Bidirectional power conversion device and control method therefor

Abstract

To provide a bidirectional power conversion device which improves conversion efficiency in a bidirectional manner in the case of conversion from AC power to DC power and in the case of conversion from DC power to AC power.SOLUTION: A control method for a bidirectional power conversion device 1 comprises: AC terminals T3 and T4 to which AC power is inputted or from which AC power is outputted; a first converter 10 connected to the AC terminals T3 and T4 and comprising an inverter circuit 11 including an LC resonance circuit 12 and a first switch S1; a second converter 20 connected to the first converter 10 via an intermediate part 30; and DC terminals T1 and T2 which are connected to the second converter 20 and to which DC power is inputted or from which DC power is outputted. In the case of conversion from DC power to AC power, the second converter 20 is controlled in such a manner that an intermediate voltage V2 of the intermediate part 30 outputted by the second converter 20 is changed according to an AC voltage V1 outputted by the first converter 10.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a bidirectional power conversion device and a control method thereof. [Background technology]

[0002] The bidirectional power converter uses two conversion circuits, and the input and output parts change depending on the power supply direction. From the viewpoint of circuit configuration, the conversion circuit connected to the AC terminal is called a power factor correction circuit, and has the role of converting power from AC to DC when charging the battery. When charging the battery, the output of the power factor correction circuit becomes the input of a DC / DC converter, which is a conversion circuit connected to the DC terminal, and the DC / DC converter performs voltage conversion according to the DC voltage of the battery, which is a load connected to the output terminal. When discharging the battery, the DC voltage of the battery connected to the output terminal becomes the input of the DC / DC converter, and the bidirectional power converter executes the power conversion pattern during charging in the reverse direction. In a bidirectional power converter for applications that correspond to large power and a wide range of voltages, there is a power converter in Patent Document 1 as a prior art using a dual active bridge circuit. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2021-112073 A Summary of the Invention [Problem to be solved by the invention]

[0004] The power conversion device of Patent Document 1 has a configuration that uses a conversion circuit that performs bidirectional conversion between AC power and DC power using a switching element, and a bidirectional converter that performs voltage conversion of the DC power using a switching element and a transformer, and therefore has a problem of low conversion efficiency between AC power and DC power.

[0005] It may be possible to apply a class E power conversion circuit using a resonant circuit that has high conversion efficiency between AC and DC power, but it is difficult to increase the conversion efficiency of the class E power conversion circuit in both directions, AC and DC power.

[0006] The present invention has been made in view of the above problems, and an object of the present invention is to provide a bidirectional power conversion device having good conversion efficiency in both directions, when converting AC power to DC power and when converting DC power to AC power. [Means for solving the problem]

[0007] A control method for a bidirectional power conversion device according to one aspect of the present invention is a control method for a bidirectional power conversion device including: an AC terminal for inputting AC power or for outputting AC power; a first converter including an inverter circuit connected to the AC terminal and having an LC resonant circuit and a first switch; a second converter connected to the first converter via an intermediate unit; and a DC terminal connected to the second converter and for inputting DC power or for outputting DC power. When converting DC power to AC power, the control method for the bidirectional power conversion device controls the second converter so as to change an intermediate voltage of the intermediate unit output by the second converter in accordance with the AC voltage output by the first converter. Effect of the Invention

[0008] According to the present invention, it is possible to provide a bidirectional power conversion device that has good conversion efficiency in both cases of converting AC power to DC power and converting DC power to AC power. [Brief description of the drawings]

[0009] [Figure 1] FIG. 1 is a circuit diagram showing a configuration of a bidirectional power conversion device according to an embodiment. [Diagram 2]FIG. 2 shows waveforms of the intermediate voltage V2, intermediate current I2, AC voltage V1, AC current I1, voltage Vs1 across the switch circuit, and power conversion efficiency when the AC voltage V1 as the input is an effective value of 100 V, the intermediate voltage V2 as the output is a constant value of 380 V, and the on-duty ratio is 0.4 during charging operation of the bidirectional power conversion device according to the embodiment. [Diagram 3] FIG. 3 shows waveforms of the intermediate voltage V2, intermediate current I2, AC voltage V1, AC current I1, voltage Vs2 across the third switch, and power conversion efficiency when the AC voltage V1 as output is an effective value of 100 V, the intermediate voltage V2 as input is a constant value of 380 V, and the on-duty ratio is 0.4 during discharging operation of the bidirectional power conversion device according to the comparative example. [Figure 4] FIG. 4 shows waveforms of the intermediate voltage V2, intermediate current I2, AC voltage V1, AC current I1, voltage Vs2 across the third switch, and power conversion efficiency when the AC voltage V1 as output is 100 V effective value, the intermediate voltage V2 as input is a variable voltage ranging from 0 V to a maximum value of +380 V, and the on-duty ratio is 0.4 during discharging operation of the bidirectional power conversion device according to the embodiment. [Diagram 5] FIG. 5 is a diagram in which the distribution of losses at turn-on with respect to the AC voltage and the switching frequency of the third switch and the control trajectory of the third switch are simultaneously plotted when the AC voltage V1 as the output is an effective value of 100 V, the intermediate voltage V2 as the input is a variable voltage ranging from 0 V to a maximum value of +200 V, and the on-duty ratio is 0.4 in the discharge operation of the bidirectional power conversion device according to the embodiment. [Figure 6] FIG. 6 is a diagram in which the distribution of losses at turn-on with respect to the AC voltage and the switching frequency of the third switch and the control trajectory of the third switch are simultaneously plotted when the AC voltage V1 as the output is an effective value of 100 V, the intermediate voltage V2 as the input is a variable voltage ranging from 0 V to a maximum value of +250 V, and the on-duty ratio is 0.4 in the discharge operation of the bidirectional power conversion device according to the embodiment. [Figure 7]FIG. 7 is a diagram in which the distribution of losses at turn-on with respect to the AC voltage and the switching frequency of the third switch and the control trajectory of the third switch are simultaneously plotted when the AC voltage V1 as the output is an effective value of 100 V, the intermediate voltage V2 as the input is a variable voltage ranging from 0 V to a maximum value of +380 V, and the on-duty ratio is 0.4 in the discharge operation of the bidirectional power conversion device according to the embodiment. [Figure 8] FIG. 8 is a diagram illustrating the operation of the bidirectional power conversion device 1 in a discharge operation when the intermediate voltage V2 is controlled to change by a half wavelength in a 50 Hz sine wave shape within a range from 0 V to +380 V so as to match the phase and frequency of the AC voltage V1. [Figure 9] FIG. 9 is a diagram illustrating the operation of the bidirectional power conversion device 1 in a discharge operation when control is performed such that the intermediate voltage V2 is shifted in phase by −7° with respect to the AC voltage V1 and is changed by a half wavelength in a 50 Hz sine wave shape in the range from 0 V to +380 V. [Figure 10] FIG. 10 is a diagram illustrating the operation when the discharge operation of the bidirectional power conversion device 1 is controlled so that the intermediate voltage V2 is shifted in phase by +28° with respect to the AC voltage V1 and is changed by a half wavelength in a 50 Hz sine wave shape in the range from 0 V to +380 V. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0010] The embodiments will be described with reference to the drawings. In the description of the drawings, the same parts are given the same reference numerals and the description will be omitted.

[0011] The bidirectional power converter can convert electric energy regardless of the direction of the power, and can perform two operations because the input and output change depending on the direction of the power. In this embodiment, charging refers to a case where the input is connected to an AC power source and the output is connected to a DC load such as a battery, and AC power is converted into DC power, and discharging refers to a case where the input is connected to a DC power source such as a battery, AC power is generated at the output, and DC power is converted into AC power. However, the types of power sources and loads are not limited to these, and other power sources and loads can also be applied.

[0012] A bidirectional power converter includes at least two conversion circuits. One of them is a power factor correction circuit, and the other is a DC / DC converter. A typical power factor correction circuit consists of an input choke inductor and four switches connected in a bridge, and is used to minimize the phase difference between the voltage and current waveforms of the input section. On the other hand, a typical DC / DC converter that can be used in a bidirectional power converter is a dual active bridge, which is an isolated bidirectional converter. In each circuit, a switching element such as a semiconductor transistor is used as a switch to switch on and off.

[0013] To achieve high efficiency and miniaturization of bidirectional power conversion equipment, the use of a resonant circuit is one option. A resonant circuit uses the current of an internal resonant circuit when the switch is turned on, which makes the voltage across the switch zero, enabling zero-voltage switching that reduces switching losses, and enabling highly efficient switching operation at high frequencies. Furthermore, the resonant circuit can reduce the size of the circuit by reducing the capacitance and inductance of passive components due to the high frequency of the switching operation.

[0014] An example of a resonant circuit is the class E power conversion circuit. The class E power conversion circuit has an inverter circuit and a rectifier circuit. The inverter circuit has an input choke inductor, a switch, a shunt capacitor connected in parallel with the switch, and an LC resonant circuit, and generates a high-frequency AC current by repeatedly turning the switch on and off. The rectifier circuit rectifies the high-frequency current generated by the inverter circuit.

[0015] A resonant circuit is easily affected by the output impedance, and large switching losses occur when the conditions for zero voltage switching are no longer met. On the other hand, in applications where there is little fluctuation in the output voltage and output current, the conditions for zero voltage switching are more likely to be met, making the resonant circuit suitable as a power factor correction circuit.

[0016] However, in the discharge operation of a general bidirectional power converter, the input of the power factor correction circuit is a DC voltage and the output is an AC voltage, so that the large change in the output voltage of the resonant circuit functioning as a power factor correction circuit makes it difficult to achieve zero voltage switching, resulting in a decrease in efficiency. For this reason, it has been difficult to use a resonant circuit functioning as a power factor correction circuit in the discharge operation of a bidirectional power converter up until now. That is, in a resonant circuit such as a class E power converter, the conditions for achieving zero voltage switching are different when converting AC power to DC power and when converting DC power to AC power, so it is necessary to optimize the class E power converter.

[0017] (Embodiment) FIG. 1 is a circuit diagram showing a configuration of a bidirectional power converter 1 according to an embodiment. The bidirectional power converter 1 includes DC terminals T1 and T2, AC terminals T3 and T4, a first converter 10, a second converter 20, an intermediate unit 30, and a control unit 40 that controls the first converter 10 and the second converter 20. The first converter 10 is connected to the AC terminals T3 and T4. The second converter 20 is connected to the DC terminals T1 and T2. The first converter 10 and the second converter 20 are connected via the intermediate unit 30. The AC terminals T3 and T4 receive AC power during charging operation, and output AC power from the first converter 10 during discharging operation. The DC terminals T1 and T2 receive DC power during discharging operation, and output DC power from the second converter 20 during charging operation. The control unit 40 controls the first converter 10 so that the intermediate voltage V2 of the intermediate unit 30 output by the first converter 10 is a constant voltage during charging operation. In addition, in the case of a discharging operation, the control unit 40 controls the second converter 20 so as to change the intermediate voltage V2 of the intermediate unit 30 output by the second converter 20 in accordance with the AC voltage V1 output by the first converter 10.

[0018] An AC voltage detection circuit 4 is connected between the AC terminals T3 and T4 to detect an AC voltage V1. A control unit 40 monitors the instantaneous value of the AC voltage V1 detected by the AC voltage detection circuit 4.

[0019] The bidirectional power conversion device 1 shown in Fig. 1 is an example in which the first converter 10 is configured as a resonant circuit. The first converter 10 includes an inverter circuit 11 and a rectifier circuit 13. The inverter circuit 11 generates a high-frequency current of about several MHz from a low-frequency AC voltage V1 of, for example, 50 Hz input from AC terminals T3 and T4. The rectifier circuit 13 rectifies the high-frequency current generated by the inverter circuit 11 to a DC voltage or a low-frequency AC voltage.

[0020] The inverter circuit 11 includes a first inductor L1 as an input choke inductor, a switch circuit 14 including a first switch S1, a first capacitor C1 as a shunt capacitor, and an LC resonant circuit 12. In the LC resonant circuit 12, a resonant inductor Lr and a resonant capacitor Cr are connected in series. The first inductor L1 is connected between one end of the switch circuit 14 and one AC terminal T3. The first capacitor C1 is connected in parallel to the switch circuit 14. The LC resonant circuit 12 is connected between one end of the switch circuit 14 and the rectifier circuit 13. Although an example in which the switch circuit 14 is configured by one first switch S1 has been shown, the switch circuit 14 may be configured by connecting two or more switches in series.

[0021] The rectifier circuit 13 includes a second switch S2, a second capacitor C2, and a second inductor L2. The second switch S2 is connected in parallel to the inverter circuit 11. The second capacitor C2 is connected in parallel to the second switch S2. The second inductor L2 is connected between one end of the second switch S2 and the second converter 20.

[0022] By configuring the first converter 10 as a resonant circuit, it is possible to satisfy the conditions for achieving zero voltage switching, which can reduce switching losses. By using a resonant circuit such as a class E power conversion circuit, which is a circuit configuration aimed at realizing zero voltage switching, as the first converter 10, it is possible to reduce high losses that occur in converters using hard switching.

[0023] The bidirectional power converter 1 shown in FIG. 1 is an example in which the second converter 20 is configured as a bidirectional buck-boost type converter circuit. The second converter 20 includes an input / output filter 21 configured with a third capacitor C3 and a third inductor L3, a third switch S3 connected in parallel to the input / output filter 21, a fourth switch S4 connected in series to one end of the third switch S3, and a fourth capacitance C4 connected in parallel to one end of the fourth switch S4. The second converter 20 operates as a boost circuit during charging operation and as an inverter circuit during DC discharging operation. By configuring the second converter 20 in this way, it functions as a DC / DC converter during charging, converts the DC voltage V3 during discharging, and can control the intermediate voltage V2 to match the frequency and phase of the AC voltage V1. Therefore, it is possible to reduce the loss at the time of turn-on in the first converter 10, which is a resonant circuit, both during charging and discharging.

[0024] The first to fourth switches S1 to S4 are switching elements such as semiconductor transistors. The control unit 40 controls the on / off of the first switch S1 and the second switch S2 of the first converter 10 and the third switch S3 and the fourth switch S4 of the second converter 20 independently.

[0025] The operation of the bidirectional power converter 1 according to the embodiment will be described below.

[0026] 2, in charging operation of the bidirectional power converter 1 with certain circuit parameters, the horizontal axis plots time (ms) and the vertical axis plots, from top to bottom, intermediate voltage V2, intermediate current I2, AC voltage V1, AC current I1, voltage Vs1 across the switch circuit 14, and power conversion efficiency of the first converter 10. Fig. 2 shows waveforms when operating with AC voltage V1 as the input voltage at an effective value of 100 V and intermediate voltage V2 as the output voltage at a constant +380 V.

[0027] Under the conditions of FIG. 2, the AC voltage V1 has a sine waveform with a frequency of 50 Hz. In a power conversion device that obtains power from a general AC power system, it is required to control the input current so that the power factor approaches 1 as much as possible. For this reason, unless otherwise specified, the following description will be given assuming that the bidirectional power conversion device 1 is controlled so that the power factor of the input current is high. In FIG. 2, it can be seen that the waveform of the AC current I1 is synchronized with the AC voltage V1, and a high power factor has been achieved. It can also be seen that the efficiency of the power conversion is high, at 98% or more. This efficiency in the charging operation is the standard for evaluating the efficiency of the discharging operation.

[0028] Next, a discharge operation in which DC power is converted into AC power in the bidirectional power converter 1 according to a comparative example will be described with reference to FIG.

[0029] Fig. 3 shows waveforms obtained when the bidirectional power converter 1 is operated in a discharge operation with the same circuit parameters as those in Fig. 2, with the AC voltage V1 as the output voltage set to an effective value of 100 V, the intermediate voltage V2 as the input voltage set to a constant 380 V, and the on-duty ratio of the third switch S3 set to 0.4, according to a comparative example of this embodiment. In Fig. 3, the horizontal axis represents time (ms), and the vertical axis represents, from the top, the intermediate voltage V2, the intermediate current I2, the AC voltage V1, the AC current I1, the voltage Vs2 across the third switch S3, and the power conversion efficiency of the first converter 10.

[0030] In the conditions of FIG. 3, the input and output voltages and currents are set on the assumption that the same power is transported as during charging. During charging, the first converter 10 operates as a power factor correction circuit, whereas during discharging, the first converter 10 is required to output an AC voltage V1 and an AC current I1. In FIG. 3, the AC voltage V1 and the AC current I1 contain harmonic components and have waveforms different from sine waves. It can also be seen that the average power conversion efficiency is around 60%, which is 30 points or more lower than the average power conversion efficiency during charging, which is the benchmark shown in FIG. 2.

[0031] During discharging operation, the AC voltage V1 output from the first converter 10 varies from 0 V to 141.4 V at a frequency of 50 Hz, which changes the impedance seen from the constant intermediate voltage V2, resulting in a waveform with high total harmonic distortion. As shown in Figure 3, if the same control as during charging operation is used during discharging operation, it becomes difficult to obtain high average power conversion efficiency and low total harmonic distortion as during charging shown in Figure 2, so it is necessary to separate the control during charging operation and the control during discharging operation.

[0032] Next, a discharging operation in the bidirectional power converter 1 according to this embodiment, which is a case where DC power is converted into AC power, will be described with reference to FIG.

[0033] Fig. 4 shows waveforms when the bidirectional power converter 1 according to this embodiment is operated in a discharge operation with the same circuit parameters as those in Fig. 3, with the AC voltage V1 as the output voltage set to an effective value of 100 V, the intermediate voltage V2 as the input voltage set to a variable voltage ranging from 0 V to a maximum value of 380 V, and the on-duty ratio of the third switch S3 in the rectifier circuit 13 of the first converter 10 set to 0.4. As in Fig. 3, Fig. 4 plots time (ms) on the horizontal axis and, from the top, the intermediate voltage V2, intermediate current I2, AC voltage V1, AC current I1, voltage Vs2 across the third switch S3, and power conversion efficiency of the first converter 10 on the vertical axis.

[0034] In the conditions of Fig. 4, the intermediate voltage V2 is not a constant value but is controlled to change from 0V to +380V to match the phase and frequency of the AC voltage V1. Here, the intermediate voltage V2, which is the output of the second converter 20, functions as the input voltage of the first converter 10. At a frequency of 100Hz, the intermediate voltage V2 is 0V when the AC voltage V1 is 0V, and is +380V when the AC output voltage is 141.4V or -141.V. In other words, the intermediate voltage V2 is generated with the same phase and twice the frequency as the AC voltage V1, thereby obtaining a waveform as shown in Fig. 4.

[0035] The waveforms of the AC voltage V1 and AC current I1, and the envelope of the voltage Vs2 across the third switch S3, are very close to a 50Hz sine wave, which makes it possible to achieve an average power conversion efficiency of about 98% and low total harmonic distortion. Under the conditions of Figure 4, the intermediate voltage V2 during discharge is changed in accordance with the change in the AC voltage V1, thereby making it possible to avoid deterioration of efficiency and total harmonic distortion.

[0036] Fig. 5 shows a contour plot of the loss at turn-on when the bidirectional power converter 1 with certain circuit parameters is operated with the AC voltage V1 at an effective value of 100V, the intermediate voltage V2 at a variable voltage from 0V to a maximum value of +200V, and the on-duty ratio of the third switch S3 at 0.4, and the operating locus of the switching frequency of the third switch S3 when the average output power is 1.1kW and the AC voltage V1 is sinusoidal. The horizontal axis represents the instantaneous value of the AC voltage V1, and the vertical axis represents the switching frequency of the third switch S3. Under the conditions of Fig. 5, the intermediate voltage V2 is controlled to change from 0V to +200V so as to match the phase and frequency of the AC voltage V1.

[0037] In the conditions of FIG. 5, the horizontal axis is from 0V to 141.4V, which represents the absolute value of the fluctuation range of the instantaneous value when the effective value of the AC voltage V1 is 100V, and the vertical axis is from 2MHz to 4MHz, which represents the fluctuation range of the switching frequency of the third switch S3. Here, when the average output power is 1.1kW, the switching frequency of the third switch S3 is 2.92 to 3.0MHz, and zero voltage switching is achieved in the entire range of the AC voltage V1, and the loss when the third switch S3 is turned on is zero. The lightest colored area indicates that the loss when the third switch S3 is turned on is zero, and is the area where zero voltage switching is achieved under the condition that the voltage Vs2 across the third switch S3 when turned on is 0V.

[0038] Under the condition that the on-duty ratio of the third switch S3 is 0.4, the locus of the average output power of 1.1 kW passes through the region where zero voltage switching is possible in the range of 0V to 141.4V, which is the fluctuation range of the AC voltage V1 with an effective value of 100V, when the switching frequency of the third switch S3 is 2.92 to 3.0MHz. In other words, under this condition, it can be seen that zero voltage switching is established in the entire region for the change of the AC voltage V1 of 50Hz or 60Hz. Also, it can be seen that when the control described in the explanation of FIG. 5 is performed, the operating locus of the switching frequency of the third switch S3 with respect to the instantaneous value of the AC voltage V1 becomes a straight line. In this way, by using a resonant circuit such as an E-class circuit as the first converter 10, the condition for zero voltage switching to be established in both the charging operation and the discharging operation is satisfied, which contributes to reducing losses, and therefore it is possible to achieve high efficiency.

[0039] Fig. 6, like Fig. 5, shows a contour plot of loss at turn-on when the bidirectional power converter 1 with certain circuit parameters is operated with the AC voltage V1 at an effective value of 100V, the intermediate voltage V2 at a variable voltage from 0V to a maximum value of +250V, and the on-duty ratio of the third switch S3 at 0.4, and shows the operation locus of the switching frequency of the third switch S3 when the average output power is 1.3 to 1.8kW and the AC voltage V1 is sinusoidal. Under the conditions of Fig. 6, the intermediate voltage V2 is controlled to change from 0V to +250V so as to match the phase and frequency of the AC voltage V1.

[0040] In the plot of Fig. 5, the intermediate voltage V2 is a variable voltage ranging from 0V to a maximum value of +200V, and the switching frequency region in which the loss when the third switch S3 is turned on is zero over the entire operating range of the AC voltage V1 is from 2.92 to 3.0MHz. In contrast, in the plot of Fig. 6, the intermediate voltage V2 is a variable voltage ranging from 0V to a maximum value of +250V, and the switching frequency region in which the loss when the third switch S3 is turned on is zero over the entire operating range of the AC voltage V1 is from 2.8 to 3.0MHz. In this way, by changing the maximum value of the intermediate voltage V2, it is possible to change the switching frequency region in which the loss when the third switch S3 is turned on is zero.

[0041] In addition, in the plot of FIG. 5, the intermediate voltage V2 is a variable voltage from 0V to a maximum value of +200V, and the locus of the average output power passing through the region where the loss when the third switch S3 is turned on is zero in the entire operating range of the AC voltage V1 is limited to 1.1 kW. In contrast, in the plot of FIG. 6, the intermediate voltage V2 is a variable voltage from 0V to a maximum value of +250V, and it can be seen that the locus of the average output power passing through the region where the loss when the third switch S3 is turned on is zero in the entire operating range of the AC voltage V1 includes 1.3 to 1.8 kW. In this way, by increasing the maximum value of the intermediate voltage V2, the region where the loss when the third switch S3 is turned on is zero is widened. In addition, when changing the value of the AC power output by the first converter 10, the desired average output power can be obtained by changing the maximum value of the intermediate voltage V2 output by the second converter 20.

[0042] Fig. 7, like Fig. 5, shows a contour plot of loss at turn-on when the bidirectional power converter 1 with certain circuit parameters is operated with the AC voltage V1 at an effective value of 100V, the intermediate voltage at a variable voltage from 0V to a maximum value of +380V, and the on-duty ratio of the third switch S3 at 0.4, and shows the operation locus of the switching frequency of the third switch S3 when the average output power is 2.0 to 4.0kW and the AC voltage V1 is sinusoidal. Under the conditions of Fig. 7, the intermediate voltage V2 is controlled to change from 0V to +380V so as to match the phase and frequency of the AC voltage V1.

[0043] Here, when the average output power is 2 kW, zero voltage switching is achieved in the entire range of the AC voltage V1, and the switching frequency is 3.0 MHz. When the average output power is 4 kW, zero voltage switching is achieved in the entire range of the AC voltage V1, and the operating switching frequency is 2.6 MHz. The range in which the loss becomes zero in the entire operating range of the AC voltage V1 includes 3.0 to 2.6 MHz. Therefore, for example, under the conditions of FIG. 7, when the required average output power is changed from 2 kW to 4 kW, the required average output power can be obtained while achieving zero voltage switching by simply changing the switching frequency of the third switch S3 from 3.0 MHz to 2.6 MHz.

[0044] Next, a case where the intermediate voltage V2 is out of phase with respect to the AC voltage V1 during a discharging operation of the bidirectional power converter 1 with certain circuit parameters will be described with reference to Figs. 8 to 10.

[0045] Fig. 8 is a diagram explaining the operation when the discharge operation of the bidirectional power converter 1 is controlled to change the intermediate voltage V2 by a half wavelength in a range from 0V to +380V to match the phase and frequency of the AC voltage V1. Fig. 9 is a diagram explaining the operation when the discharge operation of the bidirectional power converter 1 is controlled to change the intermediate voltage V2 by a half wavelength in a range from 0V to +380V to a 50Hz sine wave with a phase shift of -7° with respect to the AC voltage V1. Fig. 10 is a diagram explaining the operation when the discharge operation of the bidirectional power converter 1 is controlled to change the intermediate voltage V2 by a half wavelength in a range from 0V to +380V to a 50Hz sine wave with a phase shift of +28° with respect to the AC voltage V1.

[0046] 8-10, the horizontal axis represents time (ms) and the vertical axis represents, from top to bottom, intermediate voltage V2, intermediate current I2, AC voltage V1, AC current I1, voltage Vs2 across third switch S3, and power conversion efficiency of first converter 10. The waveforms shown are for AC voltage V1 operating at an effective value of 100 V, and intermediate voltage V2 operating at a variable voltage ranging from 0 V to a maximum value of +380 V. Such simulations were performed in ±1° increments, centering on the case where there is no phase shift of intermediate voltage V2 relative to AC voltage V1 (Fig. 8).

[0047] 8, when there is no phase shift, the waveforms of the intermediate current I2, the AC voltage V1, and the AC current I1, as well as the waveform of the intermediate voltage V2, and the envelope of the voltage Vs2 across the third switch S3 are very close to a 50 Hz sine wave. This makes it possible to achieve an average power conversion efficiency of about 98% and low total harmonic distortion in the first converter 10.

[0048] 9, when the phase is shifted by -7°, the waveforms of the intermediate current I2, the AC voltage V1, and the AC current I1, and the envelope of the voltage Vs2 across the third switch S3, are 50 Hz sine waves that contain slight harmonic distortion, relative to the waveform of the intermediate voltage V2. Meanwhile, the first converter 10 achieves a high average power conversion efficiency of about 98%. However, when the phase of the intermediate voltage V2 with respect to the AC voltage V1 is shifted further negatively than -7°, the average power conversion efficiency of the first converter 10 rapidly deteriorates.

[0049] 10, when the phase is shifted by +28°, the waveforms of the intermediate current I2, AC voltage V1, and AC current I1, and the envelope of the voltage Vs2 across the third switch S3 are 50 Hz sine waves containing harmonic distortion, relative to the waveform of the intermediate voltage V2. Meanwhile, the first converter 10 achieves a high average power conversion efficiency of about 85%. However, when the phase of the intermediate voltage V2 with respect to the AC voltage V1 is shifted further to the positive side than +28°, the average power conversion efficiency of the first converter 10 rapidly deteriorates.

[0050] As described above, when the phase of the intermediate voltage V2 is in the range of -7° to +28° with respect to the AC voltage V1, the loss when the third switch S3 is turned on is reduced, and highly efficient discharge operation is possible.

[0051] As described above, the bidirectional power converter 1 according to the embodiment can provide a bidirectional power converter with good conversion efficiency in both cases of converting AC power to DC power and converting DC power to AC power.

[0052] As described above, the embodiment of the present invention has been described, but the description and drawings forming a part of this disclosure should not be understood as limiting this invention. From this disclosure, various alternative embodiments, examples and operating techniques will become apparent to those skilled in the art. [Explanation of symbols]

[0053] 1. Bidirectional power converter 2. Load 3 AC power supply 10 First converter 11 Inverter circuit 12 LC resonant circuit 13 Rectifier circuit 14 Switch Circuit 20 Second converter 21 Input / Output Filters 30 Middle Section 40 Control section I1 AC current I2 intermediate current S1 First switch S2 Second switch T1,T2 DC terminal T3,T4 AC terminal V1 AC voltage V2 Intermediate voltage V3 DC voltage

Claims

1. an AC terminal for inputting AC power or outputting AC power; a first converter including an inverter circuit having an LC resonant circuit and a first switch connected to the AC terminal; a second converter connected to the first converter via an intermediate portion; a DC terminal connected to the second converter and receiving DC power or outputting DC power; A method for controlling a bidirectional power conversion device comprising: When converting DC power into AC power, the second converter is controlled so as to change an intermediate voltage of the intermediate section output by the second converter in accordance with the AC voltage output by the first converter. A method for controlling a bidirectional power conversion device.

2. When converting AC power into DC power, the first switch of the first converter is controlled so that an intermediate voltage at the intermediate section output by the first converter is made a constant voltage. A method for controlling a bidirectional power conversion device according to claim 1.

3. In the case of converting DC power into AC power, when the value of the AC power output by the first converter is changed, the maximum value of the intermediate voltage output by the second converter is changed. A method for controlling a bidirectional power conversion device according to claim 1.

4. the first converter further comprises a rectifier circuit having a second switch; In the case of converting DC power into AC power, when changing the value of the AC power output by the first converter, a switching frequency of the second switch is changed. A method for controlling a bidirectional power conversion device according to claim 1.

5. When converting DC power to AC power, the phase of the intermediate voltage output by the second converter is controlled within a range of −7° to +28° with respect to the phase of the AC voltage output by the first converter. A method for controlling a bidirectional power conversion device according to claim 1.

6. an AC terminal for inputting AC power or outputting AC power; a first converter including an inverter circuit having an LC resonant circuit and a first switch connected to the AC terminal; a second converter connected to the first converter via an intermediate portion; a DC terminal connected to the second converter and receiving DC power or outputting DC power; a control unit for controlling the operation of the first converter and the second converter; Equipped with the control unit controls the second converter so as to change an intermediate voltage of the intermediate section output by the second converter in response to the AC voltage output by the first converter when converting DC power into AC power. Bidirectional power converter.

7. The first converter is the inverter circuit includes the first switch, an input choke inductor connected between one end of the first switch and the AC terminal, and the LC resonant circuit, and generates a high-frequency current; a rectifier circuit connected to an output of the inverter circuit, the rectifier circuit having a second switch and rectifying the high-frequency current generated by the inverter circuit into a DC voltage or a low-frequency AC voltage; A resonant circuit having The bidirectional power converter according to claim 6 .

8. The bidirectional power conversion device according to claim 6 or 7, wherein the second converter is a bidirectional buck-boost type conversion circuit.

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