JP6729249B2 - Power converter controller - Google Patents

Description

The present invention relates to a control device for a power converter.

Patent Document 1 describes an electric motor drive device that drives an electric motor. For example, the electric motor drive device includes a converter, an inverter, and a capacitor. The converter converts an AC voltage into a DC voltage, and outputs this DC voltage between a pair of DC buses. The capacitor is connected between the pair of DC buses. The inverter converts a DC voltage between the pair of DC buses into an AC voltage and outputs the AC voltage to the electric motor.

In an inverter device having an LC filter in the DC link section, the DC voltage may pulsate at the resonance frequency of the LC filter with respect to load fluctuations and output frequency fluctuations. That is, the DC voltage includes a pulsating component. In Patent Document 1, the amplitude of the ripple component of the DC voltage is reduced by control.

Japanese Patent No. 4067021

However, in the technique described in Patent Document 1, the amplitude of the AC voltage output by the inverter pulsates according to the pulsating component of the DC voltage. In this case, it is difficult to maintain the amplitude of the AC voltage at its upper limit value. Therefore, the average value of the amplitude of the AC voltage becomes smaller than the upper limit value. Such reduction of the average value of the amplitude of the AC voltage is not desirable.

The voltage utilization factor is introduced here. The voltage utilization rate is the ratio of the average value of the amplitude of the AC voltage output by the inverter to the DC voltage. In other words, the voltage utilization rate is an index indicating how much the AC voltage is output on average with respect to the DC voltage input to the inverter. Since it is desirable that the upper limit of the average value of the amplitude of the AC voltage is high, it is also desirable that the upper limit of the voltage utilization rate is also high.

Then, this application aims at providing the motor drive device which can suppress the amplitude of the pulsating component of DC voltage, suppressing suppressing the upper limit of a voltage utilization factor.

1st aspect of the control apparatus of the power converter concerning this invention inputs the direct-current voltage (Vdc) containing a pulsation component (Vdch), converts the said direct-current voltage into alternating voltage, and loads the said alternating voltage into load (M1. ), a device for controlling a power converter (2) that flows an alternating current to the load, a pulsating component detection unit (4) for detecting the pulsating component, and controlling the power converter. A control circuit (3) for increasing the load power factor, which is the cosine value of the phase difference between the AC voltage and the AC current, in accordance with the increase in the instantaneous value of the pulsating component.

A second aspect of the control device for the power converter according to the present invention is the control device for the power converter according to the first aspect, comprising a current detection unit (5) for detecting the alternating current, The circuit (3) has a first voltage phase command (θv*) for the voltage phase (θv) of the AC voltage so that the load power factor increases in accordance with the increase of the instantaneous value of the pulsating component (Vdch). *) is corrected based on the current value (θi) of the alternating current and the instantaneous value of the pulsating component (Vdch) to generate a second voltage phase command (θv*), and the power converter (2 ) Is generated based on the second voltage phase command.

A third aspect of the control device for a power converter according to the present invention is the control device for a power converter according to the second aspect, wherein the control circuit (3) includes the first voltage phase command (θv* *) and the current phase (θi), the first power factor command (PF**) for the load power factor is calculated, and according to the increase of the instantaneous value of the pulsating component (Vdch), The second power factor command (PF*) is calculated by performing correction to increase the first power factor command, and the second voltage phase command (θv*) is calculated based on the second power factor command and the current phase. To calculate.

A fourth aspect of the control device for the power converter according to the present invention is the control device for the power converter according to the third aspect, wherein the control circuit (3) includes the second power factor command (PF* ) Is greater than 1, the second power factor command is set to 1, and/or the second power factor command is less than -1, the second power factor command is set to -1. Set.

A fifth aspect of the control device of the power converter according to the present invention is the control device of the power converter according to any one of the first to fourth aspects, wherein the control circuit (3) includes the pulsation. The load power factor is changed with a correction value (H) that increases in accordance with an increase in the instantaneous value of the component (Vdch), and the ratio of the amplitude (Vm) of the AC voltage to the DC voltage (Vdc) or the AC current. The correction value is calculated so that the absolute value of the correction value becomes larger as the amplitude of is smaller.

A sixth aspect of the control device for a power converter according to the present invention is the control device for a power converter according to any one of the first to fifth aspects, in which the direct-current voltage (Vdc) is present between them. A first DC busbar (LH) and a second DC busbar (LL) to be applied are connected to the power converter (2), and a capacitor (between the first DC busbar and the second DC busbar) is connected between the first DC busbar and the second DC busbar. C1) is connected, and on the side opposite to the power converter (2) with respect to the capacitor, a reactor (L1) is provided on the first DC bus or the second DC bus, The pulsating component detection unit (4), the voltage of the reactor with the potential of one end of the reactor on the side of the capacitor as a reference potential (VL), as a reverse phase of the pulsating component (Vdch), or, The voltage of the reactor with the potential of the other end of the reactor as a reference potential is detected as the pulsating component.

According to the first aspect of the control device for a power converter according to the present invention, by increasing the load power factor according to the increase in the instantaneous value of the pulsating component, the power conversion can be performed as described in detail in the embodiment. The current input to the device can be increased in response to an increase in the instantaneous value of the pulsating component. Therefore, the further increase of the DC voltage which is the input voltage of the power converter, that is, the further increase of the instantaneous value of the pulsation component is suppressed. Conversely, when the instantaneous value of the pulsation component is small, the current input to the power converter is reduced. This suppresses further reduction of the instantaneous value of the pulsating component.

As described above, when the instantaneous value of the pulsating component of the DC voltage is large, further increase of the instantaneous value of the pulsating component is suppressed, and when the instantaneous value of the pulsating component is small, further reduction of the instantaneous value of the pulsating component is suppressed. To be done. Therefore, the amplitude of the pulsating component can be reduced.

Moreover, it is not necessary to reduce the amplitude of the AC voltage. That is, it is not necessary to reduce the voltage utilization rate (=AC voltage amplitude/DC voltage).

According to the second aspect of the control device for a power converter of the present invention, the load power factor is controlled by correcting the first voltage phase command and generating the second voltage phase command. Therefore, the conventional control based on the voltage command can be easily used.

According to the third aspect of the control device for a power converter of the present invention, the load power factor can be controlled more accurately by correcting the first power factor command and calculating the second power factor command.

According to the fourth aspect of the control device for a power converter according to the present invention, the second voltage phase command can be appropriately calculated.

According to the fifth aspect of the control device for a power converter of the present invention, the absolute value of the correction value increases as the ratio or the amplitude of the alternating current decreases. Therefore, it is possible to suppress the decrease in the correction amount of the DC current due to the decrease in the ratio or the amplitude of the AC current. As a result, it is possible to suppress the reduction of the effect due to the reduction of the ratio or the amplitude of the alternating current.

According to the sixth aspect of the power converter control device of the present invention, the pulsation component can be easily detected.

It is a figure which shows roughly an example of a structure of a load drive device. It is a figure which shows typically an example of a DC voltage, a pulsation component, and a reactor voltage. It is a block diagram which shows roughly an example of an internal structure of a control circuit. It is a block diagram which shows roughly an example of an internal structure of a voltage phase correction part. It is a figure which shows typically an example of the voltage control rate and phase difference concerning a comparative example. It is a figure which shows typically an example of the voltage control rate and phase difference concerning this Embodiment. It is a block diagram which shows roughly another example of an internal structure of a voltage phase correction part. It is a block diagram which shows roughly another example of an internal structure of a voltage phase correction part. It is a figure which shows roughly another example of a structure of a load drive device. It is a figure which shows roughly an example of an internal structure of a detection part.

<Structure of load drive device>
FIG. 1 schematically shows an example of the configuration of the load driving device. The load driving device includes, for example, a rectifier 1, a reactor L1, a capacitor C1, a power converter 2, a control circuit 3, and a detector 4.

The rectifier 1 rectifies an N-phase (N is a natural number) phase AC voltage input from the AC power source E1 into a rectified voltage and outputs the rectified voltage between the DC bus lines (power source lines) LH and LL. In the example of FIG. 1, the rectifier 1 is a diode rectifier circuit. The rectifier 1 is not limited to the diode rectifier circuit, and may be another rectifier circuit (for example, a self-excited rectifier circuit or a separately excited rectifier circuit).

Further, in the example of FIG. 1, the rectifier 1 is a three-phase rectifier circuit to which a three-phase AC voltage is input. However, the number of phases of the AC voltage input to the rectifier 1, that is, the number of phases of the rectifier 1 is not limited to three and may be set appropriately.

The capacitor C1 is connected between the DC buses LH and LL. The capacitor C1 is, for example, a film capacitor. When the capacitance of the capacitor C1 is reduced, the DC voltage Vdc applied between the DC buses LH and LL is not sufficiently smoothed. In other words, the capacitor C1 allows pulsation of the rectified voltage rectified by the rectifier 1. Therefore, the DC voltage Vdc has a pulsating component due to the rectification of the N-phase AC voltage. For example, if full-wave rectification is used, this pulsating component has a frequency that is 2N times the frequency of the N-phase AC voltage. Hereinafter, this pulsating component will be referred to as a rectifying component. In the example of FIG. 1, since the rectifier 1 full-wave rectifies the three-phase AC voltage, the DC voltage Vdc pulsates at a frequency that is six times the frequency of the three-phase AC voltage.

Reactor L1 forms an LC filter with capacitor C1. In the example of FIG. 1, reactor L1 is provided on DC bus LH between rectifier 1 and capacitor C1 (that is, on the side opposite to power converter 2 with respect to capacitor C1). However, the present invention is not limited to this, and reactor L1 may be provided on DC bus LL between rectifier 1 and capacitor C1.

If the capacitance of the capacitor C1 is small as described above, the resonance frequency of this LC filter tends to be high. Similarly, the resonance frequency tends to increase as the inductance of the reactor L1 decreases.

The power converter 2 converts the DC voltage Vdc into an AC voltage based on the control signal S from the control circuit 3. Then, the power converter 2 outputs this AC voltage to the load M1. The power converter 2 is, for example, an inverter circuit. In the example of FIG. 1, a three-phase inverter circuit is shown as the power converter 2. The power converter 2 includes, for example, switching elements S1 to S6 and diodes D1 to D6.

The switching elements S1 to S6 are, for example, insulated gate bipolar transistors. The switching elements S1 and S2 are connected in series with each other between the DC buses LH and LL, and the switching elements S3 and S4 are connected in series with each other between the DC buses LH and LL, and the switching element S5. S6 is connected in series between the DC buses LH and LL. The switching elements S1 to S6 are turned on/off based on the control signal S from the control circuit 3.

The diodes D1 to D6 are connected in parallel to the switching elements S1 to S6, respectively. The forward direction of the diodes D1 to D6 is from the DC bus LL to the DC bus LH. The switching elements S1 to S6 may have a parasitic diode in the forward direction from the DC bus LL to the DC bus LH. Such switching elements S1 to S6 are, for example, MOS (Metal-Oxide-Semiconductor) field effect transistors. In this case, the diodes D1 to D6 may not be provided.

A connection point connecting the switching elements S1 and S2 is connected to one end of the output line Pu, a connection point connecting the switching elements S3 and S4 is connected to one end of the output line Pv, and a connection point connecting the switching elements S5 and S6. Is connected to one end of the output line Pw. The other ends of the output lines Pu, Pv, Pw are connected to the load M1.

By appropriately controlling the switching elements S1 to S6, the power converter 2 converts the DC voltage Vdc into an AC voltage (three-phase AC voltage in the example of FIG. 1) and outputs the converted AC voltage to the output line Pu. , Pv, Pw to the load M1. Hereinafter, the AC voltage and the AC current output by the power converter 2 are also referred to as the output AC voltage and the output AC current, respectively.

The load M1 may be, for example, a rotating machine (for example, an induction machine or a synchronous machine). Although the three-phase load M1 is illustrated in FIG. 1, the number of phases is not limited to this. In other words, the power converter 2 is not limited to a three-phase power converter.

The control circuit 3 outputs the control signal S to the power converter 2 (specifically, the switching elements S1 to S6) to control the output of the power converter 2.

Further, here, the control circuit 3 is configured to include a microcomputer and a storage device. The microcomputer executes each processing step (in other words, procedure) described in the program. The storage device includes 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. It is possible. The storage device stores various kinds of information and data, stores a program executed by a microcomputer, and provides a work area for executing the program. It should be noted that it can be understood that the microcomputer functions as various means corresponding to each processing step described in the program, or realizes various functions corresponding to each processing step. Further, the control circuit 3 is not limited to this, and various procedures executed by the control circuit 3 or various means or various functions to be realized may be partially or entirely realized by hardware.

<Pulsation component of DC voltage Vdc>
In this load drive device, the DC voltage Vdc pulsates due to a factor other than the rectification of the rectifier 1. Since the resonance frequency of the resonance circuit formed by the capacitor C1 and the reactor L1 is set higher than the frequency of the rectification component Vrec, for example, the DC voltage Vdc also includes the pulsation component Vdch having a frequency higher than the frequency of the rectification component Vrec. Contains. FIG. 2 schematically shows an example of the DC voltage Vdc, the pulsating component Vdch, and the voltage VL of the reactor L1. As illustrated in FIG. 2, the DC voltage Vdc pulsates even at a frequency higher than the frequency of the rectified component Vrec.

In the present embodiment, it is intended to reduce the amplitude of the pulsating component Vdch of the DC voltage Vdc by control.

<Basic principle>
Prior to the description of the control according to the present embodiment, the basic principle of reducing the amplitude of the pulsating component Vdch of the DC voltage Vdc will be described.

The DC voltage Vdc tends to decrease as the DC current idc input to the power converter 2 increases. This is because the current flowing from the capacitor C1 to the power converter 2 increases as the direct current idc increases. Conversely, when the direct current idc decreases, the direct current voltage Vdc tends to increase.

Therefore, the DC current idc is increased according to the increase of the instantaneous value of the pulsating component Vdch. Thus, if the direct current idc increases during the increase of the instantaneous value of the pulsating component Vdch, it is possible to suppress the further increase of the pulsating component Vdch. Therefore, the amplitude of the pulsating component Vdch can be reduced.

Conversely, the direct current idc is reduced in accordance with the reduction of the instantaneous value of the pulsating component Vdch. Thus, if the DC current idc is reduced during the reduction of the instantaneous value of the pulsation component Vdch, it is possible to suppress the further reduction of the pulsation component Vdch. Therefore, the amplitude of the pulsating component Vdch can be reduced.

As a more specific example, the DC current idc may be corrected using the following formula.

idc″=idc′+K·Vdch (1)

Here, idc″, idc′, and K represent the corrected direct current, the uncorrected direct current, and the gain, respectively.

According to the equation (1), the DC current idc″ increases as the instantaneous value of the pulsating component Vdch increases, and the DC current idc″ decreases as the instantaneous value of the pulsating component Vdch decreases. As a result, the amplitude of the pulsating component Vdch can be reduced. In the following, an increase in the instantaneous value of the pulsating component Vdch will be simply referred to as an increase in the pulsating component Vdch, and a decrease in the instantaneous value of the pulsating component Vdch will also be simply referred to as a decrease in the pulsating component Vdch.

By the way, it can be considered that the voltage VL of the reactor L1 corresponds to the pulsating component Vdch. The reason will be briefly described. First, the DC voltage Vdc is the sum (Vrec+Vdch) of the rectified component Vrec and the pulsating component Vdch. Considering the voltage VL with the potential at one end of the reactor L1 on the capacitor C1 side as the reference potential, the output voltage of the rectifier 1 is equal to the sum of the voltage VL and the DC voltage Vdc according to Kirchhoff's law. Since it can be considered that the output voltage of the rectifier 1 is almost equal to the rectified component Vrec, Vrec=Vdc+VL is established. By substituting Vdc=Vrec+Vdch into this equation, VL=-Vdch is established. That is, the voltage VL ideally has a reverse phase of the pulsating component Vdch. In other words, the positive/negative of the voltage VL is different from the positive/negative of the pulsation component Vdch (see also FIG. 2).

Substituting VL=-Vdch into the equation (1) leads to the following equation.

idc″=idc′−K·VL (2)

Therefore, if the DC current idc' is corrected as shown in the equation (2), the amplitude of the pulsating component Vdch can be reduced. More generally, the DC current idc″ decreases as the instantaneous value of the voltage VL increases, in other words, the DC current idc″ increases as the instantaneous value of the voltage VL decreases. As described above, the correction can reduce the amplitude of the pulsation component Vdch. Note that, hereinafter, an increase in the instantaneous value of the voltage VL is also simply referred to as an increase in the voltage VL, and a decrease in the instantaneous value of the voltage VL is also simply referred to as a decrease in the voltage VL.

<Control according to this embodiment>
As described above, the amplitude of the pulsating component Vdch can be reduced by increasing the direct current according to the increase of the pulsating component Vdch (or the decrease of the voltage VL). In the present embodiment, the direct current is not directly controlled, but the load power factor, which is the power factor on the load M1 side, is controlled. Then, by controlling the load power factor, the DC current is equivalently increased according to the increase of the pulsating component Vdch (or the decrease of the voltage VL). Specifically, the control circuit 3 controls the power converter 2 to increase the load power factor according to the increase of the pulsating component Vdch (or the decrease of the voltage VL).

Hereinafter, control using the voltage VL will be described first. For example, the load power factor is corrected using the following formula.

cos θ2=cos θ1−K·VL (3)

Here, θ2 indicates the phase difference after correction of the output AC voltage and output AC current, and θ1 indicates the phase difference of the output AC voltage and output AC current before correction. Therefore, the cosine value cos θ1 of the phase difference θ1 shows the load power factor before correction, and the cosine value cos θ2 of the phase difference θ2 shows the load power factor after correction.

Next, it will be described below that the DC current idc increases as the voltage VL decreases by using the equation (3).

The input power and the output power of the power converter 2 are ideally equal to each other. Therefore, when the power converter 2 outputs a three-phase AC voltage, the following formula is established.

idc·Vdc=√3·io_rms·Vo_rms·cos θ2 (4)

Here, idc shows the direct current input into the power converter 2, and io_rms and Vo_rms show the effective value of an output alternating current and an output alternating voltage, respectively.

Next, the voltage control rate D is introduced. The voltage control rate D is a ratio of the amplitude Vm of the output AC voltage to the DC voltage Vdc (=Vm/Vdc=√2·Vo_rms/Vdc). By transforming the equation (4) using this voltage control rate D, the following equation can be derived.

idc·Vdc=√3·io_rms·D·Vdc/√2·cos θ2...(5)

By multiplying both sides of the equation (5) by the reciprocal of the DC voltage Vdc, the following equation is derived.

idc=√(3/2)·io_rms·D·cos θ2 (6)

Substituting equation (3) into equation (6) leads to the following equation.

idc=√(3/2)・io_rms・D・(cos θ1-K・VL)
= √(3/2)・io_rms・D・cos θ1−√(3/2)・io_rms・D・K・VL ・・・(7)

In consideration of Expression (6), the first term on the right side of Expression (7) can be considered as the direct current idc when the load power factor is not corrected. This DC current idc is called a DC current idc1 in order to distinguish it from the DC current idc when the load power factor is corrected, and the DC current idc when the load power factor is corrected is called a DC current idc2. When expressed by using the direct currents idc1 and idc2, the following equation can be derived from the equation (7).

idc2=idc1·−√(3/2)·io_rms·D·K·VL (8)

Although the voltage control rate D and the effective value io_rms of the output AC current exist in the second term on the right side of Expression (8), the voltage VL exists. Therefore, the DC current idc1 is corrected by the voltage VL. That is, the DC current idc1 is corrected so that the DC current idc2 increases as the voltage VL decreases, or conversely, the DC current idc2 decreases as the voltage VL increases.

As described above, it is understood that the amplitude of the pulsating component Vdch of the DC voltage Vdc can be reduced by correcting the load power factor so as to satisfy the expression (3). More generally, the control circuit 3 controls the power converter 2 to increase the load power factor according to the decrease in the voltage VL, thereby reducing the amplitude of the pulsating component Vdch.

<Specific example of control>
As described above, the control circuit 3 may correct the voltage phase command for the phase of the output AC voltage (hereinafter referred to as the voltage phase) in order to increase the load power factor according to the increase of the pulsating component Vdch. Absent. For example, a specific example of the control circuit 3 will be described below.

FIG. 3 is a functional block diagram schematically showing an example of the internal configuration of the control circuit 3. In the example of FIG. 3, the control circuit 3 includes a voltage command generator 31, an orthogonal/polar coordinate converter 32, a voltage phase corrector 33, a rotary/fixed coordinate converter 34, a control signal generator 35, and a fixed/rotary coordinate converter 36. It has and.

The voltage command generator 31 generates a voltage command V* for the output AC voltage. The method of generating the voltage command V* is not particularly limited, but an example thereof will be briefly described. In the example of FIG. 3, the control circuit 3 when the load M1 is an electric motor is shown. In the example of FIG. 3, the control circuit 3 is provided with a subtractor 37, and the rotational speed ω of the electric motor and the rotational speed command ω* for the rotational speed ω are input to the subtractor 37. .. The rotation speed command ω* is input to the subtractor 37 from the outside, for example. The rotation speed ω is detected by, for example, a rotation speed detection unit (not shown). The rotation speed detection unit may be a so-called rotation speed sensor (for example, a rotary encoder), or may have an arithmetic circuit that calculates the rotation speed ω based on the current flowing in the electric motor. The subtractor 37 subtracts the rotation speed ω from the rotation speed command ω* to calculate the deviation Δω, and outputs the deviation Δω to the voltage command generation unit 31.

In the example of FIG. 3, the voltage command generator 31 also receives the currents id and iq flowing through the electric motor. The currents id and iq are the d-axis component and the q-axis component of the alternating current flowing through the electric motor in the dq axis rotating coordinate system, respectively. The dq axis rotating coordinate system is configured by the d axis set in phase with the interlinkage magnetic flux to the armature due to the field of the electric motor, and the q axis whose phase advances 90 degrees with respect to the d axis. Therefore, the dq axis rotating coordinate system rotates in synchronization with the electric motor.

The current (output AC current) flowing through the electric motor is detected by, for example, the current detection unit 5 (see FIG. 1). The current detection unit 5 is, for example, a current detection circuit, detects the currents iu, iv, iw flowing through the output lines Pu, Pv, Pw, and outputs them to the fixed/rotational coordinate conversion unit 36. The fixed/rotating coordinate conversion unit 36 performs coordinate conversion on the currents iu, iv, iw to calculate the currents id, iq in the dq axis rotating coordinate system. The phase difference between the dq axis rotating coordinate system and the fixed coordinate system required for coordinate conversion may be calculated, for example, by integrating the rotating speed ω (or the rotating speed command ω*).

In the example of FIG. 1, the current detector 5 detects the currents iu, iv, iw, but it may detect any two. Since the sum of the currents iu, iv, iw is ideally zero, the remaining one current can be calculated from these two currents. Further, in the example of FIG. 1, the current detection unit 5 directly detects the currents iu, iv, iw, but may detect the direct current flowing through the DC bus LH or the DC bus LL. Specifically, the current detector 5 may detect a DC current flowing through the DC bus LH or the DC bus LL between the capacitor C1 and the power converter 2. This DC current matches the current corresponding to the switch pattern of the switching elements S1 to S6 among the currents iu, iv, and iw. Therefore, the currents iu, iv, iw can be grasped based on the switch pattern and the direct current. Such current detection is called a so-called 1-shunt method.

The voltage command generator 31 generates the voltage command V* based on, for example, the deviation Δω and the currents id and iq. For example, the voltage command generator 31 can generate the voltage command V* by using feedforward control based on the voltage equation of the electric motor and control such as proportional-plus-integral control for the deviation Δω. This voltage command V* is expressed by the component of each axis in the control coordinate system. For example, the voltage command V* includes a d-axis voltage command Vd* that is the d-axis component thereof and a q-axis voltage command Vq* that is the q-axis component thereof. That is, the voltage command V* is expressed in a rectangular coordinate system. The voltage command generator 31 outputs this voltage command V* to the orthogonal/polar coordinate converter 32.

In the above example, the control circuit 3 calculates the voltage command V* using the dq axis rotating coordinate system, but another rotating coordinate system may be used. Hereinafter, the coordinate system for calculating the voltage command V* is also referred to as a control coordinate system.

The orthogonal/polar coordinate conversion unit 32 performs coordinate conversion from the rectangular coordinate system to the polar coordinate system for the voltage command V*. In the polar coordinate system, the voltage command V* is expressed by its size and phase, so the orthogonal/polar coordinate conversion unit 32 causes the amplitude command D*, which is the size of the voltage command V*, and the voltage phase command θv*, which is its phase. * And will be calculated. The phase here is the phase in the control coordinate system. The orthogonal/polar coordinate conversion unit 32 outputs the amplitude command D* to the rotating/fixed coordinate conversion unit 34, and outputs the voltage phase command θv** to the voltage phase correction unit 33.

The voltage VL is also input to the voltage phase correction unit 33. The voltage VL is detected by the detector 4 (see FIG. 1). The detection unit 4 is a voltage detection circuit that detects the voltage VL and outputs it to the control circuit 3 (more specifically, the voltage phase correction unit 33). The detection unit 4 detects the voltage VL with reference to, for example, the potential of one end of the reactor L1 on the capacitor C1 side.

The voltage phase correction unit 33 corrects the voltage phase command θv** to generate the voltage phase command θv* so that the load power factor increases in accordance with the decrease in the voltage VL. In the example of FIG. 3, for example, the voltage phase correction unit 33 includes a power factor calculation unit 331, a power factor correction unit 332, a phase calculation unit 333, and a current phase calculation unit 334.

The currents id and iq are input from the fixed/rotational coordinate conversion unit 36 to the current phase calculation unit 334. The current phase calculator 334 calculates the current phase θi, which is the phase, based on the currents id and iq. For example, the current phase calculation unit 334 calculates the current phase θi by converting the currents id and iq from the rectangular coordinate system to the polar coordinate system. The current phase θi is the phase in the same coordinate system as the voltage phase command θv**, and here is the current phase in the control coordinate system. The current phase calculator 334 outputs the current phase θi to the power factor calculator 331 and the phase calculator 333.

The voltage phase command θv** is also input to the power factor calculation unit 331. The power factor calculation unit 331 calculates the power factor command PF** based on the voltage phase command θv** and the current phase θi. FIG. 4 is a functional block diagram schematically showing an example of a more specific internal configuration of the voltage phase correction unit 33. As illustrated in FIG. 4, the power factor calculation unit 331 includes a subtractor 3311 and a calculation unit 3312. The voltage phase command θv** and the current phase θi are input to the subtractor 3311. The subtractor 3311 subtracts the current phase θi from the voltage phase command θv**, calculates the phase difference command θ**, and outputs the phase difference command θ** to the calculation unit 3312. The phase difference command θ** is a command regarding the phase difference between the output AC voltage and the output AC current. The calculation unit 3312 calculates the cosine value (cos θ**) of the phase difference command θ**, and outputs the result to the power factor correction unit 332 as the power factor command PF**.

The voltage VL is also input to the power factor correction unit 332. The power factor correction unit 332 calculates the power factor command PF* based on the power factor command PF** and the voltage VL. Specifically, the power factor correction unit 332 corrects the power factor command PF** so that the power factor command PF* increases as the voltage VL decreases.

In the example of FIGS. 3 and 4, the power factor correction unit 332 includes a multiplier 3321 and a subtractor 3322. The voltage VL and the gain K are input to the multiplier 3321. The gain K may be set in advance and stored in the storage medium of the control circuit 3, for example. The multiplier 3321 multiplies the gain K and the voltage VL, and outputs the result to the subtractor 3322. The power factor command PF** is also input to the subtractor 3322. The subtractor 3322 subtracts the output of the multiplier 3321 from the power factor command PF**, and outputs the result as the power factor command PF*. That is, the power factor correction unit 332 of FIG. 4 substantially calculates the equation (3). That is, the load power factor is corrected based on the equation (3).

The power factor command PF* and the current phase θi are input to the phase calculator 333. The phase calculator 333 calculates the voltage phase command θv* based on the power factor command PF* and the current phase θi. For example, the phase calculation unit 333 includes a calculation unit 3331 and an adder 3332. The power factor command PF* is input to the calculation unit 3331. The calculation unit 3331 calculates the inverse cosine value of the power factor command PF* and outputs the result to the adder 3332 as the phase difference command θ*. The current phase θi is also input to the adder 3332. The adder 3332 adds the current phase θi to the phase difference command θ* and outputs the result as the voltage phase command θv* to the rotating/fixed coordinate conversion unit 34. The following equations show arithmetic expressions performed by the voltage phase correction unit 33 in FIG.

θv*=cos ⁻¹ {cos(θv**−θi)−K·VL}+θi (9)

The rotation/fixed coordinate conversion unit 34 performs coordinate conversion on the voltage command indicated by the amplitude command D* and the voltage phase command θv* to generate voltage commands Vu*, Vv*, Vw* in the fixed coordinate system. Then, these commands are output to the control signal generation unit 35. The control signal generator 35 generates the control signal S based on the voltage commands Vu*, Vv*, Vw*. For example, the control signal generation unit 35 generates the control signal S based on the comparison between each of the voltage commands Vu*, Vv*, Vw* and the carrier (for example, triangular wave). Such a method of generating the control signal S is a method used in pulse width modulation.

The power converter 2 operates based on the control signal S, and ideally outputs the output AC voltage indicated by the voltage commands Vu*, Vv*, Vw* to the load M1.

With such a control circuit 3, the load power factor is controlled so that the load power factor increases in accordance with the reduction of the voltage VL. In other words, the load power factor is controlled so that the load power factor decreases as the voltage VL increases. Therefore, the pulsating component Vdch of the DC voltage Vdc can be suppressed.

Moreover, according to this control, the amplitude command D* does not need to be corrected based on the voltage VL. Here, as a comparative example, a control for correcting the amplitude command D* instead of correcting the voltage phase command θv** will be briefly described. For example, the product of the voltage VL and the gain K is subtracted from the amplitude command D* to calculate the corrected amplitude command D*'.

Then, for example, based on the voltage command represented by the amplitude command D*′ and the voltage phase command θv*, the control signal S is generated in the same manner as described above. As a result, the amplitude of the output AC voltage increases as the voltage VL decreases. FIG. 5 schematically shows an example of the voltage control rate D and the phase difference θ according to the comparative example. The voltage control rate D is the ratio of the amplitude of the output AC voltage to the DC voltage Vdc. As shown in FIG. 5, the phase difference θ is almost constant, but the amplitude of the voltage control rate D pulsates. The pulsation control of the voltage control rate D can reduce the pulsation component of the DC voltage Vdc. However, since the voltage control rate D pulsates, the average value Da of the voltage control rate D becomes smaller than the maximum value Dp of the voltage control rate D.

FIG. 6 schematically shows an example of the voltage control rate D and the phase difference θ according to the present embodiment. As shown in FIG. 6, according to the present embodiment, the voltage control rate D is substantially constant, but the phase difference θ pulsates. In the present embodiment, the pulsation of the phase difference θ reduces the amplitude of the pulsation component Vdch of the DC voltage Vdc. In the present embodiment, since it is not necessary to pulsate the voltage control rate D according to the voltage VL, it is possible to avoid or suppress the decrease in the voltage control rate D. Note that the maximum value Dp of the voltage control rate D is determined according to the value of the DC voltage Vdc, and in the present embodiment, this maximum value Dp can be adopted as the upper limit value of the voltage utilization rate. That is, according to the present embodiment, it is possible to avoid or suppress a decrease in the upper limit value of the voltage utilization rate.

Further, in the above-described specific example, the potential of one end of the reactor L1 on the capacitor C1 side is adopted as the reference potential of the voltage VL. However, the potential of the other end of the reactor L1 may be adopted. In this case, since the polarity of the voltage VL is reversed, the load power factor may be controlled so as to increase as the voltage VL increases, in other words, to decrease as the voltage VL decreases.

It can also be described that the detection unit 4 is a pulsation component detection unit that detects the voltage VL based on the potential at one end of the reactor L1 on the side of the capacitor C1 as the pulsation component Vdch of the opposite phase. When detecting the voltage VL based on the potential of the other end of the reactor L1, the detection unit 4 can also be described as detecting the voltage VL as the pulsation component Vdch of the same phase.

<Limiter>
FIG. 7 is a diagram schematically showing another example of the internal configuration of the voltage phase correction unit 33A. The voltage phase correction unit 33A of FIG. 7 is different from the voltage phase correction unit 33 of FIG. 4 in the internal configuration of the power factor correction unit 332. The voltage phase correction unit 33A in FIG. 7 further includes a limiter 3323. The power factor command PF* is input to the limiter 3323. Limiter 3323 determines whether power factor command PF* is greater than one. The judgment of the size can be made by using, for example, a comparator. The judgments of other sizes are the same.

When the power factor command PF* is larger than 1, the limiter 3323 sets the power factor command PF* to 1 and outputs the power factor command PF* to the calculation unit 3331. If the power factor command PF* exceeds 1, the calculation of the inverse cosine value by the calculation unit 3331 is not performed properly. In the example of FIG. 7, since the limiter 3323 sets the power factor command PF* to 1 when the power factor command PF* exceeds 1, the calculation unit 3331 can appropriately calculate the voltage phase command θv*.

Similarly, limiter 3323 determines whether power factor command PF* is greater than -1. When the power factor command PF* is less than -1, the power factor command PF* is set to -1. As a result, even when the calculation result is less than -1, the calculation unit 3331 can appropriately calculate the voltage phase command θv*.

As described above, the voltage phase command θv* is calculated even when the power factor command PF* is less than −1 or exceeds 1. That is, the voltage phase command θv** is corrected to calculate the voltage phase command θv*. Therefore, even in such a case, the amplitude of the pulsating component Vdch of the DC voltage Vdc can be reduced.

<Correction value H>
As described above, in the present embodiment, control circuit 3 controls power converter 2 to increase the load power factor in accordance with increase in pulsation component Vdch (that is, decrease in voltage VL). Specifically, as illustrated in the equation (3), the control circuit 3 changes the load power factor with a correction value (the second term on the right side of the equation (3)) that increases according to an increase in the pulsation component Vdch. ing. Hereinafter, this correction value is referred to as a correction value H. The correction value H is represented by “−K·VL” in the equation (3).

As can be understood from the equation (8), when the correction represented by the equation (3) is performed, the DC current idc is affected by the voltage control rate D and the effective value io_rms of the output AC current. Hereinafter, the second term on the right side of the equation (8) will be referred to as a correction value Hi for the current. That is, when the load power factor is corrected with the correction value H, the DC current idc is corrected with the correction value Hi approximately.

The correction value Hi is proportional to the voltage control rate D and the effective value io_rms, as shown in the equation (8). Therefore, when the voltage control rate D and the effective value io_rms are small, the absolute value (correction amount) of the correction value Hi becomes small, and the effect of reducing the amplitude of the pulsating component Vdch of the DC voltage Vdc becomes small. Since the voltage control rate D and the effective value io_rms tend to increase as the rotational speed ω increases, it can be said that the effect of reducing the pulsating component Vdch decreases when the rotational speed ω decreases. Therefore, it is intended to reduce the influence of the voltage control rate D or the effective value io_rms of the output AC current.

First, it is intended to reduce the influence of the voltage control rate D. As can be understood from the equation (8), the correction value Hi includes the voltage control rate D and the gain K as factors. Therefore, the gain K is set to be larger as the voltage control rate D is smaller. That is, the correction value H is calculated such that the absolute value of the correction value H (for example, −K·VL) increases as the voltage control rate D decreases.

Thereby, in the correction value Hi, it is possible to suppress the reduction of the product D·K due to the reduction of the voltage control rate D. As a result, reduction of the absolute value of the correction value Hi can be suppressed. As a more specific example, the gain K may be set by the reciprocal of the voltage control rate D as shown in the following equation.

K=K'/D (10)

Here, K'is, for example, a preset value. Substituting equation (10) into equation (8) cancels the voltage control rate D. Therefore, even if the voltage control rate D changes, the correction value Hi ideally does not change. Therefore, even if the voltage control rate D is reduced, the effect of reducing the amplitude of the pulsating component Vdch of the DC voltage Vdc is not impaired.

Next, it is intended to reduce the influence of the effective value io_rms of the output alternating current. As can be understood from the equation (8), the correction value Hi includes the effective value io_rms and the gain K as factors. Therefore, the gain K may be set larger as the effective value io_rms is smaller. In other words, the correction value H is calculated such that the smaller the effective value io_rms, in other words, the smaller the amplitude of the output AC current, the larger the absolute value of the correction value H.

As a result, the reduction of the product io_rms·K due to the reduction of the effective value io_rms can be suppressed. As a result, reduction of the absolute value of the correction value Hi can be suppressed. As a more specific example, the gain K may be set to the reciprocal of the effective value io_rms as shown in the following equation.

K=K'/io_rms (11)

Thereby, even if the effective value io_rms changes, the correction value Hi ideally does not change. Therefore, even if the effective value io_rms is reduced, the effect of reducing the pulsating component Vdch of the DC voltage Vdc is not impaired.

Of course, the gain K may be set based on both the voltage control rate D and the effective value io_rms. That is, the gain K may be set to be larger as the voltage control rate D is smaller and larger as the effective value io_rms is smaller. As a more specific example, the gain K may be set to the reciprocal of the product of the voltage control rate D and the effective value io_rms, as shown in the following equation.

K=K'/(D.io_rms) (12)

Thereby, even if each of the voltage control rate D and the effective value io_rms changes, the correction value Hi ideally does not change. Therefore, even if the voltage control rate D and the effective value io_rms are reduced, the effect of reducing the pulsating component Vdch of the DC voltage Vdc is not impaired.

Further, with reference to the equation (8), the correction value Hi includes √(3/2) as a coefficient. Therefore, in order to cancel this coefficient as well, the gain K may be set by the reciprocal of √(3/2). The following formula shows an example of the gain K.

K=√(2/3)·K′/(D·io_rms) (13)

Note that √3 in the equation (13) is due to √3 in the equation (1). That is, when the power converter 2 outputs a three-phase AC voltage, √3 of the equation (1) exists as a coefficient, and when the power converter 2 outputs a single-phase AC voltage, this √3 Does not exist. Therefore, in this case, the following formula may be adopted as the gain K.

K=√2·K′/(D·io_rms) (14)

FIG. 8 is a diagram schematically showing another example of the internal configuration of the voltage phase correction unit 33B. The voltage phase correction unit 33B of FIG. 8 is different from the voltage phase correction unit 33 of FIG. 4 in the internal configuration of the power factor correction unit 332. The voltage phase correction unit 33B of FIG. 8 further includes dividers 3324 and 3325. The gain K′ and the voltage control rate D are input to the divider 3324, for example. The divider 3324 divides the gain K′ by the voltage control rate D, and outputs the result (K′/D) to the divider 3325. The effective value io_rms of the current is also input to the divider 3325. The effective value io_rms is calculated based on the currents iu, iv, iw or the currents iq, id. The divider 3325 divides the result of the divider 3324 by the effective value io_rms, and outputs the result (K′/D/io_rms) to the multiplier 3321.

A multiplier that multiplies the gain K′ by √(2/3) or √2 may be provided.

<Reference potential of voltage VL>
In the above example, the potential at one end of the reactor L1 on the side of the capacitor C1 is adopted as the reference potential of the voltage VL. However, the potential of the other end of the reactor L1 may be adopted as the reference potential of the voltage VL. In this case, since the polarity of the voltage VL is reversed, the voltage VL has the same phase as the pulsating component Vdch. In this case, the control circuit 3 may control the power converter 2 so that the load power factor increases as the voltage VL increases. As a specific example, “−” in the second term on the right side of Expression (3) may be replaced with “+”.

<Coordinate system>
In the above example, the power factor command PF** is calculated using the voltage phase command θv** and the current phase θi in the control coordinate system. However, the coordinate system is arbitrary. For example, the voltage phase command and the current phase in the fixed coordinate system may be used. A specific example will be outlined. First, the voltage command V* generated by the voltage command generator 31 is subjected to coordinate conversion to calculate the voltage commands Vu**, Vv**, Vw** in the fixed coordinate system. Then, the amplitude command and the voltage phase command in the fixed coordinate system are calculated based on the voltage commands Vu**, Vv**, Vw**. Further, the current phase in the fixed coordinate system is calculated based on the currents iu, iv, iw detected by the current detector 5. Then, the cosine value of the difference between the voltage phase command and the current phase is calculated as the power factor command PF**. Next, based on the power factor command PF** and the voltage VL, as described above, the power factor command PF* is calculated, and the current phase is added to the arc cosine value thereof to calculate the corrected voltage phase command. To do. Next, the voltage commands Vu*, Vv*, Vw* are calculated based on the corrected voltage phase command and the amplitude command. This also controls the load power factor according to the voltage VL.

<Pulsation component Vdch of DC voltage Vdc>
In the above example, the load power factor is corrected using the voltage VL, but since the voltage VL corresponds to the pulsating component Vdch as described above, the load power factor may be corrected using the pulsating component Vdch. FIG. 9 is a diagram schematically showing another example of the configuration of the load driving device. The load driving device shown in FIG. 9 differs from the load driving device shown in FIG. The detection unit 4 in FIG. 9 detects the DC voltage Vdc instead of the voltage VL. Then, the detection unit 4 extracts the pulsating component Vdch from the DC voltage Vdc and outputs the pulsating component Vdch to the control circuit 3.

FIG. 10 schematically shows an example of the internal configuration of the detection unit 4. For example, the detection unit 4 may include the harmonic extraction unit 40. The harmonic extraction unit 40 extracts the pulsating component Vdch from the DC voltage Vdc. The harmonic extraction unit 40 includes, for example, a low pass filter 41 and a subtractor 42. The DC voltage Vdc is input to the low-pass filter 41. The low-pass filter 41 removes at least the pulsating component Vdch of the DC voltage Vdc, and outputs the removed DC voltage Vdc to the subtractor 42. The subtractor 42 subtracts the output of the low-pass filter 41 from the DC voltage Vdc that does not pass through the low-pass filter 41, calculates the pulsation component Vdch, and outputs the pulsation component Vdch to the control circuit 3.

The detection unit 4 may include a high-pass filter instead of the configuration of FIG. The high-pass filter extracts the pulsating component Vdch from the DC voltage Vdc and outputs this pulsating component Vdch to the control circuit 3.

The control circuit 3 controls the power converter 2 so that the load power factor increases in accordance with the increase of the pulsating component Vdch. For example, the load power factor is corrected using the following formula.

cos θ2=cos θ1+K·Vdch (15)

This also makes it possible to reduce the amplitude of the pulsating component Vdch of the DC voltage Vdc.

Further, by appropriately setting the cutoff frequency of the filter in the detection unit 4, the component to be removed can be easily adjusted. For example, the detection unit 4 may remove the DC component of the DC voltage Vdc and extract the pulsation component Vdch′ higher than the DC component. Then, the control circuit 3 may control the power converter 2 so as to increase the load power factor according to the increase of the pulsating component Vdch'.

In the above example, the harmonic extraction unit 40 is provided in the detection unit 4, but it may be provided in the control circuit 3.

Further, according to the detection unit 4 of FIG. 1, the process of applying the filter to the DC voltage Vdc is not necessary, so that the process can be simplified. In other words, the pulsation component Vdch can be easily detected.

In the present load drive device and control circuit, the various embodiments described above can be appropriately modified or omitted within the scope of the invention as long as they do not contradict each other.

2 Power converter 3 Control circuit 4 Detector 5 Current detector C1 Capacitor L1 Reactor LH, LL DC bus M1 Load

Claims (6)

A DC voltage (Vdc) containing a pulsating component (Vdch) is input, the DC voltage is converted to an AC voltage, the AC voltage is output to a load (M1), and a power converter that flows an AC current to the load ( A device for controlling 2),
A pulsating component detection unit (4) for detecting the pulsating component,
By controlling the power converter, the load power factor, which is the cosine value of the phase difference between the AC voltage and the AC current, a control circuit (3) that increases in accordance with an increase in the instantaneous value of the pulsating component, A power converter control device comprising. A current detection unit (5) for detecting the alternating current is provided,
The control circuit (3),
The first voltage phase command (θv**) for the voltage phase (θv) of the AC voltage is changed to the AC voltage so that the load power factor increases in accordance with the increase of the instantaneous value of the pulsating component (Vdch). Compensate based on the current phase of the current (θi) and the instantaneous value of the pulsating component (Vdch) to generate the second voltage phase command (θv*),
The control device for the power converter according to claim 1, wherein the control signal (S) for controlling the power converter (2) is generated based on the second voltage phase command. The control circuit (3),
Calculating a first power factor command (PF**) for the load power factor based on the first voltage phase command (θv**) and the current phase (θi),
The second power factor command (PF*) is calculated by performing correction to increase the first power factor command according to the increase of the instantaneous value of the pulsation component (Vdch),
The control device for the power converter according to claim 2, wherein the second voltage phase command (θv*) is calculated based on the second power factor command and the current phase. The control circuit (3),
If the second power factor command (PF*) exceeds 1, set the second power factor command to 1,
And/or
The control device for a power converter according to claim 3, wherein the second power factor command is set to -1 when the second power factor command is less than -1. The control circuit (3),
Varying the load power factor with a correction value (H) that increases in accordance with an increase in the instantaneous value of the pulsation component (Vdch),
The correction value is calculated such that the absolute value of the correction value increases as the ratio of the amplitude (Vm) of the AC voltage to the DC voltage (Vdc) or the amplitude of the AC current decreases. The control device for the power converter according to claim 4. A first direct current bus (LH) and a second direct current bus (LL) to which the direct current voltage (Vdc) is applied to each other are connected to the power converter (2),
A capacitor (C1) is connected between the first DC busbar and the second DC busbar,
A reactor (L1) is provided on the side opposite to the power converter (2) with respect to the capacitor, on the first DC bus or the second DC bus.
The pulsating component detection unit (4), the voltage of the reactor with the potential of one end of the reactor on the side of the capacitor as a reference potential (VL) is detected as a reverse phase of the pulsating component (Vdch), or, The control device for a power converter according to claim 1, wherein a voltage of the reactor having a potential of the other end of the reactor as a reference potential is detected as the pulsating component.

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