JP2014003746A - Control device for drive system - Google Patents

Abstract

Provided is a control device for a drive system in which driving efficiency is improved by making a DC output voltage supplied from a converter device to an inverter device variable according to a rotation speed of an electric motor driven by the output of the inverter device. To do.
A drive for converting AC power into variable voltage DC power by a converter device, and inversely converting the DC power to AC power having a variable voltage and variable frequency by an inverter device, and driving an electric motor by the output. A variable voltage command device 44 that outputs a DC voltage command value for generating a DC output voltage of the converter device 14 corresponding to the rotational speed of the electric motor 13 is provided. Further, the current efficiency calculation value calculated by the overall system efficiency calculation circuit 42 is compared with the previous efficiency calculation value, and the DC voltage command value to the converter device 14 is set so as to maximize the overall system efficiency according to the comparison result. An efficiency comparison circuit 43 that provides a correction command value is provided.
[Selection] Figure 4

Description

  The present invention relates to an inverter device for controlling an electric motor used in a paper machine and the like, and a drive system control device using a converter device for supplying DC power to the inverter device.

  Drive systems using an inverter device that controls an electric motor and a converter device that supplies DC power to the inverter device are widely used in various industrial fields (for example, see Patent Document 1). This drive system converts AC power supplied from an AC power source into DC power by a converter device, supplies this DC power to an inverter device, and controls the rotational speed and output of the motor by variable voltage variable frequency control by the inverter device. Torque etc. are controlled.

JP 2010-259227 A

  A paper machine drive system is known as such a drive system. In a paper machine drive system, the rotation speed, output torque, and the like of an electric motor that drives a paper machine roll are controlled by a variable voltage variable frequency output from an inverter device. In this case, the system is designed so that the operating efficiency of the drive system is optimized at the maximum paper production speed (design paper production speed) that can be produced by the paper machine. That is, the DC output voltage of the converter device in the drive system is controlled to a constant value in accordance with the operation at the maximum paper making speed (design paper making speed).

  By the way, a paper machine is usually used not only to produce one type of paper but also to produce a plurality of types of paper. In this case, since the paper making speed varies depending on the paper type, the actual operation speed of the electric motor varies depending on the paper type. However, the DC output voltage of the converter device in the drive system is controlled to a constant value according to the operation at the maximum papermaking speed (design papermaking speed), so it is difficult to operate in the optimum state in terms of operating efficiency. Met.

  In other words, the paper machine drive system is optimally designed to match the maximum paper making speed (design paper making speed) of the paper machine, and the DC output voltage of the converter device is a constant value (rated value) even at low paper speed operation. Therefore, the harmonic loss of the motor, the switching loss of the inverter device, and the like are not reduced as much as the lower papermaking speed compared with the design papermaking operation. As described above, in actual paper machine operation, there are various operating conditions depending on the brand (type) of product paper, and the operation paper making speed is often much lower than the design paper making speed. In this case, the operating efficiency of the drive system is not optimized.

  SUMMARY OF THE INVENTION An object of the present invention is to provide a control device for a drive system with improved operating efficiency by making the DC output voltage supplied from the converter device to the inverter device variable according to the rotational speed of the motor driven by the inverter device output. Is to provide.

  The drive system control device according to the present invention converts alternating current power into variable voltage direct current power by a converter device, reversely converts this direct current power into variable voltage variable frequency alternating current power by an inverter device, and this reverse conversion is performed. A drive system control device for driving an electric motor with AC power having a variable voltage and variable frequency, wherein the efficiency of the drive system is determined from an input power to the converter device and an operating power of the motor output from the inverter device. A system-wide efficiency calculation circuit that calculates in a cycle; a variable voltage command device that outputs a voltage command value for generating a DC output voltage of the converter device in accordance with a rotation speed of the motor; and the system-wide efficiency calculation circuit. The calculated current efficiency calculation value is compared with the previous efficiency calculation value, and the entire system according to the comparison result As the rate is maximized, characterized in that a efficiency comparison circuit for providing a correction instruction value to the DC voltage command value for the converter device.

  According to the present invention, the drive system can be controlled with the DC output voltage that optimizes the overall efficiency of the system at the actual operating speed. That is, the switching loss of the power conversion element of the drive system and the harmonic loss of the motor can be reduced by controlling the DC output voltage of the converter device during the medium / low speed operation. As a result, the efficiency of the entire system is improved, and an energy saving effect can be expected.

It is a figure which shows the drive system of a general paper machine. It is a circuit diagram which shows an example of the drive system used by this invention. It is a circuit diagram which shows the other example of the drive system used by this invention. It is a circuit diagram which shows the control apparatus of the drive system concerning one embodiment of this invention. It is a wave form diagram explaining the relationship between the output voltage current waveform and DC input voltage of the inverter apparatus used by this invention. It is a characteristic view explaining the relationship between the DC input voltage of the inverter and system efficiency in one embodiment of the present invention. It is a figure explaining the search operation | movement of the maximum efficiency point in one embodiment of this invention.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

  FIG. 1 shows a schematic configuration of a general paper machine drive system. In FIG. 1, the product paper 11 is fed by a plurality of rolls 12 at a predetermined paper making speed s while maintaining a predetermined tension t. Each roll 12 is coupled to a corresponding electric motor 13 via a transmission as required, and is rotated by the electric motor 13. The operation of the electric motor 13 is controlled by a drive system having a converter device 14 and an inverter device 15. Converter device 14 converts AC power supplied from AC power supply 17 into DC power. The inverter device 15 reversely converts the DC power supplied from the converter device 14 into AC power having a variable voltage and variable frequency, and controls the rotational speed, output torque, and the like of the motor 13 by the AC output.

  FIG. 2 shows a main circuit configuration example of the drive system according to the embodiment of the present invention. This drive system is applied to the paper machine shown in FIG. 1, and parts corresponding to those in FIG.

  The converter device 14 of this drive system has an antiparallel thyristor converter 21, and its input side is connected to an AC power supply 17 via an AC reactor 22. Further, a DC reactor 23 and an output capacitor 24 are connected to the output side, and AC power supplied from the AC power supply 17 is converted into variable voltage DC power and output from both ends of the output capacitor 24. That is, the output voltage v (Udc) across the output capacitor 24 can be changed to an arbitrary value.

  In addition to the anti-parallel thyristor converter 21 described above, the converter device 14 uses a unidirectional thyristor or IGBT (insulated gate bipolar transistor), but also a diode converter as shown in FIG. What obtains a direct-current variable voltage output using 31 and the chopper circuit 32 may be used.

  The inverter device 15 includes an IGBT and a flywheel diode. The inverter device 15 reversely converts the DC power supplied from the converter device 14 into AC power having a variable voltage and variable frequency, and outputs the AC power. That is, the inverter device 15 performs variable voltage variable frequency (VVVF) control of the electric motor 13 by the AC output, and controls its rotation speed, output torque, and the like.

  In the present invention, the DC output voltage supplied from the converter device 14 to the inverter device 15 is made variable in accordance with the rotational speed of the electric motor 13 driven by the output of the inverter device 15, thereby improving the operation efficiency. The control device of the drive system for this purpose will be described with reference to FIG.

  Here, the drive system to be controlled is the same as that shown in FIG. 1 or FIG. 3, and the corresponding parts are denoted by the same reference numerals. That is, the drive system converts the AC power supplied from the AC power source 17 into DC power of DC variable voltage, and converts the DC power output from the converter device 14 to AC variable voltage variable frequency AC. And an inverter device 15 that converts the electric power into electric power, and the electric motor 13 is driven by AC power of AC variable voltage and variable frequency output from the inverter device 15.

  The control device includes an electric motor operating power calculation circuit 41, an overall system efficiency calculation circuit 42, an efficiency comparison circuit 43, a variable voltage command device 44, an upper / lower limit value circuit 45, and calculation circuits 46 and 47.

  The motor operating power calculation circuit 41 obtains the operating power value of the motor 13 supplied from the inverter device 15. This operating power value is obtained by calculation using a torque signal and a rotational speed signal, which are control information of the inverter device 15 that controls the drive of the electric motor 13, or by using an actual torque τ and an actual rotational speed ω of the electric motor. In this embodiment, since a plurality of motors 13 are driven and controlled by a plurality of inverter devices 15 corresponding thereto, torque signals τ and rotation speed signals ω of these (n) motors 13 are obtained. By using them, the total operating power ΣPm can be obtained from equation (1) described later.

  The overall system efficiency calculation circuit 42 is connected to the input power Pconv to the converter device 14 and the operating power of the motor 13 output from the inverter device 15, that is, the total motor operating power value ΣPm obtained by the motor operating power calculation circuit 41 described above. Thus, the overall efficiency ηs of the drive system is calculated at a predetermined cycle. That is, the efficiency equation of a drive system having a drive system of a plurality (n) of inverter devices 14 and motors 13 is expressed by the following equation (1): total motor operating power value ΣPm and converter device input power value Pconv Can be expressed as the overall efficiency value ηs of the system.

The input power value Pconv to the converter device 14 is detected by a power meter (not shown) provided on the input side of the converter device 14.

In the above equation (1), τ _i is the motor output torque [N · m], and ω _i is the motor rotational angular velocity [rad / s].

  The efficiency comparison circuit 43 compares the previous efficiency calculation value calculated by the overall system efficiency calculation circuit 42 at a predetermined cycle with the current efficiency calculation value. Then, a correction command value for the DC voltage command value output from the variable voltage command device 44 to the converter device 14 is given so as to maximize the overall system efficiency according to the comparison result.

  As shown in FIG. 5, the variable voltage command device 44 is set with a characteristic of the DC voltage Udc corresponding to (substantially proportional to) the rotational speed of the electric motor 13. Based on this characteristic, a voltage command to the converter device 14 is set. The value is output.

  The upper and lower limit circuit 45 sets upper and lower limit values for the voltage command value from the variable voltage command device 44. That is, the upper limit Udc upper limit and the lower limit motor induced voltage Ec are set as shown in FIG. 5 for the characteristic of the DC voltage Udc that is a voltage command value to the converter device 14. The upper and lower limit values of the voltage command value are set so that the DC output voltage of the converter 14 is variably controlled within a range where the actual operation of the electric motor 13 is not affected. The Udc upper limit depends on the device rating, and the lower limit. Ec is set in a range where a predetermined output can be obtained so that a torque drop at a low frequency output does not occur when the motor 13 is operated at a low speed.

  The arithmetic circuit 46 is used to add the voltage correction value from the efficiency comparison circuit 43 to the voltage command value from the variable voltage command device 44. Further, the arithmetic circuit 47 obtains a deviation between the voltage command value to the converter device 14 and the output voltage from the converter device 14, and the DC voltage controller 48 controls the output voltage of the converter device 14. Used.

  In the above configuration, when the paper is produced by the drive system of the paper machine shown in FIG. 1, the paper making speed suitable for the type of paper to be produced is determined, and the speed command device (not shown) A speed command for realizing the rotational speed of the electric motor 13 corresponding to the paper making speed is given. The inverter device 15 outputs AC power having a voltage and a frequency corresponding to a given speed command by pulse width modulation (hereinafter referred to as PWM) control.

  Information about the rotational speed of the electric motor 13 corresponding to the paper making speed is also given to the variable voltage command device 44. The variable voltage command device 44 generates a DC output voltage corresponding to the rotational speed of the motor 13 to be operated based on a characteristic of the DC voltage Udc (shown in FIG. 5) corresponding to a preset rotational speed of the motor 13. Output voltage command value. The voltage command value is input to a control unit (not shown) of the converter device 14 via the arithmetic circuit 46, the upper / lower limit value circuit 45, the arithmetic circuit 47, and the DC voltage controller 48. That is, based on the voltage command value output from the variable voltage command device 44, the converter device 14 generates a DC output voltage corresponding to the paper making speed, and drives the motor 13 by the variable voltage variable frequency control of the inverter device 15.

  FIG. 6 shows an output voltage waveform and an output current waveform of the inverter device 15 when the DC output voltage Udc of the converter device 14 is changed (Udc1, Udc2) in the PWM control by the triangular wave comparison method of the inverter device 15. ing. In FIG. 6, the DC output voltage of the converter device 14 is within a range in which the output voltage fundamental wave effective value 61a of the inverter device 15 (the output voltage fundamental wave 62a of the line voltage) and the output current fundamental wave 63a of the inverter device 15 do not change. By reducing Udc from Udc1 to Udc2, the current ripple 64a of the output current waveform of the inverter device 15 can be suppressed to 64b.

  That is, when the paper making speed is low depending on the type of paper to be produced, the DC output voltage of the converter device 14 remains at 100% as in the prior art even though the output voltage waveform of the inverter device 15 is low. If it exists, the DC voltage input into the inverter apparatus 15 shown in FIG. 6 will be in a high state with Udc1. For this reason, the pulse width is narrowed and the current ripple 64a of the output current waveform is increased. On the other hand, when the DC output voltage of the converter device 14 is changed according to the paper making speed as in the present invention, the DC voltage input to the inverter device 15 shown in FIG. 6 becomes a low value of Udc2. For this reason, the pulse width is widened, and the current ripple of the output current waveform is as small as 64b.

  As a result, the harmonic component included in the output current of the inverter device 15 is reduced, so that the harmonic loss of the electric motor 13 is reduced. Further, the output voltage value of the converter device 14 is reduced from Udc1 to Udc2 in a state where the output current fundamental wave 61a of the inverter device 15 does not change, and thus is determined by the voltage and current at the time of commutation in the inverter device 15. Switching loss of the power conversion element can be reduced.

  Thus, the inverter device 15 performs the variable voltage variable frequency control and drives the motor 13 by the DC output voltage of the converter device 14 corresponding to the paper making speed. 42 is used to calculate at a constant period. The efficiency comparison circuit 43 compares the overall system efficiency value ηs in the current cycle calculated by the overall system efficiency calculation circuit 42 according to the above-described arithmetic expression with the overall system efficiency value calculated in the previous cycle. As a result, a voltage correction value is output in a direction in which the overall system efficiency value ηs increases, and the voltage command value output from the variable voltage command device 44 is corrected by the arithmetic circuit 46.

  Here, the variable voltage command device 44 outputs a voltage command value based on the characteristics of the DC voltage Udc corresponding to the paper making speed shown in FIG. 5, that is, the rotational speed of the electric motor 13, to the converter device 14. The converter device 14 generates a DC output voltage corresponding to the papermaking speed based on the voltage command value, and the inverter device 15 inputs the DC output voltage and performs variable voltage variable frequency control. However, the overall system efficiency value ηs in this operating state is not always the highest. In order to optimize the efficiency of the drive system, the overall efficiency value ηs of the drive system needs to be increased, which means that the operation efficiency of the electric motor 13, the inverter device 15, and the converter device 14 is improved. In order to improve the efficiency of the entire drive system, it is necessary to reduce the switching loss of power conversion of the drive system and the harmonic loss of the electric motor 13 that cause the loss. For this purpose, it is necessary to determine how the overall system efficiency value ηs changes by changing the DC output voltage of the converter device 14.

  Therefore, the efficiency comparison circuit 43 outputs a voltage command value (referred to as an initial voltage command value) commensurate with the paper making speed from the variable voltage command device 44, and a DC output voltage (initial DC voltage) of the converter device 14 based on this voltage command value. The overall efficiency value ηs in the initial cycle is calculated in a state where the inverter device 15 is operated and the electric motor 13 is driven. Since the calculated overall efficiency value ηs is the initial period, there is no comparison target (efficiency value in the previous period), and therefore a voltage correction value in a previously assumed efficiency improvement direction, for example, a voltage increasing direction is output to the arithmetic circuit 46. Then, the initial voltage command value output from the voltage command device 44 is corrected. Based on the corrected voltage command value, the converter device 14 generates a DC output voltage that is slightly higher than the initial DC output voltage so far and supplies it to the inverter device 15. The inverter device 15 drives the electric motor 13 so as to realize a predetermined paper making speed with an input voltage slightly higher than the previous cycle.

  The efficiency comparison circuit 43 compares the overall system efficiency value ηs in the current cycle in which the motor 13 is driven by the inverter device 15 having a slightly higher DC input voltage with the overall system efficiency value calculated in the previous cycle. As a result, if the overall system efficiency value ηs of the current cycle is higher than the previous cycle, the voltage correction value in the voltage rising direction is output again, and the voltage command value output from the variable voltage command unit 44 by the arithmetic circuit 46 is output. Correct.

  Based on the voltage command value corrected in the upward direction, the converter device 14 outputs a higher DC output voltage than before. The inverter device 15 drives the electric motor 13 so as to realize a predetermined papermaking speed with a higher DC input voltage.

  In the next cycle, the efficiency comparison circuit 43 calculates the efficiency value ηs of the entire system in which the motor 13 is driven by the inverter device 15 having a higher DC input voltage than before in the previous cycle (current cycle described above). Compare with the overall efficiency value. As a result, if the overall system efficiency value ηs is higher than the previous cycle, the voltage correction value in the voltage rising direction is output again, and the arithmetic circuit 46 outputs the voltage correction value to the voltage command value output from the variable voltage command device 44. Repeat the correction.

  On the other hand, when the overall system efficiency value ηs of the current cycle is lower than the previous cycle, a voltage correction value in the downward direction is output to the arithmetic circuit 46 in order to restore the voltage command value corrected in the previous upward direction. The voltage command value output from the variable voltage command device 44 is corrected so as to return to the original value.

  This correction is limited by the upper / lower limit circuit 45 within the range of the Udc upper limit value and the lower limit value Ec shown in FIG.

  FIG. 7 illustrates the correction operation described above. Each characteristic example is shown when the load factor of the drive system of the inverter device 15 is high, medium, and low according to the paper making speed corresponding to the type of paper to be produced. For example, when the load factor is high, the system efficiency a at a certain point in time is higher than the efficiency of the previous cycle (not shown), so the voltage command value is corrected in the upward direction, and operation is performed with a higher DC voltage. As a result, the system efficiency b in the next cycle is higher than the efficiency a of the previous cycle. In this case, as described above, the voltage command value is further corrected in the upward direction, and the operation is performed with a higher DC voltage. In the example of the figure, the system efficiency c in the next cycle, that is, the system efficiency c when operating at a higher DC voltage is lower than the system efficiency b in the previous cycle. In this case, the voltage command value is corrected so as to decrease to restore the DC voltage to the original value. That is, in the state where the load factor is high, the system efficiency is the highest at the point b, and the system efficiency can be maintained in the optimum state by controlling so as to maintain the DC voltage at the point b.

  Thus, in order to search for the system maximum efficiency point at which the overall system efficiency value becomes maximum regardless of whether the load factor is high, medium, or low, the voltage command value is slightly changed. That is, the efficiency comparison circuit 43 sequentially compares the system efficiency values of the previous time and the current time, and obtains the DC voltage at the maximum efficiency point b where the efficiency is maximum. And a voltage correction value is added to a voltage command value so that it may become the calculated DC voltage value, and a voltage command value is corrected. By this correction, the drive system is controlled to be the system maximum efficiency point.

  In addition, although the case where the paper machine was driven as a drive system was demonstrated, of course, it is not limited to a paper machine, If it is a drive object with a comparatively little operation speed change, it can implement similarly.

  Although several embodiments of the present invention have been described, these embodiments have been presented by way of example and are not intended to limit the scope of the invention. These novel embodiments can be implemented in various other forms, and various omissions, replacements, and changes can be made without departing from the scope of the invention. These embodiments and modifications thereof are included in the scope and gist of the invention, and are included in the invention described in the claims and the equivalents thereof.

DESCRIPTION OF SYMBOLS 13 ... Electric motor 14 ... Converter apparatus 15 ... Inverter apparatus 17 ... AC power supply 41 ... Electric motor operation electric power calculation circuit 42 ... Whole system efficiency calculation circuit 43 ... Efficiency comparison circuit 44 ... Variable voltage Commander 45 ... Upper / lower limit value circuit 48 ... DC voltage controller

Claims (4)

AC power is converted to variable voltage DC power by a converter device, this DC power is converted back to AC power of variable voltage variable frequency by an inverter device, and the motor is driven by the AC power of variable voltage variable frequency that has been reversely converted. A control device for the drive system,
An overall system efficiency calculation circuit that calculates the efficiency of the drive system in a predetermined cycle from the input power to the converter device and the operating power of the motor output from the inverter device;
A variable voltage command device that outputs a voltage command value for generating a DC output voltage of the converter device according to the rotation speed of the motor; and a current efficiency calculation value calculated by the overall system efficiency calculation circuit as a previous efficiency calculation value. An efficiency comparison circuit that provides a correction command value to the DC voltage command value to the converter device so that the overall system efficiency is maximized according to the comparison result;
A drive system control device comprising: The variable voltage command device outputs a DC voltage command value that makes the DC output voltage of the converter device approximately proportional to the rotational speed of the electric motor,
The efficiency comparison circuit determines an increase or decrease in efficiency when the DC output voltage of the converter device is changed, and gives a correction command value in the direction of increasing efficiency to the DC voltage command value based on the determination result The drive system control device according to claim 1, wherein:   2. The overall system efficiency calculation circuit uses, as the electric motor operating power value, a value calculated using a torque signal and a rotation speed signal, which are control information of an inverter device that drives and controls the electric motor. Or the control apparatus of the drive system of Claim 2.   4. The drive system control device according to claim 1, wherein the drive system drives a paper machine.

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