JP5306268B2 - Power converter and control method of power converter - Google Patents

Description

  The present invention relates to a power conversion technique, and more particularly, to a power conversion device and a power conversion method capable of suppressing a bias magnetism generated in an input-side transformer provided on the input side of the power converter.

  Patent Document 1 is known as a conventional bias suppression device. In the apparatus disclosed in this document, a voltage detection circuit for detecting a DC component in a converter AC output voltage, a current detection circuit for detecting the polarity of a differential value of a transformer secondary current connected to the converter, and these And a control circuit that varies the correction gain of the DC component of the converter AC output voltage in accordance with the value detected in.

  In this device, the differential value of the transformer secondary current is calculated from the DC voltage component obtained by the detection circuit and the transformer secondary current. Based on this secondary current differential value, the correction gain is changed by using the correction gain variable means, and the voltage correction value is obtained by multiplying the detected value of the DC voltage by the changed correction gain. The output voltage command value of the converter is corrected by the voltage correction value, and becomes a waveform in which a DC component is superimposed on a normal AC voltage command. For this reason, it becomes possible to suppress the magnetism of the transformer by this output voltage waveform. In this apparatus, by calculating the differential value of the current and using it for the control, the demagnetization phenomenon can be instantaneously suppressed without being overcurrent by the correction.

JP-A-9-294380

  A transformer connected to an AC power source; and a power converter connected to the transformer for converting the power of the AC power source into a variable voltage variable frequency power. The direct current flowing in the direct current circuit of the power converter that converts to alternating current fluctuates at a frequency N times the output frequency of the power converter.

  Under the condition where the power supply frequency of the transformer and the fluctuation frequency of the direct current coincide with each other, a direct current component flows in the secondary winding of the transformer, and this direct current component causes a demagnetization phenomenon in which the magnetic flux of the transformer is biased. When the magnetism phenomenon occurs in the transformer, a large excitation current flows transiently. For this reason, problems such as an increase in harmonic current and overheating of the transformer due to overcurrent occur.

  As a countermeasure, in general, a transformer is detected by adding a detector to the converter, and the magnetism suppression control is performed on the output voltage of the converter from the detected value, or another method. There has been known a method for suppressing or eliminating a magnetic demagnetization phenomenon by applying a DC voltage from the power source to eliminate the magnetic demagnetization. However, in these systems, the number of parts constituting the converter increases, and the volume and cost of the converter increase.

  In addition, it is also possible to prevent the magnetization by self-equilibrium action by increasing the resistance to demagnetization by inserting a gap in the iron core of the transformer or by increasing the cross-sectional area of the iron core to reduce the magnetic flux density. However, this method increases the external dimensions, weight, and cost of the transformer. Also, standard products cannot be used.

  The present invention has been made in view of these problems, and provides a power conversion device and a control method for the power conversion device that can suppress a magnetic demagnetization phenomenon without adding a demagnetization specification to a detector or a transformer. It is to provide.

  In order to solve the above problems, the present invention employs the following means.

  A main transformer, a forward converter connected to the main transformer for converting an AC power supply voltage into a DC voltage, and an inverse converter connected to the forward converter for converting the DC voltage into an AC voltage and supplying the load to a load A power conversion device including a voltage generator, a voltage command generator that generates an output voltage command, and an output voltage command generated by the generator to a pulse generator that controls a switching element included in the power conversion device. A control device that controls an output voltage and an output frequency of the converter, the control device generating a phase shift signal that shifts a phase of an AC output of the power converter; A shift condition determiner that detects that the output is within a predetermined frequency range, and the phase shift calculation when the shift condition determiner detects that the output of the power converter is within a predetermined range. The output of is supplied to the voltage command generator shifts the output phase of the power converter.

  The present invention has the above-described configuration, and therefore provides a power conversion device and a control method for the power conversion device that can suppress a magnetic demagnetization phenomenon without adding specifications for preventing magnetic demagnetization to a detector or a transformer. be able to.

It is a figure which shows the whole structure of the power converter device concerning this embodiment. It is a figure which shows other embodiment. It is a figure explaining other embodiment. It is a figure explaining other embodiment. It is a figure explaining the demagnetization phenomenon in an input transformer. It is a figure which shows the electric current and voltage and magnetic flux which flow into a power converter when it drive | operates on the conditions where the power fluctuation frequency of a DC circuit corresponds with a power supply frequency. It is a figure which shows the relationship between the magnitude | size of the DC component which flows into the secondary side current of a transformer, and the phase of a converter output voltage. It is a figure explaining a phase shift pattern and a frequency shift pattern. The waveform at the time of shifting the output phase of a power converter is shown.

  Embodiments of the present invention will be described below with reference to the accompanying drawings.

[Embodiment 1]
FIG. 1 is a diagram illustrating an overall configuration of a power conversion device according to the present embodiment. In FIG. 1, 1 is an AC power source, 2 is a transformer that converts the voltage of the AC power source 1 into an input voltage of a power converter, and 3 is a power converter that converts power output from the transformer 2 into desired power. And 4 are AC motors driven by the power output from the power converter.

  Reference numeral 5 denotes a power converter control device that operates the power converter 3 so that the output torque or speed of the AC motor 4 satisfies desired characteristics. Reference numeral 6 denotes a current detector that detects and outputs the output current of the power converter 3. Reference numeral 7 denotes a speed detector which detects and outputs the speed of the AC motor 4.

  Output signals of the current detector 6 and the speed detector 7 are input to a power converter control device 5, and the power converter control device 5 performs various arithmetic processes and outputs a signal for operating the power converter 3. .

  Next, the operation of the power converter control device 5 will be described. First, in the power converter control device 5, the deviation between the speed command value ωrref output from the speed command generator 51 and the speed detection value ωr output from the speed detector 7 is input to the speed controller 52, and the speed control is performed. The instrument 52 calculates and outputs the torque current command value Iqref so that the speed detection value matches the speed command value.

  The current coordinate converter 53 receives the three-phase AC current detection value output from the current detector 6 and the phase θ output from the phase calculator 54. The current coordinate converter 53 uses the phase θ to An excitation current detection value Id and a torque current detection value Iq, which are DC current detection values, are calculated from the three-phase AC current detection values and output.

  The deviation between the torque current command value Iqref calculated by the speed controller 52 and the torque current detection value Iq output from the current coordinate converter 53 is input to the torque current controller 55, and the torque current controller 55 detects the torque current. The q-axis voltage command value Vq is calculated and output so that the value Iq matches the torque current command value Iqref.

  The deviation between the excitation current command value Idref output from the excitation current command setter 56 and the excitation current detection value Id output from the current coordinate converter 53 is input to the excitation current controller 57, and the excitation current controller 57 The d-axis voltage command value Vd is calculated and output so that the current detection value Id matches the excitation current command value Idref.

  The q-axis voltage command value Vq output from the torque current controller 55, the d-axis voltage command value Vd output from the excitation current controller 57, and the phase θ output from the phase calculator 54 are input to the voltage coordinate converter 58. Then, the voltage coordinate converter 58 calculates and outputs a three-phase AC voltage command value from the d-axis voltage command value Vd and the q-axis voltage command value Vq using the phase θ.

  On the other hand, the speed detection value ωr output from the speed detector 7 and the torque current detection value output from the current coordinate converter 53 are input to the frequency calculator 59. For example, when an induction motor is used as a load, the frequency calculator 59 adds the slip frequency ωs corresponding to the motor load to the speed detector ωr to calculate and output the frequency command ω1.

  The frequency command ω1 calculated by the frequency calculator 59 is input to the phase calculator 54. The phase calculator 54 integrates the frequency command ω1 to calculate the phase θ and outputs it.

  The three-phase AC voltage command value output from the voltage coordinate converter 58 is input to the pulse generator 60. In the pulse generator 60, the output voltage of the power converter 3 matches the three-phase AC output voltage command value. Thus, a pulse signal for turning on / off the switching element of the power converter 3 is calculated and output.

  As described above, the power converter controls the output AC voltage so that the output torque or speed of the AC motor 4 has desired characteristics.

  FIG. 5 is a diagram for explaining the demagnetization phenomenon in the input transformer. FIG. 5 shows an example in which a multi-level inverter in which single-phase inverters are connected in series to output a multi-level output voltage is used as the power converter 3.

  In FIG. 5, 1 is an AC power source, 2 is a transformer, 3 is a power converter in which a plurality of single-phase cell inverters 10 are connected in series, and AC power output from the transformer 2 is converted to AC with variable voltage and variable frequency. Convert to electricity. Reference numeral 4 denotes an AC motor driven by the power output from the power converter 3. Each single-phase cell inverter 10 in the power converter 3 converts the AC voltage into a DC voltage by the forward converter 11, smoothes the converted DC voltage by the smoothing capacitor 12, and performs pulse width modulation ( PWM) AC voltage is output.

  The outputs of the cell inverters 10, that is, the outputs of the U-phase cell unit 14u, the V-phase cell unit 14v, and the W-phase cell unit 14w are added together in each unit and output to the AC motor 4 as a three-phase AC voltage. Each phase cell unit is connected to a U-phase transformer 21u, a V-phase transformer 21v, and a W-phase transformer 21w corresponding to each phase, and the voltage of the AC power supply 1 is used as the input voltage of the power converter. Convert. The output signals of the current detector 6 and the speed detector 7 are input to the power converter control device 5, and the power converter control device 5 performs various arithmetic processes and outputs signals for operating the power converter 3. Output. The main operation of the power converter control device 5 is as described above.

Here, when a single-phase inverter is used, the power Pdc for one phase of the motor of the single-phase inverter is expressed by equation (1). As shown in the second term of the equation (1), the power Pdc for one phase greatly fluctuates at twice the output frequency ω1 of the power converter. Here, φ in the equation (1) is a power factor angle of the electric motor.

  For this reason, a direct current proportional to the power Pdc flows through the direct current circuit of the single-phase cell inverter, and, like the power Pdc, fluctuates at twice the output frequency of the power converter.

  FIG. 6 shows the current flowing through the power converter and the transformer when the power fluctuation frequency of the DC circuit matches the power supply frequency, for example, when the power supply is 50 Hz and the output frequency of the power converter is operated at 25 Hz. It is a figure which shows a voltage and magnetic flux. Although there are three phases, only one phase is displayed.

  When the converter output voltage command shown in FIG. 6 (a) and the output frequency of the converter output current shown in FIG. 6 (b) are 25 Hz, the direct current flowing in the DC circuit of the single-phase inverter shown in FIG. 6 (c) Fluctuates at twice 50 Hz. Under the condition that coincides with the power supply frequency of 50 Hz, as shown in FIG. 6D, the secondary current of the transformer is biased on one side and a DC component is included. When a DC current component flows in this way, as shown in FIG. 6E, a demagnetization phenomenon in which the magnetic flux of the transformer is deviated occurs. When the demagnetization phenomenon occurs, transiently excessive excitation is caused. Current may flow, causing higher harmonics, increased transformer noise (beats), and thermal problems due to increased losses.

    FIG. 7 is a diagram showing the relationship between the magnitude of the DC component flowing in the secondary current of the transformer shown in FIG. 6D and the phase of the converter output voltage. In FIG. 7, three phases U, V, and W are displayed. As shown in FIG. 7, the magnitude and polarity of the direct current vary with the phase of the converter output. Moreover, the phase which changes with U, V, and W phases differs.

    The present invention pays attention to this characteristic, and the phase of the output is +90 degrees and −90 degrees so that the DC current amounts of all phases U, V, and W cancel each other on the positive side and the negative side and become zero on average. The DC bias is prevented by shifting within the range.

  FIG. 1 is a diagram illustrating a control operation of the power converter according to the present embodiment. As shown in FIG. 7, in order to average the amount of direct current flowing on the secondary side of the transformer to zero, the output phase of the converter may be shifted between +90 degrees and -90 degrees.

  Therefore, as shown in FIG. 1, a phase shift computing unit 100, a phase shift condition determining unit 101, and a phase shift switching unit 102 are installed. The phase shift calculator calculates and outputs a phase shift amount Δθ that changes in proportion to time in a cycle set between +90 degrees and −90 degrees.

  The phase shift condition determiner 101 receives the output frequency command ω1, and outputs a determination flag indicating that the phase shift condition is satisfied when the output frequency command is within the bandwidth set around the output frequency at which the demagnetization occurs. The output determination flag is input to the phase shift switch 102, and the phase shift switch 102 changes the phase shift amount Δθ output from the phase shift calculator 100 to the phase shift amount Δθ = 0 based on the determination flag. Output. The output of the phase shift switch 102 is added to the output phase θ of the phase calculator 54, and θ + Δθ after the addition is input to the current coordinate converter 53 and the voltage coordinate converter 58, and each coordinate converter has a DC current detection value Id. , Iq and AC voltage command are calculated and output.

  By shifting the output phase of the power converter in this way, the DC current component flowing on the secondary side of the transformer can be canceled out and averaged to zero even in the operating state in which the bias is generated. For this reason, in a power converter that installs a transformer between the power source and the power converter and drives the motor at a variable speed, the transformer is designed to prevent the input side transformer from being demagnetized during operation at a specific frequency. The magnetic demagnetization phenomenon of the transformer can be suppressed without taking any special measures for increasing the magnetic demagnetization tolerance and without adding a detector for suppressing the magnetic demagnetization.

[Embodiment 2]
FIG. 2 is a diagram showing another embodiment. In this example, the change pattern of the phase shift amount is changed from that in FIG. 1 in order to suppress the fluctuation (rapid change) of the motor torque due to the phase shift.

  In the phase shift pattern, the phase change occurs abruptly at the point where Δθ turns from increasing to decreasing, or at the point where Δθ turns from decreasing to increasing, so that the motor torque fluctuates. In order to suppress this fluctuation amount, it is only necessary to mitigate sudden changes in the phase shift pattern. One method is to add a filter such as a first-order lag.

  However, as shown in FIG. 7, in order to cancel the DC current amount between the positive side and the negative side by the phase shift, it is necessary to approximate the pattern in which the phase shifts in the range of +90 degrees and −90 degrees. Therefore, setting the filter time constant and the shift width is complicated. Therefore, paying attention to the relationship between the phase and the frequency, the phase shift pattern is calculated and generated as follows.

  That is, since the phase is represented by the integration of the frequency, the relationship between the ideal phase shift pattern θ and the frequency f is as shown in FIG. That is, preventing a sudden change in phase shift is equivalent to limiting the rate of change with a rate limiter or the like to frequency changes from the positive side to the negative side and from the negative side to the positive side. However, only by limiting the frequency change rate, a phase shift between +90 degrees and -90 degrees does not occur. Therefore, the area S1 of the integral value of the frequency shown in FIG. 8A and FIG. It is preferable to change (increase) the change width of the frequency according to the change rate limit amount so that the integral value S2 of the frequency shown matches.

Next, generation of the frequency pattern shown in FIG. 8B used for suppressing the bias will be described. The relationship between the shift period T and the frequency change width Δh1ω1 is expressed by the equation (2) because the phase shift width is 90 degrees (π / 2). Further, the allowable torque fluctuation amount Δτ approximates the allowable speed change dωr / dt by the frequency change dω1 / dt, and when the inertia J of the mechanical system including the motor is used, the change rate limit value β is expressed by Equation (3). Is done.

  Here, it is desirable that the shift period T be smaller than the time constant at which the demagnetization occurs from the viewpoint of suppressing the demagnetization. On the other hand, if the frequency change rate limit range determined by the allowable torque fluctuation amount Δτ occupies most of the shift cycle T, the deviation from the ideal pattern that increases or decreases in proportion to time increases. The offset effect is degraded.

Accordingly, the ratio α of ΔT in the shift period T shown in FIG. 8B determined by the change rate limit β determined from the allowable torque fluctuation amount Δτ is defined as α = ΔT / T, and FIGS. When the frequency change width Δhω1 in FIG. 8B is obtained from the condition in which the frequency areas of b) coincide with each other, the frequency change width Δhω1 in FIG.

From the frequency change rate calculated from Δhω1 and ΔT obtained by equation (4) and equation (2), ΔT is expressed by equation (5).

  FIG. 2 is a diagram for explaining the control operation of the power conversion device according to the present embodiment based on the above relationship. In this example, a phase shift parameter calculator 200, a frequency shift calculator 201, and an integrator 202 are installed.

  The phase shift parameter calculator 200 receives the set value Δτ from the torque fluctuation allowable value setter 203 and the ratio rate α from the shift cycle ratio setter 204.

  In the phase shift parameter calculator 200, the frequency change rate β is calculated by the equation (3) from the torque fluctuation allowable value Δτ and the inertia J of the mechanical system including the motor, and ΔT is calculated from the frequency change rate β and the ratio α as (5). Next, the frequency change width Δhω1 is calculated from the equation (4) from ΔT and the rate α, and the shift period T is calculated from ΔT and the rate α by T = ΔT / α. To do. The frequency shift calculator 201 receives the calculated frequency change rate β, the shift periods T and ΔT, and the frequency change width Δhω1, and calculates the frequency shift amount Δω1 from the frequency shift pattern obtained using the input parameters. Output.

  The calculated frequency shift amount Δω1 is input to the integrator 202, and the integrator 202 integrates the frequency shift amount to calculate and output the phase shift amount Δθ. The output frequency command ω1 is input to the phase shift condition determiner 101, and when the output frequency command enters within the set bandwidth centered on the output frequency at which the demagnetization occurs, a determination flag for establishment of the phase shift condition is output. The output determination flag is input to the phase shift switch 102. The phase shift switch switches between the phase shift amount Δθ and the phase shift amount Δθ = 0 output from the integrator 202 based on the determination flag and outputs them. The output of the phase shift switch 102 is added to the output phase θ of the phase calculator 54, and θ + Δθ after the addition is input to the current coordinate converter 53 and the voltage coordinate converter 58, and the DC current detection value Id is input by each coordinate converter. , Iq and AC voltage command are calculated and output.

  FIG. 9 shows a waveform when the output phase of the power converter is shifted by applying the present invention under the same conditions as in FIG. 6. By applying the present invention, the transformer is demagnetized. Even in the conditions, the demagnetization phenomenon is suppressed.

  Thus, according to the present embodiment, it is possible to suppress the magnetism phenomenon of the transformer while suppressing the torque fluctuation due to the phase shift within the allowable range.

[Embodiment 3]
FIG. 3 is a view for explaining still another embodiment of the apparatus of the present invention. 2 is different from the example of FIG. 2 in that a torque fluctuation allowable value calculator 205 is installed to increase or decrease the allowable torque fluctuation amount Δτ according to the load state.

  In the second embodiment, the allowable torque fluctuation amount is given as a fixed value. However, the allowable torque fluctuation amount may vary depending on the operation state. For example, in the case where the forward converter is configured with a diode rectifier as shown in FIG. 5, when the torque fluctuation due to the phase shift increases to the negative side, the regenerative state occurs, the DC voltage increases, the overvoltage protection device operates, As a result, the switching element may be damaged.

  In particular, when the load is small, regeneration due to phase shift tends to occur. Therefore, the allowable torque fluctuation amount Δτ is increased or decreased according to the load state.

  FIG. 3 is a diagram for explaining the third embodiment of the present invention on the assumption of the above relationship. As shown in FIG. 3, a torque fluctuation allowable value calculator 205 is installed. Torque fluctuation allowable value calculator 205 receives a torque current, and torque fluctuation allowable value calculator 205 calculates and outputs an allowable torque fluctuation amount based on the magnitude of the input torque current. Specifically, a torque fluctuation allowable value is calculated by taking a margin for the current torque current so that the torque current does not swing to the negative side. Note that torque [%] ≈torque current [%] assuming that the magnetic flux is constant. However, when field weakening is performed, the magnetic flux weakening ratio may be multiplied as a coefficient. The calculated allowable torque fluctuation amount Δτ is input to the phase shift parameter calculator 200 together with the ratio rate from the shift cycle ratio setter 204, and thereafter the control operation described in the second embodiment is performed.

  According to the present embodiment, the allowable range of torque fluctuation due to phase shift is varied according to the operating state (load state) of the motor, so that the malfunction of the transformer (for example, overvoltage due to regeneration, etc.) can be prevented and Magnetic phenomenon can be suppressed.

[Embodiment 4]
FIG. 4 shows still another embodiment of the apparatus of the present invention. In the example of FIG. 3, a frequency shift switching unit 206 is installed, and Δω1 calculated by the frequency shift calculating unit 201 is changed by a frequency command calculating unit 59. It differs in that it is added to the calculated ω1.

  In the example of FIG. 3, the phase shift amount Δθ obtained by integrating the frequency shift amount Δω1 is added to θ calculated by the phase calculator 54, but a signal obtained by adding the frequency shift amount Δω1 to the frequency ω1 is obtained. Even if integration is performed, the same phase shift operation can be obtained.

  Therefore, in the example of FIG. 4, when the output frequency command ω1 is input to the phase shift condition determining unit 101 and the output frequency command is within the set bandwidth centering on the output frequency at which the bias is generated, the phase shift condition is determined. An establishment determination flag is output, and the output determination flag is input to the frequency shift switch 206. Based on the determination flag, the frequency shift switch 206 switches between the frequency shift amount Δω1 and the frequency shift amount Δω1 = 0 output from the frequency shift calculator 201 and outputs the result.

  The output of the frequency shift switch 206 is added to the output frequency ω1 of the frequency calculator 59, and ω1 + Δω1 after the addition is integrated by the phase calculator 54. The integrated phase is determined by the current coordinate converter 53 and the voltage coordinate converter 58. And the DC current detection values Id and Iq and the AC voltage command are calculated and output by each coordinate converter.

  In the above embodiment, the output phase of the converter is phase-shifted between +90 degrees and -90 degrees. However, even if the phase is shifted between integer multiples of 180 degrees as shown in FIG. The current can be zero as an average value. Although a control system using a speed detector has been shown, even in a speed sensorless control system that uses an estimated calculation of the rotational speed of the AC motor 4, any system that controls the frequency and phase of the output voltage of the power converter can be used. By applying the present invention, it is possible to suppress the magnetism of the transformer.

  As described above, according to the present invention, in a power conversion device in which a transformer is installed between a power source and a power converter and the electric motor is driven at a variable speed by the power converter, the phase shift computing unit, the phase shift condition The determination unit and the phase shift switching unit 2 are installed, and the phase shift computing unit computes and outputs a phase shift amount Δθ that changes in a cycle set between +90 degrees and −90 degrees. The output frequency command ω1 is input to the phase shift condition determiner, and a determination flag for establishment of the phase shift condition is output under the condition that the output frequency command is within the set bandwidth centered on the output frequency at which the demagnetization occurs. The output determination flag is input to the phase shift switch, and the phase shift switch switches and outputs the phase shift amount Δθ and the phase shift amount Δθ = 0 output from the phase shift calculator based on the determination flag. The output of the phase shift switch is added to the output phase θ of the phase calculator, and θ + Δθ after the addition is input to the current coordinate converter and the voltage coordinate converter, and the DC current detection value and the AC voltage command are sent by each coordinate converter. Calculate and output.

  This makes it possible to demagnetize without adding a measure for increasing the demagnetization resistance and a detector for suppressing the demagnetization against the demagnetization phenomenon of the input side transformer of the converter that occurs during operation at a specific frequency. The phenomenon can be suppressed.

DESCRIPTION OF SYMBOLS 1 AC power supply 2 Transformer 3 Power converter 4 AC motor 5 Power converter control apparatus 6 Power converter output current detector 7 Speed detector 51 Speed command generator 52 Speed controller 53 Current coordinate converter 54 Phase calculator 55 Torque current controller 56 Excitation current command setter 57 Excitation current controller 58 Voltage coordinate converter 59 Frequency command calculator 100 Phase shift calculator 101 Phase shift condition determiner 102 Phase shift switcher 200 Phase shift parameter calculator 201 Frequency shift Arithmetic unit 202 Integrator 203 Torque fluctuation allowable value setting unit 204 Shift cycle ratio setting unit 205 Torque fluctuation allowable value calculation unit 206 Frequency shift switching unit

Claims (11)

A main transformer, a forward converter connected to the main transformer for converting an AC power supply voltage into a DC voltage, and an inverse converter connected to the forward converter for converting the DC voltage into an AC voltage and supplying the load to a load A power conversion device equipped with a device;
A voltage command generator that generates an output voltage command, and an output voltage command generated by the generator to a pulse generator that controls a switching element that constitutes the power converter, and an output voltage and an output frequency of the converter A control device for controlling
The control device
A phase shift calculator for generating a phase shift signal for shifting the phase of the AC output of the power converter;
A shift condition determiner for detecting that the output of the converter is in a predetermined frequency range;
When the shift condition determiner detects that the output of the power converter is within a predetermined range, the output of the phase shift calculator is supplied to the voltage command generator, and the output phase of the power converter The power converter characterized by shifting.   The power converter according to claim 1, wherein the phase shift calculator calculates a phase shift amount in which the phase changes in a range of an integral multiple of 180 degrees.   3. The power conversion device according to claim 1, wherein the phase shift calculator calculates a phase shift amount in which the phase increases or decreases in proportion to time. A main transformer, a forward converter connected to the main transformer for converting an AC power supply voltage into a DC voltage, and an inverse converter connected to the forward converter for converting the DC voltage into an AC voltage and supplying the load to a load A power conversion device equipped with a device;
A voltage command generator that generates an output voltage command, and an output voltage command generated by the generator to a pulse generator that controls a switching element that constitutes the power converter, and an output voltage and an output frequency of the converter A control device for controlling
The control device
An integrator for calculating a phase shift signal for shifting the phase of the AC output of the power converter by integrating a frequency shift calculator output for generating a frequency shift signal;
A shift condition determiner for detecting that the output of the converter is in a predetermined frequency range;
When the shift condition determiner detects that the output of the power converter is within a predetermined range, the output of the phase shift calculator is supplied to the voltage command generator, and the output phase of the power converter A power conversion device comprising a phase shift switching device for shifting the power.   5. The power conversion device according to claim 4, wherein the phase shift amount obtained by integrating the frequency shift amount of the frequency shift computing unit is in a range of an integral multiple of 180 degrees.   6. The power conversion device according to claim 4, wherein the phase shift amount obtained by integrating the frequency shift amount of the frequency shift computing unit is increased or decreased in proportion to time.   5. The power conversion device according to claim 4, wherein the frequency shift computing unit changes when the frequency shift amount changes from the positive side to the negative side and from the negative side to the positive side, being limited by the set change rate, A phase conversion amount obtained by integrating the frequency shift amount thus obtained changes the phase in an integer multiple of 180 degrees.   8. The power conversion device according to claim 7, wherein the frequency shift computing unit includes a frequency shift parameter computing unit, a torque variation allowable amount setting unit, and a shift cycle ratio setting unit, and the frequency shift computing unit includes the set torque variation allowable amount. And a parameter obtained by calculating from the shift cycle ratio.   9. The electric power converter according to claim 8, wherein the torque fluctuation allowance calculator for calculating the torque fluctuation allowance used in the frequency shift parameter calculator increases or decreases the torque fluctuation allowance according to the torque current. Conversion device. A main transformer, a forward converter connected to the main transformer for converting an AC power supply voltage into a DC voltage, and an inverse converter connected to the forward converter for converting the DC voltage into an AC voltage and supplying the load to a load In the control method of the power converter, the output voltage command is supplied to a pulse generator that controls the switching elements constituting the power converter, and the output voltage and the output frequency of the converter are controlled.
A phase shift calculator for generating a phase shift signal for shifting the phase of the AC output voltage of the power converter;
When the output of the converter is within a predetermined frequency range, the output of the phase shift calculator is supplied to the voltage command generator to shift the output phase of the power converter. Control method. A main transformer, a forward converter connected to the main transformer for converting an AC power supply voltage into a DC voltage, and an inverse converter connected to the forward converter for converting the DC voltage into an AC voltage and supplying the load to a load In the control method of the power converter, the output voltage command is supplied to a pulse generator that controls the switching elements constituting the power converter, and the output voltage and the output frequency of the converter are controlled.
A phase shift signal that shifts the phase of the AC output voltage of the power converter, an integrator that integrates and calculates a frequency shift calculator output that generates a frequency shift signal;
When the output of the converter is in a predetermined frequency range in which the transformer is biased, the output of the phase shift calculator is supplied to the voltage command generator to shift the output phase of the power converter A method for controlling a power conversion device.