JP2008167506A - Dc-dc converter and its control method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a DC-DC converter in which control of an output voltage is easy even when duty ratio and the number of input conversion circuits connected in parallel are changed, and to provide its control method. <P>SOLUTION: The DC-DC converter 100 comprises: an input conversion section 110, in which a plurality of input conversion circuits 111..., each having a switching element 112 and a coil 113 to boost an inputted DC voltage and output it by allowing the switching element 112 to carry out its switching operation, are connected in parallel; an output voltage detection section 120, which detects an output voltage of the input conversion section 110; and a duty ration control section 130, which, based on the output voltage detected by the output voltage detection section 120, controls the duty ratio of a plurality of the switching elements 112... of a plurality of the input conversion circuits 111... in a current discontinuous mode. The output voltage detection section 120 detects the output voltage of the input conversion section 110 synchronizing with the timing when either one of the switching elements 112 of a plurality of the input conversion circuits 111... is turned from ON to OFF. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a DC-DC converter and a control method thereof.

Conventionally, a DC-DC converter that boosts or steps down an input DC voltage and outputs it is known.
As control of the DC-DC converter, there are known controls called a current continuous mode and a current discontinuous mode, which are classification based on the behavior of a current (coil current) flowing in a coil constituting the DC-DC converter.

In the current discontinuous mode, when the switching element of the DC-DC converter is off, the coil current of the DC-DC converter once becomes zero (the coil current becomes discontinuous).
On the other hand, in the continuous current mode, the coil current of the DC-DC converter does not always become zero (the coil current becomes continuous) regardless of whether the switching element of the DC-DC converter is on or off.
The DC-DC converter in the discontinuous current mode can easily achieve so-called soft switching because the coil current is zero when the switching elements constituting the converter are turned on. It is possible to reduce power loss due to switching.
In particular, in recent years, the switching frequency of the switching elements constituting the DC-DC converter has been increased (high), and the number of switching operations per unit time tends to increase. large.

In addition, a plurality of input conversion circuits for boosting or stepping down each input DC voltage and outputting it, and connecting these input conversion circuits in parallel, the number of input conversion circuits (the number of parallel operations) for performing a switching operation is provided. A DC-DC converter that can handle a large current and cope with a large fluctuation in current value by appropriately changing the current is also known. For example, it is as described in Patent Document 1 and Patent Document 2.
In the case of such a DC-DC converter in which a plurality of input conversion circuits are connected in parallel, the cycle of the output voltage is usually obtained by shifting the timing (phase) at which the switching element of each input conversion circuit is turned on. Fluctuations are suppressed.

A DC-DC converter that performs so-called PWM (Pulse Width Modulation) control that controls the duty ratio of the switching element of the input conversion circuit (the ratio of the ON time of the switching element to the switching period) and that controls in the current discontinuous mode is Normally, the duty ratio of the switching element is controlled (adjusted) based on the detected output voltage.
In the case of periodically detecting (sampling) the output voltage of such a DC-DC converter instead of continuously detecting (analog detection), conventionally, the timing at which the switching element of the input conversion circuit is turned on from off is used as a reference. The output voltage was detected (for example, in synchronization with the timing when the switching element is turned on).

  However, when the output voltage of the DC-DC converter is periodically detected on the basis of the timing when the switching element of the input conversion circuit is turned on from the OFF, and the control is performed in the current discontinuous mode based on this, the following problems are caused. Have.

  The output voltage Vout of the input conversion circuit 511 is periodically detected at the timing when the switching element 512 of the input conversion circuit (boost circuit) 511 of the conventional DC-DC converter shown in FIG. When the duty ratio is controlled as the target voltage value, the average value of the output voltage Vout of the input conversion circuit 511 is higher than the target voltage value at the time of low load (duty ratio: small) shown in FIG. On the other hand, at the time of medium load (duty ratio: medium) shown in FIG. 11 and at the time of high load (duty ratio: large) shown in FIG. 12, the average value of the output voltage Vout of the input conversion circuit 511 is the target voltage. The difference between the detected value of the output voltage and the target voltage value is also different.

Thus, in the current discontinuous mode, (1) the duty ratio changes according to the load, (2) the off time of the switching element of the input conversion circuit (from when the switching element is turned off until it is turned on again) Includes a charging period and a discharging period of the output side capacitor (capacitor 503 in the case of FIG. 9), and the ratio of the charging period and the discharging period changes according to the ON time (in other words, the duty ratio) of the switching element. The timing at which the upper peak of the output voltage (the point at which the output voltage changes from rising to falling) and the lower peak (the point at which the output voltage changes from falling to rising) within the switching period appears according to the duty ratio. Change.
Therefore, even if the output voltage is detected at the timing when the switching element 512 is turned on from off (a fixed point in the switching cycle), the timing at which the output voltage is detected and the timing at which the upper peak or lower peak of the output voltage appears. The output voltage is not stable because the output voltage is not stable due to irregularities such as when the average value of the output voltage is higher or lower than the target voltage value depending on the duty ratio value. There is a problem that voltage control is not easy.

Also, as shown in FIG. 16, when a plurality of input conversion circuits 511 are prepared as shown in FIGS. 13 to 15, these are connected in parallel, and the timing (phase) at which the switching operation is performed is shifted as shown in FIG. 16. The difference (offset) between the average value of the output voltage and the detected value (target voltage value) of the output voltage varies irregularly to the positive or negative side according to the (duty ratio), and the output voltage is not stable. is there.
Further, in a DC-DC converter of a type in which a plurality of input conversion circuits are connected in parallel, as described above, even in the control of appropriately increasing the number of input conversion circuits (parallel number) that perform switching operation as the load increases. If the relationship between the detected value of the output voltage and the average value of the output voltage changes irregularly according to the duty ratio, there is a problem that the output voltage is likely to fluctuate before and after the parallel number is changed, and the output voltage is not stable.

In continuous current mode, the duty ratio does not change even if the load fluctuates, and the switching time of the switching element of the input conversion circuit corresponds to the charging time and discharging time of the output side capacitor, respectively. The timing at which the upper peak of the output voltage (the point where the output voltage turns from rising to falling) and the lower peak (the point where the output voltage turns from rising to falling) appear is the timing when the switching element is turned on and turned off. There is no problem that these timings always correspond and these timings are shifted due to load fluctuations.
JP 2004-15992 A JP 2001-95232 A

  In view of the above situation, the present invention provides a DC-DC converter that can easily control an output voltage even when a duty ratio changes, and a control method thereof.

  The problem to be solved by the present invention is as described above. Next, means for solving the problem will be described.

That is, in claim 1,
An input conversion unit having a switching element and a coil, wherein the switching element performs a switching operation to connect in parallel a plurality of input conversion circuits that step up or step down the input DC voltage,
An output voltage detector for detecting an output voltage of the input converter;
A duty ratio controller that controls the duty ratios of the switching elements of the plurality of input conversion circuits in a current discontinuous mode based on the output voltage detected by the output voltage detector;
Comprising
The output voltage detection unit detects an output voltage of the input conversion unit in synchronization with a timing at which any of the switching elements of the plurality of input conversion circuits is turned off.

In claim 2,
DC having a switching element and a coil, and having an input conversion unit connected in parallel with a plurality of input conversion circuits for boosting or stepping down an input DC voltage by performing a switching operation of the switching element A method for controlling a DC converter, comprising:
Detecting the output voltage of the input conversion unit in synchronization with the timing when any of the switching elements of the plurality of input conversion circuits is turned off from on,
Based on the detected output voltage, the duty ratios of the switching elements of the plurality of input conversion circuits are controlled in a current discontinuous mode.

  The effect of the present invention is that the output voltage can be easily controlled even if the duty ratio and the number of parallel circuits change.

  Below, the structure of the DC-DC converter 100 which is one Embodiment of the DC-DC converter which concerns on this invention using FIG. 1 is demonstrated. The method for controlling the DC-DC converter 100 corresponds to an embodiment of the method for controlling the DC-DC converter according to the present invention.

  The DC-DC converter 100 boosts and outputs an input DC voltage, and mainly includes an input side filter 102, an input conversion unit 110, an output side filter 103, an output voltage detection unit 120, a duty control unit 130, and a driver 140. -It has 140 ... etc.

  Although the DC-DC converter 100 of the present embodiment is configured to boost and output the input DC voltage, the present invention is not limited to this, and the configuration that steps down and outputs the input DC voltage, etc. Alternatively, the input DC voltage (positive or negative) may be inverted and output.

The input conversion unit 110 is an embodiment of the input conversion unit according to the present invention, and is formed by connecting input conversion circuits 111, 111.
The input conversion circuits 111, 111,... Are circuits that boost and output the input DC voltage, that is, boost circuits.
The direct current voltage input from the power source 200 to the DC-DC converter 100 is input to the input conversion circuits 111, 111,. The DC voltage input to the DC-DC converter 100 is boosted by the input conversion circuits 111, 111... And then output from the DC-DC converter 100 through the output filter 103. In the case of this embodiment, the DC voltage output from the DC-DC converter 100 is input to the motor 300 as a load and used for driving the motor 300.
The input side filter 102 and the output side filter 103 remove (attenuate) predetermined frequency components of the DC voltage input to the DC-DC converter 100 and the DC voltage output from the DC-DC converter 100, respectively.

  The input conversion circuit 111 mainly includes a switching element 112, a coil 113, and a diode 115.

The switching element 112 is formed of an N-channel MOSFET as an example, and conducts conduction and interruption between the source and drain, that is, performs a switching operation when a signal is input to the gate.
One end of the coil 113 forms an input terminal of the input conversion circuit 111 and is connected to the output terminal of the input side filter 102. The other end of the coil 113 is connected to the drain of the switching element 112. The source of the switching element 112 is connected to the ground, and the gate of the switching element 112 is connected to the corresponding driver 140. The anode of the diode 115 is connected to the connection portion between the other end of the coil 113 and the drain of the switching element 112. The cathode of the diode 115 forms the output terminal of the input conversion circuit 111 and is connected to the input terminal of the output side filter 103. As an example, the output side filter 103 includes a capacitor having one end connected to the output terminal of the input conversion unit 110 and the other end connected to the ground.

  When the switching element 112 performs a switching operation at a predetermined duty ratio (on-duty), the input conversion circuit 111 boosts and outputs the DC voltage input to the DC-DC converter 100.

The output voltage detection unit 120 detects a DC voltage (output voltage of the input conversion unit 110) output from the DC-DC converter 100, and outputs information related thereto.
Further, the output voltage detection unit 120 does not continuously detect (analog detection) the output voltage of the DC-DC converter, acquires a signal (detection timing signal) output from the duty control unit 130, and acquires the signal. Sometimes the output voltage of the input converter 110 is detected.

  Based on the output voltage of the input conversion unit 110 detected by the output voltage detection unit 120, the duty ratio control unit 130 of the switching elements 112, 112... Of the input conversion circuits 111, 111. The duty ratio is controlled.

  The duty ratio control unit 130 is connected to the output voltage detection unit 120, can acquire information related to the output voltage of the input conversion unit 110 detected by the output voltage detection unit 120, and outputs the output of the input conversion unit 110. A signal (detection timing signal) related to the timing for detecting the voltage can be transmitted to the output voltage detection unit 120.

The duty ratio control unit 130 detects a detection timing signal when the switching element 112 (SW1 in FIG. 1) of one of the input conversion circuits 111, 111. Is transmitted to the output voltage detector 120.
Therefore, the output voltage detection unit 120 detects the output voltage of the input conversion unit 110 in synchronization with the timing at which the switching element 112 (SW1 in FIG. 1) of one predetermined input conversion circuit 111 is turned off. Will be.

The duty ratio control unit 130 compares the target voltage value with the detected value of the output voltage based on the information related to the output voltage of the input conversion unit 110, and the detected value of the output voltage approaches the target voltage value (detection of the output voltage). The duty ratio of the input conversion circuits 111, 111,... Is adjusted (controlled) so that the value becomes the same value as the target voltage value. More specifically, when the detected value of the output voltage is lower than the target voltage value, the duty ratio of the input conversion circuits 111, 111,... Is increased, and the detected value of the output voltage exceeds the target voltage value. If so, the duty ratio of the input conversion circuits 111, 111,... Is reduced, and an operation signal corresponding to the duty ratio is transmitted to the drivers 140, 140,.
Further, the duty ratio controller 130 shifts the phase (timing) of the switching operation of the input conversion circuits 111, 111... By shifting the phase (timing) of the operation signal transmitted to the drivers 140, 140. The fluctuation of the output voltage of the input conversion unit 110 is reduced.
In this embodiment, the magnitude of the phase (timing) deviation of the switching operation of the input conversion circuits 111, 111,... Is the input conversion circuit 111 that performs the switching operation of the switching cycle of the input conversion circuits 111, 111,. However, the present invention is not limited to this, and it is possible to arbitrarily set the phase shift of the switching operation (including all the phases being the same). .

  The drivers 140, 140... Transmit gate signals corresponding to the duty ratio adjusted by the duty ratio control unit 130 to the gates of the input conversion circuits 111, 111,.

  Hereinafter, the behavior when one input conversion circuit 111 performs a switching operation will be described with reference to FIGS.

As shown in FIG. 2, when the switching operation of the switching element 112 of the input conversion circuit 111 in the current discontinuous mode and a predetermined duty ratio, the current I _L flowing through the coil 113 at the time when the switching element 112 is turned on from zero elevated, the switching element 112 is lowered current I _L flowing through the coil 113 from the time when turned off, the coil 113 in the middle off time (time until the switching element 112 is turned on again after turned off) The flowing current _IL becomes zero.
Current I _L flowing through the coil 113, while the switching element 112 is turned on to flow to the ground via the switching element 112, the output-side filter through a diode 115 while the switching element 112 is turned off (capacitor) It flows to 103. Therefore, the current _{I SW} which flows through the switching element 112 switching element 112 corresponds to the current _{I L} flowing through the coil 113 during the turned on, the current _{I D} flowing through the diode 115 switching element 112 is turned off corresponding to the current _{I L} flowing through the coil 113 between.

  The voltage Vx at the connection point of the switching element 112, the coil 113, and the diode 115 is a value based on the on-resistance of the switching element 112 while the switching element 112 is on, and the output side filter when the switching element 112 is off. The value corresponds to the voltage across the (capacitor) 103. The voltage Vx becomes a value corresponding to the voltage of the power source 200 after a while after the switching element 112 is turned off.

Depending on the behavior of the current I _L flowing through the coil 113, the current I _SW flowing through the switching element 112, the current I _D flowing through the diode 115, and the voltage Vx, the timing at which the switching element 112 is turned off and the capacitor on the output side (this embodiment) In the example, the filling start timing of the output side filter 103) is synchronized, and the output voltage Vout of the input conversion circuit 111 is shifted to the lower peak (from falling to rising at the timing when the switching element 112 is turned off to on. ) And a substantially sawtooth waveform.
Therefore, when the output voltage is detected in synchronization with the timing when the switching element 112 of the input conversion circuit 111 is turned off, the lower peak value of the output voltage Vout of the input conversion circuit 111 is detected. . As shown in FIG. 3 and FIG. 4, the same is true even if the duty ratio of the input conversion circuit 111 increases.

The output voltage of the input conversion circuit 111 is detected in synchronization with the timing when the switching element 112 of the input conversion circuit 111 is turned from on to off, and the detected output voltage value approaches the target voltage value (detection of output voltage). Controlling the duty ratio of the input conversion circuit 111 so that the value becomes the same value as the target voltage value has the following advantages.
That is, since the value of the output voltage detected by the output voltage detection unit 120 is always smaller than the average value of the output voltage, the value of the detected output voltage is the same as the value of the target voltage. Nevertheless, it is possible to prevent a situation in which the average value of the output voltage actually supplied to the load (motor 300) is lower than the target voltage value (voltage shortage), and the output voltage can be easily controlled. Become.

In the following, the behavior when the four input conversion circuits 111 and the input conversion circuits 111... Constituting the input conversion unit 110 perform the switching operation with their phases shifted will be described with reference to FIGS.
When the four input conversion circuits 111 and the input conversion circuits 111 perform switching operations with their phases shifted, the output voltage Vout of the input conversion unit 110 is the output of the four input conversion circuits 111 and the input conversion circuits 111. It is expressed as the sum of voltages.
As shown in FIG. 5 to FIG. 7, the output voltage Vout of the input conversion unit 110 is one of the input conversion circuit 111, the input conversion circuit 111,..., Regardless of the size of the load (the duty ratio). The switching element 112 has a substantially saw-tooth waveform that becomes a lower peak (a point from falling to rising) at the timing when the switching element 112 is turned off.
Therefore, when variation in output voltage between the individual input conversion circuits 111 and the input conversion circuits 111... Can be ignored, one switching element 112 of the four input conversion circuits 111 and the input conversion circuits 111. If the output voltage is detected in synchronization with the timing at which the signal is turned from on to off, the lower peak value of the output voltage Vout of the input conversion unit 110 is detected.

  As described above, when the four input conversion circuits 111 and the input conversion circuits 111... Perform the switching operation by shifting the phases, the output voltage detection unit is the same as the case where the single input conversion circuit 111 performs the switching operation. Since the value of the output voltage detected by 120 is always smaller than the average value of the output voltage of the input converter 110, the value of the detected output voltage of the input converter 110 is the same value as the value of the target voltage. It is possible to prevent a situation in which the average value of the output voltage actually supplied to the load (motor 300) becomes lower than the target voltage value (insufficient voltage) in spite of Control becomes easy.

  As shown in FIG. 8, when the load (current Iout supplied to the motor 300) is gradually increased over time, the duty ratio of the input conversion circuit 111 is controlled to be gradually increased. The output voltage is detected in synchronization with the turn-off timing, and the lower peak value of the output voltage Vout of the input converter 110 is detected, so that the average value of the output voltage is always held at a value larger than the target voltage value. The output voltage is stabilized.

  In the present invention, the number of input conversion units having input conversion circuits is not limited to four, and an arbitrary number can be selected.

As described above, the DC-DC converter 100 is
An input conversion circuit 111, an input conversion circuit 111, etc., which have a switching element 112 and a coil 113, and which output a boosted or reduced input DC voltage by switching the switching element 112 in parallel are arranged in parallel. A connected input converter 110;
An output voltage detector 120 for detecting an output voltage of the input converter 110;
Duty ratio control for controlling the duty ratio of the switching elements 112, 112,... Of the input conversion circuit 111, the input conversion circuit 111,... In the current discontinuous mode based on the output voltage detected by the output voltage detection unit 120. Part 130;
Comprising
The output voltage detection unit 120 detects the output voltage of the input conversion unit 110 in synchronization with the timing at which one of the switching elements 112 of the input conversion circuit 111, the input conversion circuit 111,... .
With this configuration, the output voltage detection timing and the charging start timing of the output-side capacitor (the output-side filter 103 in this embodiment) are synchronized, and it is easy even if the duty ratio and the parallel number change. It is possible to control the output voltage.

Moreover, the control method of the DC-DC converter according to the present invention includes:
An input conversion circuit 111, an input conversion circuit 111, etc., which have a switching element 112 and a coil 113, and which output a boosted or reduced input DC voltage by switching the switching element 112 in parallel are arranged in parallel. A control method for a DC-DC converter 100 including a connected input conversion unit 110, comprising:
The output voltage of the input conversion unit 110 is detected in synchronization with the timing when any of the switching elements 112, 112,... Of the input conversion circuit 111, the input conversion circuit 111,.
Based on the detected output voltage, the duty ratios of the switching elements 112, 112,... Of the input conversion circuit 111, the input conversion circuit 111,.
With this configuration, the output voltage detection timing and the charging start timing of the output-side capacitor (the output-side filter 103 in this embodiment) are synchronized, and it is easy even if the duty ratio and the parallel number change. It is possible to control the output voltage.

The figure which shows one Embodiment of the DC-DC converter which concerns on this invention. The time chart which shows the behavior at the time of low load of the input conversion circuit of one Embodiment of the DC-DC converter which concerns on this invention. The time chart figure which shows the behavior at the time of middle load of the input conversion circuit of one Embodiment of the DC-DC converter which concerns on this invention. The time chart figure showing the behavior at the time of high load of the input conversion circuit of one embodiment of the DC-DC converter concerning the present invention. The time chart which shows the output voltage at the time of low load of one Embodiment of the DC-DC converter which concerns on this invention. The time chart which shows the output voltage at the time of medium load of one Embodiment of the DC-DC converter which concerns on this invention. The time chart which shows the output voltage at the time of high load of one Embodiment of the DC-DC converter which concerns on this invention. The figure which shows the output voltage behavior at the time of output current increase in one Embodiment of the DC-DC converter which concerns on this invention. The figure which shows the conventional input conversion circuit (boost circuit). The time chart which shows the behavior in the low load of the input conversion circuit of the conventional DC-DC converter. The time chart which shows the behavior in the time of middle load of the input conversion circuit of the conventional DC-DC converter. The time chart which shows the behavior in the time of high load of the input conversion circuit of the conventional DC-DC converter. The time chart which shows the output voltage at the time of the low load of the conventional DC-DC converter. The time chart which shows the output voltage at the time of medium load of the conventional DC-DC converter. The time chart which shows the output voltage at the time of high load of the conventional DC-DC converter. The figure which shows the output voltage behavior at the time of the output current increase in the conventional DC-DC converter.

Explanation of symbols

DESCRIPTION OF SYMBOLS 100 DC-DC converter 110 Input conversion part 111 Input conversion circuit 112 Switching element 113 Coil 120 Output voltage detection part 130 Duty ratio control part

Claims (2)

An input conversion unit having a switching element and a coil, wherein the switching element performs a switching operation to connect in parallel a plurality of input conversion circuits that step up or step down the input DC voltage,
An output voltage detector for detecting an output voltage of the input converter;
A duty ratio controller that controls the duty ratios of the switching elements of the plurality of input conversion circuits in a current discontinuous mode based on the output voltage detected by the output voltage detector;
Comprising
The output voltage detection unit is a DC-DC converter that detects an output voltage of the input conversion unit in synchronization with a timing at which any of the switching elements of the plurality of input conversion circuits is turned off. DC having a switching element and a coil, and having an input conversion unit connected in parallel with a plurality of input conversion circuits for boosting or stepping down an input DC voltage by performing a switching operation of the switching element A method for controlling a DC converter, comprising:
Detecting the output voltage of the input conversion unit in synchronization with the timing when any of the switching elements of the plurality of input conversion circuits is turned off from on,
A control method for a DC-DC converter, which controls a duty ratio of switching elements of the plurality of input conversion circuits in a current discontinuous mode based on the detected output voltage.

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