JP2012029438A - Power conversion apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a power conversion apparatus capable of reducing a ripple component in output current of a semiconductor switching element.SOLUTION: Double-frequency component adder circuits 15a to 15c correct a hysteresis band by adding a double frequency component of output current to a hysteresis band generated by switching frequency control amplifiers 11a to 11c and limiter circuits 14a to 14c. The switching frequency can be high because the hysteresis band at a peak (top and bottom of a waveform) of the waveform of the output current becomes low. The other, the switching frequency can be low because the hysteresis band at a vicinity of zero point of the output current becomes high. Speed in which the output current follows current commands can be high, because the switching frequency at a vicinity of peak of waveform of the output current becomes high. Thereby the ripple current can be small.

Description

  The present invention relates to a power converter having a semiconductor switching element, and more particularly to a power converter that performs switching control following a current command using a hysteresis comparator.

  2. Description of the Related Art Conventionally, a power conversion device that performs on / off control of a switch element by a hysteresis comparator has been proposed so that an output current that follows a current command can be obtained. For example, at the time of overload when the output current increases, the switching frequency is lowered by increasing the hysteresis width. On the other hand, when the output current is reduced, the switching frequency is increased by reducing the hysteresis width.

  For example, Japanese Patent Laying-Open No. 2007-20262 (Patent Document 1) discloses a configuration of a power converter for accurately controlling a switching frequency to a desired value. Specifically, the power conversion device includes means for detecting the switching frequency of the semiconductor switching element, and adjustment means for adjusting the hysteresis width so that the detected switching frequency follows the command value. By performing feedback control of the switching frequency, the conversion efficiency of the power conversion device can be stabilized.

JP 2007-20262 A

  According to the configuration of the conventional power converter, the switching frequency can be controlled by increasing or decreasing the hysteresis width of the hysteresis comparator. However, at a constant switching frequency, the hysteresis width is constant, that is, linear.

  On the other hand, the difference between the current command and the output current, that is, the current deviation is small near the peak of the waveform of the output current, but is large near the zero point of the waveform. When the current deviation changes as described above with the hysteresis width kept constant, the current deviation becomes small near the peak of the waveform of the output current, so the speed at which the output current follows the current command decreases. On the other hand, in the vicinity of the zero point of the output current waveform, the current deviation increases, so the speed at which the output current follows the current command increases.

  When the tracking speed is reduced, a large ripple component (ripple current) is generated in the output current. For this reason, the subject that the distortion rate of an output voltage deteriorates may arise.

  The present invention has been made to solve the above-described problems, and provides a power conversion device capable of reducing a ripple component included in an output current of a semiconductor switching element.

  A power conversion device according to one aspect of the present invention compares a deviation between an output current and a current command with a hysteresis width so that the self-excited semiconductor switching device and the output current of the self-excited semiconductor switching device follow the current command. A hysteresis comparator for changing the switching frequency of the self-excited semiconductor switching element, a detection unit for detecting the switching frequency of the self-excited semiconductor switching element, a detected value of the switching frequency detected by the detection unit, and the switching frequency A setting unit that sets a hysteresis width based on a deviation between the command value and a correction unit that corrects the hysteresis width set by the setting unit and applies the corrected hysteresis width to the hysteresis comparator. . The correction unit sets the hysteresis width near the peak of the output current waveform to be smaller than the width set by the setting unit, while the hysteresis width is set by the setting unit near the zero point of the output current waveform. Larger than the width.

  According to the present invention, the speed at which the output current follows the current command can be increased at the peak of the waveform of the output current of the semiconductor switching element. Thereby, a ripple current can be reduced.

It is a block diagram of the power converter device which concerns on embodiment of this invention. It is a figure which shows the structural example of the circuit applicable to each of the double frequency component addition circuit 15a-15c shown in FIG. It is a 1st figure explaining operation | movement of the power converter device which has a structure which abbreviate | omitted the double frequency component addition circuit from the structure of FIG. FIG. 7 is a second diagram for explaining the operation of the power conversion apparatus having a configuration in which the double frequency component addition circuit is omitted from the configuration of FIG. 1. It is a figure explaining operation | movement of the power converter device which concerns on embodiment of this invention provided with the structure shown in FIG. It is a figure for demonstrating the 1st modification of embodiment of this invention. It is a figure for demonstrating operation | movement of the triangular wave addition circuit shown in FIG. It is a figure for demonstrating the 2nd modification of embodiment of this invention. It is a figure for demonstrating operation | movement of the rectangular wave addition circuit shown in FIG.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. In the drawings, the same or corresponding parts are denoted by the same reference numerals and description thereof will not be repeated.

  FIG. 1 is a configuration diagram of a power conversion device according to an embodiment of the present invention. Referring to FIG. 1, power conversion device 100 according to the embodiment of the present invention is an uninterruptible power supply device including a three-phase inverter 50. The power conversion device 100 includes a DC power source 1, an inverter 50, a reactor 3, and a capacitor 4.

  The inverter 50 converts DC power from the DC power source 1 into AC power. The inverter 50 includes IGBT elements 2a to 2f as semiconductor switching elements. IGBT elements 2a and 2b are connected in series. IGBT elements 2c and 2d are connected in series. IGBT elements 2e and 2f are connected in series. A diode D is connected in antiparallel to each of the IGBT elements 2a to 2f. The AC output from the inverter 50 is supplied to the load 5 through a filter circuit including the reactor 3 and the capacitor 4.

  The power conversion device 100 further includes current sensors 6a to 6c, subtraction units 8a to 8c, 17a to 17c, hysteresis comparators 9a to 9c, gate circuits 10a to 10c, switching frequency control amplifiers 11a to 11c, and limiters. Circuits 14a to 14c and double frequency (2f) component addition circuits 15a to 15c are provided.

  Current sensors 6 a to 6 c detect the output current of inverter 50. The subtracting units 8a to 8c calculate a deviation (current deviation) between the current command 7 and the output current detected by the current sensors 6a to 6c. The hysteresis comparators 9a to 9c compare the current deviation with the hysteresis widths 18a to 18c. Gate circuits 10a-10c generate gate drive signals for IGBT elements 2a-2f based on outputs from hysteresis comparators 9a-9c, respectively. The switching frequency control amplifiers 11a to 11c set a hysteresis width. The frequency / voltage converters 13 a to 13 c detect the switching frequency 16. The subtractors 17a to 17c calculate a deviation (frequency deviation) between the switching frequency 16 and the frequency command 12, and give the frequency deviation to the switching frequency control amplifiers 11a to 11c. The limiter circuits 14a to 14c limit the hysteresis width set by the switching frequency control amplifiers 11a to 11c within a predetermined range.

  Next, the operation for one phase of the inverter 50 will be described. The operation for the remaining two phases is similar to the operation described below, and is different only in that the phase is different by 120 ° from the operation for one phase described below. For this reason, subsequent detailed description regarding the operation | movement for the remaining two phases is not repeated. Specifically, the operation of the IGBT elements 2a and 2b (for U phase) will be described below.

  A current command Isu * is applied so that the output AC voltage of IGBT elements 2a and 2b is constant. A deviation (= Isu * −Iu) between the output current Iu detected by the current sensor 6a and the current command Isu * is input to the hysteresis comparator 9a.

  The frequency / voltage converter 13a detects the switching frequency 13a of the IGBT elements 2a and 2b based on the output of the hysteresis comparator 9a. The subtraction unit 8a calculates a deviation (= Fu * -Fu) between the switching frequency and the switching frequency command Fu *. The deviation is amplified by the switching frequency control amplifier 11 a and is limited by the limiter circuit 14. Thereby, a hysteresis width is generated.

  When the switching frequency Fu detected by the frequency / voltage converter 13a is larger than the switching frequency command Fu *, the hysteresis width is increased by the switching frequency control amplifier 11a. As a result, the switching frequency Fu decreases. On the other hand, when the switching frequency Fu is smaller than the switching frequency command Fu *, the hysteresis width is reduced by the switching frequency control amplifier 11a. As a result, the switching frequency Fu increases.

  Thus, in the embodiment of the present invention, control is performed so that the switching frequency follows the switching frequency command. As a result, fluctuations in the inductance value of the reactor 3, fluctuations in the voltage of the DC power supply 1, fluctuations in the output AC voltage, and the like are suppressed, and the switching frequency is accurately controlled to the command value (switching frequency command). be able to.

  The double frequency component adding circuit 15a corrects the hysteresis width by adding a frequency component twice the output current to the above hysteresis width. The hysteresis width 18a (= ΔIu) thus obtained is input to the hysteresis comparator 9a.

  The hysteresis comparator 9a inverts the output when the current deviation exceeds the hysteresis width 18a. The gate circuit 10a generates a gate drive signal for driving the IGBT elements 2a and 2b based on the on / off output of the hysteresis comparator 9a. The IGBT elements 2a and 2b are subjected to switching control (on / off control) by the gate drive signal, and convert DC power from the DC power source 1 into AC power. The AC power output from the IGBT elements 2 a and 2 b is supplied to the load 5 through the filter circuit including the reactor 3 and the capacitor 4. As a result, a stable AC voltage is supplied to the load.

  FIG. 2 is a diagram illustrating a configuration example of a circuit applicable to each of the double frequency component addition circuits 15a to 15c illustrated in FIG. Referring to FIG. 2, the double frequency component addition circuit 15 includes an amplifier (Amp) 21, a multiplier 22, a sine wave generator 23, and an adder 24.

  The amplifier 21 amplifies the hysteresis width from a limiter circuit (not shown) (for example, the limiter circuit 14a). Multiplier 22 doubles the phase θ of the output current of inverter 50 (for example, IGBT elements 2a and 2b connected in series). The phase θ can be generated based on, for example, a current command 7 (for example, a current command Isu *). The sine wave generator 23 receives the phase 2θ given from the multiplier 22 and generates a sine wave. As a result, a double frequency component of the output current is generated. The adder 24 adds the output of the sine wave generator 23 to the hysteresis width from the amplifier 21. Thereby, the hysteresis width is corrected.

  3 and 4 are diagrams illustrating the operation of the power conversion apparatus having a configuration in which the double frequency component addition circuit is omitted from the configuration in FIG. Referring to FIGS. 3 and 4, in order to accurately control the switching frequency to the command value (switching frequency command), the hysteresis width ΔIu generated by the switching frequency control amplifier 11a and the limiter circuit 14 is constant.

  The difference between the current command Isu * and the output current Iu, that is, the current deviation is small near the peak of the waveform of the output current Iu, but is large near the zero point of the waveform.

  As described above, the hysteresis comparator 9a inverts the output when the current deviation exceeds the hysteresis width ΔIu. The gate circuit 10a switches on / off the IGBT elements 2a and 2b when the output of the hysteresis comparator 9a is inverted. Therefore, near the peak of the waveform of the output current Iu, the current deviation is small, so that the output of the hysteresis comparator 9a is difficult to reverse. On the other hand, near the zero point of the waveform of the output current Iu, the current deviation is large. The output of the hysteresis comparator 9a is easily inverted. For this reason, the speed at which the output current Iu follows the current command Isu * is small near the peak of the waveform of the output current Iu, whereas the output current Iu is at the current command Isu * at the zero point of the waveform of the output current Iu. Increases the speed of following. When the follow-up speed is reduced due to the small current deviation, a large ripple component is generated in the output current. For this reason, the problem that the distortion rate of an output voltage deteriorates arises.

  FIG. 5 is a diagram for explaining the operation of the power conversion device according to the embodiment of the present invention having the configuration shown in FIG. Referring to FIGS. 1 and 5, according to the embodiment of the present invention, double frequency component adding circuit 15a has a hysteresis width before correction (that is, a hysteresis width generated by a switching frequency control amplifier and a limiter circuit). In addition, the hysteresis width is corrected by adding a frequency component twice the output current. As a result, the corrected hysteresis width periodically changes at twice the frequency of the output current. Since the hysteresis width is small at the peak of the output current waveform (the peak and valley of the waveform), the switching frequency can be increased. On the other hand, since the hysteresis width becomes large at the zero point of the output current waveform, the switching frequency can be lowered. Note that the average value of the switching frequency during one cycle of the waveform of the output current is a value that follows the frequency command 12.

  Since the switching frequency increases near the peak of the output current waveform, the speed at which the output current follows the current command can be increased. As a result, the ripple current can be reduced. Therefore, according to the embodiment of the present invention, it is possible to suppress deterioration of the distortion rate of the output voltage. On the other hand, the switching frequency decreases near the zero point of the output current waveform. As a result, if the output current is averaged over one period, the period during which the switching element is turned on / off is kept constant.

  In the above embodiment, in order to correct the hysteresis width, a frequency component that is twice the output current is added to the hysteresis width generated by the frequency / voltage converter 13 and the limiter circuit. However, the correction of the hysteresis width is not limited to the frequency component twice the output current. For example, even multiple frequency components can be used. In this case, in the configuration of FIG. 2, the multiplier 22 may multiply the phase θ by 2n (n is an integer equal to or greater than 1).

  Preferably, the even frequency component is a frequency component whose phase changes by (2m + 1) π (m is an arbitrary integer greater than or equal to 0) during T / 4, that is, 2 × ( 2m + 1) frequency components, specifically, a 2 × frequency component, a 6 × frequency component, a 10 × frequency component,... Also in this case, the valley of the waveform of the frequency component and the peak of the waveform of the output current overlap in time (the peak of the waveform of the frequency component and the valley of the waveform of the output current overlap in time). By aligning the phases, the peak of the frequency component and the zero point of the waveform of the output current can be overlapped in time. Therefore, the hysteresis width can be reduced in the vicinity of the peak of the waveform of the output current. Furthermore, the hysteresis width can be increased near the zero point of the output current waveform. However, the hysteresis width correction process can be simplified by using a double frequency component (that is, m = 0).

  As described above, the hysteresis width is corrected by reducing the hysteresis width generated by the frequency / voltage converter 13 and the limiter circuit at the peak of the output current waveform, and at the zero point of the output current waveform. What is necessary is just to enlarge a hysteresis width. Furthermore, the average value of the switching frequency in one cycle of the output current (in other words, the on / off cycle of the switching element) does not have to be changed by correcting the hysteresis width. Therefore, in the present invention, the waveform used for correcting the hysteresis width generated by the frequency / voltage converter 13 and the limiter circuit is not limited to a sine wave (or cosine wave).

  FIG. 6 is a diagram for explaining a first modification of the embodiment of the present invention. Referring to FIG. 6, power conversion device 100 </ b> A includes triangular wave addition circuits 35 a to 35 c instead of double frequency component addition circuits 15 a to 15 c.

  FIG. 7 is a diagram for explaining the operation of the triangular wave adder circuit shown in FIG. With reference to FIGS. 6 and 7, the valley portion of the triangular wave overlaps the peak and valley portions of the waveform of the output current on the time axis. On the other hand, the zero point of the waveform of the output current and the peak of the triangular wave overlap on the time axis. As a result, the hysteresis width decreases at the peak of the output current waveform, and the hysteresis width increases at the zero point of the output current waveform.

  FIG. 8 is a diagram for explaining a second modification of the embodiment of the present invention. Referring to FIG. 8, power conversion device 100 </ b> B includes rectangular wave addition circuits 45 a to 45 c instead of double frequency component addition circuit 15.

  FIG. 9 is a diagram for explaining the operation of the rectangular wave adder circuit shown in FIG. Referring to FIGS. 8 and 9, the valley portion of the rectangular wave overlaps with the peak and valley of the waveform of the output current on the time axis. On the other hand, the zero point of the output current waveform and the peak portion of the rectangular wave overlap on the time axis. Therefore, the hysteresis width decreases at the peak of the output current waveform, and the hysteresis width increases at the zero point of the output current waveform.

  In this embodiment, the case of a three-phase PWM inverter is shown, but switching control that follows a current command is performed using a hysteresis comparator, such as a single-phase circuit or a converter circuit that converts alternating current into direct current. Since it can be applied to a power converter, the same effect can be obtained.

  The embodiment disclosed this time should be considered as illustrative in all points and not restrictive. The scope of the present invention is defined by the terms of the claims, rather than the description above, and is intended to include any modifications within the scope and meaning equivalent to the terms of the claims.

  1 DC power supply, 2a to 2f IGBT element, 3 reactor, 4 capacitor, 5 load, 6a to 6c current sensor, 7 current command, 8a to 8c, 17a to 17c subtraction unit, 9a to 9c hysteresis comparator, 10a to 10c gate circuit 11a to 11c switching frequency control amplifier, 12 frequency command, 13a to 13c frequency / voltage converter, 14a to 14c limiter circuit, 15a to 15c double frequency component addition circuit, 16 switching frequency, 18a to 18c hysteresis width, 21 amplifier , 22 multiplier, 23 sine wave generator, 24 adder, 35a-35c triangular wave adder circuit, 45a-45c rectangular wave adder circuit, 50 inverter, 100, 100A, 100B power converter, D diode.

Claims (7)

A self-excited semiconductor switching element;
Hysteresis for changing the switching frequency of the self-excited semiconductor switching element by comparing the deviation between the output current and the current command with a hysteresis width in order to make the output current of the self-excited semiconductor switching element follow the current command A comparator,
A detection unit for detecting a switching frequency of the self-excited semiconductor switching element;
A setting unit that sets the hysteresis width based on a deviation between a detected value of the switching frequency detected by the detecting unit and a command value of the switching frequency;
A correction unit that corrects the hysteresis width set by the setting unit and gives the corrected hysteresis width to the hysteresis comparator;
The correction unit reduces the hysteresis width at the peak of the output current waveform to be smaller than the width set by the setting unit, while setting the hysteresis width at the zero point of the output current waveform. A power converter that is larger than the width set by the setting unit.   The correction unit adds a waveform that becomes a peak at the peak of the waveform of the output current and that becomes a valley at the zero point of the waveform of the output current to the hysteresis width set by the setting unit. The power converter according to claim 1, wherein the width is corrected.   The power converter according to claim 2, wherein the waveform is a waveform having a frequency that is an even multiple of the frequency of the output current.   4. The power converter according to claim 3, wherein the waveform is a waveform that is a frequency component of 2 × (2m + 1) times the output current when m is an integer of 0 or more.   The power converter according to claim 4, wherein m is 0.   The power converter according to claim 2, wherein the waveform is a triangular wave.   The power converter according to claim 2, wherein the waveform is a rectangular wave.

Images