JP2004007880A - Power supply device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To reduce the cost of a power supply device by reducing a switching frequency while clearing the higher harmonic regulation. <P>SOLUTION: Input power from a power source 1 is converted into direct-current voltage, and the voltage for a load 4 is obtained through a voltage boosting chopper circuit 3. When this is done, the switching device 3c of the voltage boosting chopper circuit 3 is caused to switch, and short-circuited through a voltage boosting choke coil 3a to improve the power factor. At this time, a controller 15 turns on and off the switching device 3c based on the result of comparison of a detected input current from an input current detecting part 12 and a reference signal of sinusoidal input current. While doing this, the controller 15 causes a power supply phase detecting part 10 to detect zero crossing. Then, the controller inhibits the operation of the switching device 3c for a predetermined period from a predetermined point before the zero crossing to the point of the zero crossing. <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a power supply device suitable for a compressor motor or the like of an air conditioner, and more particularly to a power supply device of a boost chopper type having a power factor improving function and a harmonic current suppressing function.
[0002]
[Prior art]
As an example of the power factor improving and harmonic current suppressing means, there is a method described in Japanese Patent Application Laid-Open No. 54-101148. In this method, as shown in FIG. 7, an input power supply (AC power supply) 1 is full-wave rectified by a rectifier circuit 2 and this AC / DC converted voltage is converted to a predetermined voltage by a boost chopper circuit (power factor improving means) 3. Increase the pressure.
[0003]
The step-up chopper circuit 3 includes a step-up choke coil (reactor) 3a connected in series to the positive terminal side of the rectifier circuit 2, a backflow prevention diode 3b connected in series to the step-up choke coil 3a, and a step-down choke coil 3a and the backflow prevention. A switching element (for example, IGBT; insulated gate transistor) 3c connected between the diode 3b and the negative terminal of the rectifier circuit 2 and a smoothing capacitor 3d for smoothing the output voltage are provided.
[0004]
The operation is switched by the switching element 3c via the boost choke coil 3a and short-circuited, and the switched voltage is supplied from the backflow prevention diode 3b to the smoothing capacitor 3d to be the voltage of the load 4. When the load 4 is applied to, for example, a compressor motor of an air conditioner, an inverter circuit 4a and a motor 4b can be assumed.
[0005]
As shown in FIG. 8, in the step-up chopper circuit 3, the switching element 3c is set so that the absolute value of the input current falls within a predetermined range (current control range; δ) similar to the absolute value of the input voltage. Is turned on and off for control. In this case, assuming that an input current reference signal (a so-called sinusoidal signal) is Ir, the switching element 3c is turned on and off so that the input current falls between Ir + δ / 2 and Ir-δ / 2. .
[0006]
The switching frequency of the switching element 3c is mainly determined by the current control range, the input power supply reactor capacity, the output voltage, and the like. The switching frequency is naturally set to be sufficiently higher than the frequency of the input power supply 1. For example, in the case of home electric appliances and the like, the switching frequency is generally set to a value of several tens kHz to several tens kHz.
[0007]
By the way, when the switching frequency is set high, the switching loss is large, the switching element 3c itself becomes large, or a plurality of switching elements 3c are required. Furthermore, high-speed switching increases the amount of noise generated, which necessitates the addition of a noise filter. In addition, the reactor must be compatible with high frequencies, thus increasing the cost.
[0008]
Therefore, if the inductance of the reactor is increased and the output voltage is set small so that the switching frequency becomes low, the input current may greatly deviate from the zero cross point at the zero cross point of the input power source as shown in FIG. That is, the ON timing (or OFF timing) of the switching element 3c may deviate from the zero cross point.
[0009]
In this case, the third harmonic component reduced by the step-up co-chopper circuit 3 is dispersed to the third and subsequent higher orders, and the higher order components increase. Therefore, problems such as exceeding the power supply harmonic regulation limit value occur.
[0010]
As described above, in the above-described conventional power supply device, it is difficult to lower the switching frequency due to the relationship with the power supply harmonic regulation limit value, and switching has to be performed at a high frequency, resulting in an increase in cost.
[0011]
Therefore, an object of the present invention is to reduce the cost of a power supply device by lowering the switching frequency while clearing the power supply harmonic regulation.
[0012]
[Means for Solving the Problems]
In order to solve the above-mentioned problems, the present invention provides a power supply device that converts a power supply into a DC voltage and converts it into a load voltage, thereby improving the power factor by short-circuiting the converted voltage via at least a reactor (coil). In the above, while switching the switching element of the power factor improvement means including the reactor, based on the comparison result of the input current and the sine-wave input current reference signal, the switching element is turned on and off, the power factor improvement means of the While the output voltage is used as the load voltage, a zero cross of the AC power supply is detected, and the switching operation of the switching element is prohibited for a predetermined period from a predetermined time before the zero cross to the zero cross. .
[0013]
Preferably, when the input current of the boost chopper circuit becomes equal to or more than a predetermined value at a zero crossing point of the AC power supply, the switching operation prohibition period is included in a switching signal. As a result, the switching operation is prohibited only in the vicinity of the zero crossing point, so that the influence on the power factor improvement is extremely small, while the input current waveform is improved and the higher harmonics are reduced.
[0014]
As a first aspect, the input current reference signal includes an amplitude value determined according to a deviation between an output voltage command value (a load voltage command value) and an output voltage of the boost chopper circuit, It can be obtained by multiplying the input voltage waveform or the absolute value of the input voltage waveform.
[0015]
In a second aspect, the input current reference signal includes an output voltage of the boost chopper circuit or an amplitude value determined according to the load, and an input voltage waveform or an absolute value of the input voltage waveform of the boost chopper circuit. Can also be obtained by multiplication with
[0016]
Further, as a third aspect, the input current reference signal includes an amplitude value determined according to an effective value of an input current of the boost chopper circuit or an average value of absolute values of the input current, and an input value of the boost chopper circuit. It can also be obtained by multiplying the voltage waveform or the absolute value of the input voltage waveform.
[0017]
As described above, the amplitude value of the input current reference signal can be determined according to the use of the power supply device. For example, when a load fluctuation (rotation speed fluctuation) occurs in one rotation such as a compressor, the input current reference signal is determined according to the load. The amplitude value of the signal is determined, that is, an optimum input current reference signal is obtained.
[0018]
The multiplication of the amplitude value and the absolute value is preferably performed by chopping the input voltage waveform or the absolute value of the input voltage waveform with a PWM signal corresponding to the amplitude value of the input current reference signal.
[0019]
According to this, the multiplication can be performed by hardware of at least a chopper circuit including transistors. For example, the power supply voltage of the chopper circuit is set to the input voltage Vi, and an input current reference signal is obtained by chopping the input voltage Vi using a pulse modulation (PWM) signal according to the amplitude value. Therefore, it is not necessary to use a high-speed CPU as the control means, and cost reduction is achieved.
[0020]
The output voltage command value is preferably set to be lower than the voltage peak value of the input power supply. According to this, switching by the switching element of the boost chopper circuit is appropriately performed, for example, the switching frequency can be reduced, and the input current can be reduced. The waveform can be made sinusoidal, and high-order harmonics are reduced.
[0021]
The amplitude value may be empirically obtained and stored in advance according to the output voltage or the load state. Further, the amplitude value may be obtained in advance as a function of the load amount. When the load is a motor, the number of rotations of the motor may be used as the load. Thus, an amplitude value suitable for the use of the power supply device is used.
[0022]
The power supply device of the present invention can be applied to, for example, all types of home electric appliances, but is particularly suitable as a power supply device for a compressor motor of an air conditioner.
[0023]
BEST MODE FOR CARRYING OUT THE INVENTION
Next, an embodiment of the present invention will be described in detail with reference to FIGS. In FIG. 1, the same parts as those in FIG. FIGS. 2A and 4A correspond to FIG. 8B.
[0024]
The power supply device of the present invention inhibits switching in the boost chopper from a predetermined time before the zero-cross point of the input current waveform to the same zero-cross point (see FIG. 2), and makes the input current at the zero-cross point zero. Regardless of the frequency, the switching element of the step-up chopper means can be turned on (or off) at zero input current to reduce high-order harmonic current.
[0025]
In FIG. 1, the power supply device includes a power supply phase detection unit 10 for detecting a phase of an input power supply 1, a current sensor (for example, CT) 11 for detecting an input current Ii of a boost chopper circuit 3, and an input current detection unit 12 An input voltage detecting unit 13 for detecting an input voltage Vi of the boost chopper circuit 3, an output voltage detecting unit 14 for detecting an output voltage Vo of the boost chopper circuit 3, and a switching element according to the detected values. The control unit 15 outputs a signal for turning on and off the switch 3c, and a drive unit 16 drives the switching element 3c based on the signal.
[0026]
The operation of the power supply device will be described with reference to the waveform diagram of FIG. 2A and the time chart of FIG. 2B. The control unit 15 determines the output voltage command value (the applied voltage command value of the load 4). A signal (switching signal) for switching the switching element 3c is generated based on the deviation from the output voltage Vo.
[0027]
At this time, a zero-cross point of the input power supply waveform is detected based on a detection signal from the power-supply phase detection unit 10, and a time (switching operation prohibition period) until a predetermined time before the zero crossing point is calculated. Include in signal.
[0028]
As shown in FIG. 3, first, a deviation between the output voltage command value and the detection voltage Vo detected by the output voltage detection unit 14 is calculated by the calculating unit 15a, and based on the calculated deviation, the input current reference signal is generated by the current reference signal amplitude generating unit 15b. An Ir amplitude value (a so-called reference sinusoidal amplitude value) is created.
[0029]
The generated amplitude value is multiplied by the detection voltage Vi by the input voltage detection unit 13 by the calculating means 15c, and a hysteresis is generated based on the input current reference signal Ir resulting from the multiplication. It should be noted that the input voltage waveform or the absolute value of the input voltage waveform may be used as the detection voltage Vi.
[0030]
The value of the input current reference signal Ir having the hysteresis is compared with the input current Ii detected by the input current detection unit 12 by the hysteresis comparator 15d, and a switching signal of the switching element 3c is created based on the comparison result.
[0031]
The boosting chopper circuit 3 is controlled by this switching signal, that is, the switching element 3c is switched by using the reference current reference signal Ir as a reference sine wave as in the related art, and the input current waveform shown in FIG. 2A is obtained.
[0032]
On the other hand, based on a power supply phase signal (for example, a voltage phase) detected by the power supply phase detection unit 10, an operation state signal including a switching operation permission period and a predetermined time (operation inhibition period) is obtained by the switching operation time generation unit 15e. .
[0033]
In this case, the zero-cross point of the input power supply waveform is detected, operation is permitted for a predetermined time from the zero-cross point between the zero-cross point and the next zero-cross point, and after this predetermined time, switching operation is prohibited until the next zero-cross point. I do. Note that the switching operation prohibition period is empirically obtained in advance, and for example, the operation prohibition time may be set longer as the frequency of the input power supply 1 is lower.
[0034]
The operating state signal thus obtained and the switching signal obtained by the hysteresis comparator 15d are calculated by the AND means 15f, and the switching signal resulting from this calculation is output to the drive unit 16.
[0035]
As a result, as shown in FIG. 2A, at the zero-cross point of the input power supply 1, the input current is forced to the zero state, so that the on-timing (or off-timing) of the switching element 3c changes to the zero-crossing point. Never leave.
[0036]
Therefore, it is not necessary to increase the inductance of the reactor so as to lower the switching frequency, and even if the output voltage is not set lower, the noise of higher harmonic components does not increase and the higher harmonic components are It does not exceed the harmonic regulation value. In addition, the switching element 3c does not require a large-sized switching element or a large number of switching elements, so that the cost can be reduced.
[0037]
Moreover, if the output voltage command value is set lower than the voltage peak value of the input power supply 1, the input current waveform will take the form shown in FIG. 4, and the peak value of the input current will be suppressed. Therefore, the number of times of switching can be reduced. That is, the switching frequency can be lowered.
[0038]
The switching operation prohibition period is included in the switching signal when the input current Ii of the boost chopper circuit 3 becomes equal to or more than a predetermined value at the zero crossing point of the input power supply 1. That is, when the input current is in a low state, for example, the switching frequency does not increase and the high-order harmonics are small.
[0039]
In the above embodiment, the current reference signal amplitude is determined according to the deviation between the output voltage command value and the output voltage Vo. However, the current reference signal amplitude in the current reference signal amplitude creation unit 15b is determined according to the load 4. It may be. In this case, an amplitude value associated with the size of the load 4 may be empirically obtained and stored in advance, and an amplitude value corresponding to the size of the load may be output.
[0040]
Further, instead of the size of the load 4, an effective input current value reflected by the load state may be used. In that case, the control unit has the configuration shown in FIG. In the figure, the same parts as those in FIG. 3 and corresponding parts are denoted by the same reference numerals, and redundant description will be omitted.
[0041]
In FIG. 5, a control unit 15 calculates an effective value by an effective value calculation unit 15g based on a detection current Ii detected by an input current detection unit 12, and inputs the effective value to a current reference signal amplitude creation unit 15b based on the input current effective value. An amplitude value of the current reference signal Ir is created.
[0042]
In this case, as described above, the current reference signal amplitude creating means 15b creates the amplitude of the input current reference signal Ir as a reference shown in FIG. 2, and if the effective value of the input current is large, the amplitude of the Ir is large. It becomes.
[0043]
By the way, a CPU such as a microcomputer is used for the control unit 15. However, if the CPU is also used as a control unit of an air conditioner, for example, the processing load on the CPU increases, which may hinder air conditioning control. .
[0044]
Therefore, it is preferable that the calculation means 15c of the control unit 15 be realized by a hardware circuit shown in FIG. 6 so as to reduce the processing load on the CPU. The calculation means 15c is composed of a chopper circuit 20 using transistors and a low-pass filter circuit 21 combining a follower circuit using an operational amplifier and an RC circuit. The chopper circuit 20 and the low-pass filter 21 are commonly used circuits, but may have other circuit configurations.
[0045]
In this case, the power supply voltage of the transistor circuit is set to the input voltage Vi, the input voltage Vi is chopped by the PWM signal, and the chopped input voltage Vi is passed through the low-pass filter circuit 21 to obtain the input current reference signal Ir.
[0046]
Further, as the input voltage Vi, an input voltage waveform or an absolute value of the input voltage waveform is used, and a PWM signal having a cycle (duty) corresponding to the amplitude value of the current reference signal by the current reference signal amplitude creating means 15b is used. .
[0047]
The signal output from the output voltage error amplifier is based on pulse width modulation (PWM). For example, a PWM signal based on the output voltage can be easily created by a microcomputer mounted in an air conditioner or the like. Therefore, the control unit 15 also serves as, for example, a CPU that is a control unit of an air conditioner, thereby reducing the cost of the power supply device.
[0048]
In addition, as a method of calculating the input current reference signal Ir, the amplitude value of the force current reference signal Ir is determined according to the effective value of the input current of the boost chopper circuit 3 or the average value of the absolute value of the input current. The amplitude value may be multiplied by the calculating means 15c with the input voltage waveform of the boost chopper circuit 3 or the absolute value of the input voltage waveform.
[0049]
Further, the amplitude value may be empirically obtained and stored in advance according to the output voltage or the load state, or may be obtained in advance as a function of the load amount.
[0050]
Further, as the size and amount of the load, the rotation speed of the motor 4b may be used, and the amplitude value of the input current reference signal Ir may be obtained according to the rotation speed. This power supply device is particularly suitable for driving a compressor motor of an air conditioner.
[0051]
【The invention's effect】
As described above, according to the present invention, the switching element of the power factor improving means is switched, and the switching element is turned on and off based on the comparison result between the input current and the sinusoidal input current reference signal, and the power factor is changed. While the output voltage of the improvement means is set to the load voltage, the zero crossing of the input power supply is detected, and the operation of the switching element is set as the inhibition period for a predetermined period from a predetermined time before the zero crossing to the zero crossing. At this point, the input current is forcibly reduced to zero, the input AC waveform near the zero-cross point is improved (sine-wave shaped), and the high-order harmonic current can be reduced.
[0052]
Also, it is not necessary to increase the inductance of the reactor so as to lower the switching frequency of the switching element, and even if the output voltage is not set lower, the noise of the higher-order harmonic components does not increase. The component does not exceed the power supply harmonic regulation value, and a large-sized switching element or a large number of switching elements are not required, that is, the cost of the device can be reduced.
[Brief description of the drawings]
FIG. 1 is a schematic circuit diagram showing an embodiment of a power supply device according to the present invention.
FIG. 2 is a schematic waveform diagram and a time chart for explaining the operation of the embodiment.
FIG. 3 is a schematic block diagram showing a control unit of the embodiment.
FIG. 4 is a schematic waveform chart and a time chart for explaining another operation example of the embodiment.
FIG. 5 is a schematic block diagram showing a modification of the control unit shown in FIG. 3;
FIG. 6 is a schematic circuit diagram for explaining arithmetic means of the control unit in FIGS. 3 and 5;
FIG. 7 is a schematic circuit diagram for explaining a conventional power supply device.
FIG. 8 is a schematic waveform diagram illustrating the operation of the power supply device of the conventional example.
FIG. 9 is a schematic waveform diagram illustrating the operation of the power supply device of the conventional example.
[Explanation of symbols]
1 Input power supply (AC power supply)
2 Rectifier circuit 3 Step-up chopper circuit 3a Step-up choke coil 3b Backflow prevention diode 3c Switching element (IGBT)
3d smoothing capacitor 4 load 10 power supply phase detector 11 current sensor (CT)
12 Input current detector 13 Input voltage detector 14 Output voltage detector 15 Controller Ii Input current Vi Input voltage Vo Output voltage Ir Input current reference signal

Claims (11)

When the AC power supply is converted into a DC voltage to be a load voltage, the converted voltage is short-circuited through at least a reactor (coil) to improve a power factor.
The switching element of the power factor improving means including the reactor is switched, and the switching element is turned on and off according to the result of comparison between the input current and the sine-wave input current reference signal. , The zero-cross of the AC power supply is detected, and the switching operation of the switching element is inhibited for a predetermined period from a predetermined time before the zero cross to the zero cross. 2. The power supply device according to claim 1, wherein the switching operation prohibition period is included in a switching signal when the input current of the power factor improving unit becomes equal to or more than a predetermined value at a zero crossing point of the AC power supply. 3. The input current reference signal includes an amplitude value determined according to a deviation between an output voltage command value (load voltage command value) and an output voltage of the power factor improvement means, an input voltage waveform of the power factor improvement means or 3. The power supply device according to claim 1, wherein the power supply device is obtained by multiplying the input voltage waveform by an absolute value. The input current reference signal is obtained by multiplying an output voltage of the power factor improving means or an amplitude value determined according to the load by an input voltage waveform of the power factor improving means or an absolute value of the input voltage waveform. Item 3. The power supply device according to item 1 or 2. The input current reference signal includes an amplitude value determined according to an effective value of an input current of the power factor improving means or an average value of absolute values of the input current, and an input voltage waveform or an input voltage waveform of the power factor improving means. The power supply device according to claim 1, wherein the power supply device is obtained by multiplying the absolute value by the absolute value of 6. The multiplication of the amplitude value and the absolute value is performed by chopping the input voltage waveform or the absolute value of the input voltage waveform by a PWM signal corresponding to the amplitude value of the input current reference signal. The power supply device according to claim 1. The power supply device according to claim 3, wherein the output voltage command value is set lower than a voltage peak value of the input power supply. The power supply device according to claim 4, wherein the amplitude value is a value empirically obtained in advance according to an output voltage or a load state. The power supply device according to claim 4, wherein the amplitude value is a value previously obtained as a function of the amount of the load. The power supply device according to claim 9, wherein the load is a motor, and the number of rotations is a load amount. The power supply device according to any one of claims 1 to 10, which is used as a power supply for a motor of an air conditioner.

Images