Power conversion device and air conditioner

Abstract

Provided are a power conversion device and the like in which the driving of a motor is easily continued even if an instantaneous voltage drop or an instantaneous power failure occurs. This power conversion device (100) comprises a converter circuit (10), an inverter circuit (20), a DC voltage detection unit (40), and motor current detection units (51, 52), and also comprises a control unit (60) for controlling the inverter circuit (20). If an instantaneous voltage drop or an instantaneous power failure of an AC power supply (E1) is detected, the control unit (60) performs an instantaneous power failure control for reducing the speed of a motor (M1) such that the motor current becomes equal to or less than a predetermined value. The predetermined value is lower than an overcurrent threshold value, which is a criterion for determining whether to temporarily stop the motor (M1).

Description

Power converters and air conditioners

[0001] This disclosure relates to power converters and air conditioners.

[0002] Regarding inverter control in the event of instantaneous voltage drops or power outages, for example, the technology described in Patent Document 1 is known. Specifically, Patent Document 1 describes an inverter for a compressor that reduces the rotational speed of the compressor when the power supply voltage drops below a predetermined instantaneous voltage threshold.

[0003] Japanese Patent Publication No. 2018-119701

[0004] The technology described in Patent Document 1 does not particularly consider the motor current when reducing the motor's rotational speed. It is desirable to have a control system that takes the motor current into account and allows the motor to continue driving even when a momentary voltage drop or power outage occurs, but such a technology is not described in Patent Document 1.

[0005] Therefore, the objective of this disclosure is to provide a power conversion device, etc., that facilitates the continuation of motor operation even when momentary voltage drops or momentary power outages occur.

[0006] To solve the aforementioned problems, the power conversion device according to this disclosure comprises a converter circuit that converts an AC voltage applied from an AC power source into a DC voltage, an inverter circuit that converts the DC voltage on the output side of the converter circuit into an AC voltage and applies the AC voltage to a motor, a DC voltage detection unit that detects the DC voltage on the output side of the converter circuit, and a motor current detection unit that detects the motor current flowing through the windings of the motor, and a control unit that controls the inverter circuit based on data including the detected values ​​of the DC voltage detection unit and the motor current detection unit, wherein when the control unit detects an instantaneous voltage drop or momentary power outage of the AC power source, it performs momentary power outage control to reduce the rotational speed of the motor so that the motor current is less than or equal to a predetermined value, and the predetermined value is lower than the overcurrent threshold which is the criterion for deciding whether or not to stop the motor.

[0007] According to this disclosure, it is possible to provide a power conversion device, etc., that makes it easier for the motor to continue driving even when a momentary voltage drop or momentary power outage occurs.

[0008] This is a configuration diagram of the power converter according to the first embodiment. This is a functional block diagram of the control unit of the power converter according to the first embodiment. This is the composite vector V when no momentary power outage occurs in the power converter according to the first embodiment. １ This is an explanatory diagram. In the power converter according to the first embodiment, when momentary power outage control is performed in the event of a momentary power outage, the composite vector V １ This is an explanatory diagram. In the power converter according to the first embodiment, when momentary power outage control and field weakening control are performed in the event of a momentary power outage, the composite vector V １ This is an explanatory diagram. This is a flowchart of the process executed by the control unit of the power converter according to the first embodiment. This is a waveform diagram when momentary power interruption control is performed in the power converter according to the first embodiment. This is the composite vector I when momentary power interruption control is performed in the power converter according to the first embodiment. １ This is an explanatory diagram. This is a configuration diagram of a power converter according to the second embodiment. This is a configuration diagram of an air conditioner according to the third embodiment. This is a waveform diagram of a comparative example where momentary power interruption control is not performed. This is the composite vector I in the comparative example where momentary power interruption control is not performed. １ This is an explanatory diagram.

[0009] <First Embodiment> <Configuration of Power Conversion Device> Figure 1 is a configuration diagram of the power conversion device 100 according to the first embodiment. The power conversion device 100 shown in Figure 1 is a device that converts an AC voltage applied from an AC power source E1 into a DC voltage, and further converts this DC voltage into a predetermined AC voltage before applying it to a motor M1. The motor M1 may be, for example, a permanent magnet synchronous motor, or it may be another type of motor. As shown in Figure 1, the power conversion device 100 includes a converter circuit 10, an inverter circuit 20, a power supply voltage detection unit 30, a DC voltage detection unit 40, motor current detection units 51, 52, a control unit 60, and a gate drive circuit 80.

[0010] The converter circuit 10 is a circuit that converts the AC voltage applied from the AC power supply E1 into a DC voltage. The input side of the converter circuit 10 is connected to the AC power supply E1 via three-phase wiring KR, KS, and KT, and the output side is connected to the inverter circuit 20 via a pair of DC lines K1 and K2. As shown in Figure 1, the converter circuit 10 includes a diode bridge circuit 11, a DC reactor 12, and a smoothing capacitor 13.

[0011] The diode bridge circuit 11 is a full-wave rectifier circuit and is equipped with six diodes D1 to D6. The diode bridge circuit 11 is configured as a "leg" in which a pair of diodes are connected in series, and includes a first leg (not shown by reference numerals, the same applies hereafter), a second leg, and a third leg.

[0012] The first leg consists of a pair of diodes D1 and D2 connected in series. The cathode of diode D1 is connected to the positive DC line K1. The anode of diode D1 is connected to the cathode of the other diode D2. The anode of the other diode D2 is connected to the negative DC line K2. The same applies to the remaining second and third legs. These first, second, and third legs are connected in parallel to each other.

[0013] The connection point between diodes D1 and D2 in the first leg is connected to the AC power supply E1 via the R-phase wiring KR. The connection point between diodes D3 and D4 in the second leg is connected to the AC power supply E1 via the S-phase wiring KS. The connection point between diodes D5 and D6 in the third leg is connected to the AC power supply E1 via the T-phase wiring KT. The three-phase AC voltage applied from the AC power supply E1 is converted to a DC voltage (pulsating DC voltage) by the diode bridge circuit 11.

[0014] The DC reactor 12 and the smoothing capacitor 13 are elements for smoothing the pulsating DC voltage applied from the diode bridge circuit 11. As shown in Figure 1, the DC reactor 12 is provided on the positive DC line K1. More specifically, on the positive DC line K1, the DC reactor 12 is provided between the connection point between the DC line K1 and the smoothing capacitor 13 and the diode bridge circuit 11.

[0015] The smoothing capacitor 13 is connected to a pair of DC lines K1 and K2 on the output side of the diode bridge circuit 11. That is, one end (one lead wire) of the smoothing capacitor 13 is connected to the positive DC line K1, and the other end (the other lead wire) is connected to the negative DC line K2. For example, a film capacitor or an electrolytic capacitor can be used as such a smoothing capacitor 13.

[0016] The inverter circuit 20 converts the DC voltage at the output of the converter circuit 10 into an AC voltage and applies this AC voltage to the motor M1. The inverter circuit 20 comprises a "leg" consisting of a pair of switching elements connected in series, namely a first leg (not shown, the same applies hereafter), a second leg, and a third leg. These first, second, and third legs are connected in parallel to the smoothing capacitor 13.

[0017] The first leg consists of a pair of switching elements Q1 and Q2 connected in series. The second and third legs are similar. In the example in Figure 1, IGBTs (Insulated Gate Bipolar Transistors) are used as such switching elements Q1 to Q6, but other types of switching elements such as MOSFETs (Metal-Oxide-Semiconductor Field-Effect Transistors) or bipolar transistors may also be used.

[0018] In the first leg of the inverter circuit 20, the connection point between the pair of switching elements Q1 and Q2 is connected to the U-phase winding of the motor M1 via wiring KU. In the second leg, the connection point between the switching elements Q3 and Q4 is connected to the V-phase winding of the motor M1 via wiring KV. In the third leg, the connection point between the switching elements Q5 and Q6 is connected to the W-phase winding of the motor M1 via wiring KW.

[0019] Furthermore, to prevent the destruction of switching elements Q1 to Q6 due to commutation, a freewheeling diode (not shown) is connected in antiparallel to each of the switching elements Q1 to Q6. Note that if the switching elements Q1 to Q6 have parasitic diodes (not shown), the parasitic diodes function as freewheeling diodes, so there is no particular need to provide separate freewheeling diodes.

[0020] The power supply voltage detection unit 30 detects the power supply voltage (AC voltage) of the AC power supply E1 and is connected to wirings KR, KS, and KT, respectively. The DC voltage detection unit 40 detects the DC voltage on the output side of the converter circuit 10 (i.e., the DC voltage across the smoothing capacitor 13) and is connected to wirings K1 and K2.

[0021] The motor current detection units 51 and 52 detect the motor current flowing through the windings of the motor M1. In the example shown in Figure 1, the motor current detection unit 51 detects the U-phase motor current and is connected to the U-phase wiring KU. Another motor current detection unit 52 detects the V-phase motor current and is connected to the V-phase wiring KV. The moment-by-moment detection values ​​from the power supply voltage detection unit 30, the DC voltage detection unit 40, and the motor current detection units 51 and 52 are output to the control unit 60.

[0022] The control unit 60 controls the inverter circuit 20 via the gate drive circuit 80. For example, a microcomputer (MPC) can be used as such a control unit 60. Although not shown in the diagram, the microcomputer is composed of electronic circuits including a CPU (Central Processing Unit), ROM (Read Only Memory), RAM (Random Access Memory), and various interfaces. It reads the program stored in the ROM, loads it into the RAM, and the CPU executes various processes.

[0023] The control unit 60 generates a predetermined PWM signal (Pulse Width Modulation) based on data including the detection values ​​from the power supply voltage detection unit 30, the DC voltage detection unit 40, and the motor current detection units 51 and 52, and controls the inverter circuit 20 with this PWM signal. The method for generating the PWM signal is well known, so its explanation is omitted. The PWM signal generated by the control unit 60 is output to the gate drive circuit 80.

[0024] The gate drive circuit 80 applies a predetermined voltage to each gate of the switching elements Q1 to Q6 based on the PWM signal input from the control unit 60. This switches the switching elements Q1 to Q6 on and off as predetermined, and applies an AC voltage to the three-phase winding of the motor M1.

[0025] <About instantaneous voltage drops and momentary power outages> For example, if lightning strikes a designated power transmission / distribution line (not shown) electrically connected to AC power source E1, or if a sudden load change occurs, the power supply voltage of AC power source E1 may drop instantaneously. This phenomenon is called an "instantaneous voltage drop." Also, the phenomenon in which the power supply voltage of AC power source E1 becomes nearly zero due to a temporary failure in the power system, etc., is called a "momentary power outage." Hereafter, instantaneous voltage drops and momentary power outages will be collectively referred to as "momentary power outages, etc."

[0026] When a momentary power failure or the like occurs, the power supply voltage of the AC power supply E1 instantaneously drops, so the upper limit value of the AC voltage that can be output from the inverter circuit 20 to the motor M1 also drops. In such a state, if power continues to be supplied to the motor M1 at the same level as before the occurrence of a momentary power failure or the like, the motor current may increase and exceed a predetermined overcurrent threshold value. The above-mentioned "overcurrent threshold value" is a threshold value serving as a criterion for determining whether or not to stop the motor M1 once (that is, whether or not to perform protection control against overcurrent), and is set in advance. Considering the operation of equipment (for example, an air conditioner) using the motor M1 as a drive source and the comfort of the user, it is desirable that the drive of the motor M1 continue even when a momentary power failure or the like occurs.

[0027] Therefore, in the present embodiment, when detecting an instantaneous voltage drop or momentary power failure of the AC power supply E1, the control unit 60 performs control to decelerate the rotational speed of the motor M1 (hereinafter, "momentary power failure control") so that the motor current becomes less than a predetermined value. The above-mentioned "predetermined value" is a predetermined threshold value lower than the overcurrent threshold value and is set in advance. By decelerating the motor M1 so that the motor current becomes less than the predetermined value in this way, it is possible to suppress the motor current from reaching the overcurrent threshold value. Therefore, even when a momentary power failure or the like occurs, it becomes easier to continue driving the motor M1.

[0028] FIG. 2 is a functional block diagram of the control unit 60. As shown in FIG. 2, the control unit 60 includes a three-phase / two-axis conversion unit 61, an axis error calculation unit 62, a PLL circuit 63, an integrator 64, a speed control unit 65, subtractors 66 and 67. In addition to the above-described configuration, the control unit 60 further includes a current control unit 68, a voltage command calculation unit 69, a V1 conversion unit 70, a modulation rate conversion unit 71, a V1 inverse conversion unit 72, a two-axis / three-phase conversion unit 73, and a PWM signal generation unit 74.

[0029] The three-phase / two-axis conversion unit 61 is based on the detected values of the motor current at the motor current detection units 51 and 52 (see FIG. 1) and the phase θ of the rotor of the motor M1 (see FIG. 1). dc and, based on this, the current in the three-phase coordinate system (I u , I v , I w ) is converted into the detected values of the currents on the d-axis and q-axis (I dc , Iqc Converts to (I). Note that the actual direction of the magnetic flux of the magnet in motor M1 is defined as the d-axis, and the axis perpendicular to this d-axis is defined as the q-axis. Also, the d-axis assumed in the control unit 60 is defined as the dc-axis (similarly for the qc-axis). In other words, the current detection value (I dc , I qc ) refers to the motor currents of the d-axis and q-axis assumed in the control unit 60.

[0030] The axis error calculation unit 62 calculates the current detection values ​​(I) of the dc axis and qc axis. dc , I qc ) and the d-axis voltage command V d ＊ And, q-axis voltage command V q ＊ And the actual rotational speed ω of motor M1 r Based on this, the axis error Δθ is calculated. Note that the axis error Δθ is the phase θ calculated by the integrator 64, which is the phase of the actual magnetic flux of the magnet in the motor M1 (see Figure 1). dc This is the difference between and .

[0031] The PLL circuit 63 controls the actual rotational speed ω of the motor M1 (see Figure 1) based on PI control (Proportional Integral Control) so that the axis error Δθ becomes zero. r The calculation is performed. As a result, the d-axis and q-axis assumed in the control unit 60 match the d-axis and q-axis corresponding to the actual magnetic flux of the motor M1, so that the motor M1 can be controlled without a position sensor. Note that "PLL" in the PLL circuit 63 is an abbreviation for "Phase Locked Loop".

[0032] The integrator 64 controls the actual rotational speed ω r By integrating, the phase θ of the rotor of motor M1 (see Figure 1) can be obtained. dc The integrator 64 performs the calculation. The calculation result of the integrator 64 is output to the 3-phase / 2-axis conversion unit 61 and also to the 2-axis / 3-phase conversion unit 73. The speed control unit 65 receives predetermined load determination information and a predetermined rotational speed command ω r ＊ And the actual rotational speed ω of motor M1 (see Figure 1) r Based on that, the q-axis current command I q ＊ Calculate.

[0033] The subtractor 66 receives a predetermined d-axis current command I d ＊ And the current detection value I, which is the calculation result of the 3-phase / 2-axis conversion unit 61. dc The difference ΔI between and d The following calculation is performed. Note that in field weakening control when the output voltage of the inverter circuit 20 (see Figure 1) is saturated, the d-axis current command I d ＊ Although it is set to a negative value, normally the d-axis current command I d ＊ This is set to zero. Another subtractor 67 receives the q-axis current command I, which is the result of the calculation by the speed control unit 65. q ＊ And the current detection value I, which is the calculation result of the 3-phase / 2-axis conversion unit 61. qc The difference ΔI between and q Calculate.

[0034] The current control unit 68 controls the difference ΔI d ΔI q The second d-axis current command I is set so that it becomes zero. d ＊＊ and the second q-axis current command I q ＊＊ The voltage command calculation unit 69 calculates the second d-axis current command I, which is the calculation result of the current control unit 68. d ＊＊ and the second q-axis current command I q ＊＊ Using the following equations (1) and (2), the d-axis voltage command V d ＊ and q-axis voltage command V q ＊ Perform the calculation.

[0035]

[0036]

[0037] Note that L is included in formula (1) q is the q-axis inductance of motor M1 (see Figure 1). Also, R included in equations (1) and (2) is the winding resistance of motor M1, and ω r ＊This is the rotational speed command for motor M1. Also, L included in equation (2) d is the d-axis inductance of motor M1, and Ke is the induced voltage constant.

[0038] The V1 conversion unit 70 converts the d-axis voltage command V d ＊ And, q-axis voltage command V q ＊ Using and based on the following equation (3), the d-axis voltage command V d ＊ and q-axis voltage command V q ＊ V1 is a value that indicates the magnitude (absolute value) of the composite vector. * Calculate.

[0039]

[0040] Furthermore, the V1 conversion unit 70 calculates the phase angle θ of the composite vector based on the following equation (4). Ｖ１ ＊ Calculate.

[0041]

[0042] The modulation rate conversion unit 71 calculates the value V1 which is the result of the calculation in equation (3). * And, DC voltage E dc Using and based on the following equation (5), the modulation rate KhV1 * Calculate.

[0043]

[0044] Note that the DC voltage E included in equation (5) dc The value used is the value detected by the DC voltage detection unit 40 (see Figure 1).

[0045] The V1 inverse transformer 72 shown in Figure 2 calculates the d-axis component of the V1 modulation rate, KhV1, based on the following equations (6) and (7). d * And, KhV1 is the q-axis component of the V1 modulation rate. q * The calculation is performed on and .

[0046]

[0047]

[0048] Note that KhV1 included in Expression (6) and Expression (7) * is the V1 modulation rate calculated by the above-described Expression (5). Also, sinθ included in Expression (6) Ｖ１* is the phase angle θ of the above-described synthesized vector Ｖ１* (the calculation result of Expression (4)) in terms of sine. Also, cosθ included in Expression (7) Ｖ１* is the phase angle θ of the above-described synthesized vector Ｖ１* in terms of cosine.

[0049] The two-axis / three-phase conversion unit 73 calculates the modulation rate commands for three phases (KhV dc , KhV u ＊ , KhV v ＊ , KhV w ＊ ) based on the d-axis component and q-axis component of the V1 modulation rate (the calculation results of Expression (6) and Expression (7)) and the phase θ that is the calculation result of the integrator 64.

[0050] The PWM signal generation unit 74 generates a predetermined PWM signal based on the modulation rate commands for three phases (KhV u ＊ , KhV v ＊ , KhV w ＊ ) which are the calculation results of the two-axis / three-phase conversion unit 73. Based on this PWM signal, the on / off states of the switching elements Q1 to Q6 (see FIG. 1) of the inverter circuit 20 (see FIG. 1) are switched. As a result, a predetermined three-phase alternating current flows through the windings of the motor M1 (see FIG. 1), thereby driving the motor M1.

[0051] FIG. 3 is an explanatory diagram of the synthesized vector V １ when no momentary power failure or the like has occurred. Note that the horizontal axis in FIG. 3 is the d-axis and the vertical axis is the q-axis. As shown in FIG. 3, the vector V ｄ of the d-axis voltage and the vector V q of the q-axis voltage are combined to obtain the synthesized vector V １ . The broken-line arc F1 shown in FIG. 3 is the synthesized vector V １This indicates the upper limit of the magnitude. Incidentally, when the output voltage of the inverter circuit 20 (see Figure 1) is made sine wave, the modulation rate KhV1 * The upper limit is set to approximately 1.154. The control unit 60 (see Figure 1) controls the composite vector V １ The voltage commands for the d-axis and q-axis are generated appropriately so that the magnitude of the motor remains below a predetermined upper limit (fitting within the dashed arc F1). This prevents motor M1 (see Figure 1) from losing steps.

[0052] Figure 4 shows the composite vector V when momentary power outage control is performed in the event of a momentary power outage. １ This is an explanatory diagram. When a momentary power outage occurs, the power supply voltage of the AC power supply E1 (see Figure 1) drops instantaneously. As a result, the DC voltage E on the output side of the converter circuit 10 (see Figure 1) drops. dc It also decreases, and from the relationship in equation (5) above, the composite vector V １ The upper limit of the magnitude also decreases. The dashed arc F1 shown in Figure 4 is the composite vector V when no momentary power outage occurs, similar to Figure 3. １ This indicates the upper limit of the magnitude. Also, the dashed arc F2 represents the composite vector V when a momentary power outage occurs. １ This indicates the upper limit of the size.

[0053] As described above, when a momentary power interruption of the AC power supply E1 is detected, the control unit 60 (see Figure 1) performs momentary power interruption control and decelerates the motor M1 so that the motor current falls below a predetermined value. As a result, from the relationship between equations (1) and (2) described above, the d-axis voltage command V d ＊ and q-axis voltage command V q ＊ Each of the values ​​decreases, and furthermore, from the relationship in equation (3), the d-axis voltage command V d ＊ and q-axis voltage command V q ＊ The composite vector V １ The magnitude of also becomes smaller. As a result, the composite vector V １Since the size is kept below a predetermined upper limit (the diameter of the dashed arc F2), motor M1 can be prevented from losing synchronization. In addition, because the motor current is kept below a predetermined value by momentary power interruption control, it is possible to prevent the motor current from exceeding the overcurrent threshold (i.e., motor M1 from stopping temporarily).

[0054] Furthermore, as will be explained below, the control unit 60 may appropriately perform field weakening control, and may also decelerate the motor M1 in the event of a momentary power outage or the like. Here, "field weakening control" is a control that generates a magnetic flux opposite to the magnetic flux of the permanent magnet (not shown) of the motor M1 by flowing a predetermined field weakening current (negative d-axis current).

[0055] Figure 5 shows the combined vector V when momentary power outage control and field weakening control are performed in the event of a momentary power outage. １ This is an explanatory diagram. The control unit 60 controls, for example, the V1 modulation rate KhV1 of the above-mentioned equation (5) * When the value reaches a predetermined upper limit (i.e., when the output voltage of the inverter circuit 20 saturates), field weakening control is performed. Such field weakening control may be performed during normal operation, but it may also be performed when a momentary power outage occurs. In field weakening control, the d-axis current command I d ＊ Since this becomes a negative value, the q-axis voltage command V can be obtained from the relationship in equation (2) described above. q ＊ The value of becomes smaller. Furthermore, from the relationship in equation (3), the d-axis voltage command V d ＊ and q-axis voltage command V q ＊ The composite vector V １ Its size will also decrease.

[0056] This results in the composite vector V １ Since the magnitude is kept below a predetermined upper limit (the diameter of the dashed arc F2), motor M1 can be prevented from losing synchronization. Furthermore, because the motor current is kept below a predetermined value by momentary power interruption control, it is possible to prevent the motor current from exceeding the overcurrent threshold. Incidentally, in the example in Figure 5, the composite vector V １Although the size has reached a predetermined upper limit (the diameter of the dashed arc F2), a predetermined margin is provided before the motor M1 loses step, so there is no particular risk of the motor M1 being impeded.

[0057] Thus, when the control unit 60 detects an instantaneous voltage drop or momentary power outage of the AC power supply E1, for example, it controls the inverter circuit 20 so that a field weakening current flows through the windings of the motor M1 while performing momentary power outage control (i.e., it performs field weakening control). This results in the combined vector V １ If there is a predetermined margin relative to the upper limit, the motor M1 can be driven at high speed by utilizing that margin in field weakening control.

[0058] <Processing of the Control Unit> Figure 6 is a flowchart of the processing performed by the control unit (see also Figure 1 as appropriate). Note that when "START" is reached in Figure 6, the motor M1 is driven by AC power supplied via the power converter 100. In step S101, the control unit 60 reads each detected value. That is, the control unit 60 reads the detected values ​​of the power supply voltage detection unit 30, the DC voltage detection unit 40, and the motor current detection units 51 and 52.

[0059] In step S102, the control unit 60 determines whether or not a momentary power outage has occurred. Specifically, the control unit 60 first calculates the peak value and effective value of the power supply voltage (AC voltage) based on the value detected by the power supply voltage detection unit 30. The effective value of the power supply voltage is updated at predetermined time intervals (for example, every second). On the other hand, the peak value of the power supply voltage is detected at a predetermined sampling period shorter than the predetermined time interval.

[0060] When a momentary power outage occurs, the peak value of the power supply voltage drops instantaneously, while the RMS value of the power supply voltage is retained (stored). As a result, the ratio of the peak value of the power supply voltage to the RMS value × √2 of the power supply voltage drops instantaneously. When the ratio of the peak value of the power supply voltage to the RMS value × √2 of the power supply voltage falls below a predetermined value, the control unit 60 determines that a momentary power outage has occurred. In this way, the control unit 60 detects a momentary voltage drop or momentary power outage of the AC power supply E1 based on the value detected by the power supply voltage detection unit 30.

[0061] In the configuration shown in Figure 1, an LC filter is formed by the DC reactor 12 and the smoothing capacitor 13. Therefore, a predetermined time delay occurs between the moment the power supply voltage drops instantaneously due to a momentary power outage, etc., and the subsequent drop in the DC voltage. In the first embodiment, as described above, since momentary power outages, etc., are detected based on the detection value of the power supply voltage detection unit 30, momentary power outages, etc., can be detected at an earlier timing compared to when the detection value of the DC voltage is used.

[0062] If no momentary power interruption or the like occurs in step S102 (S102: No), the control unit 60 continues normal operation (S107). If a momentary power interruption or the like occurs in step S102 (S102: Yes), the control unit 60 proceeds to step S103. In step S103, the control unit 60 determines whether or not momentary power interruption control is required. In step S103, the control unit 60 first determines the estimated value KhV1 of the modulation rate after the DC voltage on the output side of the converter circuit 10 has decreased due to the effects of a momentary interruption or the like. ES This is calculated based on the following equation (8).

[0063]

[0064] Furthermore, KhV1 included in equation (8) is the V1 modulation rate immediately before the detection of a momentary power interruption, etc., and is calculated based on equation (5) described above. VS This is the rate of fluctuation of the power supply voltage, and is calculated based on the value detected by the power supply voltage detection unit 30. More specifically, the ratio of the peak value of the power supply voltage immediately after the detection of a momentary power outage, etc., to the peak value of the power supply voltage immediately before the detection of a momentary power outage, etc., is the rate of fluctuation of the power supply voltage. VS That is the case.

[0065] Estimated value of the V1 modulation rate: KhV1 ES If the value is below a predetermined upper limit, the control unit 60 determines that momentary power interruption control is not required (S103: No) and continues normal operation (S107). In this case, a predetermined DC voltage corresponding to the load of the motor M1 (the DC voltage on the output side of the converter circuit 10) can be secured even during a momentary power interruption without performing momentary power interruption control. As a result, the motor current remains below a predetermined value even without performing momentary power interruption control. Meanwhile, the estimated value of the modulation rate KhV1 ESIf the value exceeds a predetermined upper limit, the control unit 60 determines that momentary power interruption control is required (S103: Yes), and proceeds to step S104.

[0066] In this manner, the control unit 60 estimates the modulation rate of the inverter circuit 20 (i.e., the V1 modulation rate) when instantaneous power interruption control is not performed, based on the value detected by the power supply voltage detection unit 30, and determines whether the motor current (motor current when instantaneous power interruption control is not performed) reaches a predetermined value based on this estimated modulation rate. When an instantaneous voltage drop or instantaneous power interruption of the AC power supply E1 is detected, and the control unit 60 determines that the motor current will not reach a predetermined value even without instantaneous power interruption control, the control unit 60 refrains from performing instantaneous power interruption control.

[0067] Furthermore, the determination process in step S102 is not performed while waiting for an increase in motor current, but is calculated based on the fluctuation rate of the power supply voltage (see equation (8)), so the necessity of momentary power interruption control can be determined at an early stage. In addition, it prevents the motor M1 from being unnecessarily decelerated by momentary power interruption control even when there is no particular need to decelerate the motor M1 in the event of a momentary power interruption.

[0068] In step S104, the control unit 60 performs momentary power interruption control. That is, the control unit 60 decelerates the motor M1 so that the motor current falls below a predetermined value. Details of step S104 will be described later.

[0069] Next, in step S105, the control unit 60 determines whether the momentary power interruption has been resolved. For example, if the ratio of the peak value of the power supply voltage to the effective value of the power supply voltage (a value held at predetermined intervals) × √2 becomes equal to or greater than a predetermined value, the control unit 60 determines that the momentary power interruption of the AC power supply E1 has been resolved (power has been restored). If the momentary power interruption has not been resolved in step S105 (S105: No), the control unit 60 returns to the process in step S104 and continues the momentary power interruption control. If the momentary power interruption has been resolved in step S105 (S105: Yes), the control unit 60 proceeds to step S106. In step S106, the control unit 60 accelerates the motor M1 with a predetermined rotational acceleration. Then, in step S107, the control unit 60 performs normal operation. That is, the control unit 60 restores the rotational speed of the motor M1 to the rotational speed before the detection of the momentary power interruption. Thus, when the instantaneous voltage drop or interruption of the AC power supply E1 is resolved (S105: Yes), the control unit 60 accelerates the motor M1 with a predetermined rotational acceleration (S106) and restores it to the rotational speed before the instantaneous voltage drop or interruption of the AC power supply E1 was detected (S107). After performing the process in step S107, the control unit 60 terminates the series of processes (END).

[0070] <About instantaneous power interruption control> In instantaneous power interruption control, the control unit 60 controls the inverter circuit 20 (see Figure 1) based on PI control, for example. More specifically, in instantaneous power interruption control, the control unit 60 calculates a correction value for the rotational speed command or rotational acceleration command of the motor M1 based on PI control that takes the difference between the target value (predetermined value) of the motor current and the detected values ​​of the motor current detection units 51 and 52 as input, and controls the inverter circuit 20 based on the correction value.

[0071] For example, the control unit 60 calculates a correction value for the rotational acceleration command of the motor M1, and then calculates a correction value for the rotational speed command of the motor M1 by integrating (successively summing) this correction value for the rotational acceleration command. By performing PI control in this way, the motor M1 can be smoothly decelerated with an appropriate acceleration (negative acceleration) while bringing the motor current closer to the target value (predetermined value). The correction value for the rotational acceleration command of the motor M1 is calculated repeatedly at a period that can follow changes in the power supply voltage and DC voltage.

[0072] Furthermore, when the control unit 60 performs momentary power interruption control, it is preferable to set the value of the rotational speed command for motor M1 immediately before the start of this momentary power interruption control as the upper limit value of the rotational speed command for motor M1 in said momentary power interruption control. This keeps the rotational speed of motor M1 below the upper limit value, thereby preventing motor M1 from being unnecessarily accelerated by PI control.

[0073] Figure 11 shows the waveform diagrams of a comparative example where momentary power interruption control is not performed. The horizontal axis of each waveform diagram in Figure 11 represents time. The vertical axes of each waveform diagram in Figure 11, from top to bottom, represent the power supply voltage, motor current, and motor M1 rotation speed. Incidentally, while Figure 11 shows only one phase of power supply voltage and motor current, in reality, there are three phases of power supply voltage and motor current (the same applies to Figure 7).

[0074] As shown in Figure 11, assume that an instantaneous voltage drop occurred at time t1, and that the instantaneous voltage drop was resolved at time t2. In this comparative example, no instantaneous power interruption control is performed in the interval from time t1 to t2, and the rotational speed of motor M1 remains approximately constant. As a result, the motor current increases in the interval from time t1 to t2 compared to before the instantaneous voltage drop occurred.

[0075] Figure 12 shows the composite vector I in a comparative example where momentary power interruption control is not performed. １ This is an explanatory diagram. Note that the explanatory diagram in Figure 12 corresponds to the waveform diagram in Figure 11. Also, the horizontal axis in Figure 12 is the d-axis, and the vertical axis is the q-axis. The composite vector I shown in Figure 12. １ is the d-axis current I d and q-axis current I qIt is a composite vector, and its magnitude is expressed by the following equation (9).

[0076]

[0077] In Figure 12, the dashed half-line G3 represents the composite vector I, which changes with the drive state of motor M1. １ This shows the trajectory when the current changes. For example, before the detection of a momentary power outage (before time t1 in Figure 11), the d-axis current I d Assume that the current is zero, and that field weakening control was performed during the momentary power outage (times t1 to t2 in Figure 11). In this case, the q-axis current I q While the negative d-axis current I is maintained at a predetermined value d Because it flows, the composite vector I follows the dashed half-line G3. １ It changes.

[0078] Figure 7 shows the waveform when momentary power interruption control is performed in the power converter according to the first embodiment. The horizontal and vertical axes of each waveform in Figure 7 are the same as those in Figure 11. In the example in Figure 7, momentary power interruption control is started from time t1 when the momentary voltage drop occurs, and continues until time t2 when the momentary voltage drop is resolved. After time t1, the rotational speed of the motor M1 gradually decreases based on PI control, and then begins to increase. As shown in Figure 7, in the interval from time t1 to t2, the motor current has hardly increased compared to before the momentary voltage drop occurred.

[0079] Figure 8 shows the composite vector I when momentary power interruption control is performed in the power converter according to the first embodiment. １ This is an explanatory diagram. Note that the explanatory diagram in Figure 8 corresponds to the waveform diagram in Figure 7. The dashed arc G2 in Figure 8 represents the composite vector I, which changes with the driving state of the motor M1. １ This shows the trajectory as it changes. The dashed arc G1 represents the composite vector I in the comparative example described above (see Figure 12). １ It shows the trajectory.

[0080] When the control unit 60 (see Figure 1) performs momentary power interruption control, the q-axis current command I is generated in conjunction with the deceleration of the motor M1. q ＊(The command value of the torque current) becomes smaller. As a result, the composite vector I from the relationship in equation (9) above １ The magnitude of becomes smaller (i.e., the motor current becomes smaller). In the example in Figure 8, the composite vector I １ Since the curve changes in a predetermined manner along the dashed arc G2, the motor current can be reduced compared to the comparative example (dashed arc G1).

[0081] <Effects> According to the first embodiment, when a momentary power interruption or the like is detected in the AC power supply E1, the control unit 60 decelerates the motor M1 so that the motor current falls below a predetermined value. Therefore, it is possible to suppress the inverter circuit 20 from stopping due to an increase in motor current. As a result, even if a momentary power interruption or the like occurs, the motor M1 is more likely to continue to run, thus improving the reliability of the power converter 100.

[0082] Furthermore, in the first embodiment, the control unit 60 detects momentary power interruptions, etc., based on the detected value of the power supply voltage. As a result, the control unit 60 can detect momentary power interruptions, etc., at an early timing with almost no influence from the LC filter formed by the DC reactor 12 (see Figure 1) and the smoothing capacitor 13 (see Figure 1) (the influence of the time delay when momentary power interruptions, etc., are reflected in the DC voltage). Therefore, the process of decelerating the motor M1 can be started at an early timing when a momentary power interruption, etc., occurs.

[0083] Furthermore, in instantaneous power interruption control, the control unit 60 decelerates the motor M1 based on, for example, PI control. As a result, the motor M1 is decelerated with a moderate negative acceleration, which suppresses control instability compared to when the motor M1 is decelerated rapidly. Also, even if an instantaneous power interruption occurs (S102: Yes in Figure 6), if there is no particular need to perform instantaneous power interruption control (S103: No), the control unit 60 does not decelerate the motor M1. This prevents the motor M1 from being decelerated unnecessarily, making it easier for the motor M1 to continue normal operation.

[0084] ≪Second Embodiment≫ The second embodiment differs from the first embodiment in that the power converter 100A (see Figure 9) does not specifically include a power supply voltage detection unit 30 (see Figure 1). Furthermore, the second embodiment differs from the first embodiment in that it detects momentary power interruptions, etc., based on the DC voltage on the output side of the converter circuit 10 (see Figure 9). Other aspects are the same as the first embodiment. Therefore, we will explain the parts that differ from the first embodiment, and omit explanations of overlapping parts.

[0085] Figure 9 is a configuration diagram of the power converter 100A according to the second embodiment. As shown in Figure 9, the power converter 100A includes a converter circuit 10, an inverter circuit 20, a DC voltage detection unit 40, motor current detection units 51 and 52, a control unit 60A, and a gate drive circuit 80.

[0086] The control unit 60A controls the inverter circuit 20 based on data including the detected values ​​from the DC voltage detection unit 40 and the motor current detection units 51 and 52. The control unit 60A also detects instantaneous voltage drops or momentary power outages of the AC power supply E1 based on the time derivative of the value detected by the DC voltage detection unit 40. For example, if the absolute value of the time derivative of the DC voltage is greater than or equal to a predetermined value, the control unit 60A determines that a momentary power outage or the like has occurred.

[0087] As described above, the power converter 100A includes an LC filter (DC reactor 12 and smoothing capacitor 13), so a predetermined time delay occurs before momentary power interruptions are reflected in the drop in DC voltage. If momentary power interruptions were detected based solely on the drop in DC voltage, the time delay caused by the LC filter would require a predetermined amount of time for the drop in DC voltage to reach a predetermined value. In contrast, the second embodiment uses a value obtained by applying the time derivative to the detected value of the DC voltage detection unit 40, so momentary power interruptions can be detected at an earlier timing. When a momentary power interruption is detected, the control unit 60A starts momentary power interruption control and decelerates the motor M1 so that the motor current falls below a predetermined value. The details of the momentary power interruption control are the same as in the first embodiment, so their explanation is omitted.

[0088] <Effects> According to the second embodiment, the control unit 60A detects momentary power interruptions, etc., based on the time derivative of the DC voltage. This allows momentary power interruption control to be started at an earlier timing, thereby suppressing the increase in motor current. Furthermore, since there is no particular need to provide the power supply voltage detection unit 30 (see Figure 1) described in the first embodiment, the cost required for the power converter 100A can be reduced.

[0089] ≪Third Embodiment≫ In the third embodiment, an air conditioner W1 (see Figure 10) equipped with a power converter 100 (see Figure 10) having the configuration described in the first embodiment will be described.

[0090] Figure 10 is a configuration diagram of the air conditioner W1 according to the third embodiment. The solid arrows in Figure 10 indicate the flow of refrigerant in the heating cycle, and the dashed arrows in Figure 10 indicate the flow of refrigerant in the cooling cycle. The air conditioner W1 is a device that performs air conditioning, such as cooling and heating operations. As shown in Figure 10, the air conditioner W1 includes a compressor 91, an outdoor heat exchanger 92, an outdoor fan 93, an expansion valve 94, an indoor heat exchanger 95, an indoor fan 96, and a four-way valve 97. In the example in Figure 10, the compressor 91, outdoor heat exchanger 92, outdoor fan 93, expansion valve 94, and four-way valve 97 are installed in the outdoor unit U1. The indoor heat exchanger 95 and indoor fan 96 are installed in the indoor unit U2.

[0091] Furthermore, the air conditioner W1 is equipped with a power converter 100 similar to that in the first embodiment, which is used to drive the motor M1 of the compressor 91. That is, the power converter 100 includes a converter circuit 10, an inverter circuit 20, and a control unit 60. The motor M1 is the drive source for the compressor 91 and is connected to the output side of the inverter circuit 20.

[0092] The compressor 91 is a device that compresses a low-temperature, low-pressure gaseous refrigerant and discharges it as a high-temperature, high-pressure gaseous refrigerant. Examples of such compressors 91 include scroll compressors and rotary compressors.

[0093] The outdoor heat exchanger 92 is a heat exchanger in which heat exchange takes place between the refrigerant flowing through its heat transfer tubes (not shown) and the outside air. The outdoor fan 93 is a fan that blows outside air into the outdoor heat exchanger 92. The outdoor fan 93 is equipped with an outdoor fan motor 93a, which is its driving source, and is installed near the outdoor heat exchanger 92. The expansion valve 94 is a valve that reduces the pressure of the refrigerant condensed in the "condenser" (one of the outdoor heat exchanger 92 and the indoor heat exchanger 95). The refrigerant reduced in pressure by the expansion valve 94 is then led to the "evaporator" (the other of the outdoor heat exchanger 92 and the indoor heat exchanger 95).

[0094] The indoor heat exchanger 95 is a heat exchanger in which heat exchange takes place between a refrigerant flowing through its heat transfer tubes (not shown) and indoor air (air from the air-conditioned room). The indoor fan 96 is a fan that supplies indoor air to the indoor heat exchanger 95. The indoor fan 96 is equipped with an indoor fan motor 96a, which is its driving source, and is installed near the indoor heat exchanger 95.

[0095] The four-way valve 97 is a valve that switches the flow path of the refrigerant according to the operating mode of the air conditioner W1. For example, during cooling operation (see dashed arrow in Figure 10), the refrigerant circulates sequentially through the compressor 91, outdoor heat exchanger 92 (condenser), expansion valve 94, and indoor heat exchanger 95 (evaporator). On the other hand, during heating operation (see solid arrow in Figure 10), the refrigerant circulates sequentially through the compressor 91, indoor heat exchanger 95 (condenser), expansion valve 94, and outdoor heat exchanger 92 (evaporator).

[0096] <Effects> According to the third embodiment, the air conditioner W1 is equipped with a power conversion device 100 similar to that of the first embodiment. Therefore, even if a momentary power outage occurs, the motor M1 continues to run, thus preventing the air conditioning operation from being temporarily stopped midway. This increases the reliability of the air conditioner W1 and also enhances user comfort. Furthermore, since it is less likely that the compressor 91 will need to be stopped and restarted in the event of a momentary power outage, the efficiency of the air conditioning operation can be improved.

[0097] <Modifications> Although the power converters 100, 100A and the air conditioner W1 according to this disclosure have been described in each embodiment above, the invention is not limited to these descriptions and various modifications can be made. For example, the converter circuit 10 is not limited to the configuration shown in Figure 1. That is, a converter circuit having a plurality of switching elements and performing power conversion from AC power to DC power using a switching method may be used.

[0098] Furthermore, in the first embodiment, a case was described in which the control unit 60 (see Figure 1) reduces the rotational speed of the motor M1 based on PI control so that the detected value of the motor current approaches a predetermined target value (predetermined value) in the momentary power interruption control, but the invention is not limited to this. That is, a control other than PI control may be performed as a momentary power interruption control to reduce the rotational speed of the motor M1 so that the motor current is below a predetermined value.

[0099] Furthermore, in the first embodiment, the process of calculating a correction value for the rotational speed command by integrating the correction value for the rotational acceleration command of the motor M1 based on PI control was described in the momentary power interruption control, but the invention is not limited to this. For example, in the momentary power interruption control, the control unit 60 (see Figure 1) may directly calculate the correction value for the rotational speed command of the motor M1 based on PI control.

[0100] Furthermore, while each embodiment describes the case where a three-phase AC voltage is applied to the power converter 100 (see Figure 1) from a three-phase AC power source E1 (see Figure 1), it is not limited to this case. In other words, each embodiment can also be applied when a single-phase AC voltage is applied to the power converter 100 from a single-phase AC power source.

[0101] Furthermore, although the third embodiment describes a case in which the air conditioner W1 (see Figure 10) is equipped with a four-way valve 97, it is not limited to this. That is, the four-way valve 97 may be omitted as appropriate, and the air conditioner may be used for cooling only or heating only. Also, the third embodiment can be applied to various types of air conditioners, such as multi-split air conditioners for buildings, packaged air conditioners, and room air conditioners. In addition, the third embodiment can be applied to other refrigeration cycle devices such as chillers, water heaters, air conditioning and water heating systems, chillers, and refrigerators.

[0102] Furthermore, each embodiment is described in detail for the purpose of clearly illustrating this disclosure and is not necessarily limited to having all the configurations described. In addition, it is possible to add, delete, or replace some of the configurations in each embodiment with other configurations. Moreover, some or all of the above-described configurations, functions, processing units, processing means, etc., may be implemented in hardware, for example, by designing them as integrated circuits. Also, the mechanisms and configurations shown are those deemed necessary for explanation and do not necessarily represent all of the mechanisms and configurations in the product.

[0103] 10 Converter circuit 11 Diode bridge circuit 12 DC reactor 13 Smoothing capacitor 20 Inverter circuit 30 Power supply voltage detection unit 40 DC voltage detection unit 51, 52 Motor current detection unit 60, 60A Control unit 80 Gate drive circuit 91 Compressor 92 Outdoor heat exchanger 93 Outdoor fan 94 Expansion valve 95 Indoor heat exchanger 96 Indoor fan 97 Four-way valve 100, 100A Power conversion device E1 AC power supply M1 Motor Q1, Q2, Q3, Q4, Q5, Q6 Switching element W1 Air conditioner

Claims

1. A power conversion device comprising: a converter circuit that converts an AC voltage applied from an AC power source into a DC voltage; an inverter circuit that converts the DC voltage on the output side of the converter circuit into an AC voltage and applies the AC voltage to a motor; a DC voltage detection unit that detects the DC voltage on the output side of the converter circuit; and a motor current detection unit that detects the motor current flowing through the windings of the motor; and a control unit that controls the inverter circuit based on data including the detected values ​​of the DC voltage detection unit and the motor current detection unit; wherein, when the control unit detects an instantaneous voltage drop or momentary power outage of the AC power source, it performs momentary power outage control to reduce the rotational speed of the motor so that the motor current is less than or equal to a predetermined value, and the predetermined value is lower than an overcurrent threshold which is a criterion for determining whether or not to temporarily stop the motor.

2. The power conversion device according to claim 1, characterized in that, in the instantaneous power interruption control, the control unit calculates a correction value for the motor's rotational speed command or rotational acceleration command based on PI control that takes the difference between the predetermined value and the value detected by the motor current detection unit as input, and controls the inverter circuit based on the correction value.

3. The power conversion device according to claim 1, further comprising a power supply voltage detection unit for detecting the power supply voltage of the AC power supply, wherein the control unit detects an instantaneous voltage drop or momentary power outage of the AC power supply based on the value detected by the power supply voltage detection unit.

4. The power conversion device according to claim 1, characterized in that the control unit detects an instantaneous voltage drop or momentary power outage of the AC power supply based on a value obtained by taking the time derivative of the value detected by the DC voltage detection unit.

5. The power conversion device according to claim 1, characterized in that when the control unit detects an instantaneous voltage drop or momentary power outage of the AC power supply, it determines that the motor current will not reach the predetermined value even without performing the momentary power outage control, and therefore does not perform the momentary power outage control.

6. The power conversion device according to claim 5, further comprising a power supply voltage detection unit for detecting the power supply voltage of the AC power supply, wherein the control unit estimates the modulation rate of the inverter circuit when the momentary power interruption control is not performed based on the value detected by the power supply voltage detection unit, and determines whether or not the motor current reaches the predetermined value based on the estimated value of the modulation rate.

7. The power converter according to claim 1, characterized in that when the control unit performs the instantaneous power interruption control, it sets the value of the motor's rotational speed command immediately before the start of the instantaneous power interruption control as the upper limit value of the motor's rotational speed command in the instantaneous power interruption control.

8. The power conversion device according to claim 1, characterized in that when the control unit detects an instantaneous voltage drop or momentary power outage of the AC power supply, it controls the inverter circuit so that a field weakening current flows through the motor windings while performing the momentary power outage control.

9. The power conversion device according to claim 1, characterized in that when the instantaneous voltage drop or momentary interruption of the AC power supply is resolved, the control unit accelerates the motor at a predetermined rotational acceleration and restores it to the rotational speed before the instantaneous voltage drop or momentary interruption of the AC power supply was detected.

10. An air conditioner comprising a power conversion device according to any one of claims 1 to 9, and a compressor driven by the motor, an outdoor heat exchanger, an expansion valve, and an indoor heat exchanger.

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