JP2002112533A - Constant-power control device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a constant-power control device that is simply constituted, using one converter, and the cost of which is thus reduced. SOLUTION: A rectifying circuit Re is connected with an alternating-current power supply AC, and a discontinuous current-type step-up/down chopper circuit CHa, that converts the output voltage of the rectifying circuit Re into a prescribed direct-current voltage is connected. An inverter Inv, that converts a direct-current voltage into a high-frequency voltage, is connected with the step- up/step-down chopper circuit, and an HID lamp is connected with the inverted Inv. A control circuit Cont, that on/off-controls a switching element Sa installed in the step-up/down chopper circuit, keeps the on/off period T constant and the on-time 'ton' of the switching element for at least half a cycle of alternating current, and inputs the output voltage of the rectifying circuit at point P and controls pulse width modulation(PWM), so that the on time of the switching element is in proportion to the inverse of the maximum value of the output voltage.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a constant power control device which has a simple configuration using one converter and has a reduced cost.

[0002]

2. Description of the Related Art A DC power supply is used as a power supply, and the output voltage of the DC power supply is converted to a predetermined voltage by a chopper circuit.
Further, this DC voltage is converted into a high-frequency voltage by a high-frequency power source such as an inverter circuit or the like, for example, a high-pressure discharge lamp (Hi).
gh Intensity Disrchge La
mps (hereinafter abbreviated as HID lamp) may be controlled by constant power. FIG. 4 is a circuit diagram showing an example of a constant power control device using a boost chopper circuit functioning as an active smoothing filter and a step-down chopper circuit as a chopper circuit.

In FIG. 4, an output voltage of an AC power supply AC is rectified by a rectifier circuit Re. The output voltage of the rectifier circuit Re is
The voltage is boosted by the boost chopper circuit CHx, and then reduced by the step-down chopper circuit CHy. As described later, the step-up chopper circuit CHx is used for improving the power factor by acting as an active smoothing filter, and the step-down chopper circuit CHy is used for performing constant power control of the load.

The output voltage of the step-down chopper circuit CHy is passed through a smoothing capacitor Cy to an inverter of a full bridge configuration.
And is converted into a high-frequency voltage of a predetermined frequency. This high frequency voltage is supplied to the HID lamp as a load.

The boost chopper circuit CHx includes a reactor L
x, a diode Dx, a switching element Sx, and a capacitor Cx. The switching element Sx is a MOS
Electronic switching elements such as FETs can be used. The switching element S is supplied by a signal Ux from the control circuit Xa.
x is turned on, energy is accumulated in the reactor Lx during the ON period of the switching element Sx, and the switching element Sx is turned on.
Power is transmitted to the output side with the back electromotive force generated at the moment when x is turned off. By appropriately selecting the ON / OFF cycle of the switching element Sx, a predetermined boosted DC voltage can be obtained at the output terminal of the boost chopper circuit CHx.

The boost chopper circuit CHx can function as an active smoothing filter. That is, the pulsating current waveform that has been subjected to the dual-wave rectification by the rectifier Re is switched at a high frequency over the entire period. Thus, the input current waveform becomes an average value of each switching current in each cycle. Therefore, even if a large capacitor is included in the load, the load becomes equivalent to a pure resistance load, and the input switching current has a sine wave shape from which waveform distortion has been removed, so that the power factor can be improved.

The step-down chopper circuit CHy is a MOSFET
And the like, a switching element Sy, a reactor Ly, and a freewheel diode FDy. An oscillation circuit is provided in the switching control circuit Xb, and the switching element Sy is turned on and off by an output signal Uy from the oscillation circuit. The ON / OFF control of the switching element Sy at this time controls the output voltage of the step-down chopper circuit CH by pulse width modulation (PWM), and performs constant power control of the HID lamp of the load.

[0008] The inverter Inv of the full bridge configuration is
It is configured using an electronic switch such as a MOSFET, and the electronic switch is alternately turned on and off by a control signal from a control circuit (not shown). By appropriately selecting the ON / OFF cycle of the electronic switch, a high-frequency voltage having a predetermined frequency can be obtained.

[0009]

SUMMARY OF THE INVENTION As shown in FIG.
The conventional constant power control device requires two converter circuits, a boost chopper circuit acting as an active smoothing filter and a step-down chopper circuit performing constant power control. For this reason, there is a problem that the device is complicated, the control circuit is complicated, and the cost is high.

The present invention has been made in view of the above problems, and has as its object to provide a constant power control device having a simple configuration and reduced cost.

[0011]

SUMMARY OF THE INVENTION It is an object of the present invention to provide a constant power control apparatus comprising: an AC power supply; a rectifying circuit for rectifying an AC voltage; A current discontinuous buck-boost chopper circuit for converting to a voltage, a load connected to the buck-boost chopper circuit, and a control circuit for controlling on / off of a switching element provided in the buck-boost chopper circuit; The output voltage of the rectifier circuit is input to the switching element, the on / off cycle of the switching element is fixed, the on time of the switching element is fixed at least for half an AC cycle, and the on time of the switching element is set to the maximum value of the output voltage. Is achieved by controlling the pulse width modulation (PWM) to be proportional to the reciprocal of

According to a second aspect of the present invention, in the constant power control device according to the first aspect, a high-frequency power supply for converting a DC voltage to a high-frequency voltage is connected to the buck-boost chopper circuit, and the high-frequency power supply is illuminated. It is characterized by connecting a lighting lamp.

According to the above feature of the invention according to claim 1,
Connect a buck-boost chopper circuit between the rectifier circuit and the load,
The on-off cycle of the switching element provided in the buck-boost chopper circuit is constant, the on-time of the switching element is constant at least for half an AC cycle, and the on-time of the switching element is the reciprocal of the maximum value of the output voltage of the rectifier circuit. Is controlled by pulse width modulation (PWM) so as to be proportional to. Therefore, the function as the active smoothing filter and the constant power control of the load can be performed with a single converter, so that the cost can be reduced and the control circuit can be simply configured.

According to the above feature of the invention according to claim 2,
When the lighting lamp is connected to the high frequency power supply, the function as an active smoothing filter can be realized with a single converter, and constant power control of the lighting lamp can be performed.

[0015]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a circuit diagram showing a constant power control device according to the present invention. The same parts as those in the conventional example of FIG. 4 or corresponding parts are denoted by the same reference numerals, and detailed description thereof will be omitted.

In the present invention, as shown in FIG. 1, a discontinuous current step-up / step-down chopper circuit CHa is connected between the rectifier circuit Re and the inverter Inv. This step-up / step-down chopper circuit CHa
Switching element Sa using SFET, reactor L
a, a diode Da. The voltage of the input terminal P of the step-up / step-down chopper circuit CHa, that is, the rectifier circuit R
e, the voltage input to the step-up / step-down chopper circuit CHa is input to the control circuit Cont, and the switching element Sa is turned on / off by a signal Ua from the control circuit Cont, thereby realizing a function as an active smoothing filter. The power factor is improved by removing the distortion, and the constant power control of the load is performed.

Conventionally, as shown in FIG. 4, between a rectifier circuit Re and an inverter Inv, there are provided a boost chopper circuit CHx acting as an active smoothing filter and a step-down chopper circuit CHy for performing constant power control of a load. One converter
However, in the present invention, a single converter having only the current discontinuous type step-up / step-down chopper circuit CHa is used.
Are used.

Discontinuous current step-up / step-down chopper circuit CHa
When the switching element Sa is turned on, the current flows from the power supply (rectifier circuit Re) through the path of the switching element Sa, the reactor La, and the power supply, and accumulates energy in the reactor La. When the switching element Sa is turned off after a predetermined period, the energy stored in the reactor La
Flows from the reactor La to the HID lamp of the load.

Discontinuous current step-up / step-down chopper circuit CHa
Is the relationship between the input voltage Vin and the output voltage Vout, assuming that the conduction ratio of the switching element Sa is α, (Vout / V
in) = α / (1−α). Therefore, when α is 0.
When Vout / Vin = 1 at 5 and α is made smaller than this, Vout / Vin becomes 1 or less, that is, Vou
t is smaller than Vin and operates as a step-down chopper circuit. When α is larger than 0.5, Vout / V
In becomes 1 or more, and the circuit operates as a step-up chopper circuit.

Next, the operation of the discontinuous current type step-up / step-down chopper circuit CHa will be described with reference to the waveform diagram of FIG. FIG.
In the graph, the horizontal axis represents time (τ). Vin
(Τ) is calculated from the rectifier circuit Re to the step-up / step-down chopper circuit C.
It is a pulsating waveform of a voltage which is input to Ha and is obtained by rectifying both sides of an AC sine wave. Vin (τ) is formed in a sine wave shape, and the maximum value is Vm. ip (τ) is the maximum value of the current when the switching element Sa is turned on, and Ip is ip
An envelope ia (τ) connecting (τ) is the input current (average current) of the discontinuous current step-up / step-down chopper circuit CHa.

Ta is one cycle of alternating current, T is the on / off cycle of the switching element Sa, and ton is the switching element Sa.
Is an ON period, and toff is an OFF period of the switching element Sa. In addition, a discontinuous current type step-up / step-down chopper circuit C
Let the output voltage of Ha be Vout (τ).

Each time the switching element Sa is turned on, the average current ia (τ) input to the discontinuous current step-up / step-down chopper circuit CHa is ia (τ) = (１ ／) · ｛i
p (τ)｝ · {ton (τ) / T (τ)}. Further, assuming that the reactance of the reactor La of the current discontinuous type step-up / step-down chopper circuit CHa is Li, the maximum value ip (τ) of the current when the switching element Sa is turned on is:
ip (τ) = {Vin (τ) / Li} · ton or ip (τ) = {Vout (τ) / Li} · toff
Becomes

From this, ia (τ) = (1/2) ·
[｛Vin (τ) / Li｝ · ton] ｛｛ton (τ)
/ T (τ)｝, this equation is transformed to ia
(Τ) = (1/2) ｛{Vin (τ) / Li}｝ ｛to
n2 (τ) / T (τ)｝. Here, assuming that T (τ) is constant and ton is constant at least during a half cycle of alternating current, ton2 (τ) / T (τ) = constant. That is, if K is a constant, ton2 (τ) / T
(Τ) = K. In this way, as shown in FIG. 3, the load is controlled by pulse width modulation (PWM) by turning on / off the switching element Sa.

At this time, ia (τ) = (1/2) · ｛V
in (τ) / Li｝ · K, and since the reactance Li is constant, it can be replaced by K / Li = Ka (constant). Therefore, ia (τ) ∝Vin
(Τ). That is, ia (τ) can be represented in the same sine wave form as Vin (τ) as shown in FIG.

As described above, each time the switching element Sa is turned on, the average current ia (τ) input to the discontinuous current step-up / step-down chopper circuit CHa is represented in a sine wave shape, so that the load is a pure resistance load. Become equivalent. That is, the discontinuous current step-up / step-down chopper circuit CHa can function as an active smoothing filter.

Next, the instantaneous input power of the discontinuous current step-up / step-down chopper circuit CHa is Pin (τ), and the output power is Po.
ut (τ). If the loss in the inverter Inv is neglected, the output power Pout (τ) of the discontinuous current step-up / step-down chopper circuit CHa is supplied to the HID lamp of the load.

Here, Pin (τ) = ia (τ) · Vi
n (τ) = (1/2) · {Vin2 (τ) / Li} ·
{Ton2 (τ) / T (τ)} holds. Therefore, the average power Pin input during one cycle is represented by the following equation.

[0028]

(Equation 1)

Here, assuming that the maximum value of the input voltage is Vm, Vin (τ) = Vm · sin (2π / Ta) (τ)
Therefore, the following equation holds for the average power Pin.

[0030]

(Equation 2)

From this, ton is obtained by the following equation.

[0032]

(Equation 3)

By the way, from the above (Equation 2), Pin =
Since {1 / (4LiT)} · (Vm · ton) 2, from equation (3), if the ton time is controlled so that the relationship of ton∝ (1 / Vm) is established, Pin becomes constant. Pout can be kept constant. Where Li,
T is a constant.

Further, Pout = η · (Vm2 / 4Li)
Since (ton2 / T), if η and Li are constant, Pout becomes constant by performing on / off control of the switching element Sa so that ton∝ (1 / Vm). Thus, constant power control of the load can be performed. That is, the switching element S is subjected to pulse width modulation (PWM) so that ton is proportional to the reciprocal of Vm.
By performing on / off control of “a”, the current discontinuous type step-up / step-down chopper circuit CHa can act as an active smoothing filter, and the load can be controlled with constant power.

FIG. 2 is a circuit diagram showing a specific example of the control circuit of FIG. In FIG. 2, A is the voltage of the input terminal P of the step-up / step-down chopper circuit CHa, that is, the maximum value Vm of the pulsating voltage which is the output voltage of the discontinuous current type rectifier circuit. ) To calculate the switching element S
This is a ton time calculator for outputting the ON time of a.

B is a drive circuit for outputting an on / off signal Ua of the switching element Sa, C is a logic circuit formed by two NOR circuits, and D is a delay for delaying a signal input to the gate of one of the NOR circuits. A circuit E is an on-trigger signal generating source for generating an on-trigger signal having a constant period.

Next, the operation of the circuit of FIG. 2 will be described. The ton time calculator A operates to increase the ton and increase the output of the discontinuous current step-up / step-down chopper circuit CHa when the HID lamp is started. Also, HI
After the D lamp is turned on, the constant power control is performed.
A signal ton for turning on the switching element Sa calculated by (Equation 3) is formed and output to the logic circuit C.
That is, the output signal from the ton time calculator A gives a timing to turn off the switching element Sa.

The signal from the on-trigger signal source E gives a timing to turn on the switching element Sa, and a signal is input to one NOR circuit via the delay circuit D. The logic circuit C thus forms a predetermined output signal from the output signal from the ton time calculator A and the output signal from the on-trigger signal generation source E, and the signal Ua from the drive circuit B as shown in FIG. The on / off control of the switching element Sa is performed with appropriate characteristics.

In the example of FIG. 1, an inverter Inv is connected to the output side of the discontinuous current step-up / step-down chopper circuit CHa.
An HID lamp as a load is connected to the output side of the inverter Inv to perform constant power control. The present invention can be applied to a case where a load is directly connected to the output side of the step-up / step-down chopper circuit CHa. The load is not limited to a lighting lamp such as an HID lamp, and a general load may be connected.

[0040]

As described above, according to the first aspect of the present invention, the buck-boost chopper circuit is connected between the rectifier circuit and the load, and the switching element provided in the buck-boost chopper circuit is provided. The pulse width modulation (PWM) is performed so that the on-off cycle is constant, the on-time of the switching element is constant at least for half an AC cycle, and the on-time of the switching element is proportional to the reciprocal of the maximum value of the output voltage of the rectifier circuit. ) Control. Therefore, a single converter
The realization of the function as an active smoothing filter and the constant power control of the load can be performed by the filter, so that the cost can be reduced and the control circuit can be simply configured.

According to the second aspect of the present invention, when a lighting lamp is connected to a high-frequency power supply, the function as an active smoothing filter can be realized with a single converter, and the lighting lamp can be realized. Constant power control can be performed.

[Brief description of the drawings]

FIG. 1 is a circuit diagram showing a constant power control device according to an embodiment of the present invention.

FIG. 2 is a circuit diagram illustrating an example of a control circuit.

FIG. 3 is a waveform diagram of a step-up / step-down chopper circuit.

FIG. 4 is a circuit diagram showing a conventional constant power control device.

[Explanation of symbols]

 AC AC power supply Rx Rectifier circuit CHa Step-up / step-down chopper circuit Inv Inverter HID lamp Load Cont control circuit

Claims (2)

[Claims] An AC power supply, a rectifier circuit for rectifying an AC voltage, a discontinuous current step-up / step-down chopper circuit for converting an output voltage of the rectifier circuit to a DC voltage, and a load connected to the step-up / step-down chopper circuit. A control circuit for controlling on / off of a switching element provided in the step-up / step-down chopper circuit, and inputting an output voltage of a rectifier circuit to the control circuit to make an on / off cycle of the switching element constant and to set an on time of the switching element. The pulse width modulation (P) is set to be constant at least during the half cycle of the alternating current and to make the on-time of the switching element proportional to the reciprocal of the maximum value of the output voltage.
WM) A constant power control device characterized by performing control. 2. A high-frequency power supply for converting a DC voltage to a high-frequency voltage is connected to the step-up / step-down chopper circuit, and a lighting lamp is connected to the high-frequency power supply.
3. The constant power control device according to 1.