Power conversion system

Abstract

To provide a power conversion system capable of converting DC power into AC power in a simple control form where it is not necessary to consider an interval time of a switching element.SOLUTION: A power conversion system comprises: a 6-phase transformer 2a including a primary side coil L1 including six input terminals and a secondary-side coil L2 including three output terminals constituting three phases; a changeover switch circuit 3 which includes a plurality of switching elements M each turning on / turning off output of a DC power source 5 and by which the DC power source 5 is switched to each input terminal of the 6-phase transformer 2a and supplied; and a control section 4 which controls the changeover switch circuit 3. The switching elements M are turned on / turned off in a predetermined order in changeover timing of 1.39 ms by the control section 5 and DC power is supplied to the input terminals. Thus, a voltage is generated in the secondary-side coil L2, and 3-phase AC power is outputted from the output terminals.SELECTED DRAWING: Figure 3

Description

[Technical field]

[0001] The present invention relates to a power conversion system that converts DC power into AC power. [Background technology]

[0002] Since the power generated by photovoltaic power generation or fuel cell power generation is DC power, in order to use it in conjunction with commercial AC power, it must be converted into AC power with a matching frequency. Conventionally, such power conversion has been performed by converting the power into AC power by PWM controlling an inverter circuit (see, for example, Patent Document 1). On the other hand, there is a device that converts AC power into DC power by using a multi-phase transformer without using an AC / DC converter (see, for example, Patent Document 2). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2001-309664 A [Patent Document 2] Patent Publication No. 2022-71713 Summary of the Invention [Problem to be solved by the invention]

[0004] Conventional inverter circuits used in power conversion systems that convert DC to AC are configured by connecting multiple sets of circuits, each of which has two switching elements connected in series, in parallel. Therefore, if the switching elements connected in series are turned on at the same time, a short-circuit current will flow and the elements will be damaged, so a dead time (interval time) is provided during which both switching elements are turned off at the same time. However, in PWM control, the dead time is minimized to increase conversion efficiency. In this case, because high-speed, complex switching control is performed, there is a problem that a short circuit can occur due to malfunction caused by slight timing deviation or noise if the dead time is shortened. In addition, the length of the interval time differs depending on the power module (switching element), gate driver circuit, and switching frequency used, so a new design was required each time. On the other hand, the technology using a multi-phase transformer disclosed in the above Patent Document 2 does not require consideration of dead time and does not generate high-frequency noise. Therefore, if this technology using a multi-phase transformer can be applied to DC / AC conversion, it is expected that the above problems will be solved.

[0005] In view of these problems, the present invention aims to provide a power conversion system that can convert DC power to AC power with a simple control form by using a multi-phase transformer, eliminating the need to consider the interval time of switching elements. [Means for solving the problem]

[0006] In order to solve the above problem, the power conversion system of the invention of claim 1 comprises a 3n-phase multi-phase transformer having a primary winding with input terminals consisting of 3n phases (n is a natural number) and a secondary winding with three output terminals that constitute the three phases, a DC power supply arranged on the primary side of the multi-phase transformer, a change-over switch circuit having a plurality of switching elements that turn on / off the output of the DC power supply and switches and supplies the DC power supply to each input terminal of the multi-phase transformer, and a control unit that controls the change-over switch circuit, wherein the control unit turns on / off each switching element in a predetermined order at a constant switching timing, and DC power is supplied to the input terminals, thereby generating a voltage in the secondary winding and outputting three-phase AC power from the output terminals. According to this configuration, by turning on / off the switching elements of the changeover switch circuit at a fixed switching timing and generating three-phase AC using a multi-phase transformer, DC / AC conversion is possible without PWM control. Therefore, it is easy to prevent situations where switching elements connected in series are turned on at the same time. In addition, because a transformer is used, it is possible to insulate the input and output, unlike conventional PWM-controlled circuits. In addition, the switching of the switching elements of the changeover switch circuit can be performed with a control signal having a lower frequency than that of conventional PWM control, and the control circuit can be simplified.

[0007] Another aspect of the present invention is characterized in that, in the above configuration, the multi-phase transformer is a six-phase transformer in which the primary winding has two windings, a first winding and a second winding, each having three input terminals for a total of six terminals, and the secondary winding has a third winding and has three output terminals, and each winding consists of three winding parts wound around respective legs of an iron core having three legs, the first winding and the second winding are star-connected, the second winding is formed with 0.73 times the number of turns of the first winding, and both neutral points are connected, while the third winding is delta-connected or star-connected. According to this configuration, by sequentially switching two of the six terminals on the primary side to apply a DC voltage, a six-phase induced magnetic field is generated in the three legs of the iron core, and three-phase power can be output from the secondary side by this induced magnetic field. Thus, DC power can be converted into three-phase AC power.

[0008] Another aspect of the present invention is characterized in that, in the above configuration, the multi-phase transformer is a 12-phase transformer in which the primary winding has four windings, namely a first winding to a fourth winding, each having three input terminals for a total of 12 terminals, and the secondary winding has a fifth winding and has three output terminals, and each winding is made up of three winding parts wound around respective legs of an iron core having three legs, and the first winding to the fourth winding are all star-connected, and the neutral points of the first winding and the second winding are connected to each other, while the third winding and the fourth winding are formed by branching off from a common predetermined position midway through the second winding, and the fifth winding is delta-connected or star-connected. With this configuration, by sequentially switching two of the twelve terminals on the primary side to apply a DC voltage, a twelve-phase induced magnetic field is generated in the three legs of the iron core, and three-phase power can be output from the secondary side by this induced magnetic field. Thus, DC power can be converted into three-phase AC power.

[0009] Another aspect of the present invention is characterized in that, in the above configuration, the individual switching elements are turned on / off in a predetermined order at a predetermined switching timing of 0.5 ms to 2.0 ms. According to this configuration, the switching elements of the changeover switch circuit are turned on / off at a predetermined switching timing of 0.5 ms to 2.0 ms, and three-phase AC is generated using a multi-phase transformer. Therefore, by performing DC / AC conversion with a control signal of a lower frequency than conventional PWM control, the control circuit can be simplified, high-output elements such as IGBTs can be used, and no high-frequency noise is generated. Effect of the Invention

[0010] According to the present invention, by turning on / off the switching elements of the changeover switch circuit at a fixed switching timing and generating three-phase AC using a multi-phase transformer, DC / AC conversion is possible without PWM control. Therefore, it is easy to prevent situations where switching elements connected in series are turned on at the same time. In addition, since a transformer is used, it is possible to insulate the input and output, unlike conventional PWM-controlled circuits. In addition, the switching of the switching elements of the changeover switch circuit can be performed with a control signal having a lower frequency than that of conventional PWM control, and the control circuit can be simplified. [Brief description of the drawings]

[0011] [Figure 1] 1 is a circuit block diagram showing an example of a power conversion system according to the present invention. [Diagram 2] FIG. 11 is a circuit block diagram in which the multi-phase transformer is a six-phase transformer. [Diagram 3] FIG. 3 is a circuit diagram of the changeover switch circuit and the multi-phase transformer of FIG. 2. [Figure 4] 4 is an output waveform diagram of a counter circuit. FIG. [Diagram 5] FIG. 2 is a circuit diagram of a drive control circuit. [Figure 6] 5 is an operation sequence diagram of each switching element of the changeover switch circuit. FIG. [Figure 7] 1 is an explanatory diagram of a current flowing through a primary side of a six-phase transformer in response to a first signal. FIG. [Figure 8] FIG. 11 is an explanatory diagram of the current flowing through the primary side of the six-phase transformer in response to a second signal. [Figure 9] FIG. 2 is an explanatory diagram of the output voltage of each phase of a six-phase transformer. [Figure 10] FIG. 2 is an explanatory diagram of line voltages output by a six-phase transformer. [Figure 11] FIG. 1 is a vector diagram of the voltages generated by a six-phase transformer, where (a) is an explanatory diagram of the primary side and (b) is an explanatory diagram of the secondary side. [Figure 12] FIG. 11 is a circuit block diagram in which the multi-phase transformer is a 12-phase transformer. [Figure 13] FIG. 11 is an operation sequence diagram of each switching element of a changeover switch circuit when the multi-phase transformer is a 12-phase transformer. [Figure 14] FIG. 2 is an explanatory diagram of the output voltage of each phase of a 12-phase transformer. [Figure 15] FIG. 1 is a vector diagram illustrating the voltages generated by a 12-phase transformer, where (a) is an explanatory diagram of the primary side and (b) is an explanatory diagram of the secondary side. [Figure 16]14 is an explanatory diagram of a current flowing in the primary side of a 12-phase transformer in response to a second signal in FIG. 13. FIG. [Figure 17] FIG. 2 is an explanatory diagram of a three-phase AC waveform. [Figure 18] The voltage vectors of each phase are shown at point A1 in FIG. [Figure 19] FIG. 19 is a vector explanatory diagram of the winding ratio based on FIG. 18. [Figure 20] FIG. 4 is an explanatory diagram of windings around a transformer core. [Figure 21] FIG. 2 is an explanatory diagram of vectors between R phase and S phase in a multi-phase transformer. [Figure 22] FIG. 4 is an explanatory diagram of a changeover switch circuit. [Diagram 23] 5 is an explanatory diagram of an operation sequence of the changeover switch circuit. FIG. [Figure 24] 5 is an explanatory diagram of an operation sequence of the changeover switch circuit. FIG. [Diagram 25] FIG. 2 is an explanatory diagram of line voltages output by a 12-phase transformer. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0012] Hereinafter, an embodiment of the present invention will be described in detail with reference to the drawings. Fig. 1 shows a basic configuration of a power conversion system according to the present invention. The power conversion system 1 includes a multi-phase transformer 2, a changeover switch circuit 3 that operates the input to the multi-phase transformer 2, and a control unit 4 that controls the changeover switch circuit 3. By switching and inputting DC power to a plurality of input terminals of the multi-phase transformer 2, for example, 380V DC power output by a DC power source 5 is converted into 200V three-phase AC power of 50Hz or 60Hz. The control unit 4 includes an oscillation circuit 6, a counter circuit 7, and a drive control circuit 8.

[0013] First, a case where the multi-phase transformer 2 is a six-phase transformer 2a will be described. 2 shows a configuration in which the multi-phase transformer 2 is a six-phase transformer 2a. The six-phase transformer 2a has six input terminals on the primary side for forming six phases, and three output terminals on the secondary side for outputting three-phase AC power.

[0014] 3 is a circuit diagram of the six-phase transformer 2a and the changeover switch circuit 3. In the six-phase transformer 2a, the primary winding L1 is composed of two windings, a first winding 11 and a second winding 12, and the secondary winding L2 is composed of one third winding 13. Each of the windings 11, 12, 13 has three windings, an R-phase winding portion (11a, 12a, 13a), an S-phase winding portion (11b, 12b, 13b), and a T-phase winding portion (11c, 12c, 13c). It has six terminals R1in, S1in, T1in, R2in, S2in, and T2in as input terminals for applying voltages to the first winding 11 and the second winding 12, and three terminals Rout, Sout, and Tout connected to the third winding 13 as output terminals.

[0015] The three winding portions of each of the windings 11, 12, and 13 are wound around the respective legs of an iron core 10 having three legs (R-phase leg 10a, S-phase leg 10b, and T-phase leg 10c). All of the windings are star-connected, and the neutral points Q of the first winding 11 and the second winding 12 are connected to each other. The number of turns of the first winding 11 and the second winding 12 is wound at a ratio of 1:(√3-1). That is, the number of turns of the second winding 12 is 0.73 times that of the first winding 11, and the first winding 11 and the second winding 12 wound around the same leg of the iron core 10 are wound so as to generate a phase-to-phase voltage. Although the third winding 13 is star-connected, it may be delta-connected.

[0016] The changeover switch circuit 3 is configured to have 12 switching elements M, each of which is, for example, an IGBT. Specifically, six pairs of two switching elements M connected in series are connected in parallel (MR1 and MR1', MS1 and MS1', MT1 and MT1', MR2 and MR2', MS2 and MS2', and MT2 and MT2'). This circuit is connected in parallel to a DC power source 5, and an output terminal is disposed between the two switching elements M connected in series, and each output terminal is connected to each input terminal (R1in, S1in, T1in, R2in, S2in, T2in) of the six-phase transformer 2a.

[0017] The control unit 4 includes an oscillator circuit 6, a counter circuit 7, and a drive control circuit 8. The oscillator circuit 6 outputs a signal with a frequency synchronized with the commercial power frequency of 50 Hz or 60 Hz. In the case of a six-phase transformer 2a, the oscillator circuit 6 outputs a signal with a timing that divides one period of the AC voltage waveform it generates into 12 equal parts. That is, when synchronized with 60 Hz, a signal is output at intervals of 1.39 ms (not shown).

[0018] The counter circuit 7 outputs a timing signal for driving each switching element M of the changeover switch circuit 3 based on the output signal of the oscillation circuit 6. Fig. 4 shows the timing signals S output by the counter circuit 7. As shown in Fig. 4, the counter circuit 7 outputs 12 types of timing signals S (a first signal s1 to a twelfth signal s12) for controlling the 12 switching elements M based on the output signal of the oscillation circuit 6.

[0019] 5 shows the drive control circuit 8. The drive control circuit 8 has a combination signal generation circuit 8a that generates drive signals that turn on / off the individual switching elements M in a predetermined combination, and a drive circuit 8b that drives the individual switching elements M based on the signals from the combination signal generation circuit 8a. It has 12 input sections that respectively input the timing signals S output by the counter circuit 7, and the 12 switching elements M are individually driven by the output signals of the drive control circuit 8.

[0020] 6 shows an operation sequence diagram of the changeover switch circuit 3, and shows combinations of 12 types of timing signals (first signal s1 to twelfth signal s12) and switching elements M. The timing signal S is a signal for dividing one period of the AC waveform to be generated into 12 equal parts and generating voltages corresponding to each divided part. This signal combination is generated by the combination signal generation circuit 8a shown in FIG. Here, a case where an AC voltage of 60 Hz is output will be described. The 12 switching elements M operate to generate voltages for each of the 12 equal sections of one period. The counter circuit 7 sequentially outputs a first signal s1, a second signal s2, ... a twelfth signal s12 at a constant interval of 1.39 ms, and the drive control circuit 8 drives the changeover switch circuit 3 using these signals, and the individual switching elements M are sequentially turned on in pairs as shown in FIG. 6.

[0021] 6 shows that, in response to an initial first signal s1, the combination signal generation circuit 8a generates a signal that simultaneously turns on MR1 and MT1' of the switching elements M. This signal causes the drive circuit 8b to turn on MR1 and MT1' of the switching elements M. Fig. 7 shows the flow of current flowing from DC power supply 5 at this time. As indicated by arrow I1 in Fig. 7, a voltage is applied to R-phase winding portion 11a and T-phase winding portion 11c of first winding 11, causing a current to flow and generating a magnetic field in iron core 10. This magnetic field induces a positive voltage in the first winding 13a of the third winding 13, which is the secondary winding L2, and induces a negative voltage in the third winding 13c. As a result, a positive voltage is generated at the Rout terminal of the output terminals, and a negative voltage is generated at the Tout terminal.

[0022] Fig. 8 shows the flow of DC current generated by the next second signal s2. The second signal s2 indicates that the combination signal generation circuit 8a generates a signal that simultaneously turns on MR1 and MR2' of the switching elements M. This signal causes the drive circuit 8b to turn on MR1 and MR2' of the switching elements M, and a current indicated by the arrow I2 in Fig. 8 flows. In this way, a voltage is sequentially applied to the primary winding L1 in each of the 12 divided sections, causing a current to flow, and a voltage is generated in the third winding 13, which is the secondary winding L2.

[0023] 9 and 10 are explanatory diagrams of the voltages output by the six-phase transformer 2a upon receiving the input of the 12-divided voltage. FIG. 9 shows the voltages V R ,V S,V T 9, and Fig. 10 shows the phase-to-phase voltage (line voltage). For example, in response to the initial first signal s1, a voltage is applied to the first winding portion 11a and the third winding portion 11c of the first winding 11, so that a positive voltage is induced in the R phase of the second winding 13 and a negative voltage is induced in the T phase, as shown in the divided area of ​​s1 in Fig. 9. In addition, V R-S is the line voltage between the secondary RS phases, V S-T is the line voltage between the secondary ST phases, V T-R indicates the line voltage between the secondary TR phases. The line voltage is the voltage of the phases that form an equilateral triangle, as will be described later.

[0024] Note that V11a, V11b, and V11c respectively indicate voltages generated on the secondary side by applying voltages to the R-phase winding portion 11a, the S-phase winding portion 11b, and the T-phase winding portion 11c of the first winding 11. Also, V12a, V12b, and V12c respectively indicate voltages generated on the secondary side by applying voltages to the R-phase winding portion 12a, the S-phase winding portion 12b, and the T-phase winding portion 12c of the second winding 12. Also, for example, V11a-12a indicates a voltage obtained by superimposing a reverse-phase voltage of the R-phase winding portion 12a of the second winding 12 on a voltage generated on the secondary side by the R-phase winding portion 11a of the first winding 11.

[0025] Voltages are generated in this way in each of the 12 divided areas, and when the output voltages of each output terminal generated by dividing one period into 12 equal parts are viewed on the time axis, it can be seen from Figures 9 and 10 that voltages with a phase shift of 120 degrees are generated. As a result, a three-phase AC voltage is output from the secondary side of the six-phase transformer 2a. Although this output voltage waveform is shown as a neat rectangle for illustrative purposes, in reality a distorted waveform is generated. This waveform then passes through a waveform shaping circuit (not shown), such as a low-pass filter, to become a waveform close to a sine wave.

[0026] Fig. 11 is a vector explanatory diagram of the voltages generated by the six-phase transformer 2a, and the generated voltages are explained using vector diagrams. Fig. 11(a) shows, in vector form, six types of voltages generated in the secondary winding L2 by mutual induction caused by application of a DC voltage to the primary winding L1. Fig. 11(b) shows, in vector form, the voltages output to the three output terminals Rout, Sout, and Tout of the third winding 13, which is the secondary winding L2. In this manner, by applying voltages to the individual windings of the first winding 11 and the second winding 12 in a predetermined order as shown in FIG. 6, it is possible to generate three-phase AC voltages with a phase shift of 120 degrees on the secondary side, as shown in FIG. 11.

[0027] Here, the reason why the number of turns of the second winding 12 is set to 0.73 times that of the first winding 11 will be explained. As shown in FIG. 11, voltages V12a, V12b, V12c generated on the secondary side by the second winding 12, which has fewer turns, are 0.73 times larger than voltages V11a, V11b, V11c generated on the secondary side by the first winding 11, in proportion to the turns ratio of the first winding 11 and the second winding 12. 9 causes a current to flow through the R-phase winding portion 11a of the first winding 11 and the R-phase winding portion 12a of the second winding 12, and a voltage of V11a+V12a is generated in the R-phase of the third winding 13, which is 1.73 times V11a due to the turn ratio of the first winding 11 and the second winding 12. As a result, in generating the line voltage waveform of the secondary winding L2, an intermediate value of three stages of output voltage can be generated as shown in FIG.

[0028] In this way, by sequentially switching two of the six terminals on the primary side of the six-phase transformer 2a to apply a DC voltage, a six-phase induced magnetic field is generated in the three legs 10a, 10b, and 10c of the iron core 10, and this induced magnetic field can be used to output three-phase power from the secondary side, thereby converting the DC power into three-phase AC power. And, because the switching element M of the changeover switch circuit 3 is turned on / off at a fixed switching timing of 1.39 ms and a three-phase AC is generated using the six-phase transformer 2a, DC / AC conversion can be performed without PWM control. Therefore, it is easy to prevent a situation where the switching elements M connected in series are turned on at the same time. In addition, by performing DC / AC conversion with a lower frequency control signal than conventional PWM control, the control circuit can be simplified, high output elements such as IGBTs can be used, and no high frequency noise is generated.In addition, since a transformer is used, it is possible to insulate the input and output, unlike conventional PWM controlled circuits.

[0029] Here, the reason why the switching elements M connected in series do not turn on at the same time will be explained. By controlling the individual switching elements M to turn on at the switching timing shown in the operation table of the switching elements M in FIG. 6, when looking at the operation timing of the switching elements MR1 ​​and MR1' connected in series, for example, a situation does not occur in which one turns on immediately after the other turns off (for example, immediately after the switching element MR1 turns off when the third signal s3 ends) (at the next fourth signal s4, the switching element MS1' turns on, but MR1' does not turn on). In this way, a situation does not occur in which one turns off immediately after the other connected in series turns on. Therefore, the switching elements M connected in series do not turn on at the same time.

[0030] Next, a power conversion system in which the multi-phase transformer is a 12-phase transformer 2b will be described. 12 shows the main parts of a power conversion system using a 12-phase transformer 2b, and shows a changeover switch circuit 3 and the 12-phase transformer 2b. When the multi-phase transformer 2 is a 12-phase transformer 2b, the changeover switch circuit 3 is composed of 24 switching elements M, for example, IGBTs, and 24 types of drive signals are output from the drive control circuit 8 to the changeover switch circuit 3. Therefore, the oscillator circuit 6 and the counter circuit 7 output a signal in which one period of the AC waveform they generate is divided by 24 (not shown).

[0031] The following description focuses on the changeover switch circuit 3 and the 12-phase transformer 2b. The changeover switch circuit 3 has a set of two series-connected switching elements M, the number of which corresponds to the number of input terminals of the multi-phase transformer 2, similar to the power conversion system 1 using the 6-phase transformer 2a. Specifically, the changeover switch circuit 3 has 12 pairs of switching elements M, namely, a pair of NR1 and NR1', a pair of NS1 and NS1', a pair of NT1 and NT1', ... a pair of NR4 and NR4', a pair of NS4 and NS4', and a pair of NT4 and NT4', and is connected in parallel to the DC power source 5. Then, it has an output terminal between two switching elements M connected in series, and each output terminal is connected to one of the 12 input terminals of the 12-phase transformer 2b. Incidentally, the gate (base) of each switching element M is connected to the control unit 4, but is omitted.

[0032] The 12-phase transformer 2b has a primary winding L1 composed of four windings (a first winding 21, a second winding 22, a third winding 23, and a fourth winding 24) and a secondary winding L2 composed of one winding, a fifth winding 25. Each winding has three winding parts corresponding to the three-phase power: an R-phase winding part (21a, 22a, 23a, 24a, 25a), an S-phase winding part (21b, 22b, 23b, 24b, 25b), and a T-phase winding part (21c, 22c, 23c, 24c, 25c). The three winding parts of each winding are wound around three legs (R-phase leg 10a, S-phase leg 10b, T-phase leg 10c) of iron core 10, respectively. Thus, the primary winding L1 has three terminals for each of the three windings, giving a total of twelve input terminals, and the secondary winding L2 has three output terminals.

[0033] In addition, the first winding 21 has three input terminals R1in, S1in, and T1in, the second winding has three input terminals R2in, S2in, and T2in, the third winding 23 has three input terminals R3in, S3in, and T3in, and the fourth winding 24 has three input terminals R4in, S4in, and T4in.

[0034] The first to fourth windings 21, 22, 23, and 24 are all star-connected, and the fifth winding 25 is delta-connected. However, as described below, the third winding 23 and the fourth winding 24 are not completely star-connected. Also, the fifth winding 25 may be star-connected.

[0035] The neutral point Q of the first winding 21 and the second winding 22 are connected to each other, and the second winding 22 is wound around the iron core 10 so that its polarity is opposite to that of the first winding 21. The third winding 23 and the fourth winding 24 are formed by branching off from the same point in the middle of the second winding 22, and the third winding 23 and the fourth winding 24 share the neutral point Q of the second winding 22. The relationship between the first winding 21 and the second winding 22 is such that the voltage generated by the first winding 21 + the voltage generated by the second winding 22 = the line voltage, and the number of turns of the second winding 11 is 0.73 times (√3-1 times) that of the first winding 21, similar to the six-phase transformer 2a described above.

[0036] Specifically, the third winding 23 and the fourth winding 24 are wound around the iron core 10 as follows. The R-phase winding portion 23a of the third winding 23 branches off from the middle of the T-phase winding portion 22c of the second winding 22 and is pulled out and wound around the R-phase leg 10a. The tip of this branch is the input terminal R3in. The S-phase winding portion 23b branches off from the middle of the R-phase winding portion 22a of the second winding 22, is drawn out, and is wound around the S-phase leg 10b. The tip of this portion is the input terminal S3in. The T-phase winding portion 23c branches off from the middle of the S-phase winding portion 22b of the second winding 22, is drawn out, and is wound around the T-phase leg 10c. The tip of this portion is the input terminal T3in.

[0037] Each phase of the fourth winding 24 is wound as follows: The R-phase winding portion 24a is branched off from the middle of the S-phase winding portion 22b of the second winding 22, which is the same portion as the T-phase winding portion 23c of the third winding 23, and is pulled out and wound around the R-phase leg 10a. The tip of the R-phase winding portion 24a is the input terminal R4in. The S-phase winding portion 24b is branched off from the middle of the T-phase winding portion 22c of the second winding 22 and wound around the S-phase leg 10b, similar to the R-phase winding portion 23a of the third winding 23. The tip of the S-phase winding portion 24b is the input terminal S4in. The T-phase winding portion 24c is branched off from the middle of the R-phase winding portion 22a of the second winding 22, which is the same portion as the S-phase winding portion 23b of the third winding 23, and is wound around the T-phase leg 10c. The tip of the T-phase winding portion 24c is the input terminal T4in.

[0038] 13 is an operation sequence diagram of each switching element M of the changeover switch circuit 3 that supplies DC power source 5 to 12-phase transformer 2b. It shows timing signals S (first signal s1 to twenty-fourth signal s24) for equally dividing one period of the AC waveform to be generated into 24 and generating voltages corresponding to each divided portion. When outputting an AC voltage of 60 Hz, the 24 switching elements M operate to generate voltages for each section obtained by dividing one period into 24 equal parts. The counter circuit 7 sequentially outputs the first signal s1 to the 24th signal s24 at intervals of 0.69 ms, and the drive control circuit 8 drives the 24 switching elements M of the changeover switch circuit 3 individually in a predetermined combination based on these signals. As a result, the individual switching elements M are turned on sequentially in pairs as shown in FIG.

[0039] Fig. 14 is an explanatory diagram of the voltages output from the three output terminals Rout, Sout, and Tout on the secondary side of the 12-phase transformer 2b. As shown in Fig. 14, the voltages generated on the secondary side are generated sequentially by waveforms in which one period is divided into 24 equal parts. When the output voltages of each output terminal thus generated are viewed on the time axis, it can be seen that phase voltages with a phase shift of 120 degrees are generated. In this way, a three-phase AC voltage is generated on the secondary side of the 12-phase transformer 2b. In addition, this output voltage waveform diagram is shown as a neat rectangle for explanatory purposes, but in reality, a distorted waveform is generated. This waveform then passes through a waveform shaping circuit (not shown), such as a low-pass filter, to become a waveform close to a sine wave.

[0040] Fig. 15 is a vector explanatory diagram of the voltages generated by the 12-phase transformer 2b, and uses a vector diagram to explain the output voltage shown in Fig. 14. Fig. 15(a) shows, in vector form, 12 types of voltages generated in the secondary winding L2 by mutual induction caused by application of a DC voltage to the primary winding L1. Fig. 15(b) shows, in vector form, the voltages output to the three terminals (output terminals) of the fifth winding 25, which is the secondary winding L2. 15, V21a, V21b, and V21c respectively indicate voltages generated on the secondary side by voltages applied to the R-phase winding portion 21a, the S-phase winding portion 21b, and the T-phase winding portion 21c of the first winding 21. Also, V22a, V22b, and V22c respectively indicate voltages generated on the secondary side by voltages applied to the R-phase winding portion 22a, the S-phase winding portion 22b, and the T-phase winding portion 22c of the second winding 22.

[0041] Furthermore, V23a, V23b, and V23c respectively indicate voltages generated on the secondary side by voltages applied to the R-phase winding portion 23a, the S-phase winding portion 23b, and the T-phase winding portion 23c of the third winding 23, and V24a, V24b, and V24c respectively indicate voltages generated on the secondary side by voltages applied to the R-phase winding portion 24a, the S-phase winding portion 24b, and the T-phase winding portion 24c of the fourth winding 24. And V R , V S , V T are the terminal voltages of the output terminals Rout, Sout, and Tout, respectively, and V R-S is the line voltage between the R phase and S phase of the secondary side, V S-T is the line voltage between the secondary S phase and T phase, V T-R indicates the line voltage between the secondary side T phase and R phase.

[0042] The changeover switch circuit 3 sequentially switches the supply destination of the DC voltage and applies a voltage in the specified order shown in FIG. 13 by combining two of the three input terminals (R1in, ...T4in) of each of the first winding 21 to the fourth winding 24. This acts to generate a 12-phase voltage as shown in FIG. 15(a) when viewed from the secondary side of the 12-phase transformer 2b. As a result of this action, voltages that are 120 degrees out of phase are output to the three-phase output terminals on the secondary side, generating a three-phase AC voltage.

[0043] Here, the reason why the number of turns of the second winding 22 is set to 0.73 times that of the first winding 21 will be explained. 15, the voltages generated on the secondary side by application of a DC voltage to the primary side are voltages V22a, V22b, and V22c generated by the second winding 22, which has fewer turns, which are smaller than the voltages V21a, V21b, and V21c generated by the first winding 21. To be precise, the voltages are generated at a magnitude 0.73 times that of the first winding 21 and the second winding 22. 13, a current flows through the S-phase winding portion 21b of the first winding 21 and the S-phase winding portion 22b of the second winding 22, and a voltage is generated in the S-phase of the fifth winding 13. This voltage V S generates a voltage of V21b+V22b, but the voltage is 1.73 times V21b due to the turn ratio of the first winding 21 and the second winding 22. As a result, in generating the line voltage waveform of the secondary winding L2, an intermediate value can be generated as in the case of the above-mentioned six-phase transformer 2a. FIG. 25 is an explanatory diagram of the line voltage generated by the 12-phase transformer 2b. As shown in FIG. 25, intermediate values ​​of six output voltage stages can be generated, and then a sine wave can be generated in the process of generating the waveform.

[0044] Next, the third winding 23 and the fourth winding 24 will be described in detail. As described above, the third winding 23 and the fourth winding 24 are branched off and drawn out from the middle of the second winding 22, specifically from a position 56.5% from the neutral point Q of the second winding 22. The drawn out winding is formed with 52% of the number of turns of the first winding 21. With this number of turns, even if a voltage is applied between any of the 12 input terminals (R1in,...T4in), the phase voltage (V R , V S , V T ), line voltage (V R-S , V S-T , V T-R) can be made to have a predetermined phase and a constant absolute value, and a three-phase AC with little distortion can be generated. For example, the second signal s2 in FIG. 13 will be described as an example.

[0045] 16 is an explanatory diagram of the current flowing through the primary side of the 12-phase transformer 2b in response to the second signal s2. It can be seen that this signal causes a current to flow through the S-phase winding portion 21b of the first winding 21 and the S-phase winding portion 22b of the second winding 22 to the T-phase winding 23c of the third winding 23. This current generates voltages in the S and T phases of the secondary side. The voltage V S is a composite value of voltage V21b from the first winding 21 and a voltage generated by a portion (56%) of the second winding 22. The voltage generated in the T phase is 52% of the voltage generated by the first winding 21, generated by the T-phase winding portion 23c of the third winding 23. As a result, as shown in the section s2 in Fig. 14, a positive voltage of a set magnitude is generated in the S phase, and a negative voltage of a set magnitude is generated in the T phase. Then, a three-phase AC voltage is output from the secondary side by the action of successive timing signals S.

[0046] This is an application of the technology using the 12-phase transformer 2b of the power conversion device of Patent Document 2, which performs AC / DC conversion, to DC / AC conversion.

[0047] In this way, by sequentially switching two of the twelve terminals on the primary side of the 12-phase transformer 2b and applying a DC voltage, a 12-phase induced magnetic field is generated in the three legs 10a, 10b, and 10c of the iron core 10, and this induced magnetic field can be used to output three-phase power from the secondary side, thereby converting the DC power into three-phase AC power. And, because the switching element M of the changeover switch circuit 3 is turned on / off at a fixed switching timing of 0.69 ms and a 3-phase AC is generated using the 12-phase transformer 2a, DC / AC conversion can be performed without PWM control. Therefore, it is easy to prevent a situation where the switching elements M connected in series are turned on at the same time. In addition, by performing DC / AC conversion using a lower frequency control signal compared to conventional PWM control, the control circuit can be simplified, high-output elements such as IGBTs can be used, and no high-frequency noise is generated.

[0048] In the above embodiment, the switching timing of the switching element M is 1.39 ms in the configuration using the 6-phase transformer 2a and 0.69 ms in the configuration using the 12-phase transformer 2b, but the switching timing when generating a 50 Hz three-phase AC is 1.67 ms in the 6-phase transformer 2a and 0.83 ms in the 12-phase transformer 2b. In this way, the switching timing of the switching element M is set according to the frequency of the AC to be generated and the number of phases of the multi-phase transformer, but a preferable three-phase AC can be generated by switching control of a relatively low frequency with a time interval of 0.5 ms to 2.0 ms. However, if the AC to be generated is not 50 Hz or 60 Hz, the switching timing may not be within this range.

[0049] The power conversion system 1 of the present invention can convert DC power into three-phase AC power with a simple control form by using not only the above-mentioned 6-phase or 12-phase transformers but also a 3n-phase (n is a natural number) multi-phase transformer, and the reason for this will be explained below. FIG. 17 shows a three-phase AC voltage waveform diagram, and FIG. 18 shows the voltage vectors of each phase at the time point A1 (phase θ0) in FIG. 17. Note that Vo is the phase voltage (maximum phase voltage), V M is the three-phase AC line voltage (maximum line voltage). A typical three-phase transformer generates three phase AC voltages V, each of which is shifted by 120° as shown in Figure 17. R ,V S ,V T When looking at an arbitrary phase point in Fig. 17, for example point A1, the phases are as shown in Fig. 18. The relationship between the phases is not limited to point A1, and at any timing, each phase of RST has a phase difference of 120°.

[0050] In the present invention, DC / AC conversion is performed using a multi-phase transformer 2 in which the windings of a three-phase transformer are connected to other phases at a fixed ratio, thereby making it possible to generate voltages of any phase, such as the vectors shown by the dashed lines Vs1+Vt2, Vr1+Vs2, and Vt1+Vr2 in Figure 18.

[0051] On the other hand, when looking at the configuration for AC / DC conversion, it is possible to extract DC voltage even with three-phase AC by connecting a rectifier circuit, but noise called ripple will exist if a smoothing circuit is not provided. This ripple can be reduced by extracting a voltage at the middle phase of the three-phase AC, in other words, by using a multi-phase transformer to create a voltage at the middle phase of the three-phase AC, thereby reducing noise. The present invention uses a multi-phase transformer 2 that can be used for this AC / DC conversion in the reverse direction, and outputs an AC voltage by applying a DC voltage to the multi-phase inputs of the multi-phase transformer 2 in a predetermined sequence via a changeover switch circuit 3.

[0052] For example, between the R phase and the S phase, a voltage whose phase is 0 to 60° or 180° to 240° ahead of the phase θ of the R phase can be extracted, between the S phase and the T phase, a voltage whose phase is 60° to 120° or 240° to 300° ahead of the phase θ of the R phase can be extracted, and between the R phase and the T phase, a voltage whose phase is 120° to 180° or 300° to 360° ahead of the phase θ of the R phase can be extracted.

[0053] Focusing on the R-phase to S-phase, Fig. 19 to Fig. 21 are explanatory diagrams for extracting voltages between the R-phase and S-phase that are 0 to 60° or 180° to 240° ahead of the phase θ of the R-phase, Fig. 19 is a vector explanatory diagram of the winding ratio based on Fig. 18, Fig. 20 is an explanatory diagram of the windings around the iron core 10 of the multi-phase transformer 2, and Fig. 21 is an explanatory diagram of the R-phase to S-phase vector. In Fig. 20, symbols corresponding to the individual windings of the 12-phase transformer 2b in Fig. 12 above are given. If the turns ratios for winding to extract the target phase voltage from each phase are a, b, and c for R, S, and T, respectively, the turns ratio between the R phase and the S phase can be expressed by the following equation (1). √3V R×a-√3V S ×b=V M ×sin(α+θ)(-1≦a,b≦1) (1)

[0054] In addition, V R : R phase voltage, V S : S phase voltage, V M : line voltage, a: R phase turns ratio, b: S phase turns ratio, c: T phase turns ratio, α: any phase. Here, a, b, and α have the relationship represented by the following formulas (2) to (4). (cosα) 2 +(sinα) 2 =1 (2) (a+b / 2) 2 +(-√3×b / 2) 2 =1 (3) (a+b / 2)=cosα, (√3×b / 2)=sinα ···(4)

[0055] Equation 1 is the R phase voltage V R and S-phase voltage V S This shows that by extracting these in a ratio of a:b, it is possible to obtain a voltage waveform whose phase is shifted by α from the R-phase voltage. This formula is shown in a vector diagram in Figure 21. Once α is determined from equations (1) to (3), the turn ratios a and b can be calculated (not described in detail), and the turn ratio between the R phase and the S phase can be calculated.

[0056] In addition, in Figure 19, the phase-to-phase voltage V M The ratios of a, b, and c are expressed with the number of turns that generates a voltage of 1 unit. In FIG. 20, the sum of the voltages generated by the first winding 21 (21a) and the second winding 22 (22a) is the interphase voltage V M The ratio of a to b is determined with the total number of turns of the first winding 21 and the second winding 22 being one unit. For example, if a is 0.8, then b is 0.32. Also, α is the phase determined by how many phases the multi-phase transformer has, and is, for example, 30° for 6 phases, 15° for 12 phases, and 7.5° for 24 phases.

[0057] Based on the turns ratio thus calculated, a specific number of turns is determined based on the number of turns of the star-connected windings (the above-mentioned first windings 11, 21), and is wound around the iron core 10. Fig. 20 is an explanatory diagram of a multi-phase transformer 2 wound with the calculated ratio of a and b, and in comparison with Fig. 12 which illustrates a 12-phase transformer 2b, the second winding (second windings 22a, 22b, 22c shown in Fig. 12) is wound with 0.73 times the number of turns of the windings of each phase (first windings 21a, 21b, 21c shown in Fig. 12) which are star-connected and wound with the standard number of turns. Note that Fig. 20 shows only the R-phase winding. Then, a winding with a turn ratio a (corresponding to the R-phase first winding 21a and a part of the R-phase second winding 22a) is wound around the R-phase leg 10a of the iron core 10, around which the R-phase first winding 21a and second winding 22a are wound, and a winding with a turn ratio b (corresponding to the S-phase winding portion 23b) branching off from the position of the turn ratio a is wound around the S-phase leg 10b, around which the S-phase first winding 21b is wound.

[0058] Similarly, calculations can be made between S phase and T phase and between R phase and T phase. Between S phase and T phase, a voltage that is 60° to 120° or 240° to 300° ahead of the phase θ of the R phase can be extracted, and between R phase and T phase, a voltage that is 120° to 180° or 300° to 360° ahead of the phase θ of the R phase can be extracted. A 3n-phase (n is a natural number) multi-phase transformer 2 can be manufactured, and this multi-phase transformer 2 can be used to construct a power conversion system that converts DC power to AC power.

[0059] Next, the switching operation of the changeover switch circuit 3 will be described. Fig. 22 is an explanatory diagram of the changeover switch circuit 3, and Figs. 23 and 24 are explanatory diagrams of the operation sequence of the changeover switch circuit 3. However, in Figs. 22 to 24, when the multi-phase transformer 2 has an odd number of phases, k=(n+1) / 2, and when the multi-phase transformer 2 has an even number of phases, k=n / 2. For example, in the case of 6 phases, n=2, k=1, and in the case of 9 phases, n=3, k=2. Also, Fig. 23 shows the 1st to 3n+2nd control, and Fig. 24 shows the 3n+1st to 6n+2nd control.

[0060] For example, in the case of a 12-phase transformer, the control of each switching element M shown in Fig. 13 above is the switching control when n=4 and k=2 in Figs. 23 and 24. That is, Fig. 23 shows the sequence from s1 to s14, and Fig. 24 shows the sequence from s13 to s26. However, s25 and s26 are s1 and s2. In addition, since two switching elements M are used for input switching of one phase, 3n×2 switching elements M are used for input switching of the 3n-phase multi-phase transformer 2, and the number of elements R1 to Rk+1 in Figures 23 and 24 is 3n×2.

[0061] For ease of explanation, the individual reference characters of the switching elements M are different in Figures 23 and 24 from those in Figure 13. Also, "V+" in Figures 23 and 24 indicates that the High side of the switching elements M connected in series in the changeover switch circuit 3 is turned on, and "V-" indicates that the Low side of the switching elements M connected in series is turned on.

[0062] In this way, the switching element M of the changeover switch circuit 3 is turned on / off at a constant switching timing, and a three-phase AC can be generated using the multi-phase transformer 2. [Explanation of symbols]

[0063] 1 power conversion system, 2 multi-phase transformer, 2a 6-phase transformer, 2b 12-phase transformer, 3 change-over switch circuit, 4 control unit, 5 DC power supply, 6 oscillator circuit, 7 counter circuit, 8 drive control circuit, 8a combined signal generation circuit, 8b drive circuit, 10 core, 11 first winding, 12 second winding, 13 third winding, 21 first winding, 22 second winding, 23 third winding, 24 fourth winding, 25 fifth winding, L1 primary winding, L2 secondary winding, M switching element.

Claims

1. a 3n-phase multi-phase transformer having a primary winding with input terminals consisting of 3n phases (n is a natural number) and a secondary winding with three output terminals constituting three phases; A DC power source disposed on a primary side of the multi-phase transformer; a changeover switch circuit having a plurality of switching elements that turn on / off the output of the DC power source and that switches and supplies the DC power source to each of the input terminals of the multi-phase transformer; A control unit that controls the changeover switch circuit, a control unit that turns on / off each of the switching elements in a predetermined sequence at a constant switching timing to supply DC power to the input terminal, thereby generating a voltage in the secondary winding and outputting three-phase AC power from the output terminal.

2. The multi-phase transformer is a six-phase transformer in which the primary winding has two windings, a first winding and a second winding, each having three input terminals, for a total of six terminals, and the secondary winding has a third winding and has three output terminals; Each winding consists of three windings wound around respective legs of a three-legged core; The first winding and the second winding are star-connected, the second winding is formed with a number of turns that is 0.73 times that of the first winding, and the neutral points of both windings are connected together.

2. The power conversion system according to claim 1, wherein the third winding is delta-connected or star-connected.

3. The multi-phase transformer is a 12-phase transformer, the primary winding having four windings, namely a first winding to a fourth winding, each having three input terminals, for a total of 12 terminals, and the secondary winding having a fifth winding and three output terminals; Each winding consists of three windings wound around respective legs of a three-legged core; The first winding to the fourth winding are all star-connected, and the neutral points of the first winding and the second winding are connected to each other, while the third winding and the fourth winding are formed by branching off from a common predetermined position in the middle of the second winding, 2. The power conversion system according to claim 1, wherein the fifth winding is delta-connected or star-connected.

4. 4. The power conversion system according to claim 2, wherein the individual switching elements are turned on / off in a predetermined order at a predetermined switching timing between 0.5 ms and 2.0 ms.

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