JP7198578B2 - rolling system - Google Patents

Description

The present invention relates to a control device for a rolling system and a rolling system.

As a background art of this technical field, the abstract of Patent Document 1 below describes "Providing a converter that maintains stable operation and reduces loss of switching elements against fluctuations in power supply voltage and load" and "PWM The modulation rate of the modulated wave that generates the signal and the carrier wave are fixed, and the power factor control and the constant voltage control of the DC voltage are performed.Regarding the power factor 1 control, the modulated wave is adjusted so that the AC current and the power supply voltage are in phase. Adjust the phase.Regarding the control of the DC voltage, it is adjusted by changing the magnitude of the dead time."

JP-A-11-299245

The converter that realizes the control of the power factor of 1.0 described above is also applied as a variable speed drive device to drive a motor for a rolling mill. Ancillary equipment such as pumps and fans are also provided around the rolling mill. Many of these incidental facilities are motor loads, and are often driven by on/off control at a constant rotational speed, with a steady power factor of about 0.5 to 0.8. The entire system of the rolling system is a complex combination of variable speed drives with a power factor of 1.0 and various incidental equipment. In order to reduce the reactive power of the entire system, reactive power compensators, power factor correction capacitors, etc. have been applied.
However, the operating conditions of the rolling system and ancillary facilities change from moment to moment, and depending on the operating conditions and the selection of the power factor correction device, deviations from the strict target power factor may occur. Therefore, it has been difficult to continuously achieve the target power factor (for example, 1.0, 0.995, etc.) throughout the system. In addition, in order to achieve a strict target power factor in recent years only with a reactive power compensator, it was necessary to select a detailed capacity, and it was necessary to select a combination of reactive power compensators with various capacities. Furthermore, installing a dedicated reactive power compensator raises a problem of increasing installation cost and securing installation space. Moreover, it was difficult to achieve highly accurate power factor correction only with power factor correction capacitors.
SUMMARY OF THE INVENTION It is an object of the present invention to provide a rolling system capable of realizing highly accurate power factor compensation at a low cost.

In order to solve the above problems, the rolling system of the present invention includes a rolling mill drive motor, rolling mill incidental equipment including at least a pump and a fan, and a circuit breaker connected to the secondary winding of a transformer. A measurement unit that is attached to a connected electric circuit and measures electric circuit power factor information for specifying the power factor in the electric circuit; A variable speed drive device that converts and outputs to another frequency, and a control unit that controls the variable speed drive device, and the control unit controls the variable speed drive device based on the power factor information It is possible to output a command value for generating reactive power, and whether the power factor in the electric circuit is a leading power factor or a lagging power factor, the current vector in the secondary winding is the current with the target power factor. It is characterized by being close to the vector .

ADVANTAGE OF THE INVENTION According to this invention, although it is cheap, highly accurate power factor compensation can be implement|achieved.

1 is a power system diagram of a rolling system according to an embodiment of the present invention; FIG. It is a block diagram of a control part. FIG. 5 is a vector diagram in a comparative example; 4 is a vector diagram according to the present embodiment; FIG. FIG. 4 is another vector diagram according to the present embodiment;

<Configuration of Embodiment>
FIG. 1 is a power system diagram of a rolling system 1 according to one embodiment of the present invention.
The rolling system 1 includes a transformer 22, a circuit breaker 24, an instrument transformer 26, an instrument current transformer 28, a measuring section 30, a power factor improving capacitor 32, and a control section 40 (rolling system control device) and an in-facility electric circuit 50 . Furthermore, the rolling system 1 includes M (M is plural) circuit breakers 52-1 to 52-M (hereinafter sometimes collectively referred to as circuit breakers 52) and the same number of transformers 58-1 to 58-M. (the same, transformer 58), the same number of converters 60-1 to 60-M (the same, converter 60), the same number of inverters 62-1 to 62-M (the same, inverter 62), and the same number of circuit breakers 64 -1 to 64-M (same as circuit breaker 64) and the same number of rolling mill drive motors 66-1 to 66-M (same as motor 66). Furthermore, the rolling system 1 includes multiple circuit breakers 51 , multiple transformers 55 , and multiple distribution systems 57 . Motors 66-1 to 66-M for driving rolling mills are for driving rolling mills (not shown).

The transformer 22 has a primary winding 22a connected to the power receiving system 20, steps down the voltage received from the power receiving system 20, and outputs the voltage from the secondary winding 22b. The circuit breaker 24 is connected between the secondary winding 22b and the in-facility electric circuit 50, and is turned off to protect the rolling system 1 when a predetermined overcurrent flows. Potential transformer 26 measures the output voltage of secondary winding 22b, and potential current transformer 28 measures the output current from secondary winding 22b. The measurement unit 30 measures the reactive current, reactive power and power factor in the secondary winding 22b based on the measurement results of the instrument transformer 26 and the instrument current transformer 28, and transmits the measurement results to the control unit 40. supply. These pieces of information are all pieces of information that can specify the power factor in the in-facility electric circuit 50, so these pieces of information may also be referred to as "electric line power factor information".

The transformer 58 converts the voltage of the in-facility electric circuit 50 into a voltage suitable for the converter 60 . The converter 60 converts the supplied AC voltage into a DC voltage. The inverter 62 PWM (Pulse Width Modulation)-modulates the supplied DC voltage and supplies it to the motor 66 . Thereby, the motor 66 can be driven at a desired rotational speed. Therefore, these converters 60 and inverters 62 function as "variable speed drives" for the corresponding motors 66, respectively. When a predetermined overcurrent flows, the circuit breaker 52 is turned off to protect the corresponding transformer 58 and the like. Also, the circuit breaker 64 turns on/off the connection between the corresponding inverter 62 and the motor 66 .

In addition, the in-facility electric circuit 50 is connected to a plurality of power distribution systems 57 via a plurality of circuit breakers 51 and transformers 55, respectively. Although the details of the power distribution system 57 are omitted from the drawing, each power distribution system 57 includes ancillary equipment such as pumps and fans, lighting equipment, air conditioning equipment, and the like. Devices included in these incidental facilities have many inductive loads, and in the plurality of distribution systems 57, the overall steady power factor is about 0.5 to 0.8. Therefore, the power factor improving capacitor 32 is connected to the in-facility electric circuit 50 to bring the power factor in the in-facility electric circuit 50 closer to 1.0.

FIG. 2 is a block diagram of the control unit 40. As shown in FIG.
The control unit 40 includes general computer hardware such as a CPU (Central Processing Unit), a DSP (Digital Signal Processor), a RAM (Random Access Memory), and a ROM (Read Only Memory). , control programs executed by the CPU, microprograms executed by the DSP, various data, and the like are stored. In FIG. 2, the inside of the control unit 40 shows functions implemented by control programs, microprograms, etc. as blocks.

In FIG. 2, the control unit 40 receives a reactive power signal Pq, which is the measurement result of reactive power, from the measuring unit 30 (see FIG. 1) via the receiving terminal 43 . Filter 41 attenuates the high frequency component of reactive power signal Pq and outputs the result as reactive power signal Pqave. A subtractor 42 subtracts the reactive power signal Pqave from a predetermined reactive power target value Pqtg and outputs the result as a total reactive power calculated value Pq*. Here, the reactive power target value Pqtg is zero, for example.

Distribution ratio output units 44-1 to 44-M respectively output distribution ratios A1 to AM for distributing total reactive power calculated value Pq* to converters 60-1 to 60-M. Here, if the reactive power that can be generated in a certain converter 60-k (1≤k≤M) is defined as reactive power generation capacity Ppk (that is, Pp1 to PpM), the distribution ratio Ak is "Ak=Ppk/(Pp1+Pp2+... +PpM)”. Reactive power generation capacity Ppk is a constant according to the capability of converter 60-k in this embodiment.

The reactive power calculators 46-1 to 46-M multiply the total reactive power calculated value Pq* by the corresponding distribution ratios A1 to AM, respectively, and output the multiplication results as reactive power calculated values Pq01* to Pq0M*. do. The command value generators 48-1 to 48-M correct the calculated reactive power values Pq01* to Pq0M*, and output the results as reactive power command values Pq1* to PqM*. Correction processing in the command value generators 48-1 to 48-M includes dead zone processing and limit processing, which will be described below.

Here, the dead zone process is a process of setting the reactive power command value Pqk* to zero when the calculated reactive power value Pq0k* (where 1≤k≤M) is within a predetermined range including zero. . This is because when the reactive power calculated value Pq0k* is sufficiently small, the reactive power signal Pqave of the entire rolling system 1 is also small, so the reactive power compensation is stopped and priority is given to the operating efficiency of the converter 60-k. be.

Further, the limit processing means that when the calculated reactive power value Pq0k* exceeds the reactive power generation capacity (reactive power that can be generated) of converter 60-k, reactive power command value Pqk* is set to the reactive power command value Pqk* in converter 60-k. This is a process of limiting to a value equal to or less than the power generation capacity. As a result, the generated reactive power can be set to a value equal to or less than the respective reactive power generation capacities for all converters 60-k. Each of converters 60-1 to 60-M generates reactive power based on supplied reactive power command values Pq1* to PqM*. This compensates for the reactive power of the entire rolling system 1 .

<Comparative example>
Here, a comparative example of this embodiment will be described. This comparative example does not include the control unit 40 shown in FIG. Each converter 60 independently controls reactive power so that its power factor approaches 1.0.
FIG. 3 is a vector diagram in this comparative example. The illustrated current vectors I1, Ih, and Ix are all current vectors in the secondary winding 22b of the transformer 22. FIG. First, the current vector I1 is a current vector of a target power factor (for example, 1.0, 0.995, etc.).

A current vector Ix is a current vector at a steady power factor that flows through the plurality of power distribution systems 57 via the plurality of circuit breakers 51 . As described above, the power distribution system 57 includes ancillary equipment such as pumps and fans. A current vector Ic is a current vector generated by the power factor correction capacitor 32 . A current vector Ih is a current vector resulting from the power factor being improved by the current vector Ic.

In order to set the power factor of the entire rolling system 1 to 1.0, it is preferable to set the current vector Ic so that the current vector I1 and the current vector Ih match. That is, it is preferable to set the capacity of the power factor correction capacitor 32 so as to realize such a current vector Ic. However, depending on the overall operating state of the rolling system 1, the operating conditions of the incidental equipment such as pumps and fans also fluctuate from moment to moment, and the current vector Ix fluctuates. Therefore, even if the steady-state power factor of the current vector Ih is set to the target power factor, a leading phase or a lagging phase occurs momentarily, and the current vector Ih includes a reactive current component Ihx as shown in the figure. become.
Thus, if the power factor improvement of the rolling system 1 is performed only by the power factor correction capacitor 32, the power factor tends to deviate from 1.0, and it becomes difficult to achieve the preset power factor target.

<Operation of Embodiment>
FIG. 4 is a vector diagram in this embodiment.
The meanings of the current vectors I1, Ix, Ic and Ih are the same as in FIG. The current vector Iv1 is a leading-phase current vector, and the current vector Iv2 is a lagging-phase current vector. These current vectors Iv1 and Iv2 represent the range of current vectors that can be generated by control unit 40 and converter 60. FIG. As a result, the phase that could not be compensated by the current vector Ic by the power factor correction capacitor 32 can be compensated by the control unit 40 and the converter 60, and the current vector Ih can be set to the target power factor (for example, 1.0 or 0.995). etc.) can be brought close to the current vector I1.

Further, according to the present embodiment, the converter 60 can generate the current vector Iv2 or the like of the lagging power factor. Therefore, regardless of whether the power factor in the in-facility electric circuit 50 is the leading power factor or the lagging power factor, the control unit 40 can bring the current vector Ih close to the current vector I1 of the target power factor.

FIG. 5 is another vector diagram in this embodiment, showing an operating state when the operation of the power factor improving capacitor 32 is stopped.
In FIG. 5, current vectors I1, Ix, Ih, Iv1 and Iv2 have the same meanings as in FIG. Also, since the operation of the power factor correction capacitor 32 is stopped, the current vector Ic (see FIG. 4) is not shown. In this example, power factor control of converter 60 allows current vector Ih to approach current vector I1 of the target power factor.

<Effect of the embodiment>
As described above, the rolling system control device (40) according to the present embodiment includes the receiving terminal (43) for receiving the electric circuit power factor information from the measuring unit (30), and the variable speed drive device based on the electric circuit power factor information. command value generators (48-1 to 48-M) for outputting command values (Pq1* to PqM*) for generating reactive power with a leading power factor or a lagging power factor with respect to (60, 62); .
By generating reactive power with a leading power factor or a lagging power factor for the variable speed drive device (60, 62) based on the electric circuit power factor information, inexpensive and highly accurate power factor compensation can be realized.

Also, the command value generators (48-1 to 48-M) output command values (Pq1* to PqM*) so as to set the power factor in the electric circuit (50) within a predetermined range.
Thereby, the power factor in the electric circuit (50) can be set within a predetermined range.

A plurality of variable speed drive devices (60, 62) are provided in the rolling system (1), and the rolling system controller (40) controls the reactive power generation capacity (Ppk ) further has a distribution ratio output unit (44-1 to 44-M) that outputs a distribution ratio (A1 to AM) according to the distribution ratio ( A1 to AM), command values (Pq1* to PqM*) are output for each variable speed drive device (60, 62).
Thereby, the command values (Pq1* to PqM*) can be generated according to the reactive power generation capacity (Ppk) of each variable speed drive device (60, 62).

Further, the rolling system controller (40) outputs reactive power calculated values (Pq01* to Pq0M*) corresponding to the variable speed drive devices (60, 62) according to the distribution ratios (A1 to AM). The power calculation units (46-1 to 46-M) are further provided, and the command value generation units (48-1 to 48-M) are configured such that the corresponding reactive power calculation values (Pq01* to Pq0M*) are predetermined values including zero. If the value is within the range, set the command value (Pq1* to PqM*) to zero.
Thereby, when the generated reactive power is small, the compensation of the reactive power is stopped, and the efficiency of the variable speed drive device (60, 62) can be improved.

[Modification]
The present invention is not limited to the embodiments described above, and various modifications are possible. The above-described embodiments are illustrated for easy understanding of the present invention, and are not necessarily limited to those having all the described configurations. Further, other configurations may be added to the configurations of the above embodiments, and part of the configurations may be replaced with other configurations. Also, the control lines and information lines shown in the drawings are those considered to be necessary for explanation, and do not necessarily show all the control lines and information lines necessary on the product. In practice, it may be considered that almost all configurations are interconnected. Possible modifications to the above embodiment are, for example, the following.

(1) In the above embodiment, the control unit 40 receives the reactive power signal Pq from the measuring unit 30, but instead of the reactive power signal Pq, other electrical circuit power factor information (for example, reactive current, power factor, etc.) Reactive power command values Pq1* to PqM* may be generated based on these.

(2) In the control unit 40 of the above embodiment, the command value generators 48-1 to 48-M output reactive power command values Pq1* to PqM* to the converters 60-1 to 60-M. However, instead of this, a command value of reactive current to be generated by each of converters 60-1 to 60-M may be output. Needless to say, commanding reactive current to converters 60-1 to 60-M is equivalent to commanding reactive power.

(3) In the above embodiment, reactive power generation capacity Ppk was a constant corresponding to the capability of converter 60-k. However, reactive power generation capacity Ppk may be varied according to the operating state of converter 60-k. For example, in the converter 60-k, the smaller the active power supplied from the in-facility electric circuit 50 (the power output to the corresponding inverter 62-k), the more power the converter 60-k has. The reactive power generation capacity Ppk may be increased.

(4) In the above embodiment, an example in which the present invention is applied to the rolling system 1 has been described, but the present invention is applicable not only to the rolling system 1, but also to various electric power facilities, factory facilities, railway vehicles, ships, and the like. You may That is, the control unit 40 generally includes a “measurement unit that is attached to an electric circuit and measures electric circuit power factor information for specifying the power factor in the electric circuit, and a converter that converts the AC voltage input from the electric circuit. a converter for outputting, a receiving terminal for receiving the electric circuit power factor information from the measuring unit; and a leading power factor or a lagging power factor for the converter based on the electric circuit power factor information. and a command value generator that outputs a command value for generating reactive power.

1 rolling system 30 measuring unit 40 control unit (control device for rolling system)
43 Receiving terminals 44-1 to 44-M Distribution ratio output units 46-1 to 46-M Reactive power calculation units 48-1 to 48-M Command value generation unit 50 In-equipment electric circuit (electric circuit)
60-1 to 60-M converter (variable speed drive)
62-1 to 62-M inverter (variable speed drive device)
66-1 to 66-M Motor A1 to AM Distribution ratio Ppk Reactive power generation capacity Pq01* to Pq0M* Reactive power calculation value Pq1* to PqM* Reactive power command value

Claims (7)

A motor for driving a rolling mill, ancillary equipment of the rolling mill including at least a pump and a fan, and a circuit breaker connected to the secondary winding of a transformer are connected to an electric circuit to reduce the power factor in the electric circuit. a measurement unit that measures electric circuit power factor information for identification;
a variable-speed drive device that converts the frequency of the AC voltage input from the electric circuit into another frequency and outputs it to drive the motor for driving the rolling mill;
a control unit that controls the variable speed drive device,
The control unit
capable of outputting a command value for generating reactive power to the variable speed drive device based on the electric circuit power factor information;
Regardless of whether the power factor in the electric circuit is a leading power factor or a lagging power factor, the current vector in the secondary winding is brought close to the current vector of the target power factor.
A rolling system characterized by: further comprising a power factor correction capacitor connected to the electrical circuit;
2. The rolling system according to claim 1, wherein the control section causes the variable speed drive device to compensate for a phase that could not be compensated by the power factor improving capacitor. The rolling system according to claim 1, wherein the control section outputs a command value for generating reactive power to the variable speed drive device without using a power factor improving capacitor. The power factor improving capacitor can stop operating, and the control section controls the power factor in the electric circuit to the variable speed drive device even when the power factor improving capacitor stops operating. 4. The rolling system according to claim 3, further comprising a function of approximating a predetermined target power factor. The control unit
The rolling system according to claim 1, further comprising a command value generator that outputs a command value so as to set the power factor in the electric circuit within a predetermined range. A plurality of the variable speed drive devices are provided,
further comprising a distribution ratio output unit for outputting a distribution ratio according to the reactive power generation capacity in each variable speed drive device;
6. The rolling system according to claim 5, wherein the command value generator outputs the command value for each variable speed drive device according to the distribution ratio. further comprising a reactive power calculation unit that outputs a reactive power calculation value corresponding to the variable speed drive device according to the distribution ratio;
The rolling system according to claim 6, wherein the command value generator sets the command value to zero when the corresponding reactive power calculated value is a value within a predetermined range including zero.

Images