Power Conversion Device

Abstract

To reduce component costs and power consumption and improve reliability while suppressing failures and shortening of the life of power conversion device.SOLUTION: A power conversion device (1) is provided with a detection unit (15) that detects the DC link voltage (Vdc). A control unit (20) executes a pulsation generation operation that controls an inverse converter (12) so that a motor (3) does not rotate and the pulsation caused by the frequency of the input AC is generated in the DC link voltage (Vdc), and a power supply information identification process that identifies the unbalanced information (UB) related to the input AC frequency (fp), pulsation phase (θest), presence / absence of open phase (PR), and unbalance rate based on the detected value of DC link voltage (Vdc) during pulsation generation operation.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present disclosure relates to a power conversion device that performs power conversion on input AC power supplied from an AC power source. [Background technology]

[0002] Patent Document 1 discloses a power conversion device having a rectifier that converts input AC supplied from an AC power source into DC and outputs the DC, an inverter that converts the DC output by the rectifier into AC and supplies the AC to an electric motor, a capacitor connected between input nodes of the inverter, a zero-cross detection circuit that detects zero-crossing of the voltage of the input AC, and a frequency calculation unit that calculates the frequency of the input AC according to the detection result of the zero-cross detection circuit. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Patent No. 4056047 Summary of the Invention [Problem to be solved by the invention]

[0004] In the above-mentioned Patent Document 1, a zero-cross detection circuit that requires a large number of components and consumes a large amount of power is provided in the power conversion device, which increases the number of components in the power conversion device, leading to higher component costs, increased power consumption, and a higher probability of failure, resulting in lower reliability.

[0005] Another method for determining power supply information, such as the frequency of the input AC, without using a zero-crossing detection circuit is to determine the power supply information, such as the frequency of the input AC, based on a pulsating component that occurs in the voltage of the capacitor due to the frequency of the input AC while the motor is rotating. However, when using this method, it is necessary to perform rotation control on the motor that is not based on actual power supply information until the power supply information can be determined. Therefore, during rotation control until the power supply information is determined, overvoltage and overcurrent may occur, which may lead to failure or a shortened lifespan of the power conversion device.

[0006] An object of the present disclosure is to reduce component costs and power consumption, and improve reliability while suppressing breakdowns and shortening of the lifespan of a power conversion device. [Means for solving the problem]

[0007] A first aspect of the present disclosure is a power conversion device including a rectifier (11) that converts input AC supplied from an AC power source (2) into DC and outputs the DC, an inverter (12) that converts the DC output from the rectifier (11) into AC and supplies the AC to an electric motor (3), a capacitor (14) connected between input nodes (12a, 12b) of the inverter (12), and a control unit (20) that controls the inverter (12), and further includes a detection unit (15) that detects detection targets (Vdc, Idc, Ipu, Ipv, Ipw, Vn) that are voltages or currents at predetermined locations, and the control unit (20) controls the voltages or currents at predetermined locations. The method is characterized by executing a pulsation generating operation that controls the inverter (12) so as to generate pulsations due to the frequency of the input AC in the detection objects (Vdc, Idc, Ipu, Ipv, Ipw, Vn) without causing a rotational motion of the motor (3), and a power supply information identification process that identifies power supply information including at least one of the frequency (fp) of the input AC, the phase (θest) of the pulsation, the presence or absence of a phase loss (PR), and unbalance information (UB) related to the unbalance rate, based on the detected values ​​of the detection objects (Vdc, Idc, Ipu, Ipv, Ipw, Vn) during the pulsation generating operation.

[0008] In the first aspect, by providing a detection unit (15) that detects the detection targets (Vdc, Idc, Ipu, Ipv, Ipw, Vn) that generate pulsation, it is not necessary to provide a zero-cross detection circuit that requires a large number of components and consumes a large amount of power. This reduces the number of components, component costs, and power consumption of the power conversion device (1), and also increases reliability.

[0009] Furthermore, after causing the control unit (20) to perform the pulsation generating operation and the power supply information specifying process, the control unit (20) can start the rotation control of the electric motor (3) that reflects the power supply information, thereby preventing breakdowns and shortened life of the power conversion device (1) that may be caused by rotation control that is not based on actual power supply information.

[0010] A second aspect of the present disclosure is the first aspect, characterized in that the capacitance of the capacitor (14) is set to allow pulsation of the output voltage of the rectifier (11).

[0011] In the second mode, the capacity of the capacitor (14) can be made smaller than when it is set so as not to allow pulsation in the output voltage of the rectifier (11), and therefore the power consumption required to generate pulsation due to the frequency of the input AC can be reduced.

[0012] A third aspect of the present disclosure is characterized in that, in the first or second aspect, the detection object (Vdc, Idc, Ipu, Ipv, Ipw, Vn) is the voltage (Vdc) of the capacitor (14) or the output voltage (Vn) of the rectifier (11).

[0013] In the third aspect, the voltage (Vdc) of the capacitor (14) or the output voltage (Vn) of the rectifier (11) has a waveform in which a peak value and a bottom value appear for each pulsation period, making it easy to identify the pulsation frequency (fest, ωest) and power supply information.

[0014] A fourth aspect of the present disclosure is characterized in that, in any one of the first to third aspects, the power supply information determination process determines the pulsation frequencies (fest, ωest) of the detection objects (Vdc, Idc, Ipu, Ipv, Ipw, Vn) based on the detection values ​​of the detection objects (Vdc, Idc, Ipu, Ipv, Ipw, Vn) during the pulsation generating operation, and determines the power supply information based on the pulsation frequencies (fest, ωest).

[0015] In the fourth aspect, the power supply information is specified based on the pulsation frequency (fest, ωest), which makes it easy to specify the power supply information relatively accurately. [Brief explanation of the drawings]

[0016] [Figure 1] FIG. 1 is a block diagram showing the configuration of a power conversion device according to the first embodiment. [Figure 2A] FIG. 2A is a timing chart illustrating the power supply voltage and phase current during a pulsation generating operation when DC power is consumed by the electric motor. [Figure 2B] FIG. 2B is a timing chart illustrating the DC link voltage, the DC link current, the phase of the pulsating component of the DC link voltage, and the motor current during a pulsation generating operation when DC power is consumed by the electric motor. [Figure 3] FIG. 3 is a timing chart showing the DC link voltage in a normal state where there is no missing phase and in an open-phase state where there is a missing phase. [Figure 4] FIG. 4 is a timing chart showing the DC link voltage in a normal state where the unbalance rate is 0% and when the unbalance rate is 20%. [Figure 5] FIG. 5 is a timing chart showing the DC link voltage in a normal state where the unbalance rate is 0% and when the unbalance rate is 50%. [Figure 6] FIG. 6 is a block diagram showing the configuration of a pulsating frequency identifying unit and a phase identifying unit according to the third modification of the first embodiment. [Figure 7] FIG. 7 is a view corresponding to FIG. 1 of the second embodiment. [Figure 8] FIG. 8 is a view corresponding to FIG. 1 of the third embodiment. [Figure 9] FIG. 9 is a view corresponding to FIG. 1 of the fourth embodiment. [Figure 10A] FIG. 10A is a diagram equivalent to FIG. 2A in the case where AC power is consumed by the electric motor. [Figure 10B] FIG. 10B is a diagram equivalent to FIG. 2B in the case where AC power is consumed by the electric motor. DETAILED DESCRIPTION OF THE INVENTION

[0017] Hereinafter, embodiments of the present disclosure will be described with reference to the drawings. Note that the following embodiments are essentially preferred examples and are not intended to limit the scope of the present invention, its applications, or its uses.

[0018] First Embodiment 1 shows a power conversion device (1) according to a first embodiment of the present disclosure. The power conversion device (1) converts input AC power supplied from a three-phase AC power supply (2) into AC power having a desired frequency and a desired voltage, and supplies the AC power to an electric motor (3).

[0019] The power converter (1) includes a rectifier (11), an inverter (12), a reactor (13), a capacitor (14), a detector (15), and a controller (20).

[0020] The rectifier (11) converts input AC power supplied from the three-phase AC power supply (2) into DC power and outputs the DC power to first and second output nodes (11a, 11b). Specifically, the rectifier (11) is a full-wave rectifier circuit. The rectifier (11) has six diodes (11D) connected in a bridge configuration. The cathodes of these diodes (11D) face the first output node (11a) and the anodes face the second output node (11b).

[0021] The inverter (12) converts the DC output from the rectifier (11) into three-phase AC by switching operation and supplies the AC to the electric motor (3). Specifically, the inverter (12) has six switching elements (12S) and six freewheeling diodes (12D). The six switching elements (12S) are bridge-connected. More specifically, the inverter (12) has three switching legs connected between its first and second input nodes (12a, 12b). Each switching leg is made up of two switching elements (12S) connected in series.

[0022] In each of the three switching legs, the midpoint between the upper arm switching element (12S) and the lower arm switching element (12S) is connected to a coil of each phase (u-phase, v-phase, w-phase coil) of the electric motor (3). A free wheel diode (12D) is connected in anti-parallel to each switching element (12S).

[0023] One end of the reactor (13) is connected to a first output node (11a) of the rectifier (11), and the other end of the reactor (13) is connected to a first input node (12a) of the inverter (12).

[0024] The capacitor (14) is connected between the first and second input nodes (12a, 12b) of the inverter (12). Therefore, the reactor (13) is connected between the three-phase AC power supply (2) and the capacitor (14).

[0025] The capacitance of the capacitor 14 is set so that it can hardly smooth the output voltage of the rectifier 11, but can suppress the ripple voltage caused by the switching operation of the inverter 12. The ripple voltage is a voltage fluctuation caused by the switching frequency of the switching element 12S.

[0026] In other words, the capacitance of the capacitor 14 is set to tolerate fluctuations in the output voltage of the rectifier 11 and to absorb voltage fluctuations between the first and second input nodes 12a, 12b (DC side nodes) of the inverter 12 caused by switching operations. More specifically, the capacitance of the capacitor 14 is set to suppress voltage fluctuations across the capacitor 14 during a switching period to 1 / 10 or less of the average voltage of the capacitor 14.

[0027] By setting the capacitance value C of the capacitor (14) to satisfy the following formula (A), it is possible to suppress the voltage fluctuation of the capacitor (14) during a switching period to 1 / 10 or less of the average value of the voltage of the capacitor (14). In formula (A), the output voltage fluctuation of the rectifier (11) superimposed on the DC link voltage (Vdc), which is the voltage of the capacitor (14), is ignored. The average value of the DC link voltage (Vdc) is denoted by VAdc, the peak value of the load current when the AC power is at its maximum power by Imax, and the switching period is denoted by Ts.

[0028] C≧(10·Imax·Ts) / VAdc ···(A) Here, the switching period is a period during which the switching element (12S) repeatedly turns on and off. In the first embodiment, the switching period is the carrier period of the carrier wave because the switching element (12S) is controlled by PWM control.

[0029] An electrolytic capacitor is used as a smoothing capacitor for smoothing the output voltage of the rectifier 11. On the other hand, the capacitance of the capacitor 14 in this embodiment is about 0.01 to 0.1 times that of the smoothing capacitor. As an example, the capacitor 14 is made of a film capacitor.

[0030] Therefore, pulsation occurs in the DC link voltage (Vdc), which is the voltage of the capacitor (14), due to the frequency of the input AC supplied from the three-phase AC power supply (2). Because the three-phase AC power supply (2) is a three-phase power supply, the frequency of the pulsation due to the frequency of the three-phase AC power supply (2) is six times the frequency of the three-phase AC power supply (2).

[0031] The capacitor (14) constitutes an LC filter (LC) together with an inductance component between the three-phase AC power supply (2) and the capacitor (14). The inductance component includes a reactor (13).

[0032] The detection unit (15) detects a DC link voltage (Vdc) as a detection target, which is the voltage of the capacitor (14) as a predetermined location.

[0033] The control unit (20) executes a pulsation generating operation of controlling the inverter (12) so as to generate pulsation in a DC link voltage (Vdc) due to the frequency of the input AC without causing the electric motor (3) to perform rotational motion, and a power supply information identification process of identifying, as power supply information, the frequency (fp) of the input AC, the phase (θest) of the pulsation, the presence or absence of a phase loss (PR), and unbalance information (UB) related to an unbalance rate, based on a detected value of the DC link voltage (Vdc) during the pulsation generating operation.

[0034] Specifically, the control unit 20 includes an inverter driving unit 21 and a power supply information determining unit 22. The functions of the control unit 20 are realized by a microcomputer or the like.

[0035] The inverter driver (21) outputs a control signal to the inverter (12) to control the switching operation of each switching element (12S).

[0036] The inverter driver 21 performs a rotation control operation to control the inverter 12 to rotate the electric motor 3 at a desired rotational speed, and a pulsation generation operation to control the inverter 12 to prevent the electric motor 3 from rotating and to generate pulsation in the DC link voltage Vdc due to the frequency of the input AC current. The rotational movement of the electric motor 3 does not include movement to a specific position when current begins to flow between the electric motor 3 and the capacitor 14, nor does it vibrate slightly due to an alternating magnetic field. Therefore, if the start of the pulsation generation operation is the start of current flow, the electric motor 3 may rotate to a specific position when the pulsation generation operation begins. Furthermore, the electric motor 3 may vibrate slightly due to an alternating magnetic field during the pulsation generation operation.

[0037] In the rotation control operation and pulsation generating operation, the inverter driving unit (21) performs PWM control to control a plurality of switching elements (12S) with a switching signal corresponding to a comparison result between the modulated wave of each phase and a carrier wave, which is a predetermined triangular wave. Specifically, if the modulated wave is larger than the carrier wave, the upper arm switching element (12S) is turned on and the lower arm switching element (12S) is turned off, whereas if the modulated wave is smaller than the carrier wave, the upper arm switching element (12S) is turned off and the lower arm switching element (12S) is turned on.

[0038] Furthermore, the inverter driver (21) controls the switching element (12S) of the inverter (12) so that DC power is consumed by the electric motor (3) during the pulsation generating operation.

[0039] 2A and 2B illustrate examples of power supply voltages (Vpu, Vpv, Vpw), three-phase phase currents (Ipu, Ipv, Ipw) of the three-phase AC power supply (2), DC link voltage (Vdc), DC link current (Idc) flowing from rectifier (11) to capacitor (14), phase (θest) of the pulsation component of the DC link voltage (Vdc), and motor currents (Imu, Imv, Imw) during pulsation generation operation. During pulsation generation operation, pulsation occurs in the DC link voltage (Vdc), phase currents (Ipu, Ipv, Ipw), and DC link current (Idc). In the example of FIGS. 2A and 2B, the frequency of the power supply voltages (Vpu, Vpv, Vpw) is 60 Hz. The pulsation frequency of the DC link voltage (Vdc), phase currents (Ipu, Ipv, Ipw), and DC link current (Idc) is 360 Hz, which is six times the frequency of the power supply voltages (Vpu, Vpv, Vpw). Furthermore, the motor currents (Imu, Imv, Imw) during the pulsation generating operation are DC currents. Since DC power is supplied to the motor (3) during the pulsation generating operation, the direction of the magnetic flux generated in the motor (3) does not change, and the motor (3) does not rotate. If the pulsation generating operation starts at the start of energization, the motor (3) may rotate from its position before energization to a position where the rotor magnet and the generated magnetic flux align, and then remain at that position. This rotation is not included in the rotational motion of the motor (3).

[0040] The power supply information determination unit (22) determines the frequency (fp) of the input AC, the phase (θest) of the pulsation, the presence or absence of an open phase (PR), and unbalance information (UB) related to the unbalance rate, based on the DC link voltage (Vdc) detected by the detection unit (15). The power supply information determination unit (22) includes a pulsation frequency determination unit (22a), a power supply frequency determination unit (22b), a phase determination unit (22c), an open phase determination unit (22d), and an unbalance information determination unit (22e).

[0041] The pulsation frequency identifying unit (22a) identifies the reciprocal of the period T1 (see FIG. 2B) of the peak value of the DC link voltage (Vdc) detected by the detecting unit (15) as the pulsation frequency (fest).

[0042] The power supply frequency specifying unit (22b) specifies the frequency of the input AC based on the pulsating frequency (fest) specified by the pulsating frequency specifying unit (22a). Specifically, the power supply frequency specifying unit (22b) specifies 1 / 6 of the pulsating frequency (fest) specified by the pulsating frequency specifying unit (22a) as the frequency (fp) of the input AC.

[0043] The phase identifying unit (22c) performs a Fourier transform on the DC link voltage (Vdc) detected by the detecting unit (15). Then, based on the pulsation frequency (fest) identified by the pulsation frequency identifying unit (22a), the phase identifying unit (22c) identifies the phase (θest) of the component of the pulsation frequency (fest) included in the DC link voltage (Vdc).

[0044] The open-phase determination unit (22d) determines whether or not there is an open phase (PR) in the input AC based on whether or not the pulsation frequency (fest) determined by the pulsation frequency determination unit (22a) is equal to or lower than a predetermined frequency threshold. Fig. 3 shows the DC link voltage (Vdc) in a normal state where there is no open phase and in an open-phase state where there is an open phase. When the frequency of the power supply voltages (Vpu, Vpv, Vpw) is 60 Hz, if there is no open phase in the input AC, the pulsation frequency (fest) is 360 Hz, whereas if there is an open phase in the input AC, the pulsation frequency (fest) is 120 Hz. Therefore, by setting the frequency threshold value higher than 120 Hz and lower than 360 Hz, the phase loss determination unit (22d) can determine that there is a phase loss in the input AC when the pulsation frequency (fest) identified by the pulsation frequency identification unit (22a) is equal to or lower than the predetermined frequency threshold value, and can determine that there is no phase loss in the input AC when the pulsation frequency (fest) identified by the pulsation frequency identification unit (22a) exceeds the predetermined frequency threshold value.

[0045] When the frequency of the power supply voltages (Vpu, Vpv, Vpw) is 50 Hz, if there is no loss of phase in the input AC, the pulsation frequency (fest) is 300 Hz, whereas if there is a loss of phase in the input AC, the pulsation frequency (fest) is 100 Hz. Therefore, by setting the frequency threshold higher than 100 Hz and lower than 300 Hz, the loss-of-phase determination unit (22d) can determine whether there is a loss of phase (PR).

[0046] Furthermore, the unbalance information specifying unit (22e) specifies unbalance information (UB) related to the unbalance rate of the input AC based on the specified pulsation frequency (fest). Specifically, the unbalance information specifying unit (22e) determines whether the pulsation frequency (fest) specified by the pulsation frequency specifying unit (22a) is equal to or greater than a first threshold, and if so, specifies as unbalance information (UB) that the unbalance rate is low. If the pulsation frequency (fest) specified by the pulsation frequency specifying unit (22a) is less than the first threshold, the unbalance information specifying unit (22e) determines whether the pulsation frequency (fest) specified by the pulsation frequency specifying unit (22a) is equal to or greater than a second threshold that is lower than the first threshold, and if so, specifies as unbalance information (UB) that the unbalance rate is medium. Conversely, if the pulsation frequency (fest) is less than the second threshold, specifies as unbalance information (UB) that the unbalance rate is high.

[0047] Figure 4 shows the DC link voltage (Vdc) under normal conditions when the unbalance rate is 0% and when the unbalance rate is 20%. As shown in the figure, under normal conditions when the unbalance rate is 0%, the pulsation frequency (fest) of the DC link voltage (Vdc) is six times the frequency of the input AC (power supply voltages (Vpu, Vpv, Vpw)). On the other hand, when the unbalance rate is 20%, the frequency component four times the frequency of the input AC (power supply voltages (Vpu, Vpv, Vpw)) becomes dominant in the DC link voltage (Vdc).

[0048] Figure 5 shows the DC link voltage (Vdc) when the unbalance rate is 0% and when it is 50%. As shown in the figure, when the unbalance rate is 50%, the DC link voltage (Vdc) is dominated by a frequency component that is twice the frequency of the input AC (power supply voltages (Vpu, Vpv, Vpw)).

[0049] Therefore, if the frequency of the power supply voltages (Vpu, Vpv, Vpw) is 60 Hz, by setting the first threshold to 240 Hz, which is four times the frequency of the power supply voltages (Vpu, Vpv, Vpw), and setting the second threshold to 120 Hz, which is twice the frequency of the power supply voltages (Vpu, Vpv, Vpw), an unbalance rate of 20% or less can be set to a low level, an unbalance rate of more than 20% and less than 50% can be set to a medium level, and an unbalance rate of more than 50% can be set to a high level. Note that the first and second thresholds may also be set to other values.

[0050] Similarly, when the frequency of the power supply voltages (Vpu, Vpv, Vpw) is 50 Hz, the first threshold can be set to 200 Hz, which is four times the frequency of the power supply voltages (Vpu, Vpv, Vpw), and the second threshold can be set to 100 Hz, which is twice the frequency of the power supply voltages (Vpu, Vpv, Vpw).This allows an unbalance rate of 20% or less to be set to a low level, an unbalance rate of more than 20% and less than 50% to be set to a medium level, and an unbalance rate of more than 50% to be set to a high level.

[0051] Note that FIG. 2B illustrates an actual value of the DC link voltage (Vdc), and FIGS. 3 to 5 illustrate an ideal waveform of the DC link voltage (Vdc) for the sake of explanation.

[0052] To drive the electric motor (3) using the power conversion device (1) configured as described above, first, the inverter driver (21) is caused to perform a pulsation generating operation while the electric motor (3) is not rotating. As a result, pulsation due to the frequency of the input AC is generated in the DC link voltage (Vdc) while the electric motor (3) is not rotating. Next, the power supply information determination unit (22) is caused to determine the frequency (fp) of the input AC, the phase (θest) of the pulsation, the presence or absence of an open phase (PR), and unbalance information (UB) related to the unbalance rate, based on the DC link voltage (Vdc) detected by the detection unit (15) during the pulsation generating operation by the inverter driver (21). Thereafter, the inverter driving unit (21) executes a rotation control operation to rotate the electric motor (3) at a desired rotation speed based on the frequency (fp) of the input AC, the phase (θest) of the pulsation, the presence or absence of a phase loss (PR), and the unbalance information (UB) relating to the unbalance rate, which are identified by the power supply information identifying unit (22).

[0053] When the capacity of the capacitor 14 is small, the power conversion device 1 is more likely to malfunction due to overvoltage or overcurrent if a rotation control operation is performed without reference to actual power supply information. Furthermore, if the input AC is three-phase, operating the power conversion device 1 with a missing phase or a high unbalance rate increases the ripple current flowing into the capacitor 14, shortening its lifespan due to self-heating. This problem is particularly pronounced when an electrolytic capacitor is used as the capacitor 14.

[0054] In the first embodiment, as described above, the control unit (20) can start the rotation control operation that reflects the power supply information after executing the pulsation generating operation and the power supply information specifying process, thereby preventing the power conversion device (1) from failing or having a shorter life due to the rotation control operation that is not based on the power supply information.

[0055] Therefore, according to the first embodiment, by providing the detection unit (15) that detects the DC link voltage (Vdc) that generates pulsation, it is not necessary to provide a zero-cross detection circuit that requires a large number of components and consumes a large amount of power. This reduces the number of components, component costs, and power consumption of the power conversion device (1), and also increases reliability.

[0056] Furthermore, when the first embodiment is applied to a general power conversion device that includes a detection unit (15) that detects the DC link voltage (Vdc) for a purpose other than identifying the power supply information, it is not necessary to provide a separate detection device that can identify the power supply information, and therefore it is possible to suppress an increase in the number of parts and the cost of parts.

[0057] Furthermore, since the capacitance of the capacitor (14) can be made smaller than when it is set so as not to allow pulsation in the output voltage of the rectifier (11), it is possible to reduce the power consumption required to generate pulsation in the DC link voltage (Vdc) due to the frequency of the input AC.

[0058] Furthermore, since the capacitance of the capacitor (14) can be made smaller than when it is set so as not to tolerate pulsation in the output voltage of the rectifier (11), a film capacitor small enough to be mounted on a circuit board can be used as the capacitor (14), and reliability can be improved compared to when an electrolytic capacitor, the life of which is reduced by pulsation in the output voltage of the rectifier (11), is used.

[0059] Furthermore, the DC link voltage (Vdc) having a waveform in which a peak value appears at each pulsation period is used to identify the power supply information. Therefore, the pulsation frequency (fest, ωest) and the power supply information can be easily identified based on the period T1 of the peak value of the DC link voltage (Vdc).

[0060] Furthermore, since the power supply information is specified based on the pulsation frequency (fest, ωest), it is easy to specify the power supply information relatively accurately.

[0061] First Modification of First Embodiment In the first modification of the first embodiment, the pulsation frequency identifying unit (22a) of the power supply information identifying unit (22) identifies the pulsation frequency (fest) based on the cycle T2 (see FIG. 2B ) of the bottom value of the DC link voltage (Vdc) detected by the detecting unit (15). Specifically, the pulsation frequency identifying unit (22a) identifies the reciprocal of the cycle T2 of the bottom value of the DC link voltage (Vdc) as the pulsation frequency (fest).

[0062] The other configurations are the same as those in the first embodiment, so detailed explanations thereof will be omitted.

[0063] Therefore, according to the present first modification, the DC link voltage (Vdc) having a waveform in which a bottom value appears at each pulsation period is used to identify the power supply information, and therefore the pulsation frequency (fest, ωest) and the power supply information can be easily identified based on the period T2 of the bottom value of the DC link voltage (Vdc).

[0064] Second Modification of First Embodiment In the second modification of the first embodiment, the pulsation frequency identifier (22a) of the power supply information identifier (22) identifies the pulsation frequency (fest) based on a period (time difference) T3 (see FIG. 2B ) between the timings at which the DC link voltage (Vdc) detected by the detector (15) transitions from being below a predetermined comparison value (CV) to being above it. Specifically, the pulsation frequency identifier (22a) identifies the reciprocal of the period T3 between the timings at which the DC link voltage (Vdc) transitions from being below the predetermined comparison value (CV) to being above it, as the pulsation frequency (fest). Alternatively, the pulsation frequency identifier (22a) may identify the reciprocal of the period between the timings at which the DC link voltage (Vdc) transitions from being above the predetermined comparison value (CV) to being below it, as the pulsation frequency (fest).

[0065] The other configurations are the same as those in the first embodiment, so detailed explanations thereof will be omitted.

[0066] Third Modification of First Embodiment In the third modification of the first embodiment, the pulsation frequency identifying unit (22a) of the power supply information identifying unit (22) includes a filter (31), an αβ conversion unit (32), a dq conversion unit (33), a subtractor (34), and a proportional-integral control unit (35), as shown in Fig. 6. The pulsation frequency identifying unit (22a) identifies the angular frequency of the pulsation as a pulsation frequency (ωest). The phase identifying unit (22c) is configured with an integrator.

[0067] The filter (31) performs filtering to extract the fundamental frequency component of the DC link voltage (Vdc) detected by the detector (15).

[0068] The αβ conversion unit (32) performs αβ conversion on the fundamental frequency component extracted by the filter (31) to generate an α-axis voltage (V α ) and β-axis voltage (V β ) is output.

[0069] The dq conversion unit (33) converts the α-axis voltage (V α ) and β-axis voltage (V β ) is subjected to dq transformation using the phase (θest) to output the q-axis voltage (Vq).

[0070] The subtractor (34) calculates the command voltage (Vq * The dq converter (33) subtracts the q-axis voltage (Vq) output from the dq converter (33) from 0, which is the sum of the q-axis voltages (Vq) and Vq of the dq-axis voltages (Vq) and outputs the result of the subtraction.

[0071] The proportional-plus-integral control section (35) calculates the pulsation frequency (ωest) by proportional-plus-integral (PI) control based on the result of the subtraction by the subtractor (34).

[0072] The phase identification unit (22c) integrates the ripple frequency (ωest) calculated by the proportional-plus-integral control unit (35) to identify the phase (θest) of the component of the ripple frequency (ωest) contained in the DC link voltage (Vdc).

[0073] The other configurations are the same as those in the first embodiment, so detailed explanations thereof will be omitted.

[0074] Second Embodiment 7 shows a power conversion device (1) according to a second embodiment of the present invention. In the second embodiment, a detection unit (15) detects a DC link current (Idc) instead of a DC link voltage (Vdc).

[0075] The power supply information determination unit (22) determines the frequency (fp) of the input AC, the phase (θest) of the pulsation, the presence or absence of a missing phase (PR), and unbalance information (UB) based on the DC link current (Idc) detected by the detection unit (15).

[0076] Specifically, for example, the DC link current (Idc) detected by the detection unit (15) is input to the pulsation frequency identifying unit (22a) of Modification 3 of Embodiment 1, instead of the DC link voltage (Vdc). This enables the pulsation frequency identifying unit (22a) to output the pulsation frequency (ωest), and the phase identifying unit (22c) to identify the phase (θest) of the component of the pulsation frequency (ωest) contained in the DC link current (Idc).

[0077] The other configurations are the same as those of the third modification of the first embodiment, so the same components are given the same reference numerals and detailed descriptions thereof will be omitted.

[0078] In the second embodiment, the configuration for detecting the DC link current (Idc) is applied to the third modification of the first embodiment, but may be applied to the first embodiment or the second modification of the first embodiment.

[0079] Third Embodiment 8 shows a power conversion device (1) according to a third embodiment of the present invention. In the third embodiment, a detection unit (15) detects a U-phase phase current (Ipu) of a three-phase AC power supply (2) as a detection target instead of a DC link voltage (Vdc). In the present embodiment, the detection target is the U-phase phase current (Ipu), but it is sufficient that the detection target is the phase current of any one of the phases, and the detection target may be the V-phase or W-phase phase current (Ipv, Ipw).

[0080] The power supply information determination unit (22) determines the frequency (fp) of the input AC, the phase (θest) of the pulsation, the presence or absence of a missing phase (PR), and unbalance information (UB) based on the phase current (Ipu) detected by the detection unit (15).

[0081] Specifically, for example, the phase current (Ipu) of the U phase detected by the detection unit (15) is input to the pulsation frequency identification unit (22a) of the third modification of the first embodiment, instead of the DC link voltage (Vdc). This enables the pulsation frequency identification unit (22a) to output the pulsation frequency (ωest), and the phase identification unit (22c) to identify the phase (θest) of the component of the pulsation frequency (ωest) contained in the phase current (Ipu).

[0082] The other configurations are the same as those of the third modification of the first embodiment, so the same components are given the same reference numerals and detailed descriptions thereof will be omitted.

[0083] In the third embodiment, the configuration in which the phase current (Ipu) is to be detected is applied to the third modification of the first embodiment, but it may also be applied to the first embodiment or the first and second modifications of the first embodiment.

[0084] Fourth Embodiment 9 shows a power conversion device (1) according to a fourth embodiment of the present invention. In the fourth embodiment, a detection unit (15) detects the voltage between the first and second output nodes (11a, 11b) of the rectifier (11), i.e., the output voltage (Vn) of the rectifier (11), instead of the DC link voltage (Vdc).

[0085] The power supply information determination unit (22) determines the frequency (fp) of the input AC, the phase (θest) of the pulsation, the presence or absence of a missing phase (PR), and unbalance information (UB) relating to the unbalance rate, based on the output voltage (Vn) detected by the detection unit (15).

[0086] The other configurations are the same as those in the first embodiment, so the same components are given the same reference numerals and detailed descriptions thereof are omitted.

[0087] In the first to fourth embodiments and the first to third modifications of the first embodiment, the inverter driver (21) controls the switching element (12S) of the inverter (12) during the pulsation generating operation so that DC power is consumed by the electric motor (3). However, an alternating magnetic field may be generated in the electric motor (3) so that AC power is consumed by the electric motor (3). FIG. 10A is a diagram equivalent to FIG. 2A illustrating a case in which the inverter (12) is controlled during the pulsation generating operation so that AC power is consumed by the electric motor (3). FIG. 10B is a diagram equivalent to FIG. 2B illustrating a case in which the inverter (12) is controlled during the pulsation generating operation so that AC power is consumed by the electric motor (3). To rotate the electric motor (3), it is necessary to synchronize the alternating magnetic field generated by the electric motor (3) with the magnetic poles of the electric motor (3). To achieve this, it is necessary to gradually increase the frequency of the alternating magnetic field from a low frequency. Therefore, a high-frequency alternating magnetic field is generated from the start of power supply to the electric motor (3), and the magnetic poles of the electric motor (3) are not synchronized with the alternating magnetic field, thereby realizing a pulsation generating operation that generates the pulsation without causing the electric motor (3) to rotate.

[0088] Furthermore, in the first embodiment and the first to third modifications of the first embodiment, the phase loss determination unit (22d) may determine whether or not there is a phase loss (PR) in the input AC based on the difference between the maximum and minimum values ​​of the DC link voltage (Vdc) detected by the detection unit (15), i.e., the peak-to-peak value Pk (see FIG. 3). For example, the phase loss determination unit (22d) may determine that there is a phase loss if the peak-to-peak value Pk is greater than a predetermined threshold, and may determine that there is no phase loss if the peak-to-peak value Pk is equal to or less than the predetermined threshold. As shown in FIG. 3, when there is a phase loss in the input AC, the peak-to-peak value Pk is larger than when there is no phase loss. Therefore, by setting the predetermined threshold as a value between the peak-to-peak value Pk when there is a phase loss and the peak-to-peak value Pk when there is no phase loss, it is possible to appropriately determine whether or not there is a phase loss (PR).

[0089] In the first embodiment and the first to third modifications of the first embodiment, the phase loss determination unit (22d) may determine whether or not there is a phase loss (PR) in the input AC based on the minimum value of the DC link voltage (Vdc) detected by the detection unit (15). For example, the phase loss determination unit (22d) may determine that there is a phase loss if the minimum value of the DC link voltage (Vdc) is lower than a predetermined threshold, and that there is no phase loss if the minimum value is equal to or greater than the predetermined threshold. As shown in FIG. 3, when there is a phase loss in the input AC, the minimum value of the DC link voltage (Vdc) is lower than when there is no phase loss. Therefore, by setting the predetermined threshold to a value between the minimum value when there is a phase loss and the minimum value when there is no phase loss, it is possible to appropriately determine whether or not there is a phase loss (PR).

[0090] In the first embodiment and the first to third modifications of the first embodiment, the unbalance information identifying unit (22e) may identify the unbalance information (UB) based on a change in the maximum or minimum value of the DC link voltage (Vdc).

[0091] In the first to fourth embodiments and the first to third variations of the first embodiment, the power supply information determination unit (22) determines all of the input AC frequency (fp), pulsation phase (θest), presence or absence of a phase (PR), and unbalance information (UB) as power supply information, but it may also be configured to determine only some of the input AC frequency (fp), pulsation phase (θest), presence or absence of a phase (PR), and unbalance information (UB), and it is sufficient to determine at least one of the input AC frequency (fp), pulsation phase (θest), presence or absence of a phase (PR), and unbalance information (UB). [Industrial Applicability]

[0092] INDUSTRIAL APPLICABILITY As described above, the present disclosure is useful for a power conversion device that performs power conversion on input AC supplied from an AC power supply. [Explanation of symbols]

[0093] 1 Power conversion device 2 Three-phase AC power supply 3 Electric motor 11 Rectifier 12 Inverse converter 12a, 12b Input nodes 14 Capacitor 15 Detector 20 Control Unit Vdc DC link voltage Idc DC link current Ipu phase current IPV phase current Ipw phase current Vn Output voltage fp frequency θest phase PR Phase loss UB unbalance information fest pulsation frequency ωest pulsation frequency

Claims

1. a rectifier (11) that converts input AC supplied from an AC power source (2) into DC and outputs the DC; an inverter (12) that converts the direct current output by the rectifier (11) into alternating current and supplies the alternating current to the electric motor (3); a capacitor (14) connected between the input nodes (12a, 12b) of the inverter (12); a control unit (20) that controls the inverter (12), a detection unit (15) that detects a voltage (Vdc) of the capacitor (14), a DC link current (Idc), a phase current (Ipu, Ipv, Ipw) of a U-phase, a V-phase, or a W-phase of the AC power supply (2), or an output voltage (Vn) of the rectifier (11) as detection targets (Vdc, Idc, Ipu, Ipv, Ipw, Vn), the control unit (20) performs a pulsation generating operation of controlling the inverter (12) to generate pulsation caused by the frequency of the input AC in the detection objects (Vdc, Idc, Ipu, Ipv, Ipw, Vn) without causing the electric motor (3) to perform rotational motion, and a power supply information identification process of identifying power supply information including at least one of a frequency (fp) of the input AC, a phase (θest) of the pulsation, presence or absence of a missing phase (PR) of the input AC, and unbalance information (UB) related to an unbalance rate of the input AC, based on detection values ​​of the detection objects (Vdc, Idc, Ipu, Ipv, Ipw, Vn) during the pulsation generating operation.

2. The power conversion device according to claim 1, The power conversion device is characterized in that the capacitance of the capacitor (14) is set to allow pulsation of the output voltage of the rectifier (11).

3. 3. The power conversion device according to claim 1, A power conversion device characterized in that the detection target (Vdc, Idc, Ipu, Ipv, Ipw, Vn) is the voltage (Vdc) of the capacitor (14) or the output voltage (Vn) of the rectifier (11).

4. The power conversion device according to any one of claims 1 to 3, The power conversion device, characterized in that the power supply information identification process identifies pulsation frequencies (fest, ωest) of the detection objects (Vdc, Idc, Ipu, Ipv, Ipw, Vn) based on detection values ​​of the detection objects (Vdc, Idc, Ipu, Ipv, Ipw, Vn) during the pulsation generating operation, and identifies the power supply information based on the pulsation frequencies (fest, ωest).

Images