JP2021029065A - Series multiplex power conversion device - Google Patents

Abstract

To provide a series multiplex power conversion device which reduces a harmonic component included in an AC output voltage while realizing high operation efficiency.SOLUTION: A control apparatus of a series multiplex power conversion device has a first (second) carrier wave having a frequency four times as high as an AC voltage command value in PWM control for each of converters of first to N-th stages, and generates a control command of a first (second) phase arm by comparing the AC voltage command value (a voltage obtained by inverting the polarity of the AC voltage command value) with the first (second) carrier wave. For first to N-th first (second) carrier waves corresponding to the converters of the first to N-th stages, a first phase difference is set between the first (second) carrier waves which are adjacent to each other in the order from N-th to first (from first to N-th). For (N+1)-th to I-th (I is an integer) first carrier waves corresponding to the converters of (N+1)-th to I-th stages, a second phase difference is set between the first carrier waves and the I-th second carrier wave corresponding to the converter of the I-th stage and between the first carrier waves and (I+1)-th second carrier wave corresponding to a converter of (I+1)-th stage. The first phase difference is equal to 2π/N, and the second phase difference is equal to π/N.SELECTED DRAWING: Figure 6

Description

The present invention relates to a series multiplex power converter.

Japanese Unexamined Patent Publication No. 2013-258841 (Patent Document 1) discloses a series multiplex power converter in which a plurality of converters are multiplexed in series. Patent Document 1 employs a method of multiplexing the AC side with a transformer. In this method, the AC voltage terminal of each converter is connected to the secondary winding of each transformer, and the primary winding of each transformer is connected in series and connected to the power system. The AC output voltage of each converter is combined in series and output to the power system.

Japanese Unexamined Patent Publication No. 2013-258841

The series multiplex power converter can reduce the harmonic components included in the AC output voltage waveform of the entire device by synthesizing the output voltages of a plurality of converters. However, since the power loss of the entire device increases due to the power loss generated by each converter, there is a concern that the operating efficiency of the series multiplex power converter will decrease.

As a measure to reduce the power loss generated by each converter, a method of lowering the switching frequency of the switching elements constituting each converter to suppress the switching loss can be adopted. However, when the switching frequency is lowered, the waveform of the AC output voltage cannot be changed finely, and it becomes difficult to bring the waveform closer to a sine wave. As a result, the content of harmonic components contained in the AC output voltage increases.

The present invention has been made to solve the above problems, and an object of the present invention is to reduce harmonic components contained in an AC output voltage while achieving high operating efficiency in a series multiplex power converter. It is to be.

A series multiplex power converter according to an aspect of the present invention is coupled to an AC power system. The series multiplex power converter is connected to N transformers (N is an integer of 2 or more) in which the primary windings are multiplex connected in series to the AC power system, and to the secondary windings of N transformers, respectively. , PWM control of the AC output voltage of the 1st to Nth stage converters that perform bidirectional power conversion between AC power and DC power, and the AC output voltage of each stage converter so as to match the AC voltage command value. It is provided with a control device for performing the above. Each stage transducer has a single phase full bridge circuit with a first phase arm and a second phase arm. Each of the first phase arm and the second phase arm is composed of a three-level circuit. In the PWM control of the converter in each stage, the control device has a first carrier wave and a second carrier wave having a frequency four times the AC voltage command value, and the first carrier wave is compared between the AC voltage command value and the first carrier wave. It is configured to generate a control command for the phase arm and generate a control command for the second phase arm by comparing the voltage obtained by reversing the polarity of the AC voltage command value with the second carrier wave. In the first to first N first carrier waves corresponding to the first to Nth stage converters, the first phase difference is set between the adjacent first carrier waves in the N to first order. .. In the first to first Nth second carrier waves corresponding to the first to Nth stage converters, the first phase difference is set between the second carrier waves adjacent to each other in the order of the first to Nth stages. .. The first carrier wave of the N + 1-I corresponding to the N + 1-I stage converter (I is an integer of 1 or more and N or less) is placed between the first carrier wave of the I and the second carrier wave corresponding to the I stage converter. A second phase difference is set between the and the second carrier of the I + 1 corresponding to the converter of the first I + 1 stage. The first phase difference is equal to 2π / N and the second phase difference is equal to π / N.

According to the present invention, in a series multiplex power converter, it is possible to reduce harmonic components included in an AC output voltage while achieving high operating efficiency.

It is a schematic block diagram which shows the main circuit configuration of the series multiplex power conversion apparatus which concerns on embodiment. It is a figure which shows the specific circuit structure of the converter shown in FIG. It is a figure which shows the structure of the single-phase full bridge three-level circuit. It is a waveform diagram for demonstrating the two-pulse PWM control which concerns on a comparative example. It is a waveform diagram for demonstrating the two-pulse PWM control of a four-stage series multiplex converter. It is a waveform diagram for demonstrating the two-pulse PWM control of the four-stage series multiplex converter which concerns on embodiment. It is a figure explaining the effect which 2 pulse PWM control of a 4-stage series multiplex converter which concerns on embodiment play. It is a waveform diagram for demonstrating the two-pulse PWM control of the four-stage series multiplex converter which concerns on embodiment. It is a circuit block diagram which shows the part concerning the control of the 4-stage series multiplex converter among the control apparatus shown in FIG. It is a block diagram which shows the structure of the PWM control unit shown in FIG. It is a block diagram which shows the structural example of the carrier wave generator shown in FIG. It is a block diagram which shows the structural example of the 1st stage control part shown in FIG. It is a waveform diagram for demonstrating the two-pulse PWM control of the three-stage series multiplex converter which concerns on embodiment. It is a waveform diagram for demonstrating the two-pulse PWM control of the 5-stage series multiplex converter which concerns on embodiment.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. The same or corresponding parts in the drawings are designated by the same reference numerals, and the description thereof will not be repeated.

(Main circuit configuration of series multiplex power converter)
FIG. 1 is a schematic block diagram showing a main circuit configuration of the series multiplex power conversion device 1 according to the embodiment. The series multiplex power converter 1 is typically applied to a BTB (Back to Back) system used for power transfer of an asynchronous AC system or a different frequency AC system. The series multiplex power converter 1 is, for example, a 50-60 Hz frequency converter.

With reference to FIG. 1, the series multiplex power converter 1 is connected between power systems 2 and 3 having different AC frequencies. Each of the power systems 2 and 3 has a plurality of phases (for example, three phases). The series multiplex power converter 1 includes AC voltage detectors 12 and 52, current detectors 13 and 53, a DC voltage detector 14, a power converter 10, and a control device 11.

The AC voltage detector 12 detects the AC voltage of the power system 2 and outputs a signal indicating the detected value to the control device 11. The current detector 13 detects the current flowing through the power system 2 and outputs a signal indicating the detected value to the control device 11. The AC voltage detector 52 detects the AC voltage of the power system 3 and outputs a signal indicating the detected value to the control device 11. The current detector 53 detects the current flowing through the power system 3 and outputs a signal indicating the detected value to the control device 11.

The power conversion unit 10 is connected between the power system 2 and the power system 3. Specifically, the power conversion unit 10 is connected to one power system 2 via transformers 21 to 24, and to the other power system 3 via transformers 61 to 64. The power converter 10 includes transformers 21 to 24, converters 25 to 28, DC buses 15 to 17, smoothing capacitors C1 and C2, converters 65 to 68, and transformers 61 to 64. The DC bus 15 to 17 and the smoothing capacitors C1 and C2 form a DC circuit of each converter.

The primary windings of transformers 21-24 are connected to the power system 2. Each primary winding of the transformers 21 to 24 is connected in series to each phase and is star-shaped. As a result, the voltage obtained by synthesizing the AC output voltages of the converters 25 to 28 in series with each phase is output to the power system 2. The AC terminals of the phase power conversion circuits of the converters 25 to 28 are connected to one end 33 of each phase secondary winding of the transformers 21 to 24. An AC terminal of another phase power conversion circuit connected to the smoothing capacitors C1 and C2 is connected to the other end 34 of each phase secondary winding of the transformers 21 to 24. The converters 25 to 28 constitute a multi-phase full bridge circuit.

For example, the power conversion circuit of the converter 25 that converts the DC voltage between the DC positive bus 15 and the DC negative bus 17 into each phase AC voltage is connected to one end 33 of each phase secondary winding of the transformer 21. To. A power conversion circuit that converts the DC voltage between the DC positive bus 15 and the DC negative bus 17 into each phase AC voltage is connected to the other end 34 of each phase secondary winding of the transformer 21. The DC circuits of the two power conversion circuits connected to each phase secondary winding are common.

Each of the converters 25 to 28 is composed of a power converter using a self-extinguishing element such as a GCT (Gate Commutated Turn-Off thyristor) or an IGBT (Insulated Gate Bipolar Transistor). In the present embodiment, the converters 25 to 28 are all configured as a three-level circuit. Each of the three DC voltage terminals of the converters 25 to 28 is connected to the DC positive bus 15, the DC neutral bus 16, and the DC negative bus 17, respectively.

The smoothing capacitors C1 and C2 are connected in series between the DC positive bus 15 and the DC negative bus 17, and smooth the voltage between the DC positive bus 15 and the DC negative bus 17. A DC neutral point bus 16 is connected to the connection points of the smoothing capacitors C1 and C2.

The DC voltage detector 14 detects the inter-terminal voltage of the smoothing capacitor C1 and the inter-terminal voltage of the smoothing capacitor C2, and outputs a signal indicating the detected value to the control device 11.

Each of the converters 65 to 68, like the converters 25 to 28, is composed of a power converter using a self-extinguishing element such as a GCT or an IGBT. Each of the converters 65 to 68 is configured as a three-level circuit. Each of the three DC voltage terminals of the converters 65-68 is connected to the DC positive bus 15, the DC neutral bus 16, and the DC negative bus 17, respectively.

The AC terminals of the converters 65-68 are connected to the secondary windings of the transformers 61-64. Specifically, AC terminals of each phase power conversion circuit of the converters 65 to 68 are connected to one end 69 of each phase of the secondary windings of the transformers 61 to 64. An AC terminal of another phase power conversion circuit connected to the smoothing capacitors C1 and C2 is connected to the other end 70 of each phase of the secondary windings of the transformers 61 to 64, respectively. Each of the converters 65-68 constitutes a polyphase full bridge circuit.

The primary windings of transformers 61-64 are connected to the power system 3. Each primary winding of the transformers 61-64 is connected in series with each phase and star-shaped. As a result, the voltage obtained by synthesizing the AC output voltages of the converters 65 to 68 in series with each phase is output to the power system 3.

As described above, the power conversion unit 10 has a configuration in which the DC terminals of the converters 25 to 28 and the DC terminals of the converters 65 to 68 are connected via the DC bus lines 15 to 17. In the example of FIG. 1, the DC terminals of the converters 25 to 28 are connected to a common DC circuit, but the DC terminals of the converters 25 to 28 may be connected to independent DC circuits. .. Similarly, the DC terminals of the converters 65 to 68 may be connected to DC circuits independent of each other.

The power conversion unit 10 transfers power from one power system 2 (or power system 3) to the other power system 3 (or power system 2). Specifically, when power is exchanged from the power system 2 to the power system 3, the converters 25 to 28 convert the AC voltage supplied from the transformers 21 to 24 into a desired DC voltage, and the converted DC. The voltage is supplied to the converters 65 to 68 via the DC bus 15 to 17. The converters 65 to 68 convert the DC voltage supplied from the converters 25 to 28 via the DC bus 15 to 17 into a desired AC voltage, respectively. The transformers 61 to 64 output a voltage obtained by serially combining the AC output voltages of the converters 65 to 68 to the power system 3.

Further, when power is interchanged from the power system 3 to the power system 2, the converters 65 to 68 convert the AC voltage supplied from the transformers 61 to 64 into a desired DC voltage, and the converted DC voltage. Is supplied to the converters 25 to 28 via the DC bus 15 to 17. The converters 25 to 28 convert the DC voltage supplied from the converters 65 to 68 via the DC bus 15 to 17 into a desired AC voltage, respectively. The transformers 21 to 24 output a voltage obtained by serially combining the AC output voltages of the converters 25 to 28 to the power system 2.

Here, in the specification of the present application, in order to distinguish the four converters 25 to 28 whose AC side is multiplexed in series by the transformers 21 to 24, the converter 28 is referred to as “first stage converter 28”. The converter 27 may be referred to as a "second stage converter 27", the converter 26 may be referred to as a "third stage converter 26", and the converter 25 may be referred to as a "fourth stage converter 25". .. Further, the entire converters 25 to 28 may be referred to as a "four-stage serial multiplex converter 20".

Further, in order to distinguish the four converters 65 to 68 in which the AC side is multiplexed in series by the transformers 61 to 64, the converter 68 is referred to as a "first stage converter 68", and the converter 67 Is referred to as a "second stage converter 67", the converter 66 may be referred to as a "third stage converter 66", and the converter 65 may be referred to as a "fourth stage converter 65". Further, the entire converters 65 to 68 may be referred to as a "four-stage serial multiplex converter 60".

In each of the four-stage series multiplex converters 20 and 60, the first-stage converter to the fourth-stage converter may be connected in series multiplex, and the order is not particularly limited.

(Circuit configuration of converter)
FIG. 2 is a diagram showing a specific circuit configuration of the converters 25 to 28 and the converters 65 to 68 shown in FIG. Since the converters 25 to 28 and the converters 65 to 68 have the same circuit configuration, FIG. 2 typically describes the circuit configuration of the converter 25.

With reference to FIG. 2, the converter 25 is configured as a three-level circuit and has switching elements S1R to S8R, S1S to S8S, S1T to S8T and diodes D1R to D12R, D1S to D12S, D1T to D12T. The switching element is, for example, GCT, but the switching element is not limited to this as long as it is a self-extinguishing type switching element.

Here, in order to comprehensively explain the configuration of each phase of the converter 25, the reference numerals R, S, and T are collectively referred to as the reference numeral “k”. The anode of the switching element S1k is connected to the DC positive bus 15, and its cathode is connected to the anode of the switching element S2k. The cathode of the switching element S2k is connected to one end 33 of the k-phase secondary winding. The anode of the switching element S3k is connected to one end 33 of the k-phase secondary winding, and its cathode is connected to the anode of the switching element S4k. The cathode of the switching element S4k is connected to the DC negative bus 17. The diodes D1k to D4k are connected in antiparallel to the switching elements S1x to S4x, respectively. The cathode of the diode D9k is connected to the connection points of the switching elements S1k and S2k, and its anode is connected to the DC neutral generatrix 16. The cathode of the diode D10k is connected to the DC neutral generatrix 16, and its anode is connected to the connection points of the switching elements S3k and S4k.

The anode of the switching element S5k is connected to the DC positive bus 15, and its cathode is connected to the anode of the switching element S6k. The cathode of the switching element S6k is connected to the other end 34 of the k-phase secondary winding. The anode of the switching element S7k is connected to the other end 34 of the k-phase secondary winding, and its cathode is connected to the anode of the switching element S8k. The cathode of the switching element S8k is connected to the DC negative bus 17. The diodes D5k to D8k are connected in antiparallel to the switching elements S5k to S8k, respectively. The cathode of the diode D11k is connected to the connection points of the switching elements S5k and S6k, and its anode is connected to the DC neutral generatrix 16. The cathode of the diode D12k is connected to the DC neutral generatrix 16, and its anode is connected to the connection points of the switching elements S7k and S8k. The diodes D1k to D4k and D5k to D8k function as freewheeling diodes, and the diodes D9k to D12k function as clamp diodes.

That is, one power conversion circuit is composed of switching elements S1k to S4k and diodes D1k to D4k, D9k, and D10k, and the connection points of the switching elements S2k and S3k serve as AC terminals, and the secondary winding of the k-phase of the transformer. It is connected to one end 33 of the wire. Further, another power conversion circuit is configured by the switching elements S5k to S8k and the diodes D5k to D8k, D11k, D12k, and the connection point of the switching elements S6k and S7k serves as an AC terminal, and the secondary winding of the k phase of the transformer. It is connected to the other end 34 of the wire. Therefore, the AC terminals of the two power conversion circuits are connected to both ends of the k-phase secondary winding, and the two power conversion circuits form a single-phase full-bridge three-level circuit.

When the power systems 2 and 3 are three-phase, a total of six power conversion circuits are connected in parallel between the DC bus 15 and the DC bus 17. In other words, three single-phase full-bridge three-level circuits are connected in parallel between the DC bus 15 and the DC bus 17.

Returning to FIG. 1, the control device 11 controls the operations of the converters 25 to 28 and the converters 65 to 68. In the present embodiment, the control device 11 applies PWM (Pulse Width Modulation) control as a control method for the switching elements constituting each converter. The control device 11 receives signals from the AC voltage detectors 12, 52, the current detectors 13, 53, the DC voltage detector 14, and the like, and executes PWM control. The control device 11 generates gate pulse signals GC1 to GC4, which are control commands for controlling the converters 25 to 28, by PWM control, and transmits the generated gate pulse signals GC1 to GC4 to the converters 25 to 28, respectively. Output. Further, the control device 11 generates gate pulse signals GC5 to GC8, which are control commands for controlling the converters 65 to 68, by PWM control, and converts the generated gate pulse signals GC5 to GC8 into converters 65 to 68. Output to each.

(2-pulse PWM control)
Next, the PWM control of the four-stage series multiplex converters 20 and 60 in the control device 11 will be described.

In the present embodiment, "2-pulse PWM control" is applied to the PWM control of each converter in the 4-stage series multiplex converter. In the specification of the present application, the two-pulse PWM control outputs a maximum of two pulse voltages in a half cycle of an AC voltage command value (a section of an electric angle of 0 ° to 180 ° or a section of an electric angle of 180 ° to 360 °). As described above, it is a control for generating a control command of the converter.

<2-pulse PWM control according to a comparative example>
First, as a comparative example of the two-pulse PWM control according to the present embodiment, a general two-pulse PWM control will be described using the single-phase full-bridge three-level circuit shown in FIG.

With reference to FIG. 3, the single-phase full-bridge three-level circuit is a u-phase power conversion circuit (hereinafter, also referred to as “u-phase arm”) connected in parallel between the DC positive bus 15 and the DC negative bus 17. ) And an x-phase power conversion circuit (hereinafter, also referred to as “x-phase arm”). The AC terminal u of the u-phase arm (connection point of the switching elements S2 and S3) is connected to one end 33 of the secondary winding of the u-phase, and the AC terminal x of the x-phase arm (connection point of the switching elements S6 and S7). Is connected to the other end 34 of the x-phase secondary winding.

FIG. 4 is a waveform diagram for explaining the 2-pulse PWM control according to the comparative example. FIG. 4 shows the on / off relationship between the voltage command value and the switching elements S1 to S8. In the figure, V is the output voltage at the AC terminal u of the u-phase arm, Vx is the output voltage at the AC terminal x of the x-phase arm, and the line output voltage Vux (u-phase voltage Vu and x-phase voltage Vx). Difference) corresponds to the AC output voltage of the converter.

In PWM control, the height of the AC voltage command value Vux * (line voltage command value) and the carrier waves Ca and Cb are compared, and based on the comparison result, the combination of on / off of the switching elements S1 to S4 of the u-phase arm is performed. It is determined. Further, the heights of the AC voltage command value −Vux * and the carrier waves Ca and Cb are compared, and the on / off combination of the switching elements S5 to S8 of the v-phase arm is determined based on the comparison result.

The carrier waves Ca and Cb are, for example, triangular wave signals. The carrier wave Ca is used for switching the switching elements (S1, S3, S5, S7) of the upper group of each phase arm. The carrier wave Ca is also referred to as an "upper carrier wave". The carrier wave Ca has a maximum value of + Vd and a minimum value of 0.

The carrier wave Cb is used for switching the switching elements (S2, S4, S6, S8) of the lower group of each phase arm. The carrier wave Cb is also referred to as a "lower carrier wave". The maximum value of the carrier wave Cb is 0, and the minimum value is −Vd. Vd corresponds to the DC voltage between the DC positive bus 15 and the DC negative bus 17. The upper carrier wave Ca and the lower carrier wave Cb have the same frequency and phase. The carrier waves Ca and Cb have a frequency four times that of the AC voltage command value Vux *.

The switching elements S1 to S4 of the u-phase arm are turned on and off at the timing when the amplitudes of the AC voltage command value Vux * and the carrier waves Ca and Cb intersect. Specifically, in the u-phase arm, when the polarity of the AC voltage command value Vux * is positive, the switching elements S1 and S3 are switched at the timing when the AC voltage command value Vux * and the carrier wave Ca intersect. When the polarity of the AC voltage command value Vux * is negative, the switching elements S2 and S4 are switched at the timing when the AC voltage command value Vux * and the carrier wave Cb intersect.

The switching elements S5 to S8 of the x-phase arm are turned on and off at the timing when the amplitudes of the AC voltage command value −Vux * and the carrier waves Ca and Cb intersect. Specifically, in the x-phase arm, when the polarity of the AC voltage command value −Vux * is positive, the switching elements S5 and S7 are switched at the timing when the AC voltage command value −Vux * and the carrier wave Ca intersect. When the polarity of the AC voltage command value −Vux * is negative, the switching elements S6 and S8 are switched at the timing when the AC voltage command value −Vux * and the carrier wave Cb intersect.

As a result, as shown in FIG. 4, each of the output voltages Vu and Vx takes three values of ± Vd / 2,0, and the line output voltage Vux takes five values of ± Vd and ± Vd / 2,0. ..

As is clear from FIG. 4, in PWM control, two of the four switching elements in one carrier cycle (cycle of one carrier wave) are turned on and off once, and the remaining two are not turned on and off. Therefore, the switching element 1 The average switching frequency per unit is 1/2 of the frequency of the carrier waves Ca and Cb. In 2-pulse PWM control, the frequencies of the carrier waves Ca and Cb are four times the frequency of the AC voltage command value Vux *, so the average switching frequency per switching element is the frequency of the AC voltage command value Vux *. It will be doubled.

Normally, in PWM control, as the frequency of the carrier wave is lowered, the average switching frequency per switching element decreases, so that the power loss (switching loss) generated in the switching element can be suppressed. Therefore, the operating efficiency of the converter can be improved.

However, on the other hand, if the frequency of the carrier wave is lowered, the waveform of the AC output voltage cannot be changed finely, and it becomes difficult to bring the waveform closer to a sine wave. As a result, the content of harmonic components contained in the AC output voltage increases. Such a phenomenon also appears in a series multiplex converter in which the converters of FIG. 3 are connected in series.

FIG. 5 is a waveform diagram for explaining 2-pulse PWM control of the 4-stage series multiplex converter. FIG. 5A shows a waveform of a half cycle (a section of an electric angle of 0 ° to 180 °) of the AC voltage command value Vux *. The polarity of the AC voltage command value Vux * is positive.

FIG. 5A further shows the waveforms of the carrier waves Cu1 to Cu4 and Cx1 to Cx4. The carrier waves Cu1 and Cx1 are carriers used for 2-pulse PWM control of the first-stage converter 28 in the four-stage series multiplex converter 20. The carrier waves Cu2 and Cx2 are carrier waves used for 2-pulse PWM control of the second-stage converter 27. The carrier waves Cu3 and Cx3 are carrier waves used for 2-pulse PWM control of the third-stage converter 26. The carrier waves Cu4 and Cx4 are carrier waves used for 2-pulse PWM control of the fourth-stage converter 25. The carrier waves Cu1 to Cu4 and Cx1 to Cx4 have the same amplitude and frequency as the carrier waves Ca and Cb in FIG.

Specifically, the carrier wave Cu1 is used for switching the switching elements S1 to S4 of the u-phase arm of the first stage converter 28. The carrier wave Cu1 corresponds to the upper carrier wave (carrier wave Ca in FIG. 4). The carrier wave Cx1 is used for switching the switching elements S5 to S8 of the x-phase arm of the first stage converter 28. The carrier wave Cx1 corresponds to the lower carrier wave (carrier wave Cb in FIG. 4). However, in FIG. 5A, the comparison between the negative polarity AC voltage command value −Vux * and the carrier wave Cx1 is shown by superimposing the comparison between the positive polarity AC voltage command value Vux * and the carrier wave Cu1. The carrier wave Cx1 is positively and negatively inverted. As a result, the carrier wave Cx1 has a waveform that is out of phase with the carrier wave Cu1 by 1/2 carrier period (that is, π).

The carrier wave Cu2 corresponds to the upper carrier wave (carrier wave Ca) of the second stage converter 27, and the carrier wave Cx2 corresponds to the lower carrier wave (carrier wave Cb) of the second stage converter 27. Similar to the carrier wave Cu1 and Cx1, the carrier wave Cx2 has a waveform that is out of phase with the carrier wave Cu2 by 1/2 carrier period.

The carrier wave Cu3 corresponds to the upper carrier wave (carrier wave Ca) of the third-stage converter 26, and the carrier wave Cx3 corresponds to the lower carrier wave (carrier wave Cb) of the third-stage converter 26. Similar to the carrier wave Cu1 and Cx1, the carrier wave Cx3 has a waveform that is out of phase with the carrier wave Cu3 by 1/2 carrier period.

The carrier wave Cu4 corresponds to the upper carrier wave (carrier wave Ca) of the fourth-stage converter 25, and the carrier wave Cx4 corresponds to the lower carrier wave (carrier wave Cb) of the fourth-stage converter 25. Similar to the carrier wave Cu1 and Cx1, the carrier wave Cx4 has a waveform that is out of phase with the carrier wave Cu4 by 1/2 carrier period.

Further, a phase difference is provided between the four carrier waves Cu1 to Cu4. In the example of FIG. 5A, the same phase difference is provided between adjacent carriers in the order of Cu4 → Cu3 → Cu2 → Cu1. The phase difference is equal to 1/2 of one carrier period divided into four equal parts (ie, π / 4). According to this, between the eight carriers Cu1 to Cu4 and Cx1 to Cx4, a phase difference π / 4 equal to each other between adjacent carriers is generated in the order of Cx4 → Cx3 → Cx2 → Cx1 → Cu4 → Cu3 → Cu2 → Cu1. It is provided.

In the 2-pulse PWM control of the 4-stage serial multiplex converter 20, the 2-pulse PWM control shown in FIG. 4 is performed in each of the first-stage converter 28 to the fourth-stage converter 25. Specifically, in the 2-pulse PWM control of the first-stage converter 25, the height of the AC voltage command value Vux * and the carrier waves Cu1 and Cx1 are compared, and the switching elements S1 to S8 are turned on and off based on the comparison result. The combination of is determined. The on / off combination of the switching elements S5 to S8 based on the comparison result between the AC voltage command value Vux * and the carrier wave Cx1 is based on the comparison between the AC voltage command value −Vux * shown in FIG. 4 and the lower carrier wave Cb. It is substantially the same as the combination of the switching elements S5 to S8.

Similar to the 2-pulse PWM control of the 1st-stage converter 25, in the 2-pulse PWM control of the 2nd-stage converter 26, the height of the AC voltage command value Vux * and the carrier waves Cu2 and Cx2 are compared, and the comparison result shows. Based on this, the on / off combination of the switching elements S1 to S8 is determined. In the 2-pulse PWM control of the third-stage converter 27, the height of the AC voltage command value Vux * and the carrier waves Cu3 and Cx3 are compared, and the on / off combination of the switching elements S1 to S8 is determined based on the comparison result. To. In the 2-pulse PWM control of the fourth-stage converter 28, the height of the AC voltage command value Vux * and the carrier waves Cu4 and Cx4 are compared, and the on / off combination of the switching elements S1 to S8 is determined based on the comparison result. To.

FIG. 5B shows waveforms of the output voltage Vu of the u-phase arm and the output voltage Vx of the x-phase arm in each of the first-stage converter 28 to the fourth-stage converter 25. The output voltage Vu1, Vx1 of the first stage converter 28, the output voltage Vu2, Vx2 of the second stage converter 27, the output voltage Vu3, Vx3 of the third stage converter 26, and the output voltage Vu4 of the fourth stage converter 25. , Vx4 each have three values of 0, ± Vd / 2. In FIG. 5B, each output voltage is represented by an absolute value.

The AC output voltage Vux of the 4-stage series multiplex converter 20 is a series combination of the AC output voltages Vu1 to Vu4 and Vx1 to Vx4 of the first-stage converter 28 to the fourth-stage converter 25. FIG. 5C shows the waveform of the AC output voltage Vux of the 4-stage series multiplex converter 20. As shown in FIG. 5C, the AC output voltage is the sum of the AC output voltages of the first-stage converter 28 to the fourth-stage converter 25 in the section of the electric angle of 0 ° to 180 °.

In the comparative example, the phases of the carrier waves Cu1 to Cu4 are shifted by π / 4 between the first-stage converter 28 and the fourth-stage converter 25, and the phases of the carrier waves Cx1 to Cx4 are π, respectively. Due to the / 4 shift, the AC output voltage Vux is 0, Vd / 2, Vd, 3Vd / 2,2Vd, 5Vd / 2,3Vd, 7Vd / 2,4Vd in the section of the electric angle of 0 ° to 180 °. It will be either.

However, as described with reference to FIG. 4, in the 2-pulse PWM control, a harmonic component is included in the output voltage of the converter in each stage. Therefore, even in the AC output voltage Vux of the 4-stage series multiplex converter 20, the harmonic component obtained by synthesizing the harmonic components of the four converters is included.

In this embodiment, in order to solve such a problem, a two-pulse PWM control that makes it possible to reduce the content of harmonic components in the AC output voltage of the four-stage series multiplex converter is proposed. is there.

<2-pulse PWM control according to this embodiment>
Hereinafter, the 2-pulse PWM control of the 4-stage serial multiplex converter 20 according to the present embodiment will be described.

FIG. 6 is a waveform diagram for explaining 2-pulse PWM control of the 4-stage series multiplex converter according to the present embodiment, and is a diagram to be compared with FIG. FIG. 6A shows a waveform of a half cycle (a section of an electric angle of 0 ° to 180 °) of the AC voltage command value Vux *.

FIG. 6A further shows the waveforms of the carrier waves Cu1 to Cu4 and Cx1 to Cx4. Similar to FIG. 5, the carrier waves Cu1 and Cx1 are carriers used for 2-pulse PWM control of the first-stage converter 28 in the four-stage series multiplex converter 20, and the carrier waves Cu2 and Cx2 are the second-stage converter 27. This is a carrier wave used for 2-pulse PWM control. The carrier waves Cu3 and Cx3 are carriers used for the 2-pulse PWM control of the third-stage converter 26, and the carrier waves Cu4 and Cx4 are carriers used for the two-pulse PWM control of the fourth-stage converter 25. The carrier waves Cu1 to Cu4 and Cx1 to Cx4 have the same amplitude and frequency as the carrier waves Cu1 to Cu4 and Cx1 to Cx4 in FIG.

However, in the present embodiment, the phase difference of the carrier waves Cu1 to Cu4 and Cx1 to Cx4 is different from that of the comparative example of FIG. Specifically, between the four carrier waves Cu1 to Cu4, a phase difference equal to each other is provided between adjacent carriers in the order of Cu4 → Cu3 → Cu2 → Cu1. The phase difference is equal to one carrier period divided into four equal parts (that is, 2π / 4 = π / 2). The carrier waves Cu1 to Cu4 correspond to one embodiment of the "first carrier wave".

Further, between the four carrier waves Cx1 to Cx4, equal phase differences are provided between adjacent carriers in the order of Cx1 → Cx2 → Cx3 → Cx4. The phase difference is equal to one carrier period divided into four equal parts (that is, 2π / 4 = π / 2). The carrier waves Cx1 to Cx4 correspond to one embodiment of the "second carrier wave".

Further, the carrier wave Cu4 has a phase difference of π / 4 between each of the carrier wave Cx1 and the carrier wave Cx2. The carrier wave Cu3 has a phase difference of π / 4 between each of the carrier wave Cx2 and the carrier wave Cx3. The carrier wave Cu2 has a phase difference of π / 4 between each of the carrier wave Cx3 and the carrier wave Cx4. The carrier wave Cu1 has a phase difference of π / 4 between each of the carrier wave Cx4 and the carrier wave Cx1.

According to this, between the eight carrier waves Cu1 to Cu4 and Cx1 to Cx4, a phase difference π / 4 equal to each other between adjacent carriers in the order of Cx1 → Cu4 → Cx2 → Cu3 → Cx3 → Cu2 → Cx4 → Cu1. It is provided.

In the 2-pulse PWM control of the 4-stage serial multiplex converter 20, the 2-pulse PWM control shown in FIG. 4 is performed in each of the first-stage converter 28 to the fourth-stage converter 25. Specifically, in the 2-pulse PWM control of the first-stage converter 25, the height of the AC voltage command value Vux * and the carrier waves Cu1 and Cx1 are compared, and the switching elements S1 to S8 are turned on and off based on the comparison result. The combination of is determined. In the 2-pulse PWM control of the second-stage converter 26, the height of the AC voltage command value Vux * and the carrier waves Cu2 and Cx2 are compared, and the on / off combination of the switching elements S1 to S8 is determined based on the comparison result. To. In the 2-pulse PWM control of the third-stage converter 27, the height of the AC voltage command value Vux * and the carrier waves Cu3 and Cx3 are compared, and the on / off combination of the switching elements S1 to S8 is determined based on the comparison result. To. In the 2-pulse PWM control of the fourth-stage converter 28, the height of the AC voltage command value Vux * and the carrier waves Cu4 and Cx4 are compared, and the on / off combination of the switching elements S1 to S8 is determined based on the comparison result. To.

FIG. 6B shows waveforms of the output voltage Vu of the u-phase arm and the output voltage Vx of the x-phase arm in each of the first-stage converter 28 to the fourth-stage converter 25. The output voltage Vu1, Vx1 of the first stage converter 28, the output voltage Vu2, Vx2 of the second stage converter 27, the output voltage Vu3, Vx3 of the third stage converter 26, and the output voltage Vu4 of the fourth stage converter 25. , Vx4 each have three values of 0, ± Vd / 2. In FIG. 6B, each output voltage is represented by an absolute value.

The AC output voltage Vux of the 4-stage series multiplex converter 20 is a series combination of the AC output voltages Vu1 to Vu4 and Vx1 to Vx4 of the first-stage converter 28 to the fourth-stage converter 25. FIG. 6C shows the waveform of the AC output voltage Vux of the 4-stage series multiplex converter 20. As shown in FIG. 6C, the AC output voltage is the sum of the AC output voltages of the first-stage converter 28 to the fourth-stage converter 25 in the section of the electric angle of 0 ° to 180 °.

Also in the present embodiment, as in the comparative example of FIG. 5C, the AC output voltage Vux is 0, Vd / 2, Vd, 3Vd / 2,2Vd, in the section of the electric angle of 0 ° to 180 °. It is one of 5Vd / 2,3Vd and 7Vd / 2,4Vd.

However, in the present embodiment, since the phase difference shown in FIG. 6A is provided between the eight carriers Cu1 to Cu4 and Cx1 to Cx4, the four-stage series multiplexing converter 20 is compared with the comparative example. Harmonic components contained in the AC output voltage can be reduced. The effect of the 2-pulse PWM control of the 4-stage series multiplex converter according to the present embodiment will be described with reference to FIG. 7.

FIG. 7A is a waveform of the AC output voltage Vux of the 4-stage series multiplex converter according to the comparative example, which is the same as the waveform of FIG. 5C. FIG. 7B is a waveform of the AC output voltage Vux of the 4-stage series multiplex converter according to the present embodiment, which is the same as the waveform of FIG. 6C.

FIG. 7 (C) is a diagram showing the results of analysis of harmonic components contained in each of the AC output voltage of FIG. 7 (A) and the AC output voltage of FIG. 7 (B). The vertical axis of FIG. 7C shows the content rate (%) of the harmonic component in the AC output voltage, and the horizontal axis shows the order of the harmonic component. FIG. 7 (D) is a partially enlarged version of the graph of FIG. 7 (C).

In FIGS. 7 (C) and 7 (D), the content in the comparative example is shown in black or shaded, and the content in the present embodiment is shown in white. According to FIG. 7C, third-order, fifth-order, seventh-order, ... 49th-order harmonic components are observed in both the comparative example and the present embodiment. The content of harmonic components is highest in the third harmonic.

Comparing the comparative example with the present embodiment, it can be seen that the content of the third harmonic is smaller in the present embodiment than in the comparative example. In the 5th and 7th harmonics as well, the content of the present embodiment is smaller than that of the comparative example, as in the case of the 3rd harmonic.

As described above, according to the 2-pulse PWM control of the 4-stage series multiplex converter according to the present embodiment, the content rate of harmonic components is compared with the 2-pulse PWM control of the 4-stage series multiplex converter according to the comparative example. Can be reduced.

FIG. 8 is a waveform diagram for explaining 2-pulse PWM control of the 4-stage series multiplex converter according to the present embodiment. FIG. 8 shows a waveform of one cycle (electrical angle 0 ° to 360 °) of the AC voltage command value Vux *). In the example of FIG. 8, the AC voltage command value Vux * is obtained by superimposing a third harmonic component on the AC voltage command value of a sine wave. In this way, the line voltage n fundamental wave amplitude can be made larger than the amplitude of the carrier wave, so that the voltage utilization rate can be improved.

In FIG. 8, the relationship between the AC voltage command value Vux * and the eight carrier waves Cu1 to Cu4 and Cx1 to Cx4 in the section of the electric angle of 0 ° to 180 ° is as shown in FIG. That is, between the eight carriers Cu1 to Cu4 and Cx1 to Cx4, phase differences π / 4 equal to each other are provided between adjacent carriers in the order of Cx1 → Cu4 → Cx2 → Cu3 → Cx3 → Cu2 → Cx4 → Cu1. ing. Switching of the u-phase switching elements S1 and S3 in the converter of each stage is performed at the timing when the positive polarity AC voltage command value Vux * and the carrier wave Cu match. Switching of the x-phase switching elements S6 and S8 in the converter of each stage is performed at the timing when the AC voltage command value Vux * of the positive pole line and the carrier wave Cx match.

Even in the section of the electric angle of 180 ° to 360 °, between the eight carriers Cu1 to Cu4 and Cx1 to Cx4, between adjacent carriers in the order of Cx1 → Cu4 → Cx2 → Cu3 → Cx3 → Cu2 → Cx4 → Cu1. A phase difference π / 4 equal to each other is provided.

Here, in the present embodiment, in the carrier wave Cu1, a phase difference of 1/2 carrier period (that is, π) is provided between the upper carrier wave and the lower carrier wave. As shown in FIG. 4, in the PWM control of the single-phase full bridge three-level circuit, the upper carrier wave Ca and the lower carrier wave Cb are usually in the same phase. On the other hand, in the present embodiment, the upper carrier wave and the lower carrier wave have opposite phases. In each of the carrier waves Cu2 to Cu4 and Cx1 to Cx4, the upper carrier wave and the lower carrier wave have opposite phases.

(Control structure of control device)
Next, the control structure of the control device 11 in the series multiplex power conversion device 1 according to the present embodiment will be described.

FIG. 9 is a circuit block diagram showing a portion of the control device 11 shown in FIG. 1 regarding control of the 4-stage series multiplex converter 20.

With reference to FIG. 9, the control device 11 includes subtractors 110, 112, current control units 114, two-phase / three-phase conversion units 116, 3f superimposition calculation unit 118, adders 120, 122, 124, 132, and PWM control. Includes parts 126, multipliers 128, 130, and square root 134.

The d-axis current feedback value Id and the q-axis current feedback value Iq are the d-axis component and the q-axis component of the alternating current flowing through the power system 2 detected by the current detector 13 (FIG. 1), and are the three-phase alternating current IR. , IS, IT detection values were obtained by 3-phase / 2-phase conversion. The d-axis current command Id * and the q-axis current command Iq * are the d-axis component and the q-axis component of the AC current command, and convert the three-phase current command values IR *, IS *, and IT * into three-phase / two-phase. It was obtained by

The subtractor 110 calculates the deviation Δd (= Id−Id *) between the d-axis current feedback value Id and the d-axis current command Id *. The subtractor 112 calculates the deviation Δq (= Iq−Iq *) between the q-axis current feedback value Iq and the q-axis current command Iq *.

The current control unit 114 generates a d-axis voltage command Vd * and a q-axis voltage command Vq * so that each of the deviations Δd and Δq becomes 0. The current control unit 114 generates the d-axis voltage command Vd * and the q-axis voltage command Vq * by, for example, amplifying the deviations Δd and Δq according to the proportional control or the proportional integral control.

The two-phase / three-phase conversion unit 116 converts the d-axis voltage command Vd * and the q-axis voltage command Vq * into two-phase / three-phase, so that the three-phase AC voltage command value (R-phase voltage command value VR #, S-phase voltage command value VS #, T-phase voltage command value VT #) is generated.

The 3f superimposition calculation unit 118 calculates the superimposition ratio of the third harmonic component superimposed on each of the AC voltage command values VR #, VS #, and VT #. The 3f superimposition calculation unit 118 calculates the superimposition ratio of the third harmonic component based on the d-axis voltage command Vd * and the q-axis voltage command Vq * generated by the current control unit 114, and is based on the calculated superimposition ratio. To generate the third harmonic component of each phase. Specifically, the 3f superimposition calculation unit 118 calculates in advance a suitable superimposition ratio of the third harmonic according to the amplitude value of the AC voltage, and the amplitude value of the obtained AC voltage and the third harmonic. The relationship with the superposition ratio can be tabulated.

The adder 120 adds the R-phase voltage command value VR # and the third harmonic component of the R-phase to generate the R-phase voltage command value VR *. The adder 122 adds the S-phase voltage command value VS # and the third harmonic component of the S-phase to generate the S-phase voltage command value VS *. The adder 124 adds the T-phase voltage command value VT # and the T-phase third harmonic component to generate the T-phase voltage command value VT *.

The multiplier 128 calculates ^{the squared value Vd * 2} of the d-axis voltage command Vd *. The multiplier 130 calculates ^{the squared value Vq * 2} of the q-axis voltage command Vq *. The adder 132 adds the squared value Vd * ^{2 of the d-axis voltage command and the squared value Vq * 2} of the q-axis voltage command. The square root 134 calculates the amplitude of the fundamental wave of the AC voltage command value V # by calculating the square root (= (Vd * ² + Vq * ² ) ^{1/2) of the addition result of the adder 132.}

The PWM control unit 126 generates gate pulse signals GC1 to GC4 (FIG. 1) for controlling the four-stage series multiplex converter 20 based on the AC voltage command values VR *, VS *, and VT *. The PWM control unit 126 generates gate pulse signals GC1 to GC4 based on the amplitude of the line voltage.

FIG. 10 is a block diagram showing the configuration of the PWM control unit 126 shown in FIG. With reference to FIG. 10, the PWM control unit 126 includes a first stage control unit 141, a second stage control unit 142, a third stage control unit 143, a fourth stage control unit 144, and a carrier wave generator 145.

The carrier wave generator 145 generates carrier waves Cu1 to Cu4 and Cx1 to Cx4. The carrier wave is, for example, a triangular wave signal. The carrier waves Cu1 to Cu4 and Cx1 to Cx4 have twice the frequency of the AC voltage command value Vux *. The phase difference shown in FIG. 6 is provided between the carrier waves Cu1 to Cu4 and Cx1 to Cx4.

The first-stage control unit 141 generates a gate pulse signal GC1 which is a control command for controlling the on / off of the switching elements S1 to S8 in the first-stage converter 28 based on the AC voltage command value Vux *.

The second-stage control unit 142 generates a gate pulse signal GC2, which is a control command for controlling the on / off of the switching elements S1 to S8 in the second-stage converter 27, based on the AC voltage command value Vux *.

The third-stage control unit 143 generates a gate pulse signal GC3, which is a control command for controlling the on / off of the switching elements S1 to S8 in the third-stage converter 26, based on the AC voltage command value Vux *.

The fourth-stage control unit 144 generates a gate pulse signal GC4, which is a control command for controlling the on / off of the switching elements S1 to S8 in the fourth-stage converter 25, based on the AC voltage command value Vux *.

FIG. 11 is a block diagram showing a configuration example of the carrier wave generator 145 shown in FIG. With reference to FIG. 11, the carrier generator 145 includes a triangle wave generator 150, phase delay portions 151 to 157, and inverting generators 161 to 168.

The triangular wave generator 150 generates a triangular wave having a frequency four times that of the AC voltage command value Vux *.

The phase delay units 151 to 157 are configured to delay the input signal by the phase Δθ and output it. In the case of the 4-stage series multiplex converter 20, the phase delay amount Δθ in each phase delay portion is set to π / 4. In the case of an n-stage series multiplex converter in which n units are connected in series, the phase delay amount Δθ is set to π / n.

The inverting devices 161 to 168 are configured to invert the sign of the input signal and output it.

In the configuration example of FIG. 11, the triangular wave generated by the triangular wave generator 150 is the upper carrier wave Cx1 of the x-phase arm of the first stage converter 28, and the code of the upper carrier wave Cx1 is inverted by the inversion device 161 is x. It becomes the lower carrier wave Cx1 of the phase arm.

The upper carrier Cx1 delayed by the phase Δθ (= π / 4) by the phase delay unit 151 becomes the upper carrier Cu4 of the u-phase arm of the fourth stage converter 25, and the sign of the upper carrier Cx4 is inverted by the inverting device 162. This is the lower carrier wave Cu4 of the x-phase arm.

The upper carrier wave Cu4 delayed by the phase Δθ (= π / 4) by the phase delay unit 152 becomes the upper carrier wave Cx2 of the x-phase arm of the second stage converter 27, and the sign of the upper carrier wave Cx2 is inverted by the inversion device 163. This is the lower carrier wave Cx2 of the x-phase arm.

The upper carrier Cx2 delayed by the phase Δθ (= π / 4) by the phase delay unit 153 becomes the upper carrier Cu3 of the u-phase arm of the third stage converter 26, and the sign of the upper carrier Cu3 is inverted by the inverter 164. This is the lower carrier wave Cx3 of the x-phase arm.

The upper carrier wave Cu3 delayed by the phase Δθ (= π / 4) by the phase delay unit 154 becomes the upper carrier wave Cx3 of the x-phase arm of the third stage converter 26, and the sign of the upper carrier wave Cx3 is inverted by the inverting device 165. This is the lower carrier wave Cx3 of the x-phase arm.

The upper carrier Cx3 delayed by the phase Δθ (= π / 4) by the phase delay unit 155 becomes the upper carrier Cu2 of the u-phase arm of the second stage converter 27, and the sign of the upper carrier Cu2 is inverted by the inversion 166. This is the lower carrier wave Cu2 of the u-phase arm.

The upper carrier wave Cu2 delayed by the phase Δθ (= π / 4) by the phase delay unit 156 becomes the upper carrier wave Cx4 of the x-phase arm of the fourth stage converter 25, and the sign of the upper carrier wave Cx4 is inverted by the inversion device 167. This is the lower carrier wave Cx4 of the x-phase arm.

The upper carrier Cx4 delayed by the phase Δθ (= π / 4) by the phase delay unit 157 becomes the upper carrier Cu2 of the u-phase arm of the first stage converter 28, and the sign of the upper carrier Cu1 is inverted by the inverting device 168. This is the lower carrier wave Cu1 of the u-phase arm.

FIG. 12 is a block diagram showing a configuration example of the first stage control unit 141 shown in FIG. With reference to FIG. 11, the first stage control unit 141 includes a multiplier 160, comparators COM1 to COM4, and reversers I1 to I4.

The multiplier 160 multiplies the AC voltage command value Vux * by "-1". The multiplication value of the multiplier 160 deserves the AC voltage command value −Vux *.

The comparator COM1 receives the AC voltage command value Vux * at the non-inverting input terminal (+ terminal) and the upper carrier wave Cu1 at the inverting input terminal (-terminal). The comparator COM1 compares the high and low of the AC voltage command value Vux * and the upper carrier wave Cu1, and outputs a signal indicating the comparison result. The output signal of the comparator COM1 becomes a gate pulse signal of the switching element S1 of the first stage converter 28.

The inverting device I1 inverts the output signal of the comparator COM1. The output signal of the inverting device I1 becomes a gate pulse signal of the switching element S3 of the first stage converter 28.

The comparator COM2 receives the AC voltage command value Vux * at the non-inverting input terminal (+ terminal) and the lower carrier wave Cu1 at the inverting input terminal (-terminal). The comparator COM2 compares the AC voltage command value Vux * and the height of the lower carrier wave Cu1, and outputs a signal indicating the comparison result. The output signal of the comparator COM2 becomes the gate pulse signal of the switching element S2 of the first stage converter 28.

The inverting device I2 inverts the output signal of the comparator COM2. The output signal of the inverting device I2 becomes a gate pulse signal of the switching element S4 of the first stage converter 28.

The comparator COM3 receives the AC voltage command value −Vux * at the non-inverting input terminal (+ terminal) and the upper carrier wave Cx1 at the inverting input terminal (− terminal). The comparator COM1 compares the high and low of the AC voltage command value −Vux * and the upper carrier wave Cx1, and outputs a signal indicating the comparison result. The output signal of the comparator COM3 becomes a gate pulse signal of the switching element S5 of the first stage converter 28.

The inverting device I3 inverts the output signal of the comparator COM3. The output signal of the inverting device I3 becomes a gate pulse signal of the switching element S7 of the first stage converter 28.

The comparator COM4 receives the AC voltage command value −Vx * at the non-inverting input terminal (+ terminal) and the lower carrier wave Cx1 at the inverting input terminal (− terminal). The comparator COM4 compares the high and low of the AC voltage command value −Vux * and the lower carrier wave Cx1, and outputs a signal indicating the comparison result. The output signal of the comparator COM4 becomes a gate pulse signal of the switching element S6 of the first stage converter 28.

The inverting device I4 inverts the output signal of the comparator COM4. The output signal of the inverting device I4 becomes a gate pulse signal of the switching element S8 of the first stage converter 28.

(Other configuration examples)
In the above-described embodiment, the 2-pulse PWM control of the 4-stage series multiplex converter has been described, but the 2-pulse PWM control according to the present embodiment is also applied to the series multiplex converter having a number of stages other than 4. be able to.

(1) 2-Pulse PWM Control of 3-Stage Series Multiplex Converter FIG. 13 is a waveform diagram for explaining 2-pulse PWM control of a 3-stage series multiplex converter. FIG. 13 shows a waveform of a half cycle (a section of an electric angle of 0 ° to 180 °) of the AC voltage command value Vux *.

FIG. 13 further shows the waveforms of the carrier waves Cu1 to Cu3 and Cx1 to Cx3. The carrier waves Cu1 and Cx1 are carriers used for 2-pulse PWM control of the first-stage converter in the three-stage serial multiplex converter, and the carrier waves Cu2 and Cx2 are carriers used for two-pulse PWM control of the second-stage converter. The carrier waves Cu3 and Cx3 are carriers used for 2-pulse PWM control of the third-stage converter. The carrier waves Cu1 to Cu3 and Cx1 to Cx3 have the same amplitude and frequency as the carrier waves Cu and Cx in FIG.

In the three-stage series multiplex converter, the three carriers Cu1 to Cu3 are provided with equal phase differences between adjacent carriers in the order of Cu3 → Cu2 → Cu1. The phase difference is equal to one carrier period divided into three equal parts (ie, 2π / 3).

Further, between the three carrier waves Cx1 to Cx3, phase differences equal to each other are provided between adjacent carriers in the order of Cx1 → Cx2 → Cx3. The phase difference is equal to one carrier period divided into three equal parts (ie, 2π / 3).

Further, the carrier wave Cu3 has a phase difference of π / 3 between each of the carrier wave Cx1 and the carrier wave Cx2. The carrier wave Cu2 has a phase difference of π / 3 between each of the carrier wave Cx2 and the carrier wave Cx3. The carrier wave Cu1 has a phase difference of π / 3 between each of the carrier wave Cx3 and the carrier wave Cx1.

According to this, between the six carrier waves Cu1 to Cu3 and Cx1 to Cx3, a phase difference π / 3 equal to each other is provided between adjacent carriers in the order of Cx1 → Cu3 → Cx2 → Cu2 → Cx3 → Cu1. ..

Further, although not shown, in each of the carrier waves Cu1 to Cu3 and Cx1 to Cx3, the upper carrier wave and the lower carrier wave have opposite phases.

In the 2-pulse PWM control of the 3-stage series multiplex converter, the 2-pulse PWM control shown in FIG. 4 is performed in each of the first-stage converter to the third-stage converter. Specifically, in the 2-pulse PWM control of the first-stage converter, the height of the AC voltage command value Vux * and the carrier waves Cu1 and Cx1 are compared, and based on the comparison result, the switching elements S1 to S8 are turned on and off. The combination is decided. In the 2-pulse PWM control of the second-stage converter, the height of the AC voltage command value Vux * and the carrier waves Cu2 and Cx2 are compared, and the on / off combination of the switching elements S1 to S8 is determined based on the comparison result. .. In the 2-pulse PWM control of the third-stage converter, the height of the AC voltage command value Vux * and the carrier waves Cu3 and Cx3 are compared, and the on / off combination of the switching elements S1 to S8 is determined based on the comparison result. ..

(2) 2-Pulse PWM Control of 5-Stage Series Multiplex Converter FIG. 14 is a waveform diagram for explaining 2-pulse PWM control of a 5-stage series multiplex converter. FIG. 14 shows a waveform of a half cycle (a section of an electric angle of 0 ° to 180 °) of the AC voltage command value Vux *.

FIG. 14 further shows the waveforms of the carrier waves Cu1 to Cu5 and Cx1 to Cx5. Carrier waves Cu1 and Cx1 are carriers used for 2-pulse PWM control of the first-stage converter in a 5-stage serial multiplex converter, and carrier waves Cu2 and Cx2 are carriers used for 2-pulse PWM control of the second-stage converter. The carrier waves Cu3 and Cx3 are carriers used for 2-pulse PWM control of the third-stage converter. Carrier waves Cu4 and Cx4 are carriers used for 2-pulse PWM control of the 4th stage converter, and carrier waves Cu5 and Cx5 are carriers used for 2-pulse PWM control of the 5th stage converter. The carrier waves Cu1 to Cu5 and Cx1 to Cx5 have the same amplitude and frequency as the carrier waves Cu and Cx in FIG.

In the 5-stage series multiplex converter, equal phase differences are provided between the five carriers Cu1 to Cu5 in the order of Cu5 → Cu4 → Cu3 → Cu2 → Cu1 between adjacent carriers. The phase difference is equal to one carrier period divided into five equal parts (ie, 2π / 5).

Further, between the five carrier waves Cx1 to Cx5, equal phase differences are provided between adjacent carriers in the order of Cx1 → Cx2 → Cx3 → Cx4 → Cx5. The phase difference is equal to one carrier period divided into five equal parts (ie, 2π / 5).

Further, the carrier wave Cu5 has a phase difference of π / 5 between each of the carrier wave Cx1 and the carrier wave Cx2. The carrier wave Cu4 has a phase difference of π / 5 between each of the carrier wave Cx2 and the carrier wave Cx3. The carrier wave Cu3 has a phase difference of π / 5 between each of the carrier wave Cx3 and the carrier wave Cx4. The carrier wave Cu2 has a phase difference of π / 5 between each of the carrier wave Cx4 and the carrier wave Cx5. The carrier wave Cu1 has a phase difference of π / 5 between each of the carrier wave Cx5 and the carrier wave Cx1.

According to this, between the 10 carrier waves Cu1 to Cu5 and Cx1 to Cx5, Cx1 → Cu5 → Cx2 → Cu4 → Cx3 → Cu3 → Cx4 → Cu2 → Cx5 → Cu1 are equal to each other in the order of adjacent carriers. A phase difference π / 5 is provided.

Further, although not shown, in each of the carrier waves Cu1 to Cu5 and Cx1 to Cx5, the upper carrier wave and the lower carrier wave have opposite phases.

In the 2-pulse PWM control of the 5-stage series multiplex converter, the 2-pulse PWM control shown in FIG. 4 is performed in each of the 1st-stage converter to the 5th-stage converter. Specifically, in the 2-pulse PWM control of the first-stage converter, the height of the AC voltage command value Vux * and the carrier waves Cu1 and Cx1 are compared, and based on the comparison result, the switching elements S1 to S8 are turned on and off. The combination is decided. In the 2-pulse PWM control of the second-stage converter, the height of the AC voltage command value Vux * and the carrier waves Cu2 and Cx2 are compared, and the on / off combination of the switching elements S1 to S8 is determined based on the comparison result. .. In the 2-pulse PWM control of the third-stage converter, the height of the AC voltage command value Vux * and the carrier waves Cu3 and Cx3 are compared, and the on / off combination of the switching elements S1 to S8 is determined based on the comparison result. .. In the 2-pulse PWM control of the 4th stage converter, the height of the AC voltage command value Vux * and the carrier waves Cu4 and Cx4 are compared, and the on / off combination of the switching elements S1 to S8 is determined based on the comparison result. .. In the 2-pulse PWM control of the 5th stage converter, the height of the AC voltage command value Vux * and the carrier waves Cu5 and Cx5 are compared, and the on / off combination of the switching elements S1 to S8 is determined based on the comparison result. ..

(3) 2-pulse PWM control of N-stage series multiplexing converter When the number of stages of the converter to be serially multiplexed is N (N is a natural number of 2 or more), 2 of the N-stage series multiplexing converter according to the present embodiment. The pulse PWM control can be expressed as follows.

For 2-pulse PWM control, 2N carrier waves Cu1 to CuN and Cx1 to CxN are used. The carrier waves CuI and CxI are carrier waves used for 2-pulse PWM control of the first-stage converter. However, I is an integer of 1 or more and N or less. The carrier waves CuI and CxI have the same amplitude and frequency as the carrier waves Cu and Cx in FIG. 5, respectively.

In the N-stage series multiplex converter, between the N carrier waves Cu1 to CuN (first carrier wave), between adjacent carriers in the order of CuN → CuN-1 → CuN-2 → ... → Cu2 → Cu1. Are provided with equal phase differences. The phase difference is equal to one carrier period divided into N equal parts (that is, 2π / N).

Further, between the N carrier waves Cx1 to CxN (second carrier wave), equal phase differences are provided between adjacent carriers in the order of Cx1 → Cx2 → ... → CxN-2 → CxN-1 → CxN. Has been done. The phase difference is equal to one carrier period divided into N equal parts (that is, 2π / N).

Further, the carrier wave CuN + 1-I in the N + 1-I stage converter has a phase difference of π / N between the carrier wave CxI of the I stage converter and the carrier wave CxI + 1 of the I + 1 stage converter.

Further, although not shown, in each of the carrier waves Cu1 to CuN and Cx1 to CxN, the upper carrier wave and the lower carrier wave have opposite phases.

By doing so, it is possible to reduce the harmonic component included in the AC output voltage of the N-stage series multiplex converter. Therefore, it is possible to suppress the generation of harmonics while increasing the operating efficiency of the N-stage series multiplex converter.

It should be considered that the embodiments disclosed this time are exemplary in all respects and not restrictive. The scope of the present invention is shown by the scope of claims rather than the above description, and is intended to include all modifications within the meaning and scope equivalent to the scope of claims.

1 Series multiplex power converter, 2,3 power system, 10 power converter, 11 controller, 12,52 AC voltage detector, 13,53 current detector, 14 DC voltage detector, 15 DC positive bus, 16 DC Neutral point bus, 17 DC negative bus, 20,60 4-stage series multiplex converter, 21-24,61-64 transformer, 25-28,65-68 converter, 110,112 subtractor, 114 current control unit , 116 2-phase / 3-phase converter, 118 3f superimposition calculation unit, 120, 122, 124, 132 adder, 126 PWM control unit, 128, 130, 160 multiplier, 134 square root, 141 first-stage control unit, 142 2nd stage control unit, 143 3rd stage control unit, 144 4th stage control unit, 145 carrier wave generator, 150 triangular wave generator, 151-157 phase delay unit, 161-168, I1 to I4 inverting generator, C1, C2 Smoothing capacitor, COM1-COM4 comparer, Ca upper carrier wave, Cb lower carrier wave, GC1 to GC8 gate pulse signal, Cu, Cu1 to Cu5, Cx, Cx1 to Cx5 carrier wave.

Claims (2)

A series multiplex power converter linked to an AC power system
N transformers (N is an integer of 2 or more) in which the primary winding is multiplexed in series with the AC power system, and
The first-stage to N-stage converters that are connected to the secondary windings of the N transformers and perform bidirectional power conversion between AC power and DC power, respectively.
It is equipped with a control device that performs PWM control of the AC output voltage of the converter in each stage so that it matches the AC voltage command value.
The converter in each stage has a single-phase full-bridge circuit having a first-phase arm and a second-phase arm, and each of the first-phase arm and the second-phase arm is composed of a three-level circuit.
In the PWM control of the converter in each stage, the control device has a first carrier wave and a second carrier wave having a frequency four times the AC voltage command value, and the AC voltage command value and the first carrier wave. The control command of the first phase arm is generated by comparison with the above, and the control command of the second phase arm is generated by comparing the voltage obtained by reversing the polarity of the AC voltage command value with the second carrier wave. Consists of
The first to Nth first carrier waves corresponding to the first to Nth stage converters have a first phase difference between the first carrier waves adjacent to each other in the N to first order. Set,
The first to Nth second carrier waves corresponding to the first to Nth stage converters have the first phase difference between the second carrier waves adjacent to each other in the order of the first to Nth stages. Is set,
The first carrier wave of the N + 1-I corresponding to the N + 1-I stage converter (I is an integer of 1 or more and N or less) is the second carrier wave of the I corresponding to the I stage converter. A second phase difference is set between the interval and the second carrier of the I + 1 corresponding to the converter of the first I + 1 stage.
A series multiplex power converter in which the first phase difference is equal to 2π / N and the second phase difference is equal to π / N. Each of the first phase arm and the second phase arm has first to fourth switching elements connected in series between the DC positive bus and the DC negative bus in this order.
Each of the first carrier wave and the second carrier wave has an upper carrier wave for controlling the switching of the first and third switching elements and a lower carrier wave for controlling the switching of the second and fourth switching elements. Including side carrier
The series multiplex power conversion device according to claim 1, wherein the upper carrier wave and the lower carrier wave have a phase difference of π.

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