JP2019176545A - Three-phase rectifier and switching control method for three-phase rectifier - Google Patents

Abstract

To suppress waveform distortion of an input current by reducing a ripple waveform in an output current of a three-phase rectifier.SOLUTION: A three-phase rectifier comprises: a full-wave rectifier circuit; a bidirectional switch circuit for turning on/turning off input of each of phases from a three-phase AC power source to the full-wave rectifier circuit; a DC reactor; a switching pattern generation unit which generates for each switching cycle a switching pattern of each of the phases for turning on/turning off the bidirectional switch circuit; a switching cycle adjustment unit which adjusts the switching cycle; and a switching control unit which performs switching control on the bidirectional switch circuit in the switching cycle adjusted by the switching cycle adjustment unit on the basis of the switching pattern generated by the switching pattern generation unit. The switching cycle adjustment unit changes the switching cycle to reduce a ripple waveform of a current flowing in the DC reactor.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a three-phase rectifier and a switching control method for the three-phase rectifier.

  There is a three-phase rectifier that inputs three-phase AC power to a bridge diode through a switch circuit having a switching element, converts the DC power into DC power, and outputs the DC power. Such a three-phase rectifier generates, for example, as shown in FIG. 13, a switching pattern corresponding to modes I to VI in which one cycle of the three-phase AC power is divided into six according to the magnitude relation of the voltage of each phase. By switching the switching element with the generated switching pattern, the three-phase AC power can be converted into DC power having an arbitrary voltage (see, for example, Patent Document 1).

Japanese Patent No. 4687824

  Here, when the waveform of the current IL flowing through the DC reactor of the three-phase rectifier is in a discontinuous mode described later, the inventor of the present invention does not have the ideal waveforms (sine waves) for the input currents Ir, Is, and It. I found out.

  For example, consider a case where the switching elements of the switch circuit are switched in the switching pattern shown in the upper diagram of FIG. 14A in the switching period T at the timing tp (see FIG. 13) of mode I. As shown in FIG. 13, in the switching period T at timing tp, the S-phase and T-phase phases when the S-phase and T-phase switches are turned on and the R-phase switch is turned off (see FIG. 14A). The voltage potential difference is the line voltage VST, and when the R-phase and T-phase switches are turned on and the S-phase switch is turned off (see FIG. 14A), the potential difference between the R-phase and T-phase phase voltages is This is the line voltage VRT, and the potential difference between the phase voltages of the R phase and the S phase when the R phase and S phase switches are turned on and the T phase switch is turned off (see FIG. 14A) is the line voltage VRS. It is.

  It is ideal that the current IL flowing through the DC reactor is constant as shown in the lower diagram of FIG. 14A and the broken line I0 shown in the lower portions of FIGS. 14B to 14C. As shown by the solid line IL shown in FIG. 14C, the slope changes at each switching of switching according to the selected phase of switching. Thus, in this specification, a state where the current becomes a straight line whose slope changes every switching and the current waveform undulates (ripple) is expressed as a ripple shape of the current waveform.

  14A and 14B to 14C, even if the output current I0 decreases, the continuous mode (IL in FIG. 14A) in which the minimum value of the current IL in one switching period T is a positive value. In the waveform 1 and the IL waveform 2 in FIG. 14B) and the critical mode in which the minimum value of the current IL is 0 (IL waveform 3 in FIG. 14C), the waveform of the current IL has a similar ripple shape. When the output current I0 further decreases, the current IL reaches a discontinuous mode (IL waveform 4 in FIG. 14D) in which the minimum value of the current IL is 0 over a period of one switching cycle T.

  Next, the current waveforms of the input currents Ir, Is, It in the critical mode and the discontinuous mode will be described. FIG. 15A is a diagram showing input currents Ir, Is, It in the critical mode of the prior art. FIG. 15B is a diagram showing a current IL in a critical mode of the prior art. FIG. 16A is a diagram showing input currents Ir, Is, and It in the discontinuous mode of the prior art. FIG. 16B is a diagram showing the current IL in the discontinuous mode of the prior art. The simulation conditions of FIGS. 15A to 15B are: DC inductor inductance L1 = 500 μH, switching frequency of the switching element of the switch circuit = 23 kHz, input voltage (line voltage) = 400V, and output current I0 = 2.3A. Also, the simulation conditions of FIGS. 16A to 16B are the same as those of FIGS. 15A to 15B in the inductance L1 of the DC reactor, the switching frequency of the switching element of the switch circuit, and the input voltage (line voltage), and the output current I0 = 1. .7A.

  In the critical mode when the output current I0 = 2.3A, as shown in FIG. 15A, the waveforms of the input currents Ir, Is, It are at a level that can be said to be sinusoidal, and as shown in FIG. Each minimum value of the waveform is also positive. However, in the discontinuous mode when the output current I0 = 1.7 A, as shown in FIG. 16A, the waveforms of the input currents Ir, Is, It are no longer at a level that can be said to be sinusoidal, but as shown in FIG. 16B. The current IL waveform also has a period in which each minimum value is zero. The reason why the waveforms of the input currents Ir, Is, It are greatly disturbed in the discontinuous mode is that a period during which the current IL does not flow occurs in one switching period T, and an ideal current value such as the output current I0 indicated by a broken line This is because it deviates greatly from the state of (constant current).

  The present invention has been made in view of the above, and a three-phase rectifier that suppresses waveform distortion of an input current by reducing a ripple waveform of a current flowing through a DC reactor of the three-phase rectifier, and a switching control method for the three-phase rectifier The purpose is to provide.

  In order to solve the above-described problems and achieve the object, a three-phase rectifier that converts three-phase AC power supplied from a three-phase AC power source into DC power is a full wave that rectifies the three-phase AC power into DC power. A rectifier circuit, a bidirectional switch circuit for turning on / off each phase input from the three-phase AC power source to the full-wave rectifier circuit, and a switching pattern for each phase for turning the bidirectional switch circuit on / off A switching pattern generator generated for each switching cycle, a switching cycle adjuster for adjusting the switching cycle, and a switching cycle adjusted by the switching cycle adjuster based on the switching pattern generated by the switching pattern generator And a switching control unit that performs switching control of the bidirectional switch circuit. The switching pattern generation unit divides one cycle of the three-phase AC power into a plurality of modes based on the magnitude relationship of the voltage of each phase of the three-phase AC power, and different carrier waveforms and control signals depending on the mode And a switching pattern that differs depending on the mode and each phase is generated from the carrier waveform and the control signal, and the switching period adjustment unit changes the switching period and flows through the DC reactor. Reduce the ripple waveform of the current.

  According to the three-phase rectifier and the switching control method for the three-phase rectifier according to the present invention, the ripple waveform of the current flowing through the DC reactor of the three-phase rectifier is reduced to suppress the waveform distortion of the input current.

FIG. 1 is a diagram illustrating an example of a configuration of a power conversion device to which the three-phase rectifier according to the embodiment is applied. FIG. 2 is a diagram illustrating an example of the configuration of the switching pattern generator according to the embodiment. FIG. 3 is a diagram illustrating an example of a frequency determination table according to a modification of the embodiment. FIG. 4 is a circuit diagram illustrating an example of a configuration of one phase switch of the bidirectional switch circuit of the embodiment. FIG. 5 is a diagram for explaining each mode according to the R-phase voltage, the S-phase voltage, and the T-phase voltage of the embodiment. FIG. 6 is a diagram illustrating an example of switching patterns in mode I and mode IV of the embodiment. FIG. 7 is a diagram illustrating an example of switching patterns in mode II and mode V of the embodiment. FIG. 8 is a diagram illustrating an example of switching patterns in mode III and mode VI of the embodiment. FIG. 9 is a diagram illustrating an example of a switching frequency control method according to the embodiment. FIG. 10 is a diagram for comparing and explaining the amplitude of the ripple waveform of the current IL according to the embodiment and the prior art. FIG. 11 is a diagram for explaining the amplitude of the ripple waveform of the current IL. FIG. 12 is a diagram for comparing and explaining the switching frequencies of the embodiment and the prior art. FIG. 13 is a diagram for explaining the relationship between the mode and the line voltage. FIG. 14A is a diagram for explaining the relationship between the output current I0 and the current IL (when the output current I0 is a sufficiently large continuous mode) in the prior art. FIG. 14B is a diagram for explaining the relationship between the output current I0 and the current IL in the related art (when the output current I0 is smaller than that in FIG. 14A but in the continuous mode). FIG. 14C is a diagram for explaining the relationship between the output current I0 and the current IL in the related art (when the output current I0 is smaller than that in FIGS. 14A and 14B and is in the critical mode). FIG. 14D is a diagram for explaining the relationship between the output current I0 and the current IL in the related art (when the output current I0 is smaller than that in FIGS. 14A to 14C and in the discontinuous mode). FIG. 15A is a diagram showing input currents Ir, Is, It in the critical mode of the prior art. FIG. 15B is a diagram showing a current IL in a critical mode of the prior art. FIG. 16A is a diagram showing input currents Ir, Is, and It in the discontinuous mode of the prior art. FIG. 16B is a diagram showing the current IL in the discontinuous mode of the prior art.

  Hereinafter, embodiments of the disclosed technology will be described in detail with reference to the drawings. In addition, this invention is not limited by the following embodiment. In addition, the following embodiments can be implemented in appropriate combinations within a consistent range. In addition, constituent elements in each embodiment include those that can be easily assumed by those skilled in the art or those that are substantially the same. The three-phase rectifier according to the disclosed technology can be widely applied to various devices, such as an air conditioner, a refrigerator, a washing machine, a cleaner, a ventilation fan, and a motor driving device used in these, a motor driving inverter control device, and the like. Useful.

(Embodiment)
[Configuration of power converter]
FIG. 1 is a diagram illustrating an example of a configuration of a power conversion device to which the three-phase rectifier according to the embodiment is applied. As shown in FIG. 1, the power converter according to this embodiment includes a three-phase AC power source 1 that generates a three-phase voltage of R phase, S phase, and T phase, a three-phase rectifier 12, and a load 7 through which an output current I0 flows. Have. The three-phase rectifier 12 of the present embodiment is a full-wave rectifier circuit including a three-phase reactor 8 and an input capacitor 9 connected to the output side of the three-phase AC power source 1 and six diodes that rectify the three-phase voltage into a DC voltage. A bridge diode 4 is provided.

  The three-phase rectifier 12 includes a switch SW-R that is a switching element that turns on / off the R-phase input of the bridge diode 4, and a switch SW-S that is a switching element that turns on / off the S-phase input. Has a bidirectional switch circuit 3 including a switch SW-T which is a switching element for turning on / off the input. The three-phase rectifier 12 calculates the current phase from the phase voltage of two predetermined phases (in this embodiment, the R phase and the S phase) of the three phases of the R phase, the S phase, and the T phase. A switching pattern generation circuit 5 that detects and generates a switching pattern of the bidirectional switch circuit 3, and a drive that controls switching of the switching elements of the bidirectional switch circuit 3 based on the switching pattern generated by the switching pattern generation circuit 5 A circuit 6 is included.

  The three-phase rectifier 12 includes a DC reactor 2, a capacitor 10, and a diode 11 that are connected to the output side of the bridge diode 4 and through which a current IL flows.

  The switching pattern generation circuit 5 and the drive circuit 6 detect the current phase from the predetermined two-phase phase voltage of the three-phase AC power supply 1, and turn on the bidirectional switch circuit 3 based on the detected two-phase detection phase. A switching pattern of each phase of R phase, S phase, and T phase for turning off / off is generated, and functions as control means for switching control of the bidirectional switch circuit 3 based on the generated switching pattern.

  The switching pattern generation circuit 5 includes a phase detector 5a and a switching pattern generator 5b. The phase detector 5a detects a current phase from phase voltages of predetermined two phases (in this embodiment, R phase and S phase) of the three-phase AC power supply 1, and uses the detected phase as a detection phase to switch a switching pattern generator. Output to 5b.

  The switching pattern generator 5b generates a switching pattern (R-phase pulse, S-phase pulse, T-phase pulse) of the bidirectional switch circuit 3 in order to suppress DC voltage pulsation and input current harmonics. The switching pattern generator 5b is configured to turn on the switches SW-S and SW-T and turn off the SW-R during one switching period T in the bidirectional switch circuit 3, and switch SW-R and SW-T. Is switched on, SW-S is turned off, a switching pattern is provided that provides a section Drt that turns off SW-S, switches SW-R and SW-S are turned on, and a section Drs that turns off SW-T. In the present embodiment, the section widths of the section Dst, the section Drt, and the section Drs are referred to as Duty.

  The switching pattern generator 5b is based on the detection phase output from the phase detector 5a at a predetermined timing such as the rise of the switching period T, and the maximum potential phase and intermediate potential of the voltage of each phase of the three-phase AC power source 1 Estimate the phase and the minimum potential phase. In the switching pattern generator 5b, the current mode of the three-phase input voltage is any of mode I to mode VI (see FIG. 5) described later corresponding to the magnitude relationship of the maximum potential phase, the intermediate potential phase, and the minimum potential phase. Specify whether it is a mode.

  Then, the switching pattern generator 5b provides a switching pattern (R-phase pulse, S-phase pulse, T-phase pulse) that provides a section Dst, a section Drt, and a section Drs in one switching cycle T at a timing according to the specified mode. ) Is repeated as long as it is in the same mode I to mode VI. Details of the operation of the switching pattern generator 5b will be described later. The switching period T is variable within a predetermined range around a predetermined period (for example, 1/20 kHz = 50 μsec) that is sufficiently short with respect to the power supply frequency (for example, 50 Hz).

  In the present embodiment, the switching pattern generator 5b generates a switching pattern based on the detected phase detected by the phase detector 12a. However, the present invention is not limited to this, and the switching pattern generator 5b may generate a switching pattern by using the R-phase, S-phase, and T-phase voltages of the three-phase AC power supply 1 as inputs.

  Based on the switching pattern (R-phase pulse, S-phase pulse, T-phase pulse) that provides the section Dst, the section Drt, and the section Drs output from the switching pattern generation circuit 5, the drive circuit 6 The switches SW-R to SW-T are subjected to switching control.

[Configuration example of switching pattern generator]
FIG. 2 is a diagram illustrating an example of the configuration of the switching pattern generator according to the embodiment. The switching pattern generator 5b of the embodiment includes a period determining unit 5b1, a sawtooth wave generating unit 5b2, a control voltage generating unit 5b3, and an adder 5b4.

  Based on the detected phase θ output from the phase detector 5a, the cycle determining unit 5b1 calculates and outputs an optimal cycle T (θ) [μs] from the following equation, for example. The optimum cycle T (θ) is a switching cycle T (see FIGS. 6 to 8) for switching the switches SW-R, SW-S, and SW-T of the bidirectional switch circuit 3.

T (θ) = 1 / {α + β · sin (γ · θ + π / 2)} (Formula 1)
However, α = 20 [kHz], β = 10 [kHz], and γ = 6.

  The numerical values of α, β, and γ in (Equation 1) are merely examples, and may be other numerical values as long as the waveform distortion of the input currents Ir, Is, It can be suppressed.

The following holds from the relationship between the period and the frequency.
Optimal frequency f (θ) = 1 / T (θ) = α + β · sin (γ · θ + 90 °) (Expression 2)

  Or the period determination part 5b1 may determine an optimal period as follows irrespective of said (Formula 1). That is, the period determination unit 5b1 may include a frequency determination table 5b1-t according to a modification of the embodiment illustrated in FIG. Then, the period determination unit 5b1 acquires the optimum period [μs] corresponding to the detection phase θ [°] in units of 1 ° output from the phase detector 5a in the frequency determination table 5b1-t, and the sawtooth wave You may output to the production | generation part 5b2. The cycle determining unit 5b1 is an example of a switching cycle adjusting unit that adjusts the switching cycle T.

  In the frequency determination table 5b1-t, as shown in FIG. 3, for example, the optimum period T89 [μs] is detected at the detection phase θ = 89 [°], and the optimum period T90 [μs] is detected at the detection phase θ = 90 [°]. ] Is stored in association with the detection period θ = 91 [°] and the optimum period T91 [μs]. Note that (Equation 1) and FIG. 3 merely show examples of the optimum period, and other numerical values and equations may be used as long as the waveform distortion of the input currents Ir, Is, It can be suppressed. Further, the association between the detection phase and the optimum period is not limited to 1 ° units, and may be larger or smaller than this.

  The sawtooth wave generator 5b2 has any of the current modes corresponding to the detected phase θ output from the phase detector 5a at a predetermined timing such as the rising edge of the switching period T, which is any of the modes I to VI (see FIG. 5). Specify whether it is a mode.

  Then, when the identified current mode is mode I or mode IV, the sawtooth wave generator 5b2 has a sawtooth wave (R phase sawtooth wave and T phase sawtooth wave) as shown in FIG. Is generated. The switching period T of the sawtooth wave (R phase sawtooth wave and T phase sawtooth wave) generated by the sawtooth wave generation unit 5b2 is the optimum period output from the period determination unit 5b1. FIG. 6 is a diagram illustrating an example of switching patterns in mode I and mode IV of the embodiment. The sawtooth wave generator 5b2 outputs the generated R phase sawtooth wave and T phase sawtooth wave. The R-phase sawtooth wave is a carrier waveform that linearly decreases from 1 to 0 in one switching period T. The T-phase sawtooth wave is a carrier waveform that increases linearly from 0 to 1 in one switching period T.

  Further, when the specified current mode is mode II or mode V, the sawtooth wave generation unit 5b2 generates a sawtooth wave (T-phase sawtooth wave) as shown in FIG. The switching period T of the sawtooth wave (T-phase sawtooth wave) generated by the sawtooth wave generation unit 5b2 is the optimum period output from the period determination unit 5b1. FIG. 7 is a diagram illustrating an example of switching patterns in mode II and mode V of the embodiment. The sawtooth wave generator 5b2 outputs the generated T phase sawtooth wave.

  Further, when the identified current mode is mode III or mode VI, the sawtooth wave generation unit 5b2 generates a sawtooth wave (R-phase sawtooth wave) as shown in FIG. The switching period T of the sawtooth wave (R-phase sawtooth wave) generated by the sawtooth wave generation unit 5b2 is the optimum period output from the period determination unit 5b1. FIG. 8 is a diagram illustrating an example of switching patterns in mode III and mode VI of the embodiment. The sawtooth wave generator 5b2 outputs the generated R-phase sawtooth wave.

  The control voltage generation unit 5b3 has any one of modes I to VI (see FIG. 5) corresponding to the detected phase θ output from the phase detector 5a at a predetermined timing such as the rising of the switching period T. It is specified whether it is.

  Then, when the specified current mode is mode I or mode IV, control voltage generation unit 5b3 generates control signal | R | and control signal | T | as shown in FIG. When the identified current mode is mode I, the control signal | R | = R and the control signal | T | = −T. When the identified current mode is mode IV, the control signal | R | = −R and the control signal | T | = T. The control voltage generator 5b3 outputs the generated control signal | R | and control signal | T |.

  Further, when the specified current mode is mode II or mode V, the control voltage generation unit 5b3 generates the control signal | S | + | T | -1 and the control signal | T | as shown in FIG. To do. When the identified current mode is mode II, the control signal | S | + | T | -1 = ST-1 and the control signal | T | = T. When the identified current mode is mode V, the control signal | S | + | T | -1 = −S + T−1 and the control signal | T | = T. The control voltage generator 5b3 outputs the generated control signal | S | + | T | -1 and the control signal | T |.

  Further, when the specified current mode is mode III or mode VI, the control voltage generation unit 5b3 generates a control signal | R | and a control signal | R | + | S | -1 as shown in FIG. To do. When the identified current mode is mode III, the control signal | R | + | S | −1 = −R + S−1 and the control signal | R | = −R. When the identified current mode is mode VI, the control signal | R | + | S | -1 = R-S-1 and the control signal | R | = R. The control voltage generator 5b3 outputs the generated control signal | R | + | S | -1 and the control signal | R |.

  The adder 5b4 generates a bidirectional switch circuit from the sawtooth wave corresponding to the current mode output from the sawtooth wave generator 5b2 and the control signal corresponding to the current mode output from the control voltage generator 5b3. A switching pattern corresponding to the current mode for switching control of the three switches SW-R, SW-S, and SW-T is generated. The switching pattern generated by the adder 5b4 will be described later with reference to FIGS.

[Configuration of Switch of Bidirectional Switch Circuit of Embodiment]
FIG. 4 is a circuit diagram illustrating an example of a configuration of one phase switch of the bidirectional switch circuit of the embodiment. Since the bidirectional switch circuit 3 shown in FIG. 4 is a known circuit composed of a diode and a switching element such as an IGBT (Insulated Gate Bipolar Transistor), detailed description thereof is omitted.

[Multiple modes divided according to phase voltage magnitude]
FIG. 5 is a diagram for explaining each mode according to the R-phase voltage, the S-phase voltage, and the T-phase voltage of the embodiment. In FIG. 5, the three-phase AC voltage is divided into six modes (sections) from mode I to mode VI depending on the magnitude relationship among the R-phase voltage, the S-phase voltage, and the T-phase voltage. The switching pattern generator 5b sets R>S> T to mode I, S>R> T to mode II, S>T> R to mode III, T>S> R to mode IV, and T>R> S to mode. V, R>T> S are classified into mode VI.

[Switching Pattern in Each Mode of Embodiment]
Hereinafter, with reference to FIGS. 6 to 8, the switching pattern of the embodiment generated by the switching pattern generator 5 b in each mode shown in FIG. 5 will be described. In each of mode I and mode IV, mode II and mode V, mode III and mode VI, the switching pattern generated by the switching pattern generator 5b is the same. Hereinafter, turning on the switch SW-R corresponding to the R phase is referred to as “turning on the R phase”, and turning off the SW-R is referred to as “turning off the R phase”. The same applies to the S phase and the T phase.

  The switching pattern generator 5b determines the R-phase control voltage | R | and S-phase control from the R-phase, S-phase, and T-phase voltages estimated based on the detected phase θ output from the phase detector 5a. A voltage | S | and a T-phase control voltage | T | are generated. The R-phase control voltage | R | is an R-phase voltage a obtained by normalizing the R-phase phase voltage between “−1” and “1”. The S-phase control voltage | S | is the S-phase voltage b obtained by normalizing the S-phase phase voltage between “−1” and “1”. The T-phase control voltage | T | is a T-phase voltage c obtained by standardizing the T-phase phase voltage between “−1” and “1”. The switching pattern generator 5b recognizes the current magnitude relationship among the R-phase voltage a, S-phase voltage b, and T-phase voltage c, and the current mode is any of Mode I to Mode VI based on the recognized magnitude relationship. Determine if it exists.

  Then, the switching pattern generator 5b generates control signals corresponding to the specified current mode based on the R-phase control voltage | R |, the S-phase control voltage | S |, and the T-phase control voltage | T | To do. The control signal has a waveform that is switched to the R-phase sawtooth wave or the T-phase sawtooth wave (see FIGS. 6 to 8). The R-phase sawtooth wave is a carrier waveform that linearly decreases from 1 to 0 in one switching period. The T-phase sawtooth wave is a carrier waveform that increases linearly from 0 to 1 in one switching period.

[Switching Pattern in Mode I and Mode IV of Embodiment]
FIG. 6 is a diagram illustrating an example of switching patterns in mode I and mode IV of the embodiment. With reference to FIG. 6, switching patterns generated by switching pattern generator 5b in modes I and IV will be described.

  As shown in FIG. 6, when the current mode is specified as mode I, the switching pattern generator 5b sets the control signal | R | = R and the control signal | T | = −T as follows. Is generated.

  That is, at the timing t10, the S phase and the T phase are turned on. Subsequently, at the timing t11 when the R-phase sawtooth wave and the control signal | R | are switched, the S-phase is turned off and the R-phase is turned on. Timing t10 to t11 is the section Dst.

  Subsequently, at the timing t12 when the R-phase sawtooth wave switches to the control signal | T |, the S-phase is turned on and the T-phase is turned off. Timing t11 to t12 is the section Drt. Subsequently, at the timing t13 when the R-phase sawtooth wave becomes 0, the R-phase is turned off and the T-phase is turned on. Timing t12-t13 is the section Drs.

  When the switching mode generator 5b specifies that the current mode is the mode IV, the control signal | R | = −R and the control signal | T | = T are set to perform the same control as in the mode I.

[Switching Pattern in Mode II and Mode V of Embodiment]
FIG. 7 is a diagram illustrating an example of switching patterns in mode II and mode V of the embodiment. With reference to FIG. 7, switching patterns generated by switching pattern generator 5b in mode II and mode V will be described.

  When the switching pattern generator 5b specifies that the current mode is mode II, as shown in FIG. 7, the control signal | S | + | T | -1 = ST-1 and the control voltage | T | = As T, the following switching pattern is generated.

  That is, at timing t20, the S phase and the T phase are turned on. Subsequently, the S phase is turned off and the R phase is turned on at timing t21 at which the T-phase sawtooth wave switches to the control signal | S | + | T | -1. Timing t20 to t21 is the section Dst.

  Subsequently, at the timing t22 at which the T-phase sawtooth wave contacts the control signal | T |, the S phase is turned on and the T phase is turned off. Timing t21-t22 is the section Drt. Subsequently, at a timing t23 when the T-phase sawtooth wave becomes 1 and the R-phase sawtooth wave becomes 0, the R phase is turned off and the T phase is turned on. Timing t22 to t23 is a section Drs.

  When the switching pattern generator 5b specifies that the current mode is mode V, the control signal | S | + | T | -1 = −S + T−1 and the control signal | T | The same control is performed.

[Switching Pattern in Mode III and Mode VI of Embodiment]
FIG. 8 is a diagram illustrating an example of switching patterns in mode III and mode VI of the embodiment. With reference to FIG. 8, switching patterns generated by switching pattern generator 5b in modes III and VI will be described.

  As shown in FIG. 8, when the switching mode generator 5b specifies that the current mode is mode III, the control signal | R | = −R, the control signal | R | + | S | −1 = −R + S−. 1, the following switching pattern is generated.

  That is, the S phase and the T phase are turned on at timing t30. Subsequently, at the timing t31 when the R-phase sawtooth wave is switched to the control signal | R |, the S-phase is turned off and the R-phase is turned on. Timing t30 to t31 is a section Dst.

  Subsequently, the S phase is turned on and the T phase is turned off at timing t32 when the R-phase sawtooth wave switches to the control signal | R | + | S | -1. Timing t31-t32 is the section Drt. Subsequently, at the timing t33 when the R-phase sawtooth wave becomes 0, the R-phase is turned off and the T-phase is turned on. Timing t32 to t33 is a section Drs.

  When the switching mode generator 5b specifies that the current mode is mode VI, the control signal | R | = R and the control signal | R | + | S | -1 = R-S-1 are set as the mode III. The same control is performed.

  In the embodiment, the case where a sawtooth wave is used as a carrier waveform to generate a switching pattern has been described. However, the present invention is not limited to this, and satisfies the restrictions on the maximum voltage phase and the minimum voltage phase. For example, a carrier waveform such as a triangular wave may be used. Further, the on time and off time for generating the switching pattern may be tabulated in advance.

[Control of switching frequency of embodiment]
FIG. 9 is a diagram illustrating an example of a switching frequency control method according to the embodiment. In FIG. 9, the current waveform of the current IL flowing through the DC reactor 2 when the frequency is constant indicates a ripple shape. Hereinafter, the amplitude of the ripple waveform of the current IL is expressed as “ripple amplitude”. As shown in FIG. 9, the sawtooth wave generator 5b2 of the switching pattern generator 5b has a timing at which the amplitude of the waveform of the current IL is maximized, that is, the ripple amplitude of the current IL is maximized (= three phases). At the time when the intermediate potential of the bidirectional switch circuit 3 becomes 0), the switching frequency f [kHz] for switching the switches SW-R, SW-S, and SW-T of the bidirectional switch circuit 3 becomes maximum, that is, the switching period T [μs]. Is controlled to be minimized.

  On the other hand, as shown in FIG. 9, the sawtooth wave generator 5b2 has the minimum amplitude of the waveform of the current IL (= 0), that is, the ripple amplitude of the current IL is minimum (= 0). At the timing (= the timing at which the intermediate potential of the three phases becomes 0), the switching frequency f [kHz] for switching the switches SW-R, SW-S, and SW-T of the bidirectional switch circuit 3 is minimized. Control is performed so that the period T [μs] is maximized.

  That is, as shown in FIG. 9, the switching frequency f [kHz] increases during the period when the ripple amplitude of the current IL decreases, so that the switching frequency f [kHz] increases during the period when the ripple amplitude of the current IL increases. By periodically controlling in this way, the ripple amplitude of the current IL is reduced without changing the average value of the switching frequency f [kHz], and the period in which the current IL = 0 is prevented from appearing so that the discontinuous mode is set. Do not reach. When the switching frequency f [kHz] is controlled to be high (the switching period T [μs] is short) during the period in which the ripple amplitude of the current IL is large, the section in which the switching element of the bidirectional switch circuit 3 is turned on and off is short. Thus, the change in the ripple amplitude of the current IL can be reduced.

  As shown in FIG. 9, the switching frequency f [kHz] is divided into six modes (mode I to mode VI) that are divided into three-phase AC voltages (R-phase voltage, S-phase voltage, and T-phase voltage). It changes in a sin wave shape with one of the modes as one cycle. The switching frequency f [kHz] that changes in a sin wave shape with one mode as one period is obtained by calculating the optimum period based on the above (Equation 1) or obtaining the optimum period with reference to the frequency determination table 5b1-t. It is obtained. However, the switching frequency f [kHz] changing with the sin wave shape is merely an example, and is not limited to the sin wave shape. If the ripple amplitude of the current IL is reduced so that the period when the current IL = 0 does not appear and the discontinuous mode is not reached, another mode in which one mode is one period (for example, It may be a triangular wave shape or the like. If it is not necessary to consider power loss due to switching (hereinafter referred to as “switching loss”) (for example, when the current value is small and the power loss is small), the switching frequency f [kHz] is set to a high frequency (for example, 30 kHz). It may be fixed to.

[Simulation comparing ripple amplitude of current IL between embodiment and conventional technology]
FIG. 10 is a diagram for comparing and explaining the amplitude of the ripple waveform of the current IL according to the embodiment and the prior art. FIG. 10 is a diagram for explaining the effect when the optimum period T (θ) is calculated and applied using the above (formula 1) in the period determining unit 5b1. In FIG. 10, the horizontal axis represents the detected phase θ [°], and the vertical axis represents the ripple amplitude [A] of the current IL.

  FIG. 11 is a diagram for explaining a ripple waveform of the current IL. As shown in FIG. 11, in the waveform of the current IL, for example, the ripple amplitude of the detection phase θ = 100 [°] is the amplitude of the current IL indicated by L100. As shown in FIG. 11, in the waveform of the current IL, for example, the ripple amplitude of the detection phase θ = 110 [°] is the amplitude of the current IL indicated by L110. The prerequisites for the simulation shown in FIG. 11 are that the inductance L1 of the DC reactor 2 is 500 μH and the input voltage (line voltage) is 400V. However, the switching frequency of the bidirectional switch circuit 3 is 20 kHz in the prior art, and is a value calculated based on the above (Equation 2) in the embodiment.

  Referring to FIG. 10, the ripple amplitude of the current IL of the embodiment has a suppressed peak value around the detection phase θ of about 105 to 135 [°] compared to the ripple amplitude of the current IL of the prior art. I understand. That is, the current ripple of the output current I0 is small. However, when the detection phase θ is around 90 to 105 [°] and around 135 to 150 [°], the ripple amplitude of the current IL of the embodiment increases as compared with the ripple amplitude of the current IL of the prior art. ing. However, since the ripple amplitude is leveled, even if the output current I0 is decreased, the output current I0 is set to a predetermined value in order to reach a discontinuous mode in which a period when the current IL = 0 appears (for example, see FIG. 16B). Since it is necessary to reduce the above, there is an effect of suppressing the discontinuous mode.

[Simulation comparing switching frequency of current IL between embodiment and conventional technology]
FIG. 12 is a diagram for comparing and explaining the switching frequencies of the embodiment and the prior art. As can be seen from FIG. 12, the average SW (switching) frequency calculated by the above (Equation 1) is equal to the average SW frequency of the conventional method at 20 kHz. This is also clear from the fact that the detection phase θ [°] shown in FIG. 12 is established in one period of 90 to 150 [°]. In this way, discontinuous modes can be suppressed without increasing the switching loss by making the average value of the switching frequency equal to that of the prior art.

[Modification of Embodiment]
(1) Information Corresponding to the Optimal Period In the embodiment, the optimal period T is a function of the detection phase θ like the optimal period T (θ), and the information associated with the optimal period T is the detection phase θ. However, the detection phase θ of the three-phase AC power can be specified from the R-phase, S-phase, and T-phase input voltages of the three-phase AC power. Therefore, the information associated with the optimum period T may be the R-phase, S-phase, and T-phase input voltages of the three-phase AC power. That is, the ripple waveform of the current flowing through the DC reactor of the three-phase rectifier may be reduced by changing the switching period according to the voltage of the three-phase AC power.

(2) ON / OFF of the cycle determining unit 5b1 of the switching pattern generator 5b In the embodiment, the cycle determining unit 5b1 of the switching pattern generator 5b is based on the input detection phase θ and has an optimum cycle T (θ). Is output. However, the present invention is not limited to this, and the switching pattern generator 5b may include a control unit that turns on / off the function of the cycle determination unit 5b1 that outputs the optimum cycle T (θ).

(3) Determination of Necessity of Adjustment of Switching Period T by Period Determination Unit 5b1 Further, the switching pattern generator 5b may include a determination unit that determines the necessity of adjustment of the switching period T by the period determination unit 5b1. Good. For example, the determination unit determines whether or not the switching period T needs to be adjusted based on the output current of the three-phase rectifier and the magnitude of the ripple amplitude of the current waveform flowing through the DC reactor. The control unit that turns on / off the function of the cycle determination unit 5b1 turns on the function of the cycle determination unit 5b1 when the determination unit determines that the switching cycle T needs to be adjusted by the cycle determination unit 5b1. On the other hand, the control unit that turns on / off the function of the cycle determination unit 5b1 turns off the function of the cycle determination unit 5b1 when the determination unit determines that the adjustment of the switching cycle T by the cycle determination unit 5b1 is not required. To do. When it is determined that the adjustment of the switching period T is not required, the period determining unit 5b1 may output the switching period T having a predetermined fixed value without adjusting the switching period T.

  The switching pattern generator 5b has a predetermined fixed value output by the cycle determining unit 5b1, for example, when the user does not need to adjust the switching cycle T and the cycle determining unit 5b1 does not adjust the switching cycle T. Switching control of the bidirectional switch circuit 3 may be performed with the switching cycle T of the value, or switching control of the bidirectional switch circuit 3 may be performed with the switching cycle T of a predetermined fixed value stored in the switching pattern generator 5b. Good.

  Furthermore, the determination unit that determines whether or not the switching cycle T needs to be adjusted by the cycle determination unit 5b1 is adjusted by the cycle determination unit 5b1 when the output current I0 of the three-phase rectifier 12 is less than a predetermined threshold. If the output current of the three-phase rectifier 12 is greater than or equal to a predetermined threshold value, it may be determined that the adjustment of the switching period T by the period determining unit 5b1 is not necessary.

  Alternatively, the determination unit that determines whether the switching period T needs to be adjusted by the period determination unit 5b1 is determined when the ripple amplitude (for example, the minimum value) of the current waveform flowing through the DC reactor is less than a predetermined threshold. If the ripple amplitude (for example, the minimum value) of the current waveform flowing through the DC reactor is greater than or equal to a predetermined threshold value, it is necessary to adjust the switching cycle T by the cycle determination unit 5b1. You may judge. In addition, what is necessary is just to obtain | require the threshold value mentioned above by experiment, for example.

  Although the embodiment has been described above, the technology disclosed in the present application is not limited by the above-described content. In addition, the above-described components include those that can be easily assumed by those skilled in the art, those that are substantially the same, and those in a so-called equivalent range. Furthermore, the above-described components can be appropriately combined. Furthermore, at least one of various omissions, replacements, and changes of the components can be made without departing from the scope of the embodiment.

DESCRIPTION OF SYMBOLS 1 3 phase alternating current power supply 2 DC reactor 3 Bidirectional switch circuit 4 Bridge diode 5 Switching pattern generation circuit 5a Phase detector 5b Switching pattern generator 5b1 Period determination part 5b1-t Frequency determination table 5b2 Sawtooth wave generation part 5b3 Control voltage generation Section 6 Drive circuit 7 Load 8 Three-phase reactor 9 Input capacitor 10 Capacitor 11 Diode 12 Three-phase rectifier SW-R, SW-S, SW-T switch

Claims (7)

A three-phase rectifier that converts three-phase AC power supplied from a three-phase AC power source into DC power,
A full-wave rectifier circuit for rectifying the three-phase AC power into DC power;
A bidirectional switch circuit for turning on / off the input of each phase from the three-phase AC power source to the full-wave rectifier circuit;
DC reactor,
A switching pattern generation unit that generates a switching pattern of each phase for turning ON / OFF the bidirectional switch circuit for each switching period;
A switching period adjusting unit for adjusting the switching period;
A switching control unit that performs switching control of the bidirectional switch circuit at a switching period adjusted by the switching period adjustment unit based on the switching pattern generated by the switching pattern generation unit;
The switching pattern generator is
Based on the magnitude relationship of the voltage of each phase of the three-phase AC power, one cycle of the three-phase AC power is divided into a plurality of modes, and different carrier waveforms and control signals are generated according to the modes, From the waveform and the control signal, a different switching pattern is generated according to the mode and each phase,
The switching cycle adjustment unit is
A three-phase rectifier characterized by reducing a ripple waveform of a current flowing through the DC reactor by changing the switching period. The switching cycle adjustment unit is
The three-phase rectifier according to claim 1, wherein the switching period is changed according to the ripple waveform.   The three-phase rectifier according to claim 1, further comprising a control unit that turns on and off the switching cycle adjustment unit. A determination unit that determines whether the switching cycle adjustment unit needs to adjust the switching cycle;
The controller is
When the determination unit determines that the switching cycle adjustment unit needs to adjust the switching cycle, the switching cycle adjustment unit is turned on and the switching control unit is adjusted by the switching cycle adjustment unit. And switching control of the bidirectional switch circuit,
When the determination unit determines that the switching cycle adjustment by the switching cycle adjustment unit is not required, the switching cycle adjustment unit is turned off, and the switching control unit is configured to switch the both with a predetermined fixed switching cycle. The three-phase rectifier according to claim 3, wherein the directional switch circuit is switching-controlled. The determination unit
When the output current of the three-phase rectifier is less than a predetermined threshold, it is determined that the switching cycle adjustment by the switching cycle adjustment unit is necessary,
5. The three-phase rectifier according to claim 4, wherein when the output current of the three-phase rectifier is equal to or greater than the predetermined threshold, it is determined that the switching period adjustment by the switching period adjustment unit is not required. The switching cycle adjustment unit is
A cycle number determination table in which the phase of the three-phase AC power is associated with a switching cycle;
The three-phase rectifier according to any one of claims 1 to 5, wherein the switching period is adjusted by a switching period associated with the phase of the three-phase AC power in the period number determination table. A switching control method for a three-phase rectifier that converts three-phase AC power supplied from a three-phase AC power source into DC power,
The three-phase rectifier
A full-wave rectifier circuit for rectifying the three-phase AC power into DC power;
A bidirectional switch circuit for turning on / off the input of each phase from the three-phase AC power source to the full-wave rectifier circuit;
DC reactor,
A switching pattern generation unit that generates a switching pattern of each phase for turning ON / OFF the bidirectional switch circuit for each switching period;
A switching period adjusting unit for adjusting the switching period;
A switching control unit that performs switching control of the bidirectional switch circuit at a switching period adjusted by the switching period adjustment unit based on the switching pattern generated by the switching pattern generation unit;
The switching pattern generator is
Based on the magnitude relationship of the voltage of each phase of the three-phase AC power, one cycle of the three-phase AC power is divided into a plurality of modes, and different carrier waveforms and control signals are generated according to the modes, From the waveform and the control signal, a different switching pattern is generated according to the mode and each phase,
The switching cycle adjustment unit is
A switching control method for a three-phase rectifier, wherein the switching period is changed to reduce a ripple waveform of a current flowing through the DC reactor.

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