JP5910264B2 - Compressor control device - Google Patents

Description

  The present invention relates to a compressor control device, and more particularly to a technique for preventing the pressure on the discharge side of a compressor from exceeding a predetermined value.

  There is a high-pressure protection device that stops the compressor when the pressure on the discharge side of the compressor exceeds a predetermined value. The high-pressure protection device includes a pressure sensor that detects the pressure on the discharge side of the compressor, and stops the compressor when the pressure value detected by the pressure sensor exceeds a predetermined pressure reference value.

  Patent Documents 1 and 2 are disclosed as techniques related to the present invention.

JP 2003-222415 A JP-A-8-82434

  However, since the pressure sensor is relatively expensive, it is desirable to omit such a high-pressure protection device from the viewpoint of cost reduction.

  Then, an object of this invention is to provide the compressor control apparatus which can protect a compressor, without using a pressure sensor.

A first aspect of the compressor control device according to the present invention includes a discharge port (10a), a suction port (10b), and an electric motor (M1), and the gas sucked from the suction port by the operation of the electric motor. A compressor control device that controls a compressor (10) that compresses and discharges from the discharge port, and is connected to a power source (E1), and converts the voltage from the power source into a desired voltage to the electric motor. And a power conversion unit (1) to be applied, a rotation speed acquisition unit (32) for acquiring the rotation speed of the electric motor, a current detection unit (33) for detecting a current flowing to the electric motor, and the current (I) And a current reference value (Iref) comparing unit (351), and when the current is larger than the current reference value, a compressor stop unit that controls the power conversion unit to stop the motor ( 35) and when the rotational speed (ω) is smaller than the rotational speed reference value (ωref1), the first value is set as the current reference value. A current reference value setting unit (34) that provides a second value larger than the first value as the current reference value to the compressor stop unit when the rotation speed is greater than the rotation speed reference value. The electric motor (M1) includes a field element and an armature, and the compressor control device includes the field magnet when the rotational speed (ω) is larger than the rotational speed reference value (ωref1). Ru with control unit for controlling the power conversion unit by the field control or flux-weakening control weakening weakening the field to the armature from the child (31).

A second aspect of the compressor control device according to the present invention has a discharge port (10a), a suction port (10b), and an electric motor (M1), and the gas sucked from the suction port by the operation of the electric motor. A compressor control device that controls a compressor (10) that compresses and discharges from the discharge port, and is connected to a power source (E1), and converts the voltage from the power source into a desired voltage to the electric motor. And a power conversion unit (1) to be applied, a rotation speed acquisition unit (32) for acquiring the rotation speed of the electric motor, a current detection unit (33) for detecting a current flowing to the electric motor, and the current (I) And a current reference value (Iref) comparing unit (351), and when the current is larger than the current reference value, a compressor stop unit that controls the power conversion unit to stop the motor ( 35) and when the rotational speed (ω) is smaller than the rotational speed reference value (ωref1), the first value is set as the current reference value. A current reference value setting unit (34) that provides a second value larger than the first value as the current reference value to the compressor stop unit when the rotation speed is greater than the rotation speed reference value. The current reference value setting unit (34) includes the current reference value when the rotational speed (ω) is larger than the rotational speed reference value (ωref1) and smaller than a second rotational speed reference value (ωref2). The second value is given to the compressor stop unit (35) as (Iref), and when the rotation speed is larger than the second rotation speed reference value, the current reference value is larger than the second value. A value is given to the compressor stop.

A third aspect of the compressor control device according to the present invention has a discharge port (10a), a suction port (10b), and an electric motor (M1), and the gas sucked from the suction port by the operation of the electric motor. A compressor control device that controls a compressor (10) that compresses and discharges from the discharge port, and is connected to a power source (E1), and converts the voltage from the power source into a desired voltage to the electric motor. And a power conversion unit (1) to be applied, a rotation speed acquisition unit (32) for acquiring the rotation speed of the electric motor, a current detection unit (33) for detecting a current flowing to the electric motor, and the current (I) And a current reference value (Iref) comparing unit (351), and when the current is larger than the current reference value, a compressor stop unit that controls the power conversion unit to stop the motor ( 35) and when the rotational speed (ω) is smaller than the rotational speed reference value (ωref1), the first value is set as the current reference value. A current reference value setting unit (34) that provides a second value larger than the first value as the current reference value to the compressor stop unit when the rotation speed is greater than the rotation speed reference value. The power source (E1) is a DC power source, and the power converter (1) includes a pair of switching elements (1xp, 1xn) connected in series between a positive electrode and a negative electrode of the DC power source. A connection point between the pair of switching elements is connected to the electric motor, each of the pair of switching elements has a control electrode, and a pulsed control voltage is input to the control electrode to turn on / off The rotation speed acquisition unit (32) conducts the control voltage detection unit (321) that detects the control voltage applied to one of the control electrodes of the pair of switching elements, and averages the control voltage. Converts the control voltage into a sinusoidal voltage of approximately sinusoidal shape A pulse / sine wave conversion unit (322) that performs, a comparison unit (323) that outputs a signal that is activated / deactivated according to a comparison result between the sine wave voltage and a predetermined value, and detects the frequency of the signal, A rotation speed calculation unit (324) that provides the rotation speed to the current reference value setting unit based on the frequency.

  According to the first aspect of the compressor control device of the present invention, in a compressor driven by an electric motor, if the current flowing through the electric motor is the same, the pressure on the high pressure side of the compressor (hereinafter referred to as high pressure) is low. The higher the high pressure, the greater the current required to obtain the same rotational speed.

  According to the first aspect, since the compressor can be stopped if the current exceeds the current reference value, the high pressure can be prevented from exceeding a predetermined value without using a pressure sensor. In addition, in the region where the rotation speed is higher than the rotation speed reference value, a larger second value is adopted as the current reference value. Therefore, it is possible to prevent the high pressure from exceeding a predetermined value while operating the compressor to a higher high pressure in the region.

In addition, when field-weakening control is performed in a region where the rotational speed is high, the pressure on the high pressure side of the compressor decreases as the rotational speed increases if the current flowing through the motor is the same. Therefore, when the field weakening control is performed, it is possible to prevent the high pressure from exceeding a predetermined value while operating the compressor to a higher high pressure in a region where the rotational speed is high.

According to the second aspect of the compressor control device of the present invention, the high pressure exceeds a predetermined value while operating at a higher high pressure in a region where the rotational speed is higher than the second rotational speed reference value. Can be prevented.

According to the third aspect of the compressor control device according to the present invention, a small control voltage is detected as compared with the case where the AC voltage output to the electric motor is detected and the rotational speed is acquired based on the frequency. The rotation speed is detected. Therefore, the pressure resistance of the pulse / sine wave conversion unit, the comparison unit, and the rotation speed calculation unit can be reduced. Further, when the control voltage detection unit detects a voltage using a resistor, a resistor having a smaller capacity (for example, a current capacity) can be employed as compared with a case where an AC voltage is detected.

It is a figure which shows a conceptual example of the apparatus which controls a compressor. It is a figure which shows a typical example of an electric current reference value. It is a figure which shows a typical example of the isoelectric current in a rotational speed-high voltage coordinate shape. It is a figure which shows a typical example of the isoelectric current in a rotational speed-high voltage coordinate shape. It is a figure which shows a conceptual example of the apparatus which controls a compressor. It is a figure which shows an example of a notional structure of a rotational speed detection part. It is a schematic diagram which shows an example of the voltage applied to an output line. It is a conceptual diagram which shows an example of a control voltage, the voltage obtained by transforming a control voltage, and a signal. It is a figure which shows an example of a notional structure of the apparatus which detects the alternating voltage applied to an output line.

Embodiment.
As illustrated in FIG. 1, the compressor 10 includes a discharge port 10a, a suction port 10b, an electric motor M1, and a compression mechanism (not shown). The compression mechanism is driven by the electric motor M1, compresses the gas sucked from the suction port 10b, and discharges the compressed gas from the discharge port 10a.

  Such a compressor 10 is used, for example, in a known refrigerant circuit to compress the refrigerant. This refrigerant circuit is mounted on, for example, a heat pump unit (for example, a hot water supply system, an air conditioner, or a refrigeration apparatus). In addition, the apparatus in which the compressor 10 is mounted is not restricted to this, but is arbitrary.

  A power converter 1 is connected to the electric motor M1, and a power source E1 is connected to the power converter 1. The power conversion unit 1 is controlled by the compressor control unit 3 to appropriately convert the voltage from the power source E1, and applies this to the motor M1. The electric motor M1 rotates according to the applied voltage, and drives the compressor 10.

  Here, as the motor M1, for example, a known permanent magnet synchronous motor including a field element having a permanent magnet and an armature having a winding is assumed. A voltage is applied by the power conversion unit 1 to the winding of the electric motor M1, and a current flows. The armature applies a rotating magnetic field to the field element by appropriately flowing current through the winding. The field element rotates relative to the armature according to the applied rotating magnetic field. The electric motor M1 is not necessarily limited to this. For example, a field element having a winding may be employed instead of the permanent magnet.

  Further, for example, an AC voltage is applied to such an electric motor M1 by the power converter 1. At this time, the power conversion unit 1 is, for example, an inverter, and a DC power source is employed as the power source E1, for example, as shown in FIG. The power converter 1 converts a DC voltage from the power source E1 into an AC voltage, and applies the AC voltage to the electric motor M1 (more specifically, an armature winding).

  More specifically, the power conversion unit 1 includes, for example, switching elements 1up, 1un, 1vp, 1vn, 1wp, 1wn. A pair of switching elements 1xp and 1xn (x represents u, v, and w) are connected in series between the positive electrode and the negative electrode of the power supply E1. A connection point between the pair of switching elements 1xp and 1xn is connected to the electric motor M1 via the output line 1x. In the illustration of FIG. 1, since a three-phase motor is assumed as the motor M1, the power conversion unit 1 includes a pair of switching elements for three phases. However, the number of phases of the motor M1 and the number of phases of the power conversion unit 1 (number of output lines) are not limited to this, and are arbitrary.

  In the example of FIG. 1, the switching elements 1xp and 1xn are insulated gate bipolar transistors. However, the present invention is not limited to this, and any transistor can be adopted. In addition, as illustrated in FIG. 1, the power conversion unit 1 may include a diode connected in parallel to each of the switching elements 1xp and 1xn. The diode is provided with its anode facing the negative side of the power source E1. As a result, application of a reverse voltage to the switching elements 1xp and 1xn can be suppressed. When the switching elements 1xp and 1xn have a parasitic diode such as a MOS field effect transistor, the diode can be substituted with the parasitic diode.

  The power converter 1 is not limited to an inverter, and may be a matrix converter that converts an AC voltage into an AC voltage having an arbitrary amplitude and frequency, for example. Here, as an example, the power conversion unit 1 will be described as an inverter.

  The compressor control unit 3 includes a switching signal generation unit 31, a current reference value setting unit 34, a compressor stop unit 35, and a rotation speed detection unit 32. The switching signal generator 31 generates a switching signal to be given to the power converter 1. For example, the switching signal generator 31 receives a command value (for example, a command value such as the rotation speed, torque, or current of the motor M1) from the outside, and generates a switching signal based on the command value by a known pulse width modulation method.

  Such a switching signal generation unit 31 generates a switching signal so that the magnitude of the output voltage of the power conversion unit 1 (here, the amplitude of the AC voltage, the same applies hereinafter) increases as the rotational speed of the electric motor M1 increases. . On the other hand, when the magnitude of the output voltage reaches a predetermined reference value (for example, an upper limit value), the switching signal generation unit 31 performs field weakening control and generates a switching signal to drive the electric motor M1 at a higher rotational speed. May be. Since such field weakening control is conventionally known, detailed description is omitted, and only an outline thereof will be described.

  The field weakening control is control that reduces the induced voltage generated in the armature winding by weakening the field of the field element, thereby increasing the rotation speed without increasing the magnitude of the output voltage. Here, since the field element of the electric motor M1 is assumed to have a permanent magnet, the field itself cannot be directly controlled. Therefore, by adopting a negative value for the d-axis current that flows through the armature winding, the magnetic field flux in the d-axis direction is reduced using the demagnetization effect due to the armature reaction, and equivalent field-weakening control is realized. To do.

  In addition, although the field element which has a permanent magnet was mentioned as an example and demonstrated, the field element which has a coil | winding instead of a permanent magnet may be employ | adopted. In this case, the field may be weakened directly by controlling the current flowing in the winding of the field element. In addition, the above-described control in a field element having a permanent magnet is also called weak flux control, as distinguished from weak field control that directly weakens the field. In addition, as a flux weakening control, a control that adopts a negative value as the d-axis current while maintaining the induced voltage generated in the armature winding substantially constant, that is, maintaining the magnitude of the output voltage at an upper limit value, for example. You can go. Hereinafter, the field weakening control and the field weakening magnetic flux control are collectively referred to as field weakening control.

  Further, as shown in FIG. 1, a current detection unit 33 is connected to the compressor control unit 3. The current detection unit 33 detects a current flowing to the electric motor M1. However, in the illustration of FIG. 1, the current detection unit 33 detects a direct current (hereinafter, current I) input to the power conversion unit 1. This is because the direct current is converted into a three-phase alternating current, for example, by the power converter 1 and flows through the motor M1, so that the direct current can also be grasped as a current flowing through the motor M1. Unlike the example of FIG. 1, the current detection unit 33 may detect at least one of the three-phase AC currents (line currents) flowing through the electric motor M <b> 1.

  The current I detected by the current detection unit 33 is input to the compressor stop unit 35. The compressor stop unit 35 includes a comparator 351 that compares the current I with the current reference value Iref. The comparator 351 is formed by an operational amplifier, for example. The compressor stop unit 35 controls the power conversion unit 1 to stop the electric motor M1 when the current I is larger than the current reference value Iref. As a result, the compressor 10 is stopped. The motor M1 can be stopped, for example, as follows. That is, for example, all of the switching elements 1up, 1un, 1vp, 1vn, 1wp, 1wn are made non-conductive. As a result, the electric motor M1 can be stopped. Alternatively, all of the switching elements 1up, 1vp, 1wp or all of the switching elements 1un, 1vn, 1wn may be made conductive. As a result, the motor M1 can be stopped. Alternatively, all of the switching elements 1up, 1vp, 1wp or all of the switching elements 1un, 1vn, 1wn may be made conductive. As a result, the output lines 1u, 1v, 1w are short-circuited, so that the motor M1 can be stopped.

  In the example of FIG. 1, for example, the compressor stop unit 35 includes a logic circuit 352. The logic circuit 352 receives the output of the comparator 351 and the output of the switching signal generator 31. The logic circuit 352 outputs a switching signal for stopping the power conversion unit 1 when the current I is larger than the current reference value Iref, and switches from the switching signal generation unit 31 when the current I is smaller than the current reference value Iref. The signal is output to the power converter 1. For example, the comparator 351 outputs an active signal when the current I is larger than the current reference value Iref. Further, for example, the switching elements 1xp and 1xn are both turned on by receiving an activated switching signal (control voltage). In this case, the logic circuit 352 is, for example, an AND circuit. As a result, the logic circuit 352 outputs the switching signal from the switching signal generation unit 31 to the power conversion unit 1 while receiving the activated signal from the comparator 351, and receives the inactivated signal from the comparator 351. Sometimes, an inactive switching signal is output to the power converter 1.

  The current reference value Iref is set by the current reference value setting unit 34. The current reference value setting unit 34 sets the current reference value Iref according to the rotational speed ω of the electric motor M1. The rotational speed ω is acquired by the rotational speed detector 32. For example, the rotation speed detection unit 32 is a rotation speed detection sensor attached to the electric motor M1. When the switching signal generator 31 generates a switching signal based on, for example, an externally input rotational speed command value, the rotational speed detector 32 receives the rotational speed command value and acquires it as the rotational speed ω. Also good.

  The current reference value setting unit 34 receives the rotation speed ω from the rotation speed detection unit 32 and sets the current reference value Iref according to the rotation speed. More specifically, when the rotational speed ω is smaller than the rotational speed reference value ωref, the first value is given to the compressor stop unit 35 (more specifically, the comparator 351) as the current reference value Iref (see also FIG. 2). . When the rotation speed ω is larger than the rotation speed reference value ωref, the second value (> first value) is given to the compressor stop unit 35 (more specifically, the comparator 351) as the current reference value Iref.

  In the example of FIG. 1, for example, the current reference value setting unit 34 includes a rotation speed reference value output unit 341, a comparator 342, and a current reference value output unit 343. The rotation speed reference value output unit 341 outputs a preset rotation speed reference value ωref to the comparator 342. Further, the rotational speed ω from the rotational speed detector 32 is also input to the comparator 342. The comparator 342 compares the rotational speed ω with the rotational speed reference value ωref, and outputs the comparison result to the current reference value output unit 343. The current reference value output unit 343 outputs the first value as the current reference value Iref when the rotational speed ω is smaller than the rotational speed reference value ωref, and the current reference value Iref when the rotational speed ω is larger than the rotational speed reference value ωref. As a second value (> first value).

  Therefore, according to the compressor control unit 3, when the rotational speed ω is smaller than the rotational speed reference value ωref, the compressor 10 is stopped when the current I is larger than the first value. When the rotational speed ω is larger than the rotational speed reference value ωref, the compressor 10 is stopped when the current I is larger than the second value (> first value).

  In FIG. 3, the rotation speed ω is taken on the horizontal axis, and the pressure of the gas (hereinafter referred to as high pressure) Hp flowing on the discharge port 10 a side of the compressor 10 flows on the coordinate on the vertical axis. Illustrated is an equicurrent line of current (current I or amplitude of line current). In the illustration of FIG. 3, equicurrent lines with squares, triangles, inverted triangles, diamonds, circles, stars, pentagons, and trapezoids are shown as current values 10A, 12A, 14A, 16A, 17A, 18A, 20A and 22A, respectively. Indicates.

  As can be understood from FIG. 3, if the rotational speed ω is constant, the higher the current flowing through the electric motor M1, the higher the high pressure Hp.

  In the illustration of FIG. 3, if the current is constant in a region where the rotational speed ω is high, the high pressure Hp decreases relatively steeply as the rotational speed ω increases. In other words, when the rotational speed ω is greater than 80 rps, the rate of decrease of the high pressure Hp with respect to the rotational speed ω is higher than the rate of decrease when the rotational speed ω is less than 8 rps.

  This is due to the following reason, for example. That is, here, in a region where the rotational speed ω is high (for example, a region where the rotational speed ω is higher than the rotational speed reference value ωref), the switching signal generator 31 drives the electric motor M1 by field weakening control. In the field weakening control, the field needs to be weakened as the rotational speed ω is increased. Therefore, the negative value of the d-axis current needs to be decreased as the rotational speed ω is increased (the absolute value needs to be increased). In other words, if the three-phase current flowing through the electric motor M1 is the same, the torque of the electric motor M1 decreases as the rotational speed ω increases, and consequently the high pressure Hp of the compressor 10 decreases.

Further, an upper limit value Hpmax (for example, 55.1 kgf / cm ² ) is set for the high pressure Hp. The current reference value Iref is set so as not to drive the compressor 10 in a state where the high voltage Hp exceeds the upper limit value Hpmax. As an example, for example, 85 rps is adopted as the rotational speed reference value ωref, and for example, 18 A is adopted as the current reference value Iref (that is, the first value) when the rotational speed ω is smaller than 85 rps. For example, 22 A is adopted as the current reference value Iref (ie, the second value). Therefore, the current reference value Iref is represented by a line indicated by a thick line in FIG.

  According to the compressor control unit 3, the compressor stop unit 35 stops the compressor 10 when the current I is larger than the current reference value Iref. Therefore, the compressor 10 stops in the region above the current reference value Iref in FIG. Therefore, the high pressure Hp can be prevented from exceeding the upper limit value Hpmax.

  Also, unlike the compressor control unit 3, if the current reference value Iref is, for example, a constant 18A regardless of the rotational speed ω, it is above the 18A isocurrent line (star in FIG. 3). Then, the compressor 10 stops. On the other hand, according to the compressor control unit 3, in the region where the rotational speed ω is greater than 85 rps, the compressor 10 stops above the 22A isocurrent line (trapezoid in FIG. 3). Therefore, the operating range of the compressor 10 can be expanded as compared with a case where the current reference value Iref is 18 A, for example, regardless of the rotational speed ω. More specifically, it is possible to widen the operation region by the region (the shaded region in FIG. 3) where the rotational speed ω is greater than 85 rps and is sandwiched between the 18 A isoelectric line and the 22 A isoelectric line. it can.

  Moreover, according to this embodiment, there is no need to provide a high-pressure protection device having a pressure sensor. Since the pressure sensor is more expensive than the current detection circuit and the voltage detection circuit, omission of the pressure sensor is effective. The rotation speed detector 32 is often used for controlling the electric motor M1, and the current detector 33 is also often used for controlling the electric motor M1. Therefore, these are often existing. Therefore, in this case, it is not necessary to add a new sensor or the like, and the conventional cost increase can be suppressed.

  In the above example, the first value and the second value are employed as the current reference value Iref. However, the value adopted as the current reference value Iref is not limited to two values, and two or more values may be adopted. For example, as illustrated in FIG. 4, when the rotational speed ω is smaller than the rotational speed reference value ωref1 (for example, 85 rps), the first value (for example, 18A) is taken, and the rotational speed ω rotates more than the rotational speed reference value ωref1. The second value (> first value, for example, 22A) is taken when the speed is smaller than the speed reference value ωref2 (for example, 95 rps), and the third value (> second value) is taken when the rotational speed ω is larger than the rotation speed reference value ωref2. For example, 24A) may be used. As a result, the operating range of the compressor 10 can be further expanded.

  Further, in the example of FIG. 1, the compressor stop unit 35 includes a comparator 351 and a logic circuit 352. Therefore, maintaining the high pressure Hp below the upper limit value Hpmax can be realized by hardware. Therefore, the reliability is higher than that realized by software.

  Further, as illustrated in FIG. 5, the power conversion unit 1 may include a switch S1. The switch S1 is provided between the power supply E1 and the power conversion unit 1a, and selects supply / cutoff of power from the power supply E1 to the power conversion unit 1a. The power conversion unit 1a is the same as the power conversion unit 1 in FIG. 1 and converts, for example, a DC voltage from the power source E1 into an AC voltage. In the illustration of FIG. 5, the two switches S1 are provided between the power source E1 and the power conversion unit 1a, but only one of them may be provided.

  The comparator 351 compares the current I with the current reference value Iref, and gives a signal to the switch S1 to cut off the switch S1 when the current I is larger than the current reference value Iref. As a result, the electric motor M1 stops, and as a result, the compressor 10 stops. Even in such a configuration, the compressor stop unit 35 can be realized by hardware, so that the reliability is high.

<Rotation speed detector 32>
In the illustration of FIG. 6, the rotation speed detection unit 32 detects the control voltage Vsu1 applied to the control electrode of the switching element included in the power conversion unit 1, and acquires the rotation speed ω of the electric motor M1 based on the control voltage Vsu1. Hereinafter, after the power conversion unit 1 is first described in detail, the rotation speed detection unit 32 will be described.

  The power converter 1 is an inverter having a pair of switching elements 1xp and 1xn as illustrated in FIG. Each of these switching elements 1xp, 1xn has a control electrode, and is turned on / off according to a control voltage applied to the control electrode. This control voltage is applied by the switching signal generator 31. Then, the switching signal generation unit 31 appropriately controls the switching elements 1xp and 1xn to cause the power conversion unit 1 to convert the DC voltage from the power source E1 into an AC voltage and output the AC voltage to the electric motor M1. In the following, first, the conversion from a DC voltage to an AC voltage will be outlined.

  The switching elements 1xp and 1xn are controlled exclusively with each other. This is to prevent a large current from flowing through the switching elements 1xp and 1xn due to the conduction of the switching elements 1xp and 1xn at the same time.

  When the switching element 1xp is turned on and the switching element 1xn is turned off, a high voltage is applied to the output line 1x by connecting the positive electrode of the power source E1. On the other hand, if the switching element 1xp is non-conductive and the switching element 1xn is conductive, the output line 1x is connected to the negative electrode of the power source E1 and a low voltage is applied. Therefore, a high voltage and a low voltage can be repeatedly applied to the output line 1x by appropriately controlling the conduction / non-conduction of the switching elements 1xp and 1xn.

  Then, by adjusting the period during which the high voltage is applied to the output line 1x and the period during which the low voltage is applied, for example, the AC voltage Vx applied to the output line 1x is approximated to a sine wave as shown in FIG. be able to. That is, the AC voltage Vx is approximated to a sine wave by broadening the pulse width at the sine wave peak and narrowing the pulse width at the valley part.

  The electric motor M1 rotates at a rotational speed ω corresponding to the frequency of the input AC voltage Vx. As described above, the AC voltage Vx is generated based on conduction / non-conduction of the pair of switching elements 1xp and 1xn. In other words, the alternating voltage Vx corresponds to the control voltage of the switching elements 1xp and 1xn, and the frequency of the fundamental component of the alternating voltage Vx is substantially equal to the frequency of the fundamental component of the control voltage of the switching elements 1xp and 1xn. Therefore, the rotation speed detector 32 detects this control voltage.

  More specifically, the rotation speed detection unit 32 includes a control voltage detection unit 321, a pulse / sine wave conversion unit 322, a comparison unit 323, and a rotation speed calculation unit 324 as illustrated in FIG. The control voltage detector 321 detects a control voltage applied to one control electrode of the pair of switching elements 1xp and 1xn. In the illustration of FIG. 1, three sets of switching elements 1xp and 1xn are provided, but the control voltage detection unit 321 may detect the control voltage of any one of the switching elements 1xp or the switching element 1xn. Here, the control voltage of the switching element 1un is detected.

  The control voltage detector 321 has, for example, a resistance, and the resistance is between the control electrode (for example, gate electrode) of the switching element 1un and one end (for example, emitter electrode) on the negative side of the power supply E1 among both ends of the switching element 1un. Between. The control voltage detector 321 outputs a pulsed control voltage Vsu1 (see also FIG. 8) applied to the resistor to the pulse / sine wave converter 322.

  In the example of FIG. 6, a buffer 325 is provided between the control voltage detection unit 321 and the pulse / sine wave conversion unit 322. Although the buffer 325 is not an essential requirement, the buffer 325 can suppress fluctuations in the control voltage Vsu1 applied to the control electrode of the switching element 1un due to the operation after the pulse / sinusoidal converter 322. As such a buffer, for example, an operational amplifier can be adopted. This is because an operational amplifier in which an inverting input terminal and an output terminal are connected functions as a buffer having a high input impedance and a low output impedance. Therefore, the output of the control voltage detector 321 may be input to the non-inverting input terminal, and the output terminal may be connected to the pulse / sine wave converter 322.

  The pulse / sine wave converter 322 receives the pulsed control voltage Vsu1 and averages it to output a substantially sinusoidal voltage (hereinafter referred to as a sine wave voltage) WV1 (see also FIG. 8). The pulse / sine wave conversion unit 322 is a filter, for example, and generates a substantially sine wave voltage WV1 by removing a harmonic component of the control voltage Vsu1. In the example of FIG. 6, a low-pass filter including a resistor 3221 and a capacitor 3223 is illustrated as the pulse / sine wave converter 322. According to this, the pulse / sine wave converter 322 can be realized with a simple configuration. Further, the waveform of the sine wave voltage WV1 can be adjusted by adjusting the time constant of the low-pass filter. The time constant is set so that the control voltage Vsu1 can be appropriately converted into a substantially sine wave in the entire range where the frequency of the fundamental wave component of the control voltage Vsu1 takes the minimum value to the maximum value.

  The comparator 323 receives the sine wave voltage WV1, compares the sine wave voltage WV1 with a predetermined value, and outputs a signal PS1 (see also FIG. 8) that is activated / deactivated according to the comparison result. In the illustration of FIG. 8, the center of the amplitude of the sine wave voltage WV1 is adopted as the predetermined value. However, the predetermined value is not limited to this, and an arbitrary value is adopted as long as the value intersects the sine wave voltage WV1. For example, the predetermined value is set in advance. In the example of FIG. 6, the predetermined value is set by the setting unit 3231, and the setting unit 3231 outputs the predetermined value to the comparison unit 323.

  The signal PS1 output by the comparison unit 323 rises at substantially the same frequency as that of the sine wave voltage WV1, and similarly falls at substantially the same frequency as that of the sine wave voltage WV1.

  The rotation speed calculation unit 324 receives the signal PS1, and detects the frequency f of the signal PS1 based on the time when the signal PS1 rises or falls. The frequency of the sine wave voltage WV1 is substantially the same as the frequency of the fundamental wave component of the control voltage Vsu1, and the frequency of the fundamental wave component of the control voltage Vsu1 is substantially the same as the frequency of the fundamental wave component of the AC voltage Vu. Therefore, the frequency f can be regarded as the frequency of the fundamental wave component of the AC voltage Vu. The rotation speed calculation unit 324 calculates the rotation speed ω of the electric motor M1 based on the detected frequency f. For example, if the motor M1 is a permanent magnet synchronous motor, the rotational speed ω can be obtained by dividing the frequency f by the number P of the field element pole pairs.

  As described above, the rotation speed detection unit 32 detects the control voltage Vsu1 and calculates the rotation speed. This control voltage Vsu1 (for example, 5V) is smaller than the AC voltage Vu (for example, the amplitude is several hundred V) applied to the output line 1u. Therefore, the withstand voltage of the pulse / sine wave conversion unit 322, the comparison unit 323, and the rotation speed calculation unit 324 can be reduced as compared with the case where the AC voltage Vu is detected.

  Further, when detecting the AC voltage Vu, in order to employ the rotation speed detecting unit 32 having a low withstand voltage, for example, as shown in FIG. 9, the AC voltage Vu is reduced by a voltage dividing circuit having resistors R1 and R2 to obtain the voltage Vu1. To detect. Thereby, a voltage Vu1 smaller than the AC voltage Vu can be detected. On the other hand, when the control voltage detector 321 detects a voltage using a resistor, the manufacturing cost is low because only one resistor may be employed. In addition, when detecting the AC voltage Vu, relatively large electric power is supplied to the resistors R1 and R2, and thus it is necessary to employ the resistors R1 and R2 having high capacities (for example, current capacities). According to the detection unit 32, it is possible to employ a resistor having a small capacitance.

Modified example.
In the embodiment, the current reference value Iref is set according to the rotational speed ω. In this modification, a current reference value Iref2 smaller than the current reference value Iref is provided. The current reference value Iref2 is, for example, a value smaller than the current reference value Iref by a predetermined value.

  When the current I is larger than the current reference value Iref2, the switching signal generation unit 31 performs droop control and generates a switching signal. The drooping control here is control for reducing the output power of the power conversion unit 1. This drooping control can be executed as follows, for example. That is, for example, the switching signal generation unit 31 performs correction to reduce the pulse width of the generated switching signal at a predetermined rate, and gives the corrected switching signal to the power conversion unit 1. Alternatively, when the switching signal generation unit 31 generates a switching signal based on a command value such as the output current, output voltage, or torque of the electric motor M1 of the power conversion unit 1, the correction is performed by reducing the command value. A switching signal is generated based on the subsequent command value.

  Since such drooping control can suppress an increase in the high pressure of the compressor 10, the operation of the compressor 10 can be continued. When the current I becomes larger than the current reference value Iref by such drooping control, the compressor 10 is stopped in the same manner as in the embodiment.

DESCRIPTION OF SYMBOLS 1 Power conversion part 10 Compressor 32 Rotation speed detection part 33 Current detection part 34 Current reference value setting part 35 Compressor stop part 321 Control voltage detection part 322 Pulse / sinusoidal wave conversion part 323 Comparison part 324 Rotation speed calculation part

Claims (3)

A compressor (10) having a discharge port (10a), a suction port (10b), and an electric motor (M1), and compressing the gas sucked from the suction port and discharging it from the discharge port by the operation of the electric motor; A compressor control device for controlling
A power converter (1) connected to a power source (E1), converts the voltage from the power source into a desired voltage and applies it to the electric motor,
A rotation speed acquisition unit (32) for acquiring the rotation speed of the electric motor;
A current detector (33) for detecting the current flowing to the motor;
A comparison unit (351) that compares the current (I) and a current reference value (Iref) is provided, and controls the power conversion unit to stop the electric motor when the current is larger than the current reference value. Compressor stop (35),
When the rotational speed (ω) is smaller than the rotational speed reference value (ωref1), the current reference value is given to the compressor stop unit, and when the rotational speed is larger than the rotational speed reference value. A current reference value setting unit (34) that gives the compressor stop unit a second value larger than the first value as the current reference value ;
The electric motor (M1) includes a field element and an armature,
The compressor controller is
When the rotational speed (ω) is larger than the rotational speed reference value (ωref1), the power conversion unit is controlled by field weakening control or field weakening magnetic flux control that weakens the field from the field element to the armature. Control part (31)
Ru comprising a compressor control system. A compressor (10) having a discharge port (10a), a suction port (10b), and an electric motor (M1), and compressing the gas sucked from the suction port and discharging it from the discharge port by the operation of the electric motor; A compressor control device for controlling
A power converter (1) connected to a power source (E1), converts the voltage from the power source into a desired voltage and applies it to the electric motor,
A rotation speed acquisition unit (32) for acquiring the rotation speed of the electric motor;
A current detector (33) for detecting the current flowing to the motor;
A comparison unit (351) that compares the current (I) and a current reference value (Iref) is provided, and controls the power conversion unit to stop the electric motor when the current is larger than the current reference value. Compressor stop (35),
When the rotational speed (ω) is smaller than the rotational speed reference value (ωref1), the current reference value is given to the compressor stop unit, and when the rotational speed is larger than the rotational speed reference value. A current reference value setting unit (34) for giving the compressor stop unit a second value larger than the first value as the current reference value;
With
The current reference value setting unit (34) is configured to output the current reference value (Iref) when the rotational speed (ω) is larger than the rotational speed reference value (ωref1) and smaller than a second rotational speed reference value (ωref2). The second value is given to the compressor stop unit (35) as a third reference value that is larger than the second value as the current reference value when the rotation speed is larger than the second rotation speed reference value. Compressor control device for the compressor stop . A compressor (10) having a discharge port (10a), a suction port (10b), and an electric motor (M1), and compressing the gas sucked from the suction port and discharging it from the discharge port by the operation of the electric motor; A compressor control device for controlling
A power converter (1) connected to a power source (E1), converts the voltage from the power source into a desired voltage and applies it to the electric motor,
A rotation speed acquisition unit (32) for acquiring the rotation speed of the electric motor;
A current detector (33) for detecting the current flowing to the motor;
A comparison unit (351) that compares the current (I) and a current reference value (Iref) is provided, and controls the power conversion unit to stop the electric motor when the current is larger than the current reference value. Compressor stop (35),
When the rotational speed (ω) is smaller than the rotational speed reference value (ωref1), the current reference value is given to the compressor stop unit, and when the rotational speed is larger than the rotational speed reference value. A current reference value setting unit (34) for giving the compressor stop unit a second value larger than the first value as the current reference value;
With
The power source (E1) is a DC power source,
The power converter (1) has a pair of switching elements (1xp, 1xn) connected in series between a positive electrode and a negative electrode of the DC power supply, and a connection point between the pair of switching elements is Each of the pair of switching elements connected to the electric motor has a control electrode, and a pulsed control voltage is input to the control electrode to be turned on / off,
The rotational speed acquisition unit (32)
A control voltage detector (321) for detecting the control voltage applied to one of the control electrodes of the pair of switching elements;
A pulse / sine wave converter (322) that averages the control voltage and converts the control voltage into a substantially sinusoidal sinusoidal voltage;
A comparator (323) for outputting a signal that is activated / deactivated according to a comparison result between the sine wave voltage and a predetermined value;
A rotation speed calculation unit (324) that detects a frequency of the signal and supplies the rotation speed to the current reference value setting unit based on the frequency;
A compressor control device.

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