JP2008253074A - Step-up chopper - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a step-up chopper which realizes stable operation and outputs desired voltage, even if there is an input impedance. <P>SOLUTION: The step-up chopper boosting DC power voltage, by on/off of a semiconductor switching element and supplying it to a load, is provided with an input voltage detector 6 for the step-up chopper 300A; an output voltage detector 5, an input current detector 7; an input impedance computing element 10 operating input impedance from a change of input voltage and input current; a conduction ratio computing part 8 for computing the conduction ratio of the switching element 2 so that output voltage becomes a desired value; and a conduction ratio restriction part 11 for restricting the conduction ratio by using maximum values of DC power voltage and output current and input impedance. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a boost chopper that supplies DC power to a current load or a power load, and more particularly to a boost chopper that enables stable operation even when an input impedance exists.

Conventionally, in a device that supplies power from a DC power supply to a load via a boost chopper, when the input voltage of the boost chopper is reduced, the boost chopper is increased by increasing the conduction ratio of the semiconductor switching element that constitutes the boost chopper. The output voltage is prevented from decreasing and the output voltage is kept constant.
However, if the distance between the DC power supply and the boost chopper is long and there is input impedance due to the wiring between them, the output voltage cannot be controlled to the desired value even if the boost chopper's conduction ratio is increased. There is.

For example, FIG. 3 shows a circuit diagram of the boost chopper when there is an input impedance.
In FIG. 3, 100 is a DC power source, 200 is an input impedance due to wiring, 300 is a step-up chopper, 301 is an inductor, 302 is a semiconductor switching element, 303 is a diode, 304 is a smoothing capacitor, and 400 is a load.

Now, the DC power supply voltage is V _batt , the magnitude of the input impedance 200 is Z _in , the input voltage of the boost chopper 300 is V _in , the output voltage is V _out , the input current is I _in , the output current is I _out , and the switching element 302. duty ratio of the (oN percentage of the period) when the d, outputs the relationship between the voltage _{V out} and the input voltage _{V in} to equation 1, equation 2 the relationship between the DC power supply voltage _{V batt} and the input voltage _{V in} The relationship between the input power and the output power of the boost chopper 300 when the efficiency η of the boost chopper 300 is assumed to be 1 (100%) is shown in Equation 3.

When formulas 1 to 3 are arranged, the relationship between the output voltage _Vout of the step-up chopper 300 and the conduction ratio d is formula 4.

As an example of Equation 4, the DC power supply voltage V _batt = 10V, the input impedance Z _in = 0.1Ω, and the output ratio I and the output voltage V _out when the output current I _out is changed to 2A, 4A, and 6A. The relationship is shown in FIG.
According to FIG. 4, when there is an input impedance Z _in, there is a region in which the output voltage V _out does not increase monotonously even if the conduction ratio d of the boost chopper 300 is increased. It can be seen that the tendency becomes more prominent as _out increases.

The following Non-Patent Document 1 discloses a technique for limiting the load according to the input voltage of the booster in order to reduce the influence of the input impedance due to the wiring between the DC power supply and the booster (boost chopper). Yes.
Further, in Patent Document 1, since a voltage drop occurs due to the impedance of the power cable when the control power is supplied via the power cable, the motor control in which the supply voltage is adjusted high in consideration of this voltage drop. An apparatus is described.

Yoshinobu Sato, Takayuki Nagakura, Hiroshi Takahashi, Naoya Eguchi, Hiroshi Harie, “Door Drive System for Railway Vehicles Using Linear Motors”, 2003 IEEJ Conference on Industrial Applications, No.3-66, p.297-298 JP 2003-199379 A (paragraphs [0057] to [0061], FIGS. 1 to 5 etc.)

  As shown in FIGS. 3 and 4, when there is an input impedance between the DC power supply and the boost chopper and the load current is large, the desired output voltage can be obtained even if the current carrying ratio of the boost chopper is increased. In addition to being not obtained, the relationship between the conduction rate and the output voltage does not increase monotonously, so that the operation of the step-up chopper becomes unstable and the equipment may be damaged.

  Note that Patent Document 1 and Non-Patent Document 1 described above do not disclose the idea of stabilizing the circuit operation by controlling the flow rate of the step-up chopper.

  SUMMARY OF THE INVENTION An object of the present invention is to provide a step-up chopper that enables a stable operation and outputs a desired voltage even when there is an input impedance.

In order to solve the above-mentioned problem, the invention according to claim 1 is a boost chopper that boosts a DC power supply voltage and supplies it to a load by turning on and off the semiconductor switching element.
Means for detecting an input voltage of the boost chopper, means for detecting an output voltage, and means for detecting an input current;
Means for calculating an input impedance from changes in the input voltage and input current;
Means for calculating a conduction ratio of the switching element so that the output voltage has a desired value;
Means for limiting the conduction ratio using the DC power supply voltage, the maximum value of the output current, and the calculated input impedance.

  According to a second aspect of the present invention, in the first aspect, the DC power supply voltage used in the means for limiting the conduction ratio is a known constant.

  The invention according to claim 3 calculates the DC power supply voltage used in the means for limiting the conduction rate in claim 1, using the input voltage, the input current, and the calculated input impedance. Means are provided.

  According to the present invention, even when there is an input impedance between the DC power supply and the boost chopper and the load current is large, the input impedance calculated from the relationship between the input voltage and the input current, the DC power supply voltage, etc. are used. Thus, by limiting the conduction rate so that the output voltage monotonously increases, the operation of the step-up chopper can be stabilized to output a desired voltage, and damage to the device can be prevented.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
FIG. 1 is a circuit diagram showing a first embodiment of the present invention.
In FIG. 1, 12 is a DC power supply, 13 is an input impedance (the magnitude is Z _in ), 300A is a boost chopper, and 14 is a load to which DC power is supplied.

  The step-up chopper 300A includes, in its main circuit, an input voltage detector 6 composed of a series circuit of resistors, an input current detector 7, an inductor 1 connected to the positive side, a diode 3, and an anode of the diode 3. Output voltage detection comprising a semiconductor switching element 2 connected between the negative electrode, a smoothing capacitor 4 connected between the cathode and the negative electrode of the diode 3, and a resistor connected to both ends of the smoothing capacitor 4. And 5.

  Further, as a control circuit for controlling on / off of the switching element 2, an input impedance calculation unit 10 for calculating input impedance by inputting each detection value by the input voltage detector 6 and the input current detector 7, and input voltage detection A conduction rate calculation unit 8 for calculating the conduction rate of the switching element 2 so that each detection value by the detector 6 and the output voltage detector 5 is inputted and the output voltage becomes a desired value, and output from the calculation unit 8 A current ratio limiting unit 11 that limits the current conduction rate using the output of the input impedance calculation unit 10, and a PWM calculation unit that calculates an on / off command of the switching element 2 according to the current conduction rate that has passed through the restriction unit 11. 9 are provided.

Next, the operation of this embodiment will be described.
In general, in a step-up chopper circuit composed of an inductor 1, a switching element 2, a diode 3, and a smoothing capacitor 4, the relationship between the input voltage V _in and the output voltage V _out varies depending on the conduction ratio d as shown in Equation 1. However, when there is an input impedance 13 (Z _in ), there is a region where the output voltage V _out does not increase monotonously even if the conduction ratio d is increased as shown in FIG.

Here, if the result obtained by differentiating the right side of the above-described Equation 4 with respect to d is 0,
2Z _in I _out (1-d) ⁻³ = V _batt (1-d) ⁻²
Then, when d is obtained from this mathematical formula,
d = 1− (2Z _in I _out / V _batt )
It becomes.
That is, the above d is a conduction ratio when the output voltage _Vout in FIG. 4 takes a maximum value. Therefore, if the conduction ratio d is limited to this value or less, the output voltage depends on the conduction ratio d. A relationship in which V _out increases monotonously can be obtained.
Therefore, Formula 5 is obtained.

_{Assuming that} the maximum value of the output current I _out of the boost chopper is I _max , the range of the conduction ratio d at which the boost chopper operates stably is expressed by Equation 6.

On the other hand, the input impedance Z _in is equal to the detected value V _in1 of the input voltage detector 6 and the detected value I _in1 of the input current detector 7 at a certain time t1, and the detected value V _in2 of the input voltage detector 6 at another time t2. And the detection value I _in2 of the input current detector 7 can be obtained by Expression 7. In the input impedance calculation unit 10 of FIG. 1, the input impedance Z _in is calculated using Equation 7.

In the duty ratio limit unit 11, the conduction ratio d is calculated according to the equation 1 by conduction ratio calculating unit 8, the input impedance Z _in and a known DC power supply voltage V _batt and the output current maximum value I _max By the above, it limits according to the said Numerical formula 6.
Thus, there is the input impedance as shown in FIG. 1, yet even when the output current I _out is large, the duty ratio using an input impedance Z _in computed from the relationship between the input voltage V _in and the input current I _in If d is limited, the relationship between the _duty ratio d and the output voltage _Vout can be monotonically increasing, and the step-up chopper 300A can be stably operated.

Next, FIG. 2 is a circuit diagram showing a second embodiment of the present invention.
The step-up chopper 300B of this embodiment is different from the first embodiment in that a DC power supply voltage calculation unit 15 that calculates a DC power supply voltage _Vbatt by the following formula 8 is added.

That is, the DC power supply voltage calculating unit 15, the input voltage V _in detected by the input voltage detector 6, an input current I _in input to the input impedance computing section 10, the input impedance computed by the input impedance computing section 10 The DC power supply voltage V _batt is calculated from Z _in .
Then, the conduction rate limiting unit 16 uses the input impedance Z _in output from the input impedance calculation unit 10 and the DC power supply voltage V _batt output from the DC power supply voltage calculation unit 15, according to Equation 6 above. Limit the rate d.

According to this embodiment, it becomes unclear DC power supply voltage V _batt by variations in voltage, even when the unavailable DC power supply voltage V _batt when calculating Equation 6 as a known value, DC By using the DC power supply voltage V _batt that is sequentially calculated by the power supply voltage calculation unit 15, the optimum _conduction ratio d can be obtained by Equation 6.

Also in the present embodiment, the step-up chopper 300A can be stably operated by making the relationship between the conduction ratio d and the output voltage _Vout a monotonically increasing relationship.

1 is a circuit diagram showing a first embodiment of the present invention. It is a circuit diagram which shows 2nd Embodiment of this invention. It is a circuit diagram of a step-up chopper when there is an input impedance. It is a graph which shows the relationship between the duty factor according to output current, and output voltage when the influence of input impedance is considered.

Explanation of symbols

1: Inductor 2: Semiconductor switching element 3: Diode 4: Smoothing capacitor 5: Output voltage detector 6: Input voltage detector 7: Input current detector 8: Current ratio calculator 9: PWM calculator 10: Input impedance calculation Units 11 and 16: Conductivity limiting unit 12: DC power supply 13: Input impedance 14: Load 15: DC power supply voltage calculation units 300A, 300B: Boost chopper

Claims (3)

In the boost chopper that boosts the DC power supply voltage and supplies it to the load by turning on and off the semiconductor switching element,
Means for detecting an input voltage of the boost chopper, means for detecting an output voltage, and means for detecting an input current;
Means for calculating an input impedance from changes in the input voltage and input current;
Means for calculating a conduction ratio of the switching element so that the output voltage has a desired value;
Means for limiting the conduction rate using the DC power supply voltage, the maximum value of the output current, and the calculated input impedance;
A step-up chopper characterized by comprising: In the step-up chopper according to claim 1,
A step-up chopper characterized in that the DC power supply voltage used in the means for limiting the conduction rate is a known constant. In the step-up chopper according to claim 1,
A step-up chopper comprising: means for calculating the DC power supply voltage used in the means for limiting the conduction ratio by using the input voltage, the input current, and the calculated input impedance.

Images