JP2016127618A - Electric power conversion system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an electric power conversion system capable of reducing distortion of an output current.SOLUTION: A capacitor C1 is connected between a pair of DC lines LH and LL, and a DC voltage Vc is applied to them. An invertor 3 converts the DC voltage Vc into a second AC voltage. A control unit 6 generates a switching signal for controlling a switching element of the invertor 3 on the basis of a voltage command value of an amplitude of the second AC voltage. The control unit 6 allows at least one part of a period that a capacitor voltage is smaller than a rectification voltage Vrec to correct so that a value obtained by subtracting the rectification voltage Vrec from the capacitor voltage is larger as the voltage command value is large (i), and does not allow at least one part of the period that a capacitor voltage is larger than the rectification voltage to correct (ii). The capacitor voltage at least includes a component in which the component of a switching frequency of the switching element of the DC voltage Vc is removed.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a power conversion device, and more particularly to a power conversion device having an LC filter in a DC link.

  Patent Document 1 describes a power conversion device. This power converter includes, for example, a rectification unit, an inverter unit, a capacitor, and a reactor. The rectifying unit rectifies the input AC voltage into a DC voltage and outputs the DC voltage to the DC link. The DC link is provided with a reactor and a capacitor. The reactor and the capacitor form an LC filter. A DC voltage applied to the capacitor is input to the inverter unit. The inverter unit converts the DC voltage into an AC voltage and outputs the AC voltage to the motor.

  In such a power converter, when a frequency component close to the resonance frequency of the LC filter is generated in the DC voltage of the capacitor, the frequency component can increase due to resonance. Therefore, in Patent Document 1, resonance suppression control for controlling the output voltage of the inverter unit is executed to suppress such resonance. The resonance suppression control will be described in detail later.

JP 2013-85444 A

  However, although the resonance suppression control suppresses the resonance of the DC voltage, the output current of the inverter unit may be distorted. FIG. 8 shows the frequency component of the alternating current output from the inverter unit. FIG. 8 shows frequency components when the resonance suppression control is always executed. In FIG. 8, the frequency f1 of the largest frequency component is the frequency of the fundamental wave of the alternating current. In the illustration of FIG. 8, a frequency component larger than other frequency components is generated on the lower frequency side than the fundamental wave (see frequency f2 in FIG. 8).

  On the other hand, when resonance suppression control is not executed at all, it is confirmed that this low frequency component is small, and this low frequency component is considered to be caused by resonance suppression control. Such low frequency components cause distortion of the output current as shown in FIG. FIG. 9 shows the vicinity of the peak of the output current, and each peak value discretely substantially follows the waveform of the low frequency component (two-dot chain line in FIG. 9). Such distortion of the output current is undesirable. This is because, for example, the maximum value of the peak of the alternating current is increased, and as a result, the copper loss is increased.

  Then, this application aims at providing the power converter device which can reduce distortion of output current.

  According to a first aspect of the power conversion device of the present invention, a pair of DC lines (LH, LL), a first AC voltage is rectified into a rectified voltage, and the rectified voltage is applied between the pair of DC lines. A diode rectifier (2), a capacitor (C1) connected between the pair of DC lines, to which a DC voltage is applied, and a pair of switching elements connected in series between both ends of the capacitor; An inverter (3) for converting the DC voltage into a second AC voltage, and a switching signal for controlling the switching element are generated based on a voltage command value for the amplitude of the second AC voltage, (I) In at least a part of a period in which the capacitor voltage is smaller than the rectified voltage, a correction that increases as the value obtained by subtracting the rectified voltage from the capacitor voltage increases And (ii) a controller (6) in which the correction is not performed in at least a part of a period in which the capacitor voltage is larger than the rectified voltage, and the capacitor voltage is the switching voltage among the DC voltages. It includes at least a component obtained by removing the switching frequency component of the element.

  A second aspect of the power conversion device according to the present invention is the power conversion device according to the first aspect, wherein the control unit (6) is configured such that the capacitor voltage is equal to the rectified voltage and a positive first reference value. Or when the capacitor voltage is smaller than a value obtained by subtracting a positive second reference value from the rectified voltage, the correction is performed, and the capacitor voltage is changed between the rectified voltage and the first reference. When the value is smaller than the sum of the values and larger than the value obtained by subtracting the second reference value from the rectified voltage, the correction is not performed.

  A third aspect of the power conversion device according to the present invention is the power conversion device according to the first aspect, wherein the control unit (6) performs the correction when the capacitor voltage is larger than the rectified voltage. The correction is performed when the capacitor voltage is smaller than the rectified voltage.

  The 4th aspect of the power converter device concerning this invention is a power converter device concerning any one 1st to 3rd aspect, Comprising: The AC voltage detection part which detects the said 1st AC voltage is provided, The control unit calculates an ideal value of the rectified voltage based on the first AC voltage, and adopts the ideal value as the rectified voltage.

  A fifth aspect of the power conversion device according to the present invention is the power conversion device according to any one of the first to third aspects, between the capacitor (C1) and the diode rectifier (2). A reactor (L1) provided on one of the pair of DC lines (LH, LL), and a voltage detector (53) for detecting a voltage across the reactor as a difference between the capacitor voltage and the rectified voltage. Prepare.

  A sixth aspect of the power conversion device according to the present invention is the power conversion device according to any one of the first to third aspects, wherein the pair of the power conversion device is between the capacitor and the diode rectifier (2). A reactor (L1) provided on one of the DC wires, a current detector (54) for detecting a current flowing through the reactor, and a voltage for differentiating the current to calculate a difference between the capacitor voltage and the rectified voltage And a calculator (55).

  According to the 1st, 4th, and 6th aspect of the power converter device concerning this invention, the distortion from the sine wave of an output current can be reduced.

  According to the 2nd aspect of the power converter device concerning this invention, distortion of an output current can be suppressed, suppressing resonance effectively.

  According to the 3rd aspect of the power converter device concerning this invention, distortion of an output current can be suppressed, suppressing resonance effectively.

  According to the 5th aspect of the power converter device concerning this invention, the calculation which calculates the difference of a capacitor voltage and a rectification voltage can be made unnecessary.

It is a figure which shows roughly an example of a structure of a power converter device. It is a figure which shows an example of a structure of an inverter roughly. It is a figure which shows an example of a capacitor voltage and a rectification voltage roughly. It is a figure which shows an example of the frequency component of the alternating current which an inverter outputs. It is a figure which shows an example of a capacitor voltage and a rectification voltage roughly. It is a figure which shows roughly an example of a structure of a power converter device. It is a figure which shows roughly an example of a structure of a power converter device. It is a figure which shows an example of the frequency component of the alternating current which an inverter outputs. It is a figure which shows an example of the alternating current which an inverter outputs.

First embodiment.
FIG. 1 is a diagram schematically illustrating an example of the configuration of the power conversion device according to the present embodiment. In the illustration of FIG. 1, the power conversion device includes a converter 2, a reactor L <b> 1, a capacitor C <b> 1, an inverter 3, and a control unit 6.

  Converter 2 is connected on its input side to three-phase input lines AL1 to AL3. These input lines AL1 to AL3 are connected to a multiphase AC power supply E1, and this multiphase AC power supply E1 is connected to the converter 2 through the input lines AL1 to AL3. AC voltage) is output. In the illustration of FIG. 1, the wiring inductance of each of the input lines AL1 to AL3 is also shown. The number of phases of the input line may be 4 or more.

  Converter 2 is connected to a pair of DC lines LH and LL on the output side. Converter 2 converts the AC voltage input via input lines AL1 to AL3 into rectified voltage Vrec, and applies this rectified voltage Vrec between DC lines LH and LL. Here, the potential applied to the DC line LH is lower than the potential applied to the DC line LL. Hereinafter, the AC voltage input to the converter 2 is also referred to as an input AC voltage.

  The converter 2 is, for example, a three-phase full-bridge diode rectifier.

  Reactor L1 is provided on DC line LH. Capacitor C1 is connected between DC lines LH and LL on the side opposite to converter 2 with respect to reactor L1.

  For example, the manufacturing cost and circuit scale can be reduced by setting the capacitance of the capacitor C1 small. On the other hand, since the capacitor C1 having a small electrostatic capacity has a poor so-called smoothing function, the DC voltage Vc applied to the capacitor C1 pulsates according to the input AC voltage. More generally, when the number of phases of the input AC voltage is N (N is an integer of 3 or more), when the converter 2 performs full-wave rectification, the DC voltage Vc is 2N times the frequency of the input AC voltage. Pulsates at frequency.

  It can be understood that the reactor L1 and the capacitor C1 constitute a so-called LC filter. The inductance of the reactor L1 is also set small, for example. Thereby, manufacturing cost and circuit scale can be reduced. This LC filter suppresses voltage noise, for example. This noise is a higher-order harmonic component higher than the pulsation of the DC voltage Vc (pulsation 2N times the frequency of the input AC voltage). In other words, the inductance of the reactor L1 and the capacitance of the capacitor C1 are set so as to reduce higher-order harmonic components while allowing the pulsation of the DC voltage Vc. From this viewpoint, the resonance frequency of the LC filter is greater than 2N times the frequency of the input AC voltage. Reactor L1 may be provided on DC line LL.

  The DC voltage Vc is input to the inverter 3. The inverter 3 converts the input DC voltage Vc into an AC voltage and outputs the AC voltage to the load 4. Below, the alternating voltage which the inverter 3 outputs is also called output alternating voltage. In the illustration of FIG. 1, the inverter 3 is connected to the load 4 via a three-phase output line. That is, the inverter 3 converts the DC voltage Vc into a three-phase AC voltage and outputs it to the load 4. However, the number of phases of the load 4 is not limited to 3, and a single-phase load 4 may be employed, or a load 4 having four or more phases may be connected.

  FIG. 2 is a diagram schematically showing an example of the internal configuration of the inverter 3. For example, the inverter 3 includes switching elements Sup, Sun, Svp, Svn, Swp, Swn and diodes Dup, Dun, Dvp, Dvn, Dwp, Dwn. The switching elements Sxp, Sxn (x represents u, v, r, hereinafter the same) are connected in series between the DC lines LH, LL (more specifically, between both ends of the capacitor C1). The connection point Px connecting them is connected to the load 4 via the output line. The diodes Dxp and Dxn are connected in parallel to the switching elements Sxp and Sxn, respectively, and their forward directions are directions from the DC line LL to the DC line LH.

  When the switching elements Sxp and Sxn are appropriately controlled by the control unit 6, the inverter 3 can convert the DC voltage Vc into an AC voltage and output it.

  The load 4 is an inductive load, for example, and is a motor as a more specific example. This motor rotates according to the input AC voltage.

  In the illustration of FIG. 1, a DC voltage detection unit 50, an AC voltage detection unit 51, and a current detection unit 52 are provided. The DC voltage detection unit 50 detects the DC voltage Vc applied to the capacitor C <b> 1 and outputs it to the control unit 6. The AC voltage detection unit 51 detects the input AC voltage applied to the input lines AL <b> 1 to AL <b> 3 and outputs this to the control unit 6. The current detection unit 52 detects the alternating current i output from the inverter 3 and outputs this to the control unit 6. These detected values are used for controlling the inverter 3 as will be described in detail later.

  In the illustration of FIG. 1, the control unit 6 includes a rectified waveform generation unit 61, a voltage difference calculation unit 62, a control limiter 63, a resonance suppression control unit 64, a motor current control unit 65, and a switching signal generation unit 66. It has.

  Here, the control unit 6 includes a microcomputer and a storage device. The microcomputer executes each processing step (in other words, a procedure) described in the program. The storage device is composed of one or more of various storage devices such as a ROM (Read Only Memory), a RAM (Random Access Memory), a rewritable nonvolatile memory (EPROM (Erasable Programmable ROM), etc.), and a hard disk device, for example. Is possible. The storage device stores various information, data, and the like, stores a program executed by the microcomputer, and provides a work area for executing the program. It can be understood that the microcomputer functions as various means corresponding to each processing step described in the program, or can realize that various functions corresponding to each processing step are realized. Further, the control unit 6 is not limited to this, and various procedures executed by the control unit 6 or various means or various functions to be realized may be realized in hardware or in part.

  In the illustration of FIG. 1, the motor current control unit 65 includes an AC current i detected by the current detection unit 52, a current command value i * for the AC current i, and a DC voltage detected by the DC voltage detection unit 50. Vc is input. Based on these, the motor current control unit 65 generates a voltage command value V ** for the amplitude of the output AC voltage of the inverter 3 by a known method.

  In the present embodiment, as described above, the LC filters formed by the reactor L1 and the capacitor C1 are provided on the DC lines LH and LL. Therefore, when a frequency component close to the resonance frequency of the LC filter is included in the DC voltage Vc, the frequency component increases due to resonance. This resonance frequency is set to be lower than the switching frequency of the inverter 3, for example.

  Therefore, the control unit 6 executes resonance suppression control that suppresses resonance at the DC voltage Vc. In this resonance suppression control, the amount of discharge of the capacitor C1 is adjusted by adjusting the amplitude of the output AC voltage, and the DC voltage Vc of the capacitor C1 is adjusted. For example, if the amplitude of the output AC voltage is increased, the discharge amount of the capacitor C1 is increased, so that the DC voltage Vc is reduced. On the contrary, if the amplitude of the output AC voltage is reduced, the discharge amount of the capacitor C1 is reduced, so that the DC voltage Vc increases.

  Therefore, the switching signal generator 66 corrects the voltage command value V ** in the resonance suppression control to generate a corrected voltage command value V *. More specifically, correction is performed to increase the correction voltage command value V * as the DC voltage Vc is larger than the rectified voltage Vrec. The rectified voltage Vrec is a rectified voltage obtained by full-wave rectifying the input AC voltage. It can be considered that the difference between the DC voltage Vc and the rectified voltage Vrec indicates a harmonic component generated in the DC voltage Vc. That is, in order to reduce the harmonic component of the DC voltage Vc, the correction voltage command value V * is increased as the harmonic component is larger than the rectified voltage Vrec. When the amplitude of the output AC voltage is increased by increasing the correction voltage command value V *, the discharge amount of the capacitor C1 increases, thereby reducing the DC voltage Vc. Therefore, the DC voltage Vc approaches the rectified voltage Vrec, and the harmonic component is reduced.

  In other words, it can be explained that the correction is performed such that the correction voltage command value V * is reduced as the DC voltage Vc is smaller than the rectified voltage Vrec. That is, when the DC voltage Vc is smaller than the rectified voltage Vrec, the amplitude of the output AC voltage is reduced, thereby reducing the discharge amount of the capacitor C1 and increasing the DC voltage Vc. Also in this case, the DC voltage Vc approaches the rectified voltage Vrec, and the harmonic component is reduced.

  As the DC voltage Vc used in the correction, the detected value itself may be used, or a voltage value obtained by removing the switching frequency component of the inverter 3 from the detected value. This is because if at least the resonance frequency is present, resonance can be suppressed based on the voltage value. That is, in the above correction, a voltage value including at least a component obtained by removing the component of the switching frequency from the detected value can be employed as the DC voltage Vc. Hereinafter, this voltage value is referred to as a capacitor voltage Vc1.

  In the present embodiment, a correction amount H (described later) that depends on the difference between the capacitor voltage Vc1 and the rectified voltage Vrec is calculated, and the voltage command value V ** is corrected based on the correction amount H, thereby correcting the voltage command value. Find V *. The correction amount H is calculated by the rectified waveform generation unit 61, the voltage difference calculation unit 62, the control limiter 63, and the resonance suppression control unit 64. This will be described in detail below.

  The input AC voltage detected by the AC voltage detector 51 is input to the rectified waveform generator 61. The rectified waveform generator 61 generates an ideal value of the rectified voltage Vrec based on the input AC voltage. The relationship between the input AC voltage and the rectified voltage Vrec is well known, and the ideal value of the rectified voltage Vrec is generated using the relationship. That is, here, an ideal value (calculated value) is adopted as the rectified voltage Vrec.

  The voltage difference calculator 62 receives the DC voltage Vc detected by the DC voltage detector 50 and the rectified voltage Vrec generated by the rectified waveform generator 61. When the voltage obtained by removing the switching frequency component of the inverter 3 is employed as the capacitor voltage Vc1, the voltage difference calculating unit 62 includes a harmonic component removing unit. This harmonic component removal unit is formed by, for example, a low-pass filter.

  The voltage difference calculation unit 62 calculates a difference ΔV (= Vrec−Vc1) between the capacitor voltage Vc1 and the rectified voltage Vrec, and outputs the difference ΔV to the control limiter 63.

  The control limiter 63 determines whether or not the resonance suppression control is necessary based on the difference ΔV, and transmits the determination result to the resonance suppression control unit 64. That is, in this embodiment, resonance suppression control is not always executed, but resonance suppression control is executed or stopped based on the difference ΔV. This is because if the resonance suppression control is always executed, the output AC current of the inverter 3 is distorted (low frequency component) as described with reference to FIGS.

  The control limiter 63 outputs a signal for stopping the resonance suppression control in at least a part of the period in which the capacitor voltage Vc1 is larger than the rectified voltage Vrec, and at least in the period in which the capacitor voltage Vc1 is smaller than the rectified voltage Vrec. A signal instructing execution of resonance suppression control is output during a part of the period.

  FIG. 3 schematically shows an example of the capacitor voltage Vc1 and the rectified voltage Vrec. In the illustration of FIG. 3, for the sake of simplicity, the capacitor voltage Vc1 is represented as a voltage in which one harmonic component is superimposed on the rectified voltage Vrec.

  For example, when the absolute value | ΔV | of the difference ΔV between the capacitor voltage Vc1 and the rectified voltage Vrec is larger than the voltage difference reference value Vref (> 0), the control limiter 63 outputs a signal instructing execution of resonance suppression control. To do. In the example of FIG. 3, the period t1 indicates a period in which the absolute value | ΔV | is larger than the voltage difference reference value Vref, and the resonance suppression control is executed in this period t1.

  For example, when the absolute value | ΔV | is smaller than the voltage difference reference value Vref, the control limiter 63 outputs a signal instructing to stop the resonance suppression control. In the example of FIG. 3, the period t2 indicates a period in which the absolute value | ΔV | is smaller than the voltage difference reference value Vref, and the resonance suppression control is stopped in this period t2.

  In other words, in the illustration of FIG. 3, the resonance suppression control is executed when the capacitor voltage Vc1 is far from the rectified voltage Vrec without performing the resonance suppression control when the capacitor voltage Vc1 is close to the rectified voltage Vrec. Since the periods t1 and t2 appear alternately within the pulsation cycle of the rectified voltage Vrec (end of 1 / 2N of the end of the input AC voltage), execution / stop of resonance suppression is also alternately performed within the pulsation cycle. .

  The resonance suppression control unit 64 receives the difference ΔV calculated by the voltage difference calculation unit 62 and the signal from the control limiter 63. Based on these, the resonance suppression control unit 64 calculates a correction amount H for resonance suppression control. The correction amount H is output to the switching signal generator 66.

  The resonance suppression control unit 64 outputs zero as the correction amount H when receiving a signal instructing to stop the resonance suppression control. Thereby, substantial correction for resonance suppression is not performed in the switching signal generator 66. That is, the resonance suppression control is stopped.

  On the other hand, when a signal instructing execution of resonance suppression control is received, the correction amount H is calculated based on the difference ΔV. For example, the correction amount H (= K · ΔV) is calculated by multiplying a positive predetermined value (hereinafter also referred to as a gain) K and the difference ΔV.

  The switching signal generator 66 corrects the voltage command value V ** based on the correction amount H. For example, if the difference ΔV is a value obtained by subtracting the capacitor voltage Vc1 from the rectified voltage Vrec (Vrec−Vc1), the correction voltage command value V * is generated by subtracting the correction amount H from the voltage command value V **. Therefore, when resonance suppression control is performed, the correction voltage command value V * is represented by {V ** − K · (Vrec−Vc1)}. According to this, when the resonance suppression control is performed, a correction voltage command value V * that is larger as the capacitor voltage Vc1 is larger than the rectified voltage Vrec can be generated. Conversely, a smaller correction voltage command value V * can be generated as the capacitor voltage Vc1 is smaller than the rectified voltage Vrec.

  If the difference ΔV is a value obtained by subtracting the rectified voltage Vrec from the capacitor voltage Vc1 (Vc1−Vrec), the correction voltage command value V * may be generated by subtracting the correction amount H from the voltage command value V **. According to this, when the resonance suppression control is performed, the correction voltage command value V * is represented by {V ** + K · (Vc1−Vrec)}.

  According to such resonance suppression control, when the capacitor voltage Vc1 is larger than the rectified voltage Vrec, the amplitude of the output AC voltage increases. Therefore, at this time, the discharge amount of the capacitor C1 increases and the DC voltage Vc decreases. Therefore, the DC voltage Vc approaches the rectified voltage Vrec. Further, when the capacitor voltage Vc1 is smaller than the rectified voltage Vrec, the amplitude of the output AC voltage is reduced. Therefore, at this time, the discharge amount of the capacitor C1 decreases, and the DC voltage Vc increases. Therefore, the DC voltage Vc approaches the rectified voltage Vrec.

  The switching signal generator 66 generates a switching signal S based on the generated corrected voltage command value V *, and outputs this to the inverter 3. The generation of the switching signal S based on the correction voltage command value V * is a known technique, and the switching signal S can be generated based on, for example, a comparison between a triangular wave and the correction voltage command value V *. The inverter 3 operates based on the switching signal S to convert the DC voltage Vc into an output AC voltage. By such control, an output AC voltage close to the correction voltage command value V * is output.

  FIG. 4 shows frequency components of the alternating current i output from the inverter 3 by the above control. As can be seen from the comparison between FIG. 4 and FIG. 8, according to the present embodiment, it can be seen that the low frequency component of the alternating current i can be reduced by about 40%. Since the low frequency component of the alternating current i can be reduced, distortion from the fundamental wave (sine wave) of the alternating current i can be reduced. Since the distortion of the alternating current i increases the peak value of the alternating current i, the copper loss is increased. In this embodiment, since the distortion of the alternating current i can be reduced, the copper loss can also be reduced.

  As described above, in the present embodiment, the resonance suppression control is not always executed, but the execution / stop of the resonance suppression control is repeated based on the capacitor voltage Vc1 and the rectified voltage Vrec.

  When the resonance suppression control is always executed unlike the present embodiment, the AC current i output from the inverter 3 is distorted (low frequency component) as shown in FIG. On the other hand, when resonance suppression control is not executed at all, it is confirmed that this low frequency component is small, and this low frequency component is considered to be caused by resonance suppression control. If the resonance suppression control is stopped in a certain period, the fluctuation in the energy of the load 4 can be reduced correspondingly, so that the fluctuation in the low frequency of the alternating current i is also reduced. Therefore, from the viewpoint of reducing the low-frequency component, the present embodiment is not limited to performing resonance suppression in the above-described period t1 and reducing resonance suppression in the period t2.

  On the other hand, in the example of the specific control described above, resonance suppression is executed when the absolute value | ΔV | is larger than the voltage difference reference value Vref, and the absolute value | ΔV | is smaller than the voltage difference reference value Vref. Sometimes resonance suppression control was stopped. That is, the resonance suppression control is executed only when the capacitor voltage Vc1 is far from the rectified voltage Vrec. According to this control, the capacitor voltage Vc1 is brought closer to the rectified voltage Vrec more effectively than in the reverse control, that is, when the resonance suppression control is executed only when the capacitor voltage Vc1 is close to the rectified voltage Vrec. be able to. In other words, resonance can be more effectively suppressed.

  In the above example, the resonance suppression control is executed when the absolute value of the difference ΔV is larger than the voltage difference reference value Vref. That is, referring to FIG. 3, when the capacitor voltage Vc1 is larger than the first value (Vrec + Vref) or when the capacitor voltage Vc1 is smaller than the second value (Vrec−Vref), the resonance suppression control is executed. . The resonance suppression control was stopped when the capacitor voltage Vc1 was smaller than the first value and larger than the second value. In such an example, the difference (Vref) between the first value and the rectified voltage Vrec is equal to the difference (Vref) between the second value and the rectified voltage Vrec.

  However, the present embodiment is not limited to this, and they may be different. In short, when the capacitor voltage Vc1 is larger than the value V1 obtained by adding the rectified voltage Vrec and the positive reference value Vref1, or the capacitor voltage Vc1 is larger than the value V2 obtained by subtracting the positive reference value Vref2 from the rectified voltage Vrec. Even if the resonance suppression control is executed when it is small (that is, the voltage command value V ** is corrected) and the capacitor voltage Vc1 is smaller than the value V1 and larger than the value V2, the resonance suppression control is stopped. Good (that is, it is not necessary to correct the voltage command value V **). In the example of FIG. 3, this corresponds to a case where the positive values (voltage difference reference value Vref) are equal in the reference values Vref1 and Vref2.

Second embodiment.
The power converter according to the second embodiment is the same as that shown in FIG. However, in the second embodiment, the control unit 6 stops the resonance suppression control when the capacitor voltage Vc1 is larger than the rectified voltage Vrec, and performs the resonance suppression control when the capacitor voltage Vc1 is smaller than the rectified voltage Vrec. carry out.

  Speaking in the case described at the end of the first embodiment, the reference value Vref1 is + ∞ (actually not less than a value obtained by subtracting the maximum value of the rectified voltage Vrec from the maximum value that the capacitor voltage Vc1 can take). Value) and the reference value Vref2 is 0.

  FIG. 5 schematically shows an example of the capacitor voltage Vc1 and the rectified voltage Vrec. In the illustration of FIG. 5, for the sake of simplicity, the capacitor voltage Vc1 is represented as a voltage in which one harmonic component is superimposed on the rectified voltage Vrec. A period t3 indicates a period in which the capacitor voltage Vc1 is smaller than the rectified voltage Vrec, and a period t4 indicates a period in which the capacitor voltage Vc1 is larger than the rectified voltage Vrec. In the second embodiment, the resonance suppression control is executed in the period t3, and the resonance suppression control is stopped in the period t4.

  Specifically, for example, the control limiter 63 outputs a signal for executing the resonance suppression control when the difference ΔV (= Vref−Vc1) is positive, and performs the resonance suppression control when the difference ΔV is negative. Outputs the signal to be executed.

  When receiving a signal for stopping the resonance suppression control, the resonance suppression control unit 64 outputs zero as the correction amount H, and when receiving a signal for executing the resonance suppression control, the correction amount H (= K · ΔV) is output. Based on the correction amount H, the switching signal generator 66 corrects the voltage command value V ** in the same manner as in the first embodiment to generate a corrected voltage command value V *, and this corrected voltage command value V *. The switching signal S is output based on

  As described above, in the second embodiment, the resonance suppression control is executed only when the capacitor voltage Vc1 is smaller than the rectified voltage Vrec. Therefore, in the period t3 in which the capacitor voltage Vc1 is smaller than the rectified voltage Vrec, a correction for reducing the voltage command value V ** is performed to obtain a correction voltage command value V * {= V * −K · (Vrec−Vc1)). calculate. As a result, the DC voltage Vc is increased to approach the rectified voltage Vrec.

  On the other hand, the resonance suppression control is not performed during the period t4 when the capacitor voltage Vc1 is larger than the rectified voltage Vrec. Therefore, in the second embodiment, correction for increasing the voltage command value V ** is not performed. Thereby, the increase of the alternating current i resulting from the increase of the voltage command value V ** can be avoided or suppressed, and the increase of the peak value of the alternating current i can be avoided or suppressed. As a result, an increase in copper loss can be avoided or suppressed.

  The second embodiment is particularly useful when the load 4 is an inductive load (for example, a motor). This will be described in detail below.

  Unlike the second embodiment, when the resonance suppression control is executed in the period t4 in which the capacitor voltage Vc1 is larger than the rectified voltage Vrec, a correction that increases the voltage command value V ** is performed to correct the corrected voltage command value V *. Is generated. However, since the inverter 3 cannot output a voltage larger than the DC voltage Vc, the amount of increase in the voltage command value V ** is limited.

  On the other hand, when the resonance suppression control is executed in the period t3 when the capacitor voltage Vc1 is smaller than the rectified voltage Vrec, a correction for reducing the voltage command value V ** is performed to generate a correction voltage command value V *. When the load 4 is an inductive load, the amplitude of the output AC voltage of the inverter 3 can equivalently take a negative value due to the electromotive force generated in the inductive component (for example, regenerative operation). At this time, since the regenerative current from the load 4 flows to the capacitor C1, the capacitor C1 is charged and the DC voltage Vc increases. Therefore, even if the DC voltage Vc is significantly smaller than the rectified voltage Vrec, the DC voltage Vc can be brought close to the rectified voltage Vrec by the resonance suppression control.

  As a specific example, when the correction voltage command value V * becomes negative due to the correction, the switching signal generation unit 66 may turn off all the switching elements Sxp and Sxn in a predetermined period. As a result, the regenerative current flows through the capacitor C1, and the DC voltage Vc increases. Therefore, the DC voltage Vc can be brought close to the rectified voltage Vrec.

  That is, the difference between the DC voltage Vc that can be reduced and the rectified voltage Vrec is larger in the period t3 in which the capacitor voltage Vc1 is smaller than the rectified voltage Vrec than in the period t4 in which the capacitor voltage Vc1 is larger than the rectified voltage Vrec. .

  Therefore, according to the second embodiment, resonance can be more effectively suppressed. In the second embodiment, since the resonance suppression control is stopped when the capacitor voltage Vc1 is larger than the rectified voltage Vrec, the low frequency component of the alternating current is suppressed as compared with the conventional case.

Third embodiment.
In the first and second embodiments, the rectified waveform generator 61 detects the input AC voltage and calculates the ideal value of the rectified voltage Vrec, and the voltage difference calculator 62 calculates the difference between the capacitor voltage Vc1 and the rectified voltage Vrec. The difference ΔV was calculated. In the third embodiment, the difference ΔV is detected using the voltage VL applied to the reactor L1 (which can be grasped as the voltage across the reactor L1).

  FIG. 6 is a diagram schematically illustrating an example of the power converter. In the illustration of FIG. 6, compared to FIG. 1, a voltage detection unit 53 is provided instead of the AC voltage detection unit 51, the rectified waveform generation unit 61, and the voltage difference calculation unit 62.

  The voltage detector 53 detects the voltage VL applied to the reactor L1. This voltage VL corresponds to the difference between the rectified voltage Vrec output from the converter 2 and the DC voltage Vc of the capacitor C1 in view of the connection relationship between the converter 2, the reactor L1, and the capacitor C1. Therefore, the voltage detection unit 53 outputs the voltage VL as the difference ΔV to the control limiter 63 and the resonance suppression control unit 64.

  Since other points are the same as those of the first and second embodiments, detailed description is avoided. If the voltage VL is used as the difference ΔV, the calculation process (calculation of the rectified waveform generation unit 61 and the voltage difference calculation unit 62) for calculating the difference ΔV can be eliminated.

  FIG. 7 is a diagram schematically showing an example of the power converter. In the illustration of FIG. 7, as compared with FIG. 1, a current detection unit 54 and a voltage calculation unit 67 are provided instead of the AC voltage detection unit 51, the rectified waveform generation unit 61, and the voltage difference calculation unit 62. .

  Current detection unit 54 detects current IL flowing through reactor L 1 and outputs this to voltage calculation unit 67. Voltage calculation unit 67 differentiates current IL, calculates voltage VL applied to reactor L1, and outputs this voltage VL as a difference ΔV to control limiter 63 and resonance suppression control unit 64.

  Since other points are the same as those of the first and second embodiments, detailed description is avoided.

  In the present invention, the above-described various embodiments can be appropriately modified and omitted within the scope of the present invention as long as they do not contradict each other.

2 Converter 3 Inverter 6 Control unit 53 Voltage detection unit 54 Current detection unit C1 Capacitor L1 Reactor LH, LL DC line

Claims (6)

A pair of DC lines (LH, LL);
A diode rectifier (2) for rectifying the first AC voltage into a rectified voltage and applying the rectified voltage between the pair of DC lines;
A capacitor (C1) connected between the pair of DC lines to which a DC voltage is applied;
An inverter (3) having a pair of switching elements connected in series between both ends of the capacitor and converting the DC voltage to a second AC voltage;
A switching signal for controlling the switching element is generated based on a voltage command value with respect to an amplitude of the second AC voltage, and (i) at least during a period in which the capacitor voltage is smaller than the rectified voltage with respect to the voltage command value In some cases, correction is performed such that the larger the value obtained by subtracting the rectified voltage from the capacitor voltage, the larger the correction is performed, and (ii) the correction is not performed in at least part of a period in which the capacitor voltage is greater than the rectified voltage. And a control unit (6),
The said capacitor voltage is a power converter device containing at least the component which removed the component of the switching frequency of the said switching element among the said DC voltage.   The control unit (6), when the capacitor voltage is larger than the sum of the rectified voltage and a positive first reference value, or when the capacitor voltage subtracts a positive second reference value from the rectified voltage. When the value is smaller than the value, the correction is performed, and when the capacitor voltage is smaller than the sum of the rectified voltage and the first reference value and larger than a value obtained by subtracting the second reference value from the rectified voltage, The power conversion device according to claim 1, wherein correction is not performed.   The control unit (6) according to claim 1, wherein the controller (6) does not perform the correction when the capacitor voltage is larger than the rectified voltage, and performs the correction when the capacitor voltage is smaller than the rectified voltage. Power conversion device. An AC voltage detector for detecting the first AC voltage;
4. The power conversion according to claim 1, wherein the control unit calculates an ideal value of the rectified voltage based on the first AC voltage, and adopts the ideal value as the rectified voltage. 5. apparatus. A reactor (L1) provided on one of the pair of DC lines (LH, LL) between the capacitor (C1) and the diode rectifier (2);
The power converter according to any one of claims 1 to 3, further comprising: a voltage detection unit (53) configured to detect a voltage across the reactor as a difference between the capacitor voltage and the rectified voltage. Between the capacitor and the diode rectifier (2), a reactor (L1) provided on one of the pair of DC lines;
A current detector (54) for detecting a current flowing through the reactor;
The power converter according to any one of claims 1 to 3, further comprising: a voltage calculation unit (55) that differentiates the current to calculate a difference between the capacitor voltage and the rectified voltage.

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