JP2014007827A - Power conversion device, motor drive control device, air blower, compressor, and refrigerating and air conditioning device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a power conversion device capable of improving circuit performance when on-duty is limited.SOLUTION: The power conversion device comprises: a three-phase rectifier; a step-up converter configuring a chopper circuit including a switching element; a switching control unit 10 for controlling the switching element; a smoothing capacitor for smoothing the output of the step-up converter; a rectified voltage detection unit for detecting a rectified voltage; and a bus voltage detection unit for detecting a bus voltage after smoothing. The switching control unit 10 is provided with a bus voltage control part 21 for calculating the on-duty of the switching element, an on-duty limiting part 22 for exerting control by limiting on-duty with a limiting value calculated on the basis of the rectified voltage and by varying a bus voltage instruction value on the basis of the rectified voltage, and a drive pulse generation part 23 for generating a drive pulse to open or close the switching element on the basis of the limited on-duty.

Description

  The present invention relates to a power conversion device.

  2. Description of the Related Art Conventionally, there is a power conversion device that converts AC power into DC and supplies it to a load. For example, Patent Document 1 below includes a rectifier that full-wave rectifies an input from an AC power supply and a boost chopper circuit having a switching element that is turned on / off by a PWM signal, and smoothes the voltage rectified by the rectifier. Active filter, an active filter control circuit for generating a PWM signal for controlling on / off of the switching element to perform PWM control of the active filter, and a maximum on-duty of the PWM signal generated by the active filter control circuit A technology relating to a power conversion device having duty change means for changing the limit value of the power supply according to the input voltage of the AC power supply is disclosed.

  In recent years, international regulations have been provided for electronic devices that generate harmonic currents in order to suppress disturbances due to harmonic components contained in the power supply current. In order to clear this regulation, in the power converter, a measure is taken to suppress the harmonic current contained in the power source current by short-circuiting the power source by AC or DC chopping in the converter. Further, it is also used as a method of suppressing the loss of the entire system by boosting the bus voltage by chopping.

JP-A-10-127047

  However, according to the above conventional technique, the on-duty of chopping is limited from the viewpoint of circuit protection, and is not limited for improving the circuit performance such as boosting and power factor.

  The present invention has been made in view of the above, and an object of the present invention is to obtain a power conversion device capable of improving circuit performance when on-duty is limited.

  In order to solve the above-described problems and achieve the object, the present invention provides a rectifier that rectifies an AC power supply, a boost converter that forms a chopper circuit including a switching element, and a switching control unit that controls the operation of the switching element. And a smoothing capacitor for smoothing the output of the boost converter, a rectified voltage detecting means for detecting a rectified voltage rectified by the rectifier, and a bus voltage detecting means for detecting a bus voltage smoothed by the smoothing capacitor, The switching control means includes an on-duty calculation means for calculating an on-duty of the switching element based on a deviation between a bus voltage command value that is a target value of the bus voltage and the bus voltage, and based on the rectified voltage. Based on the rectified voltage, the on-duty is limited by the calculated limit value. On-duty limiting means for performing control to vary the bus voltage command value; and drive pulse generating means for generating a driving pulse for opening and closing the switching element based on the on-duty limited by the on-duty limiting means. It is characterized by providing.

  According to the present invention, when the on-duty is limited, the circuit performance can be improved.

FIG. 1 is a diagram illustrating a configuration example of the power conversion device according to the first embodiment. FIG. 2 is a diagram illustrating a configuration example of the switching control unit according to the first embodiment. FIG. 3 is a diagram showing a waveform of a current flowing through the boost reactor during the boost converter operation. FIG. 4 is a diagram showing a waveform of a current flowing through the boost reactor when the switching element is repeatedly opened and closed in the boost converter. FIG. 5 is a diagram showing a waveform of a current flowing through the boost reactor when the boost converter is not operating. FIG. 6 is a diagram illustrating a waveform of a current flowing through the boost reactor during the boost converter operation. FIG. 7 is a diagram illustrating a relationship with each voltage when there is no on-duty limitation in the on-duty limiting unit. FIG. 8 is a diagram illustrating a relationship with each voltage when the on-duty is limited by the on-duty limiting unit. FIG. 9 is a diagram illustrating a relationship with each voltage when there is no on-duty limitation in the on-duty limiting unit. FIG. 10 is a diagram illustrating a relationship with each voltage when the on-duty is limited by the on-duty limiting unit. FIG. 11 is a diagram illustrating a configuration example of the motor drive control device. FIG. 12 is a diagram illustrating a configuration example of the power conversion device according to the third embodiment. FIG. 13 is a diagram showing ON / OFF of the switching element of the boost converter and the current state of the boost reactor. FIG. 14 is a diagram illustrating a configuration example of a switching control unit according to the third embodiment. FIG. 15 is a diagram illustrating a configuration example of a power conversion device including a bus current detection unit. FIG. 16 is a diagram illustrating a configuration example of a power conversion device including a bus current detection unit. FIG. 17 is a diagram illustrating a configuration example of a switching control unit that inputs a detection value from the bus current detection unit. FIG. 18 is a diagram illustrating a configuration example of a switching control unit that inputs a detection value from the bus current detection unit.

  Hereinafter, embodiments of a power conversion device according to the present invention will be described in detail with reference to the drawings. Note that the present invention is not limited to the embodiments.

Embodiment 1 FIG.
FIG. 1 is a diagram illustrating a configuration example of a power conversion device according to the present embodiment. In FIG. 1, the power converter includes a three-phase AC power source 1, a three-phase rectifier 2, a boost converter 3, a smoothing capacitor 7, a rectified voltage detector 8, a bus voltage detector 9, and a switching controller 10. And comprising.

  The three-phase rectifier 2 has a configuration in which six rectifier diodes 2 a to 2 f are bridge-connected, and rectifies the AC voltage of the three-phase AC power source 1. The step-up converter 3 includes a step-up reactor 4, a switching element 5 such as an IGBT (Insulated Gate Bipolar Transistor), and a backflow prevention element 6 such as a fast recovery diode to constitute a chopper circuit. The smoothing capacitor 7 smoothes the output of the boost converter 3. The rectified voltage detector 8 detects the DC voltage rectified by the three-phase rectifier 2. The bus voltage detector 9 detects and outputs a bus voltage that is a voltage obtained by smoothing the output voltage of the boost converter 3 by the smoothing capacitor 7. The switching control unit 10 generates a drive signal for operating the switching element 5 based on detection signals from the rectified voltage detection unit 8 and the bus voltage detection unit 9.

  FIG. 2 is a diagram illustrating a configuration example of the switching control unit 10 according to the present embodiment. In FIG. 2, the switching controller 10 includes a bus voltage controller 21, an on-duty limiter 22, and a drive pulse generator 23.

  Based on the bus voltage that is an output signal of the bus voltage detection unit 9 and the bus voltage command value that is the target value of the bus voltage, the bus voltage control unit 21 turns on the duty of the switching element 5 (corresponding to the duty_pre in FIG. 2). Is an on-duty calculation unit. The on-duty calculation is performed, for example, by proportional-integral control of the deviation between the bus voltage that is the output signal of the bus voltage detector 9 and the bus voltage command value. In addition, although proportional integral control was mentioned as a calculation method, it is an example and is not limited to this. For example, it is also possible to take a method such as adding a derivative term to perform proportional integral derivative control.

  The on-duty limiter 22 limits the on-duty calculated by the bus voltage controller 21 with a limit value calculated based on the detection value of the rectified voltage detector 8.

  The drive pulse generator 23 operates the switching element 5 based on an output value (corresponding to Don in FIG. 2) obtained by limiting the on-duty calculated by the bus voltage controller 21 by the on-duty limiting unit 22. A drive pulse is generated. For generating the drive pulse, for example, a carrier signal such as a triangular wave or a sawtooth wave is compared with the on-duty, and the pulse signal is output so that the switching element 5 is turned on only during a period when the on-duty is larger than the carrier signal.

  Next, the boost operation of the boost converter 3 will be described. The input voltage of the boost converter 3 is a rectified voltage that is an output of the three-phase rectifier 2, and this is defined as a rectified voltage Vds. Further, the output voltage of the boost converter 3 is smoothed by the smoothing capacitor 7, and the smoothed voltage is set as the bus voltage Vo.

  In the boost converter 3, when the switching element 5 is on, the backflow prevention element 6 is prevented from conducting, and the rectified voltage Vds is applied to the boost reactor 4. On the other hand, in the boost converter 3, when the switching element 5 is off, the backflow prevention element 6 is conducted, and the boost reactor 4 has a difference voltage between the rectified voltage Vds and the bus voltage Vo in the opposite direction to that when the switching element 5 is on. Be guided to.

  At this time, from the viewpoint of energy, it can be seen that the energy accumulated in the boost reactor 4 when the switching element 5 is turned on is transferred to the load when the switching element 5 is turned off. Assuming that the energy entering and exiting the boost reactor 4 is equal when the switching element 5 is turned on and off, the relationship between the on-duty Don, the rectified voltage Vds and the bus voltage Vo can be expressed as the following equation (1). it can.

    Vo = Vds / (1-Don) (1)

  Therefore, the output voltage of boost converter 3 can be controlled by controlling on-duty Don of switching element 5 in on-duty limiting unit 22 of switching control unit 10. Further, when the above equation (1) is solved for Don, it can be expressed as the following equation (2).

    Don = (Vo−Vds) / Vo (2)

By substituting a desired bus voltage command value Vo ^* into the bus voltage Vo in the above equation (2), an on-duty theoretical value for obtaining a desired bus voltage can be obtained. In FIG. 2, the bus voltage Vo and the bus voltage command value Vo ^* are input to both the bus voltage control unit 21 and the on-duty limiting unit 22, but the present invention is not limited to this. The bus voltage Vo and the bus voltage command value Vo ^* are input to the bus voltage control unit 21, and the bus voltage Vo and the bus voltage command value Vo ^* are calculated together with the calculated on-duty from the bus voltage control unit 21 to the on-duty limiting unit 22 ^. May be output.

  Here, the current waveform during the operation of boost converter 3 will be described. FIG. 3 is a diagram showing a waveform of a current flowing through the boost reactor 4 when the boost converter 3 operates. FIG. 3A shows the slope of the current ILon when the switching element 5 is on, and FIG. 3B shows the slope of the current ILoff when the switching element 5 is off. FIG. 4 is a diagram showing a waveform of a current flowing in the boost reactor 4 when the switching element 5 is repeatedly opened and closed in the boost converter 3. FIG. 4A shows a case where the amount of current change is the same in the ON period and the OFF period of the switching element 5, and FIG. 4B shows the current change in the period in which the current change amount in the ON period is OFF. FIG. 4C shows a case where the current change amount during the ON period is smaller than the current change amount during the OFF period.

  When the switching element 5 is on, the rectified voltage Vds is applied to the boost reactor 4. At this time, in the boost reactor 4, the current ILon flowing from the power source (three-phase AC power source 1 on the left side in FIG. 1) to the load side (right side in FIG. 1, the same shall apply hereinafter) increases linearly. The slope ΔILon can be expressed by the following equation (3) (FIG. 3A). Note that L is an inductance value of the boost reactor 4.

    ΔILon = Vds / L (3)

  When the switching element 5 is off, the voltage difference between the rectified voltage Vds and the bus voltage Vo is applied to the boost reactor 4 in the opposite direction (from right to left in FIG. 1) when the switching element 5 is on. The At this time, in the boost reactor 4, the current ILoff flowing from the power supply side to the load side linearly decreases, and the slope ΔILoff can be expressed by the following equation (4) (FIG. 3B).

    ΔILoff = (Vds−Vo) / L (4)

From these equations (3) and (4), when the bus voltage command value Vo ^* , the rectified voltage Vds, and the on-duty Don satisfy the relationship of the above equation (2) (equal), the switching element 5 is turned on. The amount of change in current is equal between the period and the off-period (FIG. 4A).

  Further, when the on-duty Don is larger than the value satisfying the above formula (2), the current change amount during the ON period of the switching element 5 becomes larger than the current change amount during the OFF period. By repeating the above, the current gradually increases (FIG. 4B).

  Further, when the on-duty Don is smaller than the value satisfying the above equation (2), the current change amount during the ON period of the switching element 5 is smaller than the current change amount during the OFF period. By repeating the above, the current gradually decreases (FIG. 4C).

  Therefore, by changing the on-duty Don in the switching control unit 10, it is possible to change the waveform of the current flowing from the power supply side to the load side in the boost reactor 4 of the boost converter 3.

  FIG. 5 is a diagram illustrating a waveform of a current flowing through the boost reactor 4 when the boost converter 3 is not operating. FIG. 6 is a diagram illustrating a waveform of a current flowing through the boost reactor 4 when the boost converter 3 operates. When the AC voltage of the three-phase AC power source 1 is rectified by the three-phase rectifier 2 as in the present embodiment, the input current of each phase has an energization interval of 120 degrees during 180 degrees of the power supply voltage cycle ( FIG. 5B). Further, the current in this energization section is the same as the current flowing from the power supply side to the load side in the boost reactor 4 in that section, and the currents of the respective phases can be expressed as shown in FIG. . The same applies to the operation of the step-up converter 3, and the input current of each phase has an energization interval of 120 degrees in the power supply voltage cycle of 180 degrees (FIG. 6B). Further, the current in this energization section is the same as the current flowing through the boost reactor 4 from the power supply side to the load side in that section, and the current of each phase can be expressed as shown in FIG. .

  As shown in FIGS. 3 to 6, by changing the on-duty Don in the switching control unit 10, the waveform of the current flowing through the boost reactor 4 changes, and at this time, the waveform of the input current of each phase also changes. . In the power conversion device, the current waveform flowing through the boost reactor 4 during the operation of the boost converter 3 is made equal to the amount of change in current between the period when the switching element 5 is turned on and the time when the switching element 5 is turned off, as shown in FIG. As shown in FIG. 6, by changing the fluctuation range to be small within a certain range, not only boosts the bus voltage but also improves the power factor and reduces the harmonic components included in the input current. Is possible.

  The process of limiting the on-duty Don in the on-duty limiting unit 22 will be specifically described in order to change the waveform of the current flowing through the boosting reactor 4 during the operation of the boosting converter 3 within a certain range with a small amplitude. The restriction of the on-duty Don is necessary, for example, when the AC voltage of the three-phase AC power source 1 increases from a predetermined voltage value. FIG. 7 is a diagram illustrating a relationship with each voltage when the on-duty restriction unit 22 does not restrict the on-duty Don.

When the AC voltage of the three-phase AC power source 1 increases, the rectified voltage Vds that is a voltage rectified by the three-phase rectifier 2 also increases. As can be seen from the equation (2), if the bus voltage command value Vo ^* is constant, the on-duty Don approaches 0 as the rectified voltage Vds increases. Here, since the on-duty Don is a value in the range of 0 to 1, when the rectified voltage Vds becomes equal to or higher than the bus voltage command value Vo ^* , the on-duty Don becomes 0 and the operation of the boost converter 3 stops.

  As described above, when the boost converter 3 is stopped, a desired voltage value can be obtained for the bus voltage Vo, but it is not possible to obtain the effects of improving the power factor and reducing the harmonics of the input current as described above. .

  Therefore, the on-duty limiter 22 sets a lower limit for the on-duty Don, and performs control to minimize the boost operation of the bus voltage Vo. Thereby, in the switching control part 10, the boost converter 3 can be operated without impairing the effects of improving the power factor and reducing the harmonics of the input current. FIG. 8 is a diagram illustrating a relationship with each voltage when the on-duty restriction unit 22 restricts the on-duty Don.

  The limit value of the on-duty Don at this time can be determined as the following formula (5) based on the formula (2), for example.

    Don> (Vo−Vds) / Vo (5)

Here, the bus voltage command value Vo ^* is inserted into Vo, and the value is a constant multiple such as 1.1 times or 1.5 times or a constant difference value such as +10 V or +50 V with respect to the rectified voltage Vds. And That is, normally, when the value of the bus voltage command value Vo ^* is kept constant, and the difference between the rectified voltage Vds and the bus voltage command value Vo ^* is equal to or smaller than the constant multiple or the constant difference, the bus voltage command value Vo ^{* is} set ^. Is varied based on the value of the rectified voltage Vds. The on-duty limiter 22 performs control to vary the value of the bus voltage command value Vo ^* with respect to a generator of the bus voltage command value Vo ^* (not shown).

  As described above, when the expression (2) is satisfied, the current change amount in the on-period of the switching element 5 becomes equal to the current change amount in the off-period, so that a lower limit value such as the expression (5) is provided. Thus, the current flowing through the boost reactor 4 is at least in the continuous mode.

  Further, the limit value of the on-duty Don is required, for example, when the AC voltage of the three-phase AC power source 1 is decreased from a predetermined voltage value. FIG. 9 is a diagram illustrating a relationship with each voltage when the on-duty restriction unit 22 does not restrict the on-duty Don.

When the AC voltage of the three-phase AC power source 1 decreases, the rectified voltage Vds that is a voltage rectified by the three-phase rectifier 2 also decreases. As can be seen from FIG. 9, if the bus voltage command value Vo ^* is constant, the step-up ratio increases as the rectified voltage Vds decreases. At this time, if the voltage of the bus voltage Vo may be lower than the voltage value when the bus voltage command value Vo ^* is constant, the voltage is increased more than necessary. As a method for determining whether the boost of the bus voltage Vo may be lower than the voltage value when the bus voltage command value Vo ^* is constant in the on-duty limiting unit 22, for example, as described later in the second embodiment. In addition, it can be performed using an AC voltage command value obtained from the load side.

  For this reason, the on-duty limiting unit 22 sets an upper limit on the on-duty Don, and performs control to minimize the boosting operation of the bus voltage Vo. Thereby, in the switching control part 10, the loss accompanying the step-up operation of the step-up converter 3 can be suppressed to the minimum. FIG. 10 is a diagram illustrating a relationship with each voltage when the on-duty Don is limited by the on-duty limiting unit 22.

  The limit value of the on-duty Don at this time can be determined as in the following formula (6) based on the formula (2), for example.

    Don <(Vo−Vds) / Vo (6)

Here, the bus voltage command value Vo ^* is inserted into Vo, and the value is a constant multiple such as 1.1 times or 1.5 times or a constant difference value such as +10 V or +50 V with respect to the rectified voltage Vds. And That is, normally, when the value of the bus voltage command value Vo ^* is constant, and the difference between the rectified voltage Vds and the bus voltage command value Vo ^* is equal to or more than the above-mentioned constant multiple or a certain difference, the bus voltage command value Vo ^*. Is varied based on the value of the rectified voltage Vds. The on-duty limiter 22 performs control to vary the value of the bus voltage command value Vo ^* with respect to a generator of the bus voltage command value Vo ^* (not shown).

  When the AC voltage of the three-phase AC power source 1 is stable and changes at a certain level, that is, when the state shown in FIGS. 7 and 9 is not reached, the on-duty limiting unit 22 is set to the on-duty Don. Therefore, the on-duty (duty_pre) calculated by the bus voltage controller 21 is output to the drive pulse generator 23 as the on-duty Don.

  As described above, according to the present embodiment, in the power conversion device, the switching control unit that controls the operation of the switching element of the boost converter changes the current waveform flowing through the boost converter by controlling on-deity, The on-duty is limited according to the value of the rectified voltage input to the boost converter. At this time, switching of the switching element is controlled so that the waveform of the current flowing through the boost converter changes with a constant amplitude. Further, the bus voltage command value is controlled to vary depending on the relationship with the rectified voltage. This improves circuit performance by minimizing losses in the chopper circuit of the boost converter and boosting the bus voltage, as well as improving the power factor and reducing harmonic components in the input current. It becomes.

Embodiment 2. FIG.
In the present embodiment, specifically, a load connected to the power conversion device will be described. A different part from Embodiment 1 is demonstrated.

  FIG. 11 is a diagram illustrating a state where an inverter, a motor, and an inverter control unit are connected to the power conversion device. As an example, as a load connected to the power converter, an inverter 31 that converts a DC voltage into an AC voltage and a motor 32 that is driven by application of an AC voltage that is the output of the inverter 31 are connected to the inverter 31. Is connected to the inverter control unit 33. Further, on the power conversion device side, a switching control unit 10 a is provided instead of the switching control unit 10. Here, the motor drive control device is configured as a whole in FIG.

  The inverter 31 has, for example, a switching element such as an IGBT having a three-phase bridge configuration or a two-phase bridge configuration. The inverter control unit 33 that controls the inverter 31 uses, for example, a motor current detection unit 34 that detects a current flowing from the inverter 31 to the motor 32 to calculate a voltage command that causes the motor 32 to rotate at a desired rotational speed. Then, a pulse for driving the switching element in the inverter 31 is generated.

  Although the configuration of the switching control unit 10a is the same as that of the switching control unit 10, the on-duty limiting unit 22 further acquires a voltage command from the inverter control unit 33 and controls the boost converter 3.

  Note that the converter control by the switching control unit 10a and the inverter control by the inverter control unit 33 can be realized by using an arithmetic means such as a microcomputer, for example.

  Usually, in order to increase the rotation speed of the motor 32, the AC voltage output from the inverter 31 needs to be higher with the rotation speed. The magnitude of the AC voltage output from the inverter 31 is limited by the voltage applied to the inverter 31, that is, the DC voltage (bus voltage Vo) that is the output of the smoothing capacitor 7.

  In the present embodiment, in the motor drive control device, in order to increase the rotation speed of the motor 32, the AC voltage output from the inverter 31 is greater than or equal to the voltage limited by the bus voltage Vo output from the smoothing capacitor 7. When voltage is required, the switching control unit 10a acquires the voltage command from the inverter control unit 33 and controls the boosting operation of the boosting converter 3. Thereby, it is possible to prevent the output voltage from being limited in the inverter 31.

Further, the motor 32 has a low rotation speed, and the output voltage required by the inverter 31 is less than or equal to the voltage limited by the bus voltage Vo output from the smoothing capacitor 7. When the effect of reducing harmonics of the input current is required, the switching control unit 10a operates the boost converter 3 by lowering the bus voltage command value Vo ^* as compared with the above-described operation that does not limit the output voltage of the inverter 31. To control.

As a result, it is possible to minimize the loss associated with the operation of the boost converter 3 and obtain the effects of improving the power factor and reducing the harmonics of the input current. In such a case, since the bus voltage command value Vo ^* is set to be smaller than usual, when the rectified voltage Vds increases due to the power supply voltage fluctuation, the bus voltage Vo is likely to be exceeded. Therefore, as described in the first embodiment, it is effective to set a lower limit of the on-duty Don.

  Further, in this section, the main purpose is to obtain effects such as improvement of power factor and reduction of harmonics of the input current by boosting the bus voltage Vo. For this reason, when the rectified voltage Vds decreases due to power supply voltage fluctuation, the bus voltage Vo is boosted more than necessary. Therefore, as described in the first embodiment, by providing the upper limit of the on-duty Don, the loss of the boost converter 3 is not generated more than necessary.

  In the present embodiment, in the motor drive control device, when the rotational speed of the motor is low and the output voltage of the inverter is less than or equal to the limit value by the DC voltage that is the output of the smoothing capacitor, the lower limit and the upper limit of the on-duty Don are set. By providing, as in the first embodiment, the loss is small, and effects such as power factor improvement and harmonic reduction of the input current can be effectively obtained. Even if such an air conditioner, a refrigerator, or a freezer is configured by using such a motor drive control device to drive at least one of a motor of a blower or a compressor, the same effect can be obtained.

Embodiment 3 FIG.
In the present embodiment, a configuration in which boost converters are connected in parallel in a power conversion device will be described. A different part from Embodiment 1 is demonstrated.

  FIG. 12 is a diagram illustrating a configuration example of the power conversion device according to the present embodiment. As shown in FIG. 12, the power converter includes a boost converter 3 ′ instead of the boost converter 3, and the boost converter 3 ′ includes a boost converter 3a including a boost reactor 4a, a switching element 5a, and a backflow prevention element 6a. The step-up converter 4b including the step-up reactor 4b, the switching element 5b, and the backflow prevention element 6b may be connected in parallel. In this case, the power conversion device includes a switching control unit 10b that can control two switching elements instead of the switching control unit 10.

In each of boost converters 3a and 3b, the behavior when switching elements 5a and 5b are turned on / off is the same as that in the first embodiment. However, the current waveform appearing in the conduction period of each phase of the power supply is the sum of the current of the boost reactor 4a and the current of the boost reactor 4b. FIG. 13 is a diagram showing ON / OFF of switching elements 5a and 5b in boost converter 3 ′ and the current state of boost reactors 4a and 4b. 13 (a) shows the on-duty of the switching element 5a, FIG. 13 (b) shows the current waveform of the boost reactor 4a,
13C shows the on-duty of the switching element 5b, FIG. 13D shows the current waveform of the boost reactor 4b, and FIG. 13E shows the added current waveform of the boost reactors 4a and 4b.

  In particular, by shifting the on-timing phases of the switching elements 5a and 5b, the switching ripples in the sum current of the current of the boost reactor 4a and the current of the boost reactor 4b cancel each other, and the switching of the switching elements 5a and 5b is the same. The switching ripple of the addition current becomes the smallest when the phase is 180 degrees with the on-duty. Moreover, the current ripple resulting from switching of the addition current at this time is ½ times the switching period Tsw.

  Here, when the on-duty is less than 50%, the on / off combinations of the switching element 5a and the switching element 5b are two combinations of on-off and off-off. The inclinations when the switching elements 5a and 5b are turned on and when the switching elements 5b are turned off are the same if the boost reactors 4a and 4b have the same inductance value. Therefore, in the section where the on / off combination is made, the slope ΔIdcup of the addition current can be obtained by adding ΔILon and ΔILoff, and can be expressed by the following equation (7).

    ΔIdcup = ΔILon + ΔILoff = (2 * Vds−Vo) / L (7)

  Further, in the section that is an off-off combination, the slope ΔIdcdown of the addition current can be obtained by twice the above-described ΔILoff, and can be expressed by the following equation (8).

    ΔIdcdown = 2 * ΔILoff = 2 * (Vds−Vo) / L (8)

  Here, the section Tonoff, which is an ON-OFF combination, is the same time as the ON time of the switching elements 5a and 5b, and can be expressed by the following equation (9).

    Tonoff = Don * Tsw (9)

  Further, the section Toffoff that is an off-off combination can be expressed by the following equation (10).

    Toffoff = (1 / 2−Don) * Tsw (10)

  At this time, the switching control unit 10b can be configured as shown in FIG. 14, for example. FIG. 14 is a diagram illustrating a configuration example of the switching control unit 10b according to the present embodiment. The switching control unit 10 is different from the switching control unit 10 in that drive pulse generation units 23 a and 23 b are provided instead of the drive pulse generation unit 23. In the switching control unit 10b, in the drive pulse generation units 23a and 23b, the carrier signal of the triangular wave or sawtooth wave to be compared with the on-duty is shifted by a predetermined phase by shifting the phase in the drive pulse generation units 23a and 23b. Drive pulses for the switching elements 5a and 5b can be generated. The on-duty for the same carrier signal may be set to Don and 1-Don. In any case, it is possible to obtain the effect of improving the circuit performance by limiting the above-described on-duty.

  In the switching control unit, it is also possible to obtain an on-duty by using a bus current. 15 and 16 are diagrams illustrating a configuration example of the power conversion device including the bus current detection unit. 17 and 18 are diagrams illustrating a configuration example of a switching control unit that inputs a detection value from the bus current detection unit. In FIG. 17, the switching control unit 10 c includes a bus voltage control unit 21 a, a bus current control unit 42, an on-duty limiting unit 22, and a drive pulse generation unit 23. In FIG. 18, the switching controller 10d includes a bus voltage controller 21a, a bus current controller 42, an on-duty limiter 22, and drive pulse generators 23a and 23b. 15 and 17 correspond to the configuration of the boost converter 3, and FIGS. 16 and 18 correspond to the configuration of the boost converter 3 '.

  As shown in FIGS. 15 and 16, the bus current detection unit 41 detects the current value idc flowing from the three-phase rectifier 2 to the boost reactor 4 and outputs it to the switching control unit 10c or the switching control unit 10d.

17 and 18, the bus voltage controller 21a calculates the bus current command value idc ^* based on the deviation between the bus voltage command value Vo ^* and the detected value (bus voltage Vo) from the bus voltage detector 9. The bus current control unit 42 obtains the on-duty before the limit by performing, for example, proportional integral control on the deviation between the bus current command value idc ^* and the detected value (bus current) idc of the bus current detection unit 41. . The operations after the on-duty limiter 22 are the same as in the first and second embodiments.

  As a result, the bus current control can be performed as in the first and second embodiments, and the effects of improving the power factor and reducing the harmonics of the input current can be enhanced. Even in such a configuration, the effect of improving the circuit performance by limiting the above-described on-duty can be obtained.

In the present embodiment, the on-duty before the limit is obtained using the bus voltage controller 21a and the bus current controller 42, but the present invention is not limited to this. For example, in the bus voltage controller, the bus voltage command value Vo ^* , the bus voltage Vo, and the bus current idc may be input to obtain the on-duty before the limit.

  As described above, the power conversion device according to the present invention is useful for power conversion, and is particularly suitable for connection to an AC power supply.

DESCRIPTION OF SYMBOLS 1 Three-phase alternating current power supply 2 Three-phase rectifier 2a-2f Rectifier diode 3, 3 ', 3a, 3b Boost converter 4, 4a, 4b Boost reactor 5, 5a, 5b Switching element 6, 6a, 6b Backflow prevention element 7 Smoothing capacitor 8 Rectified voltage detector 9 Bus voltage detector 10, 10a, 10b, 10c Switching controller 21, 21a Bus voltage controller 22 On-duty limiter 23 Drive pulse generator 31 Inverter 32 Motor 33 Inverter controller 34 Motor current detector 41 Bus current detector 42 Bus current controller

Claims (11)

A rectifier for rectifying the AC power supply;
A boost converter constituting a chopper circuit including a switching element;
Switching control means for controlling the operation of the switching element;
A smoothing capacitor for smoothing the output of the boost converter;
Rectified voltage detecting means for detecting a rectified voltage rectified by the rectifier;
A bus voltage detecting means for detecting a bus voltage smoothed by the smoothing capacitor;
With
The switching control means includes
An on-duty calculation means for calculating an on-duty of the switching element based on a deviation between a bus voltage command value which is a target value of the bus voltage and the bus voltage;
On-duty limiting means for limiting the on-duty with a limit value calculated based on the rectified voltage and performing control to vary the bus voltage command value based on the rectified voltage;
Drive pulse generating means for generating a drive pulse for opening and closing the switching element based on the on-duty limited by the on-duty limiting means;
A power conversion device comprising: A rectifier for rectifying the AC power supply;
A first boost converter constituting a chopper circuit including a first switching element;
Constituting a chopper circuit including a second switching element, a second boost converter connected in parallel with the first boost converter;
Switching control means for controlling operations of the first switching element and the second switching element;
A smoothing capacitor for smoothing the output of the boost converter;
Rectified voltage detecting means for detecting a rectified voltage rectified by the rectifier;
A bus voltage detecting means for detecting a bus voltage smoothed by the smoothing capacitor;
With
The switching control means includes
An on-duty calculation means for calculating an on-duty of the switching element based on a deviation between a bus voltage command value which is a target value of the bus voltage and the bus voltage;
On-duty limiting means for limiting the on-duty with a limit value calculated based on the rectified voltage and performing control to vary the bus voltage command value based on the rectified voltage;
Drive pulse generating means for generating a drive pulse for opening and closing the switching element based on the on-duty limited by the on-duty limiting means;
A power conversion device comprising: The on-duty limiting means sets the value calculated so that the rectified voltage and the bus voltage have a predetermined difference as the limiting value.
The power conversion device according to claim 1, wherein the power conversion device is a power conversion device. The on-duty limiting means sets the value calculated so that the bus current mode is a predetermined current mode as the limiting value.
The power conversion device according to claim 1, wherein the power conversion device is a power conversion device. The predetermined current mode is a continuous mode,
The power conversion device according to claim 4, wherein: A bus current detecting means for detecting a bus current which is a current of a rectified voltage rectified by the rectifier;
With
The on-duty calculation means further calculates the on-duty using the bus current.
The power conversion device according to claim 1, wherein the power conversion device is a power conversion device. The power conversion device according to any one of claims 1 to 6,
An inverter that includes a switching element and converts a DC voltage that is an output of the power converter to an AC voltage;
Inverter control means for controlling a switching element of the inverter;
A motor that is driven based on an AC voltage that is an output of the inverter;
A motor drive control device comprising: The on-duty limiting means has a ratio between a DC voltage applied to the inverter and an AC voltage output from the inverter based on a command value of the AC voltage output to the motor obtained from the inverter control means. Enable the limit value in a section that is less than or equal to a predetermined value.
The motor drive control device according to claim 7.   A blower, wherein the motor is driven by the motor drive control device according to claim 7 or 8.   A motor is driven by the motor drive control device according to claim 7 or 8.   A refrigerated air conditioner using at least one of the blower according to claim 9 and the compressor according to claim 10.

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