JPH011476A - Control device for circulating current control type cycloconverter - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed Description of the Invention] [Object of the Invention] (Field of Industrial Application) The present invention relates to a circulating current control type cycloconverter that controls current through a current control circuit so that the load current matches a load current command. Regarding a control device.

(Prior Art) A cycloconverter is a power conversion device that directly converts alternating current power of a constant frequency to alternating current power of another frequency, and
For example, it is used as a frequency converter to convert commercial frequency AC power of 50 Hz or 60 Hz to AC output of another frequency, and as a variable frequency/variable voltage AC power source for driving an AC variable speed motor. There is. Since the cycloconverter uses the voltage of the AC power source to perform commutation of a controlled rectifying element such as a cycloconverter, it has advantages such as high reliability and easy dualization.

On the other hand, the cycloconverter takes a large amount of reactive power from the power supply, and the reactive power always fluctuates in synchronization with the frequency on the negative A::r side. For this reason,
There have been problems such as increasing the capacity of the power supply system equipment and causing fluctuations in the power supply voltage, which can have various negative effects on electrical equipment connected to the same system.

In order to solve these problems, a reactive power compensation type cycloconverter device has been proposed.

This device actively utilizes the circulating current of the cycloconverter, which circulates between the positive side converter and the negative side converter, regardless of the load. By controlling the circulating current of the cyclo-converter so that the electric power and the delayed reactive power taken by the cyclo-converter are exactly equal, the fundamental wave power factor at the receiving end is always maintained at 1'-1, thereby reducing the negative impact on the power supply system. It was made so that it could be eliminated.

In that case, the leading reactive current component Ic of the phase advancing capacitor and the lagging reactive current 1r of the cycloconverter satisfy the following relationship.

Ic-1r -*Ka (Ih+Io) ・5inap+Ka
lo II sinαn -Ka (Ih+Io) ・5incrp+Ka
-1o -5in (180° -a p) -Ka
(lh+2・Io)s in αp... (1) Here, Ih: Load current IO = Circulating current αp: City side ignition control angle αn: Negative side ignition control angle The magnitude of the load current in equation (1) and firing control angle αp
, αn change moment by moment. For example, reactive power control when the magnitude of the load current 1h changes will be explained as follows.

When the load current 1h decreases and the delayed reactive current 1r of the cycloconverter decreases, Ic,>Ir, and the reactive power Q at the receiving end advances, but the circulating current IO increases to satisfy equation (1). do. the result,
The circulating current IO- is controlled so that the delayed reactive current 1r increases and finally becomes Ir-1c.

Conversely, when the load current 1h increases and the delayed reactive current 1'r of the cycloconverter increases, Ic<Ir, and the reactive power Q at the receiving end becomes delayed, but as above, formula (1) is satisfied. Circulating current for! 0 decreases. As a result, the delayed reactive current I' decreases, and the circulating current 0 is controlled so that it ultimately becomes Ir-1c.

Therefore, since the circulating current IO is negative and is influenced by the f current 1h, when reactive power control is performed as described above,
The circulating current 1o flows intermittently when its value becomes small.

As a result, since the output voltage of the cycloconverter is low during the intermittent period of the circulating current 1o, a problem arises in that the load current 1h no longer follows the command value 1h.

FIG. 3 shows a conventional circulating current control type cycloconverter and its control device. Here, from a cycloconverter 2 consisting of a positive side converter 2P and a negative side converter 2N to a current limiting reactor 3R and a current limiting reactor 3.
A device for supplying alternating current power to a load 4 via S is shown. The positive side converter 2P and the negative side converter 2N are supplied with constant frequency AC power from the power system 5 via a power supply transformer 2=6.

The cycloconverter 2 is current controlled according to a reference value of the load current 1h, that is, a load current command 1h, and a reference value of the circulating current io circulating between the positive side converter 2P and the negative side converter 2N, that is, the circulating current command 1o''. .Each output current 1p, I of both positive and negative converters 2P, 2N
n is detected by the current detector 10P and the current detector 1ON, respectively, and the adder 11 changes the load current 1h to Ih.
-1p-In -(2). Similarly, the adder 12 calculates the current It as It=Ip+In ・++ (
3).

The difference between the load current command 1h and the load current 1h obtained by the adder 11, that is, the load current deviation ΔIh, is obtained by the adder 20, and this is input to the current 1;j control circuit 2] to calculate the negative 6:j. A current control signal sh is obtained that makes the current deviation ΔIh zero.

On the other hand, by passing the negative 61f current Ih obtained by the adder 11 through the absolute value circuit 13, the absolute value of the load current I
ll is added to the current It by the adder 12.
is subtracted from by an adder 14, and further subtracted by an operational amplifier 15
Multiply by 1/2 to obtain the circulating current 1o. That is, 1o=(Ip+In-11hl)/2...(4). The difference between the circulating current command io and the actual circulating current Io, that is, the circulating current deviation ΔIo, is determined by the adder 16 as i′4, and the second current control circuit 17 outputs the second current control signal So so as to set it to zero. obtain.

Adder 22 adds a signal of the sum of both current control signals sh and So.
to form a positive side control signal Sp, which controls the positive side converter 2P via the positive side phase control circuit 25P. Similarly, a signal obtained by inverting the current control signal sh by the inverting amplifier 23 and the current control signal SO is obtained by the adder 24 to form the negative side control signal Sn, and is outputted via the negative side phase control circuit 25N. Controls negative side converter 2N.

Next, the control operation of the apparatus shown in FIG. 3 will be explained.

First, load 7+i flow control will be described. The output voltage Vp of the positive side converter 2P and the output voltage Vn of the negative side converter 2N are determined by using Kv as a coefficient and Vs as the maximum voltage value, respectively.
v @Vs @c o s an-Kv-Vs ・co
s (π-αp)...(6) Normal operation is performed in a state where both mold pressures are balanced at the negative 41 terminal. When the load current command 1h is changed sinusoidally, the negative 6:f current deviation Δ1 changes accordingly.
h also changes, causing a sinusoidal load current to load 4! αp in equations (5) and (6) so that h flows.

An or controlled. In this normal operation, the output voltage Vp of the 11- side converter 2P and the output voltage Vn of the negative side converter 2N are in a balanced state, so the circulating type i+! 'E I
Almost no O flows.

Next, circulating current control will be described.

The adder 22 adds the current control signal So output from the current control circuit 17 to the current control signal sh output from the current control circuit 21, resulting in a positive phase control circuit 25P and a negative phase control circuit 25N. The control signals Sp and Sn are input manually.

Current control circuit 17. The amplification factor of the current control circuit 21 is Kw,
Kx is as follows.

S p = Kw - Δ I h 1 K X ・ Δ
Io−(7)S n = −K w ・ΔIh+KX・
ΔIo=・(8) Here, if the relationship αn=π−αp breaks down, the positive side condenser 11− proportional to K x・Δlo
An unbalance occurs between the output voltage Vp of the converter 2P and the output voltage Vn of the negative converter 2N. Due to the voltage difference, a circulating current io flows through the current limiting reactor 3R and the current limiting reactor 3S. This circulating current 1o is the circulating current command 1
Based on o, add W depending on whether it is larger or smaller than it.
The circulating current deviation ΔIo, which is the output of the device 1b, occurs in a negative or positive direction, and the differential voltage is controlled so as to reduce it.

In this way, as a result, the circulating current Io is controlled to be equal to the circulating current command 1o.

FIG. 4 shows an equivalent circuit for one phase of a circulating current control type cycloconverter. In the figure, Vp is the output voltage of the W-side converter 2P, vn is the output voltage of the negative-side r inverter 2N, p is the output current of the positive-side converter 2P, and In
is the output current of the negative converter 2N, Ih is the load current flowing to the negative Q4, vh is the load terminal voltage, Rh is the negative A::r
4 resistance, Lh is the inductance of load 4, Rr is the resistance of current limiting reactors 3R and 3S, Lr is current limiting reactor 3
R.

Self-inductance of 3S, M is current limiting reactor 3R,
It represents the mutual inductance of 3S.

When the voltage and current are taken in the directions shown, the following equation holds true regarding the voltage, with the differential operator p being p.

Vp-(Rr+Lr-p)Ip +M-p ・In+Vh -('))Vn--M-
p-1p+Vh -(Rr +L r fist p) I n-
(10) Vd-(Rh+Lh-p)l h...(
11) Furthermore, when the circulating current is Io, the following equation holds true regarding the current.

lp-In-Ih-(12)rp+I
n-2・Io+I Ih1= (+3) where, (9)
By finding equation + equation (10), equation (9) - equation (10), and considering the relationship between equation (12) and equation (13), the following equation is obtained.

Vp+Vn= IRr+ (Lr-M)pl Ih+
2・vh...(14) Vp-Vn= iRr+u, r+M)pi×(2・10
・1lhl) ... (15) Equations (14) and (15) represent the three electric equations of the load current control system and circulating current control system, respectively.

Obtaining the load terminal voltage Vha from equation (14), (1G
) formula is obtained.

Vha-(Vp+Vn)/2-(Rr/2)Ib-I(Lr-M)p/21Ih...(
+6) In the circulating current control type cycloconverter, since the self-inductance Lr and the rlJ mutual inductance M of the current-limiting reactors 3R and 3S have the same value, (the third term on the right side of equation 1(i) becomes zero. Therefore, Negative 6: The f terminal voltage vh is expressed by equation (17).

Vha = (Vp + Vn) / 2-
(Rr/2)Ih (17) Here, the output voltage Vp of the positive converter 2P and the output voltage Vn of the negative converter 2N are equal to the .multidot.14 average voltage.

(Problems to be Solved by the Invention) The circulating current control type cycloconverter operated in the control manner described in 1-1 above has the following problems.

When the circulating current 1o is interrupted and, for example, only the positive side converter 2P supplies the load current th, the load terminal voltage V klb
is obtained from equation (16) as follows.

Vhb-Vp-(Rr+Lr p)Ih... (18) When this formula (18) is established, the positive side converter 2P operates as a simple controlled rectifier, and becomes a voltage equation of a simple controlled rectifier. Comparing equations (17) and (18), equation (18) shows that the load terminal voltage vh drops when the interruption occurs, and as a result, the load current control gain drops by the difference in the second term on the right side. Negative 6: J electric IMI h or its command value 1h* is no longer followed.

This differential voltage ΔVh-Vhb-Vha is expressed by equation (19) assuming that the resistance Rr of the reactor is sufficiently small.

ΔVh-L r ・p-1h = l19) The present invention was made in consideration of the following circumstances, and it controls the load current so as to follow the command value even in the intermittent region of the circulating current. It is an object of the present invention to provide a control device for a circulating current control type zychroconverter.

[Structure of the invention]

(Means for Solving the Problems) A control device for a circulating current control type cycloconverter according to the present invention detects the period of interruption when the circulating current is interrupted, and outputs the output of the differential calculation circuit that receives the load current as input. Only during the interruption period, it is added to the output control signal obtained by the load current control section, so that the load current follows the command value.

(Function) According to the configuration described in 1-1, during the period of interruption of the circulating current, the differential voltage Δvh in equation (19) is compensated by hli by the fc proportional to the change in the load current, and the period of interruption of the circulating current is The load terminal voltage is maintained at a predetermined value even during the middle of the cycle, thereby making it possible to cause the load current to follow the command value.

(Example) FIG. 1 shows an embodiment of the present invention.

Here, the same number 71 is used for the same components as in FIG. 3. A feature of this embodiment is that a correction circuit 30 is inserted on the output side of the current control circuit 21. This correction circuit 30 uses the output control signal s of the current control circuit 21.
an adder 31 that adds the t+li iE signal ΔS according to the present invention to and a differentiation circuit 34 that differentiates the negative Gf current 1h and sends it to the analog switch 32.

The differentiating circuit 34 inputs the load voltages -1tf and Ih, and outputs a signal corresponding to the differential molecule iJhp. As shown in FIG.
A "1" signal is output only during the period when c-) is zero, and the analog switch 32 is turned on. In the case of FIG. 2, the zero current period of the circulating current 1 oa is zero, and no "1" signal is output. The zero current period of Job is Tb,
A "1" signal is output only during this Tb period.

Similarly, the zero current period of Ioc is Tc, and this Tc
Outputs a “1” signal only for a period.

When the analog switch 32 is turned on by the “1” signal output from the off-period detection circuit 33, the correction signal ΔS output from the differentiator circuit 34 controls the output of the current control circuit 21 via the adder 31. It is added to the signal sh. Therefore, if the magnitude of the correction No. 1i ΔS is set to correspond to the differential voltage Δvh shown in equation (19), the differential voltage ΔV Il can be set to 0 even during the zero period of the circulating current lo.

In this case, the voltage h ° culm equation is Vhb-Vp-(Rr+L ・p)I h+L-p ・I
h...(20). In equation (20), the third term on the right side is the voltage component Δvh compensated by the correction signal ΔS.

In equation (20), if the resistance R'' of the reactor is made sufficiently small, equation (20) can be expressed as follows.

vhb-vp ・ (21) Similarly, the continuous voltage equation of the circulating current 1o, i.e. (17)
If we set Rr-0 in the formula, Vha - (Vp+Vn
)/2 −<22).

Output voltage vhb of equation (21) and output voltage V of equation (22)
It becomes equal to ha.

In this way, even when the circulating current 1o is intermittent, the load terminal voltage can be made to follow the command value as in the continuous region, and thereby the load current can be made to follow the command value.

In the above explanation, for convenience, the resistance R of the current limiting reactor has been treated as being sufficiently small, but the differentiating circuit 3
If the configuration is configured so that the resistance R is taken into account in the calculation in step 4, then
It is possible to perform more accurate compensation.

〔Effect of the invention〕

As described above, the present invention provides that during the interruption period of the circulating current,
By compensating for the voltage difference due to the resistance and self-inductance of the current limiting reactor, the load current can be made to follow its command value more faithfully.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing an embodiment of the present invention, FIG. 2 is a time chart for explaining the operation of the OFF period detection circuit in the device shown in FIG. 1, and FIG. 3 is a conventional circulating current control type cyclotron. FIG. 4, which is a block diagram of the converter control device, is an equivalent circuit for one phase of the cycloconverter in the device shown in FIG. 2... Cyclo converter, 2P... Positive side converter, 2N... Negative side converter, 3R, 3S... Current limiting reactor, 4... Load, 6... Power transformer, 17
．． 21... Current control circuit, 30... Correction circuit, 31
...Adder, 32...Analog switch, 33...
- Off period detection circuit, 34...differentiation circuit.

Claims (1)

[Claims] A control device for a circulating current control type cycloconverter that controls current via a current control circuit so that the load current matches a load current command includes a differentiating circuit that differentiates a load current detection signal and an off-current period of the converter circulating current. and means for adding the output of the differentiating circuit to the output signal of the current control circuit when the off-current period detection circuit detects the off-current period of the converter circulating current. A control device for a circulating current control type cycloconverter, characterized by: