JP2022184401A - Electric power conversion system - Google Patents

Abstract

To provide an electric power conversion system capable of suppressing switching loss thereof using Vienna rectifier.SOLUTION: An electric power conversion system 100 includes: inductors 102r to 102t connected with a three-phase system 101; a three-phase diode bridge 103 connected with a subsequent stage of each of the inductors; capacitors 104, 105 connected in series between two terminals on an output side of the three-phase diode bridge; connection points between each of the inductors and the three-phase diode bridge; a plurality of bidirectional switches 106r to 106t connected between connection midpoints M of the capacitors 104, 105; and a controller 110 for controlling switching of the plurality of bidirectional switches. The controller includes an on-fixed mode for controlling switching of the bidirectional switches to fix the bidirectional switch of a phase where an absolute value of an input voltage is maximum of respective phases of three-phase AC voltage to be under an on-state in all or a part of periods where the absolute value is maximum.SELECTED DRAWING: Figure 1

Description

TECHNICAL FIELD The present invention relates to a power converter, and more particularly to a power converter using a Vienna rectifier.

A three-phase PFC (Power Factor Correction) converter having a power factor improvement function has been proposed as a rectifier circuit that receives power from a three-phase system and converts it to DC voltage (Patent Document 1). In Patent Document 1, a switch is provided between each phase input (each terminal on the three-phase system side) of the three-phase diode bridge and the connection point of two capacitors connected in series between the terminals of the DC section. It is a circuit system. This circuit scheme is called a Vienna rectifier.

In the Vienna rectifier, by high-speed switching of each phase switch with PWM (Pulse Width Modulation), the current in each phase of the three-phase system can be controlled to a sine wave similar to the voltage, and the power factor can be improved.

Japanese Patent No. 5167884

However, in the Vienna rectifier, as described above, the switches of each phase are switched at high speed by PWM. As a result, switching loss occurs and power conversion efficiency decreases.

Under these circumstances, it is desired to provide a technique for reducing switching loss in a power converter using a Vienna rectifier.

An example of a technique for reducing switching loss in a power conversion device using a Vienna rectifier is described in Japanese Unexamined Patent Application Publication No. 2004-343975, which is a patent document. are different.

A brief outline of typical inventions disclosed in the present application is as follows.

A power conversion device according to a representative embodiment of the present invention is a power conversion device that converts a three-phase AC voltage into a DC voltage, and is connected to each phase terminal to which the three-phase AC voltage is input. a plurality of connected inductors, a three-phase diode bridge connected after the plurality of inductors, and a first capacitor and a second capacitor connected in series between two terminals on the output side of the three-phase diode bridge , respectively, for each of said phases, a first connection point being a connection point between said inductor and said three-phase diode bridge, and a second connection point being a connection point between said first capacitor and said second capacitor. and a controller for controlling switching of the plurality of bidirectional switches, the controller controlling the absolute value of the input voltage among the phases of the three-phase AC voltage. The operation mode is a fixed ON mode in which the switching is controlled so that the bidirectional switch of the phase having the maximum value is fixed to the ON state during all or part of the period in which the absolute value of the input voltage is the maximum. have.

Among the inventions disclosed in the present application, the effects obtained by representative ones are briefly described below.

According to a representative embodiment of the present invention, switching loss can be reduced in a power converter using a Vienna rectifier.

1 is a diagram showing an example of a circuit configuration of a power conversion device according to Embodiment 1; FIG. 4A and 4B are diagrams showing examples of various waveforms in the power converter according to the first embodiment; FIG. 4 is a diagram showing an example of a control block of a controller according to Embodiment 1; FIG. FIG. 4 is a diagram showing an example of a control block showing the operation of a correction voltage computing unit; FIG. 9 is a diagram showing an example of the relationship between the input voltage and the duty ratio fixed value in the power conversion device according to Embodiment 2; FIG. 10 is a diagram showing an example of the relationship between input voltage and efficiency in Embodiment 2; FIG. 12 is a diagram showing an example of the relationship between the input voltage and the duty ratio fixed value in the power conversion device according to Embodiment 3; FIG. 12 is a diagram showing an example of the relationship between the input voltage and the duty ratio fixed value in the power conversion device according to Embodiment 4; It is an example of the circuit structure of the power converter device which concerns on Embodiment 5. FIG.

Embodiments of the present invention will now be described. Each embodiment described below is an example for realizing the present invention, and does not limit the technical scope of the present invention.

Further, in each of the following embodiments, constituent elements having the same function are denoted by the same reference numerals, and repeated description thereof will be omitted unless particularly necessary.

(Embodiment 1)
A power converter according to Embodiment 1 will be described. This power converter is a device that converts a three-phase AC voltage into a DC voltage using a Vienna rectifier. The Vienna rectifier can reduce the withstand voltage of the switches to approximately 1/2 compared to a three-phase PWM converter using six switches. For example, a Vienna rectifier that receives power from a 3-phase 400V system can use 600V to 650V withstand voltage switches, which is more cost effective than a 3-phase PWM converter that requires 1.2 kV withstand voltage switches. In the power conversion device according to the first embodiment, while using the Vienna rectifier, as the operation mode of the controller that controls the switches, the bidirectional switch of the phase with the maximum absolute value of the phase voltage is fixed to the ON state. It is characterized by having a mode.

<Device configuration>
FIG. 1 is a diagram illustrating an example of a circuit configuration of a power converter according to Embodiment 1. FIG. As shown in FIG. 1, the power converter 100 includes inductors 102r, 102s, 102t, a three-phase diode bridge 103, capacitors 104, 105, and bidirectional switches 106r, 106s, 106t. A bidirectional switch means a switch through which current flows in both directions, and is, for example, a switching element such as a transistor.

Although the voltage of the three-phase system 101 differs depending on the country or region, it is generally between three-phase 200V and 400V.

The inductors 102r, 102s, and 102t are connected to respective phase terminals to which the three-phase AC voltage from the three-phase system 101 is input. The inductors 102r, 102s, and 102t are configured by, for example, coil elements.

The three-phase diode bridge 103 is connected after the inductors 102r, 102s and 102t.

Capacitors 104 and 105 are connected in series between two terminals on the output side of the three-phase diode bridge 103, that is, between terminals P and N of the DC output section.

The bidirectional switch 106r connects the connection point (first connection point) between the inductor 102r and the three-phase diode bridge 103 and the connection point (second connection point) M between the capacitors 104 and 105 for the r-phase. connected between Similarly, the bidirectional switch 106s is connected between the connection point between the inductor 102s and the three-phase diode bridge 103 and the connection point M of the capacitor for the s-phase. The bidirectional switch 106t is connected between the connection point between the inductor 102t and the three-phase diode bridge 103 and the connection point M of the capacitor for the t-phase. In this embodiment, the bidirectional switch 106r is configured by direct connection of the MOSFETs 111 and 112. FIG. Similarly, bidirectional switch 106s is configured by direct connection of MOSFETs 113 and 114, and bidirectional switch 106t is configured by direct connection of MOSFETs 115 and .

Further, as shown in FIG. 1, the power conversion device 100 includes voltage sensors 107r and 107s, current sensors 108r and 108s, a voltage sensor 109, and a controller 110. As shown in FIG.

The voltage sensor 107r is a sensor that detects the r-phase voltage Vr. The voltage sensor 107s is a sensor that detects the s-phase voltage Vs.

The current sensor 108r is a sensor that detects the r-phase current Ir. The current sensor 108s is a sensor that detects the s-phase current Is.

A voltage sensor 109 is a sensor that detects the voltage of the DC output section.

Each of these sensors is connected to controller 110 . The current sensor is composed of, for example, a sensor using a shunt resistor and an insulated amplifier, or a magnetic sensor such as a current sensor with a core or a coreless current sensor. Also, the voltage sensor is configured by, for example, one using a resistive voltage divider and an isolation amplifier, one using a capacitor voltage divider and an isolation amplifier, one using a highly sensitive non-contact current sensor and a series resistor, or the like.

The controller 110 controls switching of the bidirectional switches 106r, 106s, and 106t based on the detection values detected by each sensor. The controller 110 is configured by, for example, an integrated circuit, a programmable semiconductor chip, a microcomputer chip, or a circuit using discrete semiconductors. Examples of integrated circuits include ICs (Integrated Circuits) and LSIs (Large Scale Integrations). Examples of programmable semiconductor chips include PLDs (Programmable Logic Devices) and FPGAs (Field Programmable Gate Arrays).

The power conversion device 100 receives three-phase AC power from a three-phase system 101, converts it into DC power by a three-phase diode bridge 103 and bidirectional switches 106r, 106s, and 106t of each phase, and outputs it to terminals P and P of a DC output section. It is smoothed by capacitors 104 and 105 connected to N. Arbitrary loads such as an inverter and a DC-DC converter (not shown) are connected after the capacitors 104 and 105, and power is sent to these loads.

Controller 110 receives an externally input DC voltage command value (not shown), r-phase and s-phase voltages detected by voltage sensors 107r and 107s, and r- and s-phase voltages detected by current sensors 108r and 108s. The s-phase current and the DC voltage detected by the voltage sensor 109 are input. The controller 110 controls the switching cycle of the bidirectional switches 106r, 106s, and 106t based on the DC voltage command value and the three-phase phase voltages and phase currents including the t-phase calculated from the detected values input from the sensors. A ratio of ON time (duty ratio) is calculated. The duty ratio is calculated and controlled so that each phase current of the three-phase system 101 approaches a sine wave while controlling the DC voltage to be constant. As a result, the power factor of the power received from the three-phase system 101 approaches one.

In the present embodiment, phase voltages and phase currents are detected for two phases, the r phase and the s phase. .

In addition, although the DC voltage at the terminal P of the DC output section is detected in this embodiment, the present invention is not limited to this, and for example, the voltages of the capacitors 104 and 105 may be detected.

<Device operation>
The operation of the power converter 100 according to Embodiment 1 will be described below with reference to FIG.

FIG. 2 is a diagram showing examples of various waveforms in the power converter according to the first embodiment. FIG. 2 shows temporal changes in the input voltage command value Vd, the phase current I, the correction voltage Voffset, and the duty ratio D on the same time axis.

The input voltage command value Vd is the input voltage command value for the Vienna rectifier calculated by the controller 110 . The input voltage command value Vd corresponds to the target value of the input voltage of each phase in the subsequent stage of the inductor, that is, in the preceding stage of the three-phase diode bridge 103 . The input voltage command value Vd is composed of an r-phase input voltage command value Vdr, an s-phase input voltage command value Vds, and a t-phase input voltage command value Vdt. Each of these command values is a simple sine wave with a phase shift of 120°.

The phase current I is a general term for currents in each phase, and is composed of an r-phase current Ir, an s-phase current Is, and a t-phase current It. When this phase current I approaches the waveform of the phase voltage V, the power factor approaches 1 and the power factor is improved.

The correction voltage Voffset is a correction voltage to be added to the input voltage command value Vd, and is calculated by the controller. The details of the calculation method of the correction voltage Voffset will be described later.

The duty ratio D is a general term for duty ratios when the bidirectional switches of each phase are switched by PWM. The duty ratio is the ratio of the time during which the bidirectional switch is on to the switching cycle. The duty ratio D is composed of a duty ratio Dr in switching of the r-phase bidirectional switch 106r, a similar duty ratio Ds in the s-phase, and a similar duty ratio Dt in the t-phase.

Period A from time t1 to t2, period B from time t2 to t3, and period C from time t3 to t4 each correspond to a period of 60 degrees of the system phase.

<<Period A: t1 to t2>>
During the period A from time t1 to t2, the t-phase input voltage command value Vdt is negative and has the largest absolute value among the three phases. At this time, the switching control of the controller 110, which will be described later, adds the correction voltage Voffset to the input voltage command value Vdt, and the duty ratio Dt of the t-phase bidirectional switch 106t is fixed to 1, ie, the ON state. At the same time, the same correction voltage Voffset is added to the duty ratios Dr and Ds of the r-phase bidirectional switch 106r and the s-phase bidirectional switch 106s. The currents Ir, Is, It are controlled to be sinusoidal.

<<Period B: t2-t3>>
During period B from time t2 to t3, the absolute value of the s-phase input voltage command value Vds is the largest among the three phases. At this time, the correction voltage Voffset is calculated so as to fix the duty ratio Ds of the s-phase bidirectional switch 106s to one. The bidirectional switch 106t fixed in the ON state in the period A switches in the period B, and only the bidirectional switch 106s is fixed in the ON state. As in period A, also in period B, the three-phase currents Ir, Is, and It are controlled to be sinusoidal waves.

<<Period C: t3-t4>>
During period C from time t3 to time t4, the absolute value of the r-phase input voltage command value Vdr is the largest among the three phases. At this time, the correction voltage Voffset is calculated so as to fix the duty ratio Dr of the r-phase bidirectional switch 106r to one. The bidirectional switch 106s fixed in the ON state in the period B switches in the period C, and only the bidirectional switch 106r is fixed in the ON state. As in periods A and B, also in period C, the three-phase currents Ir, Is, and It are controlled to be sinusoidal waves.

As described above, period A to period C each correspond to the system phase of 60 degrees, and the bidirectional switch of each phase has a period during which switching is stopped twice in one cycle of the system. That is, the switching is stopped for a total of 120 degrees and is fixed in the ON state. By fixing to the ON state, a line voltage can be applied to the inductors 102r, 102s, and 102t without passing through the three-phase diode bridge 103, and the currents Ir, Is, and It can be controlled to sinusoidal waves. As described above, the configuration of the first embodiment can reduce the switching loss of the bidirectional switches 106r, 106s, and 106t, and improve the conversion efficiency.

《Controller operation》
The operation of the controller of the power converter according to Embodiment 1 will be described with reference to FIG. 3 . FIG. 3 is a diagram showing an example of control blocks of a controller according to the first embodiment.

As shown in FIG. 3, first, the difference Verr between the externally input DC voltage command value Vref and the DC voltage Vpn of the DC output section detected by the voltage sensor 109 is calculated.

A PI (Proportion-Integral) controller 121 is a controller often used for general feedback control. A current amplitude command value Iamp_ref is calculated. Note that the PI controller 121 corresponds to a voltage controller. Current amplitude command value Iamp_ref is multiplied by phase information sin of each phase voltage of three-phase system 101 to calculate current command value Iref for each phase.

The PI controller 122 calculates the input voltage command value Vd based on the difference Ierr between the current command value Iref and the phase current I detected by the current sensors 108r and 108s.

Based on the inputted input voltage command value Vd, the correction voltage calculator 123 generates a correction voltage Voffset that fixes the duty ratio of the bidirectional switch of the phase having the maximum absolute value among the input voltage command values Vd to 1. to calculate

The corrected voltage Voffset is added equally to the input voltage command value Vd of each phase to calculate the corrected input voltage command value Vd2 (collective term for Vdr2, Vds2, and Vdt2).

The duty calculator 124 calculates the duty ratio D (Dr, Ds, Dt) of each phase based on the input corrected input voltage command value Vd2, and generates gate signals for driving the bidirectional switches 106r, 106s, 106t. to generate

In this way, the power conversion device 100 has, as the operation mode of its controller 110, a fixed ON mode in which the bidirectional switch of the phase with the maximum absolute value of the phase voltage is fixed in the ON state.

With the operation described above, even if the current amplitude command value Iamp_ref fluctuates due to load fluctuation or the like, it is possible to always calculate an appropriate correction voltage Voffset.

The correction voltage Voffset can also be considered as a common voltage applied to the connection point M between the capacitors 104 and 105 .

Further, here, the current command value Iref for each phase is calculated from the current amplitude command value Iamp_ref using the phase information sin, but the present invention is not limited to this. may be calculated.

Also, here, a block or the like for controlling the voltage balance of the capacitors 104 and 105 is not incorporated, but such a block or the like may be added.

<<Operation of Correction Voltage Calculator>>
Here, the operation of correction voltage calculator 123 will be described with reference to FIG.

FIG. 4 is a diagram showing an example of a control block showing the operation of the correction voltage calculator. Absolute values of the input voltage command values Vdr, Vds, and Vdt of each phase are calculated by the absolute value calculator and input to the maximum voltage selector 131 .

In order to fix the bidirectional switch of the phase with the maximum absolute value of the phase voltage in the ON state, it is necessary to reduce the absolute value of the input voltage command value (one of Vdr, Vds, or Vdt) to be fixed. . For example, when the r-phase current Ir is flowing in the positive direction, when the r-phase bidirectional switch 106r is turned off, the r-phase input voltage becomes the potential of the DC output terminal P, and when it is turned on, the voltage at the connection point M of the capacitor potential (ideally zero at the same potential as the neutral point of the three-phase system 101). Here, since the potential of the terminal P>the potential of the connection point M, the duty ratio Dr of the bidirectional switch 106r approaches 1 as the input voltage command value Vdr decreases. When the r-phase current Ir flows in the negative direction, turning off the bidirectional switch 106r causes the r-phase input voltage to become the potential of the DC output terminal N, and similarly the absolute value of the input voltage command value Vdr. is closer to zero, the duty ratio Dr of the bidirectional switch 106r is closer to one.

Therefore, the maximum voltage selector 131 selects and outputs the maximum absolute value among the input voltage command values Vdr, Vds and Vdt, and the input voltage command values Vdr, Vds and Vdt are input to the polarity determiner 132 . The polarity determiner 132 determines whether the input voltage command value having the maximum absolute value is positive or negative, and outputs -1 if positive and +1 if negative. The output of the maximum voltage selector 131 and the output of the polarity determiner 132 are multiplied to calculate the correction voltage Voffset.

The calculated correction voltage Voffset is added equally to the input voltage command values Vdr, Vds, and Vdt of each phase to obtain corrected input voltage command values Vdr2, Vds2, and Vdt2. By doing so, for example, when the r-phase input voltage command value Vdr is positive and has the maximum absolute value, Vdr2=Vdr−Vdr=0, and the corrected input voltage command value Vdr2 becomes zero. and the r-phase bidirectional switch 106r can be fixed in the ON state. In addition, since the correction voltage Voffset is added equally to the other phases, the line voltage is not affected.

By the operation described above, it is possible to appropriately calculate the correction voltage Voffset to be added according to the polarities of the input voltage command values Vdr, Vds, and Vdt.

In this embodiment, the bidirectional switch of the phase with the maximum absolute value of the phase voltage is fixed to the ON state during the entire period during which the absolute value of the phase voltage is maximum. However, the present invention is not limited to this. You may make it fix to an ON state. Even in such a case, the switching loss can be reduced while improving the power factor.

(Embodiment 2)
A power converter according to Embodiment 2 will be described. This power conversion device is based on the power conversion device according to the first embodiment, and has a fixed OFF mode as well as a fixed ON mode as the operation mode of the controller. The off-fixed mode is an operation mode in which the bidirectional switch of the phase with the maximum absolute value of the phase voltage is fixed in the off state. Also, this power converter switches the operation mode of the controller between a fixed ON mode and a fixed OFF mode based on the input voltage or the step-up ratio. The step-up ratio means the ratio of the output DC voltage to the input voltage of the three-phase system.

In the power conversion device according to the first embodiment, that is, the device that operates in the fixed ON mode, the input voltage of the three-phase system is relatively low with respect to the output DC voltage, or the ratio of the output DC voltage to the input voltage, that is, It works particularly well under conditions where the boost ratio is high.

On the other hand, when the input voltage is relatively high with respect to the output DC voltage, or when the step-up ratio is low, stable operation can be expected by operating in the off-fixed mode. For example, when the maximum value of the line voltage of the three-phase system 101 is higher than the voltage of the capacitor 104 or 105, current automatically flows from the three-phase system 101 to the capacitor 104 or 105 when operating in the fixed ON mode. and it becomes difficult to control the phase current. Therefore, switching loss can be reduced over a wide range of input voltages by selecting either the fixed ON mode or the fixed OFF mode based on the input voltage or the step-up ratio.

FIG. 5 is a diagram showing an example of the relationship between the input voltage and the duty ratio fixed value in the power converter according to the second embodiment. Note that FIG. 5 assumes that the DC voltage is constant.

In FIG. 5, when the input voltage is lower than the threshold voltage Vth, the operation mode of the controller 110 is set to ON fixed mode, and the fixed value of the duty ratio in the switching of the bidirectional switch of the phase with the maximum absolute value of the phase voltage is set to 1. On the other hand, in the region where the input voltage is equal to or higher than the threshold voltage Vth, the operation mode of the controller 110 is set to the off-fixed mode, and the fixed value of the duty ratio in the switching of the bidirectional switch of the phase with the maximum absolute value of the phase voltage is set to 0. do.

By operating as described above, the switching loss of the bidirectional switches 106r, 106s, and 106t can be reduced over a wide input voltage range.

From the standpoint of maximizing the degree of reduction in switching loss while improving the power factor, the threshold voltage Vth is set to a value at which the maximum value of the line voltage of the three-phase system 101 is about 1/2 of the output DC voltage. It is desirable to set However, the threshold voltage Vth is not limited to this. For example, the threshold voltage Vth may be set within a range of greater than 0% and 50% or less of the DC voltage, or may be set within a range of 45% or more and 55% or less of the DC voltage.

FIG. 6 is a diagram showing an example of the relationship between input voltage and efficiency in the second embodiment. The conversion efficiency 201 is the conversion efficiency when switching between the fixed ON mode and the fixed OFF mode depending on whether the input voltage is lower or higher than the threshold voltage Vth. The conversion efficiency 202 is the conversion efficiency when using a three-phase modulation mode in which all three-phase bidirectional switches are switched in all input voltage ranges. As shown in FIG. 6, the conversion efficiency 201 when switching between the on-fixed mode and the off-fixed mode according to the input voltage is higher than the conversion efficiency 202 when using the three-phase modulation mode over the entire input voltage range. .

(Embodiment 3)
A power converter according to Embodiment 3 will be described. This power conversion device is based on the power conversion device according to the first embodiment, and has a fixed ON mode, a fixed OFF mode, and a three-phase modulation mode as operation modes of the controller. The three-phase modulation mode is an operation mode in which all three-phase bidirectional switches are switched. In addition, unlike the second embodiment, this power conversion device does not provide a threshold voltage at one point, but provides a three-phase modulation mode between the fixed ON mode and the fixed OFF mode with respect to the magnitude of the input voltage. This is the device for the case.

FIG. 7 is a diagram showing an example of the relationship between the input voltage and the duty ratio fixed value in the power converter according to the third embodiment. Note that FIG. 7 assumes that the DC voltage is constant.

In FIG. 7, when the input voltage is lower than the first threshold voltage Vth1, the controller 110 sets the operation mode to the fixed ON mode. When the input voltage is equal to or higher than the first threshold voltage Vth1 and lower than the second threshold voltage Vth2, the controller 110 sets the operation mode to the three-phase modulation mode. When the input voltage is equal to or higher than the second threshold voltage Vth2, the controller 110 sets the operation mode to the fixed off mode.

By operating as described above, it is possible to prevent chattering in the operation mode when the voltage of the three-phase system 101 or the DC voltage changes. Moreover, three-phase modulation is characterized in that fewer harmonics are generated than in the case of stopping the one-phase bidirectional switch shown in the first and second embodiments. Therefore, harmonic noise can be reduced by intentionally using three-phase modulation in an input voltage range above a certain level where switching loss is not a problem.

(Embodiment 4)
A power converter according to Embodiment 4 will be described. This power conversion device is based on the power conversion device according to the first embodiment, and has a three-phase modulation mode in addition to the ON fixed mode as the operation mode of the controller. This power converter switches the operation mode of the controller between a fixed ON mode and a three-phase modulation mode based on the input voltage or the step-up ratio.

Thus, switching loss can be reduced over a wide range of input voltages by selecting either the fixed-on mode or the three-phase modulation mode based on the input voltage or step-up ratio.

FIG. 8 is a diagram showing an example of the relationship between the input voltage and the duty ratio fixed value in the power converter according to the fourth embodiment. Note that FIG. 8 assumes that the DC voltage is constant.

In FIG. 8, when the input voltage is lower than the threshold voltage Vth, the operation mode of the controller 110 is set to ON fixed mode, and the fixed value of the duty ratio in the switching of the bidirectional switch of the phase with the maximum absolute value of the phase voltage is set to 1. On the other hand, in the region where the input voltage is equal to or higher than the threshold voltage Vth, the operation mode of the controller 110 is set to the three-phase modulation mode so that switching of the bidirectional switches of each phase is always performed.

By operating as described above, the switching loss of the bidirectional switches 106r, 106s, and 106t can be reduced over a wide input voltage range.

The threshold voltage Vth is preferably set to a value at which the maximum value of the line voltage of the three-phase system 101 is approximately 1/2 of the DC voltage, but is set within a predetermined range as in the second embodiment. You may do so.

(Embodiment 5)
Embodiment 5 is a modification of the circuit configuration of the power converter according to Embodiment 1. FIG.

FIG. 9 is an example of the circuit configuration of the power converter according to the fifth embodiment. In Embodiment 1, each of the bidirectional switches 106r, 106s, and 106t is composed of two MOSFETs connected in series.

On the other hand, as shown in FIG. 9, in the power converter 500 according to the fifth embodiment, each bidirectional switch can be composed of one switch and four diodes. That is, the bidirectional switches 106r, 106s, and 106t in Embodiment 1 can be replaced with bidirectional switches 506r, 506s, and 506t, respectively, as shown in FIG.

Specifically, the connection points between the inductors 102r, 102s, and 102t and the three-phase diode bridge 103 are defined as first connection points, and the connection points between the capacitors 104 and 105 are defined as second connection points. At this time, each of the bidirectional switches 506r, 506s, and 506t of each phase includes one switching element, such as a power transistor, and a first switching element forwardly connected from a first connection point to one end of the switching element. a diode, a second diode forwardly connected from the other end of the switching element to the first connection point, a third diode forwardly connected from the second connection point to the one end, and others and a fourth diode forwardly connected from the end to the second connection point.

As the switching element, instead of MOSFET, other switching element such as IGBT, thyristor, GTO, bipolar transistor, etc. may be used.

According to the fifth embodiment having such a circuit configuration, the number of switching elements (excluding diodes) with a relatively high failure rate can be reduced, and the failure rate of the power converter can be reduced.

Moreover, when using an expensive element as a switching element, cost can be reduced.

In addition, when a relatively large element is used as the switching element, the mounting space can be reduced.

Although various embodiments of the present invention have been described above, the present invention is not limited to the above-described embodiments, and includes various modifications. Further, the above-described embodiments are described in detail for easy understanding of the present invention, and are not necessarily limited to those having all the described configurations. Also, part of the configuration of one embodiment can be replaced with the configuration of another embodiment, and the configuration of another embodiment can be added to the configuration of one embodiment. These all belong to the scope of the present invention. Furthermore, numerical values, names, etc. contained in the text and drawings are only examples, and the effects of the present invention are not impaired even if different ones are used.

Moreover, it is possible to add, delete, or replace part of the configuration of each embodiment with another configuration. Further, each of the configurations, functions, circuits, etc. described above may be realized by designing a part or all of them, for example, using an integrated circuit or a programmable semiconductor chip.

DESCRIPTION OF SYMBOLS 100... Power converter, 101... Three-phase system, 102r, 102s, 102t... Inductor, 103... Three-phase diode bridge, 104, 105... Capacitor, 106r, 106s, 106t... Bidirectional switch, 107r, 107s... Voltage Sensors 108r, 108s Current sensor 109 Voltage sensor 110 Controller P, N Terminals of DC output part M Connection midpoint of capacitor

Claims (8)

A power conversion device that converts a three-phase AC voltage to a DC voltage,
a plurality of inductors each connected to a terminal of each phase to which the three-phase AC voltage is input;
a three-phase diode bridge connected after the plurality of inductors;
a first capacitor and a second capacitor connected in series between two terminals on the output side of the three-phase diode bridge;
a first connection point that is a connection point between the inductor and the three-phase diode bridge and a second connection point that is a connection point between the first capacitor and the second capacitor for each of the phases; a plurality of bidirectional switches connected between
a controller that controls switching of the plurality of bidirectional switches;
The controller turns on the bidirectional switch of the phase having the maximum absolute value of the input voltage among the phases of the three-phase AC voltage during all or part of the period during which the absolute value of the input voltage is maximum. A power conversion device having, as an operation mode, a fixed-on mode that controls the switching to fix the state. In the power converter according to claim 1,
The controller adds a correction voltage to the command voltage for each phase of the three-phase diode bridge when the operation mode is the fixed-on mode, so that the input voltage of the phase having the maximum absolute value of the input voltage is added. A power conversion device that fixes a bidirectional switch in the ON state. In the power converter according to claim 1,
When the operation mode is the fixed-on mode, the controller switches the bidirectional switch of the phase with the maximum absolute value of the input voltage during the entire period during which the absolute value of the input voltage is maximum, A power conversion device that is fixed in the ON state. In the power converter according to claim 1,
The controller has, as the operation mode, a fixed OFF mode in which the bidirectional switch of the phase having the maximum absolute value of the input voltage is fixed in an OFF state, and the ratio of the three-phase AC voltage and the DC voltage is a power conversion device that sets the operation mode to the fixed ON mode or the fixed OFF mode based on the above. In the power converter according to claim 1,
The controller has, as the operation mode, a three-phase modulation mode in which the bidirectional switches of the respective phases are switched, and the operation mode is changed to the ON mode based on the ratio between the three-phase AC voltage and the DC voltage. A power conversion device for fixed mode or said three-phase modulation mode. In the power converter according to claim 1,
The controller operates in a fixed off mode in which the bidirectional switch of the phase having the maximum absolute value of the input voltage is fixed in an off state, and a three-phase modulation mode in which the bidirectional switch of each phase is switched. mode, and the operation mode is set to the ON fixed mode, the three-phase modulation mode, or the OFF fixed mode based on the ratio between the three-phase AC voltage and the DC voltage. In the power converter according to claim 1,
The power conversion device, wherein each of the bidirectional switches of each phase includes two switching elements connected in series. In the power converter according to claim 1,
Each of the bidirectional switches of each phase includes one switching element, a first diode forwardly connected from the first connection point to one end of the switching element, and the other end of the switching element. to the first connection point in a forward direction; a third diode forwardly connected from the second connection point to the one end; and a third diode forwardly connected from the other end to the second and a fourth diode forwardly connected to the junction.

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