JP2021170934A - DC voltage conversion circuit - Google Patents

Abstract

To provide a DC voltage conversion circuit that realizes a current discontinuous mode at low output.SOLUTION: There is provided a DC voltage conversion circuit comprising: a switching element; a reflux diode connected in series with the switching element; a reactor whose one end is connected to the interconnection point in the series of the switching element and the reflux diode; a first port that is connected to the other end of the reactor and one end opposite to the interconnection point of the switching element or the reflux diode, whichever is on the low potential side, to serve as one of the input and output; a second port that is connected to both ends of the series and is the other of the input and output; a current sensor that detects the current flowing in the reactor; and a control unit that corrects the detected value of the current sensor based on the inductance of the reactor, the carrier frequency, and the respective voltages of the first and second ports to switch the switching element.SELECTED DRAWING: Figure 2

Description

The present invention relates to a DC voltage conversion circuit.

A well-known chopper circuit, which is an example of a DC / DC converter, is composed of, for example, a set of two switching elements and a reactor. The high-side switching element and the low-side switching element are connected in series with each other in the same direction. A diode is provided in antiparallel to each switching element. Regarding the control operation of the two switching elements, switching control in which one of the switching elements is selected and switched according to the direction in which the current flows (boost / step-down) and conduction / non-conduction of both switching elements are alternated. There is a seamless control that performs complementary switching (see, for example, Patent Document 1 and FIG. 3) for switching to.

When the switching element is a bipolar type such as an IGBT (Insulated Gate Bipolar Transistor), only a unidirectional current flows through the switching element, and the reverse current flows through a diode arranged in antiparallel to the IGBT. The diode has a larger conduction resistance than the IGBT itself. Therefore, even if complementary switching is performed, the conduction loss during the energy release period of the reactor cannot be reduced, so switching control should be selected.

On the other hand, when the switching element is a field effect transistor (FET) capable of bidirectional conduction, the conduction loss can be reduced by performing complementary switching. Therefore, it is meaningful to select seamless control.

Japanese Unexamined Patent Publication No. 2014-192914

However, seamless control is inferior to switching control. That is, when the output current is small, the current discontinuous mode is not set, and the ripple current has a large amplitude because it always operates in the current continuous mode. Therefore, at low output, the rate of loss generated by the resistance of the switching element or reactor increases, and the conversion efficiency decreases.

In view of these problems, it is an object of the present invention to provide a DC voltage conversion circuit that realizes a current discontinuous mode at low output.

The present disclosure includes the following inventions, provided that the present invention is defined by the claims.
The DC voltage conversion circuit according to one expression of the present disclosure includes a high-side switching element, a low-side switching element connected in series with the high-side switching element, the high-side switching element, and the low-side switching element. A reactor having one end connected to an interconnection point in the series, a first port connected to the other end of the reactor and one end of the low-side switching element, and one of an input and an output. A second port connected to both ends of the series and the other of the input and output, a current sensor that detects the current flowing through the reactor, and a control unit that switches between the high-side and low-side switching elements. Of the high-side and low-side switching elements, the switching element on which the current flows during the energy release period of the reactor is a bidirectional conducting element in which the element itself is bidirectionally conductive in the ON state. The control unit is a DC voltage conversion circuit that turns on the bidirectional conductive element, starts the energy release period, and turns it off when the current flowing through the reactor becomes zero.

Further, the control method according to one expression of the present disclosure is a DC voltage conversion circuit as a DC chopper circuit including a high-side switching element, a low-side switching element, and a reactor, and is performed by a DC switching control unit. A method for controlling a voltage conversion circuit, in which one of the switching elements is turned on and the other is turned off during the energy storage period of the reactor, a current is passed through the reactor, and each switching is performed during the energy release period of the reactor. This is a control method of a DC voltage conversion circuit that turns off the one of the elements and turns off the other when the current flowing through the reactor becomes 0 so that it can conduct in both directions.

According to the present invention, with respect to the DC voltage conversion circuit, it is possible to realize a current discontinuous mode at low output and improve the conversion efficiency.

It is a circuit diagram which shows an example of the DC voltage conversion circuit (DC / DC converter, chopper circuit). It is a timing chart which shows the generation procedure of a gate pulse at the time of discharge. It is a timing chart which shows the generation procedure of a gate pulse at the time of charging. It is a circuit diagram of the DC voltage conversion circuit 1 as a simulation model. It is a waveform diagram which shows the simulation result in the current command value i ^* _{L = + 1A, discharge, and current discontinuity modes.} It is a waveform diagram which shows the simulation result in the current command value i ^* _{L = + 3A, discharge, and current discontinuity modes.} It is a waveform diagram which shows the simulation result in the current command value i ^* _{L = + 5A, discharge, and current continuous mode.} It is a waveform diagram which shows the simulation result in the current command value i ^* _{L = -1A, charge, and current discontinuity modes.} It is a waveform diagram which shows the simulation result in the current command value i ^* _{L = -4A, charge, and current discontinuity modes.} It is a waveform diagram which shows the simulation result in the current command value i ^* _{L = -5A, charge, and current continuous mode.} It is a waveform diagram which shows the simulation result at the time of changing the current command value i ^* _{L alternately to -10A and 10A.}

[Summary of Embodiment]
The gist of the embodiment of the present invention includes at least the following.

(1) This DC voltage conversion circuit is a series of a high-side switching element, a low-side switching element connected in series with the high-side switching element, the high-side switching element, and the low-side switching element. A reactor having one end connected to the interconnection point in the above, a first port connected to the other end of the reactor and one end of the low-side switching element, and one of an input and an output, and the series. A second port, which is connected to both ends and is the other of the input and output, a current sensor that detects the current flowing through the reactor, and a control unit that switches between the high-side and low-side switching elements. Among the high-side and low-side switching elements, the switching element on which the current flows during the energy release period of the reactor is a bidirectional conducting element in which the element itself is bidirectionally conductive in the ON state. The control unit is a DC voltage conversion circuit that turns on the bidirectional conductive element, starts the energy release period, and turns it off when the current flowing through the reactor becomes zero.

In the DC voltage conversion circuit configured in this way, the control unit turns on the bidirectional conductive element during the period from the start of energy release to the time when the current becomes 0 in the energy release period of the reactor. When the current becomes 0, the control unit turns off the switching element and blocks the current that tries to flow in the opposite direction. Therefore, the absolute value of the current flowing through the reactor during the energy release period is limited from the peak value to zero. As a result, when the output is low, the discontinuous mode of the current during the energy release period is realized, and the conversion efficiency can be improved.

(2) Further, in the DC voltage conversion circuit of (1), for example, the first port is an input, the second port is an output, and the high-side switching element is the bidirectional conducting element.
In this case, in the DC current conversion circuit as the step-up chopper, the control unit turns on the high-side switching element during the period from the start of energy release to the time when the current becomes 0 in the energy release period of the reactor. When the current becomes 0, the control unit turns off the switching element and blocks the current that tries to flow in the opposite direction. Therefore, the absolute value of the current flowing through the reactor during the energy release period is limited from the peak value to zero. As a result, a discontinuous mode of current during the energy release period is realized.

(3) Further, in the DC voltage conversion circuit of (1), for example, the first port is an output, the second port is an input, and the low-side switching element is the bidirectional conducting element.
In this case, in the DC current conversion circuit as the step-down chopper, the control unit turns on the low-side switching element during the period from the start of energy release to the time when the current becomes 0 in the energy release period of the reactor. When the current becomes 0, the control unit turns off the switching element and blocks the current that tries to flow in the opposite direction. Therefore, the absolute value of the current flowing through the reactor during the energy release period is limited from the peak value to zero. As a result, a discontinuous mode of current during the energy release period is realized.

(4) Further, in the DC voltage conversion circuit according to any one of (1) to (3), the carrier to be compared with the reference value in order to obtain the control signal of the bidirectional conducting element is the control signal of the other switching element. It may be a serrated triangular wave that is synchronized with the carrier of the triangular wave for obtaining the above and has twice the amplitude.
In this case, the timing for turning off the other switching element can be easily obtained by comparing the serrated triangular wave and the reference value with each other.

(5) Further, in the DC voltage conversion circuit according to any one of (1) to (4), for example, the two switching elements are field effect transistors, and the control unit flows to the reactor during the energy release period. If the direction of the current does not change, the two switching elements can be made to perform complementary switching.
In this case, by using a pair of field effect transistors (FETs), which are typical switching elements, and performing complementary switching at high output, conduction loss is reduced as compared with the case of passing through a diode, and control is performed at low output. Therefore, a discontinuous mode can be realized. Although the same thing can be achieved by other elements, a field effect transistor having bidirectionality with a single element is preferable.

(6) From the viewpoint as a control method, this is performed by the switching control unit for a DC voltage conversion circuit as a DC chopper circuit including a high-side switching element, a low-side switching element, and a reactor. This is a method of controlling a DC voltage conversion circuit, wherein a current is passed through the reactor with one of the switching elements turned on and the other turned off during the energy storage period of the reactor, and the above-mentioned is performed during the energy release period of the reactor. This is a control method for a DC voltage conversion circuit that turns off one of the switching elements and turns off the other when the current flowing through the reactor becomes 0 so that it can conduct in both directions.

According to the control method of such a DC voltage conversion circuit, the other switching element is turned on during the period from the start of energy release to the time when the current becomes 0 in the energy release period of the reactor. When the current becomes 0, the switching element is turned off to block the current that tries to flow in the opposite direction. Therefore, the absolute value of the current flowing through the reactor during the energy release period is limited from the peak value to zero. As a result, when the output is low, the discontinuous mode of the current during the energy release period is realized, and the conversion efficiency can be improved.

[Details of Embodiment]
Hereinafter, a DC voltage conversion circuit (including a control method thereof) according to an embodiment of the present invention will be described with reference to the drawings.

<< Circuit configuration example >>
FIG. 1 is a circuit diagram showing an example of a DC voltage conversion circuit (DC / DC converter, chopper circuit). In the figure, the DC voltage conversion circuit 1, the DC voltage v _i of the first port P1, to convert the DC voltage v _o of the second port P2, or bidirectional conversion circuit capable of converting the reverse It has become. Relatively, v low voltage towards the _i, people of v _o is the relationship between the high voltage.

DC voltage converter 1 includes, as main circuit element, a capacitor 11, a reactor 12, switching elements of the high-side Q _H, low-side switching element Q _L, and includes a capacitor 13. The switching element Q _H, Q _L forms a serial body are connected to each other in series in the same direction, one end of the reactor 12 is connected to the interconnection point. One end of the other end and the switching element _{Q L} of the reactor 12 (source), is connected to the first port P1. Both ends of the series body (the drain of the switching element Q _H, the source of the switching element Q _L) is connected to the second port. The switching element _Q H, _{Q L} is the FET, respectively, have a body diode _d H, and _{d L.} Each of the switching elements Q _H, Q _L is when on, (not including a body diode) element itself can be energized in both directions.

The switching element _Q H, ON / OFF control of _{Q L} is performed by the control unit 10. The control unit 10 includes, for example, a computer, and the computer executes software (computer program) to realize a necessary control function. The software is stored in a storage device (not shown) of the control unit 10.

The circuitry for measuring a voltage sensor 14 for detecting a voltage across the voltage v _i or capacitor 11 is provided. The detection output of the voltage sensor 14 is sent to the control unit 10. The current flowing through the reactor 12 is detected by the current sensor 15. The detection output of the current sensor 15 is sent to the control unit 10. Further, a voltage sensor 16 for detecting the voltage _{vo or the voltage across the capacitor 13 is provided.} The detection output of the voltage sensor 16 is sent to the control unit 10.

Here, for example, it is considered that a constant voltage DC power supply is connected to the first port P1 and the second port P2 at both ends of the DC voltage conversion circuit 1. As a practical example of the DC power source, the v _i, battery, solar panels, etc., the v _o, there is DC bus such as a large-capacity capacitor is connected. The voltage of these DC power supplies changes depending on the state of charge and the voltage drop caused by the flowing current, but the impedance is reduced by the capacitors 11 and 13, and the voltage can be considered to be constant in a short time such as the switching cycle. Therefore, the low voltage side, the high voltage side, respectively, can be regarded as a voltage source of the voltage v _i, voltage v _o. The inductance of the reactor 12 L, the current flowing through the reactor _{i L,} the current _{i L} detection values _{i d} at the midpoint of the ripple, the carrier frequency and _{f s.} In the following description, for convenience, the case where a current flows from the low voltage side to the high voltage side is called discharge, and the reverse is called charge, and the sign of the current defines the discharge direction as "+" and the charge direction as "-".

<< List of symbols used >>
v _i : Low voltage side voltage v _o : High voltage side voltage L: Reactor inductance i _L : Reactor current (current flowing through the reactor)
i ^* _L : Reactor current command value (control command value)
_id : Reactor current sensor detection value (detected in the valley of the carrier)
i _Lx : Reactor current conversion value in current discontinuous mode <i _L >: Average value of reactor current (matches _{id in continuous mode)}
f _s: Carrier frequency T _s: carrier cycle D: low-side switching element _{Q L} of PWM (Pulse Width Modulation) the reference value D _2: PWM reference value of the high-side switching element _{Q H} K _cd: gain of the feedback control (discharge When, current continuous mode)
K _dd : Feedback control gain (current discontinuous mode during discharge)
K _cc : Feedback control gain (during charging, current continuous mode)
K _dc : Feedback control gain (current discontinuous mode when charging)

《Control theory》
A switching element Q _H of the high side, low side and the switching element Q _L, the control unit 10 so as to be alternately turned on, the switching control.
Of the switching control, the period for charging (energy storage) the reactor 12 is referred to as an energy storage period, and the period for discharging (energy release) is referred to as an energy release period.

The PWM reference value for generating the gate control pulse of the FET conducting during the energy storage period is obtained as follows.
The reactor current conversion value in the current discontinuity mode during discharge is expressed by the following equation (1) when ^{i *} _{L ≥ 0.
^{i Lx = 2Lf s i d 2}} [(1 / v i) + {1 / (v o -v i)}] ··· (1)

Also, during discharge, PWM reference value D of the low side switching element _{Q L} in the continuous current ^{mode, i} _{* L} ≧ 0 and, in _the case of _{i Lx} ≧ _{i d,} as represented by the following equation (2).
_{D = {(v o -v i} ) / v o} + {K cd Lf s (i * L -i d) / v o}
... (2)

During discharge, PWM reference value D of the low side switching element in the current discontinuous ^mode, _{i *} L> 0 and, in _the case of i Lx _{<i d,} as represented by the following equation (3).
_{D = {2Lf s (v o} -v i) / (v i v o)} 1/2 +
{Lf _s ( _{vo −} v _i ) / (2i ^* _L v _i v _o )} ^1/2 K _dd (i ^* _{L −} i _Lx )
... (3)

When charging, the reactor current conversion value in the current discontinuous mode is expressed by the following equation (4) when ^{i *} _{L <0.
^{i Lx = 2Lf s i d 2}} [{1 / (v i -v o)} - (1 / v i)] ··· (4)
Charging, PWM reference value _{D 2} of the switching element _{Q H} of the high-side in the continuous current ^mode, _{i *} L <0 and, in _the case of _{i Lx} ≧ _{i d,} as represented by the following equation (5).
_{D 2 = (v i / v} o) - {K cc Lf s (i * L -i d) / v o} ··· (5)

Charging, PWM reference value _{D 2} of the switching element _{Q H} of the high-side in discontinuous current ^mode, _{i *} L <0 and, in _the case of i Lx _{<i d,} as represented by the following equation (6).
^{_{D 2 = {2Lf s i *}} L v i / (v o (v i -v o))} 1/2 +
_{{Lf s v i / (2v} i (v i -v o) i * L)} 1/2 K dc (i * L -i Lx)
... (6)

Of the above equations, (2) and (5) are arithmetic expressions in the current continuous mode, and if a dead time is provided by inversely transforming the pulse using the reference values obtained by these equations, the other energy release period It is possible to obtain a gate control pulse of a switching element that conducts to. The PWM reference values of the switching element conducting during the energy storage period in the current discontinuous mode are obtained in (3) and (6), but the gate control pulse of the switching element conducting during the energy release period is as simple as the current continuous mode. In the reverse conversion process, it is not possible to obtain a pulse that turns off at the same time when the energy emission current becomes zero. Therefore, going back to the process of deriving these mathematical formulas, the gate control pulse of the switching element that conducts during the energy release period will be examined.

(At the time of discharge)
The following equation (7) is obtained from the continuity equation in mode I ( _{the period when the switching element Q L is} on and the switching element Q _{H is off).}
v _i = L (di _L / dt) = Lf _s i _peak / D = 2 Lfi _d / D ... (7)
The following equation (8) is obtained from the continuity equation in mode II ( _{the period when the switching element Q L is} off and the switching element Q _{H is on).}
v _i −v _o = L (di _L / dt) =-(Lf _s i _peak / D ₂ )
_{= 2Lf s i d / D 2} ··· (8)

From the condition that the average current for the entire period matches the current command value, the following equation (9) is obtained.
i ^* _L = (D + D ₂ ) (i _peak / 2) ・ ・ ・ (9)
By eliminating D from the above equations (7) and (9), the following equation (10) is obtained.
_{^{i * L = {(Lf s}} i peak / v i) + D 2} (i peak / 2) ··· (10)
_{By eliminating ipake} from equation (8), the following equation (11) is obtained.
i ^* _L = D ₂ ² v _o ( _{vo −} v _i ) / (2 Lf _s v _i ) ・ ・ ・ (11)

Organize the formula (11) to obtain equation (12) is a feed-forward term of _{D 2.}
D ₂ = {2Lf _s i ^* _L v _i / ( _vo ( _{vo −} v _i ))} ^1/2 ... (12)
The following equation (13) is obtained by partially differentiating the equation (12) with respect to i ^* _L.
∂D ₂ / ∂i ^* _L = {Lf _s v _i / (2i ^* _L v _o ( _{vo −} v _i ))} ^1/2
... (13)
The following equation (14) is obtained by adding the equation (13) to the equation (12).
D ₂ + ∂D ₂ = {2Lf _s i ^* _L v _i / v _o ( _{vo −} v _i )} ^1/2 +
{Lf _s v _i / 2i ^* _L v _o ( _{vo −} v _i )} ^1/2 ∂i ^* _L
... (14)

^{By replacing ∂i *} _L in the equation (14) with the deviation between the command value and the detected value, the calculation equation (15) of the PWM reference value incorporating the feedback control is obtained. Here, K _dd is an adjustment coefficient in the range of 0 to 1. Equation (15) is made with those obtained by multiplying the right-hand side to _{v i / (v o -v i} ) of the formula (3). ^That, _{i *} L> 0 and, in _the case of i Lx _{<i d,} the equation (15) below is obtained.
D ₂ = {2Lf _s i ^* _L v _i / ( _vo ( _{vo −} v _i ))} ^1/2 +
{Lf _s v _i / (2i ^* _L v _o ( _{vo −} v _i ))} ^1/2 K _dd (i ^* _{L −} i _L )
... (15)
Although dependent on-time ratio of the switching element Q _H of the high-side in equation (15), must be considered in sync with the timing of the low-side switching element Q _L on / off.

FIG. 2 is a timing chart showing a procedure for generating a gate pulse during discharge.
In FIG. 2, first, as shown in (a), the reference value D of the equation (3) is compared with the triangular wave carrier having a peak width of 1, a duty of 0.5, and no bias, and the reference value is equal to or larger than the carrier. by range and oN period, (c), the gating pulse G _L of the switching element Q _L object is obtained. Note that only one set of gate signals in (c) is shown, and the other illustrations are omitted.

On the other hand, as the carrier used for the gate control pulses generated in the switching element Q _H, (b), the peak width 2, duty 1, using serrated triangular wave carrier without bias. The serrated triangular wave has a shape in which the first half phase of the triangular wave carrier shown in (a) is unchanged from 0 ° to 180 °, and a straight line is further extended from the phase of 180 ° to 360 °. By comparing _{this carrier with the reference value D 3} obtained by the following equation (16), it is possible _{to select a range A in which D 3} takes a value equal to or higher than the carrier and obtain a timing to turn off the _{switching element Q H.} can. That is, it is possible to easily by comparing with each other the reference value D ₃ and serrated triangular wave to obtain a timing to turn off the switching element Q _H.
Further, by excluding the time and the dead time of the switching element Q _L is turned from the range A, it is possible to obtain a gate control pulse G _H of the switching element Q _H.
D ₃ = D + 2D ₂ ... (16)

The dead time can be set by the following procedure. A bias value E (not shown) is added to the reference value D, and the range B in which D + E is equal to or greater than the carrier is selected in comparison with the triangular wave carrier having a peak width of 1. Since the range B (not shown) includes the dead time by adding the bias value E to the reference value D, the gate control pulse _{GH in consideration of the dead time is obtained by excluding the range B from the range A.} Note the relationship of the dead time M, the carrier frequency f _s and the bias value E can be expressed by the following equation (17). For example, if a dead time of 1 microsecond is created for a carrier frequency of 20 kHz (cycle of 50 microseconds), the bias value is 0.04.
_{E = 2f s M ··· (17} )

As shown in FIG. 2 (d), rises from the reactor current is zero when the energy storage period DT _S of the switching element _{Q L} is turned on until _{i peak,} energy is stored in the reactor 12. In subsequent energy emission period D ₂ T _S, the switching element Q _L is off, the switching element Q _H is turned on, the reactor current is lowered, it becomes zero. Period D ₃ T _S from the moment it becomes 0 until the next energy storage period, the reactor current becomes discontinuous period remains zero. Such an operation is repeated. _{The dotted line of <i L} > in (d) represents the average value of the discontinuous reactor currents.

(When charging)
The following equation (18) is obtained from the continuity equation in mode I ( _{the period when the switching element Q L is} off and the switching element Q _{H is on).}
v _i −v _o = L (di _L / dt) = Lf _s i _peak / D _{2
= 2Lf s i d / D 2} ··· (18)
The following equation (19) is obtained from the continuity equation in mode II ( _{the period when the switching element Q L is} off and the switching element Q _{H is on).}
v _i = L (di _L / dt) = Lf _s i _peak / D = 2 Lfi _d / D ... (19)

From the condition that the average current for the entire period matches the current command value, the following equation (20) is obtained.
i ^* _L = (D + D ₂ ) (i _peak / 2) ・ ・ ・ (20)
_{By eliminating D 2} from the above equations (18) and (20), the following equation (21) is obtained.
_{^{i * L = [D + {}} Lf s i peak / (v i -v o)}] (i peak / 2)
... (21)
_{By eliminating ipake} from equation (19), the following equation (22) is obtained.
i ^* _L = D ² v _o v _i / {2 Lf _s (v _{o −} v _i )} ・ ・ ・ (22)

The equation (22) is rearranged to obtain the equation (23) which is a feedforward term of D.
D = {2Lf _s i ^* _L ( _{vo −} v _i ) / (v _o v _i )} ^1/2 ... (23)
The following equation (24) is obtained by partially differentiating the equation (23) with respect to i ^* _{L.
^{∂D / ∂i * L = {Lf}} s (v o -v i) / (2i * L v o v i)} 1/2
... (24)
The following equation (25) is obtained by adding the equation (24) to the equation (23).
D ₂ + ∂D = {2Lf _s i ^* _L ( _{vo −} v _i ) / (v _o v _i )} ^1/2 +
{Lf _s ( _{vo −} v _i ) / (2i ^* _L v _o v _i )} ^1/2 ∂i ^* _L
... (25)

^{By replacing ∂i *} _L in the equation (25) with the deviation between the command value and the detected value, the calculation equation (26) of the PWM reference value incorporating the feedback control is obtained. Here, K _cd is an adjustment coefficient in the range of 0 to 1. Equation (26) is made as that applied to the right-hand side of equation (6) _{(v o -v i) / v} i. ^That, _{i *} L <0 _and,, i Lx> For _{i d,} the equation (26) below is obtained.
D = {2Lf _s i ^* _L ( _{vo −} v _i ) / (v _o v _i )} ^1/2 +
^{_{{Lf s (v o -v i}} ) / (2i * L v o v i)} 1/2 K cd (i * L -i L)
... (26)
The on-time rate of the low-side switching element Q _L is determined by the equation (26), but synchronization with the on / off timing of the high-side switching element Q _{H must be considered.}

FIG. 3 is a timing chart showing a procedure for generating a gate pulse during charging.
3, (a), the reference value D ₂ of formula (6), peak width 1, as compared duty 0.5, a triangular wave carrier without bias, range reference value is greater than or equal to the carrier the by the on period is obtained gating pulse G _H of the switching element Q _H objects shown in (c). Note that only one set of gate signals in (c) is shown, and the other illustrations are omitted.

On the other hand, the gating pulse generation of the switching element Q _L, (b), the used peak width 2, duty 1, the serrated triangular wave without bias to the carrier. The serrated triangular wave, the first half phase 0 ° of the triangular wave carrier for the switching element Q _H to 180 ° is intact, between 360 ° from the phase 180 ° has a shape obtained by extending the straight line. The carrier as compared to the reference value D ₄ obtained by the following equation (27), can be obtained the timing of D ₄ selects a range C which takes a value more than the carrier, to turn off the switching element Q _L .. That is, it is possible to easily by comparing each other with serrated triangular wave and the reference value D _4, to obtain the timing of turning off the switching element Q _L.
Can be obtained gating pulse G _L of the switching element Q _L by further exclude period and dead time of the switching element Q _H is turned on from this range C.
D ₄ = 2D + D ₂ ... (27)

The dead time can be set by the following procedure. A bias value E (not shown) is added to the reference value D ₂ to select a range F (not shown) in which _{D 2} + E is greater than or equal to the carrier in comparison with the triangular wave carrier having a peak width of 1. Because it contains a dead time in the range F by the reference value D ₂ by adding a bias value E, the gating pulse G _L considering the dead time by excluding the range F in the range C. Incidentally dead time M, the relationship of the frequency f _s and a bias value E of the carrier can be expressed by the same formula as when discharge (17).

As shown in FIG. 3 (d), for charging, the reactor current when the energy storage period D ₂ T _S of the switching element Q _H is turned on, given in absolute values, increases from 0 to i _peak , Energy is stored in the reactor 12. In subsequent energy release period DT _S, on the switching element Q _L is, the switching element Q _H is turned off, the reactor current is lowered, becomes zero. Period D ₃ T _S from the moment it becomes 0 until the next energy storage period, the reactor current becomes discontinuous period remains zero. Such an operation is repeated. _{The dotted line of <i L} > in (d) represents the average value of the discontinuous reactor currents.

"inspection"
FIG. 4 is a circuit diagram of the DC voltage conversion circuit 1 as a simulation model.
In the figure, a 200V DC power supply 2 is connected to the first port P1. A 350V DC power supply 3 is connected to the second port P2. The capacitance of the capacitor 11 is 200 μF, the inductance of the reactor 12 is 500 μH, the capacitance of the capacitor 13 is 2.2 mF, and the control frequency of the control unit 10 is 20 kHz. The dead time was 1 microsecond. The state in which the current flows from the low-voltage DC power supply 2 to the high-voltage DC power supply is defined as the discharge of the DC power supply 2, and the opposite direction is defined as the charge. In this state, the control unit 10 acquires the voltage v _i based on the detection output of the voltage sensor 14. The control unit 10 based on a detection output of the current sensor 15 to obtain a sensor detection value i _d of the current i _L flowing through the reactor 12. Further, the control unit 10 acquires the _{voltage vo} based on the detection output of the voltage sensor 16.

5 to 11 are waveform diagrams showing simulation results. The conditions in each figure are as follows.
Fig. 5: Current command value i ^* _L = + 1A, discharge, current discontinuity mode Fig. 6: Current command value i ^* _L = + 3A, discharge, current discontinuity mode Fig. 7: Current command value i ^* _L = + 5A, discharge, Current continuous mode Fig. 8: Current command value i ^* _L = -1A, charging, current discontinuous mode Fig. 9: Current command value i ^* _L = -4A, charging, current discontinuous mode Fig. 10: Current command value i ^* _L = -5A, charge, current continuous mode FIG. 11: The current command value i ^* _L is continuously changed between -10A and 10A.

In each of FIGS. 5 to 10, the upper waveform diagram shows reference values D, D ₂ , D ₃ , D ₄ , carriers cw 1, cw 2, cw 3 using the line type shown in the legend. The waveform diagram in the middle shows the Kate control pulses _GL and _GH using the line type shown in the legend. In the lower waveform diagram, using the line type shown in the legend, the reactor current i _L (solid line moving up and down), the average value <i _L >, the converted value i _Lx , and the command value i ^* _{L regarding the reactor current.} , and represent the detected values _{i d.}

Discontinuous current mode at the time of discharging (5, 6), the gate control signal is outputted to the switching element Q _H as intended energy release period has a discontinuous reactor current i _L. In addition, a dead time of 1 microsecond is provided within the energy release period. The average value <i _L > and the converted value i _Lx of the reactor current are in agreement with the command value i ^* _L , and the detected value _id is higher than these.

In the current continuous mode (Fig. 7), complementary switching is performed as in seamless control, but the transition from energy storage to energy release and the transition from energy release to energy storage are each 1 microsecond within the energy release period. There is a dead time of seconds. The average value of the reactor current and the detected value _id are in agreement with the command value i ^* _L, and the converted value i _Lx is larger than these.
Similarly, during charging, both the current discontinuous mode (FIGS. 8 and 9) and the current continuous mode (FIG. 10) are controlled as intended.

FIG. 11 shows various states when the current command value i ^* _L is changed between -10A and + 10A. In order from the top, the first stage indicates a state flag, where 0 is standby, 1 is discontinuous discharge, 2 is continuous discharge, 3 is discontinuous charge, and 4 is continuous charge. The second stage is a waveform diagram in which the reactor current command value i ^* _L and the average value <i _{L> overlap.} Third stage, part of the width in the vertical drawn by a thin two-dot chain line in reactor current i _L, the dotted line in the vicinity the center is detected values i _{d. The remaining alternate long and short} dash line is the converted value i Lx. The fourth row represents the reference values D, D ₂ , D ₃ , and D _{4 according} to the line type shown in the legend.

In Figure ^{11, i} _{* L} in the range of less than ± 0.1 A two switching elements _Q H, (0 of the first stage) standby mode to the gate block both _{Q L} is provided. The transition from the current discontinuous mode to the current continuous mode and the transition from the current continuous mode to the current discontinuous mode are all performed without any problem during both discharging and charging, and the average value of the reactor current in one carrier cycle is the command value. Is consistent with.

"summary"
To summarize the above, the DC voltage conversion circuit 1 of the present embodiment is first a chopper type DC / DC converter using an FET as a switching element. The DC voltage converter 1, as a basic configuration, a switching element Q _H of the high-side, of the connected low side to the switching element Q _H series with the switching element Q _L, the switching element Q _H and the switching element Q _L One end of the reactor 12 is connected to the interconnection point in the series. Further, the other end of the reactor 12, have led to one end of the switching element Q _L, a first port P1 which serves as one input and output, have led to both ends of the series body, the other input and output a second port P2, and a control unit 10 which performs chopper control, the controls each of the switching elements Q _H, a Q _L.

At least, the high-side and low-side switching elements Q _H, of Q _L, the switching element towards the current flows to the energy release period of the reactor 12 element itself in the ON state is bidirectional conducting bidirectional conduction It is assumed that it is an element. In other words, it can be said that it is a control that is meaningful to break the continuity because it is a bidirectional conductive element. If, in FIG. 1, if performing only step-up from the first port P1 to the second port P2, the switching element Q _H of the direction which current flows to the energy release period in the reactor 12 is the element itself in the ON state bidirectional A conductive bidirectional conductive element, such as an FET. Further, in FIG. 1, if performing only step-down from the second port P2 to the first port P1, the switching element Q _L towards the current flows to the energy release period in the reactor 12 is the element itself in the ON state bidirectional A conductive bidirectional conductive element, such as an FET. When performing step-up / step-down in both directions, the two switching elements Q _H, Q _L will be referred to as a two-way conduction element together.

Then, the control unit 10 turns on the bidirectional conducting element so that a current due to the energy release of the reactor 12 flows, and turns off the element itself when the current becomes zero. That is, the current due to the energy release is conducted in the reverse direction (from the source to the drain) to the switching element main body (FET) which is a bidirectional conducting element, and the energizing resistance of the entire switching element (including the body diode) is reduced while the energy is reduced. When the current due to emission becomes 0, the switching element main body is turned off to realize the discontinuous mode.

In the DC voltage conversion circuit 1 configured in this way, the absolute value of the current flowing through the reactor 12 during the energy release period is limited from the peak value to 0, and the current does not flow in the opposite direction to that immediately before. .. As a result, a discontinuous mode of current during the energy release period is realized. In addition, it was confirmed by simulation that the desired operation can be obtained.

The DC voltage conversion circuit 1 that achieves both the current discontinuity mode and the reverse conduction of the current due to energy release performs complementary switching at all times and operates only in the current continuous mode when the output is low compared to a seamless control type FET chopper or the like. The ripple rate can be reduced. Therefore, high efficiency and low noise can be expected. It is considered to be particularly effective for controlling storage batteries and photovoltaic power generation, which are often operated with outputs lower than the rating.

"others"
In the above embodiment, the FET is used as the switching element, but it is also possible to use a set of two IGBTs in which the emitters are connected to each other instead. Such a switching element is also a bidirectional conducting element. However, a single element and bidirectional FET is considered to be the most suitable.

<< Supplement >>
It should be noted that the embodiments disclosed this time are exemplary in all respects and are not considered to be restrictive. The scope of the present invention is indicated by the scope of claims, and it is intended to include all modifications within the meaning and scope equivalent to the scope of claims.

1 DC voltage converter second DC power source 3 DC power supply 10 controller 11 condenser 12 reactor 13 capacitor 14 voltage sensor 15 a current sensor 16 voltage sensor d _H body diode d _L body diode P1 first port P2 second port Q _H switching element Q _L switching element

However, seamless control is inferior to switching control. That is, when the output current is small, the current discontinuous mode is not set, and the ripple current has a large amplitude because it always operates in the current continuous mode. Therefore, at low output, the rate of loss generated by the resistance of the switching element or reactor increases, and the conversion efficiency decreases.
On the other hand, when the switching control is adopted, the current discontinuous mode may occur at the time of low output, but it is difficult to accurately control the current according to the target value in the current discontinuous mode.

An object of the present disclosure is to provide a DC voltage conversion circuit capable of more accurately controlling a current even at a low output.

The present disclosure includes the following inventions, provided that the present invention is defined by the claims .

One end of the DC voltage conversion circuit according to one expression of the present disclosure is connected to a switching element, a freewheeling diode connected in series with the switching element, and an interconnection point in a series of the switching element and the freewheeling diode. It is connected to the reactor, the other end of the reactor, and one end of the switching element or the element on the low potential side of the freewheeling diode, which is opposite to the interconnection point, and becomes one of an input and an output. A first port, a second port connected to both ends of the series and the other of the input and the output, a current sensor for detecting the current flowing through the reactor, and a control unit for switching the switching element. With,
The control unit corrects the detected value of the current sensor based on the inductance of the reactor, the carrier frequency, and the respective voltages of the first port and the second port, and calculates the converted value of the current flowing through the reactor. It is a DC voltage conversion circuit that obtains and discriminates between the current continuous mode and the current discontinuous mode based on the converted value, and obtains a reference value in pulse width modulation control of the switching element.

According to the present disclosure, it is possible to provide a DC voltage conversion circuit capable of more accurately controlling a current even at a low output.

Claims (2)

Switching element and
A freewheeling diode connected in series with the switching element,
A reactor having one end connected to the interconnection point in the series of the switching element and the freewheeling diode,
A first port connected to the other end of the reactor and one end of the switching element or the element on the low potential side of the freewheeling diode on the opposite side of the interconnection point, which is one of an input and an output. When,
A second port connected to both ends of the series and the other of the input and output,
A current sensor that detects the current flowing through the reactor, and
A DC voltage including a control unit that corrects the detection value of the current sensor based on the inductance of the reactor, the carrier frequency, and the respective voltages of the first port and the second port, and switches the switching element. Conversion circuit. A DC voltage conversion circuit in which a switching element that opens and closes a current in the direction opposite to the current direction of the freewheeling diode is added in parallel with the freewheeling diode.

Images