JP2020129922A - Bidirectional insulation type dc-dc converter and control method - Google Patents

Abstract

To provide technology which contributes to conversion efficiency of a bidirectional converter.SOLUTION: A frequency operation unit 41 of a control unit 3 derives a switching frequency ω corresponding to a transmission power command value based on an equation: ω=(EE/(PL))(δ-(δ/π)). A signal generating unit 42 generates gate signals in switching devices S1 to S8 based on the switching frequency ω derived in the frequency operation unit 41. Then, the generated gate signals are output to the switching devices S1 to S8 to appropriately perform switching control. In the equation, ω is a switching frequency in the switching devices S1 to S8, Pis the transmission power command value, Eand Eare direct current voltage on a primary side and direct current voltage on a secondary side, L is a sum of a leakage inductance value of a trans 21 and an inductance value of a reactor subjected to series connection to the trans 21, and δ is a phase difference between alternating voltage v1 and alternating voltage v2 in a first converter 20a and a second converter 20b.SELECTED DRAWING: Figure 1

Description

The present invention relates to a bidirectional isolated DC-DC converter and a control method, and relates to a technique that can contribute to the conversion efficiency of a bidirectional isolated DC-DC converter, for example.

As an example of a power conversion device applied in various fields (for example, applied to an industrial device such as a battery simulator), there is a bidirectional isolated DC-DC converter (hereinafter, simply referred to as a bidirectional converter as appropriate) (for example, Non-Patent Document 1).

In the bidirectional converter, a pair of converters capable of bidirectional voltage conversion (first and second converters 20a and 20b in FIG. 1, which will be described later) are coupled by a transformer or the like, and gate signals are respectively supplied to switching elements of the converters. Is output and the switching control is appropriately performed, so that desired power transmission (bidirectional power transmission) can be performed between the converters.

The magnitude of output power (hereinafter, simply referred to as transmission power) in power transmission can be defined as, for example, the following theoretical formula (1). In the equation (1), P is the transmission power, ω is the switching frequency of each switching element, E ₁ and E ₂ are the primary side DC voltage and the secondary side DC voltage of the bidirectional converter, and L is the leakage inductance of the transformer. Let δ be the sum of the inductance values of the reactors connected in series with the transformer, δ be the phase difference of the AC voltage of each converter, and be the pi. Also, the effect of loss due to iron loss of the transformer shall not be considered.

P=(E ₁ E ₂ /(ωL))(δ−(δ ² /π)) (1)
As an example of the control of the transmission power, the switching frequency ω is made constant in the equation (1), and the phase difference δ is adjusted so as to correspond to the command value of the transmission power (the transmission power command value P ^{* in} the equation (3) described later). There is a configuration (hereinafter, simply referred to as a conventional control configuration) in which V is changed to perform appropriate control (that is, the phase difference δ is made variable and adjusted to perform appropriate control).

According to this conventional control configuration, the gate signal of each switching element can be generated based on the phase difference δ corresponding to the command value of the transmission power as described above, and when the phase difference δ is 90°. It can be read that the transmission power P in the equation (1) is maximum.

The conversion efficiency of the bidirectional converter can be expressed by the following formula (2) when the influence of the loss is considered. In the equation (2), η is the conversion efficiency, P _loss1 is the iron loss (hysteresis loss) of the transformer, P _loss2 is the loss other than P _loss1 (copper loss of the transformer, loss due to the switching element of each converter, etc.). To do.

η=P/(P+P _loss1 +P _loss2 ) (2)

Shigenori Inoue, Yasufumi Akagi, "Operating Voltage and Loss Analysis of Bidirectional Insulation DC/DC Converter," Dengaku D, Vol. 127, No. 2, 2007, pp. 189-197.

In the conventional control configuration as described above, when the frequency of the current flowing through the transformer (corresponding to the current i1 in FIG. 1 described later) (corresponding to the switching frequency ω in equation (1)) is constant, the magnitude of the current changes. _However , the iron loss due to the transformer (corresponding to P _loss1 in equation (2)) does not change theoretically. On the other hand, the transmission power and the loss other than the iron loss of the transformer (corresponding to the transmission power P and P _loss2 in Expression (2)) have a positive correlation with the magnitude of the current.

That is, in the case where the bidirectional converter according to the conventional control configuration is operating at a relatively small current (that is, the transmission power is less than half of the rated value; hereinafter, simply referred to as a low power output state), The ratio of transformer iron loss to total loss tends to be high. Therefore, if the iron loss of the transformer cannot be suppressed, the conversion efficiency may decrease.

The present invention has been made in view of the above technical problems, and an object thereof is to provide a technique capable of contributing to the conversion efficiency of a bidirectional converter.

One aspect of the present invention is a bidirectional converter including first and second converters coupled via a transformer and a control unit that controls output power of power transmission by the first and second converters. The first converter is connected to the first DC power supply and the primary side of the transformer, has a first switching arm having first and second switching elements connected in series, and a first switching arm having third and fourth switching elements connected in series. It has a single-phase full bridge circuit in which two switching arms are connected in parallel. The second converter is connected to the second DC power source and the secondary side of the transformer, and is connected in series with the third switching arm in which the fifth and sixth switching elements are connected in series and the seventh and eighth switching elements. And a fourth switching arm and a single-phase full bridge circuit connected in parallel. The control unit controls the first to eighth switching elements on the basis of the frequency calculation unit that derives the switching frequencies of the first to eighth switching elements based on formula (3) and the switching frequency that is derived by the frequency calculation unit. And a signal generator that generates a gate signal to be output.

ω=(E ₁ E ₂ /(P ^* L))(δ−(δ ² /π)) (3)
In Expression (3), ω is the switching frequency of the _first to eighth switching elements, E ₁ and E ₂ are the primary side DC voltage and the secondary side DC voltage, P ^* is the command value of the output power for power transmission, and L is the transformer. Leakage inductance, δ is the phase difference between the AC voltages of the first and second converters, and π is the pi.

In this bidirectional converter, the control unit further includes a phase difference correction unit, and the phase difference correction unit uses an equation based on a deviation between the detected value of the output power of power transmission and the command value P ^{* of the} output power. It may be characterized in that the phase difference δ of (3) is corrected.

Further, the reactor is inserted and connected to at least one of the first converter and the primary side of the transformer, and the second converter and the secondary side of the transformer. It may be the sum of the leakage inductance and the inductance of the inserted and connected reactor.

Another mode is a control method of a bidirectional converter in which the output power of power transmission by the first and second converters coupled via a transformer is controlled by a control unit. Based on the equation (3), the control unit calculates the switching frequencies of the first to eighth switching elements included in the first and second converters, and the switching frequency derived in the calculation process. And a generation process of generating a gate signal to be output to the first to eighth switching elements. The first converter is connected to the first DC power supply and the primary side of the transformer, has a first switching arm having first and second switching elements connected in series, and a first switching arm having third and fourth switching elements connected in series. It has a single-phase full bridge circuit in which two switching arms are connected in parallel. The second converter is connected to the second DC power source and the secondary side of the transformer, and is connected in series with the third switching arm in which the fifth and sixth switching elements are connected in series and the seventh and eighth switching elements. And a fourth switching arm and a single-phase full bridge circuit connected in parallel.

As described above, according to the present invention, it is possible to contribute to the conversion efficiency of the power conversion device.

FIG. 3 is a circuit configuration diagram for explaining a bidirectional converter 1 that is an example of the present embodiment. 1 is a schematic configuration diagram for explaining a first embodiment of a control unit 3. FIG. The waveform diagram of the alternating current voltage v1, v2 of the 1st, 2nd converter 20a, 20b which shows an example at the time of controlling by the control part 3, and current i1. FIG. 6 is a schematic configuration diagram for explaining a second embodiment of the control unit 3.

Hereinafter, a bidirectional converter and a control method according to the embodiment of the present invention will be described.

In the transmission power control configuration of the bidirectional converter according to the present embodiment, based on the following formula (3) obtained by modifying the above formula (1) (for example, as shown in Examples 1 and 2 described later, (Based on (3)), the switching frequency corresponding to the transmission power command value is derived. Then, a gate signal of each switching element of the first and second converters coupled by the transformer is generated based on the switching frequency derived as described above, and the gate signal is appropriately output to each switching element to perform switching control. It is a configuration that does.

ω=(E ₁ E ₂ /(P ^* L))(δ−(δ ² /π)) (3)
In Expression (3), ω is the switching frequency of each switching element (the frequency of the AC voltage of the first and second converters), E ₁ and E ₂ are the primary side DC voltage and the secondary side DC voltage, and P ^* is the transmission power command. Value, L is the leakage inductance of the transformer, δ is the phase difference between the AC voltages of the first and second converters, and π is the circular constant.

That is, in the control configuration according to the present embodiment, the transmission frequency can be appropriately controlled by changing the switching frequency so as to correspond to the transmission power command value (that is, the switching frequency can be varied and adjusted to be appropriately controlled). This is completely different from the conventional control configuration.

Generally, when the applied voltage and frequency to the transformer are v and f, respectively, the iron loss of the transformer (P _{loss1 in} equation (2)) and v/f have a proportional relationship. That is, the iron loss of the transformer and the frequency f are inversely proportional to each other, and the iron loss of the transformer decreases as the frequency f increases.

In the case of the control configuration according to this embodiment, the transmission power command value P ^* and the switching frequency ω in equation (3) have an inversely proportional relationship with each other. That is, as the transmission power command value P ^* in Expression (3) becomes smaller (that is, as the low power output state is entered), the switching frequency ω becomes larger and P _{loss1 in} Expression (2) becomes smaller. .. In addition, the loss in the switching element applied to each converter of the bidirectional converter has almost no effect, and P _{loss2 in} Expression (2) is also small.

Therefore, according to the control configuration of the present embodiment, even if the bidirectional converter is in a low power output state, for example, it is possible to suppress the iron loss ratio of the transformer from increasing. Then, as compared with the conventional control configuration, it is possible to contribute to the improvement of the conversion efficiency of the bidirectional converter (the conversion efficiency η in the equation (2)).

The bidirectional converter and control method of the present embodiment can be used in various fields (for example, power conversion technology etc.) as long as the switching frequency ω can be derived based on the equation (3) and the transmission power can be appropriately controlled as described above. It is possible to design by appropriately applying the common general technical knowledge in the field (1), and examples thereof include the following.

<<Circuit configuration example of the bidirectional converter according to the present embodiment>>
FIG. 1 is a circuit configuration diagram for explaining a bidirectional converter 1 which is an example of the present embodiment. In the bidirectional converter 1 shown in FIG. 1, the first and second converters 20a and 20b are coupled via a transformer 21 and are symmetrical with respect to the transformer 21. The first and second DC power supplies 22 and 23 are connected to the primary side and the secondary side of the bidirectional converter 1, respectively. The control unit 3 is connected to the first and second converters 20a and 20b.

The first converter 20a is a single-phase full circuit in which a first switching arm including switching elements S1 and S2 connected in series and a second switching arm including switching elements S3 and S4 connected in series are connected in parallel. It is composed of a bridge circuit. The primary side of the transformer 21 is connected between the AC terminals of the first converter 20a.

The second converter 20b is a single-phase full connection in which a third switching arm including switching elements S5 and S6 connected in series and a fourth switching arm including switching elements S7 and S8 connected in series are connected in parallel. It is composed of a bridge circuit. The secondary side of the transformer 21 is connected between the AC terminals of the second converter 20b.

The control unit 3 receives the transmission power command values and operating states of the first and second converters 20a and 20b, and generates gate signals for the switching elements S1 to S8 so as to correspond to the transmission power command values. In addition, the generated gate signal is output to the switching elements S1 to S8 to appropriately perform switching control (ON/OFF control).

In the bidirectional converter 1 described above, it is possible to appropriately change the mode according to the purpose. For example, as shown in FIG. 1, freewheel diodes D1 to D8 are connected in antiparallel to the switching elements S1 to S8, and capacitors Cs1 to Cs8 are connected in parallel for the purpose of reducing switching loss and suppressing surge voltage. It can be cited as connecting to. Also, instead of the capacitors Cs1 to Cs8, another general snubber circuit may be appropriately applied.

Further, for the purpose of adding a desired inductance component, for example, as shown in FIG. 1, reactors (external reactors etc.) L1, L2 etc. are inserted and connected between the first and second converters 20a, 20b and the transformer 21. (For example, connecting at least one of the reactors L1 and L2 to the transformer in series).

In addition, various forms can be applied to the switching elements S1 to S8, and an example thereof is application of a semiconductor switching element such as an IGBT.

Also, various forms can be applied to the first and second DC power supplies 22 and 23, and as an example, a DC-Link capacitor or the like connectable to the first and second converters 20a and 20b can be used. Applying a DC power supply can be mentioned.

The operating state of the first and second converters 20a and 20b detected by the control unit 3 may be appropriately detected according to the purpose. For example, the DC voltages E ₁ and E of the first and second DC power supplies 22 and 23 are necessary when the control unit 3 generates the gate signal (based on the equation (3) as described later). ₂ , detecting the leakage inductance L of the transformer 21, the phase difference δ of the AC voltages v1 and v2 of the first and second converters 20a and 20b, and the like. Further, it is possible to detect the transmission power by the first and second converters 20a and 20b (transmission power detection value P in Example 2 described later) and to perform feedback control.

<Example 1 of control unit 3>
FIG. 2 shows the first embodiment of the control unit 3, and mainly includes a frequency calculation unit 41 and a signal generation unit 42.

In the frequency calculation unit 41, the operating states of the first and second converters 20a and 20b and the transmission power command value P ^* are input, and the switching frequencies ω of the switching elements S1 to S8 are derived based on the equation (3). (Calculation process). In the formula (3) applied in the frequency calculation unit 41, E ₁ and E ₂ are DC voltages of the first and second DC power supplies 22 and 23 (the primary side DC voltage and the secondary side DC voltage of the bidirectional converter 1). , P ^* is a transmission power command value, L is a leakage inductance of the transformer 21 (for example, when reactors L1 and L2 are provided as shown in FIG. 1, the leakage inductance of the transformer 21 and the transformer 21 are connected in series). Is the sum of the inductance values of the reactors L1 and L2 (total inductance), δ is the phase difference between the AC voltages v1 and v2 of the first and second converters 20a and 20b, and π is the pi. The phase difference δ may be applied as a fixed value (angle).

The signal generator 42 receives the switching frequency ω derived by the frequency calculator 41 and the operating states (phase difference δ, etc.) of the first and second converters 20a and 20b, and performs desired switching control of the switching elements S1 to S8. A gate signal is generated so that it can be generated (generation process). This gate signal is generated so that, for example, the first and second converters 20a and 20b can obtain the AC voltages v1 and v2 and the current i1 having the waveforms shown in FIG.

In the case of FIG. 3, the AC voltage v1 is positive when the switching elements S1 and S4 are on and is negative when the switching elements S2 and S3 are on. Further, in the AC voltage v2, the switching elements S6 and S7 are positive in the ON state, and the switching elements S5 and S8 are negative in the ON state.

As described above, according to the control configuration of the first embodiment, as the transmission power command value P ^* becomes smaller (that is, as the bidirectional converter 1 enters the low power output state), it is derived by the formula (3). The switching frequency ω is increased, and P _{loss1 in} equation (2) is decreased. In addition, the switching loss in each of the switching elements S1 to S8 (for example, a semiconductor switching element such as an IGBT) applied to the first and second converters 20a and 20b has almost no effect, and P _{loss2 in the} equation (2). Is almost independent of the switching frequency ω.

Therefore, in the control configuration according to the first embodiment, even if the bidirectional converter 1 is in a low power output state, for example, it is possible to suppress the iron loss ratio of the transformer 21 from increasing, and it is easy to obtain the desired conversion efficiency η. .. In particular, in the low power output state, it is easy to obtain the conversion efficiency η superior to the conventional control configuration.

<Example 2 of control unit 3>
FIG. 4 shows a second embodiment of the control unit 3, and mainly includes a subtraction unit 43 and a phase difference correction unit 44 in addition to the frequency calculation unit 41 and the signal generation unit 42. The same parts as those of the first embodiment are designated by the same reference numerals and the detailed description thereof will be appropriately omitted.

The subtraction unit 43 receives both the transmission power detection value P detected from the first and second converters 20a and 20b and the transmission power command value P ^*, and derives the deviation between the two. The phase difference correction unit 44 corrects the phase difference δ applied to the frequency calculation unit 41 and the signal generation unit 42 based on the deviation derived by the subtraction unit 43 (correction process).

The correction of the phase difference δ by the phase difference correction unit 44 can appropriately reflect (feedback) the deviation derived by the subtraction unit 43 in the derivation of the switching frequency by the frequency calculation unit 41 and the generation of the gate signal by the signal generation unit 42. If it is good.

As an example of this, there is a method of performing correction based on general P control, PI control, and PID control. As a specific example, in the case of PI control, correction may be made based on the following equations (4) and (5). In equations (4) and (5), Kp is a proportional coefficient, Ki is an integration coefficient, δ _n-1 is a phase difference before correction, Δδ is a phase difference correction amount, and δ _n is a phase difference after correction.

Δδ=Kp(P ^* −P)+KiΣ(P ^* −P) (4)
δ _n =δ _n-1 +Δδ (5)
The phase difference δ _n corrected by the phase difference correction unit 44 is input to the frequency calculation unit 41 and the signal generation unit 42 as in other operating states, and is applied to the derivation of the switching frequency ω and the generation of the gate signal, respectively. ..

As described above, according to the control configuration of the second embodiment, in addition to the same operational effects as the first embodiment, the following can be said. That is, for example, when there are variations in the constants of the reactors L1 and L2 in the bidirectional converter 1, the variations may affect the control of the transmission power, but according to the second embodiment, It is possible to suppress variations (control transmission power as desired). This contributes to the control accuracy of the transmission power.

In the above, the present invention has been described in detail only with respect to the specific examples described, but it is obvious to those skilled in the art that various modifications can be made within the scope of the technical idea of the present invention. It goes without saying that such changes belong to the scope of the claims.

1... Bidirectional converter 20a, 20b... 1st, 2nd converter 21... Transformer 22, 23... 1st, 2nd DC power supply 3... Control part 41... Frequency operation part 42... Signal generation part 43... Subtraction part 44... Phase difference correction unit S1 to S8... Switching element

Claims (4)

First and second converters coupled via a transformer,
A control unit for controlling output power of power transmission by the first and second converters;
Equipped with
The first converter is connected to the first DC power supply and the primary side of the transformer,
It has a single-phase full bridge circuit in which a first switching arm in which first and second switching elements are connected in series and a second switching arm in which third and fourth switching elements are connected in series are connected in parallel. Then
The second converter is connected to the second DC power source and the secondary side of the transformer,
It has a single-phase full bridge circuit in which a third switching arm in which the fifth and sixth switching elements are connected in series and a fourth switching arm in which the seventh and eighth switching elements are connected in series are connected in parallel. Then
The control unit
A frequency calculation unit that derives the switching frequencies of the first to eighth switching elements based on equation (3),
A signal generator that generates a gate signal to be output to the first to eighth switching elements based on the switching frequency derived by the frequency calculator.
A bidirectional isolated DC-DC converter comprising:
ω=(E ₁ E ₂ /(P ^* L))(δ−(δ ² /π)) (3)
In Expression (3), ω is the switching frequency of the _first to eighth switching elements, E ₁ and E ₂ are the primary side DC voltage and the secondary side DC voltage, P ^* is the command value of the output power for power transmission, and L is the transformer. Leakage inductance, δ is the phase difference between the AC voltages of the first and second converters, and π is the pi. The control unit further includes a phase difference correction unit,
The phase difference correction unit corrects the phase difference δ in the equation (3) based on the deviation between the detected value of the output power of the power transmission and the command value P ^{* of the} output power. The described bidirectional insulating DC-DC converter. A reactor is inserted and connected to at least one of the first converter and the primary side of the transformer, and the second converter and the secondary side of the transformer.
The bidirectional isolated DC-DC converter according to claim 1 or 2, wherein L in the equation (3) is a sum of the leakage inductance of the transformer and the inductance of the reactor that is inserted and connected. A method for controlling output power of power transmission by first and second converters coupled via a transformer by a control unit, comprising:
By the control unit,
An arithmetic process for deriving the switching frequencies of the first to eighth switching elements formed in the first and second converters based on the equation (3),
A generation process of generating a gate signal to be output to the first to eighth switching elements based on the switching frequency derived in the calculation process,
The first converter is connected to the first DC power supply and the primary side of the transformer,
It has a single-phase full bridge circuit in which a first switching arm in which first and second switching elements are connected in series and a second switching arm in which third and fourth switching elements are connected in series are connected in parallel. Then
The second converter is connected to the second DC power source and the secondary side of the transformer,
It has a single-phase full bridge circuit in which a third switching arm in which the fifth and sixth switching elements are connected in series and a fourth switching arm in which the seventh and eighth switching elements are connected in series are connected in parallel. A method for controlling a bidirectional isolated DC-DC converter, characterized in that
ω=(E ₁ E ₂ /(P ^* L))(δ−(δ ² /π)) (3)
In Expression (3), ω is the switching frequency of the _first to eighth switching elements, E ₁ and E ₂ are the primary side DC voltage and the secondary side DC voltage, P ^* is the command value of the output power for power transmission, and L is the transformer. Leakage inductance, δ is the phase difference between the AC voltages of the first and second converters, and π is the pi.

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