JPS6380767A - Method for controlling circulating current type cycloconverter - Google Patents

Abstract

PURPOSE:To improve a power factor by feeding a flat circulating current at a rated load current or smaller, and feeding a completely circulating current proportional to the load current up to the maximum load at the time of the maximum overload. CONSTITUTION:A circulating current type cycloconverter is composed of positive and negative converters 2, 3 and a DC reactor 4 with an intermediate tape, which is connected to one phase of an AC motor 5. A controller is composed of a load current controller 7, a circulating current controller 8, and a DC reactor voltage drop compensator 9. A load current command and a detection signal are input to the controller 7, a voltage command signal is output from its deviation, and a voltage command for feeding a circulating current is obtained by the addition 10 of the output of the controller 8 and the output of the compensator 9. Thus, a flat circulating current is fed at rated load current or lower, fed proportionally to the load current from the rated load to the maximum overload, and a completely circulating current is fed at the time of the maximum overload.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a cycloconverter that supplies variable frequency AC power to an AC motor such as an induction machine, and particularly relates to a cycloconverter that supplies variable frequency AC power to an AC motor such as an induction machine, and particularly to a cycloconverter that supplies variable frequency AC power to an AC motor such as an induction machine. The present invention relates to a method for controlling a circulating current type cycloconverter in which a circulating current is caused to flow during the period.

[Conventional technology]

In order to drive an AC motor at variable speed, various studies have been conducted on the application of a circulating current type cycloconverter, which has the advantage of being able to increase the output frequency and causing less torque ripple in the motor.

Although this circulating current type cycloconverter has the above advantages, the power factor of the power supply decreases because all of the circulating current becomes a reactive component, and the circulating current and load current are distributed between the positive and negative side converters. Since the circulating current flows through a shared DC reactor (DCL) inserted in the converter, there is a drawback that the circulating current fluctuates greatly depending on the frequency and magnitude of the load current. (e.g. thyristors) and power transformers must be increased in capacity.

Therefore, conventionally, as a method to compensate for fluctuations in the circulating current due to the influence of the load current,
A compensation method disclosed in a document entitled "Study of Circulating Current Control Method Applying Non-Interference Control Theory" in JP-810 (February 1984) has been proposed. According to the deinterference method shown here, the circulating current can be flat and small,
Additionally, the converter and power transformer capacity can be reduced.

[Problem that the invention seeks to solve]

However, in order to flatten the circulating current through non-interference control, it is necessary to apply a voltage from the converter that compensates for the voltage drop that occurs in the DC reactor due to the load current. The power transformer voltage will be increased, and as a result, the power factor will not be improved.

On the other hand, as a method for eliminating the voltage drop that occurs in a DC reactor, there is a method of flowing a convex complete circulation current in accordance with the AC load current. This method can lower the power transformer voltage compared to the method of flowing a flat circulating current, but
Since the peak value of the convex circulating current is increased according to the load current, there is a drawback that the converter capacity and the power supply converter capacity become large. Figures 2 and 3 show the changes in the converter output voltage (VSCF+) and circulating current (0) with respect to the load current in the conventional method. In case, V
px, Ioz are those for full circulating current; when carrying a flat circulating current, the converter output voltage is at maximum overload current (IL, mouth) as shown in Fig. 2 V P 1
As a result, the voltage of the power transformer must be increased, resulting in a decrease in the power factor of the power supply at rated load. On the other hand, when a complete circulating current is applied, the voltage between the DC reactors becomes almost zero due to the mutual inductance of the DC reactors, and the converter output voltage can be lowered as shown in Figure 2 V p 1, but as shown in Figure 3 Ioz. As a result, a large circulating current will flow, and the power factor of the power supply at rated load will deteriorate.

As described above, the conventional technology does not take into consideration the converter voltage at maximum overload, resulting in a problem that the power factor at rated load decreases.

An object of the present invention is to improve the power factor at rated load.

[Means for solving interlayer points]

The above purpose is to connect a positive side converter and a negative side converter in antiparallel through a DC reactor, and to flow a circulating current between the two converters through the DC reactor to generate variable frequency AC power. In a control method for phase-controlling a circulating current type cycloconverter supplied to a load based on a circulating current command signal, a circulating current detection signal, a load current command signal, and a load current detection signal, when the detected load current value is within a rated value. A DC circulating current is passed through the circuit, a complete circulating current is passed when the detected load current value is an overload value, and a complete circulating current is passed when the detected load current value is in the intermediate region between the rated value and the overload value. This is achieved by changing the size proportionally depending on the amount of load.

[Effect]

According to the present invention, as shown in Figure 3 - dotted chain line 0δ, a flat circulating current flows below the rated load current,
From the rated load to the maximum overload, the circulating current is increased in proportion to the load current, and at the maximum overload, by flowing the complete circulating current, the converter output voltage is as follows: Figure 2 - Dotted chain line V p
The value is as shown in Figure 8, and at maximum overload, it is the same low value as the method that flows a complete circulating current, and the power factor at rated load can be improved compared to the conventional method that flows a flat circulating current. can.

〔Example〕

Next, nine embodiments of the present invention will be described based on the drawings.

FIG. 1 shows the configuration of a circulating current type cycloconverter and its control device.

The positive circulating current type cycloconverter is the positive side converter 2. The negative side converter 3 and the intermediate tap are composed of a DC reactor 4, and the positive side and negative side converters 2 and 3 are connected to a power transformer 1. The positive side converter shown in FIG. 1 shows one phase, and is connected from the center tap of the DC reactor 4 to one phase of the AC motor 5. In FIG. 1, one phase of the AC motor is illustrated as a path with equal eccentricity. Positive side.

The output voltages VP and VN of the negative side converter are varied by a gate pulse signal given from the phase control circuit 6.

The control circuit includes a load current control circuit 7. Circulating current control circuit 8
．． It is composed of a DC reactor voltage drop compensation circuit 9.

Only the load current command i and the detection signal i from the load current detector 14 are input as feedback signals to the load current control circuit 7, and the deviation thereof is amplified to generate the voltage command signal vL necessary to flow the load current. - is output.

On the other hand, the voltage command vo required to cause the circulating current to flow is.

Output of circulating current control circuit 8 and DCL voltage drop compensation circuit 9
A signal obtained by adding the output signals of 1 and 2 in an adder 10 is output as VQ-. Also, the circulating current i.

are the detection signal iP of the output current detector 16 of the positive side converter 2 and the detection signal iN of the output current detector 17 of the negative side converter 3 in the circulating current detection circuit 15.

The following calculation is performed on the detection signal iL of the load current detector 14, and the circulating current io is detected.

1o=-((ip+iN) it, I)
(1) The output signal of the DCL voltage drop compensation circuit 9 is the input signal of the 0-phase control circuit 6, which outputs a signal obtained by differentiating the load current and switching the signal according to the polarity of the load current. The positive side and negative side converter output voltage commands VP* and VN· are created by performing the following calculations on the respective signals ML· and Vo'' by the adder 11.12 and the polarity inverting circuit 13.

VP fist = VLI + VQ Yuki
”'(2) vN*= −VL*+ V
O* ”'(3
) Note that if the ratio of the positive side converter output voltage vp and the negative side converter output voltage vp and vs with respect to vp·, VN fist is K p + K N , then Kp.

Satisfies the KN order relational expression.

KP: KN...(
4) Organizing these relationships, vp, VN and ML・
.

The Vo fist relationship is expressed by the following equation.

2.Kp 2.Kp The above circuit configuration and calculation formula are the same for the conventional method.

Hoshigami Suerin 5th Edition 1 Voltage command volt necessary to flow a circulating current related to the present invention and voltage command vL necessary to flow a load current
If you ask for a fist, it will look like this:

The output voltages of the positive side and negative side converters are Vp and VN, their output currents are ip and iN, the terminal voltage (equivalent to phase voltage) of the AC motor that is the load is ML, and the inside thereof is resistance RM, inductance LM, and reverse. If the voltage equivalent to the electromotive force is e, the load current is iL, and the resistance and self and mutual inductances of the DC reactor are r, L, and M, the voltage equation can be expressed as follows. Regarding the direction of voltage and current, the direction shown in FIG. 1 is assumed to be positive.

vp=(r+pL) ・ip+PM-is+vL −(
7) vN=-pM-ip-(r+pL)・
iN+vt,=(8)vt,=(R+,+p LL
) Soib+eH.=(9) Also, each converter output current ip, is is expressed by the following equation with respect to the polarity of the load current iL.

it, if ≧0 then 1p=it, +io t 1s=io
-(10)it, if <O then 1p=io, 1N=-ib+io -(1
1) Therefore, the following equation is obtained from equations (10) and (11).

IP-x N= I L ip+ is= l it, l + 2・io
(12) Here, by substituting equations (7), (8) and (12) into equations (5) and (6), the following equation is obtained.

Kp @ vt, *= -(VP+VN)=-(r1P(L-M)) ・iL+vb...(13) KP evo fist=-(VP-VN) =-(r+P(L+M)) (lit, l+2・io) ... (14
) From equation (13), the load current i is the load voltage command vL
Controlled by *. As a result, the self and mutual inductance of CL is chosen to be L=M, and −・r−it, (ML
Therefore, Kp-VL*4VL.

On the other hand, the voltage command vo required for the circulating current io to flow is
From equation (14), it is determined by the differential value of the absolute value of the load current iL and the differential value of the circulating current io.

Here, in the present invention, if partial circulation and complete circulation currents as shown in FIGS. 4(b) and (0) are caused to flow, the circulating current io is expressed by the following equation.

, k io= −(It, pl it, l ) +
Ioc - (15) However, It, p: Load current (7) Peak value It,
p=Ji・I oc : A value that allows a flat circulating current to flow: a coefficient depending on the size of the load current IL. Note that k in equation (15) is determined by the following depending on the size of the load current: It shall be changed as follows.

= 0 when rated load current (I Lloo)
...(16) = 1 when IL≧maximum overload current (It, wax)
...(16-2)I bmax>I
When t, > I LIOQ, the following equation is obtained by substituting the equation (15) into the equation (14).

Kp-vo* =-(r + P (L + M)) x (
1-k)X I iLI +rX(-XIt, p+Ioa) -(17)(
17) The first term of the main tube is a signal obtained by multiplying the differential value of the load current iL (AC current) by a coefficient of (1-k), and corresponds to the voltage command of the AC component, and the second term is the magnitude of the load current. This signal corresponds to the DC voltage drop value (that is, the DC component voltage command).

In this first embodiment, in equation (15), k
The values of (16-1) and (16-2).

By changing as shown in equation (16-3), as shown in Figure 3 - dotted line Io8, a flat circulating current flows below the rated load current, and the load current flows from the rated load to the maximum overload. The circulating current will be increased in proportion to the current, and at maximum overload, the complete circulating current will flow. The converter output voltage has a value as shown in Figure 2 - dotted chain line V p s, and at the maximum overload, it becomes the same low value as in the system where full circulation current flows, and the power factor at rated load is lower than the conventional one. It can be improved compared to the method of flowing flat circulating current.

However, in the case of the first embodiment described above, the circulating current i
When o is a flat circulating current as shown in Fig. 4(a), when a convex partial circulating current is passed in Fig. 4(b), and when o is a complete circulating current as shown in Fig. 4(0), It is necessary to smoothly switch between two modes. Further, the circulating current waveform includes an alternating current component as shown in FIGS. 4(b) and 4(Q). The frequency of the convex waveform in the figure is twice the frequency of the load current (i), which is the frequency of the conventional circulating current control system (A
In the CR system, the expected convex circulating current does not flow due to the response delay of the ACR system.When the load current frequency is high, the control circuit output becomes reverse polarity due to the response delay, and in the worst case, the circulating current peaks. The value may be amplified and reach the overcurrent detection level.

Therefore, in order to solve the above problem, the converter voltage required to cause the circulating current to flow is considered by separating it into a DC component and an AC component, and the DC component voltage is supplied from the current control circuit output, and the AC component voltage is supplied to the DC reactor. Circuit 9 that compensates for the voltage drop in
The idea is to provide more. According to this method,
Figure 4(b).

When flowing a circulating current containing an AC component as shown in (c), that is, when flowing an overload current that is higher than the rated current, the DC amount is calculated by adding a signal obtained by multiplying the load current by a predetermined gain to the circulating current io. A command and a feedback signal are created, and the combined signal is input to the circulating current control circuit. On the other hand, the gain of the output of the circuit that compensates for the voltage drop of the DC reactor is lowered according to the amount of overload.6 According to the above method, flat circulation and two-part circulation are performed.

No matter which type of complete circulation current is applied, the input signal to the circulating current control circuit is a direct current component and is unrelated to the frequency of the load current. This means that the response delay of the circulating current control system (ACR system) has no relation to the frequency of the load current, and the above-mentioned problem can be eliminated. In addition, smooth control mode switching is also possible by setting the coefficient k according to the load current as described later and simultaneously varying the gain of the voltage drop compensation circuit 9 for the command of the circulating current control circuit and the feedback amount Dc+. .

That is, in the second embodiment, the AC component voltage command of (17) Daio 1 term is multiplied by the output signal of the voltage drop compensation circuit 9 of the DCL by the coefficient of (1-k) in the correction circuit 20 and output. However, the DC component voltage command in the second term is the circulating current control circuit 8.
The current command and current feedback signal of the current control circuit 8 are supplied to the command correction circuit 18 in order to be supplied as output signals of the current control circuit 8.
．． The feedback correction circuit 19 performs a first-order correction calculation.

Current command value = -・k−It, p+ Ioc ・・
・(18) Current feedback value = 10-・k・1i
1...(19) (18) is when partial circulation and complete circulation current is applied,
It shows the magnitude of the peak value of the circulating current io, which is a direct current amount in a steady state. therefore.

The feedback value shown in equation (19) also becomes a signal indicating the magnitude of the DC amount on a steady basis. I want to do it (18)
By inputting the command and feedback value shown in equation (19) to the current control circuit 8, it is possible to eliminate the frequency component of the load current from the current control system.

As described above, according to this embodiment, the circulating current can be smoothly switched from flat circulation to partial circulation to complete circulation, and the current control circuit is not affected by the frequency of the load current. , a good partial circulation current can flow.

As a result, the converter output voltage can be operated as shown in Figure 2, Vp a, compared to the conventional method.
It can be lowered to 1→Vpδ. This means that the power supply voltage can be selected low. On the other hand, when the circulating current io is below the rated load current, it can be set to a value similar to that of the conventional system Ioz, as shown in FIG. 3 I03. Therefore, in a region within the rated load current, the power supply power factor is improved compared to the conventional system.

〔Effect of the invention〕

As described above, according to the present invention, the power factor of the power supply at rated load can be improved.

[Brief explanation of the drawing]

FIG. 1 is a block diagram explaining the present invention in detail, FIGS. 2 and 3 are diagrams explaining the differences between the present invention and the conventional system, and FIG. 4 is a diagram explaining the operating waveform of the circulating current according to the present invention. , FIG. 5 is an explanatory diagram showing the relationship between load current and coefficient. 2.3... Positive side, negative side converter, 4... DC reactor with intermediate tap, 8... Circulating current control circuit, 9...
...DC reactor voltage drop compensation circuit, 15... Circulating current detection circuit, 18... Circulating current command correction circuit, 19
... Circulating current feedback correction circuit, 20... Voltage drop compensation output gain correction circuit.

Claims (1)

[Claims] 1. A positive side converter and a negative side converter are connected in antiparallel through a DC reactor, and a circulating current is passed between the two converters through the DC reactor to generate a variable frequency. In a control method for controlling the phase of a circulating current type cycloconverter that supplies AC power to a load based on a circulating current command signal, a circulating current detection signal, a load current command signal, and a load current detection signal, the detected load current value is a rated value. A DC circulating current is passed when the load current detection value is within the overload value, a complete circulation current is passed when the load current detection value is an overload value, and when the load current detection value is in the intermediate region between the rated value and the overload value. is a method of controlling a circulating current cycloconverter, which is characterized by changing the magnitude of the circulating current proportionally according to the amount of load. 2. In the control method according to claim 1, when the detected load current value exceeds the rated value, the circulating current control signal includes a DC reactor voltage drop with a gain that decreases as the load current increases. A control method for a circulating current type cycloconverter characterized by adding a compensation signal.