JP7561688B2 - Power Conversion Equipment - Google Patents

Description

The present invention relates to a power conversion device, and more specifically, to a power conversion device using a Vienna rectifier.

A three-phase PFC (Power Factor Correction) converter with a power factor correction 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 circuit system is used in which a switch is provided between each phase input (each terminal on the three-phase system side) of a three-phase diode bridge and the connection point of two capacitors connected in series between the terminals of the DC section. This circuit system is called a Vienna rectifier.

In the Vienna rectifier, the switches for each phase are switched at high speed using PWM (Pulse Width Modulation), which allows the current in each phase of a three-phase system to be controlled to a sine wave similar to the voltage, improving the power factor.

Patent No. 5167884

However, as mentioned above, the Vienna rectifier uses high-speed PWM switching of the switches for each phase. This results in switching losses and reduces the power conversion efficiency.

For these reasons, there is a need to provide a method for reducing switching losses in power conversion devices that use Vienna rectifiers.

Note that an example of a method for reducing switching losses in a power conversion device using a Vienna rectifier is described in the patent document JP 2004-343975 A, but this method is different from the method disclosed in this application.

The following is a brief summary of the representative inventions disclosed in this application.

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 includes a plurality of inductors, each of which is connected to a terminal of each phase to which the three-phase AC voltage is input, a three-phase diode bridge connected to the rear stage of 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 plurality of bidirectional switches, each of which is connected for each phase between 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, and a controller that controls the switching of the plurality of bidirectional switches, and the controller has an on-fixed mode as an operating mode, in which the bidirectional switch of the phase in which the absolute value of the input voltage is maximum among the phases of the three-phase AC voltage is controlled to be fixed to the on state during all or part of the period during which the absolute value of the input voltage is maximum.

The effects achieved by the representative inventions disclosed in this application can be briefly explained as follows:

According to a representative embodiment of the present invention, it is possible to reduce switching losses in a power conversion device using a Vienna rectifier.

1 is a diagram illustrating an example of a circuit configuration of a power conversion device according to a first embodiment. 3A to 3C are diagrams showing examples of various waveforms in the power conversion device according to the first embodiment. FIG. 2 is a diagram illustrating an example of a control block of a controller according to the first embodiment. FIG. 4 is a diagram showing an example of a control block illustrating the operation of a correction voltage calculator. 11 is a diagram showing an example of a relationship between an input voltage and a fixed duty ratio value in a power conversion device according to a second embodiment. FIG. FIG. 11 is a diagram showing an example of a relationship between an input voltage and efficiency in the second embodiment. 13 is a diagram showing an example of a relationship between an input voltage and a fixed duty ratio value in a power conversion device according to a third embodiment. FIG. FIG. 13 is a diagram showing an example of a relationship between an input voltage and a fixed duty ratio value in a power conversion device according to a fourth embodiment. 13 is an example of a circuit configuration of a power conversion device according to a fifth embodiment.

Now, we will explain the embodiments of the present invention. Note that each embodiment described below is an example for realizing the present invention, and does not limit the technical scope of the present invention.

In addition, in the following embodiments, components having the same functions are given the same reference numerals, and repeated explanations are omitted unless otherwise necessary.

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

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

The voltage of the three-phase system 101 varies depending on the country or region, but is generally between 200V and 400V.

Inductors 102r, 102s, and 102t are connected to the terminals of each phase to which the three-phase AC voltage is input from the three-phase system 101. Inductors 102r, 102s, and 102t are each composed of, for example, a coil element.

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

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

The bidirectional switch 106r is connected between 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 capacitor 104 and the capacitor 105 for the r-phase. 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. Also, 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 directly connecting the MOSFETs 111 and 112. Similarly, the bidirectional switch 106s is configured by directly connecting the MOSFETs 113 and 114, and the bidirectional switch 106t is configured by directly connecting the MOSFETs 115 and 116.

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

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.

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

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

Each of these sensors is connected to the controller 110. The current sensor is, for example, configured with a shunt resistor and an isolated amplifier, or a magnetic sensor such as a cored current sensor or a coreless current sensor. The voltage sensor is, for example, configured with a resistive voltage divider and an isolated amplifier, or a capacitor voltage divider and an isolated amplifier, or a highly sensitive non-contact current sensor and a series resistor.

The controller 110 controls the switching of the bidirectional switches 106r, 106s, and 106t based on the detection values detected by each sensor. The controller 110 is configured, for example, by an integrated circuit, a programmable semiconductor chip, a microcomputer chip, or a circuit using discrete semiconductors. Examples of the integrated circuit include an integrated circuit (IC) and a large scale integration (LSI). Examples of the programmable semiconductor chip include a programmable logic device (PLD) and a field programmable gate array (FPGA).

The power conversion device 100 receives three-phase AC power from a three-phase system 101, which is converted to DC power by a three-phase diode bridge 103 and bidirectional switches 106r, 106s, and 106t for each phase, and smoothed by capacitors 104 and 105 connected to terminals P and N of the DC output section. An arbitrary load such as an inverter or DC-DC converter (not shown) is connected downstream of the capacitors 104 and 105, and power is sent to this load.

The controller 110 receives an externally input DC voltage command value (not shown), r-phase and s-phase phase voltages detected by the voltage sensors 107r and 107s, r-phase and s-phase phase currents detected by the current sensors 108r and 108s, and a DC voltage detected by the voltage sensor 109. The controller 110 calculates the on-time ratio (duty ratio) in the switching period 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 detection values input from each sensor. The duty ratio is calculated and controlled to make each phase current of the three-phase system 101 closer to a sine wave while controlling the DC voltage to be constant. This makes the power factor of the power received from the three-phase system 101 closer to 1.

In this embodiment, the phase voltages and currents are detected for two phases, the r phase and the s phase, but this is not limited to this. For example, the phase voltages and currents of all three phases may be detected.

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

<Device Operation>
Hereinafter, the operation of the power conversion device 100 according to the first embodiment will be described with reference to FIG.

Figure 2 shows an example of various waveforms in the power conversion device according to the first embodiment. Figure 2 shows the time changes of 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 of 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 after the inductor, i.e., before 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. These command values are each a simple sine wave with a phase shift of 120°.

Phase current I is the collective term for the currents of each phase, and is composed of r-phase current Ir, s-phase current Is, and t-phase current It. When this phase current I approaches the waveform of phase voltage V, the power factor approaches 1 and 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 method for calculating the correction voltage Voffset will be described in detail later.

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

Note that 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 time period of 60 degrees of the system phase.

《Period A: t1-t2》
In a period A from time t1 to t2, the input voltage command value Vdt of the t-phase is negative and has the largest absolute value among the three phases. At this time, the input voltage The correction voltage Voffset is added to the command value Vdt, and the duty ratio Dt of the t-phase bidirectional switch 106t is fixed to 1, that is, the ON state. The same correction voltage Voffset is also added to the duty ratios Dr, Ds of the switch 106s, and the currents Ir, Is, It of each phase are controlled to become sinusoidal waves even without switching the t-phase bidirectional switch 106t.

《Period B: t2-t3》
In a period B from time t2 to t3, the absolute value of the input voltage command value Vds of the s-phase is the largest among the three phases. At this time, the correction voltage Voffset is set to a value equal to the duty ratio of the s-phase bidirectional switch 106s. Ds is calculated to be fixed to 1. The bidirectional switch 106t, which was fixed to the on state in period A, switches in period B, and only the bidirectional switch 106s is fixed to the on state. As in period A, In addition, in period B, the three-phase currents Ir, Is, and It are also controlled to have sine waves.

<<Period C: t3-t4>>
In period C from time t3 to 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 1. The bidirectional switch 106s, which was fixed to the on state in period B, switches in period C, and only the bidirectional switch 106r is fixed to the on state. As in periods A and B, in period C as well, the three-phase currents Ir, Is, and It are controlled to be sinusoidal waves.

As described above, each of periods A to C is a time for 60 degrees of the system phase, and the bidirectional switches of each phase have two periods during one system cycle during which switching is stopped. In other words, switching is stopped for a total of 120 degrees and fixed to the on state. Fixing the inductors in the on state allows the line voltage to 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 be sinusoidal waves. From the above, the configuration of embodiment 1 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 conversion device according to the first embodiment will be described with reference to Fig. 3. Fig. 3 is a diagram showing an example of a control block of the controller in the first embodiment.

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

The PI (Proportion-Integral) controller 121 is a controller often used for general feedback control, and calculates a current amplitude command value Iamp_ref by adding the proportional control output and the integral control output based on the difference Verr so as to make the difference Verr zero. The PI controller 121 corresponds to a voltage controller. The current amplitude command value Iamp_ref is multiplied by the phase information sin of each phase voltage of the three-phase system 101 to calculate the 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.

The correction voltage calculator 123 calculates a correction voltage Voffset based on the input voltage command value Vd so as to fix the duty ratio of the bidirectional switch of the phase whose absolute value of the input voltage command value Vd is the maximum to 1.

The correction voltage Voffset is added equally to the input voltage command value Vd of each phase to calculate the corrected input voltage command value Vd2 (a 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 corrected input voltage command value Vd2 and generates gate signals that drive the bidirectional switches 106r, 106s, and 106t.

In this way, the power conversion device 100 has an on-fixed mode as an operating mode of its controller 110, in which the bidirectional switch of the phase in which the absolute value of the phase voltage is maximum is fixed to the on state.

By performing the above operations, it is possible to always calculate an appropriate correction voltage Voffset even if the current amplitude command value Iamp_ref fluctuates due to load fluctuations, etc.

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

In addition, 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 this is not limited to this, and the current command value Iref for each phase may be calculated using, for example, a dq transformation.

In addition, here, no blocks for controlling the voltage balance of capacitors 104 and 105 are incorporated, but such blocks may be added.

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

Figure 4 shows an example of a control block that illustrates the operation of the correction voltage calculator. The 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 whose absolute value of the phase voltage is the maximum in the on state, it is necessary to reduce the absolute value of the input voltage command value (Vdr, Vds, or Vdt) to be fixed. For example, when the r-phase current Ir flows in a positive direction, when the r-phase bidirectional switch 106r is turned off, the input voltage of the r-phase becomes the potential of the terminal P of the DC output, and when it is turned on, it becomes equal to the potential of the connection point M of the capacitor (ideally the same potential as the neutral point of the three-phase system 101, which is zero). Here, since the potential of the terminal P is greater than the potential of the connection point M, the smaller the input voltage command value Vdr, the closer the duty ratio Dr of the bidirectional switch 106r approaches 1. Also, when the r-phase current Ir flows in a negative direction, when the bidirectional switch 106r is turned off, the input voltage of the r-phase becomes the potential of the terminal N of the DC output, and similarly, the closer the absolute value of the input voltage command value Vdr is to zero, the closer the duty ratio Dr of the bidirectional switch 106r approaches 1.

Therefore, the maximum voltage selector 131 selects and outputs the maximum absolute value from 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 with 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. In this way, for example, when the input voltage command value Vdr of the r-phase is positive and has a maximum absolute value, Vdr2 = Vdr - Vdr = 0, the corrected input voltage command value Vdr2 can be set to zero, and the bidirectional switch 106r of the r-phase can be fixed to the on state. In addition, because the correction voltage Voffset is added equally to the other phases, it does not affect the line voltage.

By performing the above operations, the correction voltage Voffset to be added depending on the polarity of the input voltage command values Vdr, Vds, and Vdt can be appropriately calculated.

In this embodiment, the bidirectional switch of the phase in which the absolute value of the phase voltage is maximum is fixed to the on state for the entire period during which the absolute value is maximum. However, the present invention is not limited to this, and the bidirectional switch of the phase in which the absolute value of the phase voltage is maximum may be fixed to the on state for a portion of the period during which the absolute value is maximum, for example, 50% or more but less than 100%. Even in such a case, it is possible to reduce switching loss while improving the power factor.

(Embodiment 2)
A power conversion device according to a second embodiment will be described. Based on the power conversion device according to the first embodiment, this power conversion device has an off-fixed mode as an operation mode of the controller in addition to the on-fixed mode. The off-fixed mode is an operation mode in which the bidirectional switch of the phase in which the absolute value of the phase voltage is maximum is fixed to the off state. This power conversion device switches the operation mode of the controller between the on-fixed mode and the off-fixed 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 a three-phase system.

The power conversion device according to embodiment 1, i.e., a device that operates in fixed on mode, operates particularly well under conditions in which the input voltage of the three-phase system is relatively low based on the output DC voltage, or under conditions in which the ratio of the output DC voltage to the input voltage, i.e., the step-up ratio, is high.

On the other hand, when the input voltage is relatively high based on the output DC voltage or when the step-up ratio is low, operation in fixed off mode is expected to provide more stable operation. For example, when the maximum value of the line voltage of three-phase system 101 is higher than the voltage of capacitor 104 or 105, operation in fixed on mode causes current to automatically flow from three-phase system 101 to capacitor 104 or 105, making it difficult to control the phase current. For this reason, by selecting between fixed on mode and fixed off mode based on the input voltage or step-up ratio, switching loss can be reduced over a wide input voltage range.

Figure 5 shows an example of the relationship between the input voltage and the fixed duty ratio value in a power conversion device according to embodiment 2. Note that in Figure 5, it is assumed 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 the fixed on mode, and the fixed value of the duty ratio for switching the bidirectional switch of the phase in which the absolute value of the phase voltage is maximum is set to 1. On the other hand, in the region in which the input voltage is equal to or higher than the threshold voltage Vth, the operation mode of the controller 110 is the fixed off mode, and the fixed value of the duty ratio for switching the bidirectional switch of the phase in which the absolute value of the phase voltage is maximum is set to 0.

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

Figure 6 is a diagram showing an example of the relationship between input voltage and efficiency in embodiment 2. Conversion efficiency 201 is the conversion efficiency when switching between fixed on mode and fixed off mode when the input voltage is lower and higher than the threshold voltage Vth. Conversion efficiency 202 is the conversion efficiency when using a three-phase modulation mode in which all three-phase bidirectional switches are switched over the entire input voltage range. As shown in Figure 6, conversion efficiency 201 when switching between fixed on mode and fixed off mode depending on the input voltage is higher than conversion efficiency 202 when using three-phase modulation mode over the entire input voltage range.

(Embodiment 3)
A power conversion device according to a third embodiment 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 and a three-phase modulation mode as operation modes of the controller in addition to the fixed-on mode. The three-phase modulation mode is an operation mode in which all three-phase bidirectional switches are switched. This power conversion device is a device in which the threshold voltage is not set at one point as in the second embodiment, but the three-phase modulation mode is set between the fixed-on mode and the fixed-off mode for the magnitude of the input voltage.

Figure 7 shows an example of the relationship between the input voltage and the fixed duty ratio value in a power conversion device according to embodiment 3. Note that in Figure 7, it is assumed 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 performing the above-described operation, chattering of the operation mode can be prevented when the voltage or DC voltage of the three-phase system 101 changes. Furthermore, three-phase modulation has the characteristic of generating fewer harmonics compared to the case where the one-phase bidirectional switch shown in the first and second embodiments is stopped. Therefore, in an input voltage range above a certain level where switching loss is not an issue, harmonic noise can be reduced by deliberately using three-phase modulation.

(Embodiment 4)
A power conversion device according to embodiment 4 will be described. This power conversion device is based on the power conversion device according to embodiment 1 and has a three-phase modulation mode as an operation mode of the controller in addition to the fixed on mode. This power conversion device switches the operation mode of the controller between the fixed on mode and the three-phase modulation mode based on the input voltage or the step-up ratio.

In this way, switching losses can be reduced over a wide input voltage range by selecting between fixed on mode and three-phase modulation mode based on the input voltage or step-up ratio.

Figure 8 shows an example of the relationship between the input voltage and the fixed duty ratio value in a power conversion device according to embodiment 4. Note that in Figure 8, it is assumed 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 the fixed on mode, and the fixed value of the duty ratio for switching the bidirectional switch of the phase where the absolute value of the phase voltage is maximum 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 the three-phase modulation mode, and the bidirectional switch of each phase is always switched.

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

It is desirable to set the threshold voltage Vth to a value at which the maximum line voltage of the three-phase system 101 is approximately half the DC voltage, but it may be set within a predetermined range, as in the second embodiment.

(Embodiment 5)
The fifth embodiment is a modification of the circuit configuration of the power conversion device according to the first embodiment.

Figure 9 shows an example of a circuit configuration of a power conversion device according to embodiment 5. In embodiment 1, the bidirectional switches 106r, 106s, and 106t are each configured with two MOSFETs connected in series.

On the other hand, as shown in FIG. 9, in the power conversion device 500 according to the fifth embodiment, each bidirectional switch can be configured with one switch and four diodes. That is, the bidirectional switches 106r, 106s, and 106t in the first embodiment can be configured as the bidirectional switches 506r, 506s, and 506t shown in FIG. 9, respectively.

Specifically, the connection point between the inductors 102r, 102s, and 102t and the three-phase diode bridge 103 is the first connection point, and the connection point between the capacitors 104 and 105 is the second connection point. In this case, the bidirectional switches 506r, 506s, and 506t of each phase can each include one switching element, for example a power transistor, a first diode connected in the forward direction from the first connection point to one end of the switching element, a second diode connected in the forward direction from the other end of the switching element to the first connection point, a third diode connected in the forward direction from the second connection point to the one end, and a fourth diode connected in the forward direction from the other end to the second connection point.

In addition, instead of MOSFETs, other switching elements such as IGBTs, thyristors, GTOs, and bipolar transistors may be used as switching elements.

According to embodiment 5, which has such a circuit configuration, it is possible to reduce the number of switching elements (excluding diodes) that have a relatively high failure rate, thereby reducing the failure rate of the power conversion device.

In addition, when expensive elements are used as switching elements, costs can be reduced.

In addition, when using a relatively large element 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-mentioned embodiments and includes various modified examples. Furthermore, the above-mentioned embodiments have been described in detail to clearly explain the present invention, and are not necessarily limited to those having all of the configurations described. Furthermore, it is possible to replace part of the configuration of one embodiment with the configuration of another embodiment, and it is also possible to add the configuration of another embodiment to the configuration of one embodiment. All of these belong to the scope of the present invention. Furthermore, the numerical values, names, etc. contained in the text and figures are merely examples, and the effect of the present invention will not be impaired if different ones are used.

In addition, it is possible to add, remove, or replace part of the configuration of each embodiment with other configurations. Furthermore, the above configurations, functions, circuits, etc. may be realized in whole or in part by designing, for example, an integrated circuit or a programmable semiconductor chip.

100...power conversion device, 101...three-phase system, 102r, 102s, 102t...inductor, 103...three-phase diode bridge, 104, 105...capacitor, 106r, 106s, 106t...bidirectional switch, 107r, 107s...voltage sensor, 108r, 108s...current sensor, 109...voltage sensor, 110...controller, P, N...terminals of DC output section, M...connection midpoint of capacitor

Claims (8)

A power conversion device that converts a three-phase AC voltage into 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 to a downstream stage of 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 plurality of bidirectional switches, each connected for each phase between 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;
A controller that controls switching of the plurality of bidirectional switches,
the controller has, as an operation mode, a fixed on mode in which the switching of the bidirectional switch of a phase having a maximum absolute value of an input voltage among each phase of the three-phase AC voltage is controlled to be fixed to an on state during all or part of a period during which the absolute value of the input voltage is maximum. 2. The power conversion device according to claim 1,
When the operation mode is the fixed on mode, the controller adds a correction voltage to a command voltage for each phase of the three-phase diode bridge, thereby fixing the bidirectional switch of a phase in which the absolute value of the input voltage is maximum to the on state. 2. The power conversion device according to claim 1,
When the operation mode is the fixed on mode, the controller fixes the bidirectional switch of the phase in which the absolute value of the input voltage is maximum to the on state during an entire period in which the absolute value of the input voltage is maximum. 2. The power conversion device according to claim 1,
The controller has, as the operation mode, a fixed off mode in which the bidirectional switch of a phase in which an absolute value of the input voltage is maximum is fixed to an off state, and sets the operation mode to the fixed on mode or the fixed off mode based on a ratio between the three-phase AC voltage and the DC voltage. 2. The power conversion device according to claim 1,
The controller has, as the operation mode, a three-phase modulation mode in which the bidirectional switches of the phases are switched, and sets the operation mode to the fixed on mode or the three-phase modulation mode based on a ratio between the three-phase AC voltage and the DC voltage. 2. The power conversion device according to claim 1,
The controller has, as the operation modes, a fixed off mode in which the bidirectional switch of the phase in which the absolute value of the input voltage is maximum is fixed to an off state, and a three-phase modulation mode in which the bidirectional switch of each phase is switched, and sets the operation mode to the fixed on mode, the three-phase modulation mode, or the fixed off mode based on a ratio between the three-phase AC voltage and the DC voltage. 2. The power conversion device according to claim 1,
A power conversion device, wherein the bidirectional switch for each phase includes two switching elements connected in series. 2. The power conversion device according to claim 1,
a first diode connected in a forward direction from the first connection point to one end of the switching element, a second diode connected in a forward direction from the other end of the switching element to the first connection point, a third diode connected in a forward direction from the second connection point to the one end, and a fourth diode connected in a forward direction from the other end to the second connection point.

Images