on the direction of the load current, and the output voltage of either converter is applied to the load.

When switching operation from a positive group converter to a negative group converter, or conversely from a negative group converter to a positive group converter, a non-circulating current type cycloconverter must temporarily reduce the load current to zero, resulting in large load current distortion. There is a drawback. Therefore, the application is limited to low frequency loads (approximately 3 times the power supply frequency) in which the load current rest period is not a big problem.

On the other hand, in the circulating current type cycloconverter, the positive group and negative group converters are always operating, and there is no need to once reduce the load current to zero. Therefore, there is an advantage that the waveform distortion of the load current is small and the upper limit of the output frequency can be increased.

In this way, the circulating current type cycloconverter has advantages such as being able to supply a sine wave current with less current distortion to the load and controlling the reactive power at the receiving end using the circulating current. A DC reactor is required between the converters, which complicates the main circuit configuration of the device, and when compared with a non-circulating current type cycloconverter, the system has the disadvantage of being expensive and larger in size and shape. In addition, since not only circulating current but also load current flows through a DC reactor, its windings and core tend to be large, and large-capacity equipment has drawbacks such as having to prepare an installation space comparable to that of a power transformer. It was hot.

[Purpose of the invention]

The present invention has been made to eliminate the above-mentioned drawbacks, and an object of the present invention is to provide a circulating current type cycloconverter device that can be made smaller and lighter.

[Summary of the invention]

In order to achieve the above object, the present invention connects the output terminals of the positive group converter and the negative group converter to the load without going through a DC reactor, and connects the secondary side leakage inductance of the power transformer to the positive group converter and the negative group converter. The pulsation of the circulating current circulating between the two
A DC reactor is used instead of the leakage inductance on the next side.

[Embodiments of the invention]

An embodiment of the present invention will be described with reference to FIGS. 1 to 5.

In FIG. 1, 1 is a three-phase AC power source (hereinafter referred to as a power source), 2 is a power transformer, 3 is a circulating current type cycloconverter body (hereinafter referred to as a cycloconverter body), and 4 is a load. The cycloconverter main body 3 consists of positive group converters 5, 6 and negative group converters 7, 8, and there is no DC reactor as in conventional devices, but both converters 5, 6, 7, 8.
The input terminal is power transformer 2 and the output terminal is load 4.
It converts the three-phase AC power of the power supply 1 into variable voltage variable frequency power and supplies it to the load 4. Power transformer 2 has a primary side delta connection,
It has two star connections and two delta connections on the secondary side, and supplies power to each converter 5, 6, 7, and 8 while insulating them. The cycloconverter body 3 uses a 12-pulse control system, and the power transformer 2 is designed to have a larger leakage inductance on the secondary side than power transformers used in conventional devices.

FIG. 2 shows an equivalent circuit of one of the positive group converters 5 in FIG. 1 and the secondary star connection 20 of the power transformer 2 connected to its AC side terminal.
21 to 26 are thyristor elements connected in a three-phase bridge, u, v, w are secondary phase voltages of the power transformer 2, and lu, lv, lw are secondary leak inductances of the power transformer 2. Note that the resistance of the secondary winding of the power transformer 2 is ignored as it is sufficiently small.

Considering the state in which thyristors 21 and 25 are conducting, the circulating current I _O is the voltage u → leakage inductance
lu→thyristor 21→negative group converters 7, 8→positive group converter 6→thyristor 25→leakage inductance lv→voltage v. Further, the load current I _L flows in the path of voltage u→leakage inductance lu→thyristor 21→load 4→positive group converter 6→thyristor 25→leakage inductance lv→voltage v.

That is, it can be seen that the secondary side leakage inductance lv of the power transformer 2 enters both the path of the circulating current I _O and the path of the load current I _L. Therefore, the secondary leakage inductance lv can serve as a conventional DC reactor, and by appropriately selecting its value, the pulsation of the circulating current I _O can be kept sufficiently small.

However, since the leakage inductances lu, lv, and lw are related to the commutation of the converters 5, 6, 7, and 8, increasing them unnecessarily is uneconomical and results in an increase in the size and shape of the device. The firing phase angle of the positive group converter 5 is α, the commutation overlap angle is u, the effective value of the phase voltage of the transformer secondary winding is V ₂ , the output current of the converter is I _P , and the leakage reactance of the transformer is xs In this case, the following relationship holds true.

xs = 2πfls ... (2) f: Power supply frequency ls: Leakage inductance (for one phase) Therefore, when the leakage inductance ls of the transformer is increased, the commutation overlap angle u increases, resulting in a narrowing of the controllable range of the converter. becomes.

When the upper limit value αlimit of the ignition phase angle is 140° and the residual commutation angle γ is 20°, α=140°, α+u=180°−
Substitute 20°=160° into equation (1) is obtained. Here, the rated secondary current of the power transformer
If I ₂ is chosen to be I ₂ =√23· _P , the value given by equation (3) will be equal to the percent leakage reactance of power transformer 2. In the design of a normal power transformer, the percentage leakage reactance is selected to be about 5 to 10%, so the value of equation (3) is two to three times that value, but it is not that difficult to manufacture.

Next, the leakage inductance of the value given by equation (3)
Let's consider how much the pulsation of the circulating current I _O can be suppressed by ls (ls = xs/2πf).

Figure 3 shows a simplified equivalent circuit of the cycloconverter device shown in Figure 1, where L _O is the power transformer 2.
This shows the value when the secondary leakage inductance of is replaced with a DC reactor. Equivalent DC reactor when all two elements of converters 5, 6, 7, and 8 are conductive
L _O is L _O =8×ls (ls is the leakage inductance of one phase on the secondary side). Also converter 5, 6, 7, 8
are all in the overlapping period and the three elements are conducting, L _O =4×1.5×ls=6ls.

The voltage E is a composite value of the secondary voltages of the power transformer 2, and since there is a voltage phase difference of 30° between the star winding and the delta winding, the voltage E has the following relationship with the secondary phase voltage _V2 .

E=2・√3V ₂ cos15゜ ...(4) Figure 4 shows the waveform diagram of the circulating current I _O , and the firing phase angles of converters 5, 6, 7, and 8 when the pulsation reaches its maximum. α is 90° and its peak value Ipeak is as shown in the following equation.

However, when ω=2πf β=(π/p) p=12: Number of control pulses L _O =8ls and substitute equations (3) and (4) into equation (5), In other words, the circulating current pulsates by 18.96% of the output current I _P.

This value does not pose much of a problem when controlling the circulating current, and can be used as a sufficient substitute for a DC reactor. In addition, when the number of control pulses of the cycloconverter main body 3 is increased, the effect becomes noticeable, and in the 24-pulse control method, the pulsation of the circulating current I _O is reduced to about 1/4 more than in the 12-pulse control method.
decrease to a certain degree.

Note that the dimensions and shape of the power transformer 2 tend to increase somewhat due to the increase in the secondary leakage inductances lu, lv, and lw of the power transformer 2, but the dimensions and shape of the power transformer 2 tend to become larger due to the elimination of the DC reactor. The effect of downsizing is much greater.

Furthermore, when compared with a non-circulating current type cycloconverter, the distortion of the output current is small and the upper limit value of the output frequency can be set high.

Therefore, according to this embodiment, the configuration of the device is simplified because the DC reactor that was conventionally required can be removed, and the wiring is accordingly simplified, making it possible to reduce the size and weight of the entire device. equipment can be provided.

Next, the reactive power control device of the device shown in FIG. 1 will be explained with reference to FIGS. 1 and 5.

In FIG. 1, 50 is a transformer, and 51 is a current transformer, which detects three-phase AC voltage and current at the receiving end. 52 is a reactive power calculation circuit, which calculates the amount of reactive power Q from the voltage and current at the power receiving end. 53,5
4 and 55 are current transformers, and the output currents I _P of the positive group converters 5 and 6, and the negative group converters 7 and 8, respectively.
Detects the output current I _N and load current _IL .

In Fig. 5, C ₁ , C ₂ , C ₃ are comparators, A ₁ ,
A ₂ is an adder, 56, 57, 58 are control compensation circuits 59 are anti-comparison amplifiers, and 60, 61 are phase control circuits.

The load current _IL is controlled as follows.

The detected load current value I _L and its command value I ^* _L are compared by the comparator C ₁ , and the deviation ε ₁ = I ^* _L − I _L is input to the control compensation circuit 56 . The control compensation circuit 56 is designed in consideration of stabilization or responsiveness of the control system, but for the sake of simplicity, only a proportional element (amplification factor K ₁ times) will be explained here. The deviation ε ₁ is multiplied by K ₁ and input to the phase control circuit 60 of the positive group converter via the adder A ₁ , and the other is input to the inverting amplifier 59 (amplification factor 1x).
The signal is inverted at , and input to the phase control circuit 61 of the negative group converter via the adder A ₂ . Here the circulating current
Considering that the output signal from the control compensation circuit 57 of the control system of I _L is sufficiently small, the positive group converters 5 and 6
The firing phase angle α _N of negative group converters 7 and 8 is α _N = 180° − α _P with respect to the firing phase angle α _P of , and the output voltages V _P and V _N of both converters are as follows: is expressed in

V _P =k _V・V _S・cosα _P ……(7) V _N =−k _V・V _S・cosα _N =−k _V・V _S・cos (180°−α _P )=V _P
...(8) However, k _V : conversion constant, V _S : power supply voltage, i.e., the output voltages V _P and V _N of both converters
match and the voltage applied to the DC reactor V _P −
Since V _N becomes zero (actually, only the voltage ripple is applied, but to simplify the explanation, the ripple will be ignored), so almost no circulating current I _O flows.

The average value (V _P +V _N )/2 of the output voltages V _P and V _N is applied to the load terminal, and the load current I _L is controlled by controlling this average value.

When I ^* _L > I _L , ε ₁ becomes a positive value and is multiplied by K _1. K ₁ ·ε 1 is input to the phase control circuit 60, and −K ₁ ·ε ₁ is input to the phase control circuit ₆₁ . is input. As a result, the output voltages V _P and V _N of each converter increase in the direction of the arrow in Figure 1, and their average value (V _P +
V _N )/2. Therefore, the load current I _L is controlled to increase in the direction of the arrow so that I _L =I ^* _L.

When I ^* _L < I _L , the load current is controlled in the same way.
_IL is always controlled to match its command value I ^* _L . If the load current command value I ^* _L is changed in a sinusoidal manner, the load current I _L will follow it and become a sinusoidal current.

Next, the control operation of the circulating current I _O will be explained.

Circulating current I _O is the output current of positive group converters 5 and 6
It can be determined by performing the following calculation from the detected values of I _P , the output current I _N of the negative group converters 7 and 8, and the load current _IL .

I _O = (I _P + I _N − | I _L |)/2 ... (9) where | I _L | is the absolute value of I _L.

Comparator C ₃ compares the circulating current detection value I _O and its command value I ^* _O , and calculates the deviation ε ₃ = I ^* _O − I _O to the next control compensation circuit 57 (for simplicity, the amplification factor K ₂ times the proportional element). The output signal K ₂ ·ε ₃ of the control compensation circuit 57 is input to the adders A ₁ and A ₂ .
As a result, the phase control circuits PH-P and PH-N
The inputs V〓 _P and V〓 _N are as follows.

V〓 _P = K ₁・ε ₁ +K ₂・ε ₃ ...(10) V〓 _N = −K ₁・ε ₁ +K ₂・ε ₃ ...(11) Therefore, both sides are equal to K ₂・ε ₃ The output voltage of the converter is unbalanced and V _P ≠ V _N .

When I ^* _O > I _O , the deviation ε ₃ = I ^* _O − I _O becomes a positive value, and V _P > V _N. Therefore, the differential voltage V _P −V _N across the secondary side leakage inductances lu, lv, and lw of power transformer 2
is applied to increase the circulating current I _O.

Conversely, when I ^* _O < I _O , ε ₃ becomes a negative value, and V _P < V _N , reducing the circulating current I _O. Eventually, it settles down to I _O = I ^* _O.

Although the output voltages V _P and V _N of both converters change due to this circulating current control, the voltage applied to the load (V _P +V _N )/2 is not affected and the load current control continues as described above. be exposed.

Next, reactive power control at the power receiving end of the cycloconverter device will be explained.

A phase advance capacitor 62 that takes a certain amount of leading reactive power is connected to the power receiving end, and if the lagging reactive power taken by the cycloconverter is controlled to be equal to this leading reactive power, only active power is always supplied from the power supply. I will do it.

First, voltage and current are detected by the transformer 50 and current transformer 51 at the receiving end, and the reactive power calculation circuit 52
Find the reactive power Q at the receiving end by

Comparator C ₂ compares the detected reactive power value Q and its command Q ^* , and inputs the deviation ε ₂ =Q ^* -Q to the control compensation circuit 58 . The control compensation circuit 58 usually uses an integral element and controls the steady-state component of the deviation ε ₂ to zero.

The output I ^* _O of the control compensation circuit 58 becomes the command value of the circulating current _IO . When viewed from the power supply side, the circulating current I _O is not related to active power and always appears as delayed reactive power. Therefore, by controlling the circulating current I _O , the reactive power Q at the receiving end can be controlled.

Normally, the reactive power command value Q ^* at the receiving end is set to zero. Further, here, the reactive power detection value Q will be explained assuming that the delay is a positive value.

When Q ^* > Q, the deviation ε ₂ =Q ^* −Q becomes a positive value, and the circulating current command value I ^* _O is determined via the control compensation circuit 58.
increase. Since the circulating current I _O is controlled to match the command value I ^* _O , the delayed reactive power taken by the cycloconverter increases, causing the delayed reactive power Q at the receiving end to increase.

Conversely, when Q ^* <Q, the deviation ε ₂ takes a negative value, reduces the circulating current I _O =I ^* _O , and reduces the delayed reactive power taken by the cycloconverter. Finally Q=
It becomes Q ^* and calms down.

If the command value Q ^* is set to zero, Q=0, and the fundamental wave power factor at the receiving end can always be kept at 1.

In this way, in the device shown in FIG. 1, the reactive power at the receiving end can be controlled by actively controlling the circulating current I _O.

〔Effect of the invention〕

According to the present invention, as described above, it is possible to provide a circulating cycloconverter device that can be made smaller and lighter.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing an embodiment of the present invention, FIGS. 2 and 3 are partial equivalent circuit diagrams of the device in FIG. 1, FIG. 4 is a waveform diagram of circulating current, and FIG. This is a reactive power control device of the device shown in the figure. 2...Power transformer, 4...Load, 5, 6...
Positive group converter, 7, 8... negative group converter.

Claims (1)

[Claims] 1. In a circulating cycloconverter device that supplies variable voltage and variable frequency power to a load using a power transformer, a positive group converter, and a negative group converter, the output terminals of the positive group converter and negative group converter are connected to the load without going through a DC reactor. A circulating cycloconverter device characterized in that the secondary side leakage inductance of the power transformer is made large enough to suppress pulsations of the circulating current circulating between the positive group converter and the negative group converter to a sufficiently small level.