JP2004072806A - Power converter - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a power factor improved power converter which copes with the voltage ripple of an AC power source. <P>SOLUTION: This power converter is equipped with a reactor whose one end is connected to the AC power source, a short circuit means whose one end is connected to the other end of the reactor, a rectifying circuit whose one end on AC input side is connected to the other end of the above reactor and whose other end is connected to the other end of the above short circuit means, a zero cross detecting circuit which detects the zero cross of the above AC power source, and a control circuit which controls the above short circuit means. The above control circuit controls short circuit action, based on delay time To and pulse width Tw of a short circuit period, and controls the delay time Td and the pulse width Tw independently. <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a power converter that converts AC power into DC power, and more particularly to a power converter that performs a short-circuit operation once or a plurality of times in a half cycle of an AC power supply to improve the power factor of the power supply.
[0002]
[Prior art]
Japanese Patent Application Laid-Open No. 10-201248 discloses a power converter that improves the power factor by performing one or more short-circuit operations in a half cycle of an AC power supply. JP-A-10-
2012248 discloses a short circuit start time (delay time) and a short period (pulse) of a short circuit based on an internal state such as a duty ratio or an output frequency of a pulse width modulation signal (PWM signal) of an inverter circuit connected to a power supply device. Width) and controlling the power factor to an optimum point in accordance with the state of the load.
[0003]
Japanese Patent Application Laid-Open No. 10-201248 discloses that a power factor is improved by calculating a delay time and a pulse width according to a load condition from a function set in advance, for example, a function of the delay time and the pulse width with respect to the PWM duty of the inverter. are doing. For this reason, under the set conditions, an optimum power factor can be ensured and stable motor control can be performed.
[0004]
[Problems to be solved by the invention]
The power supply device is a device that is connected to an AC power supply and converts the power of the AC power supply into DC power. It is known that the voltage of a commercial power supply used as an AC power supply generally fluctuates. Japanese Patent Application Laid-Open No. Hei 10-201248 does not describe a measure against voltage fluctuations of an AC power supply, and does not disclose a method for preventing a reduction in power factor due to power supply fluctuations.
[0005]
Further, in the above-described prior art, the delay time and the pulse width are determined by using a function of the delay time and the pulse width with respect to the load state amount in consideration of the motor control by the inverter, and the control of the DC voltage is not described. .
[0006]
An object of the present invention is to provide a power factor improving type power conversion device corresponding to a voltage fluctuation of an AC power supply. Another object of the present invention is to determine a delay time and a pulse width by a simple calculation, and Is to provide a power conversion device that controls the power conversion.
[0007]
[Means for Solving the Problems]
The power conversion device according to the present invention includes a reactor having one end connected to an AC power supply, a short-circuit means having one end connected to the other end of the reactor, and one end on the AC input side connected to the other end of the reactor. A rectifier circuit having a multi-terminal connected to the other end of the short-circuit means, a zero-cross detection circuit for detecting a zero cross of the AC power supply, one end being connected to the other end of the AC power supply, and the other end being the other end of the short-circuit means An input current detection circuit connected to the rectifier circuit, a smoothing capacitor connected to both ends of the DC output of the rectifier circuit, and a control circuit for controlling the short-circuit means, the control circuit performs a short-circuit operation from a zero-cross point of the AC power supply. The short-circuit operation of the short-circuit means is controlled based on a delay time Td which is a period until the start, and a pulse width Tw which is a short-circuit period, and the delay time Td and the pulse width Tw are calculated. To control respectively.
[0008]
The power converter of the present invention controls the delay time Td and the pulse width Tw as follows.
(1) The delay time is calculated from a function for the preset input current or input power, and the pulse width Tw is varied so that the DC voltage becomes a preset predetermined value.
(2) The delay time Td is set to a predetermined value (fixed value) set in advance, and the pulse width Tw is varied so that the DC voltage becomes a predetermined value set in advance.
(3) The delay time Td and the pulse width Tw are given as functions to the input current or the input power, respectively, and the pulse width Tw and the delay time Td are set from the input current or the input power detected using the functions.
(4) Determining the delay time Td The function shown in (1) or the predetermined value (fixed value) shown in (2) or the function of the delay time Td and the pulse width Tw shown in (3) is used as an AC power supply. Are provided corresponding to the voltage of the AC power supply, and are selected according to the voltage of the AC power supply.
(5) The voltage of the AC power supply is estimated from the DC voltage before the short-circuiting means short-circuits or the DC voltage when the short-circuiting operation is temporarily stopped, and corresponds to the fluctuation of the power supply voltage.
[0009]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
[0010]
FIG. 1 is a basic configuration diagram of a motor control device using the power converter of the present embodiment. As shown in FIG. 1, a power conversion device 100 according to the present embodiment includes a reactor 2 having one end connected to one output terminal of a single-phase AC power supply 1, and short-circuiting means for short-circuiting the AC power supply 1 via the reactor 2. And a rectifier circuit connected via an input current detection circuit 30 between the other end of the reactor 2 not connected to the AC power supply 1 and the other end of the AC power supply 1 not connected to the reactor 2 4, a smoothing capacitor 6 connected in series to both ends of the DC output of the rectifier circuit 4, one of the AC inputs of the rectifier circuit 4, and a connection point between a smoothing capacitor 61 and a smoothing capacitor 62 constituting the smoothing capacitor 6. The connected rectifier circuit switching means 5, a zero-cross detection circuit 8 for detecting a zero-cross of the AC power supply 1, and a DC voltage Vd across the smoothing capacitor 6 are input, and a zero-cross signal 92 is used as a reference timing. A control circuit 7 for outputting a short-circuit pulse signal 96 for operating the short-circuit means 3 and outputting a rectification circuit switching signal 97 to the rectification circuit switching means 5; and a control circuit for detecting an input current Is input from the AC power supply 1. 7 is provided with an input current detection circuit 30 for outputting an input current value 98.
[0011]
FIG. 1 also shows a motor drive system 101 including an inverter circuit 10 connected to a DC output of the power converter 100 and a compressor 20 having a built-in electric motor. Here, the control circuit 7 is configured by a semiconductor integrated circuit (IC) such as a one-chip microcomputer, and executes all operations by software processing.
[0012]
The zero-crossing detection circuit 8 inputs the voltage at both ends of the AC power supply 1, and at the timing when the AC voltage of the AC power supply 1 (hereinafter abbreviated as power supply voltage Vs) passes through the zero crossing point and the polarity changes, changes from the High signal to the Low signal. Or a zero cross signal 92 that switches from a low signal to a high signal. This zero cross signal 92 is input to the control circuit 7.
[0013]
The control circuit 7 uses the rising or falling edge of the input zero-cross signal 92 as a reference timing to start a short-circuiting operation of the short-circuiting means 3 (hereinafter, delay time Td) and a short-circuiting period (hereinafter, pulse). The width Tw) is set, and a short-circuit pulse signal 96 (High, Low signal) is output to the short-circuit means 3. The delay time Td and the pulse width Tw are stored in the control circuit 7 in advance or calculated by the control circuit 7.
[0014]
The short-circuit means 3 performs a short-circuit opening / closing operation according to the short-circuit pulse signal 96. In this embodiment, when the short-circuit pulse signal 96 output from the control circuit 7 is High, the short-circuit means 3 performs a short-circuit operation. The short-circuit means 3 includes a diode bridge and an IGBT or a power semiconductor switching element such as a bipolar transistor or a MOSFET, and short-circuits the AC power supply 1 via the reactor 2 according to the short-circuit pulse signal 96. This short-circuit switching operation improves the power factor of the AC power supply 1.
[0015]
The rectifier circuit switching means 5 is constituted by a bidirectional switch formed by a combination of a power relay, a triac, a diode bridge and a power semiconductor switching element (IGBT, bipolar transistor, MOSFET), and the like, and a rectifier circuit switching signal 97 ( The rectifier circuit 4 is switched in accordance with the High and Low signals. In this embodiment, the rectifier circuit 4 is switched to a full-wave rectifier circuit when the rectifier circuit switching signal 97 is a low signal, and is switched to a voltage doubler rectifier circuit when the rectifier circuit switching signal 97 is a high signal.
[0016]
The control circuit 7 receives a zero-cross signal 92, a DC voltage value 93 that is a DC voltage Vd across the smoothing capacitor 6, and an input current value 98, and outputs a short-circuit pulse signal 96 and a rectifier circuit switching signal 97. .
[0017]
The power converter 100 of the present embodiment performs an operation of short-circuiting the AC power supply 1 once or multiple times in the power supply half cycle via the reactor 2 to widen the flow angle of the power supply current and improve the power supply power factor. While converting AC power into DC power. The power converter 100 according to the present embodiment includes a rectifier circuit switching unit 5, and switches the rectifier circuit 4 to a full-wave rectifier circuit or a voltage doubler rectifier circuit for operation. Therefore, in addition to controlling the DC voltage Vd with the pulse width Tw, a wide range of the DC voltage Vd can be output.
[0018]
The relationship among the delay time Td, the pulse width Tw, the efficiency, the power factor, and the DC voltage Vd with respect to the input current Is of the power converter 100 of the present embodiment will be described with reference to FIG. FIG. 2 shows an experimental result in which the delay time Td and the pulse width Tw are changed so that the power factor is maximized when the input current Is is changed. 2A shows the input current Is, FIG. 2A shows the efficiency and the power factor, FIG. 2B shows the DC voltage, and FIG. 2C shows the delay time Td and the pulse width Tw. Show. Here, the input current is described on the horizontal axis in FIG. 2, but the same applies when the horizontal axis is input power. Hereinafter, in this embodiment, the case where the horizontal axis is the input current will be described.
[0019]
FIG. 2 shows experimental results of the full-wave rectifier circuit and the voltage doubler rectifier circuit. 2 shows an input current range operated by the full-wave rectifier circuit, and sections B and C are input current ranges operated by the voltage doubler rectifier circuit. In section C, the load is heavier than in section B. When the power supply device is started (when the input current is near zero), the full-wave rectifier circuit operates in the section A, and shifts to the voltage doubler rectifier circuit operation in the section B with an increase in the input current Is. When the input current Is decreases, the operation shifts from the voltage doubler rectifier circuit operation in the section B to the full-wave rectifier circuit operation in the section A. However, there is a portion where the input current values in the section A and the section B overlap and the hysteresis is reduced. You can move smoothly because you have.
[0020]
In the case of the input current Is in the section A and the section B, as shown in FIG. 2C, the delay time Td monotonously decreases with respect to the input current Is, and the pulse width Tw monotonically increases. The sum with the width Tw has a constant value. That is, the delay time Td and the pulse width Tw are associated with each other, so that if one of them is determined, the other can be determined. In other words, if the detected input current Is is the section A or the section B, the delay time Td and the pulse width Tw can be determined. Further, as shown in FIG. 2B, the DC voltage Vd is substantially constant with respect to the input current Is.
[0021]
As a first method for determining the delay time Td and the pulse width Tw, the pulse width Tw is controlled so that the DC voltage Vd is constant, and the sum of the delay time Td and the pulse width Tw is constant. I do. This method is the same as controlling the time when the short circuit is started by the short circuit means so that the DC voltage is constant, and the time when the short circuit operation ends is constant. Thereby, in the sections A and B shown in FIG. 2, the DC voltage Vd is controlled to be constant, and at the same time, the operation can be performed with the maximum power factor. It is to be noted that whether or not the current time falls within the sections A and B is determined using the current detection signal 98.
[0022]
As a second method for determining the delay time Td and the pulse width Tw, the input current detection is performed without associating the delay time Td and the pulse width Tw with each other in accordance with the input current detection signal 98 from the input current detection circuit 30. The delay time Td and the pulse width Tw are determined independently according to the signal 98. A function for obtaining the delay time Td and the pulse width Tw that can be operated at a high power factor in advance by simulation and obtaining the value of the delay time Td from the input current Is, and a function for obtaining the value of the pulse width Tw from the input current Is. It is input to the control circuit 7 in advance. This method is a good method for easily obtaining the delay time Td and the pulse width Tw.
[0023]
Next, a third method for determining the delay time Td and the pulse width Tw corresponding to the fluctuation of the power supply voltage Vs of the AC power supply 1 will be described. In this method, the delay time Td is determined according to the relationship between the input current Is and the delay time Td using the relationship shown in FIG. On the other hand, the pulse width Tw is determined so that the DC voltage Vd is constant. The function for obtaining the delay time Td based on the input current Is was obtained in advance through experiments and simulations.
[0024]
FIG. 3 shows the power supply voltage Vs dependence of the efficiency, power factor, and DC voltage Vd when the pulse width Tw is set on the horizontal axis. As shown in FIG. 3, the efficiency, the power factor, and the DC voltage fluctuate with the fluctuation of the power supply voltage Vd, but the outline of these graphs does not change. In other words, the efficiency and the power factor change in the form of a quadratic function in which the pulse width Tw shown in FIG. 3 has a maximum value peak at each of the values A, B, and C according to the power supply voltage. Further, the DC voltage Vd changes in a monotonically increasing function. Also, it can be seen that the DC voltage Vd is equal when the pulse width Tw in FIG. 3 is A, B, and C. That is, if the pulse width Tw is controlled so that the DC voltage Vd becomes constant even when the power supply voltage Vs changes, the power factor can be controlled to the maximum value.
[0025]
In the third method, the delay time Td is previously set as a value corresponding to the input current Is or the input power in the section A and the section B in FIG. 2 so that the DC voltage Vd is controlled to be constant. The pulse width Tw is determined, and the power factor improvement control corresponding to the power supply fluctuation is performed.
[0026]
As shown in FIG. 3, in the range where the above condition is satisfied, the power supply fluctuation is about ± 5% of the rated voltage. Therefore, the set value (function) of the delay time Td is stored (stored) for each of several different power supply voltages Vs, and the set value (function) of the delay time Td is changed according to the magnitude of the power supply voltage Vs. It can respond to power supply voltage fluctuations in the range.
[0027]
Here, the fluctuation of the power supply voltage Vs may be provided separately with a circuit for directly detecting the power supply voltage Vs. However, in this embodiment, the DC voltage Vd and the power supply voltage Vs at the time of stopping the power factor improvement operation, that is, at the time of stopping the short-circuit operation. Is measured in advance, and is estimated using a table storing the measurement results or a relational expression between the DC voltage Vd and the power supply voltage Vs derived from the measurement results.
[0028]
As a fourth method for determining the delay time Td and the pulse width Tw, the pulse width Tw is limited to cope with the fluctuation of the power supply voltage Vs. In the fourth method, as shown by the maximum pulse width 52 and the minimum pulse width 53 shown on the horizontal axis in FIG. 3, a set value (function) of the delay time Td with respect to the reference power supply voltage Vs is used. The pulse width Tw is determined by the third method up to about ± 5%, but when the power supply fluctuations exceed that, the pulse width Tw is fixed to a limit value, for example, a maximum pulse width 52 or a minimum pulse width 53. I do. As a result, even if the range of the power supply voltage Vs that can be operated at the maximum power factor is narrowed, a large number of delay time set values (functions) are not required, and it is not necessary to know the magnitude of the power supply voltage Vs, so that the control configuration is simplified. And the power factor does not decrease much. Here, when the pulse width Tw is a limit value (maximum value or minimum value), the DC voltage Vd is not always a constant value, but a system using the limit value of the pulse width Tw is used. May be determined from the minimum allowable power factor value or DC voltage value.
[0029]
Next, a control method for the section C in FIG. 2 will be described. In the section C of FIG. 2, the above-mentioned condition that the sum of the delay time Td and the pulse width Tw is not constant is not satisfied. However, the DC voltage Vd is changed by setting the delay time Td to a fixed value and changing the pulse width Tw. Can be kept constant. That is, if the delay time Td is fixed and the pulse width Tw is controlled so as to keep the DC voltage Vd constant, the operation can be performed with the power factor at the maximum value. In this case as well, several kinds of delay times Td (fixed values) corresponding to the magnitude of the power supply voltage Vs are stored in the control circuit 7, and if the fixed values are changed based on the magnitude of the power supply voltage Vs, the power supply voltage can be changed. It can also respond to fluctuations in Vs.
[0030]
As described in the above embodiment, the power supply device of the present invention including the power factor improvement circuit that short-circuits the power supply once or more than once in a half cycle of the power supply voltage Vs has a direct current while maintaining the power factor at the maximum value. The voltage Vd can be controlled to be constant.
[0031]
【The invention's effect】
According to the present invention, the DC voltage Vd can be controlled to be constant while the power factor of the power supply device is kept at the maximum value even when the power supply voltage varies.
[Brief description of the drawings]
FIG. 1 is an explanatory diagram of a motor control device using a power converter according to an embodiment.
FIG. 2 is an explanatory diagram of the input current dependence of the efficiency, power factor, and DC voltage of the power converter of the embodiment.
FIG. 3 is an explanatory diagram of a relationship between a change in efficiency, a power factor, a DC voltage and a pulse width when a power supply voltage fluctuates in the power converter according to the embodiment.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... AC power supply, 2 ... Reactor, 3 ... Short circuit means, 4 ... Rectifier circuit, 5 ... Rectifier circuit switching means, 6 ... Smoothing capacitor, 7 ... Control circuit, 8 ... Zero cross detection circuit, 10 ... Inverter circuit, 20 ... Compression , 30: input current detection circuit, 100: power converter, Tw: pulse width, Td: delay time.

Claims (13)

A reactor having one end connected to the AC power supply, short-circuit means having one end connected to the other end of the reactor, one end on the AC input side being connected to the other end of the reactor, and a multi-end on the AC input side being connected to the other end of the short-circuit means. A rectifier circuit connected to an end, a zero-crossing detection circuit that detects a zero-crossing of the AC power supply, and a power conversion device including a control circuit that controls the short-circuiting means.
The control circuit controls the short-circuit operation of the short-circuit means based on a delay time Td, which is a period from the zero-cross point of the AC power supply to the start of the short-circuit operation, and a pulse width Tw, which is a short-circuit period. A power converter, wherein a time Td and the pulse width Tw are controlled independently. 2. The power converter according to claim 1, wherein the power converter has one end connected to the other end of the AC power supply, and the other end connected to the other end of the short-circuit means, and the rectifier circuit. A smoothing capacitor connected to both ends of the DC output of the control circuit. An input current detection value and a DC voltage across the smoothing capacitor are input to the control circuit, and the control circuit determines the delay time Td by the input current. Alternatively, the power converter controls the input power based on a preset function, and controls the pulse width Tw to a predetermined value by the DC voltage. The power converter according to claim 1, wherein the power converter includes a smoothing capacitor connected to both ends of a DC output of the rectifier circuit, and inputs a DC voltage across the smoothing capacitor to the control circuit; The power conversion device, wherein the control circuit controls the delay time Td to a predetermined constant value, and controls the pulse width Tw to a predetermined value by the DC voltage. 2. The power conversion device according to claim 1, wherein the power conversion device includes an input current detection circuit having one end connected to the other end of the AC power supply and the other end connected to the other end of the short circuit. An input current detection value is input to a circuit, and the control circuit controls the delay time Td according to a first function set in advance for the input current or the input power, and controls the pulse width Tw to the input current or the input current. Alternatively, the power converter controls input power according to a second function set in advance. 3. The power converter according to claim 2, wherein the function includes a plurality of functions corresponding to the voltage of the AC power supply estimated from the DC voltage when the short-circuiting unit does not perform the short-circuit operation, and according to the voltage of the AC power supply. 4. A power conversion apparatus for selecting the function. The power converter according to claim 3, wherein the plurality of the constant values are provided in correspondence with the voltage of the AC power supply estimated from the DC voltage when the short-circuit means is not performing a short-circuit operation, and the voltage of the AC power supply is The power converter according to claim 1, wherein the constant value is selected according to the value. The power converter according to claim 4, wherein the power converter includes a smoothing capacitor connected to both ends of a DC output of the rectifier circuit, and inputs a DC voltage across the smoothing capacitor to the control circuit; The control circuit comprises a plurality of the first function and the second function, respectively, and the first function is provided in accordance with a voltage of the AC power supply estimated from the DC voltage when the short-circuit means is not performing a short-circuit operation. And the second function are selected. The power converter according to claim 1, wherein a limit value is provided for the delay time (Td) or the pulse width (Tw). A reactor having one end connected to the AC power supply, short-circuit means having one end connected to the other end of the reactor, one end on the AC input side being connected to the other end of the reactor, and a multi-end on the AC input side being connected to the other end of the short-circuit means. A rectifier circuit connected to an end, a zero-crossing detection circuit that detects a zero-crossing of the AC power supply, and a power conversion device including a control circuit that controls the short-circuiting means.
The control circuit controls the short-circuit operation of the short-circuit means based on a delay time Td, which is a period from the zero-cross point of the AC power supply to the start of the short-circuit operation, and a pulse width Tw, which is a short-circuit period. A power converter, wherein a time Td and the pulse width Tw are controlled in association with each other. 10. The power converter according to claim 9, wherein the control circuit controls the sum of the delay time Td and the pulse width Tw to a constant value. The power converter according to claim 10, wherein the power converter includes a smoothing capacitor connected to both ends of a DC output of the rectifier circuit, and inputs a DC voltage across the smoothing capacitor to the control circuit; The power conversion device, wherein the control circuit controls the pulse width Tw so that the DC voltage is constant. The power converter according to claim 10, wherein the constant value is changed according to a voltage of an AC power supply estimated from the DC voltage when the short-circuiting unit is not performing a short-circuit operation. A reactor having one end connected to the AC power supply, short-circuit means having one end connected to the other end of the reactor, one end on the AC input side being connected to the other end of the reactor, and a multi-end on the AC input side being connected to the other end of the short-circuit means. A rectifier circuit connected to an end, a zero-crossing detection circuit that detects a zero-crossing of the AC power supply, and a power conversion device including a control circuit that controls the short-circuiting means.
The short-circuit means performs a short-circuit operation in accordance with a time from the zero-cross point of the AC power supply to the start of the short-circuit operation and a time point at which the short-circuit operation ends from the zero-cross point,
The power conversion device, wherein the control circuit controls a time point at which the short-circuit operation is started such that the time point at which the short-circuit ends is fixed and the DC voltage is constant.

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