JP2008228511A - Power supply - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a power supply which can materialize efficient power supply, while guaranteeing boost and harmonics suppression in the case of converting AC power into DC power and supplying it to a load. <P>SOLUTION: The power unit 1 converts AC power into DC power and supplies it to a load. It has both a first filtering function of detecting the zero point of a current flowing to a reactor 16 and improving waveform in a critical mode of switching a switching element 19 and a second filtering function of improving waveform, by switching a switching element 22 in a part of input voltage waveform. It selectively actuates the first filtering function and the second filtering function, based on an output voltage value. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a power supply apparatus for converting alternating current power into direct current power and supplying it to a load.

  In recent years, in a water heater, an air conditioner, a washing dryer, and the like, a method of variably controlling the rotation speed of an electric motor for driving a compressor using an inverter is generally performed. Such an inverter controls the frequency of power applied to the motor by so-called PWM control, but the power input to the inverter needs to be DC power, so when using a commercial power supply, A power supply device that converts AC power into DC power is required.

  Here, since a capacitor input type rectifier circuit is used to convert AC power into DC power, the input current is greatly distorted depending on the impedance of the power system. When this distortion occurs, there is a problem that the harmonic current increases to cause heat generation of the capacitor and other circuit elements, resulting in deterioration and malfunction.

  Therefore, such a power supply device is provided with a filter for suppressing such harmonic current. This filter includes a passive filter composed of passive elements and an active filter that improves the waveform by the switching operation of the switching elements, but the former passive filter changes to a corresponding passive element when the main circuit configuration changes. The need arises and it is not advantageous in terms of time and cost for the design.

On the other hand, the latter active filter is easy because it requires only the same configuration to select an element that matches the input. In addition, it improves the waveform of the input current by high-frequency switching using analog control, so it eliminates almost complete harmonics. Is possible. In particular, in recent years, with the widespread use of DC motors, miniaturization / high output of electric motors has been demanded, and in order to achieve this, it is necessary to increase the input voltage of the inverter. Since the active filter can boost the voltage simultaneously with suppressing harmonics, it is very suitable for an electric motor control device using an inverter (see, for example, Patent Document 1 and Patent Document 2).
JP-A-6-105563 JP 2000-224858 A JP 2006-204008 A

  Here, when it is not necessary to reduce the size or increase the output of the motor and there is no request for boosting, the active filter is used specifically for suppressing harmonics (power factor improvement) by improving the waveform. . On the other hand, if the switching element is switched at a high frequency in the entire range of the input voltage waveform output from the rectifier circuit (Patent Document 1), switching loss (switching loss itself) and power consumption of the switching element increase.

  Thus, a method of partially switching the switching element only near the zero cross of the input voltage waveform has been developed (Patent Document 2). According to such partial switching, the number of switching operations can be reduced and the switching loss can be reduced as compared with the high-frequency switching in the entire range as described above while improving the waveform falling within the regulation value of the harmonic current. Further, since boosting is not performed, the capacity of the reactor and the switching element can be reduced. In particular, Patent Document 2 makes it possible to boost a certain amount of voltage, but there is a problem that it is difficult to improve the waveform when the motor is operated at a high output with a small amount of switching.

  On the other hand, as a method for improving the input current waveform, in addition to the method described above, the switching element is switched on (ON) by recognizing that the current flowing through the reactor has become zero, and the peak value (OFF point). There is a critical mode control system that controls the sine wave. In this critical mode control system, switching is performed by self-excitation at the reactor current zero point, so that the circuit configuration is simplified, the switching loss is reduced, and the recovery loss of the subsequent diode is also reduced. For this reason, there is an advantage that efficiency related to switching is improved.

  However, since the current flowing through the reactor is a triangular wave, the peak value is higher than the halved average value. Therefore, in order to sufficiently suppress harmonics, the output voltage must be set at a certain level or higher. For this reason, boost control that determines the voltage of the power supplied to the inverter in accordance with the input not only makes it impossible to accurately boost a low voltage when the input is small, but also suppresses harmonics sufficiently. There was a problem.

  The present invention has been made to solve the conventional technical problems, and in the case of converting AC power to DC power and supplying it to a load, it is efficient while ensuring boosting and suppressing harmonics. The present invention provides a power supply device that can realize a simple power supply.

  The power supply apparatus of the present invention converts alternating current power into direct current power and supplies it to a load. The first power source device improves the waveform in a critical mode in which the zero point of the current flowing through the reactor is detected and the switching element is switched. Both the filter function and the second filter function that improves the waveform by switching the switching element in a part of the input voltage waveform, and the first filter function and the second filter function based on the output voltage value Is selectively operated.

  According to a second aspect of the present invention, there is provided the power supply apparatus according to the second aspect, wherein when the output voltage value is higher than a predetermined value, the first filter function is operated, and when the output voltage value is low, the second filter function is operated.

  According to a third aspect of the present invention, when the output voltage value exceeds the predetermined value, the power supply device switches from the second filter function to the first filter function at the nearest zero point of the input voltage waveform. To do.

  According to the present invention, in a power supply device that converts alternating current power into direct current power and supplies the load to the load, the first filter function performs waveform improvement in a critical mode in which the zero point of the current flowing through the reactor is detected and the switching element is switched. And a second filter function that improves the waveform by switching the switching element in a part of the input voltage waveform, and selects the first filter function and the second filter function based on the output voltage value. For example, when the output voltage value is higher than a predetermined value, the first filter function is operated, and when the output voltage value is low, the second filter function is operated. Therefore, the second filter function is operated within the range that can be covered by the second filter function, and the harmonics are suppressed to a certain extent by efficient switching. It performs boosting, if the second filter as an output range that can not be handled, it is possible to perform the harmonic suppression and required boost by operating the first filter function.

  In the first filter function, switching loss and recovery loss can be reduced by switching in the critical mode. As a result, efficient power supply can be realized while ensuring the boosting and harmonic suppression functions.

  Further, when the output voltage value exceeds the predetermined value as in the invention of claim 3, the second filter function is switched to the first filter function at the nearest zero point of the input voltage waveform. It is possible to prevent an overcurrent when switching from the second filter function to the first filter function and to realize a smooth control switching operation.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

  FIG. 1 shows an electric circuit diagram of an electric motor drive device 2 to which a power supply device 1 according to an embodiment of the present invention is applied. The electric motor drive device 2 of an Example drives the electric motor 3 for a compressor drive incorporated in the compressor which comprises the refrigerant circuit of the air conditioner which is not shown in figure, for example. The electric motor 3 of the embodiment is composed of a DC brushless motor. And the electric motor drive device 2 is comprised from the power supply device 1 and the inverter circuit 4 of this invention.

  The power supply device 1 includes a rectifying unit 6 and a smoothing unit 7, converts AC power supplied from the AC power source 8 into DC power having a predetermined voltage, and outputs the DC power to the inverter circuit 4 for supply. The inverter circuit 4 is composed of a plurality of switching elements. When the switching elements are turned ON / OFF by a switching signal output from the microcomputer 9 (control means), electric power corresponding to the switching signal is supplied to the motor 3. The motor 3 is output and the motor 3 is operated at the number of revolutions corresponding to the electric power.

  The microcomputer 9 uses the inverter circuit 4 to control the rotation speed of the electric motor 3 by PWM control. The rotation speed of the electric motor 3 changes according to the change of the input voltage. Therefore, when a voltage corresponding to the duty ratio of the switching signal from the microcomputer 9 is output from the inverter circuit 4 to the electric motor 3, the electric motor 3 rotates at a rotation speed corresponding to this voltage.

  Here, when the duty ratio of the switching signal in the inverter circuit 4 is constant, the voltage output from the inverter circuit 4 is the input voltage to the inverter circuit 4, that is, the output voltage Vo of the smoothing unit 7 of the power supply device 1. It changes according to. Therefore, the rotational speed of the electric motor 3 can also be changed by the output voltage Vo to the inverter circuit 4. The microcomputer 9 can also control the rotation speed of the electric motor 3 by switching control of the power supply device 1.

  On the other hand, the rectifier 6 is provided with a full-wave rectifier circuit 12 in which a diode 11 is connected in a bridge shape, and an AC-side reactor 13 and a capacitor 14 (which constitute a high-frequency blocking filter) are input to the rectifier circuit 12. AC power supply 8 (commercial AC 100V power supply) is connected via A capacitor 15 is connected between the output of the rectifier circuit 12 and the ground for removing a ripple current caused by switching in critical mode control described later. A DC-side reactor 16 is connected to the subsequent stage of the capacitor 15, and a capacitor 18 constituting the smoothing unit 7 is connected to the subsequent stage of the reactor 16 via a diode 17. In addition, a series circuit of a switching element (MOSFET) 19 and a resistor 25 (a resistor for monitoring the current of the switching element 19) is connected between the connection point of the reactor 16 and the diode 17 and the ground. Furthermore, another DC-side reactor 20 is connected to the output of the rectifier circuit 12, and another diode 21 is connected between the reactor 20 and the capacitor 18, and the diode 21 and the reactor 20 are connected. Another switching element (IGBT) 22 is connected between the connection point and the ground.

  That is, a circuit for a capacitor 15, a reactor 16, a switching element 19 and a diode 17 for performing critical mode control (first filter function) to be described later, and simple PAM control (second filter function) to be described later. The reactor 20, the switching element 22, and the diode 21 are connected in parallel between the rectifier circuit 12 and the capacitor 18.

  The capacitor 18 of the smoothing unit 7 smoothes the pulsating current flowing through the diode 17 or 21. Switching elements 19 and 22 are turned on by a switching signal to cause a short-circuit current to flow through reactors 16 and 20, respectively. When the switching element 19 is turned on, the electric circuit on the output side of the reactor 16 is short-circuited, and a direct current flows through the reactor 16. Thereby, energy is stored in the reactor 16. The energy stored in the reactor 16 is then added to the input DC voltage when the switching element 19 is turned off, and the capacitor 18 is charged. As a result, the DC voltage output from the rectifier circuit 12 is boosted.

  The reactor 16 is provided with a winding 24 for detecting the current IL flowing through the reactor 16, and the switching element 19 is turned on at the zero point of the current IL of the reactor 16 detected by the winding 24. Then, the peak value is turned off based on the input voltage and the output voltage so as to have a sine wave shape. As a result, the current IL flowing through the reactor 16 becomes a triangular wave, and the average value of the continuous triangular wave current is ½ of the peak value. Furthermore, the ripple current associated with switching is removed by the capacitor 15 to perform critical mode control (first filter function) for controlling the input current in a sine wave shape. Thereby, the improvement of a power factor and suppression of a harmonic are performed. At this time, since the ON control of the switching element 19 is performed by self-excitation, the circuit configuration (critical mode control circuit 23 described later) is simplified. Further, since switching is performed at the zero point of the current IL, recovery loss in the diode 17 can be reduced.

  On the other hand, when the switching element 22 is turned ON, the electric circuit on the output side of the reactor 20 is short-circuited, and a direct current flows through the reactor 20. Thereby, energy is stored in the reactor 20. The energy stored in the reactor 20 is then added to the input DC voltage when the switching element 22 is turned off, and the capacitor 18 is charged. As a result, the DC voltage output from the rectifier circuit 12 is boosted. Further, by performing simple PAM control (second filter function) for controlling the ON / OFF duty ratio (time ratio, conduction ratio) of the switching element 22, the input current can be controlled in a sine wave form. Thereby, the improvement of a power factor and suppression of a harmonic are performed.

  Next, 23 is the critical mode control circuit described above, and 31 is a drive circuit connected to the critical mode control circuit 23 and the output of the microcomputer 9. The gate of the switching element 19 is connected to the drive circuit 31 and is ON / OFF controlled. The critical mode control circuit 23 receives the current IL of the reactor 16 from the terminal voltage of the winding 24, and also receives the input voltage after the rectifier circuit 12 and the output voltage after the diode 17, and further flows through the switching element 19. A terminal voltage of the resistor 25 for detecting current is also input. The critical mode control circuit 23 is also connected to the microcomputer 9.

  The critical mode control circuit 23 generates a switching signal of a critical mode (first filter function) that switches (ON) the switching element 19 at the zero point of the current IL of the reactor 23 detected by the winding 24. Output to the drive circuit 31. As a result, the DC voltage output to the inverter circuit 4 can be boosted, and the switching element 19 can be turned on by the critical mode control circuit 23 independently of the microcomputer 9, thereby simplifying the circuit configuration. . Further, since the switching element 19 is turned on at the zero point of the current IL, the recovery current flowing through the diode 17 can be reduced or eliminated, and the recovery loss can be reduced.

  Reference numeral 33 denotes a voltage detection circuit which detects a current flowing through the switching element 19 from the terminal voltage of the resistor 25 and inputs it to the microcomputer 9. The voltage of the winding 24 is also detected by the voltage detection circuit 32 and input to the microcomputer 9. Reference numeral 27 denotes a current detection circuit which detects an input current from a current transformer 34 connected between the reactor 13 and the rectifier circuit 12 and inputs the detected current to the microcomputer 9. Reference numerals 28 and 29 denote voltage detection circuits. The voltage detection circuit 28 inputs the input voltage after the rectifier circuit 12 to the microcomputer 9. The voltage detection circuit 29 supplies the output voltage after the diodes 17 and 21 to the microcomputer 9. input.

  The microcomputer 9 always takes the input voltage and output voltage from the voltage detection circuits 28 and 29 and determines the switching period of the switching element 19. That is, the driving circuit outputs a critical mode switching signal for turning off the switching element 19 so that the average value (1/2) of the peak value of the triangular wave of the repeated current IL (OFF point of the switching element 19) described above becomes a sine wave shape. To 31. As a result, the first filter function is achieved in which the harmonics are reduced to fall within the harmonic current regulation value and the power factor is improved, but the output is 1/2 of the above-described peak value. Suitable for use at high output voltage. Note that the switching frequency of the switching element 19 by the critical mode control is higher than that of the simple PAM control described later.

  On the other hand, reference numeral 26 denotes a drive circuit that switches the gate of the switching element 22. The drive circuit 26 is controlled by the microcomputer 9. The microcomputer 9 uses the drive circuit 26 to switch the switching element 22 only near the zero cross of the input voltage waveform. In the embodiment, the microcomputer 9 switches the switching element 22 at a predetermined duty ratio with a frequency outside the audible region of at least 15 kHz (frequency lower than the first filter function) as a cycle. Further, in this switching, the phase angle of the input voltage waveform is, for example, 0 ° to 35 ° (180 ° to 215 °), 35 ° to 70 ° (215 ° to 250 °), 150 ° to 180 ° (330 ° to 0 °). ) In the three ranges, and stops (OFF) in other ranges. Further, in the range of 0 ° to 35 ° (180 ° to 215 °) and 150 ° to 180 ° (330 ° to 0 °), the duty ratio for turning on the switching element 22 is set to 30%, for example, and 35 ° to 70 ° ( In the range of 215 ° to 250 °, it is set to 60%. Thus, the second filter function according to the present invention (simple PAM control similar to Patent Document 2) is achieved. As a result, while raising the voltage to some extent, the current waveform in the vicinity of the zero cross is smoothed, and the harmonics are reduced and the power factor is improved so as to be within the harmonic current regulation value. In particular, the loss in the switching element 22 in this case is significantly reduced as compared with the switching in which the PAM control is performed over the entire range of the input voltage waveform.

  Next, switching control between the first filter function and the second filter function by the microcomputer 9 will be described with reference to the flowchart of FIG. In the embodiment, the microcomputer 9 determines the output voltage according to the input (electric power). Therefore, in the control described later, the present invention will be described by a method of switching between the first filter function and the second filter function according to the input current value reflecting the output voltage required and changed in the inverter circuit 4.

  FIG. 2 shows a control flowchart of the microcomputer 9. When the microcomputer 9 is turned on in step S1 and the AC power supply 8 is applied to the compressor driving motor 3, the microcomputer 9 switches the switching elements of the inverter circuit 4 and starts the inverter operation of the motor 3 in step S2. .

  Next, in step S3, the microcomputer 9 turns off the simple PAM control (critical mode control is also turned off). This simple PAM control is the second filter function described above for switching the switching element 22 by the microcomputer 9 via the drive circuit 26. In step S3, the microcomputer 9 outputs a signal to the drive circuit 26, and turns off the application of the switching signal to the switching element 22. Thereby, at the time of starting with a light load, DC power that has not been boosted in the power supply device 1 is applied to the inverter circuit 4, and the motor 3 starts to rotate at the voltage before boosting.

  Next, in step S4, the microcomputer 9 determines whether or not the input current value (index reflecting the output voltage) input from the current detection circuit 27 is equal to or greater than a predetermined simple PAM control start current value ISPAM. When the simple PAM control start current value ISPAM is exceeded, the process proceeds to step S5, and the simple PAM control is turned on. That is, in step S5, the microcomputer 9 applies a switching signal to the switching element 22 by the drive circuit 26 to perform switching in the vicinity of the above-described zero crossing, thereby exhibiting a second filter function. During this time, the microcomputer 9 sends a command to the critical mode control circuit 23 so that the switching (ON) signal is not applied to the switching element 19. As a result, the switching element 19 remains OFF, and the power partially switched by the switching element 22 is applied to the inverter circuit 4.

  Next, in step S6, the microcomputer 9 determines whether or not the input current value has decreased to a predetermined simple PAM control end current value ISPAMOFF (a value lower than ISPAM), and the load on the motor 3 decreases to reduce the input current value. When it becomes lower than the simple PAM control end current value ISPAMOFF, the process returns to step S3 to turn off the simple PAM control.

  Here, assuming that the current value has not decreased to the simple PAM control end current value Istop, the microcomputer 9 proceeds from step S6 to step S7, and this time the input current value is higher than the predetermined critical mode control start current value ICPFC (ISPAM). ) Determine whether it has risen above. The critical mode control starting current value ICPFC is a point for switching between simple PAM control and critical mode control based on the degree of waveform improvement for suppressing the boosting and harmonics necessary in all operating states by the inverter circuit 4 that is known in advance. It is a preset input current value (corresponding to a predetermined output voltage value). If the input current value has not increased to ICPFC in step S7, the process returns to step S5 and is repeated thereafter.

  When the load of the motor 3 increases and a high output is required, and the input current value becomes equal to or greater than the critical mode control start current value ICPFC, the microcomputer 9 proceeds from step S7 to step S8 and turns on critical mode control. Turn off the simple PAM control. That is, the microcomputer 9 stops the application of the switching signal to the switching element 22 by the drive circuit 26 in step S8, and stops the second filter function. As a result, the switching element 22 remains off.

  On the other hand, the microcomputer 9 sends a command to the critical mode control circuit 23 to control the switching (ON) signal to be applied to the switching element 19 via the drive circuit 31. As a result, the electric power that is sufficiently boosted by the switching element 22 and is highly waveform-shaped is applied to the inverter circuit 4. The OFF signal of the switching element 22 is applied from the microcomputer 9 to the switching element 19 via the drive circuit 31 as described above. As a result, the first filter function based on the critical mode control described above is started instead of the second filter function.

  The waveform of the input voltage input from the voltage detection circuit 28 is monitored, and when the microcomputer 9 starts the critical mode control in step S8, the time when the input current becomes equal to or greater than the critical mode control start current value ICPFC. A command is issued to the critical mode control circuit 23 so that the switching of the switching element 19 is started at the timing when the input voltage becomes zero immediately. As a result, switching from the second filter function to the first filter function is performed at the zero point of the input voltage waveform, preventing overcurrent when switching from the second filter function to the first filter function. Thus, a smooth control switching operation can be realized.

  Thereafter, this is repeated, and after that, when the load of the motor 3 decreases and the input current value decreases to a predetermined critical mode control end current value ICPFCOFF (a value lower than ICPFC and higher than ISPAM), the microcomputer 9 performs steps S9 to S5. The process returns to the above-described simple PAM control (second filter function). Switching at this time is also performed at the nearest zero point of the input voltage waveform.

  Thus, the microcomputer 9 selectively switches between the first filter function and the second filter function. In this case, when the input current value is high, that is, when the output voltage value is required to be high, the first filter function is operated, and when the output voltage value is low, the second filter function is operated. In the range that can be covered by the second filter function is operated, the harmonics are suppressed and the voltage is boosted to some extent by efficient switching. If the output range is not supported by the second filter, the first filter The function can be operated to perform necessary boosting and harmonic suppression. As a result, the switching loss in the switching elements 19 and 22 and the recovery loss in the diode 17 can be suppressed while ensuring the boosting and harmonic suppression functions, and an efficient power supply can be realized.

  Next, FIG. 3 shows another embodiment of the present invention. In this figure, the same reference numerals as those in FIG. 1 indicate the same or similar functions. In this embodiment, since the first filter function (critical mode control) and the second filter function (simple PAM control) described above are performed by the same reactor 16, diode 17 and switching element 19, the reactor 20, diode 21 The switching element 22, the drive circuit 26, and the voltage detection circuits 32 and 33 are omitted.

  In this case, the microcomputer 9 controls the drive circuit 31 to switch the switching element 19 in the same manner as in the above embodiment, and performs the above-described simple PAM control to perform the second filter function. Further, the microcomputer 9 stops the simple PAM control by itself so that the switching (ON) signal from the critical mode control circuit 23 is applied to the switching element 19 through the drive circuit 31 and the switching element 19 is turned on. A switching signal for turning OFF is applied to the switching element 19 by the microcomputer 9 via the drive circuit 31. As a result, the above-described critical mode control is executed, and the first filter function is exhibited.

  Also in this embodiment, the switching function of the switching element 19 and the recovery loss of the diode 17 are suppressed and efficient while switching the second filter function and the first filter function to secure the boosting and harmonic suppression functions as described above. Power supply can be realized. In particular, in this case, there is a merit that the reactor 16, the switching element 19 and the diode 17 can be used for both simple PAM control and critical mode control.

  It should be noted that the numerical values and the like shown in the above embodiments are not limited thereto, and can be variously changed without departing from the spirit of the present invention. As described above, since the output voltage is determined by the input (electric power) in the embodiment, the first filter function and the second filter function are switched based on the input current value that changes depending on the output voltage that needs to be switched. However, depending on other control methods of the output voltage, the output voltage value detected by the voltage detection circuit 29 may be directly used for switching.

1 shows an electric circuit diagram of an electric motor drive device to which a power supply device of an embodiment of the present invention is applied (Embodiment 1). It is a flowchart explaining operation | movement of the microcomputer of FIG. (Example 2) which shows the electric circuit diagram of the electric motor drive device to which the power supply device of the other Example of this invention is applied.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Power supply device 2 Electric motor drive device 3 Electric motor 4 Inverter circuit 6 Rectification part 7 Smoothing part 8 AC power supply 9 Microcomputer 12 Rectification circuit 16, 20 Reactor 17, 21 Diode 19, 22 Switching element 23 Critical mode control circuit 24 Winding 26, 31 drive circuit 27 current detection circuit 28, 29, 32, 33 voltage detection circuit

Claims (3)

In a power supply device for converting AC power into DC power and supplying it to a load,
A first filter function that improves the waveform in a critical mode in which the switching element is switched by detecting the zero point of the current flowing through the reactor, and a second that improves the waveform by switching the switching element in a part of the input voltage waveform. A power supply apparatus that has both of the filter functions and selectively operates the first filter function and the second filter function based on an output voltage value.   2. The power supply device according to claim 1, wherein when the output voltage value is higher than a predetermined value, the first filter function is operated, and when the output voltage value is low, the second filter function is operated.   3. The power supply device according to claim 2, wherein when the output voltage value exceeds the predetermined value, the second filter function is switched to the first filter function at the nearest zero point of the input voltage waveform. .

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