JP2019040501A - Power conversion device and its control method - Google Patents

Abstract

To save power when PID control is applied.SOLUTION: A power conversion device comprises: a target value setting section; a feedback signal input section that allows input of a signal output from a detector for detecting a state value of a control target and that outputs a feedback signal reflecting the signal output from the detector; a subtractor that calculates a deviation of a feedback signal from a target value set by the target value setting section; and a PID computing unit that performs at least one or more of a proportional operation, an integral operation, and a differential operation with respect to the deviation. Output based on output from the PID computing unit is generated and the control target is controlled so as to become equal to or close to a target value. The power conversion device has: an upper and lower limit setting section that sets at least one of an upper limit and a lower limit for a signal; an upper and lower limit reach determining section that determines whether the feedback signal has reached at least one of the upper limit and the lower limit; a correction quantity setting section that sets a quantity of correction; and a correction quantity computing section that, on the basis of output from the upper and lower limit determining section and output from the correction quantity setting section, computes the quantity of correction, output from the PID computing unit.SELECTED DRAWING: Figure 4

Description

  The present invention relates to a power conversion device for making a control target coincide with or approach a target value, and more particularly to a power converter incorporating a PID controller (Proportional-Integral-Differential Controller, PID Controller) and a control method thereof.

  As means for controlling the controlled object to match the target value, the controlled object is fed back, the deviation from the target value is calculated, and the manipulated variable is manipulated using proportional calculation, integral calculation, and differentiation, and the deviation So-called PID control is generally used to bring the value close to 0, and is used for a wide range of controls such as pressure control, flow rate control, and temperature control.

  As shown in Patent Document 1, the configuration takes the difference between the target value by the subtractor and the FB value fed back from the object to be controlled, and the proportional calculation by the proportional calculation unit, the integral calculation by the integral calculation unit, The control object is controlled by performing a differential operation by the differential operation unit, adding and subtracting them with an adder, and supplying the result of the addition and subtraction to the control object. The operation acts to increase if the feedback value to be controlled is less than the target value, and to decrease if the feedback value is over.

  In a general application, such an operation allows the controlled object to be close to the target value. If the load conditions are the same, the value at which the manipulated variable at that time is basically constant.

JP 2010-20704 A

  However, the PID control described in the background art may cause the following problems when applied to pressure control of a vacuum pump, for example.

  In the case of a vacuum pump, control is generally performed from a normal atmospheric pressure of 0.1 MPa to a lower target pressure. For example, if the target value is 0.05 MPa, the motor is operated so that the number of rotations is increased if the pressure of the motor that drives the vacuum pump is 0.05 MPa or higher, and the pressure decreases. For example, the rotation speed is decreased and the pressure is increased, and control is performed so as to match the target value.

  Here, the target value is a vacuum, that is, 0 MPa. In this case, the PID control increases the number of rotations of the vacuum pump to make the pressure vacuum. In general, when the vacuum (0MPa) is reached, unlike 0.05MPa, there is no more than vacuum, so the target value will not be exceeded. Therefore, the operation of lowering the pump rotation speed is not achieved, and the rotation speed at the time of arrival is maintained, resulting in a state in which useless power is consumed.

  In this way, when the control target or its feedback value has a limit value, when the limit value is set as the target value, the manipulated variable at the time of arrival is not constant, and it is stable in a state in which wasteful power is consumed There is.

  An object of the present invention is to solve this problem and prevent wasteful power consumption.

  In one aspect of the present invention, a target value setting unit that allows a target value to be set or input from the outside, and an output signal of a detector that detects a state value of a control target can be input, and the output signal of the detector is reflected A feedback signal input unit that outputs a feedback signal, a subtractor that calculates a deviation between the target value set by the target value setting unit and the feedback signal, and at least one of a proportional operation, an integral operation, and a differential operation with respect to the deviation A power conversion device having a PID control function that performs the above calculation and includes a PID calculation unit that outputs the sum, generates an output based on the output of the PID calculation unit, and controls the control target to match or approach the target value It is. The power converter includes an upper / lower limit setting unit that sets at least one of an upper limit and a lower limit of a signal, an upper / lower limit arrival determination unit that determines whether the feedback signal has reached at least one of the upper limit and the lower limit, and a correction amount And a correction amount calculation unit that calculates the correction amount of the output of the PID calculator from the output of the upper and lower limit arrival determination unit and the output of the correction amount setting unit.

  Another aspect of the present invention is a method for controlling a power conversion device when the state of a control target is changed by an operation of an external device connected to the power conversion device. This control method includes a target value setting step for setting a target value for a state of a control target, a feedback generation step for detecting the state of the control target with a detector, and generating a feedback signal based on the output of the detector, A deviation acquisition step for obtaining a deviation between the value and the feedback signal, a calculation step for performing at least one of proportional calculation, integral calculation, and differential calculation using the deviation and outputting the result; an upper limit of the feedback signal; An upper / lower limit setting step for setting at least one of the lower limits, an upper / lower limit arrival determination step for determining whether the feedback signal has reached at least one of the upper limit and the lower limit, and a correction amount setting step for setting the correction amount, When the feedback signal reaches at least one of the upper and lower limits, It is to generate a control signal corrected by the correction amount results, to operate the external device based on the control signal.

  For example, when PID control is applied, it is possible to save power.

The block diagram of the PID control structure of the vacuum pump of a comparative example. The graph of an example of a pressure sensor output characteristic. The graph of the time transition of the pressure by the PID control structure of the vacuum pump of a comparative example, and motor rotation speed. The block diagram of the PID control structure of the vacuum pump of an Example. The graph of the time transition of the pressure by the PID control structure of the vacuum pump of an Example, and motor rotation speed. The graph figure of the pressure sensor output characteristic example with an upper and lower limit. The block diagram of the PID control structure of the object cooling device of an Example. The graph of the example of a temperature sensor output characteristic with an upper and lower limit. The block diagram of the PID control structure of the cooling device of an Example. The graph of the example of a temperature sensor output characteristic. The flowchart which shows the flow of control of an Example.

  Embodiments of the present invention will be described below with reference to the drawings. However, the present invention is not construed as being limited to the description of the embodiments below. Those skilled in the art will readily understand that the specific configuration can be changed without departing from the spirit or the spirit of the present invention.

  In the structures of the invention described below, the same portions or portions having similar functions are denoted by the same reference numerals in different drawings, and redundant description may be omitted.

  In the case where there are a plurality of elements having the same or similar functions, the same reference numerals may be given with different subscripts. However, when there is no need to distinguish between a plurality of elements, the description may be omitted.

  Notations such as “first”, “second”, and “third” in this specification and the like are attached to identify the constituent elements, and do not necessarily limit the number, order, or contents thereof. is not. In addition, a number for identifying a component is used for each context, and a number used in one context does not necessarily indicate the same configuration in another context. Further, it does not preclude that a component identified by a certain number also functions as a component identified by another number.

  The position, size, shape, range, and the like of each component illustrated in the drawings and the like may not represent the actual position, size, shape, range, or the like in order to facilitate understanding of the invention. For this reason, the present invention is not necessarily limited to the position, size, shape, range, and the like disclosed in the drawings and the like.

  In a typical example of the embodiment described below, control is performed such that the feedback value of the control target increases with respect to the target value when it is insufficient, and decreases when it is over. If the load conditions are the same, the value at which the manipulated variable at the time of convergence is constant. However, for example, when considering the case where PID control is applied to pressure control or the like of a vacuum pump, when the target value is set to vacuum, PID control increases the pump rotation speed so as to make the pressure vacuum. When the vacuum is reached, there is no state above the vacuum, so the target value will not be exceeded, the pump rotation speed will not be lowered, the rotation speed at the time of arrival will be maintained, and even under the same load conditions The value at which the operation amount is stable is not constant, and there is a case where wasteful power is consumed. In the embodiment, in the operation of the PID control, a function for setting the upper and lower limits of the control target, and when reaching the upper limit, the control target numerical value decreases, and when the lower limit is reached, the control target numerical value increases. The operation amount correction value is calculated, and the motor rotation speed command value that is the operation amount is corrected. As a result, even when the vacuum is set as the target value, it is possible to control the pump speed to an optimum value that can maintain the vacuum, and power saving can be achieved.

  FIG. 1 is a block diagram showing a configuration in a case where, for example, normal PID control is applied to pressure control or the like of a vacuum pump as a comparative example. In this configuration, the pressure in the pressure tank 10 is controlled from the normal atmospheric pressure 0.1 MPa to the target pressure set by the target value setting unit 1. The pressure in the pressure tank 10 is reduced by a vacuum pump 9 driven by an electric motor (motor) 8. The pressure in the pressure tank 10 is measured by the pressure sensor 11, and the measured value is input from the feedback signal input unit 17 to the power converter 18 as the feedback signal 12.

  The feedback signal 12 is subtracted from the target value 100 by the subtracter 2, and the deviation signal 3 is input to a known PID calculator 4 in Patent Document 1 or the like. The calculation result of the PID calculator 4 is inverted in sign by the sign inverter 16 and output as the motor rotation speed command value 5. The frequency / voltage converter 6 is controlled by the motor rotation speed command value 5, and the rotation of the motor 8 is controlled by the power converter output 7 that is AC power having a frequency corresponding to the frequency / voltage converter 6.

  FIG. 2 shows the output characteristics of the pressure sensor 11 that detects the pressure in the pressure tank 10 that is the object of control. The horizontal axis is the pressure measured by the pressure sensor 11, and the vertical axis is the value of the feedback signal 12 corresponding to the pressure.

  For example, if the target value set by the target value setting unit 1 is 0.05 MPa, the pressure in the pressure tank 10 is initially equivalent to an atmospheric pressure of 0.1 MPa, but the pressure is controlled by operating the rotation speed of the electric motor 8 that drives the vacuum pump 9. If the pressure is 0.05 MPa or more, the rotational speed is increased and the pressure is decreased.If the pressure is 0.05 MPa or less, the rotational speed is decreased and the pressure is increased. Control to match the target value 100.

  Here, the target value 100 is a vacuum, that is, 0 MPa. In this case, the PID control system increases the number of revolutions of the electric motor 8 that drives the vacuum pump 9 so that the pressure in the pressure tank 10 to be controlled is evacuated. In general, when the vacuum (0 MPa) is reached, unlike the case of 0.05 MPa, the pressure in the pressure tank 10 to be controlled cannot exceed the vacuum state, and therefore the target value is not exceeded. Therefore, the operation of lowering the pump rotation speed is not reached, and the pump rotation speed at the time of arrival is maintained. At that time, the number of rotations may be higher than the number of rotations originally necessary, and wasteful power is consumed.

  FIG. 3 shows an example of changes in the rotational speed of the electric motor 8 when reaching 0 MPa according to the comparative example of FIG. Depending on the conditions such as the pressure in the pressure tank 10 at the start, the motor rotation speed B when the vacuum is reached when the pressure is changed from P2 near atmospheric pressure 0.1MPa to the vacuum as in the condition 2, and the characteristics of the condition 1 As shown in Fig. 3, when the pressure is reduced to some extent, the motor speed A at the time of vacuum reaching P1 to the vacuum is different, and the speeds N1 and N2 at the time of reaching are maintained as they are. Resulting in.

  FIG. 4 is a block diagram showing the configuration of the embodiment of the present invention. Here, an example based on a PID control system as a control method will be described. Upper / lower limit setting unit 19 for setting at least one of the upper limit and lower limit of the feedback signal 12 of the pressure to be controlled, which is used for the operation of the PID control system, and the upper / lower limit value in which the feedback signal 12 is set by the upper / lower limit setting unit 19 The upper / lower limit achievement determination unit 13 is provided for determining whether or not Further, the rotational speed command of the motor 8 is determined from the rotational speed correction amount setting unit 25 that sets the rotational speed command correction amount when the upper and lower limits are reached, and the output of the upper and lower limit arrival determination unit 13 and the output of the rotational speed correction amount setting unit 25. Is provided with a rotational speed command correction amount calculation unit 14 for calculating the correction amount.

  With the above configuration, the rotational speed command correction amount calculation unit 14 outputs the correction signal 400 on condition that the feedback signal 12 reflecting the pressure to be controlled has reached the upper limit or the lower limit. The output generated by the PID calculator 4 or the like and the correction signal 400 of the rotation speed command correction amount calculation unit 14 are added by the correction amount adder 15 to generate a corrected motor rotation speed command value 500. The frequency / voltage converter 6 is controlled by the corrected motor rotation speed command value 500, and the rotation of the motor 8 is controlled by the power converter output 7.

  The rotational speed command correction amount calculation unit 14 determines the sign so that the feedback signal 12 decreases when the value of the control target has reached the upper limit value by the output of the upper / lower limit determination unit 13. The value set by the rotation speed correction amount setting unit 25 is output. If it is determined that the lower limit value has been reached, the sign is determined so that the feedback signal 12 increases, and the value set by the rotation speed correction amount setting unit 25 is output.

  FIG. 5 shows an example of changes in the rotational speed of the electric motor 8 when the target pressure is 0 MPa according to the embodiment of FIG. Similar to FIG. 3, the pressure to be controlled converges to the target value (in this case, 0 MPa) by the control using the feedback signal 12.

  Here, the upper and lower limit setting unit 19 sets the lower limit value to 0 MPa, and the rotation speed correction amount setting unit 25 sets an arbitrary value as the correction amount. As shown in FIG. 5, even if there is a difference in the pressure of the pressure tank 10 at the start, such as P1 and P2, the upper / lower limit attainment determination unit 13 determines that the pressure is 0 MPa by the feedback signal 12. Meanwhile, the corrected motor speed command value 500, which is a control signal of the frequency / voltage conversion unit 6, is larger than the motor speed command value 5 normally generated by the PID calculator 4, with the correction amount by the speed correction amount setting unit 25. It is revised downward by the minute.

  In the example of FIG. 5, under condition 1 where the initial pressure was P1, the motor speed N1 reached the lower limit of 0 MPa at time t1 (point B), and under condition 2 where the initial pressure was P2, the motor was reached at time t2. The rotation speed N2 has reached the lower limit of 0 MPa (point A). At this time, after the points A and B that have reached the lower limit of 0 MPa, the motor rotational speed continues to decrease due to the corrected motor rotational speed command value 500 corrected by the correction signal 400, but if it exceeds 0 MPa, normal PID control is performed. Return to motor speed command value 5. As a result, the motor speed finally converges to a constant motor rotation speed N0 that is necessary and sufficient to maintain 0 MPa, so that useless power is not consumed.

  In the above example, the case where the vacuum that is the lower limit of the physical pressure is set as the target value has been described by taking the vacuum pump as an example. On the other hand, when the pressure in the pressure tank 10 is increased by the compression pump, if there is an upper limit of the pressure on the performance of the pressure tank 10 due to a leak or the like, the same technique can be applied to the upper limit pressure. .

  FIG. 6 is an example of characteristics when the pressure sensor 11 in FIG. 1 and FIG. 4 has upper and lower limits. For example, this is a case where the measurement range of the pressure sensor 11 is limited to a range of 0.05 MPa to 0.15 MPa. In such a case, for example, when considering the case where the target value 100 in FIG. 1 is controlled to 0.05 MPa, which is the lower limit of the pressure sensor 11, even if the actual pressure drops below 0.05 MPa, the sensor output is 0.05 MPa. It does not change with time. For this reason, the PID control system maintains the motor rotation speed at the time of reaching 0.05 MPa, and the actual pressure further decreases, so that it cannot be controlled to 0.05 MPa.

  Also in this case, in the configuration of FIG. 4, the pressure can be controlled to 0.05 MPa by setting the lower limit value to 0.05 MPa in the upper and lower limit setting unit 19. Further, the rotational speed of the electric motor 8 at that time can also be made constant irrespective of the conditions of the pressure tank 10 pressure at the time of starting. As described above, even in a sensor whose upper and lower limits are determined, the control target can be controlled to the target value at the end of the output range, and the output range of the sensor can be used effectively.

  Thus, in addition to the case where the upper and lower limits are determined from the physical constraints of the control target as in the first embodiment, the case where the upper and lower limits are determined from the constraints on the sensor specifications is effective in reducing power consumption. .

  FIG. 7 shows an embodiment in which the present invention is applied to a temperature control device for the heating element 21. In this example, the heating element 21 is air-cooled and cooled by the cooling fan 20 driven by the electric motor 8.

  FIG. 8 shows an example of the characteristics of the temperature sensor 22 in FIG. The values measured by the temperature sensor 22 have upper and lower limits such as an upper limit of 50 ° C. and a lower limit of −10 ° C. as shown in FIG. For this reason, even if the target value 100 is set to the upper and lower limits by setting the values to the upper limit and lower limit settings by the upper and lower limit setting unit 19 in FIG. It becomes possible to control the temperature to the target value.

  FIG. 9 shows an embodiment in which the present invention is applied to temperature control of a cooling device using liquid helium. The cooling object 31 is an example of being cooled by the cooling device 30 driven by the electric motor 8. In this example, the sign inverter 16 is omitted, and the sign of the signal is set separately in the PID calculator 4 and the like.

  FIG. 10 also shows an example of the characteristics of the temperature sensor 22 in FIG. As in the case of vacuum in the case of pressure, the temperature cannot have an absolute temperature of −273 ° C. or lower. Practically, in the case of liquid helium, the cooling limit of the cooling object 31 is −269 ° C. Therefore, the upper and lower limit setting unit 19 in FIG. 9 sets the value to the lower limit setting, so that the motor speed of the cooling device 30 can be controlled to the optimum value even when the target value 100 is set to −269 ° C. It becomes.

  FIG. 11 is a flowchart showing the flow of processing for controlling pressure, taking the system of FIG. 4 as an example. The processing in FIG. 11 can be executed by software, with the rotational speed command correction amount calculation unit 14 configured by a microcomputer. In the start of processing S1101, it is assumed that the physical lower limit of the pressure is already set to 0 MPa in the upper / lower limit setting unit 19. In step S1102, it is determined whether the target pressure set by the target value setting unit 1 is 0 MPa, which is the lower limit. If the target pressure is not 0 MPa, the rotation speed command correction amount calculation unit 14 does not generate the correction signal 400 (S1103). In this case, the output generated by the PID computing unit 4 or the like is used as it is for the control, and is similar to the conventional PID control.

  When the target pressure set by the target value setting unit 1 is 0 MPa, the rotational speed command correction amount calculation unit 14 monitors whether the feedback signal 12 indicates the lower limit 0 MPa of pressure (S1104). When the feedback signal 12 is not the lower limit of pressure 0 MPa, the rotation speed command correction amount calculation unit 14 does not generate the correction signal 400 and performs control similar to the conventional PID control (S1103).

  When the feedback signal 12 is the lower limit of pressure 0 MPa, the rotation speed command correction amount calculation unit 14 generates a correction signal 400 (S1105). As the correction signal 400, a sign is determined so that the feedback signal 12 increases, and a value set by the rotation speed correction amount setting unit 25 is output. In the case of this example, the correction signal 400 is generated so as to reduce the rotational speed of the electric motor 8. As a result, the pressure in the pressure tank 10 changes in an increasing direction, but this state is maintained while the feedback signal 12 indicates the lower limit of 0 MPa. When the feedback signal 12 is out of the lower limit 0 MPa of the pressure, the process shifts to normal PID control and converges to the target pressure (S1103).

  According to the embodiment described above, the PID control method is used for applications such as vacuum pump pressure control, and even when the vacuum is set to the target value, control is performed to the optimum pump rotation speed that can maintain the vacuum. This makes it possible to save power.

1: target value setting unit 2: subtractor 3: deviation signal 4: PID computing unit 5: motor rotation speed command value 6: frequency / voltage conversion unit 7: power converter output 8: motor 9: vacuum pump 10: pressure tank 11: Pressure sensor 12: Feedback signal 13: Upper / lower limit arrival determination unit 14: Speed command correction amount calculation unit 15: Correction amount adder 16: Sign inverter 17: Feedback signal input unit 18: Power converter 19: Upper / lower limit Setting unit 20: cooling fan 21: heating element 22: temperature sensor 25: rotation speed correction amount setting unit 30: cooling device 31: object to be cooled

Claims (9)

A target value setting section that allows the target value to be set or input externally;
A feedback signal input unit that enables input of an output signal of a detector that detects a state value of a control target and outputs a feedback signal reflecting the output signal of the detector;
A subtractor for calculating a deviation between the target value set by the target value setting unit and the feedback signal;
A PID calculator that performs at least one of proportional calculation, integral calculation, and differential calculation on the deviation and outputs a sum of the calculations,
In the power conversion device having a PID control function for generating an output based on the output of the PID computing unit and controlling the control target to match or approach the target value,
An upper / lower limit setting section for setting at least one of an upper limit and a lower limit of the signal;
An upper and lower limit attainment determination unit for determining whether the feedback signal has reached at least one of the upper limit and the lower limit;
A correction amount setting section for setting a correction amount;
From the output of the upper and lower limit arrival determination unit and the output of the correction amount setting unit, a correction amount calculation unit that calculates the correction amount of the output of the PID calculator,
The power converter characterized by having. A power converter for driving an electric motor with the output,
The correction amount setting unit is a rotation number correction amount setting unit that sets a rotation number command correction amount when the feedback signal reaches at least one of the upper limit and the lower limit.
The correction amount calculation unit calculates a rotation speed command for calculating a correction amount of the rotation speed command of the motor, which is an output of the PID calculator, from the output of the upper / lower limit achievement determination unit and the output of the rotation speed correction amount setting unit. Correction amount calculation unit,
The output of the PID computing unit and the output of the rotation speed command correction amount calculation unit are added, and a correction amount adder for correcting the rotation speed command of the electric motor is provided.
The power conversion device according to claim 1. The rotation speed command correction amount calculation unit
When the upper / lower limit arrival determination unit determines that the feedback signal has reached the upper limit value, the sign is determined so that the feedback signal decreases, and the value set by the rotation speed correction amount setting unit Output
When the upper / lower limit arrival determination unit determines that the feedback signal has reached the lower limit value, the sign is determined so that the feedback signal increases, and the value set by the rotation speed correction amount setting unit Output,
The power conversion device according to claim 2. A control method for the power conversion device when changing the state of a control target by the operation of an external device connected to the power conversion device,
A target value setting step for setting a target value of the state of the controlled object;
A feedback generation step of detecting a state of the controlled object with a detector and generating a feedback signal based on an output of the detector;
A deviation obtaining step for obtaining a deviation between the target value and the feedback signal;
A calculation step of performing at least one of proportional calculation, integral calculation, and differential calculation using the deviation, and outputting the result;
An upper and lower limit setting step for setting at least one of an upper limit and a lower limit of the feedback signal;
Upper and lower limit attainment determining step for determining whether the feedback signal has reached at least one of the upper limit and the lower limit;
A correction amount setting step for setting a correction amount;
When the feedback signal reaches at least one of the upper limit and the lower limit, the control unit generates a control signal by correcting the result obtained by the calculation step with the correction amount, and operates the external device based on the control signal. Let
Control method of power converter. When the feedback signal has not reached either the upper limit or the lower limit, a control signal is generated without correcting the result obtained by the calculation step with the correction amount, and the external device is based on the control signal. Make the work,
The control method of the power converter device of Claim 4. At least one of the upper limit and the lower limit is a limit value of the feedback signal based on physical constraints of the control target.
The control method of the power converter device of Claim 4. At least one of the upper limit and the lower limit is a limit value of the feedback signal based on a restriction on the specification of the detector.
The control method of the power converter device of Claim 4. When the feedback signal reaches at least one of the upper limit and the lower limit, the control unit generates a control signal by correcting the result obtained by the calculation step with the correction amount, and operates the external device based on the control signal. When doing
When the feedback signal reaches an upper limit, the control signal is generated and the external device is operated so as to shift the control target so that the feedback signal decreases.
When the feedback signal reaches a lower limit, the control signal is generated to operate the external device so that the control target is shifted so that the feedback signal increases.
The control method of the power converter device of Claim 4. The external device is an electric motor, and the control signal controls the rotational speed of the electric motor;
The control method of the power converter device of Claim 4.

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