JP3246584B2 - AC / DC converter - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an AC / DC converter, and more particularly, to an AC / DC converter that operates efficiently while maintaining a sinusoidal input current waveform.

[0002]

2. Description of the Related Art In a converter that receives a commercial AC power supply and converts it into a DC output, it has recently been required to reduce the harmonics by bringing the input current waveform closer to a sine wave. , A harmonic suppression converter utilizing the same has been realized. inside that,
The circuit configuration of a multi-phase AC input is more complicated than that of a single-phase AC input. As an example, Heisei 1
In the DC power supply device of Japanese Patent Application No. 1-153229 filed on June 15, 2003, a three-phase AC requires at least 18 diodes and 3 FETs in a main circuit. In a paper “Modeling and Control of Sine-Wave PWM Converters” published at the Institute of Electrical and Electronics Engineers Power and Semiconductor Power Conversion Joint Study Group (SPC-92-38) in October 1992, at least three-phase AC was applied to the main circuit. It requires six diodes and six power transistors. In addition, in a paper “On a Three-Phase Input Converter with Harmonic Reduction Function” published in September 1993 at the Institute of Electronics, Information and Communication Engineers (ITE-93-09), at least a diode was included in the main circuit. 18 pieces, I
Requires 6 GBTs. In any case, the control circuits for driving the switching elements must be insulated from each other and generated so as to generate drive signals individually and in a preferable relation for each phase.

[0003]

SUMMARY OF THE INVENTION The present invention relates to an AC / DC converter comprising a small number of main circuit components and a simple control circuit even for polyphase alternating current. It is an object to provide an AC / DC converter that operates efficiently.

[0004]

To solve this problem, the present invention proposes the following means. First, as first means, there are provided n input terminals for receiving an n-phase (n is an integer of 2 or more) polyphase alternating current, and choke coils connected in series to respective lines connected to the n input terminals. , A circuit in which each input point is connected to the n lines, which is connected between an n-phase full-wave bridge rectifier circuit including n sets of diode arms and an output terminal of the n-phase full-wave bridge rectifier circuit. A smoothing capacitor, and n switching elements connected in parallel to n diodes on one side of the arm of the n-phase full-wave bridge rectifier circuit, respectively.
A control circuit for generating a control signal for controlling the switching element so as to adjust the voltage between the output terminals according to the detection value of the output terminal detection voltage, wherein the control signal is: This is a single type of signal that has a frequency sufficiently higher than the frequency of the polyphase alternating current to perform power factor improvement and that simultaneously turns on and off all of the n switching elements simultaneously. By turning on and off all the switching elements simultaneously, the power factor can be improved without detecting the input voltage and input current.
It proposes a C / DC converter.

As a second means, a pair of input terminals for receiving a single-phase alternating current, a choke coil connected in series to one or both of two lines connected to the pair of input terminals, A single-phase bridge rectifier circuit comprising two sets of diode arms, a smoothing capacitor connected between output terminals of the single-phase bridge rectifier circuit, A single-phase bridge rectifier circuit includes two switching elements connected in parallel to two diodes on one side of an arm, and a voltage between the output terminals according to a detection value of an output terminal detection voltage. And a control circuit for generating a control signal for controlling the switching element, wherein the control signal is more than the frequency of the single-phase alternating current so as to improve the power factor. A high-frequency signal of a single type for simultaneously turning on and off the two switching elements simultaneously. The control signal turns on and off the two switching elements simultaneously to improve power factor. On the other hand, the present invention proposes an AC / DC converter characterized in that the power factor is improved without detecting the input voltage and the input current.

As a third means, there is proposed an AC / DC converter characterized in that in the first means or the second means, the control circuit adjusts the output of each switching element by time ratio control. Things.

As a fourth means, in the third means, it is proposed to provide a cut-off period for each switching cycle for the current of each choke coil.

[0008]

FIG. 1 shows an embodiment of an AC / DC converter according to the present invention. First, the configuration will be described. This A
C / DC converter 1 receives three-phase commercial AC power supply 3 at input terminals 5, 7 and 9. These three lines are connected to choke coils L1, L2, L3 via a filter 11, respectively. These three lines are further connected to the input side of a bridge rectifier circuit composed of six diodes D1 to D6. The diodes D1, D2, and D3 of one arm are respectively connected in parallel with three switching elements, FETs Q1, Q
2. Connect the drain and source of Q3. This diode D1
A capacitor C1 is connected between the anodes of the diodes D1, D2, and D3, which are the output sides of the bridge rectifier circuit composed of D6 to D6, and the cathodes of the diodes D4, D5, and D6. And connected to. This output terminal 17,
A load 21 is connected between 19. The output voltage of the AC / DC converter 1 is detected by a detection / comparison circuit 15 and compared with an internal reference voltage, and an error signal is supplied to a control circuit 13. The control circuit 13 supplies on / off signals to the gates of the three FETs Q1, Q2, Q3 via resistors R1, R2, R3, respectively. This ON / OFF signal is simultaneously turned on at a frequency much higher than the frequency of the three-phase commercial AC power supply 3, for example, 100 kHz.
It is driven off at the same time.

Next, the operation of the AC / DC converter 1 configured as described above will be described. When an on-drive signal is simultaneously supplied to the gates of the three FETs Q1, Q2, and Q3, the boosting choke coils L1, L2, and L3 on the Y connection are connected to the commercial AC input voltage as shown in an equivalent circuit in FIG. Connected as a load. Therefore, if the initial value of each phase current flowing through each of the choke coils L1, L2, L3 is zero, [Equation 1]
Are represented by equations (1), (2), and (3) shown at the position of. The peak value of the current of each phase is calculated by the formula shown in the position of [Equation 1].
(5), (6), and (7). Therefore, the peak value of each current is proportional to each phase voltage. When the FETs Q1, Q2, and Q3, which are switching elements, are driven at a fixed frequency and a fixed pulse width during one cycle of the commercial AC input voltage, each current peak value is proportional to the phase voltage. Also, the amount of current integration during the ON period is proportional to the phase voltage.

[0010]

(Equation 1)

Next, the switching elements FET Q1, Q2,
A description will be given of a change in the current path from the ON period to the OFF period of Q3. When the FETs Q1, Q2, and Q3 are turned on and the direction of the current flowing from the input terminals 5, 7, and 9 to each of the choke coils L1, L2, and L3 is positive, the current of the turned on choke coil is as shown in FIG. There are two types of phase relationships, as shown in c), when two choke coils are positive, and as shown in FIG. 3A, when only one choke coil is positive. When the phase changes from on to off, one phase is positive,
The current path is different from the case where the two phases are positive. FIG.
FIG. 3 (b) shows the case where only the phase is positive and on.
FIG. 3 (c) is a case where only the u-phase and the w-phase are positive and on, and FIG.
(d) shows the current path when the switch is off in the same state as in FIG. 3 (c). When the current of the choke coil is positive, when the switching element is turned off, a current flows to one of the diodes D4 to D6 connected to the choke coil.
When the current of the choke coil is negative, the current flows through one of the diodes D1 to D3 connected in antiparallel to the FETs Q1, Q2, and Q3.

FIG. 4 shows the relationship between the phase angles of the three-phase commercial AC power supply 3. As can be seen from FIG. 4, the phase angle φ is π
The magnitude relationship or the positive / negative relationship of each phase changes every / 6. First, when only one phase is positive, this state is a period of a phase angle of 2π / 6 to 4π / 6 based on the u phase, and a period of a phase angle of 2π / 6 to 3π / 6 will be described. . Is from FETQ1 in t = tau is turned off at this time, each phase of the choke coils L1, L2, L3 of a current, i _1, i _2,
i ₃ is the equation (8), (9),
It is represented by (10). This state is continued until t = t2 in FIG. 5, w-phase current i ₃ is ahead i ₃ = 0, and the subsequent maintaining this value. The u-phase current at this time is expressed by the equation (11) described in the position of [Equation 2]. At t = t3, the u-phase and v-phase currents become zero, and then maintain the zero value at t = t4 until the FET Q1 turns on again. From time t = t0 to t = t4
By integrating the functions of the currents i ₁ , i ₂ , and i ₃ with respect to time and averaging them, the average is calculated by the equations (12), (13), and (14) described in the position of [Equation 2]. Current is provided. For the period from the phase angle of 3π / 6 to 4π / 6, [Equation 2]
In each of the mathematical expressions (8) to (14) described in the position of
Required if the phase is compatible.

[0013]

(Equation 2)

Next, when the two phases are positive, the period from the phase angle 0 to 2π / 6 is based on the u phase, and the period from the phase angle 0 to π / 6 will be described. At an arbitrary phase angle φ in this period, the currents i ₁ , i ₂ , and i ₃ of the choke coils L1, L2, and L3 of each phase are respectively expressed by Expressions (15) and (16) , (17). This state is continued until t = t2 in FIG. 6, the u-phase current i ₁ is previously
i ₁ = 0, and this value is maintained thereafter. The current of the w-phase at this time is represented by Expression (18) described in the position of [Equation 3]. Then, at t = t3, the currents of the v-phase and w-phase become zero, and then at t = t4, the zero values are maintained until the FETs Q1, Q3 are turned on again. From the time t = t0 to t = t4, the functions of the currents i ₁ , i ₂ , i ₃ are time-integrated and averaged to obtain the equation (19) described in the position of [Equation 3]. (20), (21)
Gives the average current. Phase angle π / 6 to 2π
The period of / 6 can be obtained by making the u-phase and the w-phase compatible with each other in the equations (15) to (21) described in the position of [Equation 3].

[0015]

(Equation 3)

For the period from the phase angle 4π / 6 to 5π / 6, the equations (15) to (21) described in the position of [Equation 3]
Can be obtained by substituting u phase → v phase, v phase → w phase, w phase → u phase. This can be understood from the relationship between the phases in FIG.

Similarly, for the period from the phase angle 5π / 6 to π, each equation (15) described in the position of [Equation 3]
In (21), it is required if v-phase and w-phase are interchangeable. The phase angles from π to 2π can be similarly obtained by replacing the phase in each equation.

As described above, the average current was calculated over all phase angles of the three-phase commercial AC power supply 3. The switching current waveforms have the forms shown in FIGS. 5 and 6, and each peak value is a value proportional to each phase voltage. If this switching current waveform is arranged in time sequence and illustrated, as shown in FIG. The envelope of the peak value of the current waveform is sinusoidal. FIG. 7 is a conceptual illustration, and actually shows a more detailed switching current waveform. Then, the filter 11 provided on the input side attenuates the harmonic components of the switching current waveform, and the input current waveform becomes a sine wave as shown in FIG.

The AC / DC converter 1 operates as a so-called step-up chopper, and has an output voltage Eo.
Is the peak value of the AC input voltage (the highest value including the fluctuation range)
Must be set higher. And the output voltage Eo
When is set higher, the input current waveform becomes closer to a sine wave, but the withstand voltage of the switching element and the output capacitor increases, which is a practical limit, and an appropriate design value is selected. Note that a desired DC output voltage can be obtained by inserting and connecting a DC / DC converter at the position of the load.

The AC / DC converter 1 described above
In, the current waveform of the choke coil has a period in which it becomes zero once for each switching, and under these conditions, each peak value of the switching current is proportional to the line voltage. However, even when the current waveform of the choke coil does not become zero at each switching, the input current waveform of the three-phase commercial AC power supply 3 is slightly inferior to that of FIG. A waveform with few waves can be obtained.

In the embodiment described above, the FET Q
For 1, Q2 and Q3, other types of switching elements, for example, bipolar transistors, IGBTs, etc., can be used. The diodes D1, D2, and D3 connected in parallel to the FETs Q1, Q2, and Q3 can be omitted by using the parasitic diodes of the FETs Q1, Q2, and Q3.

FIG. 10 shows an embodiment in which the present invention is applied to a six-phase AC power supply. The configuration and control method are the same as in the first embodiment shown in FIG. The phase current waveform of this embodiment is shown in FIG.
It is shown in FIG. Compared to the waveform shown in FIG. 8, it is closer to a sine wave.

FIG. 12 shows an embodiment in which the present invention is applied to a single-phase commercial AC power supply. In the case of this embodiment, a choke coil may be connected to one of the two lines as shown, or may be provided separately for both. Other configurations and control methods are the same as those of the first embodiment shown in FIG. When the switching element is off, the current reduction rate of the choke coil L1 is determined only by the difference between the output voltage Eo and the input voltage. Is proportional to Accordingly, the waveform of the input current becomes a substantially perfect sine wave having the same phase as the input voltage as shown in FIG.

[0024]

As described above, according to the AC according to the present invention,
In a DC / DC converter, the main circuit is composed of a number of switching elements corresponding to the number of phases of a polyphase alternating current and a diode having twice the number of phases, and a single control circuit for simultaneously turning on and off each switching element at the same time. It is driven by. With such a simple configuration, it is possible to reduce the harmonics of the input current of the multi-phase commercial AC power supply, operate the power supply at a high power factor, and obtain a stable DC output. Since the control circuit of the switching element is a single signal, the circuit configuration is simple and economical, and also has the effect of preventing malfunction. In addition, the number of diodes in the main circuit is small, the power loss due to the voltage drop of these diodes is reduced, and there is an effect that the efficiency is increased as a whole.

[Brief description of the drawings]

FIG. 1 shows an embodiment of an AC / DC converter according to the present invention.

FIG. 2 is an equivalent circuit for explaining the operation of the AC / DC converter shown in FIG. 1, showing a state where each switching element is turned on.

FIG. 3 is an equivalent circuit for explaining the operation of the AC / DC converter shown in FIG. 1, showing a case where each switching element is in an ON state.

FIG. 4 is a diagram for explaining the operation of the AC / DC converter shown in FIG. 1, showing the phase division of a three-phase AC power supply.

FIG. 5 is a waveform diagram of one cycle of high-frequency switching.

FIG. 6 is a waveform diagram of one cycle of high-frequency switching.

FIG. 7 is an illustration of a concept in which current waveforms by high-frequency switching are arranged along the cycle of a commercial AC power supply.

8 is an example of a waveform based on a calculated value of one phase of an AC input current waveform of the embodiment of the AC / DC converter shown in FIG. 1;

9 is another waveform based on the calculated value of one phase of the AC input current waveform of the embodiment of the AC / DC converter shown in FIG. 1;

FIG. 10 shows an embodiment in which the AC / DC converter according to the present invention is applied to a six-phase alternating current.

11 is an example of a waveform based on a calculated value of a current waveform of one phase of an AC input in the embodiment of the AC / DC converter shown in FIG. 10;

FIG. 12 shows an embodiment in which the AC / DC converter according to the present invention is applied to single-phase alternating current.

13 is an example of a waveform based on a calculated value of an AC input current waveform of the embodiment of the AC / DC converter shown in FIG. 12;

[Explanation of symbols]

1: AC / DC converter 2: Single-phase commercial AC power supply
3 ... three-phase commercial AC power supply 6 ... six-phase commercial AC power supply 5, 7, 9 ... input terminal 11 ... filter 13 ... control circuit 15 ... comparison detection circuit
17,19… Output terminal 21… Load

(Equation 1)

(Equation 2)

(Equation 3)

──────────────────────────────────────────────────続 き Continued on front page (58) Field surveyed (Int.Cl. ⁷ , DB name) H02M 7/217 H02M 1/12 H02M 7/23

Claims (4)

(57) [Claims] An input terminal for receiving n-phase (n is an integer of 2 or more) polyphase alternating current; a choke coil connected in series to each line connected to the n input terminals; A circuit in which each input point is connected to the said line,
an n-phase full-wave bridge rectifier circuit comprising n sets of diode arms; a smoothing capacitor connected between output terminals of the n-phase full-wave bridge rectifier circuit; and one of the arms of the n-phase full-wave bridge rectifier circuit A control signal for controlling the switching elements so as to adjust the voltage between the output terminals according to the detection value of the output terminal detection voltage, and n switching elements connected in parallel to the n diodes on the side of And a control circuit for generating the control signal, wherein the control signal is at a frequency sufficiently higher than the frequency of the polyphase alternating current so as to improve the power factor, and all of the n switching elements are simultaneously controlled. A single type of signal that is turned on and turned off simultaneously, and the control signal turns on and off all of the n switching elements simultaneously, thereby improving the power factor. An AC / DC converter characterized by improving a power factor without detecting an input voltage and an input current for good. 2. A pair of input terminals for receiving a single-phase alternating current, a choke coil connected in series to one or both of two lines connected to the pair of input terminals, and an input terminal connected to the two lines. A circuit with points connected,
A single-phase bridge rectifier circuit comprising two sets of diode arms; a smoothing capacitor connected between output terminals of the single-phase bridge rectifier circuit; Two switching elements connected in parallel to the diodes, a control circuit for generating a control signal for controlling the switching elements so as to adjust the voltage between the output terminals according to the detected value of the output terminal detection voltage, and In the AC / DC converter provided with the above, the control signal has a frequency sufficiently higher than the frequency of the single-phase AC so as to improve the power factor, and a single signal for simultaneously turning on and off the two switching elements. By turning on and off the two switching elements simultaneously by the control signal, the input voltage and the AC / DC converter and performing improved without power factor detecting the force current. 3. An AC / D according to claim 1 or claim 2.
An AC / DC converter according to the C converter, wherein the control circuit adjusts the output of each of the switching elements by duty ratio control. 4. The AC / DC converter according to claim 3, wherein a cut-off period is provided for the current of the choke coil for each switching cycle.