JP6070258B2 - 3-level inverter snubber circuit - Google Patents

Description

  The present invention relates to a snubber circuit of a three-level inverter, and more particularly to a snubber of an A-NPC (Advanced-Neutral Point Clamped) type three-level inverter.

  In the three-level inverter, in addition to a three-level inverter of a system (NPC system) in which four switching elements typified by conventional IGBTs are connected in series, a DC power source positive electrode side “ Switching element connected between P and AC input / output unit “AC”, switching element connected between AC input / output unit “AC” and DC power source negative electrode side “N”, and DC power source neutral point “M” And a three-level inverter of a neutral point clamp method (hereinafter referred to as A-NPC method) using a switching element connected bidirectionally between the AC input / output unit “AC”.

  FIG. 8 shows a known snubber circuit in the A-NPC system three-level inverter described in Patent Document 2. In FIG. 8, DC voltage sources E1 and E2 are connected in series to form a DC power supply circuit, and a common connection point of the DC voltage sources E1 and E2 is a DC power supply neutral point M.

  Between the positive terminal P of the DC voltage source E1 and the negative terminal N of the DC voltage source E2, a main circuit switch positive side element Tr1 and a main circuit switch negative side element Tr4 are connected in series. A common connection point of the main circuit switch positive electrode side element Tr1 and the main circuit switch negative electrode side element Tr4 is an AC input / output terminal AC.

  Between the AC input / output terminal AC and the DC power supply neutral point M, there are a main circuit switch neutral point clamp element Tr2 (current direction AC → M) and a main circuit switch neutral point clamp element Tr3 (current direction M → AC). ) Are connected in series with the current control direction reversed.

  A snubber capacitor (for surge absorption) C1 and a snubber diode (for reverse current blocking) D1 are connected between the common connection point of the main circuit switch positive electrode side element Tr1 and the positive electrode terminal P and the DC power supply neutral point M. Connected in series. A snubber resistor R1 is connected between the common connection point of the snubber capacitor C1 and the snubber diode D1 and the DC power supply neutral point M.

  A snubber capacitor (for surge absorption) C4 and a snubber diode (for reverse current blocking) D4 are connected between the common connection point of the main circuit switch negative side element Tr4 and the negative end N and the DC power source neutral point M. Connected in series. A snubber resistor R4 is connected between the common connection point of the snubber capacitor C4 and the snubber diode D4 and the DC power source neutral point M.

  The elements Tr1 to Tr4 of the main circuit switch are constituted by, for example, IGBTs, and the positive side element Tr1, the negative side element Tr4, and the neutral point clamp elements Tr2 and Tr3 are combined into a snubber capacitor C1, C4, and a snubber diode. It is protected by a snubber circuit comprising D1, D4 and snubber resistors R1, R4.

  In this protection method using a snubber circuit, an IGBT module (single-phase or three-phase) containing a plurality of elements, which is applied in a 3-level inverter application with a short distance between switching elements and a small reactance component, is used as a bridge circuit, etc. This is a snubber circuit that is used on the premise of a rating with a relatively small capacity compared to an IGBT module composed of one switching element. For this reason, the large-capacity A-NPC type three-level inverter exceeds the limit of the rated capacity of the switching element, and there is a problem that an IGBT module containing a plurality of elements cannot be used.

  Further, when an IGBT module composed of a single large-capacity switching element is used as a bridge circuit, the distance between the IGBT elements is increased and the reactance component between the elements is increased. In the snubber circuit system that protects the main circuit switch positive electrode side element Tr1, the main circuit switch negative electrode side element Tr4, and the neutral point clamp elements Tr2 and Tr3 together, suppression of the surge voltage becomes insufficient.

  Therefore, for example, as shown in FIG. 9, it is necessary to divide the snubber circuit between the positive side element Tr1 and the negative side element Tr4 of the main circuit switch and the neutral point clamping elements Tr2 and Tr3.

  9, the same parts as those in FIG. 8 are denoted by the same reference numerals. In FIG. 9, a snubber capacitor C1 and a snubber diode D1 are connected in series between the common connection point of the main circuit switch positive electrode side element Tr1 and the positive electrode terminal P and the AC input / output terminal AC. A snubber resistor R1 is connected between the common connection point of the snubber capacitor C1 and the snubber diode D1 and the DC power supply neutral point M.

  A snubber capacitor C4 and a snubber diode D4 are connected in series between the common connection point of the main circuit switch negative electrode side element Tr4 and the negative electrode terminal N and the AC input / output terminal AC. A snubber resistor R4 is connected between the common connection point of the snubber capacitor C4 and the snubber diode D4 and the DC power source neutral point M.

  A series circuit of a snubber capacitor C2 and a snubber diode D2 and a series circuit of a snubber capacitor C3 and a snubber diode D3 are connected in parallel between both ends of the series circuit of the neutral point clamping elements Tr2 and Tr3. ing.

  A snubber resistor R2 is connected between the common connection point of the snubber capacitor C2 and the snubber diode D2 and the positive terminal P.

  A snubber resistor R3 is connected between the common connection point of the snubber capacitor C3 and the snubber diode D3 and the negative terminal N.

  In FIG. 9, a CRD snubber (C1, R1, D1) is provided for the purpose of suppressing a surge voltage applied between the collector and emitter of the positive side element Tr1 when the main circuit switch positive side element Tr1 is turned off. A CRD snubber (C4, R4, D4) is provided for the purpose of suppressing a surge voltage applied between the collector and the emitter of the negative electrode side element Tr4 when the circuit switch negative electrode side element Tr4 is turned off. A CRD snubber (C2, R2, D2) is provided for the purpose of suppressing a surge voltage applied between the collector and emitter of the neutral point clamp element Tr2, and when the neutral point clamp element Tr3 is turned off. CRD snubber (C3, R3, D3) for the purpose of suppressing the surge voltage applied between the collector and emitter of the neutral point clamp element Tr3 It is provided.

JP 56-121374 A JP 2010-252548 A

  In the circuit of FIG. 9, when one side of the main circuit switch positive electrode side element Tr1 or negative electrode side element Tr4 between the positive electrode side terminal P and the negative electrode side terminal N is turned ON, the switching element on the opposite side to the ON switching element The total voltage of the voltage V1 [V] of the DC voltage source E1 between the side terminal P and the DC power supply neutral point M and the voltage V2 [V] of the DC voltage source E2 between the DC power supply neutral point M and the negative electrode side terminal N is Applied.

  At this time, if V1 [V] = V2 [V] = V [V], the voltage of 2V [V] is applied to the snubber capacitor of the switching element opposite to the switching element turned on with respect to the DC power supply neutral point M. Is charged. Thereafter, when the switching element on the opposite side is turned on by switching, a voltage of (V1 [V] + surge for the conductor reactor) is generated in the switching element, but the snubber capacitor is 2 V [V] as described above. Is charged to a voltage of. Taking the main circuit switch positive electrode side element Tr1 as an example, when this positive electrode side element Tr1 is turned on, the main circuit switch negative electrode side element Tr4 on the opposite side to the DC power supply neutral point M is supplied with a total voltage of 2V [V]. A voltage is applied. At this time, the snubber capacitor C4 is charged to 2V [V]. Thereafter, when the main circuit switch positive electrode side element Tr1 is turned ON → OFF and the negative electrode side element Tr4 is turned OFF, a voltage of (V [V] + surge) is applied to the main circuit switch negative electrode side element Tr4. C4 is charged to 2V [V], and the surge voltage of the main circuit switch negative side element Tr4 <the voltage of the snubber capacitor C4.

  For this reason, in the above example, the surge voltage of the main circuit switch negative side element Tr4 is not absorbed by the snubber capacitor C4, and the surge voltage cannot be suppressed. Electromagnetic noise is generated due to the surge voltage, which may adversely affect peripheral devices such as a control device. In addition, the rated voltage of the snubber capacitor in the snubber circuit needs to be at least 2E [V], which increases the cost.

  SUMMARY OF THE INVENTION The present invention solves the above-described problems, and an object of the present invention is to provide a snubber circuit for a three-level inverter that can suppress an increase in the voltage of the snubber capacitor and ensure the operation of absorbing the surge voltage of the snubber capacitor. is there.

  A snubber circuit for a three-level inverter according to claim 1 for solving the above-described problem is provided with a positive-side switching element connected between a positive electrode end of a DC power supply circuit having a power supply neutral point and an AC input / output terminal. , A negative-side switching element connected between the negative electrode end of the DC power supply circuit and the AC input / output end, and at least two series connected between the neutral point of the power source and the AC input / output end, opposite to each other A first snubber capacitor and a first snubber diode are connected in series between both ends of the neutral point clamping switching element that can be controlled in the withstand voltage direction, and the at least two neutral point clamping switching elements connected in series, A first snubber circuit configured by connecting a first snubber resistor between a common connection point of one snubber capacitor and a first snubber diode and a positive terminal of the DC power supply circuit; A second snubber capacitor and a second snubber diode are connected in series between both ends of the neutral point clamping switching element, and a common connection point of the second snubber capacitor and the second snubber diode and the DC power source. A second snubber circuit configured by connecting a second snubber resistor between the negative electrode terminals of the circuit, a common connection point of the positive electrode terminal and the positive electrode side switching element of the DC power supply circuit, and the AC input / output terminal A third snubber capacitor and a first switching means having reverse blocking characteristics are sequentially connected in series between the common connection point of the third snubber capacitor and the first switching means and the power supply neutral point. A third snubber circuit connected to a third snubber resistor, a common connection point of the negative end of the DC power supply circuit and the negative side switching element, and the intersection. A fourth snubber capacitor and a second switching means having reverse blocking characteristics are sequentially connected in series between the input and output terminals, and a common connection point of the fourth snubber capacitor and the second switching means and the power source And a fourth snubber circuit configured by connecting a fourth snubber resistor between the sex points.

  According to the above configuration, since the voltage of the snubber capacitor does not exceed the voltage of the switching element, the surge voltage of the switching element can be reliably absorbed by the snubber capacitor.

  Further, the snubber circuit of the three-level inverter according to claim 2 is characterized in that, in the first aspect, the on / off control of the positive side switching element and the neutral point clamping switching element which can be controlled in the one withstand voltage direction During this period, the neutral-point-clamping switching elements that are simultaneously controlled in a reverse relationship with each other and can be controlled in the other withstand voltage direction are on-controlled in the first period, and in the negative voltage side switching element and the other withstand voltage direction. On / off control of the neutral point clamping switching element that can be controlled is simultaneously controlled in a reverse relationship with each other in the second period following the first period, and can be controlled in the one withstand voltage direction. The switching element is on-controlled during the second period, and the first switching means is off-controlled during the second period and is on during the first period. The second switching means is off-controlled during the first period and is on-controlled during the second period, and the on / off switching of each of the first and second switching means is performed with respect to each other. The neutral-point-clamping switching element that can be controlled in the reverse withstand voltage direction is executed at the timing when both are ON-controlled.

  According to the above configuration, the switching of each of the first and second switching means is performed at the timing when both the neutral point clamping switching elements are on-controlled. An increase in voltage can be reliably suppressed, which makes it possible to reliably suppress an increase in voltage of the snubber capacitor, thereby further ensuring a surge absorbing operation of the snubber capacitor.

(1) According to the first and second aspects of the invention, since the voltage of the snubber capacitor does not exceed the voltage of the switching element, the surge voltage of the switching element can be reliably absorbed by the snubber capacitor. Thereby, generation of electromagnetic noise can be reduced and malfunction of peripheral devices can be prevented.
(2) According to the invention described in claim 2, it is possible to surely suppress the voltage increase of the snubber capacitor, and thereby it is possible to surely suppress the voltage increase of the snubber capacitor, and thereby the surge absorption of the snubber capacitor. Operation is more reliable.

1 is a circuit diagram of Embodiment 1 of the present invention. The circuit diagram showing the state at the time of switching of the upper side switch element in Example 1 of this invention. The circuit diagram showing the motion from the surge absorption of the snubber in Example 1 of this invention to regeneration. The circuit diagram showing the state of the electric current block in Example 1 of this invention. The circuit diagram showing the state at the time of switching of the lower side switch element in Example 1 of this invention. The time chart of the main circuit switch and subswitch in Example 1 of this invention. The circuit diagram of Example 2 of the present invention. The circuit diagram which shows an example of the conventional snubber circuit of an A-NPC system. The circuit diagram which shows the other example of the conventional snubber circuit of an A-NPC system.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings, but the present invention is not limited to the following embodiments. FIG. 1 is a circuit diagram of a snubber circuit according to the first embodiment of the present invention, and the same parts as those in FIG. 9 are denoted by the same reference numerals.

  1 differs from FIG. 9 in that a sub-switch S1 and a reverse blocking diode d1 are connected in series instead of the snubber diode D1 between the snubber capacitor C1 and the AC input / output terminal AC. Instead of the snubber diode D4, a sub switch S4 and a reverse blocking diode d4 are connected in series between C4 and the AC input / output terminal AC, and the other parts are the same as in FIG. .

  The sub-switches S1 and S4 may be composed of thyristors, transistors, IGBTs, etc. in addition to MOS-FETs.

  2 to 5 are circuit diagrams (the same circuit diagram as FIG. 1) for explaining the operation of the first embodiment, and FIG. 6 is a time chart. First, as shown in FIG. 2, the main circuit switch neutral point clamp element Tr3 is ON, and the main circuit switch positive side element Tr1 and the main circuit switch neutral point clamp element Tr2 are alternately switched (in FIG. During the period when the main circuit switch positive electrode side element Tr1 is switched: the first period), the sub switch S1 is turned on and the sub switch S4 is turned off.

  As a result, the snubber capacitor C1, the snubber resistor R1, and the reverse blocking diode d1 act as a CRD snubber, and the voltage surge of the main circuit switch positive side element Tr1 is absorbed.

  At this time, since the sub switch S4 is OFF, charging of the snubber capacitor C4 is prevented, and the total voltage of the DC voltage sources E1 and E2 is prevented from being applied to the snubber capacitor C4.

  Specifically, when the main circuit switch positive electrode side element Tr1 is turned OFF (at the OFF timing in the period when the main circuit switch positive electrode side element Tr1 in FIG. 2 is switched), as shown by the one-dot chain line in FIG. Is passed through the path of the snubber capacitor C1 → subswitch S1 → reverse blocking diode d1 → AC input / output terminal AC, the snubber capacitor C1 absorbs the surge voltage, and the voltage of the capacitor C1 is When the voltage exceeds E (V), the surge voltage absorbed by the snubber capacitor C1 is discharged via the snubber resistor R1 and regenerated by the DC voltage source E1, as indicated by a dotted line in FIG.

  Note that the discharge path by the parasitic antiparallel diode of the sub-switch S1 itself is blocked by the reverse blocking diode d1 as shown by a one-dot chain line in FIG. There is no discharge without passing through the resistor (snubber resistor R1).

  Further, when the main circuit switch positive electrode side element Tr1 is ON (at the ON timing in the switching period of the main circuit switch positive electrode side element Tr1 in FIG. 2), as shown by the dotted line in FIG. Therefore, the snubber capacitor C1 is not short-circuited via the parasitic antiparallel diode of the main circuit switch positive-side element Tr1 and the sub switch S1.

  Next, as shown in FIG. 5, the main circuit switch neutral point clamp element Tr2 is ON, and the main circuit switch negative side element Tr4 and the main circuit switch neutral point clamp element Tr3 are alternately switched (FIG. 5). In the period during which the main circuit switch negative side element Tr4 is switched: the second period), the sub switch S1 is turned off and the sub switch S4 is turned on.

  As a result, the snubber capacitor C4, the snubber resistor R4, and the reverse blocking diode d4 act as a CRD snubber as in the case of FIGS. 2 to 4, and the voltage surge of the main circuit switch positive electrode side element Tr4 is absorbed.

  At this time, since the sub switch S1 is OFF, charging of the snubber capacitor C1 is prevented, and the total voltage of the DC voltage sources E1 and E2 is prevented from being applied to the snubber capacitor C1.

  The ON / OFF switching of each of the sub switches S1 and S4 is performed by switching between the switching period of the main circuit switch positive side element Tr1 and the switching period of the main circuit switch negative side element Tr4, and the main circuit switch. The neutral point clamp elements Tr2 and Tr3 are both executed at the ON timing.

  That is, the period in which the main circuit switch positive electrode side element Tr1 in FIG. 2 is switched → the period in which the main circuit switch negative electrode side element Tr4 in FIG. 5 is switched (or the period in which the main circuit switch negative electrode side element Tr4 is switching). → At the time of switching during the period when the main circuit switch positive electrode side element Tr1 is switched), at the time Tx when both the main circuit switch neutral point clamping elements Tr2 and Tr3 are turned on.

  As a result, the voltage increase of the snubber capacitors C1 and C4 can be reliably suppressed, and the surge absorbing operation is ensured.

  When the snubber capacitors C1 and C4 are precharged, the snubber resistors R1 and R4 function as inrush current preventing resistors, thereby preventing an overcurrent from flowing through the capacitors C1 and C4.

  FIG. 7 shows a circuit diagram of Embodiment 2 of the present invention. 7 differs from FIG. 1 in that a reverse blocking subswitch (for example, a reverse blocking IGBT) S′1 is connected instead of the subswitch S1 and the reverse blocking diode d1, and the subswitch S4 and the reverse blocking diode d4 are replaced. In addition, a reverse blocking sub-switch (for example, reverse blocking IGBT) S′4 is connected, and the other parts are the same as in FIG.

  In the second embodiment, the reverse blocking sub-switches S′1 and S′4 themselves have the reverse blocking function of the d1 and d4 even without the reverse blocking diodes d1 and d4. Snubber operation and control can be performed based on the same principle as in FIG.

  As described above, according to the first and second embodiments, since the voltage of the snubber capacitor (C1, C4) does not exceed the voltage of the switching element (Tr1, Tr4), the surge voltage is absorbed by the snubber circuit at the time of switching. Operation is reliable (the snubber circuit function is enabled), electromagnetic noise generation can be reduced, and peripheral equipment malfunctions can be prevented.

  In addition, the voltage of the snubber capacitor can be lowered (the voltage of 2E [V] was required, but it can be reduced to the surge by E [V] + conductor reactor), and the snubber capacitor can be reduced in size and cost. Is possible.

E1, E2 ... DC voltage source C1-C4 ... Snubber capacitor D1-D4 ... Snubber diode d1, d4 ... Reverse blocking diode R1-R4 ... Snubber resistance Tr1 ... Main circuit switch positive side element Tr2, Tr3 ... Main circuit switch Neutral point clamp element Tr4 ... Main circuit switch negative side element S1, S4 ... Sub switch S'1, S'4 ... Reverse blocking type sub switch

Claims (2)

A positive-side switching element connected between the positive electrode end of the DC power supply circuit having a power supply neutral point and the AC input / output end;
A negative-side switching element connected between the negative electrode end of the DC power supply circuit and the AC input / output terminal;
A neutral point clamping switching element connected in series between at least two power supply neutral points and the AC input / output end, and capable of controlling in a reverse withstand voltage direction;
A first snubber capacitor and a first snubber diode are connected in series between both ends of the at least two series-connected neutral point clamping switching elements, and a common connection point of the first snubber capacitor and the first snubber diode. And a first snubber circuit configured by connecting a first snubber resistor between the positive end of the DC power supply circuit,
A second snubber capacitor and a second snubber diode are connected in series between both ends of the neutral point clamping switching element, and a common connection point of the second snubber capacitor and the second snubber diode is connected to the DC power supply circuit. A second snubber circuit configured by connecting a second snubber resistor between negative electrode ends;
A third snubber capacitor and a first switching means having reverse blocking characteristics are sequentially connected in series between the common connection point of the positive electrode end and the positive electrode side switching element of the DC power supply circuit and the AC input / output terminal, A third snubber circuit configured by connecting a third snubber resistor between a common connection point of the third snubber capacitor and the first switching means and the power supply neutral point;
A fourth snubber capacitor and a second switching means having reverse blocking characteristics are sequentially connected in series between the common connection point of the negative electrode end and negative electrode side switching element of the DC power supply circuit and the AC input / output terminal, A fourth snubber circuit configured by connecting a fourth snubber resistor between a common connection point of the fourth snubber capacitor and the second switching means and the power supply neutral point;
A three-level inverter snubber circuit comprising: On-off control of the positive-side switching element and the neutral point clamping switching element that can be controlled in the one withstand voltage direction is simultaneously controlled in a reverse relationship with each other in the first period, and can be controlled in the other withstand voltage direction. The neutral point clamping switching element is ON-controlled during the first period,
On-off control of the negative-point side switching element and the neutral point clamping switching element that can be controlled in the other withstand voltage direction is simultaneously controlled in a reverse relationship with each other in a second period following the first period, The neutral point clamping switching element that can be controlled in one withstand voltage direction is ON-controlled in the second period,
The first switching means is off-controlled during the second period and is on-controlled during the first period, and the second switching means is off-controlled during the first period and on-control during the second period And
The on / off switching of each of the first and second switching means is performed at a timing when both of the neutral point clamping switching elements that can be controlled in the reverse withstand voltage directions are on-controlled. The snubber circuit of the three-level inverter according to claim 1.

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