JP2006042579A - Switching control method, rectifier, and drive system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a switching control method in which a loss of reactor and a noise of the rector is minimized, while reducing switching loss at a PWM converter. <P>SOLUTION: A DC voltage applied on the both ends of a smoothing capacitor 4 is set to the level of the peak value of AC voltage obtained from a three-phase power source 1. As a result, a DC voltage, corresponding to the voltage value of the AC voltage, will be applied to both ends of the smoothing capacitor 4. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a rectification technique for performing rectification from alternating current to direct current.

  As a technique for performing AC-AC conversion, a technique using a back-to-back converter is known (for example, Non-Patent Document 1). In this method, for example, a reactor is inserted between a PWM (pulse width modulation) converter and an input power supply, and rectification is performed by the PWM converter. Thereby, harmonic noise can be reduced.

  On the other hand, in a PWM inverter, a technique of operating by two-phase modulation control has been proposed (for example, Patent Document 1). In addition, a technique for changing a DC voltage input to a PWM inverter by controlling a PWM converter has been proposed (for example, Patent Document 2).

JP 56-115183 A Japanese Patent Laid-Open No. 11-299290 “The back to back converter / control and design”, [online], Anders Carlsson, May 22, 1998, [searched July 12, 2004], Internet <URL: http://www.iea.lth.se /publications/point/Theses/pdf_files/LTH-IEA-1017.pdf>

  It is desirable that two-phase modulation control is also performed in the PWM converter in terms of reducing switching loss. However, the iron loss in the reactor increases and the noise generated from the reactor increases.

  The present invention has been made from such a viewpoint, and an object thereof is to provide a technique for reducing the loss of the reactor and the noise of the reactor while reducing the switching loss in the PWM converter.

  A first aspect of the switching control method according to the present invention is a method of controlling a PWM converter (3) that inputs a multiphase AC voltage via a reactor (2), rectifies the voltage and outputs a DC voltage. . The PWM converter is subjected to two-phase modulation control, and the DC voltage (Vdc) is variable according to the voltage value of the multiphase AC voltage.

  A second aspect of the switching control method according to the present invention is the switching control method according to the first aspect, wherein the DC voltage (Vdc) is set to a peak value (Vm) of a line voltage of the multiphase AC voltage. It is set almost equal.

  A third aspect of the switching control method according to the present invention is the switching control method according to the first aspect or the second aspect, wherein the DC voltage (Vdc) is applied across the smoothing capacitor (4). .

  A fourth aspect of the switching control method according to the present invention is the switching control method according to any of the first aspect, the second aspect, and the third aspect, and is based on the DC voltage (Vdc). The multiphase motor (6) is inverter-controlled.

  The rectifier according to the present invention inputs a multiphase AC voltage via the reactor (2) and the reactor, performs two-phase modulation control, rectifies this, and according to the voltage value of the multiphase AC voltage. And a PWM converter (3) that outputs a variable DC voltage.

  A drive system according to the present invention converts the DC voltage into another multiphase AC voltage, the rectifier (2, 3) according to claim 5, the smoothing capacitor (4) to which the DC voltage is applied, and the DC voltage. An inverter (5), and a motor (6) to which the other multiphase AC voltage is supplied from the inverter.

  According to the first aspect of the switching control method of the present invention, the loss of the reactor is reduced and the noise of the reactor is reduced as compared with the case where the DC voltage is constant. Compared with the case of three-phase modulation control, the switching loss of the PWM converter is reduced.

  According to the 2nd aspect of the switching control method concerning this invention, the effect of a 1st aspect is acquired notably.

  According to the third aspect of the switching control method of the present invention, the pulsation of the DC voltage can be reduced.

  According to the fourth aspect of the switching control method of the present invention, since the DC voltage can be lowered, the loss of the motor can also be reduced.

  According to the rectifier of the present invention, the loss of the reactor is reduced and the noise of the reactor is reduced as compared with the case where the DC voltage is constant. Compared with the case of three-phase modulation control, the switching loss of the PWM converter is reduced.

  According to the drive system of the present invention, the DC voltage can be lowered, so that the loss of the motor can be reduced.

  FIG. 1 is a block diagram showing the configuration of a drive system to which the present invention can be applied. The drive system includes a reactor 2, a PWM converter 3, a smoothing capacitor 4, an inverter 5, and a motor 6. A buck converter is used.

  The reactor 2 is provided for each phase. The PWM converter 3 receives a three-phase AC voltage from the three-phase power source 1 via the reactor 2 and rectifies it to output a DC voltage. Therefore, the PWM converter 3 can be grasped as a rectifier together with the reactor 2.

  The DC voltage is applied across the smoothing capacitor 4. The pulsation of the DC voltage is reduced by the electrostatic capacity of the smoothing capacitor 4. The inverter 5 converts the DC voltage into another three-phase AC voltage and supplies it to the motor 6. The motor 6 is driven according to another three-phase AC voltage.

  The PWM converter 3 has the same configuration as the inverter 5. However, in this case, the inverter 5 is not necessarily a PWM inverter.

  The PWM converter 3 and the inverter 5 include a pair of switching elements (for example, insulated gate bipolar transistors: hereinafter referred to as “IGBT”) provided for each phase and connected in series with each other. A diode is connected in reverse parallel to this. Here, the reverse parallel indicates that the diode and the IGBT are connected in parallel so that the forward directions are opposite to each other. With this connection, the diode functions as a freewheeling diode.

  Since the PWM converter 3 has the same configuration as that of the inverter 5, a known two-phase modulation control in the inverter 5 can be easily performed in the PWM converter 3.

  A technique for controlling the PWM converter so that the DC voltage applied across the smoothing capacitor 4 does not fluctuate even when the voltage of the three-phase power supply 1 fluctuates is known. For example, a PWM converter corresponding to a nominal three-phase voltage of 400 V (effective value) is required to correspond to a minimum voltage value of 357 V and a maximum value of 457 V, respectively.

  Therefore, even if 520V should be obtained corresponding to the peak value of the nominal voltage, if the switching operation of the PWM converter is the same, the DC voltage is set according to these minimum and maximum values. It will fluctuate from 505V to 646V. In order to avoid this, a technique has been proposed in which a predetermined command value for the DC voltage is given to the PWM converter, and the DC voltage is controlled to be constant regardless of fluctuations in the power supply voltage.

  The rectification by the PWM converter 3 can be stepped up, but cannot be stepped down (if the DC voltage is higher than the AC voltage, the free wheel diode is unnecessarily conducted). Therefore, if the DC voltage command value is set to 646 V, the PWM converter 3 can be used for smoothing capacitors not only when the minimum power supply voltage is input but also when the maximum power supply voltage is input. A DC voltage of 646 V can be applied to both ends of 4.

  However, when the value of the DC voltage is made constant as described above, the loss and noise of the reactor 2 increase when the two-phase modulation control is performed to reduce the switching loss.

  FIG. 2 is a table illustrating the loss (arbitrary unit) and noise (dB) of each part in various control modes as a table. In the figure, “Vdc constant” indicates the case where the value of the DC voltage as described above is controlled to be constant. “3 arm” indicates that the normal three-phase modulation control is employed, and “2 arm” indicates that the two-phase modulation control is employed. The data shown as the four columns in FIG. 2 shows the case where the outputs of the motor 6 are all aligned and the power supply voltage has an effective value of 357 V which is the minimum value.

  Each of the two columns on the left side of FIG. 2 shows the case where the DC voltage value is set to about 650 V, and the two columns on the right side show the case where the DC voltage value is set to 520 V. That is, in the case of controlling the two columns on the right side, the value of the DC voltage was set in correspondence with the effective value of the power supply voltage being 357 V, which is a value lower than 400 V. In other words, the result when the setting of the DC voltage is variable is shown.

  When the value of the DC voltage is fixed, the loss of the PWM converter 3 is reduced by performing the two-phase modulation control as compared with the case of performing the three-phase modulation control (244> 175). However, the iron loss of reactor 2 increases from 70 to 80 by more than 14%. Noise has also increased from 27 dB to 39 dB.

  On the other hand, even when the value of the DC voltage is variable, the loss of the PWM converter 3 is lower by performing the two-phase modulation control as compared with the case of performing the three-phase modulation control (185> 142). Moreover, the increase in the iron loss of the reactor 2 is only 4% from 51 to 53. Also, the amount of increase in noise is only 3 dB.

  Thus, by controlling the PWM converter 3 in two phases and making the DC voltage variable according to the power supply voltage, the loss of the reactor is reduced as compared with the case where the DC voltage is constant, and the reactor Reduce noise. Of course, the switching loss of the PWM converter is reduced as compared with the case of performing the three-phase modulation control.

  In other words, when three-phase modulation control is performed, if the value of the DC voltage is made variable, the loss is reduced compared to the case where the value of the DC voltage is fixed (818> 666, approximately 19% decrease). ). However, the noise is only reduced by 1 dB. In the case of performing two-phase modulation control, if the value of the DC voltage is made variable, the loss is reduced as compared with the case where the value of the DC voltage is fixed (750> 620, approximately 17% decrease). The loss reduction rate is inferior to that of three-phase modulation control, but is almost the same. Moreover, the noise when the two-phase modulation control is adopted is reduced by 10 dB.

  Such a remarkable noise reduction is because the magnitude of the amplitude of the ripple of the current flowing through the reactor 2 is more greatly affected by the DC voltage in the case of two-phase modulation than in the case of three-phase modulation. It is thought that.

  In both cases of performing three-phase modulation control and two-phase modulation control, the loss of the motor 6 can be reduced by reducing the DC voltage (308> 210, 330> 218).

  3, 4, and 5 are graphs showing current waveforms that flow in one phase of the reactor 2 in the case of three-phase modulation, and show cases where the values of the DC voltage are set to 730 V, 650 V, and 560 V, respectively. ing. FIGS. 6, 7 and 8 are graphs showing current waveforms flowing in one phase of the reactor 2 in the case of two-phase modulation, and the cases where the values of the DC voltages are set to 730V, 650V and 560V, respectively. Show. The current values are in arbitrary units in all figures.

  Each of the graphs of FIGS. 3 to 8 shows a case where the effective value and frequency of the power supply voltage are 400 V and 50 Hz, respectively. The output values of the motor 6 are equal, and the switching carrier frequency of the PWM converter 3 is 15 kHz.

  It can be seen that the amplitude of the ripple is larger in the case of the two-phase modulation as the value of the DC voltage is larger than in the case of the three-phase modulation. The greater the ripple amplitude, the greater the reactor loss (especially iron loss) and noise.

  Therefore, it is desirable to employ two-phase modulation as the control of the PWM converter 3 and make the value of the DC voltage variable according to the power supply voltage. As described above, since the PWM converter 3 cannot perform a step-down operation, it is desirable to set the value of the DC voltage to about the peak value of the power supply voltage. For example, in the example of FIG. 8, the peak value is approximately 560 (which is approximately equal to 400 × √2) with respect to the effective value of 400 V, and a desirable mode is shown.

  FIG. 9 shows a configuration for performing the above-described control, and is a block diagram partially showing the configuration of FIG. 1 in detail. The AC voltage measuring unit 7 measures the line voltage of the three-phase power source 1 and obtains the peak value Vm and the phase θ of the line voltage of the three-phase power source 1 from the measurement result. The DC voltage measuring unit 8 measures the DC voltage Vdc applied to both ends of the smoothing capacitor 4.

  The controller 9 uses the peak value Vm as a command value for the DC voltage Vdc, calculates a deviation from the DC voltage Vdc, and calculates the voltage command value Va for each phase based on this and the phase θ. Further, the switching signal S is generated based on the voltage command value Va, and the operation of the PWM converter 3 is controlled. As a result, the value of the DC voltage can be made variable following the value of the AC voltage. For the specific generation of the switching signal S, a known method can be adopted as a control technique of the PWM converter.

  10 and 11 are graphs showing the waveform of each part in arbitrary units when the current waveform shown in FIG. 4 is obtained. FIG. 10 shows a waveform for 20 ms corresponding to one cycle of the power supply voltage, and FIG. 11 is an enlarged view of FIG. In both figures, (a) is a voltage command value Va of a certain phase, (b) is a signal for controlling on / of of the switching element on the high arm side of the phase, and (c) is a switching element on the low arm side of the phase. (D) shows a current (that corresponds to FIG. 4) flowing through the reactor 2 of the phase. The switching element is turned on when a high voltage is applied, and turned off when a low voltage is applied.

  10 and 11 show the case where the three-phase modulation control is performed, the voltage command value Va is almost a sine wave, and in detail, the vicinity of the peak is divided into two. FIG. 11 shows an enlarged waveform of each part at 4 ms near the peak.

  12 and 13 are graphs showing the waveform of each part in arbitrary units when the current waveform shown in FIG. 7 is obtained. FIG. 12 shows a waveform for 20 ms corresponding to one cycle of the power supply voltage, and FIG. 13 is an enlarged view of FIG. The part which exhibits the waveform shown by (a)-(d) in both figures respond | corresponds to the part which shows the waveform shown by (a)-(d) in FIG. 10, FIG.

  Since FIG. 12 and FIG. 13 show the case where the three-phase modulation control is performed, the voltage command value Va takes a value of zero in the (1/3) period. In the remaining (2/3) period, a substantially sine wave is exhibited, and in detail, the vicinity of the peak is divided into two.

  As can be seen from a comparison between FIG. 11 and FIG. 13, when the DC voltage is fixed at 650 V, the amplitude of the ripple of the current flowing through the reactor 2 is larger in the two-phase modulation control than in the three-phase modulation control. Therefore, the loss and noise are larger in the two-phase modulation control.

  On the other hand, as shown in FIG. 8, when the DC voltage is made variable and substantially equal to the peak value of the line voltage of the power supply voltage, the amplitude of the ripple of the current flowing through the reactor 2 can be made extremely small.

It is a block diagram which shows the structure of the drive system which can apply this invention. It is a figure which illustrates the loss and noise of each part in various control modes. It is a graph which shows the current waveform which flows into one phase of the reactor 2 in three-phase modulation. It is a graph which shows the current waveform which flows into one phase of the reactor 2 in three-phase modulation. It is a graph which shows the current waveform which flows into one phase of the reactor 2 in three-phase modulation. It is a graph which shows the electric current waveform which flows into one phase of the reactor 2 in two-phase modulation. It is a graph which shows the electric current waveform which flows into one phase of the reactor 2 in two-phase modulation. It is a graph which shows the electric current waveform which flows into one phase of the reactor 2 in two-phase modulation. It is a block diagram which shows the structure of FIG. 1 partially in detail. It is a graph which shows the waveform of each part. It is a graph which shows the waveform of each part. It is a graph which shows the waveform of each part. It is a graph which shows the waveform of each part.

Explanation of symbols

2 Reactor 3 PWM converter 4 Smoothing capacitor 5 Inverter 6 Motor Vdc DC voltage Vm Crest value

Claims (6)

A method of controlling a PWM converter (3) that inputs a polyphase AC voltage via a reactor (2), rectifies the voltage and outputs a DC voltage,
A switching control method, wherein the PWM converter is subjected to two-phase modulation control, and the DC voltage (Vdc) is made variable according to a voltage value of the multiphase AC voltage.   The switching control method according to claim 1, wherein the DC voltage (Vdc) is set substantially equal to a peak value (Vm) of a line voltage of the multiphase AC voltage.   The switching control method according to claim 1, wherein the DC voltage (Vdc) is applied across the smoothing capacitor (4).   The switching control method according to any one of claims 1 to 3, wherein the multiphase motor (6) is inverter-controlled based on the DC voltage (Vdc). A reactor (2);
A PWM converter (3) for inputting a multi-phase AC voltage via the reactor, performing two-phase modulation control, rectifying this, and outputting a variable DC voltage according to the voltage value of the multi-phase AC voltage; A rectifier provided. A rectifying device (2, 3) according to claim 5;
A smoothing capacitor (4) to which the DC voltage is applied;
An inverter (5) for converting the DC voltage into another multiphase AC voltage;
And a motor (6) to which the other multiphase AC voltage is supplied from the inverter.

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