WO2019003423A1

WO2019003423A1 - Power conversion device, lighting apparatus and electric device

Info

Publication number: WO2019003423A1
Application number: PCT/JP2017/024173
Authority: WO
Inventors: 岳秋飯田; 雄一郎伊藤
Original assignee: 三菱電機株式会社; 三菱電機照明株式会社
Priority date: 2017-06-30
Filing date: 2017-06-30
Publication date: 2019-01-03
Also published as: CN110785919A; JP6825704B2; JPWO2019003423A1; CN110785919B

Abstract

The present invention is provided with: a rectifier circuit for rectifying AC power; a power factor improvement circuit having a switching element and an inverter, and into which the output of the rectifier circuit is input, and from which a DC voltage is output; a detection winding for detecting a voltage generated by the inverter; and a control unit into which the voltage detected by the detection winding is input, and which drives the switching element. The control unit executes a first control to change a switching frequency of the switching element when operation of the power factor improvement circuit is started, after which, if a second control for switching the switching element in a manner that is synchronized with the voltage obtained by the detection winding is to be executed, an amount of change in the switching frequency when transitioning from the first control to the second control is made smaller than a difference value between the switching frequency when the first control is initiated and the switching frequency when the second control is initiated.

Description

Power converter, lighting equipment, electric equipment

The present invention relates to a power conversion device, a lighting fixture, and an electrical device.

In a luminaire using an LED (Light Emitting Diode) as a light source, regulations regarding harmonics of input current are defined. For example, in Japan, a limit value is set for harmonics of input current according to Japanese Industrial Standards. Therefore, the luminaire includes a PFC (Power Factor Correction) circuit for suppressing harmonics of the input current and improving the power factor. In general, a current critical mode is used as a control method of a PFC circuit in a luminaire.

Patent Documents

1 and 2 describe the contents of power factor improvement control in the current critical mode. Dedicated control ICs for realizing control in the current critical mode are on the market.

Japanese Patent Laid-Open No. 10-294191 Japanese Patent Laid-Open Publication No. 2015-213044

In control in the current critical mode, it is necessary to detect that the current of the inductor used in the power factor correction circuit has become zero. As a zero current detection means for detecting that the inductor current has become zero, for example, a secondary winding provided in the inductor is used. However, immediately after the start of operation of the power factor correction circuit, the output voltage of the secondary winding is small, and zero current can not be accurately detected.

Therefore, it is conceivable to use a dedicated control IC having a protective function that repeats the switching operation at a constant cycle when the output voltage of the secondary winding can not be detected. For example,

Patent Documents

1 and 2 describe means for switching control of the switching element at a predetermined fixed frequency immediately after the power factor correction circuit starts to operate, and thereafter changing to a current critical mode.

However, in the control described above, when changing the control from the fixed frequency to the current critical mode, the switching frequency of the switching element suddenly changes, and the output voltage of the power factor correction circuit largely fluctuates. For example, in the case of controlling a light source such as an LED, when the output voltage of the power factor correction circuit largely fluctuates, the current supplied to the light source fluctuates and flickering of the light source occurs.

In order to avoid such an adverse effect, if it is attempted to obtain a larger output by increasing the number of turns of the secondary winding, the loss generated in the secondary winding increases, the inductor becomes larger, and the zero current Losses in the circuit to be detected will increase.

The present invention has been made to solve the above-mentioned problems, and it is an object of the present invention to provide a power conversion device, a lighting apparatus and an electric apparatus capable of reducing the amount of change in switching frequency of switching elements of a power factor correction circuit. To aim.

A power converter according to the invention of the present application includes a rectifier circuit that rectifies AC power, a switching element and an inductor, a power factor improvement circuit that receives an output of the rectifier circuit and outputs a DC voltage, and the inductor And a control unit for receiving the voltage detected by the detection winding and driving the switching element, the control unit performing the operation of the power factor improvement circuit The first control is performed to change the switching frequency of the switching element when it is started, and then the second control is performed to switch the switching element in synchronization with the voltage obtained by the detection winding. The amount of change in the switching frequency when shifting from the first control to the second control, the switching frequency at the start of the first control, and the switching frequency at the start of the second control Characterized by less than the difference value between.

A lighting apparatus according to the present invention includes a rectifier circuit that rectifies AC power, a switching element and an inductor, a power factor improvement circuit that receives an output of the rectifier circuit and outputs a DC voltage, and the inductor The control unit includes a detection winding that detects a voltage to be generated, and a control unit that receives the voltage detected by the detection winding and drives the switching element. The control unit starts operation of the power factor correction circuit. When the first control to change the switching frequency of the switching element is performed, and then the second control to switch the switching element in synchronization with the voltage obtained by the detection winding is performed. The switching frequency at the time of shifting from 1 control to the second control, the switching frequency at the start of the first control, and the switching frequency at the start of the second control; Comprising a power conversion apparatus characterized by smaller than the difference value, and the light source is an LED (Light Emitting Diode) or an organic EL (Electro Luminescence) connected to the output of the power conversion device.

An electric device according to the invention of the present application includes a rectifier circuit that rectifies AC power, a switching element and an inductor, an output of the rectifier circuit is input, and a power factor improvement circuit that outputs a DC voltage; The control unit includes a detection winding that detects a voltage to be generated, and a control unit that receives the voltage detected by the detection winding and drives the switching element. The control unit starts operation of the power factor correction circuit. When the first control to change the switching frequency of the switching element is performed, and then the second control to switch the switching element in synchronization with the voltage obtained by the detection winding is performed. The switching frequency at the time of shifting from 1 control to the second control, the switching frequency at the start of the first control, and the switching frequency at the start of the second control; Comprising a power conversion apparatus characterized by smaller than the difference value, the load and connected to the output of the power conversion device.

Other features of the present invention will be clarified below.

According to the present invention, immediately after the power factor correction circuit starts to operate, the switching element can be used without using the zero current detection unit for detecting that the inductor current of the power factor correction circuit has become zero. Since the switching frequency is changed and then the switching element is controlled in synchronization with the signal obtained by the zero current detection unit, it is possible to prevent the switching frequency of the switching element from changing suddenly.

FIG. 1 is a circuit diagram of a luminaire according to a first embodiment. It is a circuit diagram of a zero current detection unit. It is a circuit diagram of a current control circuit. It is a wave form diagram which shows the example of control of a current control circuit. It is a wave form diagram which shows operation of a power factor improvement circuit. It is a wave form diagram of current discontinuous mode. It is various waveform diagrams after the pressure | voltage rise operation start by a power factor improvement circuit. It is a wave form diagram showing another control pattern of switching frequency. 5 is a flowchart showing an operation of the lighting apparatus according to Embodiment 1. It is a hardware block diagram of a control part. It is a software block diagram of a control part. It is a wave form diagram of current continuation mode. It is a wave form diagram in the case where current continuous mode is included in the period of the 1st control. FIG. 7 is a waveform chart showing control according to Embodiment 2. It is a wave form diagram showing another control pattern of switching frequency. 7 is a flowchart showing an operation of the lighting apparatus according to Embodiment 2. FIG. 7 is a circuit diagram of a lighting apparatus according to Embodiment 3. It is a wave form diagram showing the vibration of Vpfc.

A power conversion device, a lighting fixture, and an electric device according to an embodiment of the present invention will be described with reference to the drawings. The same or corresponding components may be assigned the same reference numerals and repetition of the description may be omitted. Note that the present invention is not limited by the description of the embodiment.

Embodiment 1
FIG. 1 is a circuit diagram of the lighting fixture 100 according to the first embodiment. The lighting apparatus 100 includes a rectifying circuit 3, a power factor improvement circuit 5 that suppresses harmonics of the current input from the AC power supply 1 to improve the power factor, and a smoothing capacitor 6 that smoothes the output voltage of the power factor improvement circuit 5. And have.

The configuration of the lighting fixture 100 will be described in detail. An input filter 2 is provided between the AC power supply 1 and the rectifier circuit 3. The input filter 2 has a function of reducing high frequency noise superimposed on the current input from the AC power supply 1. The input filter 2 has a coil 21 and a capacitor 22. A series circuit having a coil 21 and a capacitor 22 is connected in parallel to the AC power supply 1. One end of the coil 21 is connected to one end of the AC power supply 1, and the other end of the coil 21 is connected to one end of the capacitor 22 and the rectifier circuit 3. The other end of the capacitor 22 is connected to the AC power supply 1 and the rectifier circuit 3.

The rectifier circuit 3 has a function of converting AC power supplied from the AC power supply 1 into DC power. That is, the rectifier circuit 3 is a circuit that rectifies AC power. The rectifier circuit 3 is disposed between the input filter 2 and the power factor correction circuit 5. The rectifier circuit 3 is composed of a diode bridge in which four diodes are combined. The configuration of the rectifier circuit 3 is not limited to this, and may be configured by combining MOSFETs (Metal Oxide Semiconductor-Field Effect Transistors) which are unidirectional conduction elements.

The capacitor 4 is connected in parallel to the output of the rectifier circuit 3. One end of the capacitor 4 is connected to the positive electrode side of the DC bus, and the other end of the capacitor 4 is connected to the negative electrode side of the DC bus. The capacitor 4 has a function of smoothing the output voltage of the rectifier circuit 3.

The power factor correction circuit 5 is disposed between the rectifier circuit 3 and the current control circuit 7. The power factor correction circuit 5 is a circuit that receives the output of the rectifier circuit 3 and outputs a DC voltage. The power factor correction circuit 5 includes a switching element 51, an inductor 52, and a diode 53. The switching element 51 is, for example, a MOSFET. The switching element 51 switches the path of the current output from the rectifier circuit 3.

The inductor 52 has a primary winding 52a and a secondary winding 52b wound around the same core. A voltage having a different polarity is applied to the primary winding 52a as the switching element 51 is turned on and off. A voltage corresponding to the voltage applied to the primary winding 52a and the turns ratio n is output to the secondary winding 52b. The secondary winding 52 b functions as a detection winding for detecting the voltage generated by the inductor 52.

The power factor correction circuit 5 boosts the output voltage of the rectifier circuit 3 and outputs it to the smoothing capacitor 6 when the switching element 51 is turned on and off. It also has a function to suppress harmonics of the input current and improve the power factor.

FIG. 1 shows an example in which the power factor correction circuit 5 is configured by a step-up chopper circuit. The drain of the switching element 51 is connected to the inductor 52 and the diode 53 on the positive electrode side of the DC bus. The source of the switching element 51 is connected to the capacitor 4 and the smoothing capacitor 6 on the negative electrode side of the DC bus. The gate of the switching element 51 is connected to the control unit 9. The control signal output from the control unit 9 is input to the gate of the switching element 51, and the on / off of the switching element 51 is controlled. Therefore, the power factor correction circuit 5 is controlled by the controller 9.

The inductor 52 is disposed between the capacitor 4 and the switching element 51 on the positive electrode side of the DC bus. One end of the inductor 52 is connected to one end of the capacitor 4, and the other end of the inductor 52 is connected to the switching element 51 and the diode 53. The diode 53 is disposed between the switching element 51 and the smoothing capacitor 6 on the positive electrode side of the DC bus. The anode of the diode 53 is connected to the inductor 52 and the switching element 51, and the cathode of the diode 53 is connected to the smoothing capacitor 6.

The power factor correction circuit 5 can be configured by circuits such as a buck-boost chopper circuit, a fly-back circuit, a fly-forward circuit, a SEPIC, a Zeta converter, a Cuk converter, as well as a boost chopper circuit.

The smoothing capacitor 6 is disposed between the power factor correction circuit 5 and the current control circuit 7 in the DC bus. One end of the smoothing capacitor 6 is connected to the positive electrode side of the DC bus, and the other end of the smoothing capacitor 6 is connected to the negative electrode side of the DC bus. A current control circuit 7 is connected to the smoothing capacitor 6. The current control circuit 7 is a circuit that controls the magnitude of the current output to the LED 8.

The control unit 9 is connected to the switching element 51. The control unit 9 receives the voltage detected by the secondary winding 52b which is a detection winding, and drives the switching element 51. The control unit 9 includes a switching control unit 91, an input voltage detection unit 92, a zero current detection unit 93, an output voltage detection unit 94, and a drive unit 95.

The switching control unit 91 is provided with detection results of the input voltage detection unit 92, the zero current detection unit 93, and the output voltage detection unit 94. Switching control unit 91 is an output in which output voltage Vpfc of power factor correction circuit 5 is stored in advance in switching control unit 91 based on the detection results of input voltage detection unit 92, zero current detection unit 93 and output voltage detection unit 94. A control signal for on / off controlling the switching element 51 is output so as to match the voltage target value. It is shown in FIG. 1 that the value of Vpfc is equal to the voltage on the high side of the smoothing capacitor 6.

The input voltage detection unit 92 is a means for detecting the voltage of the capacitor 4. The voltage of the capacitor 4 is equal to the input voltage of the power factor correction circuit 5. Thus, the input voltage detection unit 92 detects the input voltage of the power factor correction circuit 5. The input voltage detection unit 92 transmits a signal related to the detection result to the switching control unit 91.

The output voltage detection unit 94 is a means for detecting the voltage of the smoothing capacitor 6. The voltage of the smoothing capacitor 6 is equal to the output voltage of the power factor correction circuit 5. Thus, the output voltage detection unit 94 detects the output voltage of the power factor correction circuit 5. The output voltage detection unit 94 transmits a signal related to the detection result to the switching control unit 91.

The input voltage detection unit 92 and the output voltage detection unit 94 can be, for example, a voltage dividing circuit that divides a voltage to be detected into a voltage of a size that can be input to the switching control unit 91 by two resistors connected in series. .

The zero current detection unit 93 is means for detecting that the current of the primary winding 52a of the inductor 52 has become zero. The zero current detection unit 93 transmits a signal related to the detection result to the switching control unit 91.

FIG. 2 is a circuit diagram showing a configuration example of the zero current detection unit 93. As shown in FIG. The zero current detection unit 93 includes a Zener diode 932 for voltage limitation and a resistor 931 for current limitation in order to limit the voltage of the secondary winding 52 b to a size that can be input to the switching control unit 91. .

It returns to the explanation of FIG. The switching control unit 91 includes a storage unit that stores the output voltage target value of the power factor correction circuit 5. The switching control unit 91 generates a signal for on / off control of the switching element 51 so that both match based on the voltage detection result of the smoothing capacitor 6 received from the output voltage detection unit 94 and the output voltage target value described above. Output.

The signal output from the switching control unit 91 is converted into a voltage with a magnitude that can turn on and off the switching element 51 in the driving unit 95, and is output to the gate of the switching element 51.

The current control circuit 7 has a function of converting the DC voltage output from the power factor correction circuit 5 into a DC current that can be input to the LED 8. FIG. 3 is a circuit diagram showing a configuration example of the current control circuit 7. FIG. 3 shows a current control circuit 7 configured by a step-down chopper circuit.

The current control circuit 7 includes a MOSFET 71, an inductor 72, a diode 73 and a capacitor 74. The MOSFET 71 is disposed on the positive electrode side of the DC bus. The drain of the MOSFET 71 is connected to the diode 53 and the smoothing capacitor 6. The source of the MOSFET 71 is connected to the diode 73 and the inductor 72. By connecting the gate of the MOSFET 71 to the control unit 9, it is preferable to input an on / off control signal from the control unit 9 to the gate of the MOSFET 71. The cathode of the diode 73 is connected to the MOSFET 71 and the inductor 72. The anode of the diode 73 is connected to the smoothing capacitor 6 and the capacitor 74.

The current control circuit 7 can be configured by a buck-boost chopper circuit, a buck-boost chopper circuit, a flyback circuit, a flyforward circuit, a SEPIC, a Zeta converter, a Cuk converter or the like.

FIG. 4 is a waveform diagram showing a control example of the current control circuit 7. FIG. 4 shows the waveforms of the current I8 flowing to the LED 8, the current I72 flowing to the inductor 72, and the control signal Cs to the MOSFET 71. When an ON signal is input to the gate of the MOSFET 71, a current path is formed through the smoothing capacitor 6, the MOSFET 71, the inductor 72, and the capacitor 74, and the current of the inductor 72 is increased.

When an off signal is input to the gate of the MOSFET 71, a current path is formed through the inductor 72, the capacitor 74, and the diode 73, and the current of the inductor 72 decreases to zero. When the predetermined switching period Tsw has elapsed, the on signal is input to the MOSFET 71 again to restart the switching operation.

As shown in FIG. 4, the current I72 flowing through the inductor 72 has a triangular waveform. Then, the current output to the LED 8 is smoothed by the capacitor 74. Therefore, the current control circuit 7 outputs the average value of the current of the inductor 72.

When controlling the current of the LED 8 to dim the LED 8, the switching period Tsw for turning on the MOSFET 71 is fixed, and the on time Ton is changed. That is, the on-time Ton is adjusted in accordance with the target value of the output current. The ratio of the on time Ton to the switching period Tsw is called a duty. Such a control method of obtaining a desired output by adjusting the on-time Ton is called duty control.

The LED 8 is configured by an LED group in which a plurality of LEDs are connected in series and in parallel. One end of the LED group is connected to the positive electrode side of the DC bus, and the other end of the LED group is connected to the negative electrode side of the DC bus.

FIG. 5 is a waveform diagram for explaining an operation example of the power factor correction circuit 5 shown in FIG. The waveforms of the current I52 of the inductor 52, the zero current detection signal Sz output from the zero current detection unit 93, the drain voltage Vd of the switching element 51, and the gate voltage Vg of the switching element 51 are shown in FIG. There is. However, for the sake of explanation, the cycle in which the gate voltage of the switching element 51 is turned on and off is described longer than in actuality.

When the switching element 51 is turned on by a signal from the control unit 9, a closed circuit is formed by the AC power supply 1, the rectifier circuit 3, the inductor 52, and the switching element 51, and the AC power supply 1 is shorted through the inductor 52. . Therefore, the power supply current flows through the closed circuit, the current of the inductor 52 increases, and energy is stored in the inductor 52.

When the on-time set by the switching control unit 91 elapses, the switching element 51 is turned off. As a result, a closed circuit is formed by the inductor 52, the diode 53, and the smoothing capacitor 6, the current of the inductor 52 decreases, and the energy stored in the inductor 52 is released and the smoothing capacitor 6 is charged.

When the current of the inductor 52 decreases, the voltage of the secondary winding 52b also decreases. The zero current detection unit 93 connected to the secondary winding 52b detects that the current of the inductor 52 has become zero when the voltage of the secondary winding 52b becomes smaller than a predetermined value, and relates to the detection result. A signal is transmitted to the switching control unit 91. The switching control unit 91 turns on the switching element 51 again after a predetermined delay time has elapsed since the current of the inductor 52 has become zero. As a method of providing this delay time, the switching element 51 can be turned on near the bottom of the voltage oscillation in a period in which the drain voltage of the switching element 51 is freely oscillating. As a result, it is possible to suppress a sharp change in drain voltage and to suppress noise caused by switching. That is, after the voltage of the secondary winding 52b becomes 0, the switching element 51 is turned on after the fall of the first oscillation of the drain voltage is observed. This operation is called current critical mode.

Due to the on / off operation of the series of switching elements 51, the waveform of the current flowing through the inductor 52 becomes triangular. The apex of the triangular wave shape is an envelope of a sine wave as shown by a dotted line. At this time, the current input from the AC power supply 1 is smoothed by the input filter 2, the average value of the inductor current is input, and the current waveform becomes a sinusoidal current waveform and the power factor is improved.

The switching control unit 91 receives information of Vpfc which is the output voltage of the power factor correction circuit 5 from the output voltage detecting unit 94, and feedback controls the on time of the switching element 51 so as to realize the target Vpfc.

When feedback control is performed, if the on-time changes significantly, the envelope of the peak of the current I52 flowing through the inductor 52 does not become sinusoidal, and the input current can not be sinusoidal. Therefore, the response time of the feedback control is set so that the loop gain of the feedback control is equal to or less than one time (0 dB) in one half or more of one cycle of the AC power supply 1. In other words, the frequency is set to be less than or equal to one time (0 dB) at a frequency equal to or less than twice the frequency of the AC power supply 1. For example, when the power supply frequency is 50 Hz, constant current feedback control of the power supply cycle is performed by setting the loop gain of constant current feedback control to 1 times or less (0 dB) or less. Set to not respond in a cycle shorter than 1/2. As a result, within 1⁄2 cycle of the power supply cycle, the variation of the on time of the switching element 51 is suppressed, and the envelope of the peak of the current I 52 of the inductor 52 has a sinusoidal waveform.

Also, in feedback control, the same effect can be obtained by setting the on-time update cycle to a half cycle of the AC power supply 1 or a cycle longer than half thereof.

The output voltage of the secondary winding 52b of the inductor 52 is used to detect that the current of the primary winding 52a of the inductor 52 has become zero. The output voltage of secondary winding 52b is determined by voltage VL1 applied to primary winding 52a and the turn ratio n of secondary winding 52b to primary winding 52a. The magnitude of the output voltage of the secondary winding 52b can be represented by the product of VL1 and n.

The voltage VL1 of the primary winding 52a can be represented by the output voltage Vdb of the rectifier circuit 3 and the output voltage Vpfc of the power factor correction circuit 5. When the switching element 51 is on, the output voltage Vdb of the rectifier circuit 3 is applied to the primary winding 52a, so that VL1 = Vdb. On the other hand, when the switching element 51 is off, the difference between Vpfc and the output voltage Vdb of the rectifier circuit 3 is applied to the primary winding 52a, so that VL1 = Vpfc−Vdb.

Therefore, the output voltage VL2 of the secondary winding 52b when the switching element 51 is on is nVdb. The output voltage VL2 of the secondary winding 52b when the switching element 51 is off is n (Vpfc-Vdb). In the zero current detection unit 93, the output voltage VL2 of the secondary winding 52b is limited to a size that can be input to the switching control unit 91, and a signal is transmitted to the switching control unit 91.

Before the power factor correction circuit 5 starts the boosting operation, the output voltage Vpfc of the power factor correction circuit 5 and the output voltage Vdb of the rectifier circuit 3 are equal. Therefore, immediately after the power factor correction circuit 5 starts the boosting operation, the output voltage VL2 of the secondary winding 52b is zero.

In addition, while power factor improvement circuit 5 starts the boosting operation and output voltage Vpfc of power factor improvement circuit 5 is rising, a period in which the difference between Vpfc and Vdb is small is used as output voltage VL2 of secondary winding 52b. A large enough voltage can not be obtained. If the output voltage VL2 of the secondary winding 52b is not sufficiently large, zero current can not be detected.

There is a method of increasing the turns ratio n in order to obtain a voltage of a sufficient magnitude as the output voltage VL2 of the secondary winding 52b immediately after the power factor correction circuit 5 starts the boosting operation. However, when the turn ratio n is large, in the state where Vpfc is sufficiently boosted and VL2 is large, losses generated by the resistor 931 and the zener diode 932 of the zero current detection unit 93 increase. Therefore, if the turns ratio n is increased, the circuit efficiency is reduced. In addition, since heat generation of the resistor 931 and the zener diode 932 increases, it is necessary to take measures such as increasing the size of parts for heat dissipation.

Further, in order to increase the number of turns of the secondary winding 52b and to increase the turns ratio n, it is necessary to make the secondary winding 52b longer, which increases the cost. Furthermore, the increase in the number of turns of the secondary winding 52b causes the inductor 52 to be large. Therefore, it is not preferable to increase the number of turns of the secondary winding 52b in order to obtain a voltage of a sufficient magnitude as the output voltage VL2 of the secondary winding 52b.

It is possible to provide an amplification circuit in the zero current detection unit 93 in order to obtain a voltage of a sufficient magnitude as the output voltage VL2 of the secondary winding 52b immediately after the power factor correction circuit 5 starts the boosting operation. . However, the provision of the amplification circuit increases the number of parts, which increases the cost, complicates the circuit, and increases the size of the apparatus. Therefore, it is not preferable to amplify the output voltage VL2 of the secondary winding 52b by the amplification circuit.

Therefore, when zero current detection can not be performed immediately after the power factor correction circuit 5 starts the boosting operation, it is conceivable that the switching element 51 is forcibly turned on again in a predetermined cycle after the switching element 51 is turned on. FIG. 6 is a waveform diagram in the case where the switching element 51 performs switching operation at a predetermined cycle. The control exhibiting the waveform shown in FIG. 6 is referred to as a current discontinuous mode since the current I 52 of the inductor 52 is discontinuous. In this control, the switching element 51 is switched at predetermined on time and off time. The output voltage VL2 of the secondary winding 52b is not used. As a result, the switching element 51 can be turned on and off at a constant frequency even in a period when the zero current can not be detected after the start of the boosting operation of the power factor correction circuit 5.

When the operation shown in FIG. 6 is continued for a predetermined period, a voltage of a sufficient magnitude can be obtained as the output voltage VL2 of the secondary winding 52b. After the boosting operation of power factor correction circuit 5 starts, when the magnitude of output voltage VL2 of the secondary winding reaches a magnitude that can detect zero current, the control shifts to control using output voltage VL2 of secondary winding 52b. . That is, transition to the current critical mode is made. Before and after this transition, there is a problem that the switching frequency of the switching element 51 changes rapidly. When the switching frequency of the switching element 51 changes rapidly, Vpfc may be varied, the output current of the current control circuit 7 connected in the subsequent stage may be varied, and the light output of the LED 8 may flicker.

Therefore, in the first embodiment of the present invention, when the secondary winding 52b can not detect the zero current and is forced to turn on the switching element 51 forcibly again, the switching frequency becomes abrupt when transitioning to the current critical mode. We propose a method to prevent change.

FIG. 7 is a waveform diagram showing various waveforms after the start of the boosting operation by the power factor correction circuit 5 according to the first embodiment. In the period until time t1, the smoothing capacitor 6 is charged via the diode 53. Since the LED 8 is turned off during the period until the time t1, the smoothing capacitor 6 is charged to the amplitude peak value of the AC power supply 1 and held. Therefore, the output voltage Vpfc of the power factor correction circuit 5 is the peak voltage of the AC power supply 1.

At time t1, with the AC power supply 1 connected to the input filter 2, the power factor correction circuit 5 starts the boosting operation. Immediately after the power factor correction circuit 5 starts the switching operation, the difference value ΔV (Vpfc−Vp) between Vp and Vpfc is small, and the output voltage VL2 of the secondary winding 52b necessary for zero current detection can not be obtained. In a period P1 in which a sufficient output voltage VL2 can not be obtained, the switching element 51 is turned on / off by frequency control predetermined by the switching control unit 91. The “frequency control” is control to turn on and off the switching element 51 at a predetermined cycle without referring to the output voltage of the secondary winding 52 b.

A difference value threshold is shown in FIG. The difference value threshold is a difference value ΔV when Vpfc becomes high and the output voltage VL2 of the secondary winding 52b is increased to a detectable level. When the difference value ΔV reaches the difference value threshold, control in the current critical mode becomes possible. A period P1 is a period from time t1 when the boosting operation is started to t2 when the difference value ΔV reaches the difference value threshold. Frequency control is performed in period P1.

At time t2, Vpfc is boosted, the difference value ΔV rises, and the output voltage VL2 of the secondary winding 52b rises to a detectable level. The switching control unit 91 stores a difference value threshold and detects that the difference value ΔV exceeds the difference value threshold. When detecting that the difference value ΔV exceeds the difference value threshold, the switching control unit 91 changes the control of the switching element 51 from the frequency control to the current critical mode. The period after the transition to the current critical mode is shown as a period P2.

FIG. 7 shows that the switching frequency is increased as the difference value ΔV increases in the period P1 in which the power factor improvement circuit 5 is frequency controlled. That is, in the period P1, the switching frequency of the switching element 51 is not constant, and the switching frequency of the switching element 51 is increased as time passes. This makes it possible to reduce the change in switching frequency when shifting from frequency control to the current critical mode. It is preferable to change the switching frequency in period P1 so that the switching frequency at the end of frequency control matches the average switching frequency in current critical mode control.

FIG. 8 is a waveform diagram showing another control pattern of the switching frequency. In a period P1 in which the switching element 51 is frequency controlled, the switching frequency is increased as the difference value ΔV increases. In this example, the difference ΔF1, which is the difference between the switching frequency f2 at the end of frequency control and the average frequency f3 in current critical mode control, is the switching frequency f1 at time t1 at which the frequency control is started and the average frequency f3 in current critical mode control Is smaller than the difference value .DELTA.F2. This is an effect obtained by increasing the switching frequency in period P1 to make f2 larger than f1. In either case of FIGS. 7 and 8, since it is possible to suppress the rapid change of the switching frequency at time t2 which is the control change timing, it is possible to suppress the output voltage fluctuation of the power factor correction circuit 5.

The controller 9 carries out the control described above. That is, when the operation of the power factor correction circuit 5 is started, the control unit 9 executes the first control to change the switching frequency of the switching element 51, and thereafter the switching element in synchronization with the voltage obtained by the detection winding. The second control to switch 51 is executed. In the present embodiment, the frequency control corresponds to the first control, and the current critical mode corresponds to the second control. Then, in this case, the controller 9 changes the switching frequency at the time of transition from the first control to the second control, ΔF 1, the switching frequency at the start of the first control and the switching at the start of the second control. Make it smaller than the difference value ΔF2 with the frequency. FIG. 8 discloses control for making ΔF1 smaller than ΔF2. In FIG. 7, the switching frequency of the switching element 51 is continuously changed in the first control, and the switching frequency of the switching element 51 at the end of the first control is changed to the switching frequency of the switching element 51 at the start of the second control. It is shown to match. It is preferable that the change amount of the switching frequency at the time of shifting from the first control to the second control is zero. However, if ΔF 1 is smaller than ΔF 2, the fluctuation of Vpfc can be suppressed, so there is an effect of suppressing the flickering of the light source.

FIG. 9 is a flowchart showing an operation of the lighting fixture 100 according to the first embodiment. When the power factor improvement circuit 5 is powered on, the controller 9 is activated in step S1. Next, in step S2, the input voltage detection unit 92 detects the input voltage peak value Vp. The input voltage peak value Vp is a voltage peak value of the place described as Vp of FIG. Next, in step S3, the output voltage detection unit 94 detects Vpfc.

Thereafter, in step S4, the switching control unit 91 calculates the difference value ΔV (Vpfc−Vp). The calculation of the difference value ΔV is performed in a predetermined cycle. When the periodic calculation of the difference value ΔV is started, the boosting operation by the power factor improvement circuit 5 is started in step S5. This starts the frequency control described above.

After the boosting operation of the power factor correction circuit 5 is started, in step S6, the magnitude of the difference value ΔV and the difference value threshold value are determined. If the difference value ΔV is smaller than the difference value threshold, the frequency control is continued in step S7, Vpfc is detected again in step S8, and the difference value Δ is calculated using the latest Vpfc in step S9.

On the other hand, when the difference value ΔV is equal to or larger than the difference value threshold, at step S10, the frequency control is shifted to the current critical mode. The switching frequency of the switching element 51 at the start of the current critical mode is determined by the load and the circuit constant. Thereafter, the operation using the secondary winding 52b is continued, and the sequence is ended. Thus, when the difference value ΔV between Vp and the output voltage Vpfc reaches a predetermined difference value threshold by the control unit 9, the control shifts from the first control to the second control.

The switching control unit 91 can be configured by combining commercially available analog ICs. When the switching control unit 91 is configured by combining analog ICs, a circuit for realizing the calculation of the difference value ΔV, the determination of the difference between the difference value ΔV and the difference value threshold, and the control change from the first control to the second control. Becomes complicated and the number of parts increases. Therefore, by realizing the switching control unit 91 as software using an arithmetic device such as a microcomputer or a CPU, the circuit configuration can be simplified and an increase in the number of parts can be suppressed.

Each function of the drive unit 95 and the switching control unit 91 in FIG. 1 is realized by the receiving device 9 a and the processing circuit 9 b in FIG. 10. The receiving device 9 a is a device that receives various information input to the switching control unit 91. The processing circuit 9b is dedicated hardware. The processing circuit 9b corresponds to, for example, a single circuit, a complex circuit, a programmed processor, a parallel programmed processor, an ASIC, an FPGA, or a combination thereof. The respective functions of the drive unit 95 and the switching control unit 91 may be realized by the processing circuit 9 b, or the functions of the respective portions may be realized collectively by the processing circuit 9 b.

FIG. 11 is a block diagram showing the control unit 9 implemented by software. In this case, the input voltage detection unit 92, the zero current detection unit 93, and the output voltage detection unit 94 of FIG. 1 are the receiving device 30 of FIG. When the processing circuit is a CPU, each function of the switching control unit 91 and the drive unit 95 in FIG. 1 is realized by software, firmware, or a combination of software and firmware. The software or firmware is written as a program and stored in the memory 34. The processor 32, which is a processing circuit, reads out and executes the program stored in the memory 34 to realize the functions of the respective units. That is, there is a memory 34 for storing a program that results in the operations described in the flowchart of FIG. 9 and the first embodiment. It can be said that this program causes a computer to execute the above procedure or method. Here, the memory corresponds to, for example, non-volatile or volatile semiconductor memory such as RAM, ROM, flash memory, EPROM, EEPROM, magnetic disk, flexible disk, optical disk, compact disk, mini disk, DVD. Note that a part of each function of the control unit 9 may be realized by dedicated hardware, and a part may be realized by software or firmware.

The configuration and control method described above can be variously modified without losing their features. Hereinafter, some modifications will be described. In the first embodiment, for example, it is important to change the switching frequency of switching element 51 in period P1 immediately after the start of the boosting operation shown in FIG. The process of change is not particularly limited. The switching frequency of the switching element 51 may be increased continuously throughout the period P1, or the switching frequency of the switching element 51 may be increased in part of the period P1. The switching frequency may be increased stepwise in period P1.

In the first embodiment, the lighting apparatus 100 using the power conversion circuit having the rectifier circuit 3, the power factor correction circuit 5, the secondary winding 52b used as the detection winding, and the control unit 9 for controlling the LED 8 is described. did. That is, the output of this power conversion circuit was connected to the LED 8 via the current control circuit 7. However, this power conversion circuit can be generally used for devices to which power is input. For example, a load such as a motor can be connected to the output of the power conversion device. The power converter and the load are collectively referred to as an electrical device.

In the first embodiment, after performing frequency control in the current discontinuous mode shown in FIG. 6, the transition to the current critical mode is made. In other words, the switching element 51 is turned on and off in the current discontinuous mode during the period of the first control. However, the switching element 51 may be turned on and off in the current continuous mode during the period of the first control. FIG. 12 is a waveform diagram when the switching element 51 is operated in the current continuous mode. The current continuous mode is a control method of turning on the switching element 51 before the current I52 of the inductor 52 becomes zero. The current continuous mode is a control method of the switching element 51 not referring to the output voltage VL2 of the secondary winding 52b as in the current discontinuous mode.

FIG. 13 is a waveform diagram when control in the current continuous mode is adopted during the period of the first control. The power factor correction circuit 5 is operated in the current discontinuous mode in the period from time t1 to time ta, and the power factor improvement circuit 5 is operated in the current continuous mode in the period from time ta to time t2. The current continuous mode is a mode operating at a higher switching frequency than the current critical mode. The variation ΔF1 of the switching frequency when shifting from the first control to the second control is smaller than the difference value ΔF2 between the switching frequency f1 at the start of the first control and the switching frequency f2 at the start of the second control Thus, it is possible to avoid a sudden change in switching frequency at the time of control change.

As described above, the control unit 9 operates the switching element 51 in the discontinuous current mode or the continuous current mode during the first control period, and operates the switching element 51 in the current critical mode during the second control period. Can.

Although the case where the light source is the LED 8 has been described in the first embodiment, for example, a light source different from an LED such as an organic EL (Electro Luminescence) may be used. The modification described in the first embodiment can also be applied to the power conversion device, the lighting fixture, and the electric device according to the following embodiments. The power conversion device, the lighting apparatus, and the electric apparatus according to the following embodiments have many points in common with the first embodiment, and therefore, differences with the first embodiment will be mainly described.

Second Embodiment
In the first embodiment, when the difference value ΔV reaches the difference value threshold, the control is shifted from the frequency control to the current critical mode, but in the second embodiment, the control is shifted focusing on the output voltage Vpfc.

FIG. 14 is a waveform diagram showing control according to the second embodiment. In a period until the AC power supply 1 is connected and the power factor correction circuit 5 starts the boosting operation, the smoothing capacitor 6 is charged via the diode 53. Since the LED 8 is turned off during this period, the smoothing capacitor 6 is charged and held to the amplitude peak value of the AC power supply 1. Therefore, the output voltage Vpfc of the power factor correction circuit 5 is the peak voltage of the AC power supply 1.

Before the time t1 when the operation of the power factor correction circuit 5 starts, the input voltage detection unit 92 detects the input voltage peak value Vp. Information of the detected Vp is transmitted to the switching control unit 91. The switching control unit 91 stores a program or a table for deriving a threshold value of Vpfc at which the output voltage VL2 can be detected from the information of Vp. The threshold of Vpfc at which the output voltage VL2 can be detected is referred to as an output voltage threshold. The switching control unit 91 calculates an output voltage threshold value corresponding to the information of Vp received from the input voltage detection unit 92 according to the aforementioned program or table.

At time t1, the power factor correction circuit 5 starts the boosting operation. At the beginning of the boosting operation, the output voltage VL2 of the secondary winding 52b necessary for the zero current detection can not be obtained, so the frequency control of the power factor correction circuit 5 is performed. When Vpfc is boosted after the power factor correction circuit 5 starts the switching operation, the output voltage VL2 rises to a detectable level.

The switching control unit 91 changes the control of the switching element 51 from frequency control to current critical mode when Vpfc exceeds the output voltage threshold calculated above. In other words, the control unit 9 shifts from the first control to the second control when the output voltage Vpfc reaches a predetermined output voltage threshold. By changing the control at the timing when Vpfc reaches the output voltage threshold value in this way, the calculation of the difference value ΔV required in the first embodiment becomes unnecessary, so the calculation load on the switching control unit 91 can be reduced.

Furthermore, in period P1 in which frequency control of power factor improvement circuit 5 is performed, the switching frequency is increased as Vpfc becomes larger, thereby preventing the switching frequency from changing rapidly when transitioning from frequency control to the current critical mode. did. FIG. 14 shows that the switching frequency is matched before and after the control change from the frequency control to the current critical mode. Thus, it is preferable to match the switching frequency at the end of the frequency control with the average frequency of the switching at the start of the current critical mode control.

FIG. 15 is a waveform diagram showing another control pattern of the switching frequency. By increasing the switching frequency as Vpfc increases during the frequency control of the power factor correction circuit 5, the change amount ΔF3 of the switching frequency at the time of transition from the first control to the second control can be obtained at the start of the first control. The difference value ΔF4 between the switching frequency and the switching frequency at the start of the second control can be made smaller.

FIG. 16 is a flowchart showing a control method of the lighting apparatus according to the second embodiment. When the power is turned on, in step Sa, the control unit 9 is activated. Next, in step Sb, the switching control unit 91 receives information of Vp from the input voltage detection unit 92. For example, it receives information that the effective value of Vp is 100V, 200V or 242V. Then, the switching control unit 91 calculates an output voltage threshold value corresponding to Vp. By storing the correspondence between Vp and the output voltage threshold as a table in the switching control unit 91, it is possible to derive the output voltage threshold using the table. Thus, the output voltage threshold is determined from Vp when the operation of the power factor correction circuit 5 is started. It is preferable to raise the output voltage threshold if Vp is high, and lower the output voltage threshold if Vp is low.

Next, the process proceeds to step Sc. In step Sc, on / off of the switching element 51 is started based on the command from the switching control unit 91, and the operation of the power factor improvement circuit 5 is started. At the beginning of the operation of the power factor correction circuit 5, the switching element 51 is frequency controlled. Next, in step Sd, the switching control unit 91 determines whether Vpfc detected by the output voltage detection unit 94 is larger or smaller than the output voltage threshold. If Vpfc is smaller than the output voltage threshold value, the process proceeds to step Se to continue frequency control. Thereafter, Vpfc is again detected in step Sf, and the determination in step Sd is performed again. If it is determined in step Sd that Vpfc is equal to or higher than the output voltage threshold value, the process proceeds to step Sg to shift to the current critical mode. Thereafter, control in the current critical mode is continued.

In the second embodiment, the control unit 9 determines the output voltage threshold based on Vp which is a value reflecting the input voltage to the power factor correction circuit 5. That is, the output voltage threshold was made variable. However, if Vp of the power converter is predetermined, the process of determining the output voltage threshold is unnecessary. For example, if the power conversion device is a dedicated product of AC 100 V, the process of determining the output voltage threshold is unnecessary, and one predetermined output voltage threshold can be used.

Third Embodiment
FIG. 17 is a circuit diagram of the lighting fixture 200 according to the third embodiment. The lighting fixture 200 operates basically the same as the lighting fixture 100 described in the first embodiment. Although the control unit 9 mainly controls the power factor correction circuit 5 in the first embodiment, the control unit 9 of the third embodiment controls not only the power factor correction circuit 5 but also the current control circuit 7. The current control circuit 7 is a circuit that is connected to the output of the power factor correction circuit 5 and converts the direct current voltage output from the power factor correction circuit 5 into a direct current.

The control unit 9 of the third embodiment includes a current detection unit 10 that detects the current flowing through the LED 8 and a current detection unit 96 that receives the output of the current detection unit 10. For example, a shunt resistor or a Hall sensor can be used as the current detection means 10. The current detection unit 96 sends information on the LED current to the switching control unit 91. The switching control unit 91 controls the current output from the current control circuit 7 by performing on / off control of the MOSFET 71 using the driving unit 95.

If the frequency is slightly changed at the timing of changing the control of the switching element 51 of the power factor correction circuit 5 from the frequency control to the current critical mode, Vpfc oscillates. FIG. 18 is a waveform diagram showing that Vpfc oscillates with control change. FIG. 18 shows that vibration occurs from time t2 which is the timing of control change to Vpfc, and the vibration attenuates with the passage of time. This vibration is attenuated, for example, in about 100 msec.

In order to keep the output of the current control circuit 7 constant, it is necessary to respond quickly to the oscillation of Vpfc. Therefore, the control unit 9 of the third embodiment has a predetermined period before shifting from the first control to the second control, and a predetermined period after shifting from the first control to the second control. The response speed of the current control circuit 7 is increased compared to the state in which the output voltage Vpfc of the rate improvement circuit 5 is stable at a constant value. The response speed of the current control circuit 7 is a speed at which the detection result of the current detection unit 96 is reflected in the control of the MOSFET 71. As the response speed of the current control circuit 7 is higher, the detection result of the current detection unit 96 is more quickly reflected in the control of the MOSFET 71.

For example, the response speed of the current control circuit 7 in a period from 100 msec before time t2 to 100 msec after time t2 is set higher than the response speed of the current control circuit 7 after t3 when Vpfc reaches the target value. In other words, the response speed of the current control circuit 7 is made higher for a short period of time before and after the control change of the switching element 51 than in the period after t3. Thus, the output of the current control circuit 7 can be kept substantially constant.

A period in which the response speed of the current control circuit 7 is increased is referred to as a high speed response period. In order to execute the control described above, the switching control unit 91 has to specify a fast response period. Since the switching control unit 91 is a control entity of the power factor improvement circuit 5, the high speed response period can be easily specified. That is, since the switching control unit 91 periodically compares the difference value ΔV with the difference value threshold value, the timing of the control change is approaching, the timing of the control change has come, and the fixed period after the control change Can be detected. From these detection results, the above-mentioned fast response period can be easily identified.

As described above, by controlling the power factor correction circuit 5 and the current control circuit 7 using one control unit 9, the response speed of the current control circuit 7 can be increased when the control of the power factor correction circuit 5 is changed. . Thereby, it is possible to prevent the flickering of the LED 8 due to the fluctuation of the current flowing to the LED 8 due to the slight vibration of Vpfc generated when changing the control in the power factor improvement circuit 5.

The method described in the third embodiment is effective for any control in which the switching frequency may fluctuate to some extent at the timing of control change of the switching element 51. Therefore, the method of the third embodiment can be combined with the control method of the switching element 51 described in the first and second embodiments or their modifications.

The effects of the present invention may be enhanced by combining the technical features described in the above embodiments.

5 Power factor correction circuit, 51 switching elements, 52 inductors, 52a primary winding, 52b secondary winding, 9 control unit

Claims

A rectifier circuit that rectifies AC power;
A power factor improvement circuit having a switching element and an inductor, the output of the rectifier circuit being input, and a DC voltage being output;
A detection winding for detecting a voltage generated by the inductor;
A control unit which receives the voltage detected by the detection winding and drives the switching element;
The control unit executes a first control to change a switching frequency of the switching element when the operation of the power factor correction circuit is started, and thereafter, the switching element is synchronized with a voltage obtained by the detection winding. When executing the second control for switching the switching frequency, the amount of change in the switching frequency when shifting from the first control to the second control, the switching frequency at the start of the first control, and the second control Power conversion device characterized in that it is smaller than the difference value with the switching frequency at the start of the above.
In the first control, the switching frequency of the switching element is continuously changed, and the switching frequency of the switching element at the end of the first control matches the switching frequency of the switching element at the start of the second control. The power converter according to claim 1, characterized in that
An output voltage detection unit that detects an output voltage of the power factor correction circuit;
The power conversion device according to claim 1, wherein the control unit changes a switching frequency of the switching element in the first control according to an output of the output voltage detection unit.
An input voltage detection unit that detects an input voltage of the power factor correction circuit;
An output voltage detection unit that detects an output voltage of the power factor correction circuit;
3. The apparatus according to claim 1, wherein the control unit shifts from the first control to the second control when a difference between the input voltage and the output voltage reaches a predetermined difference threshold. Power converter according to claim 1.
An output voltage detection unit that detects an output voltage of the power factor correction circuit;
The power conversion device according to claim 1, wherein the control unit shifts from the first control to the second control when the output voltage reaches a predetermined output voltage threshold.
An input voltage detection unit that detects an input voltage of the power factor correction circuit;
The power conversion device according to claim 5, wherein the control unit determines the output voltage threshold according to the input voltage.
The power conversion device according to any one of claims 1 to 6, wherein a change amount of the switching frequency at the time of transition from the first control to the second control is zero.
The control unit operates the switching element in the discontinuous current mode or the continuous current mode during the first control period, and operates the switching element in the current critical mode during the second control period. The power conversion device according to any one of claims 1 to 7, wherein
And a current control circuit connected to an output of the power factor correction circuit and converting a direct current voltage output from the power factor correction circuit into a direct current.
The control unit improves the power factor during a predetermined period before shifting from the first control to the second control and a predetermined period after shifting from the first control to the second control. The power conversion device according to any one of claims 1 to 8, characterized in that the response speed of the current control circuit is increased as compared with a state in which the output voltage of the circuit is stable at a constant value.
The power conversion device according to any one of claims 1 to 9,
A light fixture comprising: a light emitting diode (LED) or a light source which is an organic electro luminescence (EL) connected to an output of the power conversion device.
The power conversion device according to any one of claims 1 to 9,
And a load connected to an output of the power conversion device.