Power conversion device and failure detection method

Abstract

To discriminate between failure of a current sensor and failure of a motor.SOLUTION: A failure detection method using a failure detector, the method comprising: calculating divided data by dividing one of a second harmonic amplitude of a fundamental wave frequency of a phase current detected by a current sensor that detects the phase current flowing between an inverter circuit and a motor and a fundamental wave amplitude of the phase current detected by the current sensor by the other; and determining a failure of the current sensor and a failure of the motor based on a change in the divided data due to a difference in the fundamental wave frequency.SELECTED DRAWING: Figure 10

Description

[Technical Field]

[0001] The present disclosure relates to a power conversion device and a fault detection method. [Background technology]

[0002] A motor control device is known that includes a motor control unit that measures the d-axis current and q-axis current of a motor, calculates d-axis control values ​​and q-axis control values ​​based on the difference between the d-axis current measurement value and the d-axis current command value and the difference between the q-axis current measurement value and the q-axis current command value, and controls the motor based on the d-axis control value and the q-axis control value, and a detection unit that detects a layer short circuit as an abnormality in the windings of the motor based on the electric secondary components of the d-axis control value and the q-axis control value, which are frequency components twice the electric rotation frequency of the motor. The detection unit in this motor control device detects the layer short circuit based on the amplitude of the electric secondary components calculated for each of the d-axis control value and the q-axis control value. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 2022-140897 Summary of the Invention [Problem to be solved by the invention]

[0004] However, with the conventional technology, there is a risk that a failure in the current sensor may also be detected as a failure in the motor (a layer short circuit).

[0005] An object of the present disclosure is to distinguish between a current sensor failure and a motor failure. [Means for solving the problem]

[0006] The present disclosure provides: an inverter circuit; a current sensor for detecting a phase current flowing between the inverter circuit and the motor; The present invention provides a power conversion device comprising: a control device that calculates division data by dividing one of the double component amplitude of the fundamental wave frequency of the phase current detected by the current sensor and the fundamental wave amplitude of the phase current detected by the current sensor by the other, and that distinguishes between a failure of the current sensor and a failure of the motor based on a change in the division data due to a difference in the fundamental wave frequency.

[0007] The present disclosure provides: Provided is a fault detection method using a fault detector, which calculates division data by dividing one of the amplitude of the double component of the fundamental frequency of the phase current detected by a current sensor that detects the phase current flowing between an inverter circuit and a motor, and the fundamental amplitude of the phase current detected by the current sensor, by the other, and distinguishes between a fault in the current sensor and a fault in the motor based on a change in the division data due to a difference in the fundamental frequency. [Effects of the Invention]

[0008] According to the present disclosure, it is possible to distinguish between a current sensor failure and a motor failure. [Brief explanation of the drawings]

[0009] [Figure 1] 1 is a diagram illustrating an example of a configuration of a power conversion device according to a first embodiment. [Figure 2] FIG. 2 is a diagram illustrating an example of the configuration of a control device. [Figure 3] FIG. 1 is a diagram showing an equivalent circuit (for one phase) of an induction motor. [Figure 4] FIG. 1 is a diagram showing a circuit in which an induction motor is connected to a three-phase symmetrical AC power supply. [Figure 5] FIG. 10 is a diagram showing the results of calculating the phase current ratio k with respect to the fundamental wave frequency ω. [Figure 6] FIG. 10 is a diagram showing an example of an operation pattern in a failure identification operation mode. [Figure 7] FIG. 1 is a diagram illustrating a first embodiment of a control device. [Figure 8] FIG. 10 is a diagram illustrating an example of the configuration of an amplitude calculator that calculates the amplitude of a double component of the fundamental frequency of a phase current detected by a current sensor. [Figure 9] FIG. 2 is a diagram illustrating an example of the configuration of a failure detector in the first embodiment of the control device. [Figure 10] 10 is a flowchart illustrating an example of a fault detection method by the fault detector. [Figure 11] FIG. 10 is a diagram illustrating a second embodiment of the control device. [Figure 12] FIG. 10 is a diagram illustrating an example of the configuration of a failure detector in a second embodiment of the control device. DETAILED DESCRIPTION OF THE INVENTION

[0010] The following describes the embodiments.

[0011] <Power conversion device according to the first embodiment> Fig. 1 is a diagram showing an example of the configuration of a power conversion device according to a first embodiment. The power conversion device 101 shown in Fig. 1 converts input power from a power source into AC power for driving a motor M. The power conversion device 101 shown in Fig. 1 is used as a motor drive device for driving the motor M.

[0012] The motor M is an electric motor having a plurality of coils. For example, the motor M is a three-phase electric motor having a U-phase coil, a V-phase coil, and a W-phase coil. The motor M is an induction motor, but may also be a synchronous motor. The motor M is an example of a load to which power is supplied from a power conversion device.

[0013] The power conversion device 101 includes a DC power supply 10, an inverter circuit 20, a current sensor 30, and a control device 50. The control device 50 may be provided outside the housing of the power conversion device 101, and may be connected to the inverter circuit 20 and the current sensor 30 by wire or wirelessly.

[0014] The power conversion device 101 includes a main circuit including a DC power supply 10 and an inverter circuit 20. The DC power supply 10 supplies DC power to the inverter circuit 20. The DC power supply 10 may include a converter that converts externally supplied AC or DC into DC, or a rectifier circuit that converts externally supplied AC into DC. The DC power supply 10 may include a DC link connecting the converter or rectifier circuit to the inverter circuit 20.

[0015] The inverter circuit 20 inversely converts the DC input from the DC power supply 10 into AC and supplies the converted AC to the motor M. The inverter circuit 20 has a plurality of semiconductor elements Q_U, Q_V, Q_W, Q_X, Q_Y, and Q_Z. The semiconductor elements Q_U, Q_V, Q_W, Q_X, Q_Y, and Q_Z are switching elements that are turned on or off in accordance with corresponding gate drive signals Gu, Gv, Gw, Gx, Gy, and Gz supplied from a gate driver (not shown).

[0016] In the following description, the multiple semiconductor elements Q_U, Q_V, Q_W, Q_X, Q_Y, and Q_Z may be collectively referred to as multiple semiconductor elements Q. Alternatively, one semiconductor element among the multiple semiconductor elements Q_U, Q_V, Q_W, Q_X, Q_Y, and Q_Z may be referred to as semiconductor element Q.

[0017] The inverter circuit 20 is a power conversion circuit that converts input direct current into alternating current by switching on and off a plurality of semiconductor elements Q. The inverter circuit 20 supplies an alternating current drive current (a three-phase drive current in the case of a three-phase motor M) to the motor M, thereby rotating the rotor of the motor M.

[0018] The semiconductor elements Q are semiconductor elements for power conversion. For example, each of the semiconductor elements Q includes a transistor and a diode connected in antiparallel to the transistor. Specific examples of the transistor include power semiconductors such as an IGBT (Insulated Gate Bipolar Transistor) and a MOSFET (Metal Oxide Semiconductor Field Effect Transistor). The diode may be a parasitic diode.

[0019] The current sensor 30 detects phase currents flowing between the inverter circuit 20 and the motor M. The current sensor 30 detects phase currents flowing in each of two of the three-phase output lines connecting the three-phase inverter circuit 20 and the three-phase motor M. In this example, the current sensor 30 detects a U-phase current flowing in the U-phase output line and a W-phase current flowing in the W-phase output line, and outputs a phase current detection value iu representing the current value of the detected U-phase current and a phase current detection value iw representing the current value of the detected W-phase current to the control device 50. The control device 50 calculates a phase current detection value for the remaining one phase from the phase current detection values ​​for the two phases based on the relationship iu + iv + iw = 0.

[0020] The current sensor 30 may detect the phase currents of the U, V, and W phases flowing through the three-phase output lines, and output phase current detection values ​​iu, iv, and iw representing the current values ​​of the detected phase currents to the control device 50. The current sensor 30 may also detect the phase currents using another known detection method.

[0021] The control device 50 generates a plurality of control signals to control the inverter circuit 20 that drives the motor M. A gate driver (not shown) is a circuit that generates a plurality of gate drive signals Gu, Gv, Gw, Gx, Gy, and Gz that drive the gates of a plurality of semiconductor elements Q in the inverter circuit 20 in accordance with the plurality of control signals. The control device 50 may or may not include a gate driver. If the control device 50 does not include a gate driver, it supplies a plurality of control signals to a gate driver included in the main circuit.

[0022] The control device 50 generates a plurality of control signals for controlling the inverter circuit 20, for example, by using V / f control that controls the ratio between the output voltage V from the inverter circuit 20 to the motor M and the output frequency f to be constant. The control device 50 may also generate a plurality of control signals for controlling the inverter circuit 20 by using vector control that uses the detected values ​​of the phase currents of the respective phases based on detection by the current sensors 30.

[0023] 2 is a diagram showing an example of the configuration of a control device. The control device 50 performs calculations on a d,q orthogonal rotating coordinate system that rotates with the primary angular frequency (fundamental frequency ωa) of the motor M. The d axis is a control axis parallel to the magnetic flux axis of the motor M, and the q axis is a control axis that is 90° ahead of the d axis. The control device 50 has a drive control circuit 60 and a fault detection circuit 70.

[0024] The drive control circuit 60 controls the driving of the inverter circuit 20. The drive control circuit 60 includes a coordinate converter 61, a PWM modulator 62, and a gate driver 63.

[0025] The coordinate converter 61 converts a two-phase voltage command value Vq in the rotating coordinate system into a phase angle θa obtained by integrating the fundamental frequency ωa, which is the command value for the output frequency of the inverter circuit 20. * ,Vd * The three-phase voltage command value Vu * ,Vv * ,Vw * Convert to.

[0026] The PWM modulator 62 outputs a three-phase phase voltage command value Vu * ,Vv * ,Vw * Based on the above, the PWM modulator 62 generates PWM signals, which are control signals for switching the semiconductor elements Q_U, Q_V, Q_W, Q_X, Q_Y, and Q_Z. PWM stands for pulse width modulation. The PWM modulator 62 generates the PWM signals using, for example, a carrier comparison method. The shape of the carrier can be a triangular wave, a sawtooth wave, or the like.

[0027] The gate driver 63 is a circuit that generates a plurality of gate drive signals Gu, Gv, Gw, Gx, Gy, and Gz in accordance with a plurality of PWM signals. The inverter circuit 20 (FIG. 1) switches a plurality of semiconductor elements Q_U, Q_V, Q_W, Q_X, Q_Y, and Q_Z in accordance with the plurality of gate drive signals Gu, Gv, Gw, Gx, Gy, and Gz supplied from the gate driver 63. As a result, the output voltage of the inverter circuit 20 (the primary voltage of the motor M) is controlled by a three-phase phase voltage command value Vu * ,Vv * ,Vw * The voltage is controlled to correspond to the

[0028] In FIG. 2, a failure detection circuit 70 distinguishes between a failure of the current sensor 30 and a failure of the motor M and detects the same.

[0029] Faults in the current sensor 30 include gain abnormalities in the current sensor 30. Faults in the motor M include a layer short circuit (also called a layer short circuit), which is an abnormality in any of the windings of each phase of the motor M. Layer short circuits include an inter-phase short circuit and an inter-turn short circuit. An inter-phase short circuit is an abnormality in which windings of different phases are short-circuited to each other, or an abnormality in which the insulation resistance between windings of different phases is reduced. An inter-turn short circuit is an abnormality in which different points in the conductors that make up the winding of one phase are short-circuited to each other, or an abnormality in which the insulation resistance between different points in the conductors that make up the winding of one phase is reduced.

[0030] The fault detection circuit 70 includes an adder 71 , a coordinate converter 72 , an amplitude calculator 73 and a fault detector 74 .

[0031] The adder 71 calculates the V-phase current detection value iv from the U-phase and W-phase current detection values ​​iu, iw based on the relationship iu+iv+iw=0.

[0032] The coordinate converter 72 converts the three-phase phase current detection values ​​iu, iv, iw into two-phase current detection values ​​(d-axis current id and q-axis current iq) in a rotating coordinate system based on the phase angle θa obtained by integrating the fundamental wave frequency ωa.

[0033] If a malfunction such as a gain abnormality occurs in the current sensor 30 or a layer short occurs in the motor M, a component twice the fundamental frequency ωa is superimposed on the detected current amount (d-axis current id and q-axis current iq) in the rotating coordinate system, as will be described in detail later.

[0034] By utilizing this feature, the amplitude calculator 73 calculates the double fundamental component (double component Id of the fundamental frequency ωa) superimposed on the d-axis current id calculated by the coordinate converter 72. (2) ) and the double fundamental component (double fundamental component Iq of the fundamental frequency ωa) superimposed on the q-axis current iq calculated by the coordinate converter 72. (2) The amplitude calculator 73 extracts the double component Id (2) and double component Iq (2) By calculating the square root of the sum of squares of and, the double component amplitude Idq (2) Furthermore, the amplitude calculator 73 calculates the square root of the sum of the squares of the d-axis current id calculated by the coordinate converter 72 and the q-axis current iq calculated by the coordinate converter 72, thereby calculating the amplitude of the fundamental wave of the phase current detected by the current sensor 30 (fundamental wave amplitude I).

[0035] The fault detector 74 detects the double component amplitude Idq (2) Dividing by the fundamental amplitude I gives the division data (=Idq (2) The fault detector 74 calculates the calculated (Idq (2) If the amplitude I of the fundamental wave is greater than the double component amplitude Idq, the fault detector 74 determines that a fault has occurred in either the current sensor 30 or the motor M, and executes the first fault detection method including the following steps S1, S2, S3, and S4. (2) Dividing by this gives the division data (=I / Idq (2) The fault detector 74 calculates the calculated (I / Idq (2) ) falls below a predetermined threshold, it is determined that a failure has occurred in either the current sensor 30 or the motor M, and a first failure detection method including the following steps S1, S2, S3, and S4 is executed.

[0036] [Process S1] The fault detector 74 detects (Idq (2) / I) exceeds a predetermined threshold or (I / Idq (2) ) is determined to be below a predetermined threshold, the fundamental frequency ωa1, the double component amplitude Idq at the fundamental frequency ωa1 (2)(ωa1) , and the fundamental amplitude I at the fundamental frequency ωa1 (ωa1) Remember.

[0037] [Process S2] The fault detector 74 detects a fundamental frequency ωa2 different from the fundamental frequency ωa1, a double component amplitude Idq at the fundamental frequency ωa2, (2)(ωa2) , and the fundamental amplitude I at the fundamental frequency ωa2 (ωa2) Get.

[0038] [Process S3] The fault detector 74 detects (Idq (2)(ωa1) / I (ωa1) ) and (Idq (2)(ωa2) / I (ωa2) ) or the absolute value of the difference between (I (ωa1) / Idq (2)(ωa1) ) and (I (ωa2) / Idq (2)(ωa2) ) is less than a predetermined value, the fault detector 74 determines that the current sensor 30 is faulty. When the fault detector 74 determines that the current sensor 30 is faulty, it outputs a current sensor fault detection signal indicating that a fault in the current sensor 30 has been detected.

[0039] [Process S4] The fault detector 74 detects (Idq (2)(ωa1) / I (ωa1) ) and (Idq (2)(ωa2) / I (ωa2) ) or the absolute value of the difference between (I (ωa1) / Idq (2)(ωa1) ) and (I (ωa2) / Idq (2)(ωa2) ) is equal to or greater than a predetermined value, the fault detector 74 determines that the motor M has failed. If it determines that the motor M has failed, the fault detector 74 outputs a motor fault detection signal indicating that a fault in the motor M has been detected.

[0040] In this way, in the first fault detection method including the steps S1, S2, S3, and S4, the control device 50 detects the double component amplitude Idq (2) and the fundamental wave amplitude I are divided by the other to calculate division data. The control device 50 then distinguishes between a fault in the current sensor 30 and a fault in the motor M based on a change in the division data due to a difference in the fundamental wave frequency ωa. In a first case in which the change is small (for example, when the absolute value of the difference in process S3 is less than a predetermined value), the control device 50 determines that the current sensor 30 is faulty. On the other hand, in a second case in which the change is larger than the first case (for example, when the absolute value of the difference in process S4 is equal to or greater than a predetermined value), the control device 50 determines that the motor M is faulty.

[0041] <First fault detection method performed by the control device> Next, we will explain the details of the first fault detection method performed by the control device 50. In explaining the details of the first fault detection method including steps S1, S2, S3, and S4, we will explain that when a fault occurs in the current sensor 30 or a fault (layer short) in the motor M, a component with twice the fundamental frequency ωa is superimposed on the detected current amounts (d-axis current id and q-axis current iq) in the rotating coordinate system.

[0042] First, it will be explained that when a failure occurs in the current sensor 30, a component with twice the fundamental frequency is superimposed on the detected current amounts (d-axis current id and q-axis current iq) in the rotating coordinate system. Note that the variables in the following equations are as follows: iu: U phase current detection value iv: V phase current detection value iw: W phase current detection value id:d-axis current iq:q-axis current ω: Fundamental frequency t: time θ: Phase difference between current and voltage I: Fundamental wave amplitude Id (2) : Double fundamental component superimposed on the d-axis current id Iq (2) : Double fundamental component superimposed on q-axis current iq Idq (2) : Amplitude of double the fundamental frequency Let's say.

[0043] Assume that current sensor 30 fails, causing the gain of the U-phase current sensor (the amplitude of the U-phase current) to change by k times the gain of the W-phase current sensor (the amplitude of the W-phase current). Because the W-phase current iw is a three-phase symmetrical AC, its phase leads the U-phase current iu by (2 / 3)π [rad]. Since no zero-phase current flows, "iu + iv + iw = 0" holds. From this equation, the V-phase current detection value iv, which cannot be obtained directly from the current sensor, can be calculated from the U-phase current detection value iu and the W-phase current detection value iw. As a result, the three-phase current detection values ​​iu, iv, and iw are expressed by the following equation (1):

[0044]

number

[0045] The equation for converting the fixed coordinate system of three-phase AC (iu, iv, iw) into the rotating coordinate system (id, iq) is expressed by equation (2).

[0046]

number

[0047] Substituting equation (1) into equation (2) and rearranging, we obtain equation (3).

[0048]

number

[0049] From the second term on the right side of equation (3), the double fundamental component (id (2) ,iq (2) ) is expressed as equation (4).

[0050]

number

[0051] id(2) and IQ (2) By calculating the square root of the sum of the squares of the fundamental frequency ω, the amplitude of the double component (Idq (2) ) is obtained. The double component amplitude Idq (2) is expressed by equation (5).

[0052]

number

[0053] Dividing both sides of equation (5) by the fundamental wave amplitude I gives equation (6).

[0054]

number

[0055] The fundamental amplitude I of the three-phase AC and the detected current values ​​id and iq in the rotating coordinate system have the relationship shown in equation (7).

[0056]

number

[0057] To summarize the above results, when a failure occurs in the current sensor 30, the following characteristic 1 can be determined from equation (3), and the following characteristic 2 can be determined from equation (6).

[0058] [Feature 1] When a failure occurs in the current sensor 30, a component with twice the fundamental frequency ω is superimposed on the detected current amounts (d-axis current id and q-axis current iq) in the rotating coordinate system.

[0059] [Feature 2] When a failure occurs in the current sensor 30, the amplitude of the double component of the fundamental frequency ω (Idq (2) ) divided by the fundamental amplitude I (Idq (2) / I) does not depend on the fundamental amplitude I and fundamental frequency ω. Similarly, (Idq (2) / I) (I / Idq (2)) It also does not depend on the fundamental wave amplitude I and the fundamental wave frequency ω.

[0060] Next, it will be explained that when a failure (rare short) occurs in the motor M, a component with twice the fundamental wave frequency is superimposed on the detected current amounts (d-axis current id and q-axis current iq) in the rotating coordinate system.

[0061] Fig. 3 is a diagram showing the equivalent circuit (for one phase) of an induction motor. Fig. 4 is a diagram showing a circuit in which an induction motor is connected to a three-phase symmetrical AC power supply. The equivalent circuit shown in Fig. 3 is connected to the power supply for each phase. Let the impedances of these equivalent circuits be Zu, Zv, and Zw, respectively. When a rare short occurs in any one of the three phases, the primary side motor constant including the excitation inductance Lm of this phase decreases, while the motor constants of the remaining two phases hardly change.

[0062] As an example, assume that a rare short occurs in the winding of phase U. Then, the impedance of phase U decreases to a certain value ZuF. The relationship between ZuF and the impedances Zv and Zw of the remaining two phases is "ZuF < Zv = Zw". Here, since a three-phase symmetrical AC power supply is connected to the induction motor, the relationship of the current magnitudes is "|iu| > |iv| = |iw|". Therefore, similar to the case where the gain of the U-phase current sensor changes by k times the gain of the W-phase current sensor, the current in each phase satisfies Equation (1). As a result, a similar equation transformation as in the previous case is possible, and it can be understood that "when a failure (rare short) occurs in the motor M, a component with twice the fundamental wave frequency ω is superimposed on the detected current amounts (d-axis current id and q-axis current iq) in the rotating coordinate system".

[0063] Here, the case where a failure (rare short) occurs in the motor M will be explained in more detail. Hereinafter, for easier explanation, in Fig. 3, the motor M is in a no-load state (I T= 0). Assuming a motor M with motor constants (R1 = 1.812 [Ω], L1 = 6 [mH], Lm = 190 [mH]), calculate the motor impedance in both a healthy state and a layer short state. In Figure 3, R1 is the primary resistance, R2 is the secondary resistance, L1 is the primary inductance, L2 is the secondary inductance, s is the slip, and I m is the excitation current, I T represents the secondary current.

[0064] The motor impedance in a healthy state is expressed by equation (8) from the equivalent circuit in Figure 3.

[0065]

number

[0066] Here, when a layer short occurs in the U-phase winding, the impedance ZuF of the U-phase is expressed by equation (9), where a is the resistance reduction coefficient of the stator winding resistance R1 and b is the inductance reduction coefficient of the stator excitation inductance Lm, where a and b are both greater than 0 and less than 1.

[0067] FIG. 5 shows the results of calculating the phase current ratio k for various fundamental frequencies ω using FIG. 4. The phase current ratio k is defined by equation (10). In equation (10), Iu represents the amplitude of the U-phase current, and Iw represents the amplitude of the W-phase current. FIG. 5 shows the calculation results when Zv and Zw shown in equation (8) and ZuF shown in equation (9) are applied to FIG. 4, assuming b = 0.5 and a = √b. In this calculation, the amplitudes of the power supply voltages (Vu, Vv, Vw) in FIG. 4 can be any values ​​as long as they are symmetrical across the three phases. The method for calculating the phase currents (iu, iw) in the circuit of FIG. 4 is commonly known as a circuit calculation method, so its description will be omitted.

[0068] The results shown in Figure 5 show that the phase current ratio k decreases below approximately 10 Hz, indicating that the phase current ratio k when a layer short occurs in the U-phase winding depends on frequency. This is because the reactance component (ωLm) in the motor impedance decreases as the frequency decreases, and the frequency-independent resistance component (R1) becomes dominant.

[0069] To summarize the above results, when a failure (layer short) occurs in the motor M, the following characteristic 3 can be seen from equation (3), and the following characteristic 4 can be seen from equation (6) and FIG. 5.

[0070] [Feature 3] When a failure (layer short) occurs in the motor M, a component twice the fundamental frequency ω is superimposed on the detected current amounts (d-axis current id and q-axis current iq) in the rotating coordinate system, just as when a failure occurs in the current sensor 30.

[0071] [Feature 4] When a fault (layer short) occurs in the motor M, the amplitude of the double component of the fundamental frequency ω (Idq (2) ) divided by the fundamental amplitude I (Idq (2) / I) does not depend on the fundamental amplitude I, but depends on the fundamental frequency ω. (2) / I) (I / Idq (2) ) also does not depend on the fundamental amplitude I but depends on the fundamental frequency ω.

[0072] Therefore, according to the above features 1, 2, 3, and 4, when a component twice the fundamental frequency ωa is superimposed on the current detection amount (id, iq) in the rotating coordinate system, the fault detector 74 detects (Idq) at two or more different fundamental frequencies ωa. (2) / I) or (I / Idq (2) ) can be determined to be a fault in the current sensor 30, and if there is such a change, it can be determined to be a fault in the motor M. In this way, the fault detector 74 can distinguish between a fault in the current sensor 30 and a fault in the motor M by performing the first fault detection method including the above-mentioned steps S1, S2, S3, and S4.

[0073] <Second fault detection method performed by the control device> Next, a description will be given of the details of the second fault detection method performed by the control device 50. The second fault detection method can be combined with the first fault detection method.

[0074] As mentioned above, when a motor fault occurs, a component with twice the fundamental frequency ω is superimposed on the d-axis current Id and the q-axis current Iq. As shown in Figure 5, the phase current ratio k depends on the fundamental frequency ω, i.e., the motor speed. Therefore, the fault detector 74 of the control device 50 can determine whether a current sensor fault or a motor fault has occurred by evaluating the amount of superimposition of the double fundamental frequency component at multiple different motor speeds. However, some power conversion devices operate the motor at a continuous, constant speed. In such cases, it is difficult to evaluate the amount of superimposition of the double fundamental frequency component at multiple different motor speeds.

[0075] Therefore, the control device 50 operates the inverter circuit 20 of the power conversion device 101 in a fault identification operation mode in which the motor M is driven at a plurality of different fundamental wave frequencies ω, and evaluates the amount of superposition of the double fundamental wave component at a plurality of different motor speeds.

[0076] 6 is a diagram showing an example of an operation pattern in the failure identification operation mode. (2) / I) or (I / Idq (2) ) crosses a predetermined threshold, it is determined that a failure has occurred in either the current sensor 30 or the motor M, and the inverter circuit 20 of the power conversion device 101 is operated in the failure identification operation mode shown in Figure 6.

[0077] In the fault identification operation mode shown in Fig. 6, the control device 50 accelerates the motor M to a predetermined speed (for example, the rated speed) and then decelerates it. In the fault identification operation mode, the fault detector 74 executes a second fault detection method including the following steps S1', S2', S3, and S4.

[0078] [Process S1'] During deceleration of the motor M, the fault detector 74 detects the fundamental frequency ωa1 and the double component amplitude Idq at the timing T1 when the motor speed reaches near the rated speed. (2)(ωa1) , and the fundamental amplitude I at the fundamental frequency ωa1 (ωa1) Get.

[0079] [Process S2'] During the subsequent deceleration of the motor M, the fault detector 74 detects the fundamental frequency ωa2 at the timing T2 when the motor speed reaches a speed close to the stopping speed, the double component amplitude Idq at the fundamental frequency ωa2, (2)(ωa2) , and the fundamental amplitude I at the fundamental frequency ωa2 (ωa2) Get.

[0080] [Process S3] This is the same as step S3 in the first fault detection method described above.

[0081] [Process S4] This is the same as step S4 in the first fault detection method described above.

[0082] Therefore, by switching from a constant speed operation mode in which the motor M is driven at a constant fundamental frequency ωa to a fault identification operation mode in which the motor M is driven at a plurality of different fundamental frequencies ωa, the fault detector 74 can distinguish between a fault in the current sensor 30 and a fault in the motor M. In this way, the fault detector 74 can distinguish between a fault in the current sensor 30 and a fault in the motor M by performing the second fault detection method including the above-described processes S1', S2', S3, and S4.

[0083] The operation pattern in the failure identification operation mode is not limited to the operation pattern shown in Fig. 6. The failure detector 74 may acquire a plurality of different fundamental frequencies ωa1, ωa2 while the fundamental frequency ωa is increasing (while the motor M is accelerating).

[0084] Alternatively, the fault detector 74 may detect the fundamental frequency ωa1, the double component amplitude Idq at the fundamental frequency ωa1, and the double component amplitude Idq at the fundamental frequency ωa1 while the motor M is operating at a constant fundamental frequency ωa1. (2)(ωa1), and the fundamental amplitude I at the fundamental frequency ωa1 (ωa1) Thereafter, the fault detector 74 may acquire the fundamental frequency ωa2, the double component amplitude Idq at the fundamental frequency ωa2, while the motor M is operating at a constant fundamental frequency ωa2 that is different from the fundamental frequency ωa1. (2)(ωa2) , and the fundamental amplitude I at the fundamental frequency ωa2 (ωa2) may be obtained.

[0085] <First Example of Power Conversion Device According to First Embodiment> Next, a description will be given of a first example of the power conversion device according to the first embodiment. The first example is an example of a configuration in which an induction motor is driven by a three-phase inverter using the V / f control method.

[0086] FIG. 7 is a diagram showing a first embodiment of a control device, and more specifically, a diagram showing an example of the configuration of a control device that executes the first fault detection method. The control device 50A shown in FIG. 7 is an example of the above-mentioned control device 50 (FIG. 2), and therefore, by referencing the above explanation, explanations of the configuration, actions, and effects similar to those of the control device 50 will be omitted. Each control block in FIG. 7 may be configured by a microcomputer, except for the gate driver 63. The control device 50A has a drive control circuit 60 and a fault detection circuit 70.

[0087] The drive control circuit 60 includes a voltage command value generator 64, a coordinate converter 61, a PWM modulator 62, and a gate driver 63. The fault detection circuit 70 includes an adder 71, a coordinate converter 72, an amplitude calculator 73, a fault detector 74, and an integrator 75. The amplitude calculator 73 includes an amplitude calculator 76 that calculates the fundamental wave amplitude I, and an amplitude calculator 77 that calculates the double component amplitude Idq. (2) and an amplitude calculator 77 for calculating:

[0088] The fundamental frequency ωa is input as a speed command value for the motor M. The voltage command value generator 64 generates a voltage command value Vq of the q axis of the rotating coordinate system so that the ratio (V / f) of the output voltage V to the motor M from the inverter circuit 20 to the output frequency f is constant. * The voltage command value Vd of the d-axis of the rotating coordinate system is generated. *is set to zero.

[0089] The integrator 75 integrates the fundamental frequency ωa to generate a phase angle θa (0≦θa<2π [rad]). The coordinate converter 61 generates a two-phase voltage command value Vq in the rotating coordinate system based on the phase angle θa. * ,Vd * The three-phase voltage command value Vu * ,Vv * ,Vw * The PWM modulator 62 converts the three-phase phase voltage command value Vu * ,Vv * ,Vw * Based on these signals, the gate driver 63 generates PWM signals, which are control signals for switching the semiconductor elements Q_U, Q_V, Q_W, Q_X, Q_Y, and Q_Z. The gate driver 63 generates gate drive signals Gu, Gv, Gw, Gx, Gy, and Gz in accordance with the PWM signals.

[0090] In a circuit in which the neutral point of the motor is not connected to the outside, the zero-phase current is zero, so (iu + iv + iw = 0) holds. Therefore, the adder 71 calculates the phase current detection value iv of the V phase by (iv = -iu - iw).

[0091] The coordinate converter 72 converts the three-phase phase current detection values ​​iu, iv, and iw into two-phase current detection values ​​(d-axis current id and q-axis current iq) in a rotating coordinate system based on the phase angle θa. The amplitude calculator 76 smoothes the d-axis current id and the q-axis current iq using a low-pass filter (LPF), and calculates the square root of the sum of the squares of the smoothed d-axis current id and the smoothed q-axis current iq to calculate the amplitude of the fundamental wave of the phase current detected by the current sensor 30 (fundamental wave amplitude I).

[0092] Figure 8 shows the amplitude of the double component of the fundamental frequency of the motor current detection value (d-axis current id and q-axis current iq) in the rotating coordinate system (double component amplitude Idq (2) ) is a diagram showing an example of the configuration of an amplitude calculator that calculates

[0093] The amplitude calculator 77 calculates the double component amplitude Idq based on the above equation (5). (2) As shown in FIG. 8, the amplitude calculator 77 includes a band-pass filter (BPF), a square sum calculator, and a square root calculator. The pass frequency of the band-pass filter is dynamically set to 2ωa. The amplitude calculator 77 calculates the double fundamental component (double component Id of the fundamental frequency ωa) superimposed on the d-axis current id. (2) ) is extracted by a bandpass filter, and the double fundamental component (double fundamental frequency component Iq (2) ) is extracted by a bandpass filter. The amplitude calculator 77 extracts the double component Id (2) and double component Iq (2) By calculating the square root of the sum of squares of and, the double component amplitude Idq (2) The band-pass filter, the sum-of-squares calculator, and the square-root calculator may have known configurations.

[0094] 9 is a diagram showing an example of the configuration of a fault detector in the first embodiment of the control device. The fault detector 74 has a memory 78 and a processing circuit 79. The fault detector 74 detects the fundamental frequency ωa, the fundamental amplitude I, and the double component amplitude Idq at the same timing. (2) is stored in the memory 78. The processing circuit 79 distinguishes between a failure in the current sensor 30 and a failure in the motor M and detects the failure according to the failure detection method shown in FIG.

[0095] FIG. 10 is a flowchart showing an example of a fault detection method by the fault detector.

[0096] In step S11, the processing circuit 79 uses the data stored in the memory 78 to calculate (Idq (2) / I) (where " / " is the division symbol). (2) The processing circuit 79 determines whether the calculated value of (Idq / I) exceeds a predetermined threshold value Fth1. (2) If the calculated value of (Idq / I) exceeds the threshold value Fth1, the process S from step S13 onwards is executed, and (Idq (2)If the calculated value of (I) is equal to or smaller than the threshold value Fth1, the process S is not executed and the process of step S11 is executed again.

[0097] In step S13, the processing circuit 79 determines whether the fundamental frequency ωa acquired from the memory 78 is less than a predetermined first threshold value (for example, 5 Hz). If the fundamental frequency ωa is less than the first threshold value (for example, 5 Hz), the processing circuit 79 determines in step S17 whether the fundamental frequency ωa is less than the first threshold value (for example, 5 Hz). (L) and (Idq (2) / I) to the first division data Ia (L) Substitute into

[0098] In step S13, if the fundamental frequency ωa is equal to or greater than a first threshold (for example, 5 Hz), the processing circuit 79 proceeds to processing in step S15. In step S15, the processing circuit 79 determines whether the fundamental frequency ωa acquired from the memory 78 is equal to or greater than a second threshold (for example, 25 Hz) that is greater than a predetermined first threshold. If the fundamental frequency ωa is equal to or greater than the second threshold (for example, 25 Hz), the processing circuit 79 converts the fundamental frequency ωa into the second fundamental frequency ωa in step S19. (H) and (Idq (2) / I) to the second division data Ia (H) Substitute into

[0099] In step S21, the processing circuit 79 calculates the first division data Ia (L) and the second division data Ia (H) If both have not been updated, the processing circuit 79 proceeds to the processing of step S11, and if both have been updated, the processing circuit 79 proceeds to the processing of step S23.

[0100] In step S23, the processing circuit 79 calculates the first division data Ia (L) and the second division data Ia (H)The processing circuit 79 determines whether the absolute value of the difference between the current sensor 30 and the motor M is less than a predetermined value Fth2. If the absolute value of the difference is less than the predetermined value Fth2, the processing circuit 79 determines in step S25 that the current sensor 30 has failed, and outputs a current sensor failure detection signal. On the other hand, if the absolute value of the difference is equal to or greater than the predetermined value Fth2, the processing circuit 79 determines in step S27 that the motor M has failed, and outputs a motor failure detection signal.

[0101] When the current sensor failure detection signal is output, the control device 50 displays information indicating a failure of the current sensor 30 on a display device provided in the power conversion device 101. When the motor failure detection signal is output, the control device 50 displays information indicating a failure of the motor M on a display device provided in the power conversion device 101.

[0102] In addition, the first division data Ia (L) and the second division data Ia (H) The fundamental frequency ωa for calculating the values ​​to be substituted into the above equations is set appropriately depending on the specifications of the motor M. In the first embodiment, a significant difference (|Ia (L) -Ia (H) The fundamental frequency ωa at which the ωa is obtained is set to values ​​less than 5 Hz and 25 Hz or more.

[0103] <Second Example of the Power Conversion Device According to the First Embodiment> Next, a second example of the power conversion device according to the first embodiment will be described. The second example is suitable for cases where it is difficult to obtain a plurality of different fundamental frequencies (ωa) due to constant speed operation of the motor M, etc.

[0104] FIG. 11 is a diagram showing a second embodiment of the control device, and more specifically, a diagram showing an example of the configuration of a control device that executes the second fault detection method. The control device 50B shown in FIG. 7 is an example of the above-mentioned control device 50 (FIG. 2), and therefore, by referencing the above explanation, explanations of the configuration, actions, and effects similar to those of the control devices 50 and 50A will be omitted. Each control block in FIG. 11 may be configured by a microcomputer, except for the gate driver 63.

[0105] 11 differs from the control device 50A in that it further includes an operation pattern generator 80 and a switch 81 as means for switching the fundamental wave frequency ωa, which is a command value, between the normal operation mode and the fault identification operation mode. When a predetermined condition for changing the fundamental wave frequency ωa is met, the fault detector outputs a fault identification operation signal for transitioning to the fault identification operation mode.

[0106] FIG. 12 is a diagram showing an example of the configuration of a fault detector in the second embodiment of the control device. When the condition of step S11 in FIG. 10 is met, a processing circuit 79 shown in FIG. 12 detects (Idq (2) However, even if the processing circuit 79 repeats the processing S a predetermined number of times, the processing circuit 79 does not obtain the first division data Ia (L) and the second division data Ia (H) If the condition that both of the above are not updated is met, the power converter outputs a fault identification operation signal to transition to the fault identification operation mode. An example of a power conversion device that meets this condition is a motor drive device that operates a fan or pump at a constant speed for a long period of time using a motor M.

[0107] In FIG. 11, when a fault identification operation signal is output, a switch 81 switches the operation pattern of the fundamental wave frequency ωa, which is the command value, from the operation pattern in the normal operation mode to the operation pattern in the fault identification operation mode generated by the operation pattern generator 80. The operation pattern in the fault identification operation mode generated by the operation pattern generator 80 is, for example, the fluctuation pattern shown in FIG. 6, but other fluctuation patterns that change the fundamental wave frequency ωa may also be used. By changing the fundamental wave frequency ωa in such a fluctuation pattern, the control device 50B changes the fundamental wave frequency ωa by a predetermined amount (first division data Ia (L) and the second division data Ia (H) After that, similar to the first embodiment, the processing circuit 79 determines whether the current sensor or the motor has failed, and outputs a corresponding failure detection signal.

[0108] In this disclosure, a processing circuit is an electronic circuit such as a CPU (Central Processing Unit), FPGA (Field Programmable Gate Array), or ASIC (Application Specific Integrated Circuit). The processing circuit may be a computer having a processor. The processing circuit executes various control operations described in this specification by executing a program such as instruction code stored in a memory, or by being a circuit designed for a specific application.

[0109] Although the embodiments have been described above, they are presented as examples and the present invention is not limited to the above embodiments. The above embodiments can be implemented in various other forms, and various combinations, omissions, substitutions, modifications, etc. can be made without departing from the spirit of the invention. These embodiments and their modifications are included within the scope and spirit of the invention, and are also included in the scope of the invention and its equivalents as set forth in the claims.

[0110] For example, the semiconductor element is not limited to a power transistor such as an IGBT or a MOSFET, but may be a diode, a thyristor, a gate turn-off thyristor, a triac, or the like.

[0111] The fault detector 74 does not have to be a component of the control device 50. For example, the fault detector 74 may be a device itself that does not include a drive control circuit 60 that controls the driving of the inverter circuit 20, or may be a component of a device that does not include a drive control circuit 60. [Explanation of symbols]

[0112] 10 DC power supply 20 Inverter circuit 30 Current Sensor 50, 50A, 50B control device 101 Power conversion device 60 Drive control circuit 70 Fault detection circuit

Claims

1. an inverter circuit; a current sensor for detecting a phase current flowing between the inverter circuit and the motor; a control device that calculates division data by dividing one of the amplitude of a double component of the fundamental wave frequency of the phase current detected by the current sensor and the amplitude of the fundamental wave of the phase current detected by the current sensor by the other, and that distinguishes between a failure of the current sensor and a failure of the motor based on a change in the division data due to a difference in the fundamental wave frequency.

2. 2. The power conversion device according to claim 1, wherein the control device determines that the current sensor is faulty in a first case in which the change is small, and determines that the motor is faulty in a second case in which the change is larger than in the first case.

3. The power conversion device according to claim 1 , wherein the change is a difference between a plurality of the divided data pieces having different fundamental wave frequencies.

4. 4. The power conversion device according to claim 3, wherein the control device determines that the current sensor has failed when the absolute value of the difference is less than a predetermined value, and determines that the motor has failed when the absolute value of the difference is equal to or greater than the predetermined value.

5. 2. The power conversion device according to claim 1, wherein the control device converts the detected values ​​of the three-phase phase currents into d-axis currents and q-axis currents of two phases in a rotating coordinate system, and calculates the double component amplitude and the fundamental wave amplitude based on the d-axis current and the q-axis current.

6. 6. The power conversion device according to claim 5, wherein the control device calculates the doubled component amplitude by calculating a square root of a sum of squares of a doubled component of the fundamental frequency extracted from the d-axis current and a doubled component of the fundamental frequency extracted from the q-axis current, and calculates the fundamental amplitude by calculating a square root of a sum of squares of the d-axis current and the q-axis current.

7. 7. The power conversion device according to claim 1, wherein when the divided data crosses a predetermined threshold, the control device distinguishes between a failure of the current sensor and a failure of the motor based on the change.

8. The power conversion device according to claim 7 , wherein the control device, when the divided data crosses the threshold, changes the fundamental frequency to obtain a plurality of the divided data having different fundamental frequencies.

9. A fault detection method using a fault detector, comprising: calculating division data by dividing one of the amplitude of the double component of the fundamental frequency of the phase current detected by a current sensor that detects a phase current flowing between an inverter circuit and a motor, and the fundamental amplitude of the phase current detected by the current sensor, by the other; and distinguishing between a fault in the current sensor and a fault in the motor based on a change in the division data due to a difference in the fundamental frequency.

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