JP2013121272A - Power conversion device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a power conversion device capable of estimating a line current with improved estimation accuracy.SOLUTION: A line current detecting unit 3 detects instantaneous values of line currents of at least two phases that flows through an alternate-current line, successively for at least n times at a timing of each period calculated by dividing m-times of a cycle of an alternate-current voltage by n. Direct-current component extracting units 512, 513 calculate an average value of a series of n instantaneous values of two line currents obtained by converting an instantaneous value of a line current of at least two phases from a three-phase fixed coordinate system into a two-phase fixed coordinate system, or a series of n instantaneous values of two currents as instantaneous values of the line currents of least two phases, as direct-current components of two currents, respectively. An estimation unit 53 calculates instantaneous values of alternate-current components of two currents at one timing while excluding direct-current components from instantaneous values of two currents at the one timing, and estimates instantaneous values of alternate-current components at a predetermined time point on the basis of the instantaneous values of the alternate-current component and an equation of a waveform as to basic wave components of two currents.

Description

  The present invention relates to a power converter, and more particularly to a technique for estimating a line current in a power converter that performs conversion between a DC voltage and an AC voltage.

  Patent Document 1 describes a three-phase inverter. Such a three-phase inverter converts an input DC voltage into an AC voltage. Such conversion is realized by appropriately switching conduction / non-conduction of the switching element of the inverter.

  In Patent Document 1, a current flowing on the output side of the three-phase inverter, that is, a three-phase line current is detected using a direct current flowing on the input side of the three-phase inverter. Such detection is performed by matching a direct current and a line current based on the switching pattern of the inverter. For example, in a predetermined cycle, a direct current is detected during a period in which two different switching patterns are employed, and these are detected as two-phase line currents determined based on the two switching patterns. The remaining one-phase line current is calculated based on the relationship that the sum of the three-phase line currents is zero.

  In addition, the technique relevant to this invention is disclosed by patent documents 2-11.

JP 2004-304925 A JP 2003-189670 A JP 2002-119062 A JP-A-10-155278 JP-A-3-230767 JP 2004-64903 A JP 2005-45848 A JP 2004-3368760 A JP 2003-259659 A JP 2004-48868 A JP 2005-269768 A

  For example, in Patent Document 1, if a DC current cannot be detected in a period due to a short period in which the switching pattern is adopted, correction for increasing the period is performed.

  However, such an increase in the period is not preferable from the viewpoint of causing distortion of the AC voltage. Therefore, the inventors of the present application have conceived that when the period in which the switching pattern is employed is short, the line current in that period is estimated using the value of the line current that has already been detected or estimated in another period. In this process, since it is not necessary to increase the period, it can contribute to suppression of distortion of the line voltage.

  However, the present invention is not limited to a power converter that detects a line current based on a direct current, but rather is directed to a case where high estimation accuracy is required in estimating a line current, particularly its fundamental component.

  Therefore, an object of the present invention is to provide a power conversion device that can improve the estimation accuracy of the fundamental wave component when estimating a line current at a predetermined time.

  A first aspect of a power conversion device according to the present invention includes three AC lines (Pu, Pv, Pw) to which a three-phase AC voltage is applied, and a power conversion circuit (2) connected to the AC line. , At least a current flowing in the AC line at a timing for each period obtained by dividing m (m is a natural number) times one cycle of the AC voltage by n (n is an integer of 2 or more, where m / n is not an integer). A line current detector (3) for detecting an instantaneous value of two-phase line currents (iu, iv, iw) at least n times continuously; and a three-phase fixed coordinate system for detecting the instantaneous value of the at least two-phase line currents. To the two-phase fixed coordinate system, or the two current instantaneous values (iα [1] to iα [p], which are the instantaneous values of the at least two-phase line currents, DC component extraction unit (512, 513) for obtaining a series of n averages of iβ [1] to iβ [n]) as DC components (iα0, iβ0) of the two currents, respectively, AC component calculation values (instantaneous values of the AC components of the two currents at the one timing described above by excluding the DC components from the instantaneous values (iα [p], iβ [p]) of the two currents in iα2 [p], iβ2 [p]), and based on the AC component calculation value and the waveform equation for the fundamental component of the two currents, the AC that is the instantaneous value of the AC component at a predetermined time point An estimation unit (53) for estimating the component estimation values (iα2 [q], iβ2 [q]).

  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 estimation unit (53) includes the alternating-current component estimated values (iα2 [q], iβ2 [q] ) And the DC components (iα0, iβ0), respectively, to calculate instantaneous values of the two currents at the predetermined time point.

  A third aspect of the power conversion device according to the present invention is the power conversion device according to the first or second aspect, in which the voltage phase (φ, φ [p], φ [q]) of the AC voltage is changed. A voltage phase acquisition unit (61) for acquiring, the estimation unit (53), the current amplitude (IM) for the two currents based on the AC component calculated value (iα2 [p], iβ2 [p]) A current amplitude calculation unit (514, 516) that calculates the current component based on the AC component calculation value, and calculates a value (ψ [p]) of the current phase for the two currents at the timing, and the value and the timing at the timing A phase angle calculator (515 to 517) that calculates a phase angle (θ) that is different from the voltage phase (φ [p]), and the phase angle is set to the voltage phase (φ [q]) at the predetermined time point. In addition, a value (ψ [q]) of the current phase at the predetermined time is calculated, and the AC component estimated values (iα2 [q], iβ2 [ q]) A line current calculation section for calculating the (52).

  A fourth 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 power conversion circuit (2) includes a pair of direct current lines (LH, LL) are connected to each other in series with each other in three phases, and connection points for connecting the first and second switching elements are respectively connected to the first and second switching elements (S1 to S6). Connected to three AC lines (Pu, Pv, Pw), and the power converter (1) is configured such that one of the three AC lines is connected to one of the pair of DC lines in each predetermined cycle (T). Of the six switching patterns that are connected and the other two of the three AC lines are connected to the other of the pair of DC lines, the first and second switching patterns different from each other, and all of the three AC lines A third switching pattern connected to one or the other of the pair of DC lines In each of the switching control unit (6) that is employed over the first to third periods and causes the power conversion circuit to perform the conversion, and each of the predetermined periods including the timing, the first When at least one of 1 and the second period (ti, tj) is smaller than a reference period, both the first and second periods are equal to or greater than the reference period in the cycle A correction unit (63) that corrects at least one of the first period and the second period, and the line current detection unit (3) generates a direct current (Idc) flowing through the pair of direct current lines. A direct current detection unit (31) for detecting, and the direct current detected in the first period equal to or greater than the reference period, the instantaneous value of the line current of the first phase determined by the first switching pattern; Deemed before the reference period The said detected DC current in the second period, and a momentary value and considered a direct current / line current corresponding portion of the second phase of the line current as determined by said second switching pattern (32).

  A fifth aspect of the power conversion device according to the present invention is the power conversion device according to the fourth aspect, wherein the predetermined time point has the first or second period shorter than the reference period. Included in one of the cycles.

  According to the first aspect of the power conversion device of the present invention, the estimation unit estimates the instantaneous value of the AC component at a predetermined time point using the waveform expression of the fundamental wave component. It is estimated using the instantaneous value of the AC component at the detection timing obtained by removing the DC component from the instantaneous value. Since the direct current component does not satisfy the equation of the waveform of the fundamental wave, it is possible to improve the calculation accuracy of the estimated value of the fundamental wave component of the alternating current component by estimating using the alternating current component excluding this.

  According to the 2nd aspect of the power converter device concerning this invention, even if the offset has arisen in the line current, the offset amount is extracted as a direct-current component. Since the direct current component (offset amount) is added to the estimated alternating current component at a predetermined time point, it is possible to estimate the line current in consideration of the offset of the line current.

  According to the third aspect of the power conversion device of the present invention, the current phase at the predetermined time point is calculated based on the phase angle and the voltage phase at the predetermined time point.

  According to the 4th aspect of the power converter device concerning this invention, a line current is detectable based on a direct current.

  According to the fifth aspect of the power conversion device of the present invention, in order to obtain the AC component of the line current, even if the predetermined period has the first or second period shorter than the reference period, There is no need to correct the second period beyond the reference period. This is because the AC component at a predetermined time is estimated. If the correction in the first period or the second period is performed, the distortion of the AC voltage is caused, but the fact that the correction is not required contributes to the reduction of the distortion of the AC voltage.

It is a figure which illustrates an example of a notional structure of a power converter. It is a figure which illustrates an example of a notional structure of a line current estimation part. It is a figure for demonstrating the timing of an electric current detection. It is a figure for demonstrating the timing of an electric current detection. It is a figure which illustrates an example of some conceptual composition of a line current estimating part. It is a figure which illustrates an example of some conceptual composition of a line current estimating part. It is a flowchart which shows an example of operation | movement of a control part. It is a figure which illustrates an example of some conceptual composition of a line current estimating part. It is a figure which illustrates an example of a voltage vector diagram. It is a figure which shows the electric current which flows through an inverter. It is a figure which shows the electric current which flows through an inverter. It is a figure which shows the electric current which flows through an inverter. It is a figure which shows the electric current which flows through an inverter. It is a figure which shows the electric current which flows through an inverter. It is a figure which shows the electric current which flows through an inverter. It is a figure which shows the electric current which flows through an inverter. It is a figure which shows the electric current which flows through an inverter. It is a figure which shows a typical example of conduction / non-conduction of a switching element, and a direct current. It is a figure which shows a typical example of conduction / non-conduction of a switching element, and a direct current. It is a figure which illustrates an example of a voltage vector diagram.

First embodiment.
<Configuration>
As shown in FIG. 1, the power conversion apparatus 1 includes a power conversion circuit 2, DC lines LH and LL, AC lines Pu, Pv and Pw, and a control unit 7. The power conversion circuit 2 is provided between a set of DC lines LH and LL and a set of AC lines Pu, Pv and Pw. The power conversion circuit 2 performs conversion between a DC voltage applied between the DC lines LH and LL and an AC voltage applied to the AC lines Pu, Pv and Pw. For example, the power conversion circuit 2 is an inverter, converts a DC voltage applied between the DC lines LH and LL into an AC voltage, and outputs the AC voltage to the AC lines Pu, Pv and Pw. Here, the potential applied to the DC line LL is lower than the potential applied to the DC line LH. The power conversion circuit 2 may be a converter, for example. In this case, an AC power source is connected to the AC lines Pu, Pv, and Pw, and the power conversion circuit 2 converts the AC voltage applied to the AC lines Pu, Pv, and Pw into a DC voltage. Alternatively, the power conversion circuit 2 may be a matrix converter that directly converts an input AC voltage into an arbitrary AC voltage without converting it into a DC voltage. Hereinafter, an inverter will be typically described as an example of the power conversion circuit 2.

  The inverter 2 includes switching elements S1 to S6 and diodes D1 to D6. The switching elements S1 to S6 are, for example, insulated gate bipolar transistors or field effect transistors. Switching elements S1 to S3 are provided between each of AC lines Pu, Pv, and Pw and DC line LH. Below, each switching element S1-S3 is also called an upper switching element, and switching element S1-S3 is collectively called an upper switching element group. The anodes of the diodes D1 to D3 are connected to the AC lines Pu, Pv and Pw, respectively, and the diodes D1 to D3 are connected in parallel to the switching elements S1 to S3, respectively.

  Each of the switching elements S4 to S6 is provided between each of the AC lines Pu, Pv, Pw and the DC line LL. Hereinafter, each of the switching elements S4 to S6 is also referred to as a lower switching element, and the switching elements S4 to S6 are collectively referred to as a lower switching element group. The anodes of the diodes D4 to D6 are connected to the DC line LL, and the diodes D4 to D6 are connected in parallel with the switching elements S4 to S6, respectively. When the switching elements S1 to S6 have a structure including a parasitic diode, the diodes D1 to D6 may be the parasitic diode.

  A switching signal S is given to the switching elements S1 to S6 from the control unit 7, respectively. The switching elements S1 to S6 are turned on by the switching signal S. When the control unit 7 provides the switching signals S to the switching elements S1 to S6 at appropriate timings, the inverter 2 converts the DC voltage into an AC voltage. The control of the inverter 2 will be described in detail later.

  In the illustration of FIG. 1, a smoothing capacitor C1 is provided between the DC lines LH and LL. As a result, the DC voltage between the DC lines LH and LL can be smoothed. However, when the pulsation of the DC voltage is allowed, the smoothing capacitor C1 is not always necessary.

  The inverter 2 can drive an inductive load 8, for example. Inductive load 8 is connected to AC lines Pu, Pv, Pw. The inductive load 8 is, for example, a motor. If an AC voltage is applied to the inductive load 8 by the inverter 2, a substantially sinusoidal AC current flows through the inductive load 8. Ideally, sinusoidal line currents iu, iv, and iw flow through the AC lines Pu, Pv, and Pw, respectively. As a result, the inductive load 8 is driven. Here, the direction of the line current flowing from the inverter 2 to the inductive load 8 is defined as positive, and the direction of the line current flowing from the inductive load 8 to the inverter 2 is defined as negative.

  This line current is detected by the line current detector 3 at predetermined timings. In order to obtain the value of the three-phase line current, it is not necessary to detect all of the three-phase line currents, and it is only necessary to detect the two-phase line currents. This is because the remaining one-phase line current can be calculated based on the two-phase line current using the relationship that the sum of the three-phase line currents is zero. Therefore, the line current detection unit 3 may detect at least one of the three-phase line currents iu, iv, and iw.

  In the illustration of FIG. 1, the line current detection unit 3 includes a DC current detection unit 31 and a DC current / line current corresponding unit 32. These cooperate to detect the line current from the DC current Idc flowing through the DC lines LH and LL, but the detection method is not limited to this detection method in the highest concept of the present application. The line current detection unit 3 may detect the line current directly from the AC line. Therefore, the method for detecting the line current from the DC current Idc will be described in the third embodiment, and the method for detecting the line current is not questioned here. Along with this, the correction unit 63 related to the technique of detecting the line current from the direct current Idc will also be described in the third embodiment.

  The control unit 7 includes a line current estimation unit 5 and a switching signal generation unit 6. The line current estimation unit 5 estimates a line current at a predetermined time point based on at least two-phase line currents detected by the line current detection unit 3. This point will be described in detail later.

  The switching signal generator 6 generates a switching signal S. The switching signal S is generated as follows, for example. That is, for example, the phase voltages Vu, Vv applied to the AC lines Pu, Pv, Pw based on the angular velocity command value ω * input from the outside and the line currents iu, iv, iw calculated by the line current estimation unit 5, respectively. , Vw, and a switching signal S is generated by comparing the phase voltage command value with the carrier waveform. Since the generation of the switching signal S is a known technique, a detailed description thereof is omitted.

  The switching signal generator 6 can determine the detection timing of the line current by the line current detector 3 as will be described in detail later. In the illustration of FIG. 1, this is shown by the switching signal generation unit 6 giving the current detection timing signal SH to the line current detection unit 3. For example, the detection timing of the line current detector 3 is a timing for every 60 degrees of the voltage phase of the AC voltage.

  Here, the control unit 7 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 7 is not limited to this, and various procedures executed by the control unit 7 or various means or various functions implemented may be realized by hardware.

<Overview of estimation of AC component of line current>
As illustrated in FIG. 2, the line current estimation unit 5 includes a three-phase / two-phase conversion unit 511, DC component extraction units 512 and 513, and an estimation unit 53.

  The three-phase / two-phase conversion unit 511 converts the line current detected by the line current detection unit 3 from a three-phase fixed coordinate system to a two-phase fixed coordinate system. In the example of FIG. 2, the three-phase / two-phase converter 511 receives the instantaneous values of the two-phase line currents ix and iy from the line current detector 3. The line currents ix and iy are two-phase line currents among the line currents iu, iv and iw. Of course, when the line current detector 3 detects all of the three-phase line currents iu, iv, iw, the instantaneous values of the three-phase line currents iu, iv, iw may be received. The three-phase / two-phase converter 511 applies, for example, a known coordinate transformation to the line currents ix, iy, calculates the α-axis and β-axis line currents iα, iβ of the two-phase fixed coordinate system, These are output to the DC component extraction units 512 and 513, respectively.

  The DC component extraction unit 512 extracts the DC component iα0 of the line current iα. More specifically, referring also to FIG. 3, the DC component extraction unit 512 includes a series of n (n is a natural number) of instantaneous values iα [k−n + 1],..., Iα [k] of the line current iα. The average of 2) is determined as the DC component iα0. Instantaneous values iα [k−n + 1],..., Iα [k] are AC voltage m periods (where m is a natural number and m / n is not an integer) divided into n periods (hereinafter referred to as calculation periods). It is detected at each timing. In the illustration of FIG. 3, a calculation period (voltage phase 60 degrees) obtained by dividing one cycle of the AC voltage into 6 is shown. That is, in the illustration of FIG. 3, m = 1 and n = 6. In the illustration of FIG. 4, m = 3 and n = 8. The DC component extraction unit 512 may obtain the average by calculation, for example, or may obtain it by a moving average or a low-pass filter, for example. An example of a specific internal configuration will be described in detail later. If n is infinite, the average of a series of n instantaneous values of the line current iα can be understood as a value obtained by dividing the integral of the m period of the line current iα by the m period of the AC voltage.

  Since the DC component extraction unit 513 extracts the DC component iβ0 of the line current iβ in the same manner as the DC component extraction unit 512, repeated description is omitted.

  In order to give the above-mentioned n line current instantaneous values to the DC component extraction units 512 and 513, the line current detection unit 3 instantaneously generates the line current instantaneously at the timing of each calculation period obtained by dividing the m period of the AC voltage into n. Detect value.

  The estimation unit 53 obtains the instantaneous values iα2 [p] and iβ2 [p] of the AC components obtained by removing the DC components iα0 and iβ0 from the instantaneous values iα [p] and iβ [p] (p is a natural number) of the line currents iα and iβ. And the instantaneous values iα2 [q] and iβ2 [q] (q is a natural number) of the AC component at a predetermined time point are estimated based on the waveform equation for the fundamental wave component. The waveform equation for the fundamental wave components iα1 and iβ1 of the line currents iα and iβ is expressed by the following equation.

iα1 = IM · sinψ (1)
iβ1 = IM · cos ψ (2)
Here, IM represents the current amplitude, and ψ represents the current phase.

  The estimation unit 53 regards the instantaneous values iα2 [p] and iβ2 [p] of the alternating current components as the instantaneous values of the fundamental wave components iα1 and iβ1, and uses Formula (1) and Formula (2) at a predetermined time point. The instantaneous values iα2 [q] and iβ2 [q] of the AC component are calculated.

  Here, for comparison, unlike the present embodiment, based on the instantaneous values iα [p] and iβ [p] including the DC components iα0 and iβ0, the equations (1) and (2) are Let us consider using it to estimate the instantaneous value of the line current at a given time. The DC components iα0 and iβ0 are substantially constant values and do not satisfy the expressions (1) and (2), respectively. Therefore, the result of this estimation method includes an error due to the DC components iα0 and iβ0.

  On the other hand, according to the present embodiment, the instantaneous values iα2 [p] and iβ2 [p] of AC components obtained by removing the DC components iα0 and iβ0 from the instantaneous values iα [p] and iβ [p] are used. Therefore, it is possible to calculate the instantaneous values iα2 [q] and iβ2 [q] of the AC components while avoiding errors due to the DC components iα0 and iβ0. In other words, the estimation accuracy of the instantaneous values iα2 [q] and iβ2 [q] of the AC component can be improved.

  The DC component extraction units 512 and 513 calculate the DC components iα0 and iβ0, respectively, by averaging n instantaneous values for each calculation period obtained by dividing the m period of the AC voltage by n. Therefore, the average value (DC components iα0, iβ0) includes n / m-order harmonic components. This n / m-order harmonic component also does not satisfy the equations (1) and (2). Therefore, according to this estimation method, errors due to n / m-order harmonic components can also be avoided.

<Specific example of estimation of AC component of line current>
As illustrated in FIG. 5, the DC component extraction unit 512 includes (n−1) (n is 6 in the illustration of FIG. 5) memories 5 a to 5 f, an addition unit 5 g, a division unit 5 h, and a low-pass filter 5 i. ing. The (n−1) memories 5a to 5f hold the input line current iα for one period,..., (N−1) periods in the calculation period (eg, voltage phase 60 degrees), and then add To 5g. Therefore, n instantaneous values iα [p],..., Iα [p−n + 1] of the line current iα are input to the adding unit 5g. Adder 5g outputs the sum of instantaneous values iα [p],..., Iα [p−n + 1] to divider 5h. The division unit 5h outputs the average obtained by dividing the sum by n to the low-pass filter 5i. The low-pass filter 5i further smoothes and outputs the average.

  The number of memories is not limited to (n−1). For example, it suffices if there is only one memory that records the addition value obtained by sequentially adding the instantaneous value iα input every calculation cycle. Then, the DC component iα0 is calculated by dividing the added value of the instantaneous value iα for m periods by n. Thus, the DC component iα0 can be calculated every m cycles of the AC voltage. Further, if there are two memories, the DC component iα0 can be calculated for each finer period. For example, a case where m = 1 and n = 6 will be described. The first memory outputs an added value of six instantaneous values iα at a timing of a voltage phase of 180 degrees. At that timing, the DC component iα0 is calculated. In addition, the first memory outputs the added value and then clears it, and sequentially adds the instantaneous value iα every voltage phase 60 degrees up to the next voltage phase 180 degrees. On the other hand, the second memory outputs an addition value of the six instantaneous values iα at the timing of the voltage phase of 360 degrees. At that timing, the DC component iα0 is calculated. The second memory clears the added value after outputting it, and sequentially adds the instantaneous value iα every voltage phase 60 degrees up to the next voltage phase 360 degrees. Thus, the DC component iα0 can be calculated every voltage phase 180 degrees (every 1/2 cycle of the AC voltage). If the number of memories is further increased, the DC component iα0 can be calculated for each finer period.

  Note that the DC component extraction unit 512 may include only a calculation unit including, for example, the memories 5a to 5f, the addition unit 5g, and the division unit 5h, or may include only the low-pass filter 5i, for example. An example of the internal configuration of the DC component extraction unit 513 is the same as that of the DC component extraction unit 512, and therefore, repeated description is avoided.

  Referring to FIG. 2 again, the estimation unit 53 uses the instantaneous values iα [p] and iβ [p] of the line currents iα and iβ at a certain detection timing to determine predetermined AC components of the line currents iα and iβ. Estimate the instantaneous value at the time. More specifically, the estimation unit 53 includes subtraction units 516 and 517, a current amplitude calculation unit 514, a power factor angle calculation unit 515, a current phase calculation unit 521, and estimation units 522 and 523, for example. .

  The subtraction unit 516 subtracts the DC component iα0 from the instantaneous value iα [p], and outputs this to the current amplitude calculation unit 514 and the power factor angle calculation unit 515 as the AC component instantaneous value iα2 [p]. The subtraction unit 517 subtracts the DC component iβ0 from the instantaneous value iβ [p], and outputs this to the current amplitude calculation unit 514 and the power factor angle calculation unit 515 as the AC component instantaneous value iβ2 [p].

  The current amplitude calculation unit 514 calculates the current amplitude IM using the following formula based on the instantaneous values iα2 [p] and iβ2 [p], and outputs this to the estimation units 522 and 523.

  IM = sqrt (Iα2 [p] ^ 2 + Iβ2 [p] ^ 2) (3)

  Here, sqrt indicates the square root of the value in parentheses, and A ^ B indicates A to the Bth power. In the illustration of FIG. 5, the RMS unit 5k is shown as a functional block that belongs to the current amplitude calculation unit 514 and executes the calculation of Expression (3). In the example of FIG. 5, the current amplitude IM calculated by Expression (3) is output through the averaging unit 5p belonging to the current amplitude calculation unit 514. The averaging unit 5p is a low-pass filter, for example, and averages the current amplitude IM. Thereby, the influence of disturbance noise etc. can be suppressed. The average part 5p is not an essential requirement.

  First, the power factor angle calculation unit 515 calculates the current phase ψ [p] based on the instantaneous values iα2 [p] and iβ2 [p] using the following equation.

  ψ [p] = arctan (Iβ2 [p] / Iα2 [p]) (4)

  Here, arctan indicates an arctangent value of a value in parentheses. In the illustration of FIG. 5, the calculation unit 5 j is shown as a functional block that belongs to the power factor angle calculation unit 515 and executes the calculation of Expression (4).

  The power factor angle calculator 515 receives the voltage phase φ [p] of the AC voltage at substantially the same time as the instantaneous values iα2 [p] and iβ2 [p].

  Referring also to FIG. 1, the voltage phase φ for the AC voltage is acquired by, for example, the voltage phase acquisition unit 61. For example, the voltage phase acquisition unit 61 calculates the voltage phase φ based on the phase voltage command values Vu *, Vv *, Vw *. For example, a known coordinate transformation is applied to the phase voltage command values Vu *, Vv *, Vw * to calculate the α-axis and β-axis phase voltage command values Vα *, Vβ * of the two-phase fixed coordinate system, and the formula ( Similar to 4), the arc tangent value of these ratios is calculated as the voltage phase φ. Alternatively, when the phase voltage command values Vu *, Vv *, and Vw * are derived based on the voltage phase command value φ *, the voltage phase command φ * can be used as the voltage phase φ. Alternatively, the AC voltage applied to the AC lines Pu, Pv, and Pw may be detected, and the voltage phase φ may be calculated based on the AC voltage.

  The power factor angle calculation unit 515 calculates the power factor angle θ using the following equation based on the current phase ψ [p] and the voltage phase φ [p].

  θ = ψ [p] −φ [p] (5)

  In the illustration of FIG. 5, the subtraction unit 5m is shown as a functional block that belongs to the power factor angle calculation unit 515 and executes the calculation of Expression (5). In the illustration of FIG. 5, the power factor angle θ calculated by the equation (5) is output through the average unit 5 n belonging to the power factor angle calculator 515. The average unit 5n is, for example, a low-pass filter, and averages the power factor angle θ. Thereby, the influence of disturbance noise or the like can be suppressed. The average part 5n is not an essential requirement.

  Referring again to FIG. 2, current phase calculation unit 521 calculates current phase ψ [q] at a predetermined time point using the following equation based on power factor angle θ and voltage phase φ [q] at a predetermined time point. calculate.

  ψ [q] = θ + φ [q] (6)

  In the example of FIG. 6, an adder 5 r is shown as a functional block that belongs to the current phase calculator 521 and executes the calculation of Expression (6).

  Based on the current amplitude IM and the current phase ψ [q], the estimation unit 522 calculates an instantaneous value iα2 [q] using the following equation.

  iα2 [q] = IM · sinψ [q] (7)

  In the example of FIG. 6, the calculation unit 5 s is shown as a functional block that belongs to the estimation unit 522 and obtains the sine value of the current phase ψ [q], and belongs to the estimation unit 522 to multiply the sine value and the current amplitude IM. A multiplication unit 5t is shown as a functional block for executing.

  The estimation unit 523 calculates an instantaneous value iβ2 [q] using the following equation based on the current amplitude IM and the current phase ψ [q].

  iβ2 [q] = IM · cos ψ [q] (8)

  In the illustration of FIG. 6, the calculation unit 5 u is shown as a functional block that belongs to the estimation unit 523 and obtains the cosine value of the current phase ψ [q], and belongs to the estimation unit 523 to multiply the cosine value and the current amplitude IM. A multiplication unit 5v is shown as a functional block for executing.

  As can be understood from the equations (1) and (2), the equations (7) and (8) are equations of the waveform for the fundamental wave component.

  In the example of FIG. 2, the DC components iα0 and iβ0 are input to the estimation units 522 and 523, but are not necessarily required in the present embodiment, and the DC components iα0 and iβ0 are input to the estimation units 522 and 523. It may not be done (see also FIG. 6). The case where the DC components iα0 and iβ0 are input to the estimation units 522 and 523 will be described in the second embodiment.

  The calculation of the current phase ψ [q] at a predetermined time is not necessarily limited to the above-described mode. For example, the difference Δφ (= φ [q] −φ [p]) between the voltage phases φ [p] and φ [q] is added to the current phase ψ [p], and the current phase ψ [q] (= ψ [p] ] + Δφ) may be calculated. Alternatively, for example, the angular velocity ω is obtained from the current phase ψ or the voltage phase φ, and the product of the time Δt between the time of the current phase ψ [p] and the time of the current phase ψ [p] and the angular velocity ω (= ω Δt) may be added to the current phase ψ [p] to calculate the current phase ψ [q] (= ψ [p] + ω · Δt). When the inductive load 8 is a motor, the angular speed ω can be obtained from the rotational speed of the motor.

  In the above example, the line current is estimated in a two-phase fixed coordinate system. However, the present invention is not limited thereto, and the line current may be estimated in a three-phase fixed coordinate system. In this case, the three-phase / two-phase converter 511 is not an essential requirement.

  When a line current is handled in a three-phase fixed coordinate system, for example, the following equation is adopted as a waveform equation of the fundamental wave component.

iu = sqrt (2/3) · IM · sinψ (9)
iv = sqrt (2/3) · IM · sin (ψ-2 / 3π) (10)
iw = sqrt (2/3) · IM · sin (ψ + 2 / 3π) (11)

  Referring to FIG. 2, the line current detection unit 3 detects two-phase line currents ix and iy, and the DC component extraction units 512 and 513 extract the DC components ix0 and iy0 of the line currents ix and iy, The subtraction units 516 and 517 calculate the instantaneous values ix2 [p] and iy2 [p] of the alternating current components obtained by removing the direct current components ix0 and iy0 from the instantaneous values ix [p] and iy [p] of the line currents ix and iy. .

  In the two expressions for the x phase and the y phase among the expressions (9) to (11), ix2 and iy2 are adopted as ix and iy on the left side. Therefore, in these two equations, there are two unknowns: current amplitude IM and current phase ψ [p]. Since there are two independent formulas and two unknowns, these two formulas can be used to find these unknowns. That is, the current amplitude calculator 514 can determine the current amplitude IM, and the power factor angle calculator 515 can determine the current phase ψ [p]. However, if the line currents ix and iy are converted into a two-phase fixed coordinate system, the current amplitude IM and the current phase ψ [p] can be obtained by simpler equations (3) and (4).

  Then, the power factor angle calculation unit 515 calculates the power factor angle θ using equation (5), and the current phase calculation unit 521 calculates the current phase ψ [q] using equation (6), for example. Based on the current amplitude IM and the current phase ψ [q], the estimation units 522 and 523 calculate the instantaneous values ix2 [q] and iy2 [q] of the AC components using the above two formulas.

  When the line current detector 3 detects the three-phase line currents iu, iv, iw, the AC components obtained by removing the respective DC components from the line currents iu, iv, iw, and the equations (9) to (11) ) May be used to estimate the three-phase instantaneous value at a predetermined time in the same manner as described above.

  If the at least two-phase line currents ix and iy detected by the line current detection unit 3 and the two-phase line currents iα and iβ are collectively expressed as two currents, the DC component extraction unit and the estimation unit 35 It can be expressed as follows. That is, the DC component extraction unit obtains a series of n averages of the instantaneous values of the two currents as the DC components of the two currents, respectively, and the estimation unit 35 calculates the DC components from the instantaneous values of the two currents at one timing. Except for the instantaneous value of the AC component of the two currents at one timing, and based on the instantaneous value of the AC component and the waveform equation for the fundamental component of the two currents, Estimate the value.

<Specific Example of Flowchart for Estimating AC Component of Line Current>
The flowchart of FIG. 7 is repeatedly executed every predetermined period (hereinafter also referred to as a control period). First, in step ST1, the line current detector 3 determines whether or not a current detection flag for detecting the line currents ix and iy is set. The current detection flag has the same function as, for example, the current detection timing signal SH in FIG. 1, and is hereinafter referred to as a current detection flag SH. How the current detection flag SH is set will be described later. If an affirmative determination is made in step ST1, the line current detector 3 detects the line currents ix and iy in step ST2.

  Next, in step ST3, the DC component extraction units 512 and 513 extract the DC component of the line current. The offset amount in the figure is synonymous with the DC component. Next, in step ST4, the current amplitude calculation unit 514 calculates the current amplitude IM, and the power factor angle calculation unit 515 calculates the power factor angle θ. In FIG. 7, the processes of steps ST3 and ST4 are collectively denoted by reference numeral 51, and in FIG. 2, the current amplitude / phase angle estimation unit 51 is shown as a functional block corresponding to this process.

  When a negative determination is made in step ST1, or after executing step ST4, a series of first processes consisting of steps ST5 and ST6 and a series of second processes consisting of steps ST7 to ST10 are executed. Either of the first process and the second process may be executed first, or may be executed in parallel with each other by, for example, a time division process.

  Here, the second process will be described first. The second process is a process for setting / clearing the current detection flag SH that triggers the execution of steps ST2 to ST4, and is executed by the current detection timing determination unit 62 belonging to the control unit 7, for example.

  In step ST7, the current detection timing determination unit 62 calculates the voltage phase φ in the next control cycle. More specifically, for example, the current detection timing determination unit 62 calculates the voltage phase φ based on the phase voltage command values Vu *, Vv *, Vw * employed in the next control cycle.

  Next, in step ST8, the current detection timing determination unit 62 determines whether or not the voltage phase φ calculated in step ST7 is a voltage phase for current detection. As described above, the timing at which the current should be detected is a timing for each calculation period obtained by dividing m times the period of the AC voltage by n, and is predetermined, for example. For example, 1 and 6 are employed as m and n, respectively, and a timing at which the voltage phase φ is 30 degrees is employed as one of timings at which a current should be detected. At this time, the timing for detecting the current is the timing at which the voltage phase φ is 30 degrees, 90 degrees, 150 degrees, 210 degrees, 270 degrees, or 330 degrees. Then, the current detection timing determination unit 62 determines whether or not the voltage phase φ calculated in step ST7 substantially corresponds to the above-described angle. For example, it is determined that the voltage phase φ substantially corresponds to the above angle in the control cycle in which the deviation between the voltage phase φ [p] and the above angle is the smallest.

  If an affirmative determination is made in step ST8, the current detection timing determination unit 62 sets the current detection flag SH in step ST9. If a negative determination is made in step ST8, the current detection timing determination unit 62 clears the current detection flag SH in step ST10.

  Next, the first process will be described. In the first process, the instantaneous value of the AC component of the line current in the current control cycle is obtained based on the current amplitude IM and the power factor angle θ obtained in steps ST3 and ST4 in the current or previous control cycle. It is processing of. In the example of FIG. 7, the first process is also executed when a positive determination is made in step ST1. However, if a positive determination is made in step ST1, the line current is detected in step ST2, so it is not always necessary to estimate the line current in that control cycle. Therefore, the first process may be executed only when a negative determination is made in step ST1. Here, it demonstrates along the illustration of FIG.

  In step ST5, the current phase calculation unit 521 calculates the current phase ψ based on the voltage phase φ and the power factor angle θ. If a positive determination is made in step ST1, ideally, the current phase ψ calculated in step ST5 can take the same value as the current phase ψ calculated in step ST4. On the other hand, for example, if the power factor angle θ is averaged by a low-pass filter or the like, the current phase ψ may be different in steps ST4 and ST5.

  Next, in step ST6, the estimation parts 522 and 523 calculate the instantaneous value of the AC component of the line current using the current amplitude IM and the current phase ψ. In FIG. 7, the processes of steps ST5 and ST6 are collectively denoted by reference numeral 52, and FIG. 3 shows a current estimation unit 52 as a functional block corresponding to this process.

  With the above operation, the instantaneous value of the alternating current can be estimated for each control period.

Second embodiment.
In the first embodiment, the instantaneous value of the AC component at a predetermined time point is estimated using the detected instantaneous value of the line current. In the second embodiment, the line current at a predetermined time point is estimated in consideration of the offset of the line current.

  An example of a conceptual configuration of the power conversion device 1 according to the second embodiment is the same as that of FIG. In the second embodiment, as illustrated in FIG. 8, DC components iα0 and iβ0 are input to the estimation units 522 and 523. As described in the first embodiment, the estimation units 522 and 523 calculate the instantaneous value of the AC component at a predetermined time. In the second embodiment, the estimation units 522 and 523 add the DC components iα0 and iβ0 to the calculated instantaneous values of the AC components, respectively, to calculate the instantaneous value of the line current at a predetermined time point.

  In the example of FIG. 8, addition units 5w and 5x are shown as function blocks belonging to the estimation units 522 and 523 and adding the DC components iα0 and iβ0 to the instantaneous values iα2 [q] and iβ2 [q] of the AC components, respectively. ing.

  Thus, the instantaneous value of the line current at a predetermined time can be estimated in consideration of the direct current component (so-called offset amount) of the line current.

  For example, when the switching generator 6 generates the switching signal so that the deviation becomes small based on the deviation between the line current estimated as described above and the line current command value, the offset of the line current is reduced. Is done. Line current offset causes increased loss and power pulsation. Further, when the inductive load is a motor, torque pulsation / rotation speed pulsation is caused, and if the pulsation is high, step-out can be caused. Therefore, such offset reduction is effective.

  Note that the estimation units 522 and 523 may not add the direct current component to the instantaneous value of the alternating current component as it is, but may perform some correction on the direct current component and add it to the instantaneous value of the alternating current component. For example, the DC component may be corrected in consideration of a detection error that occurs as a device of the line current detection unit 3. In the first embodiment, it can also be understood that the DC component is corrected and set to 0, and this value is added to the instantaneous value of the AC component.

Third embodiment.
An example of a conceptual configuration of the power conversion device 1 according to the second embodiment is the same as that of FIG. In the third embodiment, a detection method of the line current detection unit 3 and its relation will be described.

  The line current detection unit 3 includes a DC current detection unit 31 and a DC current / line current corresponding unit 32. The direct current detector 31 detects a direct current Idc flowing through the direct current lines LH and LL. In the illustration of FIG. 1, the DC current detection unit 31 is provided on the DC line LL, but may be provided on the DC line LH. The direct current / line current correspondence unit 32 receives the direct current Idc from the direct current detection unit 31 and the switching signal S from the switching signal generation unit 6. The direct current / line current correspondence unit 32 recognizes the switching pattern of the switching elements S1 to S6 based on the switching signal S, and converts the direct current Idc detected by the direct current detection unit 31 into a predetermined phase based on the switching pattern. Is regarded as the line current. Hereinafter, this point will be described in detail. First, the switching pattern will be described by describing the control of the inverter 2, and the relationship between the switching pattern and the line current will be described.

<Control of inverter 2>
The inverter 2 is controlled by the switching signal S as described below. First, the upper switching element and the lower switching element connected to the same AC line are electrically connected to each other exclusively. That is, the switching elements S1 and S4 conduct exclusively with each other, the switching elements S2 and S5 conduct exclusively with each other, and the switching elements S3 and S6 conduct exclusively with each other. This is to prevent the DC lines LH and LL from being short-circuited and a large current from flowing through the switching elements S1 to S6.

  Accordingly, there are eight types of patterns as the switching patterns of the switching elements S1 to S6. When “1” and “0” indicate that the upper and lower switching elements are conductive, and the switching patterns of the respective phases are shown side by side, the switching patterns of the switching elements S1 to S6 are the following eight types. That is, the switching pattern is (000) (001) (010) (011) (100) (101) (110) (111). For example, the switching pattern (001) is employed when the lower switching elements S4 and S5 are conductive and the upper switching element S3 is conductive.

  In addition, when these switching patterns are adopted, the vector of the voltage output by the inverter 2 (phase voltage applied to the AC lines Pu, Pv, Pw) is grasped as a binary number. These are represented by decimal numbers and are represented as voltage vectors V0 to V7, respectively. For example, when the switching pattern (100) is employed, the voltage vector V4 is employed.

  FIG. 9 is a voltage vector diagram showing the positional relationship between the voltage vectors V0 to V7. The voltage vectors V1 to V6 are arranged such that their start points coincide with the center point and their end points are radially directed outward. When the end points of the voltage vectors V1 to V6 are connected, a regular hexagon is formed. In the switching pattern corresponding to the voltage vectors V0 and V7, the AC lines Pu, Pv and Pw are short-circuited with each other, so that the voltage vectors V0 and V7 have no magnitude. Therefore, the voltage vectors V0 and V7 are arranged at the center point. Hereinafter, the voltage vectors V0 and V7 are also called zero voltage vectors, and the voltage vectors V1 to V6 are also called non-zero voltage vectors. As can be understood from the above description, in the non-zero voltage vectors V1 to V6, of the AC lines Pu, Pv, and Pw, one of the DC lines LH and LL is electrically connected to one AC line and the other is 2 Conduction with two AC lines. In the zero voltage vectors V0 and V7, all of the AC lines Pu, Pv and Pw are electrically connected to the DC line LH or the DC line LL. Hereinafter, as illustrated in FIG. 9, regions between two adjacent non-zero voltage vectors in the circumferential direction are referred to as regions R <b> 1 to R <b> 6.

  Now, the control unit 7 generates two non-zero voltage vectors Vi and Vj (i, j = 1 to 6, i ≠ j) and a zero voltage vector V0 (or zero voltage vector V7) that constitute each of the regions R1 to R6. It adopts suitably in the predetermined period T. In other words, two different switching patterns among the six switching patterns (001) (010) (011) (100) (101) (110) and the switching pattern (000) (or the switching pattern (111)). It is adopted in a predetermined cycle. An average voltage vector V in the predetermined period T is expressed by a combination of the voltage vectors. Therefore, the voltage vector V is hereinafter referred to as a combined voltage vector. For example, the voltage vectors V0, V4, V6 constituting the region R1 in the predetermined period T are employed over the periods t0, t4, t6 (t0, t4, t6 ≧ 0, T = t0 + t4 + t6), respectively. In other words, switching patterns (000), (100), and (110) are employed in the periods t0, t4, and t6, respectively. The combined voltage vector V at this time is expressed by the following equation.

  V = (t0 · V0 + t4 · V4 + t6 · V6) / T (12)

  The control unit 7 appropriately adjusts the periods t0, t4, and t6 for each predetermined period T and adopts the voltage vectors V0, V4, and V6, so that the magnitude of the voltage vector V is kept constant while the region R1 is maintained. The direction of the voltage vector V can be rotated around the center point. Similarly, the control unit 7 appropriately employs voltage vectors V0 (V7), V2, and V6 in the region R2. The same applies to the regions R3 to R6. As a result, the direction of the synthesized voltage vector V can be rotated while keeping the magnitude constant. Therefore, a three-phase AC voltage is output to the AC lines Pu, Pv, and Pw. The magnitude of the combined voltage vector V corresponds to the amplitude of the three-phase AC voltage output from the AC lines Pu, Pv, Pw, and the reciprocal of the angular velocity corresponds to the period of the three-phase AC voltage. Therefore, if the magnitude and the angular velocity are constant, the three-phase AC voltage is a symmetric three-phase AC voltage.

  As described above, the control unit 7 sets the non-zero voltage vectors Vi and Vj and the zero voltage vector which are different from each other for each predetermined period T to the periods ti (≧ 0), tj (≧ 0), t0 (or t7, or t0 + t7). ). In other words, switching patterns (001) (010) (011) (100) (101) (110) in which two switching elements belonging to one of the upper and lower switching element groups and one of the switching elements belonging to the other conduct. ), Two different switching patterns are employed over the periods ti and tj, respectively, and switch patterns (000) and (111) for conducting three switching elements belonging to only one of the upper and lower switching element groups. At least one of them is employed over at least the periods t0 and t7.

<Line current detection>
Consider the current flowing through the inverter 2 when each of the switching patterns described above is employed. Since the switching pattern corresponds to the voltage vector as described above, the following description will be made using the voltage vector. 10 to 17 show currents flowing through the inverter 2 when the voltage vectors V0 to V7 are employed, respectively. When zero voltage vectors V0 and V7 are employed as shown in FIGS. 10 and 17, the AC lines Pu, Pv and Pw are short-circuited with each other, so that no DC current Idc flows through the DC lines LH and LL.

  As shown in FIG. 11, when the non-zero voltage vector V1 is employed, the upper switching element S3 and the lower switching elements S4 and S5 are brought into conduction. Therefore, the DC current Idc flowing through the DC line LH flows through the AC line Pw in the positive direction as the line current iw via the switching element S3. The line current iw branches at the inductive load 8. The two branched currents flow in the negative direction through the AC lines Pu and Pv as line currents iu and iv, respectively. The line currents iu and iv are merged in the DC line LL via the switching elements S4 and S5, respectively, and flow as a DC current Idc. Therefore, when the non-zero voltage vector V1 is adopted, the direct current Idc is equal to the line current iw.

  As shown in FIG. 13, when the non-zero voltage vector V3 is employed, the upper switching elements S2 and S3 and the lower switching element S4 are brought into conduction. Therefore, the DC current Idc flowing through the DC line LH branches and flows through the AC lines Pv and Pw in the positive direction as line currents iv and iw via the switching elements S2 and S3, respectively. The line currents iv and iw are combined at the inductive load 8 and flow in the negative direction through the AC line Pu as the line current iu. The line current iu flows through the DC line LL as the DC current Idc via the switching element S4. Therefore, when non-zero voltage vector V3 is employed, DC current Idc corresponds to line current iu having a negative value. In the following, in order to express that the line current is negative, a minus sign is given to the sign.

  As shown in FIGS. 12 and 15 to 16, the direct current Idc and the line current are also associated when the other non-zero voltage vectors V 2 and V 4 to V 6 are employed. In FIG. 9, the line current corresponding to each non-zero voltage vector is added.

  As shown in FIG. 9, when the non-zero voltage vectors V1 to V6 are adopted, the direct current Idc corresponds to one of the line currents iu, iv, and iw. Therefore, the direct current Idc can be estimated as a line current of a phase determined based on the non-zero voltage vector. For example, the DC current Idc is detected as the line current iu during the period in which the non-zero voltage vector V4 is employed (see also FIG. 15).

  Further, as described above for the control of the inverter 2, the non-zero voltage vectors Vi and Vj are adopted over the periods ti and tj, respectively, for each predetermined period T. Moreover, as can be understood from FIG. 9, the phase of the line current that matches the direct current Idc is different for the non-zero voltage vectors Vi and Vj employed in the regions R1 to R6. For example, considering the non-zero voltage vectors V4 and V6 employed in the region R1, the DC current Idc corresponds to the u-phase line current in the period t4 when the non-zero voltage vector V4 is employed, and the non-zero voltage vector V6 is employed. Period t6 direct current Idc corresponds to w-phase line current -iw. Therefore, the DC current Idc can be detected as two different phase currents in the periods ti and tj within the predetermined period T. Since the sum of the three-phase line currents iu, iv, and iw is zero, the remaining one-phase line current can be calculated from the detected two-phase line current. Therefore, in this case, a three-phase line current is calculated every predetermined period T.

<Period correction>
However, in reality, at least one of the periods ti and tj may be shorter than the period necessary for detecting the DC current Idc, and the DC current Idc cannot be detected appropriately during that period. This will be described below.

  FIG. 18 shows an example of conduction / non-conduction of the switching elements S1 to S3 and the direct current Idc in the predetermined period T. In the illustration of FIG. 18, the voltage vectors V0, V4, V6, and V7 are employed over the periods t0, t4, t6, and t7, respectively. That is, FIG. 18 shows an example in the region R1. In the illustration of FIG. 18, the switching elements S <b> 1 to S <b> 3 are non-conductive at the beginning of the predetermined period T. Then, the switching element S1 is turned on when the period t0 has elapsed from the start of the predetermined period T, the switching element S2 is turned on when the period t4 has elapsed from the time when the switching element S1 starts to be turned on, and the switching element S2 is turned on. When the period t6 has elapsed since the start of conduction, the switching element S3 is conducting.

  Then, as illustrated in FIG. 18, the direct current Idc pulsates transiently by switching between conduction / non-conduction of the switching elements S <b> 1 to S <b> 3. Such transient pulsation decreases with the passage of time, and the DC current Idc becomes stable. In the example of FIG. 18, the period from pulsation to stability is represented by a period t11. In general, the direct current Idc is detected while avoiding such a period t11.

  However, as illustrated in FIG. 19, if the period t6 is shorter than the period t11, the DC current Idc in the period t6 cannot be detected with appropriate accuracy.

  Further, if the line current detection unit 3 converts the value of the direct current Idc from analog to digital, such conversion also requires a period t13. Therefore, even if the transient pulsation is very small and the period t11 is negligibly small, the DC current Idc cannot be detected in the period t6 when the period t6 is shorter than the period t13.

  In the example of FIG. 19, the period t4 is longer than the period tref necessary for detecting the DC current Idc (in the example of FIG. 19, the sum of the periods t11 and t13). Therefore, by detecting the DC current Idc in the period t12 excluding the first period t11 and the last period t13 in the period t4, the DC current Idc can be detected with appropriate accuracy. On the other hand, the period t6 is shorter than the period tref. Therefore, the DC current Idc cannot be detected with appropriate accuracy during the period t6. Accordingly, in the example of FIG. 19, although the value of the one-phase line current iu can be acquired in the predetermined period T, the other two-phase line currents iv and iw cannot be acquired with appropriate accuracy. For example, when both the periods ti and tj are shorter than the period tref in the predetermined period T, even a one-phase line current cannot be detected with appropriate accuracy in the predetermined period T.

  The event that the periods ti and tj are shorter than the period tref occurs, for example, when the combined voltage vector V is located in the vicinity of the non-zero voltage vectors V1 to V6 or in the vicinity of the zero voltage vectors V0 and V7. . For example, referring to FIG. 20, when combined voltage vector V is located in region R1 and in the vicinity of non-zero voltage vector V4, period t6 is shorter than period tref. In FIG. 20, a region where only one of the periods ti and tj is shorter than the period tref is indicated by hatching, and a region where both the periods ti and tj are shorter than the period tref is indicated by hatching of sand.

  In the third embodiment, the power conversion device 1 includes a correction unit 63 as illustrated in FIG. 1 so as to enable line current detection in these regions. In each of the predetermined periods T including the timing at which the line current detection unit 3 should detect the line current, the correction unit 63 performs at the predetermined period T when at least one of the periods ti and tj is shorter than the period tref. Correction is performed so that both the periods ti and tj are equal to or longer than the period tref.

  As can be understood from FIGS. 18 and 19, the adjustment of the periods ti and tj can be performed by adjusting the conduction / non-conduction timing of the switching elements S1 to S3. Therefore, the correction unit 63 corrects the periods ti and tj by adjusting the switching signal S. This can be realized, for example, by adjusting the phase voltage command values Vu *, Vv *, Vw * and the like for generating the switching signal S.

  If the predetermined period T includes the timing at which the current is detected by the correction of the correction unit 63, that is, the timing of every period (for example, every 60 degrees of voltage phase) obtained by dividing the m period of the AC voltage by n, In the predetermined period T, both the periods ti and tj are longer than the period tref. Therefore, the line current detection unit 3 can appropriately detect the line currents ix and iy during the periods ti and ij.

  In such a power conversion device, as in the first or second embodiment, the estimation unit 35 estimates the instantaneous value of the alternating current component at a predetermined time, and the predetermined time is at least in the periods ti and tj. Either one is included in a predetermined cycle T that is smaller than the period tref. In other words, the instantaneous value of the AC component at the timing when the combined voltage vector V is located within the hatched area or the hatched area of the sand is estimated.

  In order to estimate the alternating current component, the periods ti and tj do not need to be equal to or longer than the period tref, and therefore the correction unit 63 does not need to correct the periods ti and tj in the predetermined cycle T including a predetermined time point. On the other hand, if the periods ti and tj are corrected, an AC voltage having a waveform different from the AC voltage to be originally output is output and the waveform is distorted. In the third embodiment, the periods ti and tj need to be corrected. Therefore, the distortion can be reduced.

  Of course, the instantaneous value of the alternating current component may be estimated at a predetermined time point included in the predetermined period T in which both the periods ti and tj are equal to or longer than the period tref.

  Further, for example, when a circle is drawn in the area where the locus of the composite voltage vector V is hatched in the sandy area of FIG. 20, it is necessary to correct the periods ti and tj each time an instantaneous value of the line current is detected. Met. On the other hand, according to the third embodiment, in one cycle of the AC voltage (one rotation of the combined voltage vector V), the periods ti, tj are detected n / m times (for example, 6 times) for detecting the instantaneous value of the line current. May be corrected. Thereby, distortion of an alternating voltage can be suppressed.

  Further, it is desirable that the timing for detecting the current be included in a predetermined cycle T in which both the periods ti and tj are equal to or longer than the period tref. In other words, it is desirable to perform current detection at the timing when the combined voltage vector V is located in the white area in FIG. In order to easily satisfy this, it is desirable that the current detection timing is a timing at which the voltage phase φ takes substantially 30 degrees, 90 degrees, 150 degrees, 210 degrees, 270 degrees, and 330 degrees. This is because, even when the magnitude of the synthesized voltage vector V is small, the synthesized voltage vector V is more likely to be located in a white area than at other timings.

2 Inverter 3 Line Current Detection Unit 31 DC Current Detection Unit 32 DC Current / Line Current Corresponding Unit 53 Estimation Unit 61 Voltage Phase Acquisition Unit 63 Correction Unit 512, 513 DC Component Extraction Unit 514 Current Amplitude Calculation Unit 515 Power Factor Angle Calculation Unit 521 Current phase calculator

Claims (5)

Three AC lines (Pu, Pv, Pw) to which three-phase AC voltage is applied;
A power conversion circuit (2) connected to the AC line;
At least two currents flowing in the AC line at the timing of each period obtained by dividing m (m is a natural number) times one cycle of the AC voltage by n (n is an integer of 2 or more, where m / n is not an integer). A line current detector (3) for continuously detecting an instantaneous value of the phase line current (iu, iv, iw) at least n times;
The instantaneous value of two line currents obtained by converting the instantaneous value of the line current of at least two phases from a fixed coordinate system of three phases to a fixed coordinate system of two phases, or the instantaneous value of the line currents of at least two phases A series of n averages of instantaneous values (iα [1] to iα [n], iβ [1] to iβ [n]) of two currents are respectively obtained as DC components (iα0, iβ0) of the two currents. DC component extraction unit (512,513) to be obtained as
AC component that is an instantaneous value of the AC component of the two currents at the one timing excluding the DC component from the instantaneous value (iα [p], iβ [p]) of the two currents at the one timing Calculated values (iα2 [p], iβ2 [p]) are obtained, and based on the calculated AC component values and the waveform equations for the fundamental wave components of the two currents, the AC component instantaneously at a predetermined time point A power converter comprising: an estimation unit (53) that estimates an AC component estimated value (iα2 [q], iβ2 [q]).   The estimation unit (53) adds the DC components (iα0, iβ0) to the AC component estimated values (iα2 [q], iβ2 [q]), respectively, and instantaneous values of the two currents at the predetermined time point The power converter according to claim 1 which computes. A voltage phase acquisition unit (61) for acquiring a voltage phase (φ, φ [p], φ [q]) of the AC voltage;
The estimation unit (53)
A current amplitude calculator (514) that calculates a current amplitude (IM) for the two currents based on the AC component calculated values (iα2 [p], iβ2 [p]);
Based on the AC component calculated value, a value (ψ [p]) of the current phase for the two currents at the timing is calculated, and a difference between the value and the voltage phase (φ [p]) at the timing. A phase angle calculator (515) for calculating the phase angle (θ);
A value (ψ [q]) of the current phase at the predetermined time is calculated by adding the phase angle to the voltage phase (φ [q]) at the predetermined time, and the value, the current amplitude, and the waveform The power conversion device according to claim 1, further comprising: an AC component estimation unit (522, 523) that calculates the AC component estimated value (iα2 [q], iβ2 [q]) using the following equation. The power conversion circuit (2) includes first and second switching elements (S1 to S6) connected in series between a pair of DC lines (LH, LL) for three phases, and the first Connection points connecting 1 and the second switching element are respectively connected to the three AC lines (Pu, Pv, Pw),
The power converter (1)
In each of the predetermined periods (T), one of the three AC lines is connected to one of the pair of DC lines, and the other two of the three AC lines are connected to the other of the pair of DC lines. Among the six switching patterns, first and second switching patterns different from each other, and a third switching pattern in which all of the three AC lines are connected to one or the other of the pair of DC lines, respectively, A switching control unit (6) that is adopted over the first to third periods and causes the power conversion circuit to perform the conversion;
In each of the periods including the timing among the predetermined periods, when at least one of the first period and the second period (ti, tj) is smaller than a reference period, the first period in the period And a correction unit (63) that corrects at least one of the first period and the second period such that both the second period is equal to or greater than the reference period,
The line current detector (3)
A direct current detector (31) for detecting a direct current (Idc) flowing through the pair of direct current lines;
The direct current detected in the first period equal to or greater than the reference period is regarded as an instantaneous value of the line current of the first phase determined by the first switching pattern, and the second current equal to or greater than the reference period. The direct current / line current corresponding part (32) which regards the direct current detected in a period as an instantaneous value of the line current of the second phase determined by the second switching pattern. The power converter device as described in any one of these.   The power conversion device according to claim 4, wherein the predetermined time point is included in one of the periods having the first or second period shorter than the reference period.

Images