JP2014161148A - Control system for multilevel power conversion circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To solve the problem that a conventional method of adding components externally in order to equalize voltage resistance when turning off serially connected elements each including a function for simultaneously maintaining ON and OFF operations in a multilevel conversion circuit may increase device cost.SOLUTION: For controlling a multilevel conversion circuit, a cut-off control method is used with which one element is first turned off in a serial connection circuit where three or more switch elements are connected in series, OFF signals are given to the remaining switch elements after the lapse of a predetermined time, next, the first turned-off element is turned on for a short time and after voltage states of a plurality of elements are regulated, the circuit is shifted to such a mode that a high voltage is applied to the switch circuit. As a result, e.g., in a five-level conversion circuit, voltages to be applied to elements in the case where a voltage is shifted like from a zero voltage through Ed (unit voltage) and 2Ed to 3Ed are collectively cut off, such that the voltage can be suppressed low in comparison with the case where a voltage to any element is first cut off.

Description

  The present invention relates to a DC-AC conversion that generates an AC voltage with less harmonic components by combining a potential of five or more levels from a DC power source for the purpose of driving an AC motor, or an AC-DC conversion that generates a DC power source from an AC power source. The present invention relates to a control method of a multilevel power conversion circuit that performs the above.

  FIG. 4 shows a circuit example of a five-level inverter that uses an IGBT as a semiconductor switch element, which is a power conversion circuit that converts direct current into alternating current. In a DC power source (voltage is 2Ed × 2) in which DP1 and DP2 are connected in series, the positive potential is P, the negative potential is N, and the midpoint potential is M. In general, when this DC power supply is constituted by an AC power supply system, a rectifier (not shown) and a large-capacity capacitor can be constituted by series connection or the like.

  S1a to S1c, S2, S3, and S4a to S4c are first semiconductor switching elements comprising IGBTs in which eight diodes connected in series between the positive side potential P and the negative side potential N of the DC power supply are connected in reverse parallel It is a series circuit. S5 and S6 are second semiconductor switch element series circuits composed of IGBTs in which two diodes connected in series are connected in reverse parallel between the connection point of IGBTs 1c and S2 and the connection point of IGBTs 3 and S4a. . S7 and S8 are IGBTs constituting a bidirectional switch element connected between the M potential, which is the midpoint potential of the DC power supply, and the connection point between the IGBTTS5 and S6. As shown in FIG. 8 can be connected in reverse parallel or as shown in FIGS. 8 (a) and 8 (b), an IGBT having no reverse breakdown voltage and a diode can be combined. C1 is a capacitor called a flying capacitor and is connected in parallel with the second semiconductor switch element series circuit (series circuit of IGBTs 5 and S6). The average voltage at both ends of the capacitor C1 is controlled to Ed, and an intermediate potential output of one DC power supply is realized by utilizing the charge / discharge phenomenon. Here, the reason why the IGBTs 1a to S1c or S4a to S4c connected between the P potential or N potential of the DC power source and the positive side potential or negative side potential of the flying capacitor are in series is applied during this period. This is because all IGBTs have the same voltage rating according to the maximum voltage value.

A three-phase inverter can be constructed by connecting these circuit groups AU for one phase and connecting three units (AU, AV, AW) in parallel with a DC power source. Here, for AV and AW, connection with the midpoint potential M of the DC power supply is omitted.
ACM is an AC motor that is an example of the load of this system. With this circuit configuration, the potential of the output terminal AC of the converter is set to the P potential, N potential, M potential, and the intermediate potential between P-Ed and N + Ed using the on / off of the IGBT and the voltage Ed of the capacitor C1. Since it becomes possible to output, it becomes a 5-level output inverter. FIG. 9 shows an example of the output voltage (Vout) waveform.
Since this method has fewer low-order harmonic components and reduces switching loss of the switch element (IGBT) compared to the two-level type inverter, a highly efficient system can be constructed.

  5 and 6 show a basic circuit of a multilevel conversion circuit such as the five-level conversion circuit shown in FIG. FIG. 5 shows a configuration in which the IGBTs 1a to S1c are one switch element S1 and S4a to S4c are one switch element S4 except for the IGBTs 2 and S3 in the circuit of FIG. FIG. 6 shows a configuration in which the functions of the IGBTs 5 and 8 in the circuit of FIG. 4 are bidirectional switch elements ACS1, and the functions of the IGBTs 6 and IGBTTS7 are bidirectional switch elements ACS2. By adding a conversion circuit composed of a switching element such as an IGBT to the terminal portions TA1, TA2 in FIG. 5 or the terminal portions TA3, TA4 in FIG. This is an example in which IGBTTS2 and S3 are connected).

FIG. 7 shows a circuit example of a 7-level inverter when an IGBT is used as a switching element as an application circuit and the voltage ratings of all the IGBTs are all equal. The circuit of FIG. 7 charges a unit voltage (Ed) between the collector of the IGBT 3 and the emitter of the IGBT TS4 with respect to the voltage (3Ed × 2) of the DC power source configured by connecting the DC power sources DP3 and DP4 in series. Capacitor C2 to be charged, a capacitor C3 charged to a voltage of 2 units (2Ed) between the collector of IGBTTS2 and the emitter of IGBTTS5, and a voltage of 1 unit between the collector of IGBTTS10 and the emitter of IGBTTS11. By connecting a capacitor C4 to be charged to (Ed), an AC output with a 7-level potential is possible.
As shown in FIG. 7, when all the IGBTs have the same voltage rating, the IGBTTS1 needs to be four series connection circuits of IGBTTS1a to S1d, and the IGBTTS6 needs to be four series connection circuits of IGBTTS6a to S6d. .

10A to 10E show examples of operation transition diagrams for one phase of the five-level inverter circuit shown in FIG. The transition of the potential of the AC output AC when the potential at the midpoint of the DC power supply is zero will be described. In FIG. 10A, the IGBTs 1a to S1c and S2 are in the ON state, and a potential of 2Ed is output to the AC output AC. In FIG. 10B, Ed is output to the AC output AC in a state where the IGBTs 1a to S1c are turned off and the IGBTs 8, S6, and S2 are turned on. At this time, the voltage of Ed is applied between the collector of the IGBT TS1a and the emitter of S1c. FIG. 10C shows a state where the IGBT TS2 is turned off and the IGBTs 8, S6, and S3 are turned on, and a zero potential (M potential) is output to the AC output AC. At this time, the voltage of Ed is applied between the collector of the IGBT TS1a and the emitter of S1c. In FIG. 10D, -Ed is output to the AC output AC in a state in which the IGBTTS 6 is turned off and the IGBTs 8, S5, and S3 are turned on. At this time, a voltage of 2 Ed is applied between the collector of the IGBTTS 1a and the emitter of the S1c. FIG. 10E shows that −2Ed is output to the AC output AC in a state where the IGBTTS 8 is turned off and the IGBTs 4a to S4c and S3 are turned on. At this time, a voltage of 3Ed is applied between the collector of the IGBT TS1a and the emitter of the S1c.
As described above, the voltages are applied to the IGBTTS 1a to S1c in a stepwise manner from Ed to 3Ed after FIG. 10B.
The circuit example of the above five-level inverter, the basic circuit of the multi-level circuit, the operation, and the like are shown in Patent Document 1 and Patent Document 2.

Special table 2009-525717 gazette JP 2010-182974 A Japanese Patent No. 3767740

As shown in FIG. 10, in the normal operation state, when S1a to S1c are turned off, the voltage applied between the collector of S1a and the emitter of S1c is Ed. In practice, surge voltage generated by wiring inductance, etc. is superimposed during switching transients, but it is not essential for this proposal and is ignored here.
Thereafter, the switching state of the other switch element (IGBT) advances, and the IGBTs 3, S4a to S4c are in the on state and the IGBTs 1a to S1c, S2 are in the off state (N potential is output to the AC output) In the state), a voltage of 4Ed is applied between the collector of the IGBT TS1a and the emitter of S2. That is, in this state, a voltage of 3Ed is applied between the collector of the IGBT TS1a and the emitter of S1c. Therefore, when all the IGBTs have the same voltage rating, ideally three serial numbers are required as S1.

  In general, there is a limit to increasing the breakdown voltage of an IGBT, and there is a problem that the higher the breakdown voltage, the higher the cost. Further, when the IGBTs are connected in series and are turned off, it is impossible to perform switching at the same time due to variations in characteristics of the IGBTs and variations in delay time of the gate drive circuit. Therefore, conventionally, in order to equalize the voltage applied to each IGBT as much as possible, selection of element characteristics, connection of a series circuit of a resistor and a capacitor in parallel with the IGBT, and connection of a transformer between gate drive wirings , Etc. are done. However, these are all cost increasing factors and have been problems.

By the way, in the worst case when the series elements are turned off at the same time, the voltage Ed is applied only to a specific IGBT (assumed to be S1a), and no voltage is applied to the other IGBTs (S1b, S1c). . In this circuit system, a voltage is applied statically from this state up to 3Ed, and at that time, a voltage of 2Ed (obtained by 3Ed-Ed) is uniformly applied to the three elements (without current interruption). (Because it is a static voltage application, the voltage sharing is made uniform), so the voltage finally applied to each IGBT is
S1a: Ed + 2Ed / 3 = 5Ed / 3
S1b, S1c: 2Ed / 3
It becomes.
That is, assuming this case, it is necessary that the voltage rating of the IGBT required for the S1 part has a margin with respect to 5Ed / 3.

Similarly, in the 7-level method of FIG.
S1a: Ed + 3Ed / 4 = 7Ed / 4
S1b to S1d: 3Ed / 4
Therefore, the voltage rating of the IGBT required for the S1 portion needs to have a margin with respect to 7Ed / 4.
Examples of voltage equalization countermeasures for conventional series-connected IGBTs are described in FIGS.
Accordingly, an object of the present invention is applied to each semiconductor switching element in the multilevel power conversion circuit when at least three series-connected semiconductor switching elements having the function of simultaneously maintaining the on state and the off state are turned off. To provide a control system capable of reducing the voltage in the direction of equalization as much as possible without adding parts to the main circuit.

  In order to solve the above-mentioned problem, in the first invention, a power conversion circuit for converting from direct current to alternating current or from alternating current to direct current, which is a circuit for one phase, the positive terminal of the direct current power supply circuit and the negative terminal A first semiconductor switch element series circuit in which at least eight semiconductor switch elements in which diodes connected between the side terminals are connected in reverse parallel are connected in series, and one terminal connected to an intermediate potential point of the DC power supply circuit; A bidirectional switching element capable of bidirectional switching and a diode connected between two specific connection points among the connection points of the semiconductor switch elements of the first semiconductor switch element series circuit are anti-parallel. A second semiconductor switch element series circuit in which connected semiconductor switch elements are connected in series; and a capacitor connected in parallel with the second semiconductor switch element series circuit. A multi-level power conversion circuit in which the other terminal of the bidirectional switch element is connected to an intermediate connection point of the second semiconductor switch element series circuit, and is connected to a positive terminal or a negative terminal of the DC power supply circuit. In the turn-off operation of at least three serially connected semiconductor switch elements having a function of maintaining the ON state and the OFF state at the same time, any one of the at least three serially connected series switch elements is first selected. Only one semiconductor switch element is turned off, and the remaining semiconductor switch elements are turned off with a time delay from the turn-off completion time of the first semiconductor switch element turned off.

  In the second invention, in the control method of the multilevel power conversion circuit in the first invention, at least three semiconductor switch elements connected in series connected to the positive or negative DC potential are all turned off. After that, the semiconductor switch element that is turned off first is turned on for a predetermined time.

  According to a third invention, in the control method of the multilevel power conversion circuit according to the first invention, among the at least three series-connected semiconductor switch element groups connected to the DC positive potential or negative potential. The semiconductor switch elements to be turned off first are sequentially switched.

  In the fourth invention, the control method of the multilevel power conversion circuit according to any one of the first to third inventions is applied to a multilevel power conversion circuit that outputs an alternating voltage composed of a potential of 7 levels or more.

In the present invention, in the multilevel power conversion circuit, as a control method for turning off at least three semiconductor switch elements connected in series having the function of simultaneously maintaining the ON state and the OFF state, the semiconductor switch elements connected in series First, only one of the semiconductor switch elements is turned off, and the remaining semiconductor switch elements are turned off with a time delay from the turn-off time of the semiconductor switch element that was initially turned off. Further, after all the turn-off is completed, the semiconductor switch element that is turned off first is turned on for a predetermined time.
As a result, it is possible to equalize the voltages applied to the semiconductor switch elements connected in series without adding components to the main circuit.

It is a control algorithm which shows the Example of this invention. It is a time chart figure which shows the example of the control signal which shows the Example of this invention. It is a figure which shows the applied voltage to each IGBT in each time shown in FIG. It is an example of an inverter circuit by a 5-level conversion circuit. This is a basic form 1 of a multilevel conversion circuit. This is basic form 2 of the multilevel conversion circuit. It is an example of a 7 level conversion circuit based on the basic form of a multilevel conversion circuit. It is an example of a bidirectional switch circuit. It is an example of the output line voltage waveform of a 5-level inverter. It is an operation | movement transition diagram of a 5 level inverter.

  The gist of the present invention is that a first semiconductor switch element series circuit in which at least eight semiconductor switch elements connected between the positive terminal and the negative terminal of the DC power supply circuit are connected in series, and an intermediate potential point of the DC power supply circuit. A bidirectional switch element having one terminal connected thereto, a second semiconductor switch element series circuit connected between two specific connection points among the connection points of the first semiconductor switch element series circuit; And a capacitor connected in parallel with the second semiconductor switch element series circuit, wherein the other terminal of the bidirectional switch element is connected to an intermediate connection point of the second semiconductor switch element series circuit. At least three converter circuits connected to the positive terminal or the negative terminal of the DC power supply circuit and having the function of simultaneously maintaining the on state and the off state are connected in series. In the turn-off operation of the conductor switch element group, only one of the series switch element groups is turned off first, and the remaining semiconductor switch elements are turned off. The point is that the semiconductor switch element is turned off with a delay from the time, and after all the semiconductor switch elements have been turned off, the semiconductor switch element that was turned off first is turned on for a short time.

FIG. 1 shows an implementation algorithm diagram of the present invention in the five-level power conversion circuit shown in FIG.
After the start block BL1, S1 in the block BL3 (when the turn-off judgment of S1 or S4 is made, only one predetermined element in S1 or S4 is turned off in the block BL4. At this time, current flows to the IGBT side. In this case, since the current is cut off, a turn-off loss is generated in the element, and the voltage Ed is applied between the collector and the emitter, and after a predetermined time (processing by the timer block BL5), the block At BL6, other switch elements connected in series with S1 or S4 are turned off, and at this time, since there is no current cut-off operation, no turn-off loss occurs and no voltage is applied. In the process of block BL7), the element that was first turned off in block BL8 is turned on for a short time. At this time, no voltage is applied to this element, and at the same time, a voltage is applied to the other elements by Ed / 2, and then another normal algorithm is executed in block BL9, as shown in FIG. Therefore, 3Ed is applied to S1 (S1a to S1c) or S4 (S4a to S4c) at the maximum.

  FIG. 2 shows an example of a drive signal of each IGBT (S1a to S1c) when the switch element (IGBT) to be turned off first is S1a, and FIG. 3 shows the voltage of each IGBT at each time. In the operation transition diagram shown in FIG. 10, in the operation mode in which the IGBT TS1 is turned off and the voltage Ed is applied to the IGBTTS1a to S1c, the time t1 is based on the off signal from the state in which the IGBTTS1a to S1c is on to S1. First, the IGBTTS 1a is turned off, and the IGBTs 1b and S1c are turned off at time t2 when the voltage of each IGBT is statically stabilized. Thereafter, the IGBTTS1a that was initially turned off at time t3 when the on-states of the IGBTTS1b and S1c are statically stabilized is turned on for a short time. The on-time is a short period of time until the IGBT TS1a is turned on and the voltage becomes zero, and the IGBTTS1b and S1c share the voltage by Ed / 2 and stabilize. This state is maintained even if the IGBTTS1a is turned off at time t4.

  In this state, in the operation transition diagram shown in FIG. 10 at time t5, in a mode in which 2Ed is applied to IGBTTS1 (S1a to S1c), the voltage of IGBTTS1a changes from zero to Ed / 3, and the voltages of IGBTTS1b and S1c change to Ed. / 2 + Ed / 3 = 5Ed / 6. Further, in the operation transition diagram shown in FIG. 10 at time t6, when a mode in which 3Ed is applied to IGBTTS1 (S1a to S1c), the voltage of IGBTTS1a becomes Ed / 3 + Ed / 3 = 2Ed / 3, and the voltages of IGBTTS1b and S1c. Is 5Ed / 6 + Ed / 3 = 7Ed / 6.

  Therefore, in the conventional method, the voltage applied to the IGBT TS1a is 5Ed / 3, the voltage applied to the IGBTTS1b and S1c is 2Ed / 3, and an IGBT element that can withstand 5Ed / 3 is required. Then, the voltage applied to the IGBT TS1a is 2Ed / 3, the voltage applied to the IGBTTS1b and S1c is 7Ed / 6, and the IGBT element needs an element that can withstand 7Ed / 6. Can be reduced, and an IGBT having a low breakdown voltage can be applied.

Further, when the same switch element is first turned off each time in FIG. 1, only the switch element causes a turn-off loss and a thermal imbalance occurs. Therefore, in order to prevent this, the block BL9 is first turned off. The switch elements are switched sequentially every time (or every few times) to reduce thermal imbalance.
Moreover, since it becomes the same operation | movement also about IGBTTS4a-S4c, description is abbreviate | omitted.

  FIG. 7 shows the configuration of one phase of a seven-level conversion circuit using a flying capacitor. In this configuration, the 5-level conversion circuit shown in the first embodiment is expanded to 7 levels. In a DC power source (voltage is 3Ed × 2) in which DP1 and DP2 are connected in series, the positive potential is P, the negative potential is N, and the midpoint potential is M.

  S1a to S1d, S2, S3, S4, S5, and S6a to S6d are first IGBTs composed of 12 diodes connected in series between the positive side potential P and the negative side potential N of the DC power source and connected in reverse parallel. This is a semiconductor switch element series circuit. S9 to S12 are second semiconductor switch element series circuits composed of IGBTs in which four diodes connected in series are connected in reverse parallel between the connection point of IGBTs 1d and S2 and the connection point of IGBTs 5 and S6a. . S7 and S8 are bidirectional switch elements connected between the M potential, which is the midpoint potential of the DC power supply, and the connection point between the IGBTs 10 and S11. An IGBT having a reverse breakdown voltage as shown in FIG. They can be connected in reverse parallel, or can be configured with a combination of an IGBT and a diode having no reverse breakdown voltage as shown in FIGS. 8 (a) and 8 (b).

  Further, C3 is a capacitor called a flying capacitor and is connected in parallel with the second semiconductor switch element series circuit (series circuit of IGBTs 9 to S12). The average voltage across the capacitor C3 is controlled to 2Ed. C2 is a flying capacitor connected in parallel with the series circuit of IGBTs 3 and S4, and the average voltage across the capacitor C1 is controlled to Ed. C4 is a flying capacitor connected in parallel with the series circuit of the IGBTs 10 and S11, and the average voltage across the capacitor C4 is controlled to Ed. The reason why the IGBTs 1a to S1d or S6a to S6d connected between the P potential or N potential of the DC power source and the positive side potential or negative side potential of the flying capacitor is in series is applied during this period. This is because all IGBTs have the same voltage rating according to the maximum voltage value.

Even in such a configuration, the control method shown in FIG. 1 can be applied as in the case of the five-level conversion circuit. The block BL3 in FIG. 1 is “S1 or S6 turn off?”. Since the detailed description is the same as that of Example 1, it is omitted, but the result is as follows.
For example, when IGBTs 1a to S1d are collectively shut off as in the conventional case, when IGBTTS1a is shut off first, the voltage of IGBTTS1a becomes Ed + 3Ed / 4 = 7Ed / 4, and the voltages of IGBTTS1b to S1d become 3Ed / 4. Requires an element that can withstand 7 Ed / 4. In addition, when the control method of the present invention is applied, the voltage of the IGBT 1a becomes 3Ed / 4, the voltages of the IGBTs 1b to S1d become Ed / 3 + 3Ed / 4 = 13Ed / 12, and the IGBT needs an element that can withstand 13Ed / 12. .
Similar to the first embodiment, the maximum applied voltage value is reduced as compared with the conventional method, and an IGBT having a low breakdown voltage can be applied.

Further, when the same switch element is first turned off each time in FIG. 1, only the switch element causes a turn-off loss and a thermal imbalance occurs. Therefore, in order to prevent this, the block BL9 is first turned off. The switch elements are switched sequentially every time (or every few times) to reduce thermal imbalance.
Moreover, since it becomes the same operation | movement also about IGBTTS6a-S6d, description is abbreviate | omitted.

  In this embodiment circuit example, the case of the 5-level conversion circuit and the 7-level conversion circuit example has been shown. However, based on the circuit of FIG. 5 or 6, a bidirectional switch element is connected to the intermediate potential point of the DC voltage. The present invention can also be applied to a multi-level converter having 9 levels or more.

  The present invention relates to a semiconductor device connected in series in the case where a multi-level conversion circuit of five levels or more is constituted by a semiconductor device having the same breakdown voltage from a DC power source having a positive potential P, a negative potential N, and a midpoint potential M. It is a control method that realizes voltage balance without adding components, and can be applied to a high-voltage motor drive device, a grid interconnection power conversion device, and the like.

DP1, DP2, DP3, DP4 ... DC power supply ACM ... AC motor S1, S1a-S1d, S2-S5, S4a-S4c, S6a-S6d ... IGBT
S7 to S12 ... IGBT C1 to C4 ... Capacitors ACS1, ACS2 ... Bidirectional switch elements

Claims (4)

  A power conversion circuit for converting from direct current to alternating current or from alternating current to direct current, a semiconductor switching element in which a diode connected between a positive terminal and a negative terminal of a direct current power supply circuit is connected in reverse parallel as a circuit for one phase A first semiconductor switch element series circuit in which at least eight are connected in series, a bidirectional switch element capable of bidirectional switching in which one terminal is connected to an intermediate potential point of the DC power supply circuit, A second semiconductor switch element in which semiconductor switch elements connected in reverse parallel are connected in series between two specific connection points among the connection points of the semiconductor switch elements in the first semiconductor switch element series circuit An intermediate connection of the second semiconductor switch element series circuit, comprising: a series circuit; and a capacitor connected in parallel with the second semiconductor switch element series circuit. A multi-level power converter circuit connected to the other terminal of the bidirectional switch element, and connected to the positive terminal or the negative terminal of the DC power supply circuit and simultaneously maintaining the on state and the off state. In the turn-off operation of at least three semiconductor switch elements connected in series, first, only one of the at least three series switch elements connected in series is turned off, and the rest The control method of a multilevel power conversion circuit, wherein the semiconductor switch element is turned off with a time delay from a time point when the semiconductor switch element that was turned off first is turned off.   2. The control method for a multilevel power conversion circuit according to claim 1, wherein at least three semiconductor switch elements connected in series connected to the positive or negative DC potential are turned off and then turned off first. A control method for a multilevel power conversion circuit, wherein the semiconductor switch element is turned on for a predetermined time.   2. The control system for a multilevel power conversion circuit according to claim 1, wherein the semiconductor is first turned off among at least three series-connected semiconductor switch elements connected to the DC positive potential or negative potential. A control method for a multi-level power conversion circuit, characterized by sequentially switching switch elements.   The multilevel power conversion circuit control method according to any one of claims 1 to 3 is applied to a multilevel power conversion circuit that outputs an alternating voltage composed of a potential of 7 levels or more. Multilevel power conversion circuit control method.