WO2024185002A1 - Power conversion device - Google Patents

Abstract

A power conversion device equipped with a first bridge circuit, a second bridge circuit, a transformer positioned between the first bridge circuit and the second bridge circuit, and a control unit for operating the first and second bridge circuits, wherein the control unit calculates the voltage ratio between the input voltage and the output voltage, and determines an input-side Hi-period in a manner such that there are cases in which the input-side Hi-period on the first bridge circuit side is increased relative to the voltage ratio and cases in which said input-side Hi-period is decreased relative thereto.

Description

Power Conversion Equipment

The present invention relates to a power conversion device.

Conventionally, an isolated DC/DC converter, as described in Patent Document 1, is an example of a power conversion device that uses a transformer (hereinafter referred to as "transformer") to insulate the input side from the output side, converts the input direct current (DC) voltage to a DC voltage of a predetermined level, and outputs it. This DC/DC converter is of the DAB (Dual Active Bridge) type, and includes a transformer having a primary winding and a secondary winding, an input bridge circuit that is connected to the primary winding side and is the high-voltage side composed of switching elements, an output bridge circuit that is connected to the secondary winding side and is the low-voltage side composed of switching elements with a resonance function, and a control circuit that operates the switching elements of the input bridge circuit and the output bridge circuit to perform constant voltage or constant current operation.

For example, when a DC voltage of a specified voltage is input, this DC input voltage is switched by the switching elements in the input bridge circuit and converted into an AC (alternating current) voltage. The converted AC voltage is converted into an AC voltage according to the turns ratio of the transformer's primary and secondary windings and its leakage inductance. The converted AC voltage is switched by the switching elements in the output bridge circuit and converted into a specified DC voltage, and a constant DC output voltage is output.

In the input bridge circuit and output bridge circuit, the transformer current charges and discharges the parasitic capacitance of the switching elements. At this time, the voltage has a certain slope depending on the time it takes to charge the parasitic capacitance, and by performing switching when the voltage is zero (i.e., soft switching), it is possible to suppress switching losses that occur in the switching elements and also reduce surge voltages and noise caused by switching.

U.S. Pat. No. 5,027,264

The DC-DC converter described in Patent Document 1 includes, for example, a bridge circuit, a transformer, an inductance element, a capacitor, and a control unit. Such a DC-DC converter 1 performs power conversion by utilizing the electrical energy flowing through the inductance element. In some cases, the inductance element may use leakage inductance inherent in the transformer.

In the conventional DC/DC converter described in Patent Document 1, soft switching operation is possible in the input bridge circuit and the output bridge circuit by control of the control circuit. However, there is an operating range in which soft switching operation does not occur, depending on the phase difference between the input bridge circuit and the output bridge circuit (i.e., the output command value from the control circuit) and the voltage ratio between the input and output voltages. This causes problems such as increased losses and noise.

Furthermore, depending on the phase difference conditions, the magnitude of losses due to iron loss and copper loss in the transformer could become significant, resulting in a decrease in power conversion efficiency.

The object of the present invention is to provide a power conversion device that can suppress the decrease in power conversion efficiency.

One example of the present invention is a power conversion device including a first bridge circuit, a second bridge circuit, a transformer disposed between the first bridge circuit and the second bridge circuit, and a control unit that operates the first and second bridge circuits,
The control unit is a power conversion device that calculates a voltage ratio between an input voltage and an output voltage, and determines the input side Hi period so that, relative to the voltage ratio, there are cases where the input side Hi period on the first bridge circuit side is increased and cases where the input side Hi period is decreased.

The present invention makes it possible to suppress the decrease in power conversion efficiency.

FIG. 1 is a diagram illustrating an example of a configuration of a DC-DC converter according to a first embodiment. FIG. 4 is a diagram showing an example of voltage waveforms on the input/output side according to the embodiment. FIG. 11 is a diagram showing an example of voltage waveforms on the input/output side in the comparative example.

The present invention relates to a power conversion device that converts and outputs power supplied from an input side. In this embodiment, as an example of a power conversion device, a single-phase isolated DC/DC converter will be described as shown in the circuit diagram of FIG. 1.

This single-phase isolated DC/DC converter can be used bidirectionally by inverting the input and output, and has a capacitor 10 that smoothes the DC input voltage Vin. A first bridge circuit (e.g., primary bridge circuit 20) is connected to both ends of the capacitor 10. A primary winding of a transformer for input/output insulation is connected via an inductor to output nodes N1 and N2 of the primary bridge circuit. Input nodes N11 and N12 of a second bridge circuit (e.g., secondary bridge circuit 50) are connected to the secondary winding 42 of the transformer.

1, an input voltage detection unit detects a DC input voltage detection value Vin, and an output voltage detection unit detects a DC output voltage detection value Vout, although not shown in the figure.
A load ZL is connected to the output side of the secondary bridge circuit 50 via a smoothing capacitor 60. Furthermore, a control circuit 70 is provided which outputs four first control signals G1, G2, G3, G4 and four second control signals G11, G12, G13, G14 for controlling the switching of the primary bridge circuit 20 and the secondary bridge circuit 50.

The control circuit 70 (control unit) includes, for example, a microcomputer having a CPU (Central Processing Unit), ROM (Read Only Memory), RAM (Random Access Memory), input/output ports, and various other circuits. The CPU of this microcomputer realizes control to operate the first bridge circuit and the second bridge circuit by reading and executing a program stored in the ROM. Specifically, it has a function of adjusting the switching timing of the switching elements in the first bridge circuit and the second bridge circuit.

The control circuit 70 calculates an input/output voltage ratio d (d=Vout/Vin) between the input voltage detection value Vin and the output voltage detection value Vout in the first bridge circuit and the second bridge circuit, and determines the Hi period [deg] of the input side voltage _{Vin_ac} on the first bridge circuit side, the Hi period [deg] of the output side voltage Vout on the second bridge circuit side, and the output voltage phase difference [deg] between the first bridge circuit and the second bridge circuit based on the input/output voltage ratio d and the target value of the output current flowing through the load ZL. For example, the control circuit 70 may be configured to include a table in which the Hi period [deg] of the input side voltage _{Vin_ac} on the first bridge circuit side, the Hi period [deg] of the output side voltage _{Vout_ac} on the second bridge circuit side, and the phase difference [deg] of the output voltage between the first bridge circuit and the second bridge circuit are stored for the calculated input/output voltage ratio d and the target value of the output current flowing through the load ZL.

The primary bridge circuit 20 is made up of four first switching elements 201, 202, 203, and 204 connected in a bridge configuration, which are turned on/off by four first control signals G1 to G4. They are turned on/off by the control signals G1 to G4 input to the gates.

An inductor (not shown) and the primary winding 41 of the transformer 40 are connected in series between the output nodes N1 and N2 of the primary bridge circuit 20. In addition, a capacitor is connected in parallel to each of the first switching elements 201, 202, 203, and 204 (not shown).

The inductor, together with four capacitors connected in parallel to the switching elements, constitutes an LC resonant circuit, but in FIG. 1, this inductor is omitted from the configuration. In the configuration in FIG. 1, the primary-side bridge circuit 20 converts the DC input voltage Vin into an AC voltage and supplies it to the primary winding 41 side by turning on/off the first switching elements 201-204. Alternatively, the primary-side bridge circuit 20 has the function of rectifying the AC voltage supplied from the primary winding 41 side by the first diodes 211-214 and outputting a DC voltage.

The input nodes N11 and N12 of the secondary bridge circuit 50 are connected to both ends of the secondary winding 42. The secondary bridge circuit 50 has the same configuration as the primary bridge circuit 20, and four second switching elements 501, 502, 503, and 504 are connected in a bridge configuration and are turned on/off by four second control signals G11, G12, G13, and G14, respectively. Each of the switching elements 501 to 504 is driven by a gate-emitter voltage Vge, and is turned on/off by each of the second control signals G11 to G14 input to the gate.

The collector-emitter of switching element 501, input node N11, and the collector-emitter of switching element 502 are connected in series to form a first series circuit. Similarly, the collector-emitter of switching element 503, input node N12, and the collector-emitter of switching element 504 are connected in series to form a second series circuit.

These first and second series circuits are connected in parallel. Second return means, such as second diodes 511, 512, 513, and 514, are connected in anti-parallel between the collector and emitter of each of the switching elements 501 to 504. Furthermore, second capacitors (not shown in the figure), which are second capacitance elements for resonance, are connected in parallel to each of the switching elements 501 to 504. The four second capacitors form an LC resonance circuit together with the inductance of the secondary winding 42, but these second capacitors may also be formed by the parasitic capacitance of each of the switching elements 501 to 504.

The DC voltage output from the secondary bridge circuit 50 is smoothed by a smoothing capacitor 60 to become a DC output voltage Vout, which is then supplied to the load ZL.

The secondary bridge circuit 50 rectifies the AC voltage supplied from the secondary winding 42 side using the second diodes 511-514 and outputs a DC voltage. Alternatively, the secondary bridge circuit 50 has the function of converting the DC input voltage into an AC voltage and supplying it to the secondary winding 42 side by turning on/off the switching elements 501-504.

In FIG. 1, an example has been described in which no inductance element is disposed between the primary bridge circuit 20 or the secondary bridge circuit 50 and the transformer 40. The present invention is not limited to such a configuration, and may be configured such that an inductance element is disposed between the AC side of one of the primary bridge circuit 20 or the secondary bridge circuit 50 and the transformer 40. Alternatively, it may be configured such that an inductance element is disposed between the AC side of both the primary bridge circuit 20 and the secondary bridge circuit 50 and the transformer 40.

FIG. 2 is a diagram showing voltage waveforms in the isolated DC/DC converter of this embodiment. In the first row from the top in FIG. 2, the vertical axis indicates the input voltage V _{in_ac} , which is the voltage between nodes N1 and N2, and the horizontal axis indicates time or phase [deg]. In the second row in FIG. 2, the vertical axis indicates the Hi period 22 of the input voltage V _{in_ac} , and the horizontal axis indicates the input/output voltage ratio d. In the third row in FIG. 2, the vertical axis indicates the Hi period 25 of the output voltage V _{out_ac} , and the horizontal axis indicates the input/output voltage ratio d. In the fourth row in FIG. 2, the vertical axis indicates the output voltage V _{out_ac} , which is the voltage between nodes N11 and N12, and the horizontal axis indicates time or phase [deg].

2, the input voltage _{Vin_ac} has a pulse-like voltage waveform. The input voltage _{Vin_ac} has a Hi period of 22 [deg]. The amplitude 221 of the input _{voltage Vin_ac is} constant.

As shown in the second row of FIG. 2, the tendency of change in the Hi period 22 of the input voltage _{Vin_ac} with respect to the voltage ratio d changes at a voltage ratio 26 that is equal to the transformer turns ratio (=N).
When the voltage ratio is 26, the relationship is expressed as follows: output voltage detection value Vout=input voltage detection value (Vin)×transformer turns ratio N.

In this embodiment, in the case of a voltage ratio 27 lower than the voltage ratio 26, the control circuit 70 controls the Hi period 22 of the input voltage _{Vin_ac} so as to increase the Hi period 22 of the input voltage _{Vin_ac} as the voltage ratio d increases. Also, in the case of a voltage ratio 28 higher than the voltage ratio 26, the control circuit 70 controls the Hi period 22 of the input voltage _{Vin_ac} so as to decrease the Hi period 22 of the input voltage _{Vin_ac} as the voltage ratio d increases.

2, the output voltage V _{out_ac} has a _{pulse-like voltage waveform. The output voltage V out_ac has} a Hi period of 25 [deg].

As shown in the third row of FIG. 2 , in this embodiment, in the case of a voltage ratio 27 lower than voltage ratio 26, the control circuit 70 controls the Hi period 25 of the output voltage V _{out_ac} so as to decrease the Hi period 25 of the output voltage V _{out_ac} as the voltage ratio d increases, and further increase the Hi period 25 of the output voltage V _{out_ac} as the voltage ratio d increases.
Furthermore, in the case of a voltage ratio 28 higher than the voltage ratio 26, the control circuit 70 controls the Hi period 25 of the output voltage V _{out_ac} so as to reduce the Hi period 25 of the output voltage V _{out_ac} as the voltage ratio d increases.

In order to show the features of this embodiment, a comparative example will be described with reference to FIG. 3. FIG. 3 is a diagram showing a voltage waveform in an isolated DC/DC converter as a comparative example. As in FIG. 2, the first row from the top in FIG. 3 shows the input voltage V _{in_ac} , which is the voltage between nodes N1 and N2, on the vertical axis, and the horizontal axis shows time or phase [deg]. In the second row in FIG. 3, the vertical axis shows the Hi period of the input voltage, and the horizontal axis shows the input/output voltage ratio d. In the third row in FIG. 3, the vertical axis shows the Hi period of the output voltage, and the horizontal axis shows the input/output voltage ratio d. In the fourth row in FIG. 3, the vertical axis shows the output voltage V _{out_ac} , which is the voltage between nodes N11 and N12, and the horizontal axis shows time or phase [deg].

3, in the comparative example, in case 27 of a voltage ratio lower than voltage ratio 26, the control circuit 70 controls the Hi period 22 of the input voltage _{Vin_ac} so as to increase the Hi period 22 of the input voltage _{Vin_ac} as the voltage ratio d increases. Also, in case 28 of a voltage ratio higher than voltage ratio 26, the control circuit 70 controls the Hi period 22 of the input voltage _{Vin_ac} so as to keep the Hi period 22 of the input voltage _{Vin_ac} constant as the voltage ratio d increases.

3, in the comparative example, the output voltage V _{out_ac} has _a pulsed voltage waveform. The output voltage V _{out_ac} has a Hi period of 25 [deg].

3, in the comparative example, in case 27 of a voltage ratio lower than voltage ratio 26, the control circuit 70 controls the Hi period 25 of the output voltage V _{out_ac} so that the Hi period 25 of the output voltage V _{out_ac} remains constant as the voltage ratio d increases. Also, in case 28 of a voltage ratio higher than voltage ratio 26, the control circuit 70 controls the Hi period 25 of the output voltage V _{out_ac} so that the Hi period 25 of _{the output voltage V out_ac decreases} as the voltage ratio d increases.

When the voltage ratio is lower than voltage ratio 26 (27), the losses in the switching elements and the copper losses in the transformer become dominant. When the voltage ratio is higher than voltage ratio 26 (28), the iron losses in the transformer become dominant.

Comparing the Hi period of the input voltage in Figures 2 and 3, the difference between this embodiment and the comparative example can be seen. Furthermore, the difference between this embodiment and the comparative example can also be seen in the Hi period of the output voltage.

In this embodiment, by controlling the Hi period of the input voltage and the Hi period of the output voltage according to the voltage ratio, it is possible to suppress losses in the switching elements, copper losses in the transformer, and iron losses in the transformer, thereby preventing a decrease in power conversion efficiency.

According to this embodiment, the power conversion efficiency of the power conversion device can be increased compared to the conventional case. The power conversion efficiency can also be increased in the relationship between the Hi period of the input voltage and the output current flowing through the load ZL. The power conversion efficiency can also be increased in the relationship between the Hi period of the output voltage and the output current flowing through the load ZL, so that the power conversion efficiency can be increased overall in the control of the power conversion device.

20: Primary bridge circuit 40: Transformer 10, 60: Capacitor 50: Secondary bridge circuit 70: Control circuit

Claims (9)

A first bridge circuit and a second bridge circuit,
a transformer disposed between the first bridge circuit and the second bridge circuit;
A power conversion device including a control unit that operates the first and second bridge circuits,
The control unit is
Calculates the voltage ratio between the input voltage and the output voltage.
A power conversion device that determines the input side Hi period so that there are cases where the input side Hi period of a first bridge circuit is increased and cases where the input side Hi period is decreased with respect to the voltage ratio. 2. The power conversion device according to claim 1,
The control unit is
In a region where the voltage ratio is low, the input side Hi period may be increased with respect to the voltage ratio;
A power conversion device that determines the input side Hi period so that there are cases where the input side Hi period is reduced with respect to the voltage ratio in a region where the voltage ratio is high. 2. The power conversion device according to claim 1,
The control unit is
A power conversion device that determines the output side Hi period so that, when the input side Hi period is increased for the voltage ratio, the output side Hi period of a second bridge circuit is increased. 2. The power conversion device according to claim 1,
The control unit is
A power conversion device that determines the output side Hi period so that, when the input side Hi period is reduced with respect to the voltage ratio, the output side Hi period of a second bridge circuit is reduced. 2. The power conversion device according to claim 1,
The control unit is
determining the input side Hi period and the output side Hi period such that, in a region where the voltage ratio is low, when the input side Hi period increases, the output side Hi period of the second bridge circuit increases;
A power conversion device that determines the input side Hi period and the output side Hi period such that, in a region where the voltage ratio is high, when the input side Hi period decreases, the output side Hi period also decreases. 3. The power conversion device according to claim 2,
A power conversion device in which a high voltage ratio region and a low voltage ratio region are separated by a value of the voltage ratio equal to a turns ratio between the primary side and the secondary side of the transformer. 2. The power conversion device according to claim 1,
A power conversion device comprising an inductance element disposed between the AC side of at least one of a first bridge circuit and a second bridge circuit and the transformer. The power conversion device of claim 1 is a power conversion device having a DC-DC converter. A first bridge circuit and a second bridge circuit,
a transformer disposed between the first bridge circuit and the second bridge circuit;
A control method for a power conversion device including a control unit that operates first and second bridge circuits,
The control unit is
Calculate the voltage ratio between the input voltage and the output voltage.
A control method for a power conversion device, which determines the input side Hi period so that there are cases where the input side Hi period of a first bridge circuit increases and cases where the input side Hi period decreases with respect to the voltage ratio.