JP2011199938A - Power conversion apparatus and method for control of the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a power conversion apparatus that can suppress a phenomenon of magnetic deviation without adding a specification for magnetic deviation to a detector or a transformer, and to provide a method for control of the power conversion apparatus.SOLUTION: The power conversion apparatus includes the transformer, a converter which is connected to the transformer and converts an AC power supply voltage to a DC voltage, a power conversion apparatus 3 having an inverter which is connected to the converter, and a control device 5 which controls the conversion apparatus. The control device includes a zero-phase voltage generator 100 which generates a zero-phase voltage command, supplies the generated zero-phase voltage command to a pulse generator which controls switching elements constituting the power conversion apparatus, and makes the converter generate a zero-phase output voltage of a prescribed frequency, a determinator 101 which outputs a prescribed variable gain when an output frequency of the converter is within a range of a preset prescribed frequency, and a variable gain calculator 102 which multiplies an output of the zero-phase voltage generator by the variable gain and generates the zero-phase voltage command. The control device controls the power conversion apparatus on the basis of an output voltage command which is generated by adding the zero-phase voltage command being an output of the variable gain calculator to the output voltage command.

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 that detects a DC component of a converter AC output voltage, a current detection circuit that detects the polarity of a differential value of a transformer secondary current connected to the converter, and A control circuit is provided that varies the correction gain of the DC component of the converter AC output voltage in accordance with the detected value.

  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, wherein the converted DC is converted into a variable frequency 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, these methods increase the number of parts that make up the conversion, increasing the volume and cost of the converter.

  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 power converter comprising: a transformer; a converter connected to the transformer for converting an AC power supply voltage into a DC voltage; and an inverter connected to the converter for converting the DC voltage into an AC voltage and supplying the same to a load; A control device that generates an output voltage command, supplies the generated output voltage command to a pulse generator that controls a switching element that constitutes the power converter, and controls an output voltage and an output frequency of the converter; The control device generates a zero-phase voltage command, supplies the generated zero-phase voltage command to a pulse generator that controls a switching element constituting the power converter, and supplies the converter with a zero-phase output voltage having a predetermined frequency. A zero-phase voltage generator for generating the power converter, a determiner for outputting a predetermined variable gain when the output frequency of the power converter is in a predetermined frequency range, and a zero-phase voltage generator A variable gain calculator that generates a zero-phase voltage command by multiplying the output of the pressure generator by the variable gain is generated by adding the zero-phase voltage command that is the output of the variable gain calculator to the output voltage command. The power converter is controlled based on an output voltage command.

  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 explaining the power converter device concerning a 1st embodiment of the present invention. It is a figure explaining the demagnetization phenomenon in an input transformer. It is a figure which shows the electric current, voltage, and magnetic flux which flow into a power converter and a transformer in case the fluctuation frequency of a DC circuit corresponds with a power supply frequency. It is a figure which shows the change of an output voltage waveform at the time of changing the gain of the zero phase voltage added to the output voltage command of a converter. It is a figure which shows the waveform which showed the relationship of the electric current which flows into a power converter and a transformer, a voltage, and magnetic flux. It is a figure which shows the waveform which showed the relationship of the electric current which flows into a power converter and a transformer, a voltage, and magnetic flux.

  Embodiments of the present invention will be described below with reference to the accompanying drawings. FIG. 1 is a diagram illustrating a power conversion device according to a first embodiment of the present invention. In the figure, 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. Reference numeral 4 denotes an AC electric motor driven by electric 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 and speed of the AC motor 4 satisfy 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, which performs various arithmetic processes and outputs a signal for operating the power converter 3. To do.

  Next, main operations of the power converter control device 5 will be described. First, the power converter control device 5 inputs 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 to the speed controller 52 to control the speed control. 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 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 perform a three-phase AC. An excitation current detection value Id and a torque current detection value Iq, which are DC current detection values, are calculated from the current detection value and output.

  A 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 Then, the d-axis voltage command value Vd is calculated and output so that the excitation 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.

  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. In the frequency calculator 59, for example, when an induction motor is used, A frequency command ω1 is calculated by adding the slip frequency ωs corresponding to the load to the speed detector ωr and output. 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 AC voltage command value is input to the pulse generator 60, and the pulse generator 60 turns on / off the switching element of the power converter 3 so that the output voltage of the power converter 3 matches the output voltage command value. Calculate and output the signal.

  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. 2 is a diagram for explaining the demagnetization phenomenon in the input transformer. As the power converter 3, a multi-level inverter in which single-phase inverters are connected in series to output a multi-level output voltage is used. In FIG. 2, 1 is an AC power source, 2 is a transformer, 3 is a power converter configured by connecting a plurality of single-phase cell inverters 10 in series, The supplied AC power is converted to AC power having a variable voltage and variable frequency. 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 includes a forward converter 11 that converts an AC voltage into a DC voltage, and a smoothing capacitor 12 that smoothes the converted DC voltage. A pulse width modulation ( PWM) AC voltage is output. The outputs of the cell inverters 10 are added together in the U-phase cell unit 14u, the V-phase cell unit 14v, and the W-phase cell unit 14w, 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 to

  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 a signal for operating the power converter 3. . The main operation of the power converter control device 5 is as described above.

Here, the output power Pdc of the single-phase inverter is expressed by equation (1). The output of the single-phase inverter fluctuates at twice the output frequency ω1 of the power converter as shown in the second term of equation (1). In the equation (1), φ is the power factor angle of the motor.

  A DC current proportional to the power Pdc flows through the DC circuit of the single-phase cell inverter, and this current fluctuates at twice the output frequency of the power converter, as with the power Pdc.

    FIG. 3 shows the current and voltage flowing through the power converter and transformer when the fluctuation frequency of the DC circuit matches the power supply frequency, for example, when the power supply is 50 Hz and the power converter is operated at an output frequency of 25 Hz. It is a figure which shows magnetic flux. The current, voltage, and magnetic flux are three phases, but only one phase is displayed.

    When the converter output voltage command shown in FIG. 3A and the output frequency of the converter output current shown in FIG. 3B are 25 Hz, the direct current flowing through the DC circuit of the single-phase inverter shown in FIG. It fluctuates at 50 Hz, twice as much. Under the condition that the fluctuation frequency matches the power supply frequency of 50 Hz, as shown in FIG. 3D, the secondary current of the transformer is biased on one side and a DC component is included. When a direct current component flows in this way, as shown in FIG. 3 (e), the transformer has a demagnetization phenomenon in which the magnetic flux is biased, transiently excessive excitation current flows, harmonics, and transformer noise. (Beats), or loss increases, causing thermal problems.

    FIG. 4 is a diagram showing a change in the output voltage waveform when the gain of the zero-phase voltage added to the converter output voltage command is varied.

    Here, as shown in FIG. 4 (b), the frequency of the zero-phase voltage command is set to three times the output voltage command, the peak value of the zero-phase voltage command is matched with the peak value of the output voltage command, and the power factor angle of the motor The condition is that the phase of the minute is shifted. As a result, as shown in FIG. 4C, the output voltage waveform of the converter is changed, and the voltage component of 25 Hz that causes the bias magnetism phenomenon of the transformer is reduced. Since only the zero-phase voltage is changed, the line voltage waveform applied to the motor does not change. In the present invention, paying attention to such characteristics, by variably controlling the zero-phase voltage command to be added to the U, V, and W phases, the frequency component of the voltage that causes the magnet biasing phenomenon is reduced, and the DC biasing is reduced. Suppress.

  A control operation in the power conversion apparatus of the present embodiment will be described with reference to FIG. In order to generate the zero phase voltage and control the gain of the generated zero phase voltage, the zero phase voltage generator 100, the zero phase voltage variable condition determination unit 101, the zero phase voltage variable gain calculator 102, and the phase calculator 103 are provided. Install.

  The zero-phase voltage generator calculates and outputs a waveform that changes at a set cycle. The zero-phase voltage variable condition determiner 101 receives the output frequency command ω1, and determines that the zero-phase voltage variable condition is satisfied when the input frequency command ω1 falls within the frequency bandwidth set around the output frequency at which the bias is generated. Output a flag.

  The output determination flag is input to the zero-phase voltage variable gain calculator 102. The phase of the zero-phase voltage waveform output from the zero-phase voltage generator 100 is shifted in the phase calculator 103 that detects the phase of the current and calculates the phase, and is input to the zero-phase voltage variable gain calculator 102. .

  The zero-phase voltage variable gain calculator 102 multiplies the gain calculated by the zero-phase voltage waveform output from the phase calculator 103 based on the determination flag and outputs the result.

  The output of the zero phase voltage variable gain calculator 102 is added to the output voltage command Vref output from the voltage coordinate converter 58, and the output voltage command after the addition is input to the pulse generator 60, and the pulse generator 60 is input. A pulse signal corresponding to the output voltage command is supplied to the switching element of the converter 3.

  FIG. 5 is a diagram showing a waveform showing the relationship between the current, voltage, and magnetic flux flowing through the power converter and the transformer.

  As described above, by adding the zero-phase voltage to the output voltage command, it is possible to reduce the direct current component that flows on the secondary side of the transformer even in the operation state in which the bias is generated. For this reason, even in a power converter in which a power converter is connected to a power source via a transformer and the electric motor is driven at a variable speed by the power converter, the bias of the input side transformer of the converter generated during operation at a specific frequency With respect to the phenomenon, it is possible to suppress the magnetic demagnetization phenomenon of the transformer without adding a measure for increasing the magnetic demagnetization tolerance and a detector for suppressing the magnetic demagnetization.

  Note that when the load connected to the power converter is a synchronous motor, the load power factor of the power converter is 1, so the position of the zero-phase voltage command with respect to the output voltage command of the power converter as shown in FIG. The phase difference is zero. In this case, the phase calculator 103 shown in FIG. 1 is unnecessary.

DESCRIPTION OF SYMBOLS 1 AC power source 2 Transformer 3 Power converter 4 AC motor 5 Power converter control apparatus 6 Power converter output current detector 7 Speed detector 10 Single phase cell inverter 11 Forward converter 12 Smoothing capacitor 13 Inverter 14 Single phase Cell unit 21 Phase transformer 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 calculation 60 Pulse generator 100 Zero phase voltage generator 101 Zero phase voltage variable condition determiner 102 Zero phase voltage variable gain calculator 103 Phase calculator

Claims (7)

A power converter comprising: a transformer; a converter connected to the transformer for converting an AC power supply voltage into a DC voltage; and an inverter connected to the converter for converting the DC voltage into an AC voltage and supplying the same to a load; ,
A controller for generating an output voltage command, supplying the generated output voltage command to a pulse generator for controlling a switching element constituting the power converter, and controlling an output voltage and an output frequency of the converter;
The control device
A zero-phase voltage command is generated, and the generated zero-phase voltage command is supplied to a pulse generator that controls a switching element that constitutes the power converter, so that the converter generates a zero-phase output voltage having a predetermined frequency. A voltage generator;
A determinator that outputs a predetermined variable gain when the output frequency of the power converter is in a predetermined frequency range;
A variable gain computing unit that generates a zero phase voltage command by multiplying the zero phase voltage generator output by the variable gain,
A power conversion apparatus that controls the power converter based on an output voltage command generated by adding a zero-phase voltage command, which is an output of the variable gain calculator, to the output voltage command. The power conversion device according to claim 1,
A power conversion device comprising: a detection device that detects a load power factor of the power conversion device, wherein the phase of the zero-phase voltage is controlled according to the detected load power factor. A three-phase transformer, a converter connected to the three-phase transformer for converting an AC power supply voltage into a DC voltage, and an inverter connected to the converter for converting the DC voltage to an AC voltage and supplying the load to a load A power converter,
A controller for generating an output voltage command, supplying the generated output voltage command to a pulse generator for controlling a switching element constituting the power converter, and controlling an output voltage and an output frequency of the converter;
The control device
A third-phase zero-phase voltage command is generated, and the generated zero-phase voltage command is supplied to a pulse generator that controls a switching element constituting the power converter, and a zero-phase output voltage having a predetermined frequency is supplied to the converter. A zero-phase voltage generator for generating
A determinator that outputs a predetermined variable gain when the output frequency of the power converter is in a predetermined frequency range;
A variable gain computing unit that generates a zero phase voltage command by multiplying the zero phase voltage generator output by the variable gain,
A power conversion apparatus that controls the power converter based on an output voltage command generated by adding a zero-phase voltage command, which is an output of the variable gain calculator, to the output voltage command. The power conversion device according to claim 3,
A power conversion device comprising: a detection device that detects a load power factor of the power conversion device, wherein the phase of the zero-phase voltage is controlled according to the detected load power factor. A power converter comprising: a transformer; a converter connected to the transformer for converting an AC power supply voltage into a DC voltage; and an inverter connected to the converter for converting the DC voltage into an AC voltage and supplying the same to a load; ,
Electric power provided with a control device that generates an output voltage command, supplies the generated output voltage command to a pulse generator that controls a switching element that constitutes the power converter, and controls the output voltage and output frequency of the converter In the control method of the converter,
A zero-phase voltage command is generated, and the generated zero-phase voltage command is supplied to a pulse generator that controls a switching element that constitutes the power converter, so that the converter generates a zero-phase output voltage having a predetermined frequency. With a voltage generator,
When the output frequency of the power converter is in a predetermined frequency range, a zero-phase voltage command is generated by multiplying a zero-phase voltage generator output by the variable gain, and the generated zero-phase voltage command is output as the output A method for controlling a power converter, comprising: controlling the power converter based on an output voltage command generated by adding to a voltage command. In the control method of the power converter device according to claim 5,
A control method for a power converter, comprising: a detection device that detects a load power factor of the power converter, and controlling a phase of the zero-phase voltage according to the detected load power factor. In the control method of the power converter device according to claim 5,
The method of controlling a power converter, wherein the transformer is a three-phase transformer.