Power conversion device and motor drive system

Abstract

A power conversion apparatus (2) comprises: a converter circuit (21) including a smoothing capacitor (211) and a rectification circuit (210) provided with a plurality of rectification elements (D1-D6); an inverter circuit (22); and a control device (25). The control device (25) is provided with a capacitor current estimation unit (250) that estimates current (Ic) flowing through the smoothing capacitor (211), and a DC input current estimation unit (251) that estimates DC input current (Iin) outputted from the rectification circuit (210). The capacitor current estimation unit (250) estimates a capacitor current value (Ic) on the basis of a capacitance (Cm) of the smoothing capacitor (211) and a DC bus voltage value (Vdc) applied to the smoothing capacitor (211). The DC input current estimation unit (251) estimates a DC input current value (Iin) on the basis of a capacitor current estimation value (Ic) and a DC output current value (Iout) inputted to the inverter circuit (22).

Description

Technical Field

[0001] This application relates to a power conversion device and a motor drive system.

Background Art

[0002] As a power conversion device for driving a motor, there is one that converts AC power supplied from an AC power source into DC power and then converts the converted DC power back into AC power. This power conversion device generally has a configuration including a converter circuit composed of a rectifier circuit and a smoothing capacitor and an inverter circuit. The converter circuit converts AC power into DC power, and the smoothing capacitor smoothes the converted DC voltage. The inverter circuit drives the motor by converting the DC power converted by the converter circuit back into AC power again.

[0003] In order to prevent circuit breakdown when an abnormality occurs in the power conversion device, a function of detecting an abnormal state and protecting the circuit is required. For example, there are technologies such as detecting an overload state of a motor and protecting against destruction of the inverter circuit due to overcurrent.

[0004] As a technology for such requirements, a technology related to overcurrent protection of a converter circuit when an AC power source is in an unbalanced state is disclosed (for example, see Patent Document 1). In Patent Document 1, based on the current detected by a current detector provided at the output of the rectifier circuit and the phase of the AC power source, the current flowing through the diodes constituting the rectifier circuit is estimated to protect against destruction of the rectifier circuit and thus the converter circuit due to overcurrent.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0006] However, the technology disclosed in Patent Document 1 is configured to detect the current on the output side of the rectifier circuit. This results in detecting the large DC input current output from the rectifier circuit, which leads to the problem of a large current detector and thus a large power converter.

[0007] This application discloses a technology for solving the above-mentioned problems, and aims to provide a power conversion device that can protect a converter circuit without providing a current detector for detecting the current output from a rectifier circuit. [Means for solving the problem]

[0008] The power conversion device disclosed in this application is A power conversion device comprising a rectifier circuit with multiple rectifier elements and a smoothing capacitor, a converter circuit that converts AC power to DC power, an inverter circuit that converts the DC power converted by the converter circuit to AC power, and a control device that controls the inverter circuit, The control device comprises a capacitor current estimation unit for estimating the current flowing through the smoothing capacitor, and a DC input current estimation unit for estimating the DC input current output from the rectifier circuit. The capacitor current estimation unit estimates the capacitor current value flowing through the smoothing capacitor based on the capacitor capacitance of the smoothing capacitor and the DC bus voltage value applied to the smoothing capacitor. The DC input current estimation unit estimates the DC input current value output by the rectifier circuit based on the estimated capacitor current value and the DC output current value input to the inverter circuit. [Effects of the Invention]

[0009] According to this disclosure, the DC input current output by the rectifier circuit can be estimated without using a current detector, thereby protecting the converter circuit from overcurrents, and providing a compact power conversion device by eliminating the need for a current detector. [Brief explanation of the drawing]

[0010] [Figure 1] This is a schematic diagram showing the configuration of the power conversion device and motor drive system according to Embodiment 1. [Figure 2] This is a schematic diagram showing the configuration of a power conversion device and motor drive system according to a modified example of Embodiment 1. [Figure 3] This is a schematic diagram showing the configuration of the power conversion device and motor drive system according to Embodiment 2. [Figure 4] This is a schematic diagram showing the configuration of the power conversion device and motor drive system according to Embodiment 3. [Figure 5] This flowchart shows the operation of the DC bus voltage estimation unit of the power converter according to Embodiment 3. [Figure 6] This is a schematic diagram showing the configuration of the power conversion device and motor drive system according to Embodiment 4. [Figure 7] This is a schematic diagram showing the configuration of the power conversion device and motor drive system according to Embodiment 5. [Figure 8] This is a schematic diagram showing the configuration of the power conversion device and motor drive system according to Embodiment 6. [Figure 9] This figure shows an example of the hardware configuration of the control device according to Embodiments 1 to 6. [Modes for carrying out the invention]

[0011] The following description of this embodiment will be made with reference to the figures. In each figure, the same reference numerals indicate the same or corresponding parts.

[0012] Embodiment 1. Hereinafter, the power conversion device according to Embodiment 1 and the motor drive system including the same will be described with reference to the drawings. FIG. 1 is a schematic diagram showing the configuration of the power conversion device and the motor drive system according to Embodiment 1. In FIG. 1, the motor drive system 10 is configured to drive the motor 3 by converting the AC power obtained from the AC power source 1 into DC power in the power conversion device 2 and then converting the converted DC power back into AC power. That is, the motor drive system 10 drives the motor 3 using the AC power converted in the power conversion device 2 as a drive source.

[0013] <Configuration of the power conversion device 2> Next, the configuration of the power conversion device 2 will be described. The power conversion device 2 includes a converter circuit 21, an inverter circuit 22, a DC bus voltage sensor 23, a DC output current sensor 24, and a control device 25. The converter circuit 21 converts the AC power from the AC power source 1 into DC power and outputs the DC power to the inverter circuit 22.

[0014] <Configuration of the converter circuit 21> The converter circuit 21 includes a rectifier circuit 210 and a smoothing capacitor 211. The rectifier circuit 210 is composed of a plurality of rectifying elements. As shown in FIG. 1, the rectifier circuit 210 includes diodes as rectifying elements. The anode of diode D1 and the cathode of diode D2 are connected to form an AC input terminal, which is connected to the R phase of the AC power source 1. The anode of diode D3 and the cathode of diode D4 are connected to form an AC input terminal, which is connected to the S phase of the AC power source 1. The anode of diode D5 and the cathode of diode D6 are connected to form an AC input terminal, which is connected to the T phase of the AC power source 1.

[0015] The cathodes of the diodes D1, D3, and D5 are connected to each other to form the positive potential terminal of the DC voltage, and are connected to the positive potential terminal P of the smoothing capacitor 211 and the positive potential terminal of the inverter circuit 22. The anodes of the diodes D2, D4, and D6 are connected to each other to form the negative potential terminal of the DC voltage, and are connected to the negative potential terminal N of the smoothing capacitor 211 and the negative potential terminal of the inverter circuit 22.

[0016] In FIG. 1, the rectifier circuit 210 is composed of six rectifying elements each made of a diode, but the present invention is not limited to this configuration. For example, two or more diodes may be connected in series to form one rectifying element, or two or more diodes may be connected in parallel to form one rectifying element.

[0017] The smoothing capacitor 211 smoothes the DC voltage output from the rectifier circuit 210 and outputs the smoothed DC voltage to the inverter circuit 22. The smoothing capacitor 211 has a positive potential terminal P and a negative potential terminal N. In the present embodiment, the smoothing capacitor 211 is defined by a capacitance value Cm and a parasitic resistance value Rs. Note that in FIG. 1, the smoothing capacitor 211 is composed of one capacitor, but the present invention is not limited to this configuration. For example, two or more capacitors may be connected in series, in parallel, or in series-parallel to form the capacitor.

[0018] <Configuration of the inverter circuit 22> The inverter circuit 22 converts the DC power output from the converter circuit 21 into AC power and outputs the AC power to the motor 3. In FIG. 1, the inverter circuit 22 includes six switching elements Q1 - Q6. Here, an example where the switching element is an IGBT (Insulated Gate Bipolar Transistor) is shown.

[0019] The emitter of switching element Q1 and the collector of switching element Q2 are connected and connected to the U phase of motor 3. The emitter of switching element Q3 and the collector of switching element Q4 are connected and connected to the V phase of motor 3. The emitter of switching element Q5 and the collector of switching element Q6 are connected and connected to the W phase of motor 3.

[0020] The collectors of switching elements Q1, Q3, and Q5 are connected to each other, forming a positive potential terminal for the DC voltage, which is connected to the positive potential terminal P of the smoothing capacitor 211 and the positive potential terminal of the converter circuit 21. The emitters of switching elements Q2, Q4, and Q6 are connected to each other, forming a negative potential terminal for the DC voltage, which is connected to the negative potential terminal N of the smoothing capacitor 211 and the negative potential terminal of the converter circuit 21.

[0021] In Figure 1, the inverter circuit 22 consists of six switching elements, each made from an IGBT, but this is not the only configuration. For example, two or more IGBTs may be connected in series to form one switching element, or two or more IGBTs may be connected in parallel to form one switching element.

[0022] Furthermore, while Figure 1 shows an example where the switching elements of the inverter circuit 22 are composed of IGBTs, this configuration is not the only option. For example, they may be composed of MOSFETs (Metal Oxide Semiconductor Field Effect Transistors). Also, the switching elements are not limited to those composed of Si (silicon) semiconductors; wide-bandgap semiconductors such as SiC (silicon carbide) and GaN (gallium nitride) may be used. They may also be composed of switching elements such as GaN-HEMT (Gallium Nitride - High Mobility Transistor).

[0023] The converter circuit 21 and the inverter circuit 22 are connected at positive and negative potential terminals, and these are sometimes referred to as DC buses. The DC bus voltage sensor 23 detects the DC bus voltage value Vdc applied between the positive potential terminal P and the negative potential terminal N of the smoothing capacitor 211, and outputs the DC bus voltage value Vdc to the control device 25.

[0024] The DC output current sensor 24 is connected between the smoothing capacitor 211 and the inverter circuit 22, detects the DC output current value Iout input to the inverter circuit 22, and outputs the DC output current value Iout to the control device 25. In Figure 1, the DC output current sensor 24 is connected between the inverter circuit 22 and the smoothing capacitor 211 on the negative potential terminal side of the inverter circuit 22, but it may also be connected between the inverter circuit 22 and the smoothing capacitor 211 on the positive potential terminal side of the inverter circuit 22.

[0025] <Configuration and operation of control device 25> The control device 25 includes a capacitor current estimation unit 250, a DC input current estimation unit 251, and an inverter circuit control unit 252.

[0026] The capacitor current estimation unit 250 estimates the capacitor current value Ic flowing through the smoothing capacitor 211 based on the DC bus voltage value Vdc output from the DC bus voltage sensor 23, the capacitance value Cm of the smoothing capacitor 211, and the parasitic resistance value Rs. The estimated capacitor current value Ic is output to the DC input current estimation unit 251.

[0027] The capacitor current value Ic is estimated based on the following equation (1).

number

[0028] Furthermore, since the parasitic resistance Rs of the smoothing capacitor 211 is generally small, the capacitor current Ic can be estimated using equation (2) with Rs omitted.

number

[0029] The DC input current estimation unit 251 estimates the DC output current value Iin output from the rectifier circuit 210 based on the capacitor current value Ic output from the capacitor current estimation unit 250 and the DC output current value Iout output from the DC output current sensor 24. The estimated DC input current value Iin is output to the inverter circuit control unit 252.

[0030] The DC output current value Iin is estimated based on the following equation (3).

number

[0031] The inverter circuit control unit 252 is the controller of the inverter circuit 22. The inverter circuit control unit 252 outputs a control signal to the inverter circuit 22 for driving the motor 3. More specifically, the inverter circuit control unit 252 generates a control signal for the inverter circuit 22 based on the voltage command value of the voltage to be output from the inverter circuit 22.

[0032] The inverter circuit control unit 252 determines that the DC input current is an overcurrent if the DC input current value Iin output from the DC input current estimation unit 251 exceeds a predetermined current threshold. When the inverter circuit control unit 252 determines that the DC input current value is excessive, it protects the converter circuit 21 by reducing the DC input current by outputting a control signal to stop the inverter circuit 22 or reduce the AC power output to the motor 3. By performing the above operations, it becomes possible to protect the converter circuit 21 from overcurrent without providing a current detector to detect the DC input current output from the rectifier circuit 210.

[0033] <Modified form of Embodiment 1> Next, a modified version of Embodiment 1 will be described. Figure 2 is a schematic diagram showing the configuration of a power conversion device and motor drive system according to a modified version of Embodiment 1. In Figure 2, the rectifier circuit 210 and inverter circuit 22 are shown in a simplified manner because they have the same configuration as in Figure 1. The difference from Figure 1 is that a differential circuit 26 is provided in the smoothing capacitor 211.

[0034] The differentiating circuit 26 is connected between the positive potential terminal P and the negative potential terminal N of the smoothing capacitor 211. In Figure 2, the differentiating circuit 26 is constructed by connecting one terminal of the capacitor 261 and one terminal of the resistor 262 in series. In the differentiating circuit 26, the capacitor 261 has a capacitance value Cf, and the resistor 262 of the differentiating circuit 26 has a resistance value Rde.

[0035] The other terminal of capacitor 261 of the differentiating circuit 26 is connected to the positive potential terminal P of smoothing capacitor 211, and the other terminal of resistor 262 of the differentiating circuit 26 is connected to the negative potential terminal N of smoothing capacitor 211.

[0036] The voltage sensor 23a detects the voltage at the connection point between the capacitor 261 of the differentiating circuit 26 and the resistor of the differentiating circuit 26, and outputs the detected differentiating circuit voltage value Vde to the capacitor current estimation unit 250 of the control device 25.

[0037] The capacitor current estimation unit 250 provided in the control device 25 estimates the capacitor current value Ic based on the following equation (4).

number

[0038] Here, similar to equation (2), we can omit Rs in equation (4) and use the following equation (5) for estimation.

number

[0039] Through the above operation, by providing a differentiating circuit 26 in the smoothing capacitor 211, it becomes possible to estimate the DC output current by providing a voltage sensor 23a that detects a voltage smaller than that of the DC bus voltage sensor 23, without providing a DC bus voltage sensor 23 that detects high voltages.

[0040] In Figure 2, an example is shown where the differentiating circuit 26 is composed of a capacitor 261 and a resistor 262, but a differentiating circuit using an operational amplifier or the like will produce the same effect.

[0041] As described above, according to the power conversion device 2 of this embodiment 1, the control device 25 that controls the inverter circuit 22 includes a capacitor current estimation unit 250 that estimates the current Ic flowing through the smoothing capacitor 211, and a DC input current estimation unit 251 that estimates the DC input current Iin output from the rectifier circuit 210. The capacitor current estimation unit 250 estimates the capacitor current value Ic flowing through the smoothing capacitor 211 based on the capacitor capacitance Cm of the smoothing capacitor 211 and the DC bus voltage value Vdc applied to the smoothing capacitor 211, and the DC input current estimation unit 251 is configured to estimate the DC input current value Iin output by the rectifier circuit 210 based on the estimated capacitor current value Ic and the DC output current value Iout input to the inverter circuit 22. With this configuration, the DC input current Iin output by the rectifier circuit 210 can be estimated without using a current detector, so it is possible to determine whether or not there is an overcurrent based on the estimated DC input current Iin, and thus it is possible to protect the converter circuit 21 from overcurrent. moreover, By omitting the current detector, the power conversion device can be made smaller.

[0042] Furthermore, according to the motor drive system 10 of this embodiment 1, the system comprises the power converter 2 described above and a motor 3 that uses the AC power converted by the power converter 2 as its driving source. The power converter 2 can be protected from overcurrents of the DC input current value Iin output by the rectifier circuit 210, thereby suppressing damage to the power converter 2, resulting in stable operation and stable motor drive.

[0043] Embodiment 2. The power converter and motor drive system equipped therewith according to Embodiment 2 will be described below with reference to the figures. Figure 3 is a schematic diagram showing the configuration of the power converter and motor drive system according to Embodiment 2. The difference from Figure 1 of Embodiment 1 is that the power converter 2 according to Embodiment 2 does not have a DC output current sensor 24, but has an AC output current sensor 27. The other configurations are the same as in Embodiment 1 and will not be described.

[0044] The AC output current sensor 27 is connected between the inverter circuit 22 and the motor 3, and detects the AC output current flowing through the U, V, and W phases of the motor 3. It outputs the AC output current values ​​Iu, Iv, and Iw for each of the U, V, and W phases of the motor 3 to the control device 25. In Figure 3, the AC output current sensor 27 is configured to detect the AC output currents of all three phases of the motor 3: U, V, and W. However, the AC output current sensor 27 may be configured to detect the AC output currents flowing through any two of the U, V, and W phases of the motor 3, and the current flowing through the remaining phase, which does not have an AC output current detected, may be estimated from the detected values ​​of the AC output currents flowing through the two phases.

[0045] <Configuration and operation of control device 25> The control device 25 according to this second embodiment differs from that of the first embodiment in that it further includes a DC output current estimation unit 253. The DC output current estimation unit 253 estimates the DC output current value Iout to be input to the inverter circuit 22 based on the DC bus voltage value Vdc output from the DC bus voltage sensor 23, the AC output current values ​​Iu, Iv, Iw detected by the AC output current sensor 27, and the control signal output by the inverter circuit control unit 252, and outputs the estimated DC output current value Iout to the DC input current estimation unit 251.

[0046] The DC output current estimation unit 253 estimates the DC output current value Iout based on the following equation (6).

number

[0047] The circuit loss PLoss generated in the inverter circuit 22 can be determined in advance through design, but is not limited to this. The circuit loss PLoss generated in the inverter circuit 22 may also be calculated based on the AC output current values ​​Iu, Iv, Iw detected by the AC output current sensor 27 and the control signal output from the inverter circuit control unit 252.

[0048] The AC power Pout output by the inverter circuit 22 can be calculated, for example, by the following equation (7).

number

[0049] In equation (7), the q-axis output voltage command value Vq* and the d-axis output voltage command value Vd* output from the inverter circuit control unit 252 are used. However, a voltage sensor may be provided between the inverter circuit 22 and the motor 3, and the q-axis output voltage and d-axis output voltage converted based on the detected value of the voltage sensor and the rotation angle of the motor 3 or the voltage frequency output by the inverter circuit 22 may be used.

[0050] As described above, the DC output current value Iout can be estimated from equations (6) and (7), and the DC output current estimation unit 253 outputs the estimated DC output current value Iout to the DC input current estimation unit 251. The DC input current estimation unit 251 estimates the DC input current value Iin using equation (3), based on the capacitor current value Ic estimated by the capacitor current estimation unit 250 and the DC output current value Iout estimated by the DC output current estimation unit 253, similar to the first embodiment.

[0051] In Figure 3, the capacitor current estimation unit 250 estimates the capacitor current value Ic based on the DC bus voltage value Vdc output from the DC bus voltage sensor 23. However, the same effect can be achieved by using the differentiating circuit 26 described in the modified example of Embodiment 1.

[0052] The operation of the DC input current estimation unit 251 in Embodiment 2 is the same as in Embodiment 1 and the modified version thereof, so a description will be omitted.

[0053] As described above, Embodiment 2 provides the same effects as Embodiment 1. That is, the DC input current Iin output by the rectifier circuit can be estimated without using a current detector. Furthermore, even without the DC output current sensor 24 of Embodiment 1, the DC output current value Iout can be estimated even with the AC output current sensor 27 provided as in Embodiment 2, and this can be used to estimate the DC input current Iin, thus providing the same effects as Embodiment 1.

[0054] Embodiment 3. The power converter and motor drive system equipped therewith according to Embodiment 3 will be described below with reference to the figures. Figure 4 is a schematic diagram showing the configuration of the power converter and motor drive system according to Embodiment 3. The difference from Figure 1 of Embodiment 1 is that the power converter 2 according to Embodiment 3 does not have a DC bus voltage sensor 23, but has an AC input voltage sensor 28. The other configurations are the same as in Embodiment 1 and will not be described.

[0055] The AC input voltage sensor 28 is installed between the AC power supply 1 and the converter circuit 21. It detects the AC input line voltage applied between the R-phase, S-phase, and T-phase lines input to the converter circuit 21 and outputs the AC input line voltage values ​​Vrs, Vst, and Vtr applied between the R-phase, S-phase, and T-phase lines of the converter circuit 21 to the control device 25. In Figure 4, the AC input voltage sensor 28 is configured to detect the AC input line voltages of all three phases of the converter circuit 21: the R phase, S phase, and T phase. However, the AC input voltage sensor 28 may be configured to detect the AC input line voltages between any two of the R phase, S phase, and T phase of the converter circuit 21, and the line voltage of the remaining phase, for which no AC input line voltage is detected, may be estimated from the detected values ​​of the two phases.

[0056] The AC input voltage sensor 28 is provided to detect the AC input line voltages of the R, S, and T phases. Alternatively, it may be provided to detect the AC input phase voltages of the R, S, and T phases, and estimate the AC input line voltages applied between the R, S, and T phases from the AC input phase voltages applied to the R, S, and T phases of the converter circuit 21.

[0057] <Configuration and operation of control device 25> The control device 25 according to this third embodiment differs from that of the first embodiment in that it further includes a DC bus voltage estimation unit 254. The DC bus voltage estimation unit 254 estimates the DC bus voltage applied to the capacitor, which is the voltage applied between the positive potential terminal P and the negative potential terminal N of the smoothing capacitor 211, based on the AC input line voltage values ​​Vrs, Vst, Vtr output from the AC input voltage sensor 28, the capacitance value Cm of the smoothing capacitor 211, and the DC output current value Iout output from the DC output current sensor 24, and outputs the estimated DC bus voltage value Vdc_est to the capacitor current estimation unit 250.

[0058] <Operation of DC bus voltage estimation unit 254> Next, the operation of the DC bus voltage estimation unit 254 will be explained using the flowchart in Figure 5. First, the DC bus voltage estimation unit 254 extracts the maximum value from the AC input line voltage values ​​Vrs, Vst, and Vtr input from the AC input voltage sensor 28 and sets it as the maximum value Vmax (step S101).

[0059] Next, the maximum value Vmax of the extracted AC input line voltage is compared with the previously estimated DC bus voltage Vdc_est_old (step S102). In this embodiment, the previously estimated DC bus voltage value is denoted as the DC bus voltage estimate Vdc_est_old. If there is no previous DC bus voltage estimate Vdc_est_old, the process proceeds to step S103.

[0060] In step S102, if the maximum value Vmax of the AC input line voltage is greater than or equal to the previous DC bus voltage estimate Vdc_est_old (Yes in step S102), the process proceeds to step S103. In step S103, the DC bus voltage value Vdc_est is estimated to be the maximum value Vmax of the AC input line voltage and is output to the capacitor current estimation unit 250 (step S105).

[0061] In step S102, if the maximum value Vmax of the AC input line voltage is smaller than the previous DC bus voltage estimate Vdc_est_old (No in step S102), the process proceeds to step S104. In step S104, the DC bus voltage Vdc_est is estimated based on equation (8) and output to the capacitor current estimation unit 250. That is, the DC bus voltage estimate Vdc_est is obtained by subtracting the value obtained by dividing the DC output current value Iout by the capacitance value Cm of the smoothing capacitor from the previous DC bus voltage estimate Vdc_est_old (step S105).

number

[0062] The DC bus voltage estimation unit 254 stores the estimated DC bus voltage Vdc_est as the previously estimated DC bus voltage Vdc_est_old (step S106).

[0063] In Embodiment 1, the capacitor current value Ic was estimated in the capacitor current estimation unit 250 using the DC bus voltage value Vdc detected by the DC bus voltage sensor 23. In Embodiment 3, the capacitor current estimation unit 250 estimates the capacitor current value Ic based on the estimated DC bus voltage value Vdc_est estimated by the DC bus voltage estimation unit 254. The operation of the capacitor current estimation unit 250 is the same as in Embodiment 1, so a description is omitted.

[0064] In the DC input current estimation unit 251, the DC output current value Iin is estimated using equation (3) based on the capacitor current Ic estimated by the capacitor current estimation unit 250 and the DC output current value Iout detected by the DC output current sensor 24.

[0065] As described above, Embodiment 3 provides the same effects as Embodiment 1. That is, the DC input current Iin output by the rectifier circuit can be estimated without using a current detector. Furthermore, even without the DC bus voltage sensor 23 of Embodiment 1, the same effects as Embodiment 1 can be achieved with a configuration that includes an AC input voltage sensor 28, as in Embodiment 3.

[0066] Embodiment 4. The power conversion device and motor drive system equipped therewith according to Embodiment 4 will be described below with reference to the figures. Figure 6 is a schematic diagram showing the configuration of the power conversion device and motor drive system according to Embodiment 4. The difference from Figure 1 of Embodiment 1 is that the power conversion device 2 according to Embodiment 4 further has an AC input voltage sensor 28. The other configurations are the same as in Embodiment 1. Also, the operation of the AC input voltage sensor 28 in detecting the AC input line voltage values ​​Vrs, Vst, Vtr is the same as in Embodiment 3, and the detected AC input line voltage values ​​Vrs, Vst, Vtr are output to the control device 25. Therefore, the same configurations as in Embodiments 1 to 3 will not be described in Embodiment 4.

[0067] <Configuration and operation of control device 25> The control device 25 according to this fourth embodiment differs from that of the first embodiment in that it includes a rectifier element current estimation unit 255. The rectifier element current estimation unit 255 receives the DC input current value Iin estimated by the DC input current estimation unit 251 and the AC input line voltage values ​​Vrs, Vst, and Vtr detected by the AC input voltage sensor 28. Based on these, the rectifier element current estimation unit 255 estimates the rectifier element current value flowing through each rectifier element of the rectifier circuit 210 and outputs the estimated rectifier element current value to the inverter circuit control unit 252.

[0068] First, the rectifier element current estimation unit 255 estimates the AC input phase voltage values ​​based on the AC input line voltage values ​​Vrs, Vst, and Vtr detected by the AC input voltage sensor 28. As described in Embodiment 3, the AC input voltage sensor 28 may be provided to detect AC input phase voltage values ​​instead of AC input line voltage values ​​Vrs, Vst, Vtr. The AC input phase voltage values ​​are Vr for the R phase, Vs for the S phase, and Vt for the T phase, respectively.

[0069] Next, the rectifier element current estimation unit 255 determines which of the rectifier elements in the rectifier circuit 210 is conducting based on the relative magnitudes of the AC input phase voltage values. In the relationship between the magnitudes of the AC input phase voltage values, if equation (9) is satisfied, it is determined that diodes D1 and D6 are conducting. Vr>Vs>Vt···(9) If equation (10) is satisfied, it is determined that diodes D1 and D4 are conducting. Vr>Vt>Vs···(10)

[0070] If equation (11) is satisfied, it is determined that diodes D3 and D6 are conducting. Vs>Vr>Vt···(11) If equation (12) is satisfied, it is determined that diodes D3 and D2 are conducting. Vs>Vt>Vr···(12)

[0071] If equation (13) is satisfied, it is determined that diodes D5 and D4 are conducting. Vt>Vr>Vs···(13) If equation (14) is satisfied, it is determined that diodes D5 and D2 are conducting. Vt>Vs>Vr···(14)

[0072] The rectifier element current estimation unit 255 determines which rectifier elements are conducting based on equations (9) to (14), and estimates the rectifier element current flowing through the rectifier elements by estimating that a current equal to the DC input current value Iin estimated by the DC input current estimation unit 251 is flowing through the conducting rectifier elements.

[0073] The inverter circuit control unit 252 determines that the rectifier element current is overcurrent when the estimated rectifier element current output from the rectifier element current estimation unit 255 exceeds a predetermined current threshold. When the inverter circuit control unit 252 determines that the rectifier element current is overcurrent, it outputs a control signal to stop the inverter circuit 22 or reduce the AC power output to the motor 3, thereby reducing the DC input current and protecting the converter circuit 21.

[0074] In Figure 6, the DC input current estimation unit 251 estimates the DC input current based on the DC output current value output from the DC output current sensor 24. However, by including the AC output current sensor 27 described in Embodiment 2, and including the DC output current estimation unit 253 in the control device 25, and using the estimated DC output current value Iout, the DC input current Iin can be estimated, thus achieving the same effects as Embodiment 1 or 2.

[0075] As described above, Embodiment 4 provides the same effects as Embodiment 1. That is, the DC input current Iin output by the rectifier circuit can be estimated without using a current detector. Furthermore, as in this embodiment 4, the rectifier element current estimation unit 255 determines which rectifier element of the rectifier circuit 210 constituting the converter circuit 21 is experiencing current flow, and further determines whether or not it is an overcurrent. This reduces the DC input current and protects the converter circuit 21. Moreover, it becomes possible to protect the rectifier elements from overcurrent and to identify the rectifier element experiencing overcurrent, making it easier to perform checks and other inspections, such as verifying the operation of the rectifier circuit 210.

[0076] Embodiment 5. The power conversion device and motor drive system equipped therewith according to Embodiment 5 will be described below with reference to the figures. Figure 7 is a schematic diagram showing the configuration of the power conversion device and motor drive system according to Embodiment 5. It is the same as the configuration shown in Figure 6 of Embodiment 4, but with the addition of a temperature sensor 29. The temperature sensor 29 detects the temperature of the converter circuit 21 and outputs the detected temperature value of the converter circuit 21 to the control device 25. The other configurations are the same as in Embodiment 4. Therefore, the same configurations as in Embodiments 1 to 4 will not be described in Embodiment 5.

[0077] <Configuration and operation of control device 25> The control device 25 according to this fifth embodiment differs from that of the fourth embodiment in that it includes a rectifier element temperature estimation unit 256. The rectifier element temperature estimation unit 256 estimates the temperature of the diode, which is a rectifier element in the rectifier circuit 210, as the rectifier element temperature.

[0078] The rectifier element temperature estimation unit 256 estimates the rectifier element loss P_Di based on the rectifier element current value output from the rectifier element current estimation unit 255 and the rectifier element voltage generated in the rectifier element. Based on the rectifier element loss P_Di, the rectifier element thermal resistance Rth_Di, and the temperature detection value Tc detected by the temperature sensor 29, it estimates the temperature T_Di of each rectifier element in the rectifier circuit 210 and outputs the estimated rectifier element temperature T_Di to the inverter circuit control unit 252. Here, i is the diode Di number, and in Figure 7, i is a natural number from 1 to 6.

[0079] Regarding the rectifier element voltage value V_Di, it is possible to estimate the rectifier element voltage value V_Di by pre-establishing a dataset that shows the relationship between the rectifier element voltage value V_Di and the rectifier element current value I_Di. Also, the rectifier element voltage V_Di Estimation method This is not limited to examples where a dataset of rectifier element voltage values ​​V_Di corresponding to rectifier element current values ​​I_Di is provided in advance. For example, an approximation formula for the rectifier element voltage value V_Di for the rectifier element current value I_Di can be prepared, and the rectifier element voltage value V_Di can be estimated from the rectifier element current value I_Di using the approximation formula. No estimation method is limited to the effectiveness of this embodiment.

[0080] The rectifier element loss P_Di can be estimated by the product of the rectifier element voltage value V_Di and the rectifier element current value I_Di. The rectifier element thermal resistance Rth_Di is the thermal resistance between the temperature sensor 29 and the rectifier element. The rectifier element temperature estimation unit 256 estimates the rectifier element temperature T_Di based on equation (15).

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[0081] The inverter circuit control unit 252 determines that the rectifier element temperature is overheated if the estimated rectifier element temperature T_Di output from the rectifier element temperature estimation unit 256 exceeds a predetermined rectifier element temperature threshold.

[0082] When the inverter circuit control unit 252 determines that the rectifier element temperature T_Di is overheated, it outputs a control signal to stop the inverter circuit 22 or reduce the AC power output to the motor 3, thereby reducing the DC input current Iin output by the rectifier circuit 210 and protecting the converter circuit 21.

[0083] In Figure 7, the DC input current estimation unit 251 estimates the DC input current value based on the DC output current value output from the DC output current sensor 24. However, as described in Embodiment 4, the same effect can be achieved by providing the AC output current sensor 27 described in Embodiment 2, and the control device 25 with the DC output current estimation unit 253, and using the estimated DC output current value.

[0084] As described above, Embodiment 5 provides the same effects as Embodiment 1. That is, the DC input current Iin output by the rectifier circuit can be estimated without using a current detector. Furthermore, as in this embodiment 5, the rectifier element current estimation unit 255 determines which rectifier element of the rectifier circuit 210 constituting the converter circuit 21 is overheating, thereby reducing the DC input current and protecting the converter circuit 21. In addition, it becomes possible to protect the rectifier elements from overheating and to identify the overheating rectifier element, making it easier to perform inspections such as checking the operation of the rectifier circuit 210.

[0085] Embodiment 6. The power conversion device and motor drive system equipped therewith according to Embodiment 6 will be described below with reference to the figures. Figure 8 is a schematic diagram showing the configuration of the power conversion device and motor drive system according to Embodiment 6. The power conversion device 2 of Embodiment 1 is further equipped with a temperature sensor 29 in addition to the configuration of the power conversion device 2 of Figure 1. The other configurations are the same as in Embodiment 1. In addition, the temperature sensor 29 of Embodiment 6 also detects the temperature of the converter circuit 21, similar to Embodiment 5. Therefore, the description of the configurations in Embodiment 6 that are the same as in Embodiments 1 to 5 will be omitted.

[0086] <Configuration and operation of control device 25> The control device 25 according to this sixth embodiment differs from that of the first embodiment in that it further includes a capacitor temperature estimation unit 257 and a capacitor constant estimation unit 258. As in Embodiment 1, the DC input current Iin estimated by the DC input current estimation unit 251 is output to the inverter circuit control unit 252 using the capacitor current Ic estimated by the capacitor current estimation unit 250 and the DC output current value Iout detected by the DC output current sensor 24.

[0087] The capacitor temperature estimation unit 257 estimates the capacitor loss P_Cap of the smoothing capacitor 211 based on the estimated capacitor current Ic output from the capacitor current estimation unit 250 and the parasitic resistance Rs of the smoothing capacitor 211. Furthermore, based on the estimated capacitor loss P_Cap, the capacitor thermal resistance Rth_Cap, and the temperature detection value Tc detected by the temperature sensor 29, it estimates the temperature T_Cap of the smoothing capacitor 211 and outputs the estimated capacitor temperature T_Cap to the inverter circuit control unit 252.

[0088] The capacitor loss P_Cap can be estimated by the product of the square of the capacitor current Ic and the parasitic resistance Rs. That is, it can be calculated using equation (16). P_Cap=Ic 2 ·Rs···(16) The capacitor thermal resistance Rth_Cap is the thermal resistance between the temperature sensor 29 and the smoothing capacitor 211.

[0089] The capacitor temperature estimation unit 257 estimates the capacitor temperature T_Cap based on equation (17).

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[0090] The inverter circuit control unit 252 determines that the capacitor temperature is overheated if the estimated capacitor temperature T_Cap output from the capacitor temperature estimation unit 257 exceeds a predetermined capacitor temperature threshold.

[0091] When the inverter circuit control unit 252 determines that the capacitor temperature T_Cap is overheated, it outputs a control signal to stop the inverter circuit 22 or reduce the AC power output to the motor 3, thereby reducing the DC input current Iin and protecting the converter circuit 21.

[0092] The capacitor constant estimation unit 258 has a dataset of the temperature dependence of the capacitance value Cm and parasitic resistance value Rs of the smoothing capacitor 211 with respect to the capacitor temperature T_Cap. Using this dataset, it estimates the changes in the constants of the capacitance value Cm and parasitic resistance value Rs of the smoothing capacitor 211 as the temperature T_Cap of the smoothing capacitor 211 rises or falls, based on the changes in the temperature T_Cap estimated by the capacitor temperature estimation unit 257. It is quiet The capacitance value Cm and parasitic resistance value Rs are output to the capacitor current estimation unit 250 and the capacitor temperature estimation unit 257.

[0093] The temperature dependence of the capacitance and parasitic resistance of the smoothing capacitor 211 is shown in an example where a data set is provided in advance, but this is not the only method. For example, one could prepare an approximate formula for the temperature dependence of the capacitance and parasitic resistance. In any case, it is sufficient to estimate the capacitance and parasitic resistance that have changed in response to temperature changes, and this does not limit the effectiveness of this embodiment.

[0094] The capacitor current estimation unit 250 updates the capacitance value Cm and parasitic resistance value Rs used to estimate the capacitor current value, based on the estimated capacitor constant values ​​output from the capacitor constant estimation unit 258, in accordance with the temperature change of the estimated capacitor.

[0095] The capacitor temperature estimation unit 257 updates the parasitic resistance value Rs in the formula used for capacitor temperature estimation based on the capacitor constant estimation value output from the capacitor constant estimation unit 258.

[0096] As described above, Embodiment 6 provides the same effects as Embodiment 1. That is, the DC input current Iin output by the rectifier circuit can be estimated without using a current detector. Furthermore, as in this embodiment 6, the capacitor temperature estimation unit 257 estimates the temperature of the smoothing capacitor 211 and determines whether the smoothing capacitor 211 is overheated. If it is determined to be overheated, the DC input current is reduced to protect the smoothing capacitor 211 from overheating.

[0097] Furthermore, based on the temperature T_Cap of the smoothing capacitor 211 estimated by the capacitor temperature estimation unit 257, the capacitor constant estimation unit 258 estimates the capacitor constant corresponding to the temperature. It is quiet The capacitance value Cm and parasitic resistance value Rs are estimated. This allows us to use updated values ​​for the capacitance value Cm and parasitic resistance value Rs of the smoothing capacitor 211 used in equations (1), (2), (4), and (5) above, thereby improving the estimation accuracy of the capacitor current estimation unit 250 by considering the temperature dependence.

[0098] Furthermore, since the derivation of the capacitor loss P_Cap in equation (17) above includes the parasitic resistance Rs of the smoothing capacitor 211, as shown in equation (16), it is possible to improve the estimation accuracy of the capacitor temperature estimation unit 257 by updating the value of the parasitic resistance Rs while considering its temperature dependence.

[0099] Figure 9 shows an example of the hardware configuration of the control device 25 that constitutes the power converter 2 in the above-described embodiments 1 to 6. As shown in Figure 9, the control device 25 includes, for example, a processor 1000 and a storage device 1100 as processing circuits. The processor 1000 may include a CPU (Central Processing Unit), an ASIC (Application Specific Integrated Circuit), an IC (Integrated Circuit), an FPGA (Field Programmable Gate Array), various logic circuits, and various signal processing circuits. Furthermore, the processor 1000 may consist of multiple processors of the same or different types, each performing a portion of the processing. The storage device 1100 may include a RAM (Random Access Memory) configured to read and write data from the processor 1000, and a ROM (Read Only Memory) configured to read data from the processor 1000. The processor 1000 executes programs input from the storage device 1100, such as the ROM.

[0100] While this disclosure describes various exemplary embodiments and examples, the various features, aspects, and functions described in one or more embodiments are not limited to the application of a particular embodiment, but are applicable individually or in various combinations to the embodiments. Accordingly, countless variations not illustrated are conceivable within the scope of the technology disclosed herein. These include, for example, modifications, additions, or omissions of at least one component, as well as the extraction of at least one component and its combination with components of other embodiments. [Explanation of Symbols]

[0101] 1: AC power supply, 2: Power converter, 3: Motor, 10: Motor drive system, 21: Converter circuit, 210: Rectifier circuit, 211: Smoothing capacitor, 23: DC bus voltage sensor, 23a: Voltage sensor, 24: DC output current sensor, 25: Control device, 250: Capacitor current estimation unit, 251: DC input current estimation unit, 252: Inverter circuit control unit, 253: DC output current estimation unit, 254: DC bus voltage estimation unit, 255: Rectifier element current estimation unit, 256: Rectifier element temperature estimation unit, 257: Capacitor temperature estimation unit, 258: Capacitor constant estimation unit, 26: Differentiator circuit, 261: Capacitor, 262: Resistor, 27: AC output current sensor, 28: AC input voltage sensor, 29: Temperature sensor, 1000: Processor, 1100: Storage device.

Claims

1. A power conversion device comprising a rectifier circuit with multiple rectifier elements and a smoothing capacitor, a converter circuit that converts AC power to DC power, an inverter circuit that converts the DC power converted by the converter circuit to AC power, and a control device that controls the inverter circuit, The control device comprises a capacitor current estimation unit for estimating the current flowing through the smoothing capacitor, and a DC input current estimation unit for estimating the DC input current output from the rectifier circuit. The capacitor current estimation unit estimates the capacitor current value flowing through the smoothing capacitor based on the capacitor capacitance of the smoothing capacitor and the DC bus voltage value applied to the smoothing capacitor. The DC input current estimation unit estimates the DC input current value to be output by the rectifier circuit based on the estimated capacitor current value and the DC output current value input to the inverter circuit, in a power conversion device.

2. A first voltage sensor for detecting the DC bus voltage value applied to the smoothing capacitor, The power conversion device according to claim 1, further comprising a first current sensor for detecting the DC output current value input to the inverter circuit.

3. The control device is The inverter circuit is further provided with a DC output current estimation unit that estimates the DC output current value input to the inverter circuit. The DC output current estimation unit estimates the DC output current value based on the DC bus voltage value, the AC power output by the inverter circuit, and the losses of the inverter circuit. The power conversion device according to claim 1, wherein the DC input current estimation unit estimates the DC input current value to be output by the rectifier circuit based on the estimated capacitor current value and the DC output current value estimated by the DC output current estimation unit.

4. A first voltage sensor for detecting the DC bus voltage value applied to the smoothing capacitor, The inverter circuit is further equipped with a second current sensor for detecting the output current of the inverter circuit, The control device is The system includes a control unit that controls the inverter circuit, The power conversion device according to claim 3, wherein the DC output current estimation unit estimates the DC output current value based on the DC bus voltage value detected by the voltage sensor, the AC power output by the inverter circuit calculated based on the output current of the inverter circuit detected by the current sensor and the voltage command output from the control unit, and the losses of the inverter circuit.

5. The converter circuit is equipped with a second voltage sensor for detecting the AC input voltage, The control device is The system further comprises a DC bus voltage estimation unit for estimating the DC bus voltage value, The DC bus voltage estimation unit calculates the maximum AC voltage of the AC input voltage based on the output of the voltage sensor. In comparing the maximum value of the AC voltage with the previously estimated DC bus voltage, If the maximum value of the AC voltage is greater than or equal to the previously estimated DC bus voltage value, the maximum value of the AC voltage is estimated to be the DC bus voltage value. The power conversion device according to claim 1, wherein if the maximum value of the AC voltage is smaller than the previously estimated DC bus voltage, the DC bus voltage is estimated to be the value obtained by subtracting the value obtained by dividing the DC output current by the capacitance value of the smoothing capacitor from the previously estimated DC bus voltage.

6. The control device is The power conversion device according to claim 1, wherein the DC input current value estimated by the DC input current estimation unit determines that the DC input current is an overcurrent when the DC input current value exceeds a predetermined current threshold.

7. The converter circuit is equipped with a second voltage sensor for detecting the AC input voltage, The control device is The system further includes a rectifier element current estimation unit that estimates the current flowing through multiple rectifier elements, The rectifier element current estimation unit determines which of the plurality of rectifier elements is conducting based on the relative magnitudes of the phase voltage values ​​for each phase voltage of the AC input voltage detected by the second voltage sensor. The power conversion device according to any one of claims 1 to 6, wherein the estimated value of the rectifier element current flowing through the conductive rectifier element is estimated to be the same as the estimated value of the DC input current estimated by the DC input current estimation unit.

8. The converter circuit is equipped with a temperature sensor that detects the temperature of the converter circuit, The control device further includes a rectifier element temperature estimation unit that estimates the temperatures of a plurality of rectifier elements, The power conversion device according to claim 7, wherein the rectifier element temperature estimation unit estimates the temperatures of a plurality of rectifier elements based on the estimated rectifier element current value estimated by the rectifier element current estimation unit and the temperature of the converter circuit detected by the temperature sensor.

9. The converter circuit is equipped with a temperature sensor that detects the temperature of the converter circuit, The control device further comprises a capacitor temperature estimation unit for estimating the temperature of the smoothing capacitor, The power conversion device according to any one of claims 1 to 6, wherein the capacitor temperature estimation unit estimates the temperature of the smoothing capacitor based on the estimated capacitor current value and the temperature of the converter circuit detected by the temperature sensor.

10. A motor drive system comprising a power conversion device according to any one of claims 1 to 6, and a motor that uses the AC power converted by the power conversion device as a drive source.

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