JP2013150530A - Electric power conversion system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an electric power conversion system capable of stably lowering a noise level.SOLUTION: A PFC control circuit B includes a rectification element 5 and a switching element 7 connected in series, a rectification element 6, a switching element 8 and a PFC control section 9 connected in series. The PFC control section 9 varies switching frequencies of the switching element 7 and the switching element 8 on the basis of a detection value of input voltage detection means 2.

Description

  The present invention relates to a power conversion device having a function of suppressing noise caused by a switching element.

  A PFC (Power Factor Correction) circuit that suppresses harmonic current and improves a power factor, an inverter that converts direct current into alternating current, and the like include a switching element. These PFC circuits and inverters input a pulse signal to a switching element, and shape a voltage (current) waveform into a target waveform by the switching operation. A PWM (Pulse Width Modulation) signal is used as an input pulse signal.

  Along with the above switching operation, a harmonic component having the fundamental frequency of the pulse signal appears as a peak of the frequency noise level. There is a strong demand for PFC circuits and inverters that the frequency noise level satisfies a specified value defined in the EMI (Electro Magnetic Interference) standard.

  In order to satisfy this requirement, the spread spectrum method is used in the pulse control device disclosed in Patent Document 1. In the spread spectrum method, the fundamental frequency of the pulse signal is changed by a predetermined spread width Δf. By this change, the frequency noise level that is a harmonic component of the fundamental frequency can be dispersed and the peak can be lowered.

  In addition, in the spread spectrum method, as in the electric vehicle power converter disclosed in Patent Document 2, a plurality of basic frequency patterns are prepared in advance, and the fundamental frequency is varied by randomly referring to each frequency pattern. Has also been proposed.

JP 2008-5682 A JP 2010-130850 A

  However, in the conventional spread spectrum method, a specific frequency determination means and calculation method for reducing both the frequency noise level and maintaining the switching operation that is the original circuit operation by the switching operation. Has not yet been established.

  Patent Documents 1 and 2 disclose specific frequency determination means, but do not refer to the original circuit operation. In the method of Patent Document 2, although the changing fundamental frequency is in a fixed pattern, it is referred to at random, and there is a concern that the referenced fundamental frequency may be biased, which may weaken the spectrum spreading effect. Yes, it cannot be said that stable operation can be realized.

  Further, as a problem common to the methods of Patent Documents 1 and 2, the switching frequency is changed regardless of the original circuit operation, which may adversely affect the original circuit operation.

  The objective of this invention is providing the power converter device which can reduce a noise level stably.

The present invention includes a voltage input unit;
A voltage output section;
A power factor correction circuit that is connected between the voltage input unit and the voltage output unit and has a switching element and a switching control circuit that controls the switching element;
The switching control circuit is a power conversion device that controls a switching element by changing a switching frequency according to a reference voltage waveform.

In the present invention, the switching control circuit includes a frequency variation control unit for varying the frequency of the triangular wave carrier that determines the switching frequency,
The frequency variation control unit includes input voltage detection means for detecting an input voltage from the voltage input unit, and controls a variation in the frequency of a triangular wave carrier to be output according to the detected input voltage. .

  Further, according to the present invention, the frequency fluctuation control unit includes a triangular wave carrier output unit, and the triangular wave carrier output unit sets an inclination of the triangular wave carrier to be output according to an instantaneous value of the input voltage detected by the input voltage detection unit. By determining and changing the slope of the triangular wave carrier, the switching frequency is increased when the instantaneous value of the input voltage is high, and the switching frequency is controlled low when the instantaneous value of the input voltage is low. .

  According to the present invention, the power factor correction circuit is an active filter type power factor correction circuit.

  Further, the present invention is characterized in that the active filter type power factor correction circuit is a bridgeless PFC type circuit, an interleave type circuit, or a single phase active filter type circuit.

  According to the present invention, the switching frequency is controlled according to the reference voltage waveform, and the switching element is controlled. Therefore, the switching frequency can be periodically changed, and can be changed randomly as in the prior art. In this case, it is possible to prevent the frequency deviation which is a concern, and to realize a stable reduction in the frequency noise level.

  Further, according to the present invention, the input voltage from the voltage input unit is detected, and the fluctuation of the frequency of the triangular wave carrier that determines the switching frequency is controlled according to the detected input voltage. Thus, the switching frequency can be varied.

  Further, according to the present invention, the inclination of the triangular wave carrier to be output is determined according to the instantaneous value of the input voltage detected by the input voltage detecting means, the inclination of the triangular wave carrier is changed and output, and the instantaneous value of the input voltage is determined. When the input voltage is high, the switching frequency is increased, and when the instantaneous value of the input voltage is low, the switching frequency is controlled low.

  Thereby, since the switching frequency fluctuates in accordance with the change rate of the input current changed by the switching operation, the fluctuation of the switching frequency does not affect the input current shaping operation which is the original circuit operation of the PFC control circuit, The frequency noise level can be reduced while maintaining a high power factor correction operation.

  Further, according to the present invention, an active filter type power factor correction circuit can be used as the power factor correction circuit, and the active filter type power factor correction circuit is a bridgeless type circuit, an interleave type circuit, or a single-phase active type. A filter type circuit is preferable.

1 is a circuit diagram showing a configuration of a bridgeless PFC circuit 100 according to an embodiment of the present invention. 3 is a block diagram showing a configuration of a PFC control unit 9. FIG. 3 is a circuit diagram showing a configuration of a triangular wave output unit 10. FIG. It is a schematic diagram which shows operation | movement of the triangular wave output part 10 when the output of the integrating | accumulating block 19 is a1. It is a schematic diagram which shows the operation result by control of this invention. It is a simulation result about the bridgeless type PFC circuit 100 shown in FIG. 1, and is a figure which shows the noise level at the time of switching with the case where the control system of this invention is applied, and a single frequency. It is the figure which showed the simulation result of FIG. 6 by the decibel notation. It is a simulation result about the bridgeless type PFC circuit 100 shown in FIG. 1, and is a figure which shows the noise level at the time of applying the control system of the present invention and applying the random diffusion system. It is a figure which shows an input current waveform by the simulation result shown in FIG. It is a circuit diagram which shows the structure of the single phase active filter type PFC circuit 101 which is other embodiment of this invention. FIG. 11 is a diagram showing the noise level when the control method of the present invention is applied and when the random diffusion method is applied, based on the simulation results for the single-phase active filter type PFC circuit 101 shown in FIG. 10. It is a figure which shows an input current waveform by the simulation result shown in FIG. It is a circuit diagram which shows the structure of the interleave type PFC circuit 102 which is further another embodiment of this invention.

  Hereinafter, preferred embodiments of a pulse control device according to the present invention will be described with reference to the accompanying drawings.

  The present invention achieves both a reduction in frequency noise level and a power factor correction operation by varying the switching frequency according to the reference input voltage waveform.

  FIG. 1 is a circuit diagram showing a configuration of a bridgeless PFC circuit 100 according to an embodiment of the present invention. The bridgeless PFC circuit 100 includes a voltage input unit A, a PFC control circuit B, and a voltage output unit C.

The voltage input unit A includes an AC power source 1 that is an input power source, an input voltage detection unit 2 and an input current detection unit 3.
The voltage output unit C includes an output load 12 and output voltage detection means 13.

  The PFC control circuit B includes a reactor 4 that contributes to shaping the current waveform of the AC power supply 1 and boosting the DC voltage, a rectifying element 5 and a switching element 7 connected in series, a rectifying element 6 and a switching element 8 connected in series, and two sets of these Rectifier 30 having upper and lower arms connected in parallel, smoothing capacitor 11 connected to the output of rectifier 30, detection value of input voltage detection means 2, detection value of input current detection means 3, and detection value of output voltage detection means 13 Based on the PFC control unit 9 that controls the switching operation of the switching element 7 and the switching element 8, and the PFC control unit 9 outputs a triangular wave carrier that is a command signal of a control signal for switching the switching element 7 and the switching element 8 on and off The triangular wave output unit 10 is provided.

Next, the power factor improving operation of the bridgeless PFC circuit 100 will be described.
In the capacitor input type rectifier circuit as shown in FIG. 1, the input current does not flow unless the AC voltage of the AC power supply 1 is larger than the voltage stored in the smoothing capacitor 11. Since the input current flows even at other times, the AC power supply 1 is short-circuited via the reactor 4, the switching element 7, and the switching element 8 by turning on the switching element 7 and the switching element 8. . This short circuit allows an input current to flow. At this time, the PFC control unit 9 turns on the switching element 7 and the switching element 8 when the input current is small with respect to the input voltage so that the input current waveform is similar to the input voltage waveform. When the input current is larger than the input voltage, the switching element 7 and the switching element 8 are turned off. Further, when the switching element 7 and the switching element 8 are in the on state, energy is accumulated in the reactor 4, and in the off state, the energy is released to the output load 12, so that the output DC voltage is boosted. .

  FIG. 2 is a block diagram illustrating a configuration of the PFC control unit 9. The PFC control unit 9 includes a comparison circuit 14 and a pulse signal output unit 15.

  The PFC control unit 9 compares the detection results output from the input voltage detection unit 2 and the input current detection unit 3 with the comparison circuit 14 and outputs a pulse signal so that the input current waveform is similar to the input voltage waveform. The output unit 15 is controlled.

  The pulse signal output unit 15 outputs the pulse signal to the switching element 7 and the switching element 8 including the control for bringing the output voltage from the output voltage detection means 13 close to the target voltage value. The triangular wave carrier signal 16 is a signal that determines the fundamental frequency of the pulse signal output from the pulse signal output unit 15. In general, when a triangular wave having a fixed frequency is used, there is a problem that a harmonic component is superimposed and a noise level peak becomes large.

  In the present invention, the frequency of the triangular wave carrier is not fixed, but is varied according to the input voltage, so that the peak of the noise level can be suppressed without impairing the power factor correction operation. The principle will be described below.

FIG. 3 is a circuit diagram showing a configuration of the triangular wave output unit 10.
When the input voltage detection value fV from the input voltage detection means 2 is a negative value, the absolute value block 17 converts the value into a positive value and generates a pulsating flow. The value of this pulsating flow includes 0, and when 0 is input to the integration block 19 at the subsequent stage, the output also becomes 0, and the triangular wave is not output. In order to prevent this, the addition block 18 adds a constant A to the value of the pulsating flow. This constant A can be arbitrarily determined, and may be determined in consideration of setting values in other control blocks. The integration block 19 multiplies the output (fV + A) of the addition block 18 by a constant B. The output a of the integration block 19 is assumed to be a triangular wave slope. This output a is expressed by the following equation (1).

  Since the input voltage detection value fV detected by the input voltage detection means 2 changes according to the input voltage, the output a also changes according to fV. At this time, the constant A and the constant B determine the output a which is a reference value of the inclination of the triangular wave. Therefore, the constants A and B may be determined according to the inclination of the triangular wave to be output. In this embodiment, for example, A = 4 and B = 0.08.

  FIG. 4 is a schematic diagram illustrating the operation of the triangular wave output unit 10 when the output of the integration block 19 is a1. FIG. 4 shows the operation after the integration block 19.

  The integration block 20 outputs a function a1 (t) from the inclination a1 of the triangular wave output from the integration block 19 ((1) in FIG. 4) ((2) in FIG. 4).

  The slope switching detection block 21 detects that the value of the function a1 (t) output from the integration block 20 is 10 or more and 0 or less. The slope switching output block 22 outputs an output signal indicating a value 0 when the value becomes 10 or more, and outputs an output signal indicating a value 1 when the value becomes 0 or less. The signal conversion block 23 receives the output signal output from the slope switching output block 22 and subtracts 0.5 from the signal. When the input output signal indicates 0, -0.5 is output to the integration block 19, and when the input output signal indicates 1, 0.5 is output and the sign of the slope is determined. To do. By this feedback operation, the integration block 20 outputs a1 (t) and -a1 (t) to generate a triangular wave carrier signal ((3) in FIG. 4).

  As a result, when the input voltage is low, the slope of the triangular wave carrier is gently changed (low frequency), and when the input voltage is high, the slope of the triangular wave carrier is changed suddenly (high frequency). As a result, the switching frequency is varied.

  In the operation of the PFC circuit in which a current is supplied by short-circuiting the power supply, the amount of current flowing during the switching operation and the amount of current change required for power factor improvement differ depending on the waveform of the input voltage.

  FIG. 5 is a schematic diagram showing an operation result by the control of the present invention. In a region where the input voltage is small, the current change amount di / dt that flows when the power supply is short-circuited is small, but a large current change is required. According to the control of the present invention, the switching frequency is lowered in this region. That is, although the current change amount di / dt is small, the short-circuit state of the power source continues for a long time when the switching frequency is lowered, so that the total current change amount can be increased. In the region where the input voltage is high, the current change amount di / dt that flows when the power supply is short-circuited is large, but a large current change is not required. According to the control of the present invention, the current change amount di / dt is large in this region, but since the short circuit state of the power supply is short due to the high switching frequency, the total current change amount can be kept low.

  As described above, according to the control of the present invention, the switching frequency is controlled so as to meet the requirements of the PFC circuit operation, and this operation reduces the frequency noise level without impairing the power factor improvement effect. be able to.

  FIG. 6 is a diagram showing simulation results for the bridgeless PFC circuit 100 shown in FIG. FIG. 6 (1) shows the result when the switching frequency is fixed, and FIG. 6 (2) shows the result of the present invention. The horizontal axis indicates the frequency (kHz), and the vertical axis indicates the noise level (−).

  At the noise level when the frequency is fixed, a prominent peak appears for the fundamental frequency due to the switching frequency and its harmonics. In the noise level when the present invention is applied to this result, the peak has a width and the peak height can be suppressed.

  FIG. 7 is a diagram showing the simulation result of FIG. 6 in decibel notation. FIG. 7 (1) shows the result when the frequency is fixed, and FIG. 7 (2) shows the result of the present invention. The horizontal axis represents frequency (kHz), and the vertical axis represents noise level (dB).

  Comparing the result of the present invention with the result when the frequency is fixed, the noise can be suppressed by about 6 dB in the low frequency region of the noise terminal voltage standard range and about 3 dB in the high frequency region.

  FIG. 8 is a diagram showing simulation results for the bridgeless PFC circuit 100 shown in FIG. FIG. 8 (1) shows the noise level of the simulation result by the conventional random diffusion method in which the switching frequency is randomly changed, and FIG. 8 (2) shows the noise level of the simulation result by the control method of the present invention. Since the range in which the switching frequency is spread is common to both systems, it can be said that the noise suppression effect is equivalent.

  FIG. 9 is a diagram showing an input current waveform in the simulation result shown in FIG. FIG. 9 (1) shows the input current waveform of the simulation result by the random diffusion method, and FIG. 9 (2) shows the input current waveform of the simulation result by the control method of the present invention.

  Although the current waveform is greatly disturbed in the control result by the random diffusion method, the current waveform is not disturbed in the control result of the present invention. Comparing both formulas in terms of power factor for the current waveform obtained as described above, it is 96.81% in the random diffusion method, whereas it is 98.01% in the present invention. 2% improvement. In other words, in the prior art, the power factor improvement effect, which is the original circuit operation, has been reduced to suppress noise, but in the present invention, noise can be suppressed while keeping the power factor improvement effect high. Yes.

  FIG. 10 is a circuit diagram showing a configuration of a single-phase active filter type PFC circuit 101 according to another embodiment of the present invention. The single-phase active filter type PFC circuit 101 has a configuration similar to that of the bridgeless type PFC circuit 100, and portions that perform the same operation are denoted by the same reference numerals and detailed description thereof is omitted. The single-phase active filter type PFC circuit 101 includes a voltage input unit A, a PFC control circuit B, and a voltage output unit C. The voltage input unit A and the voltage output unit C are common to the bridgeless type PFC circuit. In the PFC control circuit B, the diode bridge 31 is connected to the front stage or the rear stage of the reactor 4, but the reactor 4, the rectifying element 5, the switching element 7, and the smoothing capacitor 11 are bridgeless PFC. It operates in the same manner as the circuit 100. That is, the bridgeless PFC circuit 100 and the single-phase active filter PFC circuit 101 have the same basic circuit configuration and the same basic operation as PFC control.

  FIG. 11 is a diagram showing simulation results for the single-phase active filter type PFC circuit 101 shown in FIG. FIG. 11 (1) shows the noise level of the simulation result by the conventional random diffusion method, and FIG. 11 (2) shows the noise level of the simulation result by the control method of the present invention. FIG. 12 is a diagram showing an input current waveform in the simulation result shown in FIG. FIG. 12 (1) shows the input current waveform of the simulation result by the conventional random diffusion method, and FIG. 12 (2) shows the input current waveform of the simulation result by the control method of the present invention. Similar to the result of the bridgeless type PFC circuit 100, the noise suppression effect is the same in both systems, but in the control result of the random diffusion method, the current waveform is greatly disturbed. Comparing both formulas in terms of power factor for the current waveform obtained as described above, it is 95.22% in the random diffusion method and 97.12% in the present invention. 9% improvement. That is, according to the present invention, in the single-phase active filter type PFC circuit 101 as well as the bridgeless type PFC circuit 100, noise can be suppressed while keeping the power factor improvement effect high.

  FIG. 13 is a circuit diagram showing a configuration of an interleaved PFC circuit 102 which is still another embodiment of the present invention. Similar to the single-phase active filter type PFC circuit 101 described above, the basic configuration and basic operation of this circuit are almost the same as those of the bridgeless type PFC circuit 100. According to the present invention, the bridgeless type PFC circuit 100 and the single-phase active filter are provided. Similar to the type PFC circuit 101, it is possible to suppress noise while keeping the power factor improvement effect high.

  As described above, the present invention is a technique for shaping the input AC current so as to approximate the input AC voltage waveform. Regardless of the above embodiments, the reference voltage is the AC voltage, and the object of switching control is also the AC voltage. It can be applied to a switching power supply. That is, an input current waveform whose amplitude changes in the time axis t direction is i (t), an input voltage waveform whose voltage amplitude changes in the time axis direction is v (t), and i (t) and v (t) If the phase shift of α is α, the proportionality coefficient is a and b, and the current waveform after molding is I (t), the current waveform represented by i (t) = a × v (t + a) The present invention can be applied to a switching power supply that is formed into I (t) = b × v (t). In this case, the proportionality coefficient can be applied regardless of whether the relationship between a and b is a = b or a ≠ b.

DESCRIPTION OF SYMBOLS 1 AC power supply 2 Input voltage detection means 3 Input current detection means 4 Reactor 5 Rectification element 6 Rectification element 7 Switching element 8 Switching element 9 PFC control part 10 Triangular wave output part 11 Smoothing capacitor 12 Output load 13 Output voltage detection means 14 Comparison circuit 15 Pulse signal output unit 16 Triangular wave carrier signal 17 Absolute value block 18 Addition block 19 Integration block 20 Integration block 21 Switching detection block 22 Switching output block 23 Signal conversion block 30 Rectifier 31 Diode bridge 32 Reactor 100 Bridgeless type PFC circuit 101 Single phase Active filter type PFC circuit 102 Interleave type PFC circuit A Voltage input part B PFC control circuit C Voltage output part

Claims (5)

A voltage input section;
A voltage output section;
A power factor correction circuit that is connected between the voltage input unit and the voltage output unit and has a switching element and a switching control circuit that controls the switching element;
The switching control circuit controls the switching element by changing a switching frequency according to a reference voltage waveform. The switching control circuit includes a frequency variation control unit for varying the frequency of a triangular wave carrier that determines the switching frequency,
The frequency variation control unit includes input voltage detection means for detecting an input voltage from the voltage input unit, and controls a variation in the frequency of a triangular wave carrier to be output according to the detected input voltage. The power conversion device according to claim 1.   The frequency variation control unit includes a triangular wave carrier output unit, and the triangular wave carrier output unit determines a slope of the triangular wave carrier to be output according to an instantaneous value of the input voltage detected by the input voltage detecting unit, and the triangular wave carrier The switching frequency is controlled to be high when the instantaneous value of the input voltage is high, and when the instantaneous value of the input voltage is low, the switching frequency is controlled to be low. Power conversion device.   The power conversion device according to claim 1, wherein the power factor correction circuit is an active filter type power factor correction circuit.   The power conversion device according to claim 4, wherein the active filter type power factor correction circuit is a bridgeless PFC method, an interleave method, or a single-phase active filter method.

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