JP2006166582A - Power converter - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To attain high efficiency for a power converter by suppressing generation loss of a reverse blocking IGBT constituting the power converter. <P>SOLUTION: This power converter, using a bidirectional switch SWr formed by connecting reverse blocking IGbtQur, Qru to each other in reverse parallel as a switching element, includes current detectors CTf, CTr for separately detecting currents running through gate terminals of elements Qur, Qru and a comparator for comparing the detected current values. The IGBT applied with a reverse voltage is detected and its gate voltage is turned on, thus suppressing generation of a leak current. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a power conversion device using a bidirectional switch, for example, a power conversion device such as a matrix converter (or a cycloconverter) that directly converts alternating current to arbitrary alternating current power, particularly a reverse blocking semiconductor element used as a switching element. The present invention relates to a power conversion device having an improved driving system.

For example, as shown in FIG. 9A, the most frequently used conversion device converts the AC power source Vs to DC by arbitrarily turning it on / off with switches Srp, Srn, Ssp, Ssn, Stp, Stn. In this type, the switch Sup, Sun, Svp, Svn, Swp, Swn is arbitrarily turned on / off to supply the power converted into direct current to the load M.
As a general AC / AC direct conversion device, for example, there is a matrix converter (or a cycloconverter) as shown in FIG. This is because the bidirectional switches Sru, Srv, Srw, Ssu, Ssv, Ssw, Stu, Stv, Stw are connected as shown in the figure between the power source Vs and the load M, and the AC supplied from the AC power source Vs. Electric power is directly converted into arbitrary alternating current and supplied to the load M.

In FIG. 9B, the number of switches is larger than that in FIG. 9A, but the capacitor Cdc having a large capacity as shown in FIG. Life expectancy can be expected.
As a switch used in FIG. 9B, a device capable of bidirectional on / off control is required. By the way, IGBTs (insulated gate bipolar transistors) have become the most popular switching devices used in power converters, including thyristors, GTO thyristors, transistors, and MOSFETs (metal oxide field effect transistors). A switch circuit using a MOSFET is disclosed in Patent Document 1, for example.

  However, since a general IGBT does not have a reverse breakdown voltage, diodes are connected in antiparallel. In order to realize an arbitrary switch Sij (i = r, s, t, j = u, v, w) as shown in FIG. 10A with an IGBT, for example, as shown in FIG. Used in reverse series with each other. In FIG. 10B, the current flowing through the switch Sij flows through two devices such as IGBTQf → diode Dr or IGBTQr → diode Df. For this reason, since the loss which generate | occur | produces in a device by flowing an electric current doubles, it causes a fall of efficiency.

In order to solve this problem, a reverse blocking IGBT having a reverse breakdown voltage has been developed in recent years. By using this reverse blocking IGBT, the current flow path becomes one and the efficiency can be improved. A switch using a reverse blocking IGBT is shown in FIG.
On the other hand, regarding the on / off control command for the bidirectional switch Sij when controlling the matrix converter as shown in FIG. (1) In order to prevent a short circuit of the power supply Vs, a dead time is provided.
(2) In order to prevent the load M from being released, an overlapping period for commutating the load current is provided.

The commutation pattern is disclosed in Patent Documents 2 and 3, for example. The commutation mode will be described with reference to FIGS. In order to simplify the description, a circuit Mu as shown in FIG. 12 is used as a switch circuit, and an example in which this is configured by a reverse blocking IGBT is shown in FIG.
Now, assuming that the R, S, and T phase voltages of the power source Vs are three-phase waveforms indicated by Vr, Vs, and Vt shown in FIG. 12B, voltages indicated by Er, Es, and Et at time t0 in period III, respectively. The relationship is Er>Es> Et.

FIG. 13A shows a state in which an ON command is given to Qru and Qur and a current is flowing through Qur. Here, an ON command is also given to Qru, but no current flows because the current direction is the reverse direction. A state where the load current commutates from this state to Es⇒Vu will be described.
First, an ON command is given to Qus as shown in FIG. Since Er> Es, a voltage is applied to Qus in the reverse direction, and the state of the load current does not change.

Next, an off command is given to Qur as shown in FIG. The load current commutates from Es to Vu via Qus in order to continue the current. Since Qur is turned off and Qus flows, Er-Es voltage is applied to Qur in the forward direction. Therefore, a voltage is applied in the reverse direction to Qru connected in antiparallel.
Then, as shown in FIG. 13D, an on command is given to Qsu. Since Qus is turned on first, and since Qsu is opposite to the direction of the load current, the state of the load current does not change.
Further, an off command is given to Qru as shown in FIG. Since a voltage is applied to Qru in the reverse direction, the state of the load current does not change.

  Although the example of the commutation state has been described with reference to FIG. 13, in order to change the commutation state, there is a timing for changing the on / off command to the four elements, and further, a dead time ( In the example of FIG. 13, it is necessary to provide an overlap period (in the example of FIG. 13, the simultaneous ON period of Qur and Qus) for preventing the load current from being released). On the other hand, the load current changes at the timing of the on / off signal change to the four elements only when the on / off command of one element changes (in the example of FIG. 13, only (c)). ).

JP 2000-269353 A JP 2003-333851 A JP 2004-229492 A

  However, the reverse blocking IGBT has the following problems. That is, as shown in FIG. 11, when a reverse voltage is applied to the reverse blocking IGBT (VCE <0), the current is blocked regardless of the ON / OFF signal of the gate terminal, but the voltage is applied in the reverse direction. The leakage current Ireak is larger when the off signal is applied than when the on signal is applied to the gate terminal (this point is referred to as “OHM April 2003 issue if necessary). Pp. 54-56, “New Reverse Power IGBTs Applied to Matrix Converters”.

Therefore, when an off signal is applied during a period in which a reverse voltage is applied, the leakage current is large, so that the loss of reverse blocking IGBT increases, leading to a reduction in device efficiency.
In addition, as a simple means for detecting the voltage application direction of each reverse blocking IGBT, a voltage dividing circuit with a resistor connected to both ends of the reverse blocking IGBT can be considered. Insulation circuit is necessary for transmission, and voltage must be detected in both directions.
Therefore, the subject of this invention is to reduce the generation | occurrence | production loss of the reverse blocking IGBT which comprises a power converter device, and to improve the efficiency of a power converter device.

In order to solve such problems, in the invention of claim 1, the forward voltage applied between the collector and the emitter is controlled by applying a forward voltage or a reverse voltage from the gate drive circuit to the gate terminal. In a power conversion device comprising a bidirectional switch in which reverse blocking semiconductor elements having a function of blocking a reverse voltage applied between a collector and an emitter are connected in antiparallel with each other,
Current detecting means for individually detecting currents flowing through the gate terminals of the reverse blocking semiconductor elements connected in antiparallel with each other and comparison means for comparing the detected current values are provided.

  In the first aspect of the invention, the on / off state of the reverse blocking semiconductor element can be determined according to the comparison result by the comparison means (the second aspect of the invention). The output of the current detection means is input to a gate drive circuit that constitutes the bidirectional switch and is provided corresponding to the reverse blocking semiconductor element, and the comparison means is provided in the gate drive circuit. The detected current values can be compared (invention of claim 3). Further, in the first aspect of the present invention, all the outputs of the current detection means are taken into the control device, and the on / off state of the reverse blocking semiconductor element can be determined according to the calculation result by the control device. Invention of 4).

In order to solve the above problems, the present invention can be said to utilize the gate current characteristics of the IGBT. FIG. 7 shows an IGBT and an example of its driving circuit, and FIG. 8 shows the characteristics of the gate charge of the IGBT.
In general, an IGBT can control a current flowing through the IGBT by arbitrarily applying a voltage between a gate terminal and an emitter terminal. Normally, the gate voltage of the IGBT is controlled by an amplifier called a gate drive circuit (GDU) based on an on / off signal from a control device.

  As shown in FIG. 7A, stray capacitances Cge, Ccg, and Cce exist between the terminals of the IGBT. When the gate voltage VGE is given as a step function, when Cge is charged, when Cge is charged, at the same time the collector voltage VCE applied between the collector and the emitter decreases, and the operation of charging Ccg is performed. Thus, there is a period in which the gate voltage VGE is constant. Similarly, when the Cge charge is discharged, the collector voltage VCE increases at the same time when the Cge charge is discharged, so that there is a period in which the gate current IG flows in the direction of discharging the Ccg charge and the gate voltage VGE becomes constant. .

  In the above phenomenon, as the collector voltage VCE increases as shown in FIG. 8A, Ccg increases, and as a result, the charge amount Qg of the gate current IG increases. For example, in FIG. 8A, when VCE is x <z, Qg increases as shown in FIG. 8B. As a result, the waveform of the gate current IG changes from x (Qg1) to z (Qg3) as shown in FIG. 8B.

On the other hand, the reverse blocking IGBT also operates in the same manner as a normal IGBT with respect to a forward voltage. For example, when a forward voltage is applied between the gate terminal and the emitter terminal of the IGBT, a current flows, and both IG and Qg are the same as a general IGBT.
Utilizing this characteristic and the characteristic that leakage current decreases when an ON signal is applied to the gate terminal when a voltage is applied in the reverse direction with respect to the reverse blocking IGBT, the power converter can be made highly efficient. It can be said that it is the subject of the present invention.

  According to the present invention, by paying attention to the leakage current characteristic of the reverse blocking IGBT and the characteristic of the gate current change at the time of IGBT switching, it becomes possible to detect the reverse voltage IGBT with a small and inexpensive configuration. In addition, the efficiency of power conversion devices such as matrix converters can be improved.

FIG. 1 is a circuit diagram showing the principle of the present invention.
Here, the reverse blocking IGBTs Qru and Qur are connected in antiparallel to each other to form the bidirectional switch SWr. Gate drive circuits GDUf and GDUr for outputting a gate voltage are connected between the gate and emitter of each reverse blocking IGBT based on an ON / OFF signal input from a control device (not shown). Further, current detectors CTf and CTr are inserted in order to detect the gate current flowing in Qru and Qur, and the output signals are input to the determination circuit IGC. The output signals of CTf and CTr are input to the comparator Cmp via the integration circuit I and the sample hold circuit S / H.

2A is a circuit diagram showing an application example of FIG. 1, and FIG. 2B is an operation waveform diagram thereof.
FIG. 2A shows a bidirectional switch SWs having the same configuration as that of the bidirectional switch SWr of FIG. 1, connected in series with SWr, a series connection circuit connected to the variable power supply Er-s, and a connection point between SWr and SWs. The load L is connected between the negative terminals of Er-s. Note that gate drive circuits GDUf and GDUr and a determination circuit IGC are also provided for SWs, but illustration thereof is omitted here.

Now, when an on command is given to the r group switch as shown in FIG. 2B and the current Io1 flows from the Er-s to the load L via Qru, the r group switch is turned off and the s group switch is turned on. Will be described.
When the r group switch is on, SWr is turned on, that is, Qru and Qur are turned on. Next, when switching from the r group switch to the s group switch, the switch is switched as follows in order to prevent a power supply short circuit and a load opening.
(1) An on signal is input to Qsu at time t0. Since a reverse voltage is applied to Qsu, the VCE of Qsu does not decrease. Therefore, there is no increase in Qg due to the feedback capacitance.

(2) An off signal is input to Qru at time t1. Qru tries to turn off and the collector voltage rises. For this reason, since the operation | movement which charges a feedback capacity | capacitance generate | occur | produces, Qg increases like FIG. 2B. Further, when the collector voltage of Qru rises, a reverse voltage is applied to Qur.
Furthermore, since the load L releases the energy stored by the current Io1, the current Io2 flows through the Qsu that is turned on by the ON signal in the above (1) (see FIG. 2A).
(3) An on signal is input to Qus at time t2. Since Qsu is turned on in (2), a reverse voltage is applied only for the saturation voltage VCE (sat) of Qus. Therefore, there is no increase in Qg.
(4) An off signal is input to Qur at time t3. Since a reverse voltage is applied to Qur, it does not turn on. Therefore, there is no increase in Qg.

  As described above, the increase in Qg is only Qru. The determination circuit IGC measures Qg by integrating the current detectors CTf and CTr that detect the gate currents of Qru and Qur with the integration circuit I. Then, by comparing the signal detected by each sample and hold circuit S / H after time t3 with the comparator Cmp, it can be determined which element is turned off. For example, in the case of FIG. 2B, since Qg is Qru> Qur, it can be seen that Qru is turned off. That is, a reverse voltage is applied to Qur connected in parallel with Qru.

2A and 2B, the operation of commutation by the switching operation of the bidirectional switch SWr has been described. However, as shown in FIG. 3A, a load L is connected between the connection point of SWr and SWs and the positive terminal of Er-s. The case where SWs switches can also be detected in the same manner as described above.
Further, as shown in FIG. 3B, even when the AC power supply Er-s is connected instead of the variable power supply Er-s, the operations of Qru and Qur are only reversed, and thus can be similarly detected. Further, the same applies to the case where SWs switches as shown in FIG. 3C. This concept holds true in the case of a three-phase AC power supply, and it is therefore clear that it can be applied to the matrix converter shown in FIG. 9B.

FIG. 4A shows an embodiment of the present invention. Hereinafter, differences from FIG. 1 will be mainly described.
As shown in FIG. 4A, the output voltage Vs of the determination circuit IGC is input to GDUf, and the inverted signal of Vs is input to GDUr. Vs input to each GDUf and GDUr is input to the OR circuit OR together with the ON / OFF signal from the control device via the photocoupler PC, and input to the amplifier As.

FIG. 4B is a waveform diagram for explaining the operation of FIG. 4A. This is the case of the configuration shown in FIG. 2A.
In FIG. 4B, the gate charge Qg is superimposed on the gate current of Qru by discharging the feedback current. Therefore, since the integrated value of each gate current is Q = ∫idt,
Qg (Qru) <Qg (Qur)
After time t3, the output Vs of the comparator Cmp becomes negative via the sample hold circuit S / H. Therefore, the output voltage Vs of the determination circuit IGC is obtained by inputting mutually inverted signals to GDUf and GDUr, insulated by the photocoupler PC, and then ORed by the OR circuit OR.

  Since Qru and Qur are supplied with an off signal after time t3, the gate voltage of Qur is turned on, in this case, when the output of the determination circuit IGC becomes negative. Since no reverse voltage is applied to Qur, no current flows, and since the gate voltage is turned on at the time of reverse voltage, the leakage current Ireak is reduced from the description of FIG. Reduced. The circuit shown in FIG. 4A is obviously applicable to the cases of FIGS. 3A to 3C as in FIG. 2A. Therefore, it is needless to say that the circuit can be applied to the matrix converter of FIG. 9B.

FIG. 5 shows another embodiment of the present invention. As shown in the figure, it can be said that the gate drive circuits GDUf and GDUr have the function of the determination circuit IGC.
In FIG. 5A, the output signals of the current detectors CTf and CTr that detect the gate currents of Qru and Qur are input to the gate drive circuits GDUf and GDUr of the reverse blocking IGBTs connected in antiparallel to each other. Here, since the current detectors CTf and CTr are electrically insulated, they can be input to the gate drive circuits GDUf and GDUr connected in antiparallel.

  FIG. 5A shows only the gate drive circuit GDUf in detail. The gate current detection signals of Qru and Qur are input to this, and the comparator Cmp is connected via the integrator I and the sample hold circuit S / H. To give. Similar to FIGS. 4A and 4B, when it is detected from the output Vs of the comparator Cmp that Qru is turned off, a reverse voltage is applied to Qur. Qur gate voltage is turned on. Since a reverse voltage is applied to Qur, the load current does not flow, and the leakage current Ireak decreases from the leakage current characteristic of FIG. The above operation is the same for GDUr.

Further, as shown in FIG. 5C, the potential difference Er-s between Vr and Vs becomes small after time t0 in period III. Therefore, since VCE becomes small, for example, the charge amount Qg detected from the gate current at the turn-off time of Qru also becomes small according to the characteristics of FIG. 8A, so the output voltage Vs of the comparator Cmp becomes small. As a result, the input of the OR circuit OR does not reach the H (high) level threshold value, and thus becomes the L (low) level. Therefore, the gate of the reverse voltage is not turned on immediately before the transition from the period III to IV. However, since the applied reverse voltage is small from the characteristic of FIG. 5B, the leakage current Ireak is also small and does not contribute to the efficiency reduction. In FIG. 5A, the determination circuit is provided in the gate drive circuit. However, since the output of the current detector is insulated from the main circuit, it is taken into the control device as shown in FIG. 6A. On / off may be determined according to the result of the arithmetic unit.

Configuration diagram showing the principle of the present invention Circuit diagram showing an application example of FIG. Waveform diagram explaining the operation of FIG. 2A Circuit diagram showing a first modification of FIG. 2A Circuit diagram showing a second modification of FIG. 2A Circuit diagram showing a third modification of FIG. 2A Circuit diagram showing an embodiment of the present invention Waveform diagram illustrating the operation of FIG. 4A Explanatory drawing explaining another embodiment of this invention Explanatory drawing explaining other embodiment of this invention Explanatory drawing which shows IGBT and its drive circuit example Explanatory drawing explaining the gate charge of IGBT Circuit diagram showing a typical converter example Illustration of bidirectional switch Reverse leakage IGBT leakage current characteristics explanatory diagram Circuit diagram showing a general example of a power converter Transition diagram for explaining the operation of FIG.

Explanation of symbols

Qru, Qur, Qus, Qsu ... IGBT (insulated gate bipolar transistor), CTf, CTr ... current detector, GDUf, GDUr ... gate drive circuit, IGC ... determination circuit, I ... integration circuit, S / H ... sample hold circuit, L: load, Er-s: variable power supply, Cmp: comparator, PC: photocoupler, As: amplifier, OR: OR circuit.

Claims (4)

The forward voltage applied between the collector and the emitter is controlled by applying a forward voltage or a reverse voltage from the gate drive circuit to the gate terminal, and the reverse voltage applied between the collector and the emitter is blocked. In a power conversion device composed of bidirectional switches in which reverse blocking semiconductor elements having functions are connected in antiparallel to each other,
Power conversion comprising: current detection means for individually detecting currents flowing through the gate terminals of the reverse blocking semiconductor elements connected in antiparallel to each other; and comparison means for comparing the detected current values apparatus.   The power converter according to claim 1, wherein on / off of the reverse blocking semiconductor element is determined according to a comparison result by the comparison unit.   The output of the current detection means is input to a gate drive circuit that constitutes the bidirectional switch and is provided for the reverse blocking semiconductor element, and the comparison means is provided in the gate drive circuit. The power converter according to claim 1, wherein the current values are compared. 2. The power converter according to claim 1, wherein all the outputs of the current detection means are taken into a control device, and ON / OFF of the reverse blocking semiconductor element is determined according to a calculation result by the control device.

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