JP4501144B2 - AC-DC converter - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an AC-DC converter that converts AC input power to DC output power, and particularly to an AC-DC converter that prevents a switching element provided in a conversion circuit from being damaged by external noise or the like.
[0002]
[Prior art]
A conventional AC-DC converter has a filter reactor (2d, 2e, 2f) and a filter capacitor (2a, 2b, 2c) as shown in FIG. 4, for example, and an AC input terminal of a three-phase AC power source (1). Connected between the filter circuit (2) connected to (1A, 1B, 1C), the conversion circuit (3) connected to the output terminal of the filter circuit (2), and the output terminal of the conversion circuit (3) A return diode (16) as a return rectifier and a smoothing capacitor (18) connected to the return diode (16) via a DC reactor (17) are provided. The conversion circuit (3) includes first to sixth IGBTs (Insulated Gate Bipolar Transistors) (4 to 9) that constitute three pairs of switching elements that are bridged (bridged), and first to sixth. First to sixth backflow prevention diodes (10 to 15) constituting backflow prevention rectifier elements connected in series with each of the IGBTs (4 to 9). A current detector (19) is connected between the DC reactor (17) and the DC output terminal (40A), and the current I flowing through the DC reactor (17)_LV corresponding to the current V_LDetect as. A phase voltage detection transformer (20) is connected to the AC input terminals (1A, 1B, 1C), and the U-phase, V-phase and W-phase AC input voltages V from the three-phase AC power source (1)._U, V_V, V_WIs detected. The control circuit (21) detects the detection voltage V of the phase voltage detection transformer (20)._U, V_V, V_WAnd the detection voltage V of the current detector (19)_LAnd voltage V of the smoothing capacitor (18)_DCIn response to the first to sixth on / off control signals V to the gate terminals of the first to sixth IGBTs (4 to 9) in the conversion circuit (3)._G1, V_G2; V_G3, V_G4; V_G5, V_G6To turn on / off the first to sixth IGBTs (4 to 9).
[0003]
As shown in FIG. 5, the control circuit (21) includes a reference power source (22), a first error amplifier (23), a second error amplifier (24), and a phase current reference signal generation circuit (25). A triangular wave oscillation circuit (26), a PWM comparator (27, 28, 29), a line current pulse conversion circuit (30), and a control signal output circuit (31). The reference power source (22) is a DC output voltage V output from both ends of the smoothing capacitor (18)._DCReference voltage V that defines the reference value of_RDIs generated. The first error amplifier (23) has a voltage V of the smoothing capacitor (18)._DCThe reference voltage V of the reference power supply (22)_RDTheir error voltage signal V compared to_E1Is output. The second error amplifier (24) is a detection voltage V of the current detector (19)._LOutput signal V of the first error amplifier (23)_E1Their error voltage signal V compared to_E2Is output. The phase current reference signal generation circuit (25) has a detection voltage V of the phase voltage detection transformer (20)._U, V_V, V_WAnd the output signal V of the second error amplifier (24)._E2Based on the current reference signal V of U phase, V phase and W phase_RUV, V_RVW, V_RWUIs generated. The triangular wave oscillation circuit (26) is a triangular wave signal V having a frequency (1 to 100 kHz) sufficiently higher than the frequency (50 to 60 Hz) of the three-phase AC power source (1)._TIs generated. The PWM comparators (27, 28, 29) are the U-phase, V-phase and W-phase current reference signals V of the phase current reference signal generation circuit (25)._RUV, V_RVW, V_RWUThe triangular wave signal V of the triangular wave oscillation circuit (26)_TCompared with the PWM modulation signal V of the current of each phase_PUV, V_PVW, V_PWUIs output. The line current pulse conversion circuit (30) is used for the PWM modulation signal V of each PWM comparator (27), (28), (29)._PUV, V_PVW, V_PWUIs a ternary line current pulse signal V of “1”, “0” or “−1”._SU(= V_PUV-V_PWU), V_SV(= V_PVW-V_PUV), V_SW(= V_PWU-V_PVW). The control signal output circuit (31) is used for each line current pulse signal V_SU, V_SV, V_SWThe first to sixth on / off control signals V applied to the respective gate terminals of the first to sixth IGBTs (4 to 9) of the conversion circuit (3) by discriminating the respective values of_G1, V_G2; V_G3, V_G4; V_G5, V_G6Is output.
[0004]
The control signal output circuit (31) is used for each line current pulse signal V_SU, V_SV, V_SWIs one, the first, third or fifth of the first, third or fifth IGBT (4, 6, 8) on the positive side of the corresponding arm is applied to the gate terminal. ON / OFF control signal V_G1, V_G3, V_G5Is set to a high (H) level to turn on the first, third or fifth IGBT (4, 6, 8). Each line current pulse signal V_SU, V_SV, V_SWIs “−1”, the second, fourth or sixth applied to the gate terminal of the second, fourth or sixth IGBT (5, 7, 9) on the negative side of the corresponding arm. ON / OFF control signal V_G2, V_G4, V_G6Is set to a high (H) level to turn on the second, fourth or sixth IGBT (5, 7, 9). Furthermore, each line current pulse signal V_SU, V_SV, V_SWIs “0”, the first and second IGBTs (4,5), third and fourth IGBTs (6,7) or fifth of the positive and negative sides of the corresponding arm And the first and second, third and fourth or fifth and sixth on / off control signals V applied to the gate terminals of the sixth IGBT (8, 9)._G1, V_G2; V_G3, V_G4; V_G5, V_G6Any one of the first and second IGBTs (4, 5), the third and fourth IGBTs (6, 7) or the fifth and sixth IGBTs (8, 9) are set to a low (L) level. ) Is turned off.
[0005]
The operation of the AC-DC converter shown in FIG. 4 is as follows. For example, as shown in FIG. 6A, a U-phase AC input current I of a three-phase AC power source (1)._UIs a positive half cycle, the detection voltage V of the current detector (19)_LAnd detection voltage V of phase voltage detection transformer (20)_U, V_V, V_WAnd voltage V of the smoothing capacitor (18)_DCThe first on / off control signal V PWM-modulated according to_G1Is input from the control signal output circuit (31) in the control circuit (21) to the gate terminal of the first IGBT (4) in the conversion circuit (3), and the first IGBT (4) is turned on / off. The At the same time, the second on / off control signal V input to the gate terminal of the second IGBT (5)._G2Becomes constant at a low level, and the second IGBT (5) is turned off. Also, the U-phase AC input current I of the three-phase AC power supply (1)_UIs the negative half cycle, the detection voltage V of the current detector (19)_LAnd detection voltage V of phase voltage detection transformer (20)_U, V_V, V_WAnd voltage V of the smoothing capacitor (18)_DCSecond on / off control signal V modulated in accordance with PWM_G2Is input from the control signal output circuit (31) in the control circuit (21) to the gate terminal of the second IGBT (5) in the conversion circuit (3), and the second IGBT (5) is turned on / off. The At the same time, the first on / off control signal V input to the gate terminal of the first IGBT (4)._G1Becomes constant at a low level, and the first IGBT (4) is turned off. As a result, the current I input to the U-phase arm of the conversion circuit (3)_U0Is the peak value I as shown in FIG._U0PThe positive and negative pulse current waveform is as follows. Positive and negative pulsed current I input to the U-phase arm of converter circuit (3)_U0The filter circuit (2) removes low-order harmonic components and becomes a sine wave current of only the fundamental component. The V-phase arm and the W-phase arm also perform substantially the same operation as described above. However, when the first IGBT (4) of the U-phase arm is turned on, either the fourth IGBT (7) of the V-phase arm or the sixth IGBT (9) of the W-phase arm is turned on. When the second IGBT (5) of the U-phase arm is in the on state, either one of the third IGBT (6) of the V-phase arm or the fifth IGBT (8) of the W-phase arm is in the on state. .
[0006]
Therefore, for example, when the first IGBT (4) of the U-phase arm and the fourth IGBT (7) of the V-phase arm of the conversion circuit (3) are in the ON state, the U-phase output of the three-phase AC power source (1) , Filter circuit (2), first backflow prevention diode (10), first IGBT (4), DC reactor (17), smoothing capacitor (18) and load (32), fourth IGBT (7) The fourth backflow prevention diode (13), the filter circuit (2), the current flows through the V-phase output path of the three-phase AC power supply (1), energy is stored in the DC reactor (17) and the smoothing capacitor (18) is charged. Thereafter, when the first IGBT (4) of the U-phase arm of the conversion circuit (3) is turned off, the stored energy of the DC reactor (17) and the charge of the smoothing capacitor (18) are released, and the DC reactor (17) A current flows through the path of the smoothing capacitor (18), the load (32), and the return diode (16). When the second IGBT (5) of the U-phase arm and the third IGBT (6) of the V-phase arm of the conversion circuit (3) are in the ON state, the V-phase output of the three-phase AC power source (1), Filter circuit (2), third backflow prevention diode (12), third IGBT (6), DC reactor (17), smoothing capacitor (18) and load (32), second IGBT (5), Current flows through the U-phase output path of the second backflow prevention diode (11), filter circuit (2), and three-phase AC power supply (1), energy is stored in the DC reactor (17) and a smoothing capacitor ( 18) is charged. Thereafter, when the second IGBT (5) of the U-phase arm of the conversion circuit (3) is turned off, the stored energy of the DC reactor (17) and the charge of the smoothing capacitor (18) are released, and the DC reactor (17) A current flows through the path of the smoothing capacitor (18), the load (32), and the return diode (16). When the third and fourth IGBTs (6, 7) of the V-phase arm of the conversion circuit (3) and the fifth and sixth IGBTs (8, 9) of the W-phase arm are turned on / off, or the conversion circuit The case where the first and second IGBTs (4, 5) of the U-phase arm (3) and the fifth and sixth IGBTs (8, 9) of the W-phase arm are turned on / off is substantially the same as described above. Is performed. Thus, the DC current I at a certain level as shown in FIG._LFlows to the DC reactor (17), and the DC output voltage V is applied across the smoothing capacitor (18)._DCWill occur.
[0007]
DC output voltage V output from both ends of the smoothing capacitor 18 by the on / off operation of the first to sixth IGBTs 4 to 9 of the conversion circuit 3_DCIs the reference voltage V of the reference power supply (22) by the first error amplifier (23) in the control circuit (21)._RDAnd the DC output voltage V_DCAnd reference voltage V_RDError voltage signal V_E1Is output from the first error amplifier (23). Error voltage signal V of the first error amplifier (23)_E1Is the detection voltage V of the DC reactor (17) detected by the current detector (19) in the second error amplifier (24)._LAnd the error voltage signal V_E1And detection voltage V_LError voltage signal V_E2Is output from the second error amplifier (24). Error voltage signal V of the second error amplifier (24)_E2Is the detection voltage V of the phase voltage detection transformer (20)._U, V_V, V_WIs input to the phase current reference signal generation circuit (25) together with the detection voltage V_U, V_V, V_WAnd error voltage signal V_E2From the phase current reference signal generation circuit (25), the U-phase, V-phase and W-phase current reference signals V as shown in FIG._RUV, V_RVW, V_RWUIs output. U-phase, V-phase and W-phase current reference signals V of the phase current reference signal generation circuit (25)_RUV, V_RVW, V_RWUIs the triangular wave signal V of the triangular wave oscillation circuit (26) in each PWM comparator (27, 28, 29)._TAnd the current reference signal V_RUV, V_RVW, V_RWUAnd triangular wave signal V_TIs V_RUV, V_RVW, V_RWU<V_TAt low level, V_RUV, V_RVW, V_RWU> V_TPWM modulation signal V as shown in FIGS. 7 (B), (C), (D), which becomes high at_PUV, V_PVW, V_PWUIs output from each PWM comparator (27, 28, 29). PWM modulation signal V of each PWM comparator (27, 28, 29)_PUV, V_PVW, V_PWUThe line current pulse signal V as shown in FIGS. 7 (E), (F) and (G) in the line current pulse conversion circuit (30)._PUV-V_PWU= V_SU; V_PVW-V_PUV= V_SV; V_PWU-V_PVW= V_SWIs converted to Line current pulse signal V of line current pulse conversion circuit (30)_{S U}, V_SV, V_SWAre determined by the control signal output circuit (31), that is, “1”, “0” or “−1”, respectively, and the control signal output circuit (31) to the first to first conversion circuits (3). The first to sixth on / off control signals V are applied to the gate terminals of the sixth IGBT (4 to 9)._G1, V_G2; V_G3, V_G4; V_G5, V_G6Are given respectively.
[0008]
Thus, the current I flowing through the DC reactor (17)_LAnd three-phase AC power supply (1) U-phase, V-phase and W-phase AC input voltage V_U, V_V, V_WAnd the DC output voltage V across the smoothing capacitor (18)._DCIn response to this, the first to sixth IGBTs (4 to 9) in the conversion circuit (3) are on / off controlled by the control circuit (21), and from the three-phase AC power source (1) through the filter circuit (2). AC input current I flowing in the U-phase, V-phase and W-phase arms of the converter circuit (3)_U0, I_V0, I_W0Is controlled to be sinusoidal and the DC output voltage V output from the DC output terminals (40A, 40B)_DCIs held at a certain level.
[0009]
In the AC-DC converter shown in FIG. 4, the AC input current I flowing from the three-phase AC power source (1) to the U-phase, V-phase, and W-phase arms of the conversion circuit (3) via the filter circuit (2)._U0, I_V0, I_W0Is controlled to be sinusoidal and the DC output voltage V output from the DC output terminals (40A, 40B)_DCIs maintained at a constant level, the input power factor can be increased to about 1.0 and a highly stable DC output voltage V_DCIs obtained.
[0010]
[Problems to be solved by the invention]
By the way, in the conventional AC-DC converter shown in FIG. 4, each line current pulse signal V shown in FIGS. 7 (E), (F), and (G)._SU, V_SV, V_SWDuring the period when the values of all are “0” and all of the first to sixth IGBTs (4 to 9) in the conversion circuit (3) are in the OFF state, the AC input terminals (1A, 1B, 1C) side and Impedance seen from the DC output terminal (40A, 40B) side becomes high. At this time, noise enters between the U-phase, V-phase, or W-phase AC input line and the ground (chassis) from the outside, and the surge voltage generated by this noise is converted into first to first in the conversion circuit (3). Applied to the 6 IGBTs (4 to 9) and the first to sixth backflow prevention diodes (10 to 15), and the first to sixth IGBTs (4 to 9) and the first to sixth backflow prevention diodes. The diode (10-15) could be destroyed. In order to prevent this, it is conceivable to connect a capacitor in parallel with the first to sixth IGBTs (4 to 9) and the first to sixth backflow prevention diodes (10 to 15). It is not preferable in operation. For example, when a capacitor is connected in parallel with the first to sixth backflow prevention diodes (10 to 15), the switching speed is reduced and a short-circuit current flows, and the first to sixth IGBTs (4 to 9) and the first The first to sixth backflow prevention diodes (10 to 15) may burn out.
[0011]
Therefore, an object of the present invention is to provide an AC-DC converter that can prevent the switching element of the conversion circuit from being destroyed by external noise.
[0012]
[Means for Solving the Problems]
  The AC-DC converter according to the present invention is connected between the filter circuit (2) connected to the AC input terminal (1A, 1B, 1C) and between the filter circuit (2) and the DC output terminal (40A, 40B). Converter circuit (3) and smoothing capacitor (18) connected between DC output terminals (40A, 40B), and switching elements (4-9) provided in converter circuit (3) are turned on and off. By converting the AC power supplied from the AC input terminals (1A, 1B, 1C) through the filter circuit (2) into DC power by the conversion circuit (3), the DC output terminals (40A, 40B) Take out the DC output. In this AC-DC converter, the filter circuit (2) includes a filter reactor (2d, 2e, 2f) inserted between the AC input terminals (1A, 1B, 1C) and the conversion circuit (3), and a filter reactor. (2d, 2e, 2f) and a star-connected filter capacitor (2a, 2b, 2c) connected to the connection point between the converter circuit (3) and at least between the DC output terminals (40A, 40B) Two voltage dividing capacitors (35, 36) are connected in series, and the connection midpoint of the star-connected filter capacitors (2a, 2b, 2c) and the connection midpoint of the voltage dividing capacitors (35, 36) are auxiliary capacitors. Connect to each other via (44). When a surge voltage occurs at the AC input terminals (1A, 1B, 1C) due to external noise, the filter reactor (2d, 2e, 2f) and filter of the filter circuit (2) from the AC input terminals (1A, 1B, 1C) Capacitors (2a, 2b, 2c), auxiliary capacitors (44) and voltage dividing capacitors (35, 36) between DC output terminals (40A, 40B) and ground capacitance (43) between DC output line and ground Therefore, a surge voltage is not directly applied to the conversion circuit (3). Therefore, destruction of the switching elements (4-9) in the conversion circuit (3) due to external noise can be prevented. Also, the voltage dividing capacitor (35, 36) increases the capacitance of the smoothing capacitor (18), so the DC output voltage (V_DC) Is further stabilized. Furthermore, external noise can be effectively used as DC output power.
[0013]
  Also, filter capacitors (2a, 2b, 2c) are star-connected to each output line of the filter circuit (2), and the connection midpoint of the filter capacitors (2a, 2b, 2c) and the voltage dividing capacitors (35, 36) Since the auxiliary capacitor (44) is connected to the midpoint of connection, part of the harmonic voltage applied to the filter capacitors (2a, 2b, 2c) is shared by the auxiliary capacitor (44), and the filter circuit (2 The withstand voltage of the filter capacitors (2a, 2b, 2c) in () can be lowered.
[0014]
In another embodiment of the present invention, the conversion circuit (3) includes a plurality of conversion circuits (3A, 3B) connected in parallel between the filter circuit (2) and the DC output terminals (40A, 40B). ing. Also, the reflux rectifier element (16A, 16B) connected between the output terminals of the conversion circuit (3A, 3B), each output terminal of the conversion circuit (3A, 3B) and the DC output terminal (40A, 40B) Between the DC reactor (17A, 17B, 34A, 34B) connected between the DC rectifier (16A, 16B) and the DC reactor (17A, 17B, 34A, 34B) and the voltage dividing capacitor (35, 36) and a voltage balancing rectifier element (37A, 37B, 38A, 38B) connected between the connection midpoints of (36) and a DC reactor (17A, 17B, for each output terminal of the conversion circuit (3A, 3B). 34A, 34B), a voltage dividing capacitor (35, 36), and a voltage balancing rectifier element (37A, 37B, 38A, 38B) are formed. When the switching element (4-9) in any of the conversion circuits (3A, 3B) is switched off, a current corresponding to the difference in energy stored in the DC reactor (17A or 17B, 34A or 34B) is generated. It flows to a DC circuit composed of a DC reactor (17A or 34A, 17B or 34B), a voltage dividing capacitor (35 or 36) and a voltage balancing rectifier (37A, 38A, 37B, 38B), and a voltage dividing capacitor (35 or 36) is charged. As a result, the voltage dividing capacitors (35, 36) are charged to a substantially equal voltage level, and an equal current flows through the DC reactors (17A, 34A, 17B, 34B). , 3B) is applied to the switching elements (4-9). Therefore, in the above embodiment, the switching elements (4 to 9) of the conversion circuit (3A, 3B) due to the surge voltage generated by the external noise can be prevented from being destroyed, and the unequal voltage generated due to the unbalance of the output current. There is an advantage that it is possible to suppress the destruction of the switching elements (4 to 9) in the conversion circuit (3A, 3B).
[0015]
In another embodiment of the present invention, the positive side DC reactors (17A, 17B) respectively connected to the positive side output terminals of the conversion circuit (3A, 3B) are connected and the intermediate tap is on the positive side. Connected between the positive current balancing reactor (41) connected to the DC output terminal (40A) and the negative DC reactor (34A, 34B) connected to the negative output terminal of the converter circuit (3A, 3B). And a negative current balancing reactor (42) having an intermediate tap connected to the negative DC output terminal (40B). The positive side of each converter circuit (3A, 3B) is obtained by the current based on the level difference of the current flowing through each positive output line of the multiple converter circuits (3A, 3B) flowing into the positive current balancing reactor (41). A balanced and equal current flows through the output line. Similarly, the current based on the level difference between the currents flowing through the negative output lines of the plurality of conversion circuits (3A, 3B) flows into the negative current balancing reactor (42), whereby each conversion circuit (3A, 3B) A balanced and uniform current flows through the negative output line. Therefore, since a balanced voltage is applied to the switching elements (4-9) that are turned off in the plurality of conversion circuits (3A, 3B), each conversion circuit (3A, 3A, 3B) switching elements (4 to 9) can be prevented from being destroyed, and the switching elements (4 to 9) in each converter circuit (3A, 3B) can be destroyed by an unequal voltage generated by output current imbalance. There is an advantage that can be suppressed.
[0016]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments of an AC-DC converter according to the present invention will be described below with reference to FIGS. However, in FIG. 1, the same parts as those in FIG. 4 are denoted by the same reference numerals and the description thereof is omitted, and in FIG. 2 and FIG. 3 showing another embodiment of the AC-DC converter according to the present invention, FIG. The same reference numerals are assigned to the same parts as in FIG.
As shown in FIG. 1, the AC-DC converter according to the present embodiment has a star-shaped filter capacitor (2a, 2b, 2c) connected to the U-phase, V-phase, and W-phase output lines of the filter circuit (2). Two voltage dividing capacitors (35, 36) are connected in series between the DC output terminals (40A, 40B), and the connection midpoint of the filter capacitors (2a, 2b, 2c) and the voltage dividing capacitor (35, 36) This is characterized in that the connection midpoints are connected to each other via an auxiliary capacitor (44). In FIG. 1, reference numeral (43) denotes a stray capacitance existing between the DC output line connecting the conversion circuit (3) and the DC output terminals (40A, 40B) and the ground. Other configurations are the same as those of the conventional AC-DC converter shown in FIG.
[0017]
In the above configuration, the AC input terminal (1A) of the three-phase AC power source (1) and the filter circuit during the period in which all the first to sixth IGBTs (4 to 9) in the conversion circuit (3) are in the OFF state. When external noise enters between the U-phase input line connecting the (2) and the conversion circuit (3) and the ground, a surge voltage is generated at the AC input terminal (1A). The surge voltage is applied to the first and second IGBTs (4, 5) and the first and second backflow prevention diodes (10, 11) of the U-phase arm in the conversion circuit (3). Voltage divider capacitor (35, 36) between AC input terminal (1A) and filter reactor (2d) in filter circuit (2) and filter capacitor (2a), auxiliary capacitor (44), DC output terminal (40A, 40B) In addition, since a surge current flows through the chassis connected to the ground via the stray capacitance (43) between the DC output line of the conversion circuit (3) and the ground, the first and second U-phase arms in the conversion circuit (3) No surge voltage is directly applied to the second IGBT (4, 5) and the first and second backflow prevention diodes (10, 11). Similarly, between the AC input terminal (1B) of the three-phase AC power source (1), the V-phase input line connecting the filter circuit (2) and the conversion circuit (3) and the ground, or the three-phase AC power source (1) When external noise enters between the W-phase input line connecting the AC input terminal (1C), filter circuit (2), and converter circuit (3) and the ground, surge current is also generated in the same path as above. Therefore, the third and fourth IGBTs (6, 7) of the V-phase arm and the third and fourth backflow prevention diodes (12, 13) of the V-phase arm in the conversion circuit (3) or the fifth of the W-phase arm The surge voltage is not directly applied to the sixth IGBT (8, 9) and the fifth and sixth backflow prevention diodes (14, 15). Therefore, it is possible to prevent destruction of the first to sixth IGBTs (4 to 9) and the first to sixth backflow prevention diodes (10 to 15) in the conversion circuit (3) due to external noise. The basic operation of the AC-DC converter of this embodiment is exactly the same as that of the conventional AC-DC converter shown in FIG.
[0018]
As described above, in this embodiment, when a surge voltage is generated in the AC input terminals (1A, 1B, 1C) of the three-phase AC power supply (1) due to external noise, the filter reactor (2) in the filter circuit (2) 2d, 2e, 2f) and filter capacitors (2a, 2b, 2c), backflow prevention diode (45), auxiliary capacitor (44), and voltage dividing capacitor (35, 36) between DC output terminals (40A, 40B) Since the surge current is bypassed and the surge voltage is not directly applied to the conversion circuit (3), the first to sixth IGBTs (4 to 9) and the first to sixth in the conversion circuit (3) due to external noise. It is possible to prevent the backflow prevention diodes (10 to 15) from being destroyed. Further, the voltage dividing capacitor (35, 36) also has an effect of increasing the capacitance of the smoothing capacitor (18), so that the DC output voltage V_DCThe external noise can be effectively used as the DC output power. Furthermore, the third harmonic included in the U-phase, V-phase and W-phase AC input voltages applied from the three-phase AC power source (1) to the filter capacitors (2a, 2b, 2c) in the filter circuit (2). Since the voltage is shared by the auxiliary capacitor (44), the breakdown voltage of the filter capacitors (2a, 2b, 2c) in the filter circuit (2) can be lowered.
[0019]
In FIG. 2, the first and second conversion circuits (3A, 3B) are connected in parallel between the filter circuit (2) and the DC output terminals (40A, 40B), and each of the conversion circuits (3A, 3B) is connected. The first and second freewheeling diodes (16A, 16B) are connected between the output terminals, respectively, and positive between the positive output terminal and the positive DC output terminal (40A) of each conversion circuit (3A, 3B). Side DC reactors (17A, 17B) are connected, and the negative side DC reactor (34A, 34B) is connected between the negative side output terminal and negative side DC output terminal (40B) of each converter circuit (3A, 3B). Connected and connecting the voltage dividing capacitor (35, 36) to the connection points of the first and second free-wheeling diodes (16A, 16B) and the positive and negative DC reactors (17A, 17B, 34A, 34B) A voltage balancing diode (37A, 37B, 38A, 38B) as a voltage balancing rectifier is connected between each point, and a DC reactor (17A, 17B, 34A) is connected to each output terminal of the conversion circuit (3A, 3B). , 34B), voltage dividing capacitor (35, 36) and voltage leveling Showing use diodes (37A, 37B, 38A, 38B) to another embodiment of the AC-DC converter of the present invention the formation of the DC circuit. Although not shown, the first and second conversion circuits (3A, 3B) both have the same configuration as the conversion circuit (3) shown in FIG. 1, and the first conversion circuit (3A) in the first conversion circuit (3A) has the same configuration. The first to sixth IGBTs (4 to 9) in the second conversion circuit (3B) are turned on with the switching phase delayed by π / 2 [rad] with respect to the sixth IGBT (4 to 9). It is turned off. As a result, the phase difference between the currents flowing in the first and second conversion circuits (3A, 3B) becomes π / 2 [rad], so that the AC input current flowing in each of the three phases is shaped into a sine wave. At the same time, the ripple (pulsation) of the AC input current decreases. Other configurations are the same as those of the AC-DC converter shown in FIG. The details of the basic operation of the AC-DC converter shown in FIG. 2 in a steady state are disclosed in, for example, Japanese Patent Application No. 11-321392.
[0020]
In the configuration shown in FIG. 2, the three-phase AC power supply during a period in which all of the first to sixth IGBTs (4 to 9) of either the first or second conversion circuit (3 </ b> A, 3 </ b> B) are turned off. When external noise enters between the U-phase input line connecting the AC input terminal (1A), the filter circuit (2), and the first and second conversion circuits (3A, 3B) of (1) and the ground A surge voltage is generated at the AC input terminal (1A). This surge voltage is generated by the first and second IGBTs (4) of the U-phase arm in the first or second conversion circuit (3A, 3B) in which all of the first to sixth IGBTs (4 to 9) are off. 5) and the first and second backflow prevention diodes (10, 11), the filter reactor (2d) and the filter capacitor (2a) in the filter circuit (2) from the AC input terminal (1A) ), Auxiliary capacitor (44), voltage dividing capacitor (35, 36) between DC output terminals (40A, 40B) and stray capacitance (43) between DC output line and ground of converter circuit (3). Since surge current flows through the connected chassis, the first and second IGBTs (4, 5) and the first and second reverse currents of the U-phase arm in the first and second conversion circuits (3A, 3B). No surge voltage is directly applied to the prevention diodes (10, 11). Similarly, between the V-phase input line connecting the AC input terminal (1B) of the three-phase AC power source (1), the filter circuit (2), and the first and second conversion circuits (3A, 3B) and the ground, Or from the outside between the W-phase input line connecting the AC input terminal (1C), the filter circuit (2), and the first and second conversion circuits (3A, 3B) of the three-phase AC power source (1) and the ground. Since the surge current flows through the same path as described above even when the noise of the third is invaded, the third and fourth IGBTs (6, 7) of the V-phase arm in the first and second conversion circuits (3A, 3B). And the third and fourth backflow prevention diodes (12, 13), or the fifth and sixth IGBTs (8, 9) of the W-phase arm and the fifth and sixth backflow prevention diodes (14, 15). A surge voltage is not directly applied to. Therefore, the first to sixth IGBTs (4 to 9) and the first to sixth backflow prevention diodes (10 to 15) in the first and second conversion circuits (3A, 3B) are destroyed by external noise. Can be prevented.
[0021]
In operation, currents of 5.5 [A] and 4.5 [A] flow in the positive output line and the negative output line of the first conversion circuit (3A), respectively, and the second conversion circuit. A current of 4.5 [A] and 5.5 [A] flows through the positive side output line and the negative side output line of (3B), respectively, and the first in the first or second conversion circuit (3A, 3B). When the sixth IGBT (4-9) is turned off, a current of 4.5 [A] tends to flow through the negative DC reactor (34A) on the first converter circuit (3A) side, and the positive side Since a current of 5.5 [A] is about to flow through the DC reactor (17A), the difference current ΔI₁Flows through the path of the positive side DC reactor (17A), the voltage dividing capacitor (35), and the voltage balancing diode (37A), and the voltage dividing capacitor (35) is charged. Similarly, a current of 4.5 [A] tends to flow through the positive DC reactor (17B) on the second conversion circuit (3B) side, and a current of 5.5 [A] flows through the negative DC reactor (34B). Is about to flow, the difference current ΔI₂Flows through the path of the negative side DC reactor (34B), the voltage balancing diode (38B), and the voltage dividing capacitor (36), and the voltage dividing capacitor (36) is charged. As a result, the voltage dividing capacitors (35, 36) are charged to a substantially equal voltage level, and currents of an equal level flow through the positive and negative DC reactors (17A, 34A, 17B, 34B). A balanced voltage is applied to the first to sixth IGBTs (4 to 9) and the first to sixth backflow prevention diodes (10 to 15) in the second conversion circuit (3A, 3B). Therefore, the first to sixth IGBTs (4 to 9) and the first to sixth backflows in the first and second conversion circuits (3A, 3B) due to the unequal voltage generated due to the imbalance of the output voltage. The destruction of the prevention diode (10 to 15) can be prevented.
[0022]
As described above, in the embodiment shown in FIG. 2, when a surge voltage is generated at the AC input terminals (1A, 1B, 1C) of the three-phase AC power supply (1) due to external noise, the filter circuit (2) Surge current is bypassed to the voltage divider capacitor (35, 36) between the filter reactor (2d, 2e, 2f), filter capacitor (2a, 2b, 2c), auxiliary capacitor (44) and DC output terminal (40A, 40B) Since the surge voltage is not directly applied to the first and second conversion circuits (3A, 3B), the first and second conversion circuits (external noise) (as in the embodiment shown in FIG. 1) 3A, 3B) in the first to sixth IGBTs (4 to 9) and the first to sixth backflow prevention diodes (10 to 15) can be prevented from being destroyed. In addition, when the first to sixth IGBTs (4 to 9) in the first or second conversion circuit (3A, 3B) are switched to the OFF state, they are stored in the DC reactor (17A or 17B, 34A or 34B). The current ΔI corresponding to the difference in energy₁, ΔI₂Flows through a DC circuit composed of a DC reactor (17A or 34A, 17B or 34B), a voltage dividing capacitor (35 or 36) and a voltage balancing diode (37A, 38A, 37B, 38B), and the voltage dividing capacitor (35 or 36) is charged. As a result, the voltage dividing capacitors (35, 36) are charged to a substantially equal voltage level, an equal current flows through the DC reactors (17A, 34A, 17B, 34B) and the first and second conversion circuits (3A, 3) 3B), a voltage of an equal level is applied to the first to sixth IGBTs (4 to 9), so that the first and second conversion circuits (the first and second conversion circuits by the non-uniform voltage generated by the unbalance of the output current) 3A, 3B) has an advantage of preventing the first to sixth IGBTs (4 to 9) and the first to sixth backflow prevention diodes (10 to 15) from being destroyed.
[0023]
FIG. 3 shows a case where a positive current balancing reactor (41) is connected between positive DC reactors (17A, 17B), and an intermediate tap of the positive current balancing reactor (41) and a positive DC output terminal (40A). And connecting the negative current balancing reactor (42) between the negative DC reactors (34A, 34B) to connect the intermediate tap of the negative current balancing reactor (42) to the negative DC output terminal ( 40B) shows a modified embodiment of the AC-DC converter shown in FIG. During the operation of the AC-DC converter shown in FIG. 3, currents of 5.5 [A] and 4.5 [A] are respectively applied to the positive output line and the negative output line of the first conversion circuit (3A). Assuming that a current of 4.5 [A] and 5.5 [A] flows through the positive output line and the negative output line of the second conversion circuit (3B), respectively, the first conversion circuit (3A) A difference of 1.0 [A] occurs in the level of the current flowing through the positive output line on the side and the positive output line on the second conversion circuit (3B) side. When the current based on this level difference flows through the positive current balancing reactor (41), the current in the positive output line on the first conversion circuit (3A) side is reduced so that the second conversion circuit ( Since the current of the positive output line on the 3B) side works to increase, a balanced and equal current flows through both positive output lines. The negative current balancing reactor (42) has the same effect as described above, and a balanced and uniform current flows through each negative output line. Further, when the first to sixth IGBTs (4 to 9) in the first or second conversion circuit (3A, 3B) are turned off, the positive-side DC reactor (17A) as in the embodiment shown in FIG. ), Current balancing reactor (41), voltage dividing capacitor (35), voltage balancing diode (37A), and current ΔI₁Flows, and the voltage dividing capacitor (35) is charged. In addition, the same operation as described above occurs on the second conversion circuit (3B) side, and the negative DC reactor (34B), the voltage balancing diode (38B), the voltage dividing capacitor (36), the current balancing reactor (42). The current ΔI in the path₂Flows, and the voltage dividing capacitor (36) is charged. As a result, the first to sixth IGBTs (4 to 9) and the first to sixth backflow prevention diodes (10 to 15) in the first and second conversion circuits (3A, 3B) are balanced. Of the first to sixth IGBTs (4 to 9) and the first to sixth backflow prevention diodes (10 to 15) in the first and second conversion circuits (3A, 3B). Destruction can be prevented. Therefore, the embodiment shown in FIG. 3 can provide substantially the same operational effects as the embodiment shown in FIG.
[0024]
Embodiments of the present invention are not limited to the above-described embodiments, and various modifications can be made. For example, in each of the above embodiments, an IGBT (insulated gate type bipolar transistor) is used as a switching element constituting the conversion circuit (3). However, a MOS-FET (MOS type field effect transistor), J- Other switching elements such as FETs (junction field effect transistors), junction bipolar transistors, or thyristors may be used. Further, the auxiliary capacitor (44) of the embodiment shown in FIG. 1 may be omitted depending on the case. Similarly, the smoothing capacitor (18) of each of the above embodiments may be omitted by sharing the voltage dividing capacitor (35, 36). 2 and 3, the converter circuit (3), the freewheeling diode (16), and the DC reactor (17) are arranged in two stages between the filter circuit (2) and the smoothing capacitor (18). However, it is possible to connect two or more stages in parallel. In this case, the switching phase of the conversion circuit (3) at each stage is an angle corresponding to the inverse of the number of stages of the conversion circuit (3) with respect to one switching period of the conversion circuit (3), that is, π / n [rad ] (N: The number of stages of the conversion circuit (3)) is shifted on and off, and the peak values of the U-phase, V-phase and W-phase currents on the output side of the filter circuit (2) are converted into the conversion circuit (3). As compared with the case where there is one, it becomes 1 / n times and the switching frequency becomes n times. Therefore, the inductance of the filter reactor (2d, 2e, 2f) and the capacitance value of the filter capacitor (2a, 2b, 2c) constituting the filter circuit (2) are compared with the case where the conversion circuit (3) is one. About 1 / n²Therefore, the filter circuit (2) can be further reduced in size according to the number of stages of the conversion circuit (3). In this case, an AC-DC converter having a larger capacity than that of the embodiment shown in FIGS. 2 and 3 can be obtained. Furthermore, it will be easily understood that the present invention can be applied not only to AC-DC converters for three-phase AC but also to AC-DC converters for single-phase AC or multi-phase AC of three or more phases.
[0025]
【The invention's effect】
According to the present invention, a surge current generated by noise from the outside is bypassed to the ground via the filter capacitor in the filter circuit and the voltage dividing capacitor between the DC output terminals, and the surge voltage is not directly applied to the conversion circuit. Therefore, it is possible to improve the reliability of the AC-DC converter by preventing the switching elements in the conversion circuit from being damaged by external noise.
[Brief description of the drawings]
FIG. 1 is an electric circuit diagram showing an embodiment of an AC-DC converter according to the present invention.
FIG. 2 is an electric circuit diagram showing another embodiment according to the present invention.
FIG. 3 is an electric circuit diagram showing a modified embodiment of FIG.
FIG. 4 is an electric circuit diagram showing a conventional AC-DC converter.
5 is a circuit block diagram showing the internal configuration of the control circuit of FIG.
6 is a waveform diagram showing currents of main components of the AC-DC converter of FIG.
7 is a time chart showing signals at various parts of the control circuit of FIG.
[Explanation of symbols]
(1) ・ ・ AC power supply, (1A, 1B, 1C) ・ ・ AC input terminal, (2) ・ Filter circuit, (2a, 2b, 2c) ・ ・ Filter capacitor, (2d, 2e, 2f) ・ ・Filter reactor, (3) ... Conversion circuit, (3A) ... First conversion circuit, (3B) ... Second conversion circuit, (4-9) ... First to sixth IGBTs (switching elements) ), (10-15) .. 1st to 6th backflow prevention diodes (backflow prevention rectifiers), (16A) .. 1st return diodes (reflux rectifiers), (16B) .. Second return diode (reflux rectifier), (17A, 17B) ·· Positive side DC reactor, (18) · · Smoothing capacitor, (19) · · Current detector, (20) · · Phase voltage detection Transformer, (21) ・ ・ Control circuit, (22) ・ ・ Reference power supply, (23) ・ ・ First error amplifier, (24) ・ ・ Second error amplifier, (25) ・ ・ Phase current reference signal Generator circuit, (26) .. Triangular wave oscillator circuit, (27, (28,29) ・ ・ PWM comparator, (30) ・ ・ Line current pulse conversion circuit, (31) ・ ・ Control signal output circuit, (32) ・ ・ Load, (34A, 34B) ・ ・ Negative DC reactor, ( 35,36) ・ ・ Voltage dividing capacitor, (37A, 37B, 38A, 38B) ・ ・ Voltage balancing diode (rectifier for voltage balancing), (40A, 40B) ・ ・ DC output terminal, (41) ・ ・ Positive Side current balancing reactor, (42) ・ ・ Negative current balancing reactor, (43) ・ ・ Stray capacitance, (44) ・ ・ Auxiliary capacitor

Claims (4)

A filter circuit connected to the AC input terminal, a conversion circuit connected between the filter circuit and the DC output terminal, and a smoothing capacitor connected between the DC output terminals,
By turning on / off a switching element provided in the conversion circuit, AC power supplied from the AC input terminal via the filter circuit is converted into DC power by the conversion circuit, and DC is output from the DC output terminal. In an AC-DC converter that extracts output,
The filter circuit includes a filter reactor inserted between the AC input terminal and the conversion circuit, and a star-connected filter capacitor connected to a connection point between the filter reactor and the conversion circuit, At least two voltage dividing capacitors are connected in series between the DC output terminals, and the connection middle point of the filter capacitor and the connection middle point of the voltage dividing capacitor are connected to each other via an auxiliary capacitor. AC-DC converter characterized by this.   The AC-DC converter according to claim 1, wherein the conversion circuit includes a plurality of conversion circuits connected in parallel between the filter circuit and the DC output terminal. A reflux rectifier connected between the output terminals of the converter circuit, a DC reactor connected between each output terminal of the converter circuit and the DC output terminal, the reflux rectifier and the DC reactor A voltage balancing rectifier connected between the connection point of the voltage dividing capacitor and the connection midpoint of the voltage dividing capacitor,
The AC-DC converter according to claim 2, wherein a DC circuit of the DC reactor, the voltage dividing capacitor, and the voltage balancing rectifier is formed for each output terminal of the conversion circuit.   A positive-side current balancing reactor connected between positive-side DC reactors connected to the positive-side output terminals of the conversion circuit and having an intermediate tap connected to a positive-side DC output terminal; and a negative-side output of the conversion circuit 4. The AC-DC converter according to claim 3, further comprising: a negative-side current balancing reactor connected between the negative-side DC reactors connected to the terminals and having an intermediate tap connected to the negative-side DC output terminal.

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