JP2020102962A - Power conversion device - Google Patents

Abstract

To provide a power conversion device which omits an independent low-pass filter while suppressing loss of a switching element.SOLUTION: A power conversion device comprises: a first coil L3a, L3b and a second coil L4a, L4b provided on a magnetic path of a secondary circuit 16; a first capacitor Ctank,a which connects a first end of the first coil with a first end of the second coil; a second capacitor Ctank,b which connects a second end of the first coil with a second end of the second coil; a first switching element S3 which connects the second end of the first coil with the first end of the second coil; and a second switching element S4 which connects the first end of the first coil with the second end of the second coil. The first coil and the second coil have center taps, respectively. The center taps constitute input/output ports, and alternately switch the first switching element S3 and the second switching element S4 to supply AC current to the first coil and the second coil.SELECTED DRAWING: Figure 7

Description

The present invention relates to a power conversion device that includes a primary side circuit and a secondary side circuit coupled by a magnetic path and exchanges electric power between the primary side circuit and the secondary side circuit.

2. Description of the Related Art Conventionally, an electric vehicle such as a hybrid vehicle or an electric vehicle is equipped with a drive motor, and therefore a high-voltage main battery (DC power supply) for supplying electric power to the drive motor is also installed. Further, since these electric vehicles also have various electric devices (auxiliaries) that operate at a low voltage, a low-voltage auxiliary battery is also installed to drive them. A power converter (DC-DC converter) is mounted to exchange power between the main battery and the auxiliary battery.

FIG. 1 shows the configuration of a power conversion device described in Patent Document 1 as a conventional example. In this configuration, the first to third ports are provided as input/output ports, and power is exchanged between the ports using a transformer. That is, the transformer is configured by winding the windings L1, L2, and L3 around the same core, and the switching elements S1 to S6 are arranged so that the voltages across the windings change in different phases. The current flowing in each of the windings L1 to L3 is controlled by controlling the switching of No. 1, and the transmission power between the first port, the second port, and the third port is controlled.

JP, 2018-78745, A

FIG. 2 shows a current flow in one winding L of such a power converter. In order to pass an alternating current through the winding L, the switching element S1 is turned on (upper arm is turned on) and the switching element S2 is turned on (lower arm) is repeated at a predetermined cycle. At this time, the current from the input/output port is a unidirectional current, but the current of the capacitor C arranged between the input/output ports changes greatly during switching as shown in the figure.

Therefore, the voltage fluctuates between the input/output ports, and in order to prevent this fluctuation, it is necessary to dispose a low-pass filter between the input/output port and the capacitor C.

Further, as the switching elements are turned on and off, high frequency noise is generated due to the switching of the switching elements S1 and S2, as shown in FIG. This high frequency noise includes differential noise that is transmitted between power supply lines (shown by the solid line) and common mode noise that is transmitted toward the power supply through stray capacitance (shown by the broken line). A low-pass filter is required to realize this.

However, if a low-pass filter is provided at the input/output port, there is a problem that the circuit becomes large.

The present invention is a power converter that includes a primary side circuit and a secondary side circuit coupled by a magnetic path, and exchanges electric power between the primary side circuit and the secondary side circuit. One of the circuit and the secondary side circuit connects a first winding and a second winding provided in the magnetic path, a first end of the first winding and a first end of the second winding. A first capacitor, a second capacitor connecting the second end of the first winding and the second end of the second winding, and a second end of the first winding and the second winding. A first switching element that connects the first end and a second switching element that connects the first end of the first winding and the second end of the second winding; and Each of the second windings has a center tap, and the center taps form an input/output port, and the first switching element and the second switching element are alternately switched to switch the first winding and the second winding element. Apply alternating current to the two windings.

Also, one of the primary side circuit or the secondary side circuit is a low voltage side circuit, the other of the primary side circuit or the secondary side circuit is a high voltage side circuit, the high voltage side circuit, Series connection of a third winding and a fourth winding provided in the magnetic path and a third capacitor and a fourth capacitor connecting the first end of the third winding and the first end of the fourth winding And a fifth capacitor connecting the second end of the third winding and the second end of the fourth winding, and a series connection of the second end of the third winding with the third capacitor and the fourth capacitor. A third switching element that connects the middle point of the third winding element and a second switching element that connects the second end of the fourth winding and the middle point of the series connection of the third capacitor and the fourth capacitor, and The first end of the three windings and the first end of the fourth winding form an input/output port, and the third switching element and the fourth switching element are alternately switched to switch the third winding and the fourth winding element. An alternating current is passed through the fourth winding.

According to the present invention, the current of the switching element can be reduced while the transformer has a filter function.

It is a figure which shows the structure of the power converter device of a prior art example. It is a figure which shows the electric current about one winding|winding of the power converter device of a prior art example. It is a figure which shows the high frequency noise which accompanies on/off of a switching element. It is a figure which shows the structure of the filter built-in type power converter device which incorporated the low pass filter in the transformer. It is a figure which shows the switching element and output current in the circuit of FIG. It is a figure which shows the structure which integrated the booster circuit into the power converter device of a prior art example. It is a figure which shows the structure of the power converter device which concerns on embodiment. It is a figure which shows the waveform of each part in the structure of FIG. It is a diagram obtained by extracting a portion in the configuration of FIG. 7, (a) is a circuit for the operation of the winding L _4, (b) shows a circuit for the operation of the winding L _3. It is a figure explaining the relationship between the circuit shown in FIG. 9 and the power converter device of FIG. FIG. 8 is a diagram showing a circuit when the switching elements S1 and S2 of the circuit of FIG. 7 are regarded as noise sources.

Hereinafter, embodiments of the present invention will be described with reference to the drawings. Note that the present invention is not limited to the embodiments described here.

"Filter built-in"
FIG. 4 shows the configuration of a filter built-in type power converter in which a low-pass filter is incorporated in a transformer. This power converter includes a primary circuit 14 and a secondary circuit 16.

The primary side circuit 14 includes a winding L1, a capacitor C1, a switching element S1, a winding L2, a capacitor C2, a switching element S2, a primary side capacitor Ca, and input/output terminals 1 and 2.

A series connection of a capacitor C1 and a capacitor C2 is arranged between the input/output terminals 1 and 2. Further, one end of the winding L1 is connected to the input/output terminal 1, one end of the winding L2 is connected to the winding L2, and the other end of the winding L1 and the other end of the winding L2 are The capacitors are connected by the primary side capacitor Ca and are connected by the series connection of the switching element S1 and the switching element S2. The connection point (middle point) between the switching element S1 and the switching element S2 is connected to the connection point (middle point) where the capacitor C1 and the capacitor C2 are directly connected. A parasitic diode is connected in parallel to the switching element S1 with the side connected to the other end of the winding L1 as a cathode, and the switching element S2 has a side connected to the other end of the winding L2. A parasitic diode is connected in parallel as the cathode.

The secondary side circuit 16 has the same configuration as that of the primary side circuit 14, and includes a winding L3, a capacitor C3, a switching element S3, a winding L4, a capacitor C4, a switching element S4, a secondary side capacitor Cb, and an input. It has an input/output port consisting of output terminals 3 and 4.

The magnetic core Fp is made of a magnetic material such as iron or ferrite, and the winding L1, the winding L2, the winding L3, and the winding L4 are made of a conductive wire wound around the magnetic core Fp. The magnetic core Fp forms a magnetic path for the magnetic flux generated by each of the windings L1 to L4.

The switching element S1 and the switching element S2 repeat on/off alternately (complementarily). That is, when the switching element S1 is on, the switching element S2 is off, and when the switching element S1 is off, the switching element S2 is on. Similarly, the switching elements S3 and S4 are alternately turned on and off repeatedly. As a result, an alternating current flows through each winding.

Here, the winding directions of the winding L1 and the winding L2 are opposite to each other, and when an induced electromotive force having a positive side on the winding L1 is generated, a dot is added on the winding L2. Induced electromotive force is generated in the direction opposite to that of the winding L1 having the positive side. Further, the winding directions of the winding L3 and the winding L4 are opposite to each other, and similar induced electromotive force is generated.

In such a configuration, when the switching timings of the primary circuit 14 and the secondary circuit 16 are the same, the windings L1 and L2 of the primary circuit 14 and the windings L3 and L4 of the secondary circuit 16 are The applied voltages have the same polarity. Therefore, the generated magnetic flux and induced electromotive force are canceled out, and the electric power transmitted between the primary side circuit 14 and the secondary side circuit 16 is zero. On the other hand, when the switching timings (phases) of the primary side circuit 14 and the secondary side circuit 16 are shifted, the applied voltages of the windings L1 and L2 of the primary side circuit 14 and the windings L3 and L4 of the secondary side circuit 16 are different. Then, the electric power is transmitted between the primary-side circuit 14 and the secondary-side circuit 16. That is, the DC input current Ia flows from the input/output terminals 1 and 2 of the primary side circuit 14, and the DC output current Ib flows from the input/output terminals 3 and 4. The larger the phase difference is in the range of 0 or more and π or less, the larger the power transmitted. Further, the ratio between the primary side input voltage Va and the secondary side output voltage Vb is determined according to the winding ratio between the primary side windings L1 and L2 and the secondary side windings L3 and L4.

In the circuit of FIG. 4, as shown in FIG. 5, currents alternately flow through the switching elements S3 and S4, and the two are added together to obtain a constant output current I ₀ .

In this way, the currents generated by the pair of windings in which the currents in the opposite directions flow can be added together to cancel the current ripples by the interleaved configuration, thereby suppressing the output current ripples. Further, with respect to the switching noise generated by the switching of each switching element, the leakage inductance of the winding that transmits this functions as an LC low-pass filter. Therefore, it is possible to remove the ripple at the input/output terminal without separately providing a low-pass filter.

Here, for example, when the input voltage of the primary side circuit 14 is 350 V and the output voltage of the secondary side circuit 16 is 12 V, it depends on the power transmitted from the primary side circuit 14 to the secondary side circuit 16. The current increases on the secondary side, and therefore the winding current on the secondary side and the current flowing through the switching element also increase.

Then, in the circuit shown in FIG. 4, as shown in FIG. 5, 2I _0, which is twice the output current I ₀ , flows through the switching elements S3 and S4. This is because the current in the opposite direction to the output current flows through the parasitic diodes of the switching elements S3 and S4 that are turned off. Since the conduction loss of the switching elements S3, S4 increases with the square of the current, the copper loss becomes large and the conversion efficiency deteriorates in low voltage/high current applications.

Therefore, in the secondary side circuit 16 on the low voltage side, there is a demand to reduce the current flowing through the switching elements S3, S4.

"Built-in booster circuit"
FIG. 6 shows a configuration incorporating a booster circuit. In this circuit, the input/output terminal 3 of the secondary side circuit 16 is the middle point of the capacitors C3 and C4. In this configuration, when the switching elements S3 and S4 are switched at the duty ratio of 0.5, the voltage applied to the capacitor Cb becomes 24V. Therefore, while the voltage between the input/output terminals 3 and 4 is set to 12V, the current flowing through the switching element S3 can be reduced (almost 0) and the sum of the currents flowing through the switching elements S3 and S4 can be made equal to the output current, I ₀ . .. The current flowing through the switching element S4 is 2I ₀ , and the applied voltage is 2V ₀ .

In this circuit, the current flowing through the switching elements S3, S4 can be reduced, and the loss can be reduced as compared with the circuit of FIG. However, as shown in FIG. 6, the fluctuation of the current flowing through the switching elements S3, S4 becomes large, and the current ripple of the output current becomes large.

"Circuit of Embodiment"
FIG. 7 shows the configuration of the power conversion device according to the embodiment. The primary side circuit 14 is a high voltage side circuit, and the secondary side circuit 16 is a low voltage side circuit. Further, it is assumed that the primary side input voltage is about 350V and the secondary side output voltage is about 12V. In this example, the circuit of FIG. 4 is used as it is for the primary side circuit 14 which is the high voltage side circuit, but the configuration of the illustrated secondary side circuit 16 may be adopted only for the primary side circuit, or for the primary side circuit. It may be adopted on both the secondary side and the secondary side. Further, in the secondary side circuit 16, the windings L ₃ and L ₄ are the first and second windings, the switching elements S ₃ and S ₄ are the first and second switching elements, and the capacitors C _tank,a and C _{tank, b} are called first and second capacitors, windings L1 and L2 in the primary side circuit 14 are third and fourth windings, switching elements S1 and S2 are third and fourth switching elements, and capacitors C1 and C2. Ca is called the third, fourth and fifth capacitors. Further, in the winding _{L1, L2, L 3, L} 4 in FIG, and an outer first end, a second inner end.

The secondary side circuit 16 has two windings L ₃ and L ₄ provided on the magnetic core Fp that serves as a magnetic path. Each of the windings L ₃ and L ₄ has a center tap and is divided into two windings. That is, the winding L ₃ is divided into windings L _3a and L _3b , and the winding L ₄ is divided into windings L _4a and L _4b . The winding directions of the windings L ₃ and L ₄ are opposite to each other.

Two center taps are connected to the input/output terminals 3 and 4 which are output ports. Further, a smoothing output capacitor C _out is connected between the input/output terminals 3 and 4.

The first end of the winding L ₃ and the first end of the winding L ₄ are connected by _a capacitor C _tank,a , and the second end of the winding L ₃ and the second end of the winding L ₄ are connected to each other. They are connected by C _tank,b . The second end of the winding L ₃ is connected to the first end of the winding L ₄ via the switching element S _3, and the second end of the winding L ₄ is connected to the first end of the winding L ₄ via the switching element S ₄ . It is connected to the first end of L ₃ .

In such a configuration, the switching elements S ₃ and S ₄ are alternately switched, and the phase is shifted with respect to the switching timing of the switching elements S 1 and S 2 of the primary side circuit 14, so that the power from the primary side circuit 14 is changed to the secondary side. Output from the input/output terminals 3 and 4 of the side circuit 16 (output current i _out ).

FIG. 8 shows the waveform at each part. In this example, the switching elements S1, S2 in the primary side circuit 14, are offset switching timing of the switching elements S _3, S ₄ of the low pressure side Φ only (phase difference). That is, regarding the switching timing of the primary side and the secondary side, when the switching cycle is T, a time difference of (Φ/2π)T is given.

In the figure, the time point when the switching state is switched in the primary side circuit 14 is the start time point 0. At this time, the switching element S1 is turned on and the switching element S2 is turned off. On the other hand, the switching element S ₄ is on, the switching element S ₃ is off, and the switching elements of the primary side circuit and the secondary side circuit have opposite polarities.

Then, when the time (Φ/2π)T of the opposite polarity has elapsed, the switching element S ₃ is turned on and the switching element S ₄ is turned off so that the same polarity occurs. The voltage applied to the windings _L 1, _{L 2} is an input voltage as _{V in,} repeated _{+ V in} / 2 and _{-V in} / 2, the voltage applied to the winding _L 3, _{L 4} is the output voltage is _{V out,} repeated _{+ V out} / 2 and _{-V out} / 2.

Due to the switching of the switching elements S1 and S2, trapezoidal currents i _L1 and i _L2 having a small slope in the period of the same polarity and a large slope in the period of the opposite polarity flow in the windings L ₁ and L _2, and flow from the ports. The input current i _in is an average current of the currents i _L1 and i _L2 . The direction of the input current i _a does not change because the direction of the current flowing through the windings L ₁ and L ₂ is reversed by the switching of the switching elements S1 and S2.

Further, due to the switching of the switching elements S ₃ and S ₄ , currents in the opposite directions flow through the windings L _3a and L _3b, and the sum of these flows through the center tap to output current i _out from the input/output terminals 3 and 4. Becomes That is, the charges charged in the capacitors C _tank,a , C _tank,b in the opposite polarity period are discharged in the same polarity period, and are coupled in the windings L ₃ and L ₄ , respectively, and the output current i _out is It is output from the input/output terminals 3 and 4. The currents flowing through the switching elements S ₃ and S ₄ are currents that flow to the center taps of the windings L ₃ and L ₄ , and the current value may be I ₀ . Further, as will be described later, it is possible to maintain the current ripple reduction by the interleaved configuration and the switching noise removal function by the built-in LC filter.

Further, a trapezoidal current carrying a DC component flows through the windings L ₃ and L ₄ , but this current is a DC component having opposite positive and negative polarities centered on the center tap in each winding (i _{L3, a} and i _{L3). , B} , i _L4,a and i _L4,b have opposite current directions. Therefore, no DC magnetic flux is generated in the magnetic core Fp, and it is not necessary to provide a gap for cutting the DC component in the magnetic core Fp.

"Reduction of current ripple"
In FIG. 9A, a circuit for operating only the winding L ₄ is extracted and shown. According to this circuit, the output currents from the input/output terminals 3 and ₄ have a waveform including a mountain-shaped current ripple due to the switching of the switching elements S ₃ and S ₄ .

In FIG. 9B, a circuit for operating only the winding L ₃ is extracted and shown. According to this circuit, the output currents from the input/output terminals 3 and ₄ have a mountain-shaped waveform including a current ripple having a polarity opposite to that of FIG. 9A due to the switching of the switching elements S ₃ and S ₄ .

With such an interleaved configuration, it is possible to reduce the current ripple in the output current from the input/output terminals 3 and 4 in the circuit of FIG.

FIGS. 10A and 10B show equivalent circuits rewritten while maintaining the connection relationship with the circuits of FIGS. 9A and 9B. A circuit obtained by combining the circuits of FIGS. 10A and 10B is shown in FIG. According to the circuit of FIG. 10C, the currents shown in FIGS. 10A and 10B are combined to cancel the current ripple. The circuit of FIG. 10C is equivalent to the circuit of this embodiment shown in FIG.

"Function as a low-pass filter"
FIG. 11A shows a circuit in which the switching elements S1 and S2 of the circuit of FIG. 7 are regarded as noise sources and replaced with an AC power source display. Further, FIG. 11B shows a diagram in which the upper circuit is rewritten by paying attention to an effective inductance component between the noise source and the input/output terminal.

As described above, the LC low-pass filter is formed between the noise source and the output port, whereby differential noise and common mode noise can be removed. Although the output smoothing function can be enhanced by providing the output capacitor C _out , the effect of removing noise can be obtained without providing the output capacitor C _out .

Note that the inductance component changes due to the coupling of the two windings L ₃ and L ₄ . Assuming that this coupling coefficient is k ₃₄ , the respective inductances of the windings L _3a , L _3b , L _4a , and L _4b are obtained by multiplying the inductance of each winding by (1-k ₃₄ ). ..

"Effects of the embodiment"
As described above, according to the circuit of FIG. 7, it is possible to control the power conversion by controlling the phase difference Φ. Then, current ripples can be canceled and switching noise can be filtered without the need for an independent low-pass filter. Furthermore, it is not necessary to increase the current in the switching elements S ₃ and S _{4, and} it is possible to suppress the increase in loss. The period (duty) in which the current flows through the switching elements S ₃ and S ₄ is 50%, and the breakdown voltage is twice the output voltage.

14 primary side circuit, 16 secondary side circuit, C capacitor, L winding, S switching element.

Claims (2)

A power converter including a primary-side circuit and a secondary-side circuit coupled by a magnetic path, and exchanging electric power between the primary-side circuit and the secondary-side circuit,
One of the primary side circuit or the secondary side circuit is
A first winding and a second winding provided in the magnetic path;
A first capacitor connecting a first end of the first winding and a first end of the second winding;
A second capacitor connecting the second end of the first winding and the second end of the second winding;
A first switching element connecting a second end of the first winding and a first end of the second winding;
A second switching element connecting the first end of the first winding and the second end of the second winding;
Including,
Each of the first winding and the second winding has a center tap, the center tap constitutes an input/output port, and the first switching element and the second switching element are alternately switched to switch the first winding element and the second switching element. AC current is passed through one winding and the second winding,
Power converter. The power conversion device according to claim 1, wherein
One of the primary side circuit or the secondary side circuit is a low voltage side circuit,
The other of the primary side circuit and the secondary side circuit is a high voltage side circuit,
The high voltage side circuit is
A third winding and a fourth winding provided in the magnetic path,
A series connection of a third capacitor and a fourth capacitor connecting the first end of the third winding and the first end of the fourth winding,
A fifth capacitor connecting the second end of the third winding and the second end of the fourth winding;
A third switching element connecting the second end of the third winding and the midpoint of the series connection of the third capacitor and the fourth capacitor;
A fourth switching element that connects the second end of the fourth winding to the midpoint of the series connection of the third capacitor and the fourth capacitor;
Including,
The first end of the third winding and the first end of the fourth winding form an input/output port, and the third switching element and the fourth switching element are alternately switched to switch the third winding. And applying an alternating current to the fourth winding,
Power converter.