JP2010233306A - Power conversion apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To reduce the size, weight, and cost of an auxiliary resonant commutation circuit provided in an inverter. <P>SOLUTION: A power conversion apparatus 1 converts the power of a DC power supply 2 into three-phase alternating current and supplies it to a motor 3. The IGBTs S1 to S6 of main switch elements comprise the upper and lower arms of three phases of an inverter. Capacitors Cr1, Cr2 divide the voltage of the DC power supply 2. One end of a coil Lr shared between three phases is connected to a voltage dividing point Er. IGBTs Sr1 and Sr2, Sr3 and Sr4, and Sr5 and Sr6 as auxiliary switch elements constitute bidirectional switches in pairs. The three-phase bidirectional switches are connected to the other end of the coil Lr and the three-phase output points of the inverter, respectively. When it is determined that multiple phase currents pass through the coil Lr, a controller 4 controls the IGBTs Sr1 to Sr6 so that a current in at least one phase is smaller than a preset magnitude. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a power converter that converts DC power into AC power by switching, and more particularly to a power converter that includes an auxiliary circuit that reduces loss of a main switch element.

  In order to reduce the loss of the main switch element of the inverter, a technique for performing soft switching using an auxiliary resonant commutation circuit is known. This auxiliary resonant commutation circuit is provided for each phase of the inverter, and has a configuration in which a capacitor is connected in parallel to a series connection circuit of a reactor and an auxiliary switch element. The DC power supply voltage is divided by two series capacitors, and the auxiliary resonant commutation circuit is connected from this voltage dividing point to the connection point of the upper and lower arms of each phase. Then, the auxiliary switch element corresponding to the arm to be switched is turned on to resonate the reactor and the capacitor, thereby realizing soft switching of the main switch element (for example, Patent Document 1).

JP 2000-32775 A

  However, since the conventional auxiliary resonant commutation circuit is provided independently for each phase, in the case of a three-phase inverter, three reactors and three capacitors are required, which increases the size and cost of the inverter. There was a problem of being connected.

  In order to solve the above problems, the present invention provides a power converter, two capacitors that divide the voltage of a DC power supply, one coil having one end connected to a voltage dividing point by the two capacitors, A plurality of auxiliary switch elements that connect between the other end and an output point of each phase of the polyphase alternating current, and when it is determined that a plurality of phase currents flow through the coil, a current flowing through at least one phase is previously The plurality of auxiliary switch elements are controlled to be smaller than a set size.

  According to the present invention, since only one coil for soft-switching the main switch circuit of the power converter is required, there is an effect that the power converter can be reduced in size and cost can be reduced.

It is a system configuration figure showing the composition of the embodiment of the power converter concerning the present invention. It is a time chart which shows the basic operation | movement of soft switching when the phase current in embodiment is positive (motor current Iu> 0). It is a time chart which shows the basic operation | movement of soft switching when the phase current in embodiment is negative (motor current Iu <0). It is a time chart which shows the example (when voltage command value: U phase> V phase> W phase) of the three-phase PWM drive signal for one control cycle. It is a time chart which shows a three-phase sine wave voltage command. It is a time chart explaining how the three-phase auxiliary current flows (Ir1> 0, Ir2> 0, Ir3 <0). It is a time chart which shows avoidance control in case the operation time of auxiliary current Ir1, Ir2 overlaps. It is a flowchart explaining auxiliary switch control in the power converter of an embodiment. It is a detailed flowchart of the collision avoidance process which suppresses the auxiliary current of the phase with a smaller load current absolute value at the time of the collision of the auxiliary current of two phases. It is a detailed flowchart of the collision avoidance process which suppresses the auxiliary current of the phase with a smaller voltage command value at the time of the collision of the auxiliary current of two phases. It is a detailed flowchart of the collision avoidance process which adjusts the auxiliary current of the phase with a smaller load current absolute value at the time of the collision of the auxiliary current of two phases. It is a detailed flowchart of the collision avoidance process which adjusts the auxiliary current of the phase with a smaller voltage command value at the time of the collision of the auxiliary current of two phases. It is a detailed flowchart of the collision avoidance process which suppresses the auxiliary current of one phase by overlap time at the time of collision of the auxiliary current of two phases. It is a detailed flowchart of the collision avoidance process which adjusts the auxiliary current of one phase by the overlap time when the auxiliary current of two phases collides.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. FIG. 1 is a configuration diagram of a power conversion system for explaining an embodiment of a power conversion device according to the present invention. In the present embodiment, the power conversion device converts direct current into three-phase alternating current, but the alternating current to be converted is not limited to three phases, and may be multiphase alternating current of four or more phases.

  In FIG. 1, the power conversion system includes a power conversion device 1 that is a three-phase inverter, a DC power supply 2 that supplies a DC voltage Ed to the power conversion device 1, and power that the power conversion device 1 has converted from DC to three-phase AC. And a controller 4 that controls the power conversion device 1.

  The power conversion device 1 includes main switch elements S1, S2, S3, S4, S5, and S6 using IGBTs, and diodes D1, D2, D3, D4, D5, and D6 connected in antiparallel to the main switch elements. It has. A pair of main switch elements connected in series, S1 and S2, S3 and S4, and S5 and S6 constitute an upper arm and a lower arm of each phase of the inverter, respectively. That is, the emitter of the main switch element S1 and the collector of the main switch element S2 are connected, and this connection point becomes the output point of the three-phase AC U-phase, and the U-phase of the motor 3 is connected. Similarly, the emitter of the main switch element S3 and the collector of the main switch element S4 are connected, and this connection point becomes the output point of the three-phase AC V-phase, and the V-phase of the motor 3 is connected. Similarly, the emitter of the main switch element S5 and the collector of the main switch element S6 are connected, and this connection point becomes the output point of the three-phase AC W phase, and the W phase of the motor 3 is connected.

  The collectors of the main switch elements S1, S3, and S5 are connected to the positive electrode of the DC power supply 2, and the emitters of the main switch elements S2, S4, and S6 are connected to the negative electrode of the DC power supply 2. Each gate of the main switch elements S1 to S6 is driven by a control signal output from the controller 4.

  The controller 4 includes load currents Iu, Iv, and Iw flowing through the motor 3 detected by a current sensor (not shown) (referred to as load current IL together with Iu, Iv, and Iw) and a motor detected by a rotation sensor (not shown). 3 generates a control signal for PMW control of each main switch element S1 to S6 based on the rotational position of 3 and a voltage command value given from a host device (not shown), and outputs it to the gate of each main switch element S1 to S6 To do.

  In FIG. 1, capacitors Cr1 and Cr2 using electrolytic capacitors, a coil Lr, and auxiliary switch elements Sr1 to Sr6 using IGBTs are provided as auxiliary circuits for performing soft switching of the main switch elements S1 to S6. It has been.

  Capacitors Cr1 and Cr2 have the same capacitance, and both ends of the capacitors Cr1 and Cr2 connected in series are connected to the positive electrode and the negative electrode of the DC power supply 2, and the DC voltage Ed of the DC power supply 2 is divided. The voltage at this voltage dividing point is Er. The auxiliary switch elements Sr1, Sr2, Sr3, Sr4, Sr5, and Sr6, each incorporating a diode, are connected in series in opposite directions to form a bidirectional switch circuit. One end of the coil Lr is connected to a voltage dividing point Er of the capacitors Cr1 and Cr2, and the other end of the coil Lr is connected to one end of three bidirectional switches composed of auxiliary switch elements. The other ends of the three bidirectional switch circuits are connected to the output points of the respective phases of the inverter. With the above connection, in the present invention, one coil Lr is shared by a three-phase auxiliary circuit.

  The controller 4 generates a control signal for controlling on / off of each of the auxiliary switch elements Sr1 to Sr6 and outputs the control signal to the gate of each of the auxiliary switch elements Sr1 to Sr6.

  Although not particularly limited, in the present embodiment, the controller 4 is composed of a microprocessor including an arithmetic processing unit CPU, a program ROM, a working RAM, and an input / output interface. The control function of the controller 4 is realized by the CPU executing a program stored in the ROM.

  Here, the auxiliary current flowing through the bidirectional switch composed of the auxiliary switch elements Sr1 and Sr2 is Ir1, the auxiliary current flowing through the bidirectional switch composed of the auxiliary switch elements Sr3 and Sr4 is Ir2, and the bidirectional switch composed of the auxiliary switch elements Sr5 and Sr6. The auxiliary current that flows through Ir is assumed to be Ir3. The direction shown in FIG. 1 is defined as positive for the polarities of the load current (Iu, Iv, Iw) and the auxiliary currents (Ir1, Ir2, Ir3).

  2 and 3 are time charts showing the basic operation of the soft switching control by the auxiliary circuit for one phase taking the U phase as an example. The time from when the main switch element S1 is turned on to the on state is Tr, and the time from when the main switch element S1 is turned on to when the auxiliary switch element is off is Tf, and the auxiliary switch element is on. Is Tr + Tf.

  That is, during the dead time (Td) of the complementary PWM signal of the upper and lower arms composed of the main switch elements S1 and S2, one of the auxiliary switch elements constituting the bidirectional switch of each phase depending on the polarity of the motor phase current. By turning on one of them, a current is passed through the coil Lr of the auxiliary circuit, and when the current corresponding to the phase current of the motor 3 is passed, the main switch element is turned on, and the main switch element at that time is zero. Current switching is realized. As the current of the main switch element increases after the main switch element is turned on, the current of the auxiliary circuit decreases, and the auxiliary switch element is turned off when the current of the auxiliary circuit is zero.

  When the load current IL (Iu, Iv, Iw) of each phase is positive, the auxiliary switch elements (Sr1, Sr3, Sr5) of each phase operate according to the timing of the main switch elements (S1, S3, S5).

The on-time of the auxiliary switch element is
Tr = IL × Lr / Er (1)
Tf = IL * Lr / (Ed-Er) (2)
It becomes.
Here, Tr is the time [s] in which the current change rate of Lr / Er changes from 0 [A] to IL [A] [T], and Tf is the current change rate of Lr / (Ed-Er) IL [A]. FIG. 2 shows the operation timing of the auxiliary switch element in accordance with the time [s] from 0 to 0 [A] and the timing of the U-phase main switch element S1.

  On the other hand, when the load current IL (Iu, Iv, Iw) is negative, the auxiliary switch elements (Sr2, Sr4, Sr6) of the respective phases operate at the timing of the main switch elements (S2, S4, S6).

The rise time Tr and fall time Tf required to turn on the auxiliary switch element are:
Tr = −IL × Lr / (Ed−Er) (3)
Tf = −IL × Lr / Er (4)
It becomes.
Tr is a time [s] that changes from 0 [A] to IL [A] at a current change rate of Lr / (Ed-Er), and Tf is a current change rate of Lr / Er from IL [A] to 0 [ FIG. 3 shows the operation timing of the auxiliary switch element in accordance with the time [s] that changes until A] and the timing of the U-phase main switch element S2.

Since the auxiliary switch element operates during the dead time (Td) of the complementary PWM signal of the main switch element, the rise time Tr and the fall time Tf of each auxiliary switch element are:
Tr <Td, Tf <Td (5)
Is established.

On the other hand, since the voltage Ed of the DC power supply 2 is divided by half by the capacitors Cr1 and Cr2, the voltage Er at the voltage dividing point is
Er = Ed / 2 (6)
And again
Tr = | IL | × Lr / (Ed / 2) (7)
Tf = Tr (8)
It becomes.

  The controller 4 controls the main switch elements S1 to S6 by a general triangular wave comparison PWM method. In this principle, a pulse train (PWM) is obtained by comparing a three-phase sine wave voltage command with a triangular wave as a carrier wave. The pulse width (time) of each phase PWM varies depending on the amplitude of the voltage command, but the output pulse width is uniquely determined from each command value, and the output time of the voltage vector can be obtained from a calculation formula ( For example, Relationship Between Space-Vector Modulation and Three-Phase Carrier-based PWM: A Comprehensive Analysis, Keliang Zhou & Danwei Wang, IEEE Trans.On Industrial Electronics Vol.49, No.1, pp.187-196, Feb.2002 .).

  FIG. 4 shows a three-phase PWM pulse output (for one cycle) when the three-phase voltage command is U phase> V phase> W phase. As the voltage command values of the two phases approach, the width of the generated pulse becomes closer, but when the voltage command values become equal, the pulse width becomes the same.

  In the motor drive by the three-phase sine wave voltage command value as shown in FIG. 5, the phase voltage is a voltage of any two phases from six times every 30 ° to 60 ° within one cycle of the sine wave. The values approach and become equal when 30 + 60 × n (n = 0, 1, 2, 3, 4, 5).

  Regarding the soft switching of the three-phase inverter, an auxiliary current is caused to flow in each phase in accordance with the ON timing of the driving PWM pulse of each phase.

FIG. 6 is a time chart showing how the auxiliary current flows (one PWM control cycle) in the case of Ir1> 0, Ir2> 0, and Ir3 <0. In the figure, the auxiliary currents (Ir1, Ir2, Ir3) of each phase can flow up to the phase currents (Iu, Iv, Iv) of the motor 3 in accordance with the PWM ON timing of the main switch elements S1, S3, S6. That is,
Ir1 (peak) = Iu, Ir2 (peak) = Iv, Ir3 (peak) = Iw (9)
Thus, the ON time of the auxiliary switch element is determined from the equations (1) to (4).

  However, when the voltage command values of the U phase and the V phase approach, the time (Ta) from when the main switch element S1 is turned on to when the main switch element S3 is turned on becomes shorter, or the auxiliary current Ir1 and the auxiliary current Ir2 When the peak value increases, Tf1 + Tr2> Ta, and the operation times of the auxiliary currents of the U and V2 phases overlap.

  FIG. 7 is a time chart for explaining the collision of the U-phase and V-phase auxiliary operations and the avoidance thereof. While the U-phase auxiliary current Ir1 accompanying the ON operation of the U-phase main switch element S1 is flowing, the ON timing of the V-phase main switch element S3 approaches and the V-phase auxiliary current Ir2 is reduced. When attempting to flow, the ON times of the auxiliary currents of the U-phase and V-phase two phases overlap. Therefore, during the PWM control period, a time collision of the auxiliary current for two-phase soft switching occurs.

  Further, as can be seen from FIG. 4, in order not to cause the collision of the two soft switching phases, the output time (Ta or Tb) of the voltage vector at that time is the on time Tf of the preceding soft switching phase and the subsequent time It is essential to make the soft switching phase longer than the ON time Tr of the soft switching phase.

  Therefore, the time alignment of each phase is calculated, and then the output times of the voltage vectors are compared, and the collision of the time when the auxiliary currents of the two phases flow is predicted.

  If the U-phase and V-phase current polarities match, the U-phase / V-phase time alignment Tuv is calculated.

Tuv = Tf1 + Tr2 (10)
If the current polarities of the V phase and the W phase match, the time alignment Tvw of the V phase and the W phase is calculated.

Tvw = Tf2 + Tr3 (11)
If the current polarities of the W phase and the U phase match, the W phase / U phase time alignment Twu is calculated.

Thu = Tr3 + Tr1 (12)
That is, if the equations (10), (11), and (12) become shorter than the output time of the voltage vector at that time, the on-time overlap of the auxiliary current in the corresponding phase occurs.

  There are the following three methods [1], [2] and [3] for avoiding the on-time collision of the auxiliary currents of the two phases.

  [1] In order not to turn on the auxiliary currents of the two phases at the same time, the auxiliary current of either phase is set to 0 and soft switching of the phases is not performed.

  In the present invention, since there is only one coil Lr in the auxiliary circuit, when an on-time collision between two phases of auxiliary current is predicted so that two phases of auxiliary current do not flow simultaneously through the coil Lr. The auxiliary current of any phase is set to 0 and control is performed so as not to perform soft switching of the phase. For example, when a collision between the U-phase and V-phase auxiliary currents is predicted, by setting either the U-phase auxiliary current Ir1 or the V-phase auxiliary current Ir2 to zero, the two-phase auxiliary currents are simultaneously turned on. Collisions are avoided.

  [2] In order not to turn on the auxiliary currents of the two phases at the same time, control is performed so as to shorten the on time of the auxiliary switch element of either phase.

  In the present invention, since there is only one coil Lr in the auxiliary circuit, in order to prevent a two-phase auxiliary current from flowing through the coil Lr at the same time, when a collision between two phases of auxiliary current on-time is predicted, Control is performed so as to shorten the ON time of the auxiliary switch element of any phase.

  As can be seen from the equations (1), (2), (3), and (4), the on-time (Tr, Tf) of the auxiliary switch element is proportional to the auxiliary current of the phase. Therefore, if the ON time of the auxiliary switch element of a certain phase is shortened, the auxiliary current flowing through the phase can be suppressed to be smaller than the motor current.

  As shown in FIG. 8, when a collision between the U-phase auxiliary current Ir1 and the V-phase auxiliary current Ir2 indicated by the alternate long and short dash line is predicted, the V-phase auxiliary current Ir2 is reduced as indicated by the solid line, By shortening the on-time of the phase auxiliary switch elements, collisions of the two-phase simultaneous on-time are avoided.

  [3] The avoidance logics of [1] and [2] are switched by comparing the time during which the ON times of the auxiliary currents of the two phases overlap with a predetermined time.

  In the present invention, since there is only one coil Lr in the auxiliary circuit, if the overlap of the on-time is shorter than the predetermined time so that two phases of auxiliary current do not flow through the coil Lr simultaneously, Reduce the auxiliary current. On the other hand, when the overlap time is longer than the predetermined time, the auxiliary current of any phase is set to 0 and control is performed so as not to perform soft switching of the phase.

  The on-time collision avoidance method described above suppresses or reduces the auxiliary current depending on the magnitude of the load current of each phase or the voltage command value of each phase when the collision of the auxiliary current is predicted as follows. The phase to be adjusted (hereinafter referred to as the adjustment phase) is determined.

  [3-A] For the two auxiliary current phases of the on-time collision, the soft switching of the phase having the smaller absolute value of the load current is not performed, or the auxiliary current on-time of the phase is shortened.

  [3-B] For the two auxiliary current phases of the on-time collision, the auxiliary current of the phase with the larger (or smaller) voltage command value is set to 0 and control is performed so that soft switching of the phase is not performed. Alternatively, control is performed so as to shorten the on-time of the auxiliary current of the phase.

  Next, an auxiliary circuit current control method performed by the controller 4 will be described with reference to the flowcharts of FIGS. FIG. 8 is a flowchart for explaining the on-time setting of the auxiliary circuit by the controller 4. First, in step (hereinafter, step is abbreviated as S) 10, the controller 4 reads a three-phase load current (Iu, Iv, Iw) flowing through the motor 3 measured by the current sensor. Next, in S12, the controller 4 sets the initial value of the auxiliary current to the measured value in S10. That is, the initial value Ir1 = Iu for the U phase, the initial value Ir2 = Iv for the V phase, and the initial value Ir3 = Iw for the W phase.

  Next, in S14, the controller 4 calculates the on-operation time (Tr, Tf) of the auxiliary switch element of each phase according to the equations (7) and (8). Next, in S16, the controller 4 outputs the PWM voltage vector output time of the main switch element, in other words, the time from turning on one main switch element to turning on another main switch element (Ta, Tb in FIG. 4). Equivalent). Next, in S18, the controller 4 calculates the on-time of the auxiliary switch element according to the equations (10), (11), and (12) in accordance with the output time of the voltage vector.

  Next, in S20, the controller 4 determines whether or not the output time (Ta, Tb) of the PWM voltage vector is shorter than the ON operation time (Tr + Tf) of the auxiliary switch element. If the output time of the PWM voltage vector is equal to or longer than the ON operation time of the auxiliary switch element in the determination of S20, the controller 4 completes the setting of the ON time of the auxiliary circuit without performing the collision avoidance process.

  If the output time of the PWM voltage vector is shorter than the ON operation time of the auxiliary switch element in the determination of S20, the controller 4 proceeds to S22, and after performing the collision avoidance process, the ON time setting of the auxiliary circuit is completed.

  9 to 14 are flowcharts of subroutines respectively showing detailed examples of the collision avoidance process in S22 of FIG.

  FIG. 9 is a flowchart showing the collision avoidance process-1. In this embodiment, when it is predicted that the operation times of the auxiliary switches of the two phases collide, the auxiliary current of one of the phases is set to zero by the load current at that time, and the soft switching of the corresponding phase is not performed. It is.

  First, in S32, the controller 4 selects the phase with the smaller absolute value of the load current at that time as the adjustment phase for the two phases that collide in time. Next, in S34, the controller 4 sets the on-time (Tr, Tf) of the auxiliary switch for the adjustment phase to zero, in other words, maintains the off state without turning on the auxiliary switch element for the adjustment phase. Return to routine.

  FIG. 10 is a flowchart showing the collision avoidance process-2. In this embodiment, when it is predicted that the operation times of the auxiliary switches of the two phases collide, the auxiliary current of the phase having the smaller voltage command value at that time is set to zero, and soft switching of the phase is not performed. It is.

  First, in S42, the controller 4 selects the phase having the smaller voltage command value at that time as the adjustment phase for the two phases that collide in time. Next, in S44, the controller 4 sets the on time (Tr, Tf) of the auxiliary switch for the adjustment phase to zero, in other words, maintains the off state without turning on the auxiliary switch element for the adjustment phase. Return to routine.

  FIG. 11 is a flowchart showing the collision avoidance process-3. In this embodiment, when the operation time of the auxiliary switch of the two phases is predicted to collide, the auxiliary current of the phase having the smaller absolute value of the load current at that time is reduced to avoid the collision of the two phases. It is embodiment to do.

First, in S52, the controller 4 selects the phase with the smaller absolute value of the load current (Iu, Iv, Iw) at that time as the adjustment phase for the two phases that collide in time. Next, in S54, the controller 4 shortens the ON time (Tr, Tf) of the auxiliary switch of the adjustment phase and adjusts the time alignment of the two phases to be shorter than the output time (Ta, Tb) of the voltage vector. Return to the main routine.

  FIG. 12 is a flowchart showing the collision avoidance process-4. In this embodiment, when it is predicted that the operation times of the auxiliary switches of the two phases collide, the auxiliary current of the phase with the smaller (or larger) voltage command value at that time is reduced, It is embodiment which avoids a collision. In this embodiment, as the phase of the three-phase alternating current advances, the phase with the smaller (or larger) voltage command value at that time is sequentially switched, so that soft switching can be performed equally for each phase.

  First, in S62, the controller 4 selects the phase with the smaller voltage command value at that time as the adjustment phase for the two phases that collide in time. Next, in S64, the controller 4 shortens the ON time (Tr, Tf) of the auxiliary switch for the adjustment phase, and adjusts the time alignment of the two phases to be shorter than the output time (Ta, Tb) of the voltage vector. Return to the main routine.

  FIG. 13 is a flowchart showing the collision avoidance process-5. In this embodiment, when it is predicted that the operation times of the auxiliary switches of the two phases collide, the auxiliary current is adjusted according to the load current and the overlap time at that time to avoid the collision of the two phases. .

  First, in S72, the controller 4 predicts the overlap time of the on-time of the auxiliary switch element by using the equations (10), (11), and (12) for the two phases that collide in time. Next, in S74, the controller 4 determines whether or not the overlapping time exceeds a predetermined time. If it is determined in S74 that the overlapping time exceeds the predetermined time, the collision avoidance process-1 in S30 shown in FIG. 9 is executed and the process returns. If it is determined in S74 that the overlap time does not exceed the predetermined time, the collision avoidance process-2 in S40 shown in FIG. 10 is executed and the process returns.

  FIG. 14 is a flowchart showing the collision avoidance process-6. In this embodiment, when it is predicted that the operation times of the auxiliary switches of the two phases collide, the auxiliary current is adjusted according to the load current and the overlap time at that time to avoid the collision of the two phases. .

  First, in S82, the controller 4 predicts the overlap time of the on-time of the auxiliary switch element by the equations (10), (11), and (12) for the two phases that collide in time. Next, in S84, the controller 4 determines whether or not the overlapping time exceeds a predetermined time. If it is determined in S74 that the overlapping time exceeds the predetermined time, the collision avoidance process-3 in S50 shown in FIG. 11 is executed and the process returns. If it is determined in S84 that the overlap time does not exceed the predetermined time, the collision avoidance process -4 in S60 shown in FIG. 12 is executed and the process returns.

  According to this embodiment described above, the power converter includes two capacitors that divide the voltage of the DC power supply, one coil having one end connected to a voltage dividing point by the two capacitors, and the other end of the coil. A plurality of auxiliary switch elements connected between the output points of each phase of the polyphase alternating current, and when it is determined that a plurality of phase currents flow in the coil, a current flowing in at least one phase is set in advance Since the plurality of auxiliary switch elements are controlled to be smaller than the size, the number of coils for soft-switching the main switch element is reduced from 3 to 1, thereby reducing the weight and volume of the power converter and its cost. There is an effect that can be done.

  Further, according to the present embodiment, when it is determined that the current of two phases flows through the coil, the auxiliary switch element is controlled so that the current of one phase does not flow through the coil. No interference with the coil.

  Further, according to the present embodiment, when it is determined that two phase currents flow through the coil, the auxiliary switch element is controlled so as to shorten the time during which one of the phase currents flows, so soft switching is performed as much as possible. There is an effect that can be.

  Further, according to the present embodiment, the effect of soft switching can be maximized by setting the phase for adjusting the current flowing through the coil to be the one with the smaller absolute value of the phase current at that time.

  Further, according to the present embodiment, the phase for adjusting the current flowing through the coil is set to the phase having the larger voltage command value at that time, so that the phase for current adjustment sequentially changes as the phase of the three-phase AC advances. In addition, there is an effect that the loss reduction effect of the main switch element by the soft switching is evenly distributed to each phase.

  Further, according to the present embodiment, the phase for adjusting the current flowing through the coil is set to the phase having the smaller voltage command value at that time, so that the phase for adjusting the current is sequentially changed as the phase of the three-phase AC advances. In addition, there is an effect that the loss reduction effect of the main switch element by the soft switching is evenly distributed to each phase.

DESCRIPTION OF SYMBOLS 1 Power converter 2 DC power supply 3 Motor 4 Controller (control means)
Cr1, Cr2 capacitor Lr coil S1-S6 IGBT (main switch element)
Sr1-Sr6 IGBT (auxiliary switch element)

Claims (6)

A power conversion device for converting a DC power source into polyphase AC,
A main switching circuit composed of a pair of main switch elements connected in series between both terminals of the DC power supply and having an interconnection point of the pair of main switch elements as an output point of each phase, Main switching means provided for each phase;
Two capacitors for dividing the voltage of the DC power supply;
One coil having one end connected to a voltage dividing point by the two capacitors;
A plurality of auxiliary switch elements connecting between the other end of the coil and the output point of each phase;
When it is determined that a plurality of phase currents flow in the coil, control means for controlling the plurality of auxiliary switch elements so that a current flowing in at least one phase is smaller than a preset magnitude;
A power conversion device comprising:   The said control means controls the said auxiliary | assistant switch element so that any one phase current may not flow into the said coil, when it is judged that two phase currents flow into the said coil. Power converter.   2. The control device according to claim 1, wherein when it is determined that two phase currents flow through the coil, the control unit controls the auxiliary switch element so as to shorten a time during which one of the phase currents flows. Power converter.   The power converter according to claim 2, wherein the one phase is a phase having a smaller absolute value of the phase current at that time.   4. The power conversion device according to claim 2, wherein the one phase is a phase having a larger voltage command value at that time. 5.   The power converter according to claim 2 or 3, wherein the one phase is a phase having a smaller voltage command value at that time.

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