Power transmission device

Abstract

Provided is a power transmission device with which it is possible to realize a power transmission device having a high capacity of several hundred to several thousand kw required for a high-capacity smart network.　A voltage-output-type inverter 1A connected to a DC bus A and a current-output-type inverter 1B connected to a DC bus B are provided. The AC outputs of the voltage-output-type inverter 1A and the current-output-type inverter 1B are insulated and connected via a transformer 16. This makes it possible for electric power to be circulated between the DC bus A and the DC bus B. In this instance, the voltage-output-type inverter 1A and the current-output-type inverter 1B are multi-pulse PWM inverters in which the output voltage or the output current of the AC output is controlled to a sine wave form.

Description

Power transmission device 【0001】 The present invention relates to a power transmission device applicable to a bidirectional insulated DC / DC converter and bidirectional wireless power feeding. 【0002】 As a power transmission device, a conventional bidirectional insulated DC / DC converter operates in a DAB (Dual Active Bridge) method, connecting two single-pulse rectangular wave inverters via a high-frequency transformer to exchange power (see, for example, Patent Document 1). This single-pulse rectangular wave method is a so-called single-pulse method where the output frequency and the switching frequency are the same. 【0003】 Here, the conventional bidirectional insulated DC / DC converter described above will be specifically described with reference to FIG. 7. As shown in FIG. 7, a conventional bidirectional insulated DC / DC converter 100 is a voltage-type single-phase bridge inverter in which a first inverter 102 and a second inverter 103, which are two single-pulse rectangular wave inverters, are connected via a high-frequency transformer 101. 【0004】 Thus, such a bidirectional insulated DC / DC converter 100 can exchange bidirectional power by making the voltages of the first inverter 102 and the second inverter 103 substantially the same and controlling the phase difference. As shown in FIG. 8(a), the waveforms of the AC voltages of the first inverter 102 and the second inverter 103 are single-pulse waveforms. Further, as shown in FIG. 8(b), the current waveform is also a single-pulse waveform. 【0005】 By the way, the feature of the above bidirectional insulated DC / DC converter is to miniaturize the output transformer by increasing the switching frequency from several kHz to several tens of kHz, and to realize an economical and highly efficient converter. 【0006】 Japanese Patent Application Laid-Open No. 2010-124549 【0007】However, the bidirectional isolated DC / DC converter described above has a circuit configuration of a single-pulse square wave inverter with a coupling frequency of several kHz to several tens of kHz, which makes it difficult to manufacture large-capacity transformers, and it is only possible to manufacture up to about 50 kW. The reasons for this are as follows: 【0008】 (1) Due to the high frequency, the skin effect is large, so the coil windings of the transformer must be made of Litz wire, which is made up of many thin wires with a diameter of about 0.1 to 1.0 mm twisted together. However, Litz wire is limited to about 50A, and it is difficult to manufacture for high currents. 【0009】 (2) Amorphous cores and supercores with a sheet thickness of 0.1 mm, which are suitable for high frequencies, are difficult to manufacture in large sizes, and the maximum core cross-sectional area is 50 cm². ２ Because it weighs around 30 kg, it is not possible to manufacture high-capacity machines exceeding 100 kW. 【0010】 (3) A single-pulse PWM waveform contains many harmonic currents that do not contribute to the lower-order (i.e., third, fifth, and seventh) output, and the loss due to the skin effect is added to the above item (1), further reducing efficiency. 【0011】 (4) Because the inverter is a single-phase bridge type, it is not suitable for high-capacity machines of several tens of kilowatts or more. 【0012】 Thus, due to the four points mentioned above, this method presented a problem: it was not possible to realize the large-capacity bidirectional isolated DC / DC converters of several hundred to several thousand kilowatts required for high-capacity smart networks. 【0013】 Therefore, in view of the above problems, the present invention aims to provide a power transmission device that facilitates the manufacture of transformers for interconnection and reduces losses by reducing harmonic currents. This enables the realization of high-capacity power transmission devices of several hundred to several thousand kW, which are necessary for high-capacity smart networks. 【0014】 The object of the present invention described above is achieved by the following means. The reference numerals in parentheses indicate the embodiments described later, but the present invention is not limited thereto. 【0015】The power transmission device according to claim 1 is a bidirectional isolated DC / DC converter (for example, the one shown in Figure 5) that connects a first inverter (for example, a voltage output type inverter 1A shown in Figure 5) connected to a first DC bus (for example, a DC bus A shown in Figure 5) and a second inverter (for example, a current output type inverter 1B shown in Figure 5) connected to a second DC bus (for example, a DC bus B shown in Figure 5), and isolates the AC outputs of the first inverter and the second inverter via a transformer (for example, a transformer 16 shown in Figure 5) to exchange power between the first DC bus and the second DC bus, wherein the first inverter and the second inverter are multi-pulse PWM inverters in which the output voltage or output current of the AC output is controlled in a sinusoidal manner. 【0016】 The power transmission device according to claim 2 is characterized in that, in the power transmission device according to claim 1, the frequency of the sine wave of the output voltage or output current of the AC output is from 50 Hz to 500 Hz, and the switching frequencies of the first inverter (for example, the voltage output type inverter 1A shown in Figure 5) and the second inverter (for example, the current output type inverter 1B shown in Figure 5) are 9 to 400 times the frequency of the sine wave. 【0017】 The power transmission device according to claim 3 is characterized in that, in the power transmission device according to claim 1 or 2, the first inverter (for example, the voltage output type inverter 1A shown in Figure 5) is a voltage output type, the second inverter (for example, the current output type inverter 1B shown in Figure 5) is a current output type, the output voltage of the first inverter is controlled sinusoidally by a voltage control loop, the output current of the second inverter is controlled sinusoidally by a current control loop, and further, the magnitude and phase of the sinusoidal output current of the second inverter are controlled by the current control loop to control the magnitude of the power between the first DC bus (for example, DC bus A shown in Figure 5) and the second DC bus (for example, DC bus B shown in Figure 5) to any positive or negative value. 【0018】The power transmission device according to claim 4 is a power transmission device according to claim 1 or 2, further comprising: a phase difference detection unit (31) that detects the difference between the angle of the sinusoidal output voltage of the first inverter (for example, the voltage output type inverter 1A shown in Figure 5) and the angle of the sinusoidal output current of the second inverter (for example, the current output type inverter 1B shown in Figure 5) and outputs an angle difference signal; and a PLL synchronous control unit (32), wherein the PLL synchronous control unit (32) corrects the angle difference signal output by the phase difference detection unit (31), thereby controlling the phase of the sinusoidal output current of the second inverter. 【0019】 According to the invention of claim 1, the first inverter (for example, the voltage output type inverter 1A shown in Figure 5) and the second inverter (for example, the current output type inverter 1B shown in Figure 5) are multi-pulse PWM inverters in which the output voltage or output current of the AC output is controlled in a sinusoidal manner. Therefore, it is possible to realize a large-capacity power transmission device (for example, the bidirectional isolated DC / DC converter 15 shown in Figure 5) of several hundred to several thousand kW, which is necessary for a large-capacity smart network. 【0020】 According to the invention of claim 2, the frequency of the sine wave of the output voltage or output current of the AC output is from 50 Hz to 500 Hz, and the switching frequencies of the first inverter (for example, the voltage output type inverter 1A shown in Figure 5) and the second inverter (for example, the current output type inverter 1B shown in Figure 5) are 9 to 400 times the frequency of the sine wave, making it easier to realize a large-capacity power transmission device of several hundred to several thousand kW required for a large-capacity smart network. 【0021】According to the invention of claim 3, the output voltage of the first inverter (for example, the voltage output type inverter 1A shown in Figure 5) is controlled sinusoidally by a voltage control loop, and the output current of the second inverter (for example, the current output type inverter 1B shown in Figure 5) is controlled sinusoidally by a current control loop, thus simplifying the circuit configuration. Furthermore, the AC voltage applied to the transformer (16) is kept constant by the first inverter (for example, the voltage output type inverter 1A shown in Figure 5), and the current of the first inverter (for example, the voltage output type inverter 1A shown in Figure 5) can also be controlled by controlling the magnitude and phase of the current flowing through the reactor (including leakage inductance) installed between the transformer (16) and the second inverter (for example, the current output type inverter 1B shown in Figure 5). As a result, both voltage and current can be controlled, and the magnitude of the power between the first DC bus (for example, the DC bus A shown in Figure 5) and the second DC bus (for example, the DC bus B shown in Figure 5) can be controlled to any positive or negative value. 【0022】 According to the invention of claim 4, even when the carrier frequencies of the first inverter (for example, the voltage output type inverter 1A shown in Figure 5) and the second inverter (for example, the current output type inverter 1B shown in Figure 5) are different, stable power transmission according to the command value becomes possible. 【0023】 This is a diagram showing an example of a typical three-phase bridge inverter. This is a block diagram showing an example of a typical voltage-controlled inverter. This is a block diagram showing an example of a typical voltage-controlled inverter with a current minor loop. This is a block diagram showing an example of a typical current-controlled inverter. This is a block diagram showing one embodiment of a bidirectional isolated DC / DC converter according to the present invention. (a) shows the PWM waveform (sine wave waveform) of the voltage, and (b) shows the sine wave waveform of the current. This is a diagram showing a conventional bidirectional isolated DC / DC converter. (a) shows the single-pulse waveform of the voltage, and (b) shows the single-pulse waveform of the current. 【0024】Hereinafter, an embodiment of the bidirectional isolated DC / DC converter according to the present invention will be specifically described with reference to the drawings. In the following description, when the directions of up, down, left, and right are indicated, they refer to the up, down, left, and right directions as viewed from the front as shown in the illustration. 【0025】 First, before describing the bidirectional isolated DC / DC converter according to this embodiment, we will explain the general contents of voltage-controlled inverters and current-controlled inverters. 【0026】 Figure 1 shows a three-phase bridge inverter 1. 【0027】 As shown in Figure 1, the three-phase bridge inverter 1 includes IGBTs (Insulated Gate Bipolar Transistors) Q1a to IGBTQ1f and diodes D1a to D1f. As shown in Figure 1, the collectors of IGBTQ1a, IGBTQ1c, and IGBTQ1e are connected to the positive voltage P terminal, and the emitters of IGBTQ1b, IGBTQ1d, and IGBTQ1f are connected to the negative voltage N terminal. Furthermore, as shown in Figure 1, the emitters of IGBTQ1a, IGBTQ1c, and IGBTQ1e are connected to the collectors of IGBTQ1b, IGBTQ1d, and IGBTQ1f. Diodes D1a to D1f are connected in antiparallel to IGBTQ1a to IGBTQ1f, respectively, as shown in Figure 1. Also, as shown in Figure 1, capacitor C1 is connected between the positive voltage P terminal and the negative voltage N terminal. 【0028】Thus, in the three-phase bridge inverter 1 configured as described above, IGBTQ1a to IGBTQ1f are turned on / off when a predetermined signal (switching signal) is input to the gates of IGBTQ1a to IGBTQ1f shown in Figure 1. As a result, voltages are output to the three-phase transformer consisting of U-phase, V-phase, and W-phase shown in Figure 1. Note that the signal input to the gate of IGBTQ1b in the voltage output type inverter 1 shown in Figure 1 is the inverse signal of the signal input to the gate of IGBTQ1a, the signal input to the gate of IGBTQ1d is the inverse signal of the signal input to the gate of IGBTQ1c, and the signal input to the gate of IGBTQ1f is the inverse signal of the signal input to the gate of IGBTQ1e. Therefore, IGBTQ1a and IGBTQ1b of the voltage output inverter 1 shown in Figure 1 will not be turned on at the same time, IGBTQ1c and IGBTQ1d will not be turned on at the same time, and IGBTQ1e and IGBTQ1f will not be turned on at the same time. 【0029】 Thus, such a three-phase bridge inverter 1 can be controlled by voltage and current, as shown below. A detailed explanation follows. 【0030】 Figure 2 shows an example of voltage control. Specifically, as shown in Figure 2, the voltage-controlled inverter 2 detects the output voltage of the three-phase bridge inverter 1 using the voltage detection unit 3. Then, as shown in Figure 2, the voltage detection unit 3 outputs the detected output voltage to the voltage control unit 4. In response, the voltage control unit 4 generates a signal to control the magnitude and phase of the output voltage based on the detected output voltage and inputs it to the gates of IGBTQ1a to IGBTQ1f shown in Figure 1. Thus, by controlling the magnitude and phase of the output voltage in this way, the magnitude and phase of the output current can be controlled to any desired value. 【0031】 Therefore, a voltage-controlled inverter is realized in this way. 【0032】 However, in this case, although the voltage is controlled, the current itself is not, so there is a concern that too much current may flow depending on the load conditions. 【0033】 Therefore, in order to improve accuracy, voltage control with a current minor loop can be used, as shown in Figure 3. Specifically, as shown in Figure 3, in the voltage-controlled inverter 5, an AC reactor L2 is connected to the three-phase bridge inverter 1, and the current flowing through the AC reactor L2 is detected by the current detection unit 6. Then, as shown in Figure 3, the current detection unit 6 outputs the detected output current to the current control unit 7. In response, the current control unit 7 generates a signal to control the magnitude and phase of the output current based on the detected output current, and inputs it to the gates of IGBTQ1a to IGBTQ1f shown in Figure 1. 【0034】 Thus, the current minor loop is processed in this manner. 【0035】 On the other hand, when the three-phase bridge inverter 1 outputs a signal with controlled output current magnitude and phase, which is input to the gates of IGBTQ1a to IGBTQ1f shown in Figure 1, a voltage is generated across capacitor C2 shown in Figure 3. This generated voltage is detected by the voltage detection unit 8 shown in Figure 3 and output to the voltage control unit 9. In response, the voltage control unit 9 generates a signal to control the output voltage based on the detected voltage and inputs it to the gates of IGBTQ1a to IGBTQ1f shown in Figure 1. 【0036】 Thus, the voltage measuring loop is processed in this manner. 【0037】 Therefore, voltage control with a current minor loop is achieved in this way. 【0038】 Figure 4 shows an example of current control. Specifically, as shown in Figure 4, in the current-controlled inverter 10, an AC reactor L3 is connected to a three-phase bridge inverter 1, and the current flowing through the AC reactor L3 is detected by the current detection unit 12. Then, as shown in Figure 4, the current detection unit 12 outputs the detected output current to the current control unit 13. In response, the current control unit 13 generates a signal to control the magnitude and phase of the output current based on the detected output current and outputs it to the three-phase bridge inverter 1. 【0039】Thus, a current-controlled inverter is realized in this way. 【0040】 Therefore, as explained above, voltage-controlled inverters and current-controlled inverters can be realized. 【0041】 Thus, in this embodiment, by replacing the voltage-controlled inverter and current-controlled inverter described above with a multi-pulse PWM inverter, we aim to realize a high-capacity bidirectional isolated DC / DC converter of several hundred to several thousand kW, which is necessary for high-capacity smart networks. This will be explained using a specific example shown in Figure 5. 【0042】 The bidirectional isolated DC / DC converter 15 shown in Figure 5 consists of a voltage output inverter 1A using a three-phase bridge inverter 1 and a current output inverter 1B using the same three-phase bridge inverter 1. As shown in Figure 5, DC bus A is connected to the voltage output inverter 1A, and DC bus B is connected to the current output inverter 1B. DC bus A has a positive DC bus connected to terminal P as shown in Figure 1, and a negative DC bus connected to terminal N as shown in Figure 1. Similarly, DC bus B has a positive DC bus connected to terminal P as shown in Figure 1, and a negative DC bus connected to terminal N as shown in Figure 1. This allows for the exchange (sharing) of DC power between DC bus A and DC bus B. 【0043】 Thus, as shown in Figure 5, the voltage output inverter 1A and the current output inverter 1B are connected in isolation via a transformer 16, with the AC output voltage output from the voltage output inverter 1A and the AC output current output from the current output inverter 1B being separated. The operating frequency of the transformer 16 is set to between 50 Hz and 500 Hz. 【0044】On the other hand, as shown in FIG. 5, the AC output voltage output from the voltage output type inverter 1A is detected by the voltage detection unit 17, passes through the filter circuit 18, and is negatively fed back to the subtractor 19. Further, as shown in FIG. 5, a voltage command value output from the sine wave voltage command unit 20 is input to the subtractor 19. As a result, the subtractor 19 calculates the deviation between the voltage command value and the voltage passing through the filter circuit 18. Note that a frequency such as 50 Hz or 60 Hz output from the frequency command unit 21 shown in FIG. 5 is input to the sine wave voltage command unit 20. 【0045】 Next, the calculated deviation is input to the voltage control unit 22 shown in FIG. 5. In response to this, the voltage control unit 22 controls the magnitude and phase of the voltage. That is, the magnitude and phase of the output voltage of the voltage output type inverter 1A are controlled. Note that the voltage controlled by the voltage control unit 22 is a sine wave voltage. 【0046】 Next, the voltage controlled by the voltage control unit 22 is output to the PWM circuit 23 as shown in FIG. 5. In the PWM circuit 23, the voltage controlled by the voltage control unit 22 is used as a fundamental wave, and a multi-pulse PWM signal is generated by comparing the fundamental wave with the triangular carrier output from the triangular carrier circuit 24 shown in FIG. 5. The triangular carrier frequency is 9 to 400 times the output frequency of the voltage output type inverter 1A shown in FIG. 5. Thus, the PWM signal generated in this way is output to the voltage output type inverter 1A shown in FIG. 5. That is, it is input to the gates of the IGBTs Q1a to Q1f shown in FIG. 1 as the switching frequency. 【0047】Thus, by using the voltage detection units 17, the filter circuit 18, the subtracter 19, the voltage control unit 22, and the PWM circuit 23, the voltage output type inverter 1A can be made into a multi-pulse PWM inverter that operates at a switching frequency of 9 to 400 times the output frequency and controls the output voltage in a sine wave shape. Note that, unlike the conventional waveform shown in Fig. 8(a), the waveform of such an output voltage is in a PWM shape (sine wave shape) as shown in Fig. 6(a). And the frequency of the sine wave AC output voltage of the voltage output type inverter 1A is 50 Hz to 500 Hz. 【0048】 On the other hand, the current output type inverter 1B shown in Fig. 5 incorporates an AC reactor not shown, and the AC output current flowing through this AC reactor is detected by the current detection unit 25. And as shown in Fig. 5, the current detected by the current detection unit 25 passes through the filter circuit 26 to attenuate the carrier, and the current with the attenuated carrier is negatively fed back to the subtracter 27. Further, as shown in Fig. 5, a current command value output from the sine wave current command unit 28 is input to the subtracter 27, whereby the subtracter 27 obtains the deviation between the current command value and the current with the attenuated carrier. Note that, as shown in Fig. 5, the power output from the power command unit 29 is input to the sine wave current command unit 28. Thereby, the sine wave current command unit 28 can control the power to an arbitrary value (within the range from negative to positive rated values) by changing the amplitude and phase (0 degrees or 180 degrees being the basis) of the current command. 【0049】 Incidentally, as shown in Fig. 5, for example, a frequency of 50 Hz or 60 Hz output from a frequency command unit 30 different from the frequency command unit 21 is input to the sine wave current command unit 28. At this time, since the voltage output type inverter 1A and the current output type inverter 1B are controlled separately, the carrier frequencies are different, and there is a possibility that the frequency of the sine wave AC output voltage of the voltage output type inverter 1A and the frequency of the sine wave AC output current of the current output type inverter 1B are different. At this time, a deviation occurs between the angle of the sine wave AC output voltage and the angle of the sine wave AC output current. When a deviation occurs, stable power proportional to the current command value cannot be obtained. 【0050】 Therefore, in this embodiment, in order to correct this discrepancy, as shown in Figure 5, the sinusoidal AC output voltage output from the voltage output type inverter 1A is output to the phase difference detection unit 31 through the filter circuit 18. Furthermore, as shown in Figure 5, the sinusoidal AC output current output from the current output type inverter 1B is output to the phase difference detection unit 31 through the filter circuit 26. As a result, the phase difference detection unit 31 shown in Figure 5 detects the discrepancy between the angle of the sinusoidal AC output voltage and the angle of the sinusoidal AC output current, and outputs the phase difference of this angle discrepancy as an angle discrepancy signal to the PLL synchronous control unit 32. In response to this, the PLL synchronous control unit 32 performs a correction to synchronize the angle of the sinusoidal AC output voltage and the angle of the sinusoidal AC output current based on the angle discrepancy signal. As a result, the angle of the sinusoidal AC output current synchronized with the angle of the sinusoidal AC output voltage is output from the PLL synchronous control unit 32 to the frequency command unit 30, as shown in Figure 5. In response, the frequency command unit 30 outputs a frequency synchronized with the angle of the sinusoidal AC output voltage to the sinusoidal current command unit 28. As a result, the sinusoidal current command unit 28 outputs a current command value synchronized with the angle of the sinusoidal AC output voltage, enabling stable power transmission according to the command value even when the carrier frequencies of the voltage output inverter 1A and the current output inverter 1B are different. This is particularly useful in DC power transmission in bidirectional wireless power supply, where it is necessary to control the voltage output inverter 1A and the current output inverter 1B separately. 【0051】 Thus, the deviation obtained by the subtractor 27 is input to the current control unit 33 shown in Figure 5. In response, the current control unit 33 controls the magnitude and phase of the current. In other words, it controls the magnitude and phase of the output current of the current output inverter 1B. The current controlled by the current control unit 33 is a sinusoidal current. 【0052】Next, the current controlled by the current control unit 33 is added to the current command value output from the sinusoidal current command unit 28 by the adder 34, as shown in Figure 5. In other words, feedforward control is performed. This reduces the carrier pulsation of the current controlled by the current control unit 33, thereby improving the waveform of the sinusoidal current. 【0053】 Next, the current added in the adder 34 is input to the PWM circuit 35 shown in Figure 5. The PWM circuit 35 uses the current added in the adder 34 as the fundamental wave, and generates a multi-pulse PWM signal by comparing this fundamental wave with the triangular wave carrier output from the triangular wave carrier circuit 36 ​​shown in Figure 5. The triangular carrier frequency is 9 to 400 times the output frequency of the current output inverter 1B shown in Figure 5. Thus, the PWM signal generated in this way is output to the current output inverter 1B shown in Figure 5. That is, it is input as a switching frequency to the gates of IGBTQ1a to IGBTQ1f shown in Figure 1. 【0054】 Thus, by using a current control loop comprising the current detection unit 25, filter circuit 26, subtractor 27, current control unit 33, and PWM circuit 35, the current output type inverter 1B can be made into a multi-pulse PWM inverter that controls the output current in a sinusoidal manner by operating at a switching frequency of 9 to 400 times the output frequency. Note that the waveform of such an output current is sinusoidal, as shown in Figure 6(b), unlike the conventional waveform shown in Figure 8(b). Furthermore, the frequency of the sinusoidal AC output current of the current output type inverter 1B is 50 Hz to 500 Hz. 【0055】 Therefore, by performing the control described above, it is possible to exchange power between the voltage output type inverter 1A, which is a multi-pulse PWM inverter, and the current output type inverter 1B, which is a multi-pulse PWM inverter, via the transformer 16. This makes it possible to control the magnitude of the power between DC bus A and DC bus B to any positive or negative value. 【0056】In other words, conventional bidirectional isolated DC / DC converters can control the magnitude and direction of power by controlling the phase difference of the square wave of a single-pulse inverter. However, the present invention requires controlling both the sinusoidal voltage and current applied to the transformer 16. Therefore, both the first and second inverters can be made into voltage output type inverters, with the first inverter having AC output voltage control with a current-controlled minor loop, and the second inverter having DC output voltage control with a current-controlled minor loop. However, in this circuit, the circuit becomes complex because it is necessary to control the voltage and current of both the first and second inverters using a current-controlled minor loop. Furthermore, there is a possibility that the current control of both inverters may interfere with each other, causing hunting (vertical oscillation). 【0057】 Therefore, in this embodiment, the first inverter is a voltage output type inverter 1A, and the second inverter is a current output type inverter 1B, so that voltage and current can be controlled separately. The voltage output type inverter 1A is controlled by the voltage control loop described above, and the current output type inverter 1B is controlled by the current control loop described above. As a result, the circuit configuration is simplified. 【0058】 Furthermore, in this embodiment, the voltage output inverter 1A maintains a constant AC voltage across the transformer 16, and the current of the voltage output inverter 1A can also be controlled by controlling the magnitude and phase of the current flowing through the reactor (including leakage inductance) installed between the transformer 16 and the current output inverter 1B. This makes it possible to control both voltage and current, and to control the magnitude of the power between DC bus A and DC bus B to any positive or negative value. 【0059】 Therefore, according to the embodiment described above, since the first inverter (voltage output type inverter 1A) and the second inverter (current output type inverter 1B) are multi-pulse PWM inverters in which the output voltage or output current of the AC output is controlled in a sinusoidal manner, the transformer 16 for coupling can be easily manufactured, and harmonic currents can be reduced, thereby reducing losses. 【0060】 Therefore, by using this embodiment, it becomes possible to realize a high-capacity bidirectional isolated DC / DC converter with a capacity of several hundred to several thousand kW, which is necessary for high-capacity smart networks. 【0061】 Furthermore, in this embodiment, the frequency of the sine wave of the AC output voltage or output current is set to 50 Hz to 500 Hz. This is because if it is below 50 Hz, the transformer must be made larger, which increases the size of the transformer 16 and makes the device larger, thus preventing miniaturization. Furthermore, if it is above 500 Hz, the loss due to harmonic current increases, which requires a larger amorphous iron core, causing problems such as heat generation. For this reason, in this embodiment, the frequency of the sine wave of the AC output voltage or output current is set to 50 Hz to 500 Hz. Also, this numerical range allows the use of commercial transformers 16, which is preferable because it makes it easier to realize high-capacity power transmission devices of several hundred to several thousand kW required for high-capacity smart networks. Furthermore, in this embodiment, considering the reduction of losses due to harmonic current and the switching speed of the IGBT, the switching frequencies of the first inverter (voltage output type inverter 1A) and the second inverter (current output type inverter 1B) are set to 9 to 400 times the frequency of the sine wave. Thus, setting the numerical range in this manner makes it possible to use IGBTs intended for railways, which is preferable because it facilitates the realization of high-capacity power transmission equipment ranging from several hundred to several thousand kW, necessary for high-capacity smart networks. 【0062】 Therefore, by using the numerical range described above, it becomes easier to realize the large-capacity power transmission equipment of several hundred to several thousand kilowatts required for high-capacity smart networks. 【0063】<Explanation of Modifications> The shapes and other features shown in this embodiment are merely examples, and various modifications and changes are possible within the scope of the gist of the present invention as described in the claims. For example, in this embodiment, an example is shown in which the frequency command unit 21 and the frequency command unit 30 are provided separately, but since the angle of the sinusoidal AC output voltage and the angle of the sinusoidal AC output current are synchronized using the phase difference detection unit 31 and the PLL synchronization control unit 32, the frequency command units may be shared. 【0064】 Furthermore, although this embodiment was described using a bidirectional isolated DC / DC converter as an example, it can also be applied to bidirectional wireless power supply. 【0065】 1A Voltage output inverter (first inverter) 1B Current output inverter (second inverter) 15 Bidirectional isolated DC / DC converter (power transmission device) 16 Transformer 31 Phase difference detection unit 32 PLL synchronous control unit A DC bus (first DC bus) B DC bus (second DC bus)

Claims

1. A power transmission device that connects a first inverter connected to a first DC bus and a second inverter connected to a second DC bus, and isolates the AC outputs of the first inverter and the second inverter via a transformer, thereby enabling the exchange of power between the first DC bus and the second DC bus, wherein the first inverter and the second inverter are multi-pulse PWM inverters in which the output voltage or output current of the AC output is controlled in a sinusoidal manner.

2. The power transmission device according to claim 1, wherein the sinusoidal frequency of the output voltage or output current of the AC output is from 50 Hz to 500 Hz, and the switching frequencies of the first inverter and the second inverter are 9 to 400 times the sinusoidal frequency.

3. The power transmission device according to claim 1 or 2, wherein the first inverter is a voltage output type, the second inverter is a current output type, the output voltage of the first inverter is controlled sinusoidally by a voltage control loop, the output current of the second inverter is controlled sinusoidally by a current control loop, and the magnitude and phase of the sinusoidal output current of the second inverter are controlled by the current control loop to control the magnitude of the power between the first DC bus and the second DC bus to any positive or negative value.

4. The power transmission device according to claim 1 or 2, further comprising: a phase difference detection unit that detects the difference between the angle of the sinusoidal output voltage of the first inverter and the angle of the sinusoidal output current of the second inverter and outputs an angle difference signal; and a PLL synchronous control unit, wherein the PLL synchronous control unit corrects the angle difference signal output by the phase difference detection unit and thereby controls the phase of the sinusoidal output current of the second inverter.

Images