JP2008199814A - Power factor corrected direct-current power supply - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a power factor corrected direct-current power supply wherein a favorable power factor can be obtained by a low-cost transformer for input alternating current measurement (CT), without the use of an expensive direct-current transformer (DCCT). <P>SOLUTION: The power factor corrected direct-current power supply is so constructed that the following is implemented an input current value obtained by A/D-converting an input alternating current measurement value is corrected at a zero-cross point in an input voltage value, obtained by A/D-converting an input alternating-current voltage measurement value. As a result, stable control can be carried out, even if the input alternating current becomes imbalanced; and the zero point of CT output is shifted, when the input alternating current is measured by using the inexpensive CT, or the like. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a power factor correction type DC power supply device that converts AC power into DC power at a high power factor.

  Various proposals have been made on power factor correction type DC power supply devices that efficiently convert AC power into DC power with a high power factor.

  Among them, Patent Document 1 discloses a technique for controlling a switch at a zero cross timing in order to obtain a high input power factor.

  Further, Patent Document 2 discloses a proposal for improving the power factor by detecting the input current and adjusting the balance of the waveform.

  Further, Patent Document 3 discloses an AC wattmeter and a watt hour meter in which the influence of the power factor is prevented by correcting the phase difference between voltage and current with a zero cross converter. In this technique, in order to correct the phase difference between the current transformer and the current detector output, the phase is first adjusted to the same phase and then digitally corrected.

  Further, Patent Document 4 discloses a technique for adjusting so that the time point when the zero cross point of the alternating current is detected becomes zero. This technique digitizes the CT output and detects and corrects the zero-cross point based on the signal.

  These prior arts have their merits and demerits, and new and better proposals are awaited.

JP 2005-137168 A JP 2002-095243 A JP 2005-134210 A JP 2003-121479 A

  In the power factor correction type DC power supply, the power factor is 1 if the waveform of the sine wave of the AC voltage is similar to the waveform of the AC current. Therefore, the power factor is brought close to 1 by controlling the voltage waveform and the current waveform to be the same sine wave. However, in order to bring the power factor close to 1, the influence of variations in elements used in the power factor correction type DC power supply cannot be ignored. In particular, when a switching element made of an FET is used in such a power supply device, individual FETs generally vary in ON resistance and switching time, and the balance between the positive side and negative side of the alternating current may be lost. For this reason, when CT is used for AC current measurement, the zero point is shifted from the actual zero point. The use of a direct current transformer (hereinafter referred to as DCCT) eliminates the zero point shift, but the DCCT is generally expensive and causes the price of the power supply device to rise.

  An object of the present invention is to provide a power factor correction type DC power supply device having a good power factor without using expensive DCCT in order to eliminate such problems due to variations in elements.

  More specifically, the present invention solves the CT imbalance problem by correcting (controlling) the AC input current measurement value from the CT by the polarity reversal point of the AC input voltage, thereby stabilizing the power factor correction type DC. It is to provide a power supply device.

  The power factor correction type DC power supply device of the present invention corrects an input current value obtained by A / D converting an AC input current measurement value by an input voltage value obtained by A / D converting the AC input voltage measurement value, and The input current is controlled so that the zero point coincides with the zero point of the alternating input current.

  The present invention can provide a power factor correction type DC power supply device having a stable power factor at low cost without using expensive DCCT.

  FIG. 1 shows a circuit of a power factor correction type DC power supply apparatus according to an embodiment of the present invention.

  A power factor correction type DC power supply device (hereinafter also simply referred to as a power supply device) 1 shown in FIG. 1 is a power supply device that takes out an alternating current input from an alternating current power supply 10 as a direct current.

  In FIG. 1, one terminal T <b> 11 connected to the AC power supply 10 is connected to the reactor 11, and the output of the reactor 11 is connected to the diode 13 and the FET 14. The other terminal T12 of the AC power supply 10 is connected to the diode 15 and the FET 16 via an AC input current measuring transformer 22 (hereinafter sometimes simply referred to as CT22). The outputs of the diodes 13 and 15 are connected to the + side DC load terminal T13. The sources of the FETs 14 and 16 are connected to the negative DC load terminal T14. A capacitor 17 is connected between the DC load terminals T13 and T14. Terminals T15 and T16 of the device 18 are connected to the DC load terminals T13 and T14, and a DC current sensor 24 is connected between the drains of the FETs 14 and 16 and the device terminal T16.

  In the DC power supply device 1 shown in FIG. 1, the AC input voltage of the AC power supply 10 is measured by an AC input voltage measuring transformer 21 (hereinafter sometimes simply referred to as PT21) inserted between the terminals T11 and T12. The AC input current is measured by CT22 inserted between the terminal T12, the diode 15 and the FET 16. The DC output voltage is measured by a voltmeter 23 inserted between terminals T13 and T14, and the DC output current is measured by the DC current sensor 24. The values of the measured AC input voltage, AC input current, DC output voltage, and DC output current are output to the control circuit 30. By these measured values, the control circuit 30 has the FET 14 whose gate is connected to the control circuit 30, 16 is controlled.

  The control circuit 30 receives an AC input voltage, an AC input current, a DC output voltage, and a DC output current. Based on these input values, the control circuit 30 instructs the device 18 to output the DC output voltage and the limit required by the device 18. A signal is given to the gates of the FETs 14 and 16 so as to supply a constant DC output current equal to or less than the current, and these FETs are controlled.

  In this FET control, the control circuit 30 obtains a high AC input power factor by controlling the waveforms of the AC input voltage and AC input current to be similar.

FIG. 2 is a block diagram illustrating a control circuit 30 that controls the power supply device 1. As shown in this block diagram,
1. The DC output voltage is measured between the terminals T13 and T14, the measured value is compared with the target voltage value, and the difference is input to the PI control 31. The target voltage value is a voltage value determined by the device 18.
2. The direct current sensor 24 measures the direct current, compares the measured value with the limit current value, and inputs the difference to the PI control 32. The target current value is a current value determined by the device 18.
3. Next, the value of the PI control 31 and the value of the PI control 32 are compared by the comparator 33, and the higher value is input to the multiplier 34. The multiplier 34 multiplies the value input from the comparator 33 and the AC input voltage measured by the PT 21. The result of multiplication is input to the comparator 35.
5. The comparator 35 compares the value from the multiplier 34 with the AC input current measured by the CT 22, inputs the result to the PI control 36, and inputs the value to the pulse width modulation circuit 37.
6). The result of modulation by the pulse width modulation circuit 37 controls the FETs 14 and 16. A polarity discriminator 38 is provided between the AC power supply 10 and the pulse width modulation circuit 37, and the polarity discriminator 38 determines which of the FET 14 and the FET 16 is given a signal.

  The control circuit 30 described above controls the AC voltage waveform and the AC current waveform to be similar to each other as shown in FIG. In order to obtain a target DC output voltage from the AC power supply 10, the multiplier 34 multiplies the AC input voltage by the higher DC output voltage and DC output current. That is, when the DC voltage is the target voltage, the DC output voltage is multiplied by the AC output voltage. Similarly, when the current exceeding the specified current flows, the DC output current is multiplied by the AC input voltage. The input power factor is improved by controlling the FETs 14 and 16, and the output voltage and current are controlled.

  FIG. 4 shows the target voltage and limit current when the voltage and current from the AC power source are converted to DC voltage and DC current. The current exceeding the limit current is prohibited from flowing to the device 18 and output at the target voltage. As described above, the control circuit 30 controls the FETs 14 and 16 as described above.

  In the power factor correction type DC power supply device 1 described above, the AC voltage waveform and the AC current waveform are similar to each other as shown in FIG. 3 in a normal state, and the power factor is close to 1. That is, as shown in the figure, the AC voltage waveform and the AC current waveform are similar in the normal state, and the polarity inversion point (zero cross point) of the AC voltage and the positive / negative inversion point (zero cross point) of the AC current coincide on the time axis.

  However, in the power supply device 1 shown in FIG. 1, as shown in FIG. 5, in the AC input current, the + side current may be smaller than the − side current, and the waveform of the AC input current may shift. . This is because the current values are not equal on the + side and the-side of the AC input current due to variations inherent in the elements of FET 14 and 16 of the power supply device 1 and excessive fluctuations in input and output. In this way, if the current values of the positive and negative AC input currents are not equal, the CT22 output 0 point is different from the actual zero point, and normal control cannot be performed. In some cases, the FETs 14 and 16 are damaged. Will end up.

  The present invention is a power supply apparatus that corrects (controls) an AC input current measurement value when the AC input voltage zero-crosses the AC input current measurement value, and enables stable control with inexpensive CT. Hereinafter, the correction method will be described in detail.

  FIG. 6 shows a state in which the balance between the zero point time axis at which the polarity of the AC input voltage measured by the PT 21 changes and the zero point at which the polarity of the output current measured by the CT 22 is reversed is lost. FIG. 6 (1) shows the waveform of the AC input voltage to the PT 21, (2) shows the waveform of the AC input current to the CT 22, FIG. 6 (3) shows the waveform of the AC voltage output from the CT 22, and FIG. It shows the deviation of the waveform of the alternating current output from CT22. As is clear from these figures, the zero point of the AC input voltage is shifted from the zero point of the AC output current. As described above, when the zero point of the AC output current is shifted (changed), normal power factor correction type DC power supply cannot be controlled.

  As shown in FIG. 6, when the current on the negative side is larger than the current on the positive side, the voltage generated in the resistor connected to the output of the CT22 is an AC signal due to the magnetic coupling of the transformer itself. By transmitting only the zero point, the position of the zero point of the input current is shifted from the position of the zero point generated in the resistor. If the zero point shifts in this way, normal control cannot be performed.

  In the present embodiment, normal control is performed by correcting the deviation (change) of 0 point due to CT.

  FIG. 7 is a diagram illustrating a flow of software described in a memory built in a CPU that controls the zero point correction process, and FIG.

Step 1
The AC voltage is measured with PT21. Moreover, an alternating current is measured by CT22. Further, the DC voltage is measured with the voltmeter 23.

Step 2
The measured AC voltage value is A / D converted by an A / D converter 71 as shown in FIG. Let this value be X. Also. The measured alternating current value is converted by the A / D converter 72 and output to the CPU 70. This value is Y. The DC voltage measured at the same time is A / D converted by the A / D converter 73 and output to the CPU 70. The reason why the DC voltage is measured and output to the CPU is that the CPU controls the voltage so that the target DC output voltage is obtained.

Step 3
When the polarity of the measured value X has changed (X = 0), the process proceeds to step 4; otherwise, the process proceeds to step 6.

Step 4
The value Y measured in step 2 is stored as the value Z. Then, it is assumed that the value Y measured in step 2 is located at 0 point (Z).

Step 5
In step 2, the measurement value Y is set to zero. In step 5, the CPU 70 replaces the value Y with 0, that is, performs 0 point correction with the position of Z as 0 point. The data is read again.

Step 6
If the polarity of the value X does not change in step 3, the value Y is rewritten to a new Y to make Y, but if the value Z is stored at that time, the value Z is subtracted and Y = Y−Z is set. Calculate to a new value Y. The data is read again.

  As described above, the CPU 70 corrects the waveform of the AC output current, so that the power supply device 1 can stably convert AC power into DC power and supply current to the load (device 18).

  FIG. 9 is a waveform diagram of the AC output current with respect to the AC output voltage measured by the power supply device 1 of the present embodiment. FIG. 9A is an AC voltage waveform diagram, FIG. 9B is a waveform diagram of an AC output current without applying the present invention, that is, no correction function, and FIG. 9C is a correction of this embodiment. It is a wave form diagram of alternating current output in the state provided with the function.

  As is clear from this figure, in FIG. 9 (2), the ideal 0 point (0A) is shifted and the power factor is in a reduced state. In the power supply device having the form correction function, the zero point (0A) is an ideal point, which indicates that the power factor does not decrease.

  As described above in detail, according to the present invention, even if the AC input current is unbalanced and the zero point of the output of the magnetic coupling type current measurement CT changes, it can be easily corrected by the voltage zero crossing. The correction type DC power supply device can be provided and has an excellent effect.

It is a circuit diagram showing a DC power unit of one embodiment. It is explanatory drawing which shows the control circuit in a DC power supply device. It is a figure which shows the waveform of alternating current input voltage and alternating current input current. It is a graph which shows the relationship between the target DC voltage with respect to an apparatus, and a limit direct current. It is a figure which shows the waveform of alternating current input voltage and alternating current input current. It is a wave form diagram which shows the waveform of the alternating current input voltage measured with the alternating current input voltage and alternating current input current, the alternating current voltage measured with the alternating current input voltage measurement transformer, and the alternating current input current measurement transformer. It is explanatory drawing which shows the process of controlling the waveform of alternating current output current. It is a flowchart which shows the process of correct | amending an alternating current output current waveform. (1) is a waveform diagram of an AC input voltage, (2) is a waveform diagram of an AC input current measured by an AC input current measurement CT in a conventional power supply device, and (3) is an AC input current measurement CT in this embodiment. FIG.

Explanation of symbols

1 Power factor correction type DC power supply (power supply)
10 AC power supply 11 Reactor 13 Diode 14 FET
15 Diode 16 FET
17 Capacitor 18 Device 21 AC Input Power Measurement Transformer (PT)
22 AC input current measurement transformer (CT)
23 Voltmeter 24 DC Current Sensor 30 Control Circuit 31 PI Control 32 PI Control 33 Comparator 34 Multiplier 35 Comparator 37 Pulse Width Modulation Circuit 38 Polarity Discriminator 70 CPU
71 Converter 72 Converter 73 Converter T11 Terminal T12 Terminal T13 Terminal T14 Load Terminal T15 Terminal T16 Equipment Terminal

Claims (1)

  The input current value obtained by A / D converting the AC input current measurement value is corrected by the input voltage value obtained by A / D converting the AC input voltage measurement value, and the zero point of the AC input voltage matches the zero point of the AC input current. A power factor correction type DC power supply apparatus, wherein the input current is controlled to do so.

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