JPH03212163A - Inverter unit - Google Patents

Abstract

PURPOSE:To suppress switching loss or noise by employing such load circuit with the resonance frequency varied according to the supply energy, regulating the source voltage, and controlling the switching timing of a switching element to match approximately with the zero-cross point of resonance current. CONSTITUTION:Since a load l is a discharge lamp such as a fluorescent lamp, it exhibits negative characteristic under lighting state and the load voltage drops as the load current increases. When energy supply to a load circuit 5 is regulated by varying the output frequency of an oscillation circuit 2, output voltage of a voltage control circuit 6 varies and the switching timing of switching elements SW1, SW2 is controlled to match with the zero-cross point of resonance current to the load circuit 5. Consequently, switching loss or noise is suppressed and the switching element is protected against breakdown.

Description

[Detailed description of the invention] [Industrial application field]

The present invention relates to an inverter device that includes a switching element that is controlled to be turned on and off, converts a DC power source into an AC output, and supplies the AC output to a load circuit.

[Conventional technology]

Conventionally, as this type of inverter device, for example,
As shown in FIG. 12, a pair of switching elements SW,
, SW2 is inserted between both ends of the power supply E, and both switching elements sw, , sw are turned on alternately. Each switching element sw,
, sw2 have on-periods controlled by the control circuit 1. The control circuit 1 includes an oscillation circuit 2 that outputs a pair of contradictory rectangular waves having a constant period as shown in FIGS. 13(a) and 13(b). One output V of the oscillation circuit 2 is converted into a voltage via the level shift circuit 3 (FIG. 13(C)), and then a control signal VC is generated to one switching element SW via the driver circuit 4I. (Figure 13(d)). Dimensions 18 rtR Fubizume Renhomechu + V l + K 4 nol (Generates control signal Vc to the other switching element SW2 via Engen 42 (Fig. 13(e)).Here , the level shift circuit 3 is provided as shown in FIG.
This is because, as shown in f), the voltage 0 across the switching element SW2 changes, and the reference voltage of the switching element SW1 changes. A load circuit 5 is connected between both ends of the switching element SW2. The load circuit 5 has an inductance L and a capacitor Ca connected in series, and a DC cut capacitor cb between both ends of the capacitor Ca.
and a load l are connected in series. By the way, both switching elements SW+ and SW2 are the 13th switching elements SW+ and SW2.
When on/off control is performed by the outputs Vc, , Vc2 of the driver circuits 4 + , 42 shown in FIGS. (d) and (e), both switching elements S W + and S W 2 are turned on alternately. In other words, both switching elements SW,
Potential V at the connection point of SW2. As shown in FIG. 13(f), when the switching element SW is turned on at 0 time t when the waveform becomes rectangular, the current tends to flow as it is due to the energy stored in the load circuit 5, so that the current flows through the switching SW1. The direction of the flowing current ■1 is shown in Figure 13 (h)
As shown in Fig. 12, the direction of the arrow is opposite to that of the arrow, and then the direction is reversed. Further, when the switching element SW2 is turned on at time t2, the direction of the current (2) flowing through the switching element SW2 is changed to the first direction due to the accumulated energy of the load circuit 5.
As shown in Fig. 3(g), the direction is opposite to that of the arrow in Fig. 12, and then the direction is reversed. By repeating this operation, the first
An alternating current (2) as shown in Figure 3 (i) flows through the load (1). Here, in FIG. 13, it is assumed that the output frequency of the oscillation circuit 2 is higher than the resonant frequency of the load circuit 5. That is, the phase of the resonant current is delayed with respect to the output of the oscillation circuit 2, and the direction of the currents I, I2 flowing when switching elements SW+ and SW2 is in the negative direction (12th
The direction is opposite to that shown by the arrow in the figure). If the phase relationship is reversed, as shown in FIG. 14, current will flow in the positive direction when the switching elements sw, , sw are switched. In this case, the state changes from a negative current flowing through one switching element to a positive current flowing through the other switching element, and instantaneously the switching element through which the negative current was flowing changes. Since a voltage is applied, a reverse recovery current, ie, a recovery current, flows due to the accumulation of carriers when a negative current flows. This current is shown in Fig. 14(a).
As shown in , the current becomes whisker-like, causing switching loss and noise. Therefore, the output frequency of the oscillation circuit 2 is normally set higher than the resonant frequency of the load circuit 5.

[Problem M that the invention attempts to solve]

However, even if the output frequency of the oscillation circuit 2 is higher than the resonant frequency of the load circuit 5, if the operation is as shown in FIG.
When switching, the current and voltage change rapidly, causing switching loss and noise in the switching elements sw, , sw2. Therefore, as shown in FIG. 15, it is recommended to make the frequency of the output V of the oscillation circuit 2 approximately equal to the resonant frequency of the load circuit 5. In this way, the switching elements sw, , sw2 The switching time almost coincides with the zero-crossing point of the resonant current of the load circuit 5, resulting in less switching loss and less noise. On the other hand, if you try to control the energy supplied to the load l while maintaining this state, as in the case of dimming a lighting load, the output frequency of the generator circuit 2 and the load circuit 5
It is necessary to change the resonant frequency in conjunction with the resonant frequency. Although it is easy to adjust the output frequency of the oscillation circuit 2,
Adjusting the resonant frequency of the load circuit 5 increases the number of parts and complicates the circuit configuration, making it impractical. In this case, the resonant frequency of the load circuit 5 must also be changed continuously, which is difficult to realize. The present invention aims to solve the above-mentioned problems, and uses a load circuit with a configuration in which the resonant frequency changes depending on the supplied energy, and adjusts the power supply voltage to adjust the switching timing of the switching element. ,
It is an object of the present invention to provide an inverter device in which switching loss and noise are reduced by controlling the resonant current of the load circuit so as to substantially coincide with the zero-crossing point.

[Means to solve the problem]

In order to achieve the above object, the present invention provides an inverter device that includes a switching element that is controlled on and off, converts a DC power source into an AC output, and supplies the AC output to a load circuit. The load circuit is configured such that the load circuit changes, and a zero cross detection circuit detects the zero cross point of the resonant current of the load circuit, and the switching timing of the switching element matches the zero cross point based on the output of the zero cross detection circuit. Thus, a voltage control circuit is provided to control the output voltage of the DC power supply. Further, it is desirable to provide a detection stop circuit that stops the operation of the zero-cross detection circuit at least when the load circuit is not in a stable operating state.

[Effect]

According to the configuration of claim 1, the load circuit is configured such that the resonance frequency changes depending on the supplied energy, and the zero-cross detection circuit detects the zero-cross point of the resonance current of the load circuit, and the zero-cross detection circuit detects the zero-cross point of the resonance current of the load circuit. and a voltage control circuit that controls the output voltage of the DC power supply so that the switching timing of the switching element coincides with the zero-crossing point, so that the switching timing of the switching element coincides with the zero-crossing point of the resonant current of the load circuit. Since they almost match, switching loss and noise can be reduced. Furthermore, since the output voltage of the DC power supply is controlled, even if the energy supplied to the load circuit is continuously changed, the circuit configuration does not become complicated and implementation becomes easy. Moreover, according to the configuration of claim 2, since the detection stop circuit is provided that stops the operation of the zero-cross detection circuit at least when the load circuit is not in a stable operating state, when the load circuit is not in a stable operating state, By keeping the output voltage of the DC power supply constant, it is possible to prevent excessive current from flowing through the switching elements, thereby preventing damage to the switching elements.

[Embodiment 1] The basic configuration of this embodiment is as shown in FIG. Both switching elements SW. The SW2 is controlled by the control circuit 1 to be turned on alternately. The control circuit 1 operates each switching element SW in synchronization with the rectangular wave output of the oscillation circuit 2. Drive circuit 4 +, 4 that turns on SW2 alternately
2, an oscillation circuit 2 and a drive circuit 4. Between,
A level shift circuit 3 for converting voltage is inserted. A load circuit 5 is connected between both ends of the series circuit of one switching element SW2 and the impedance 2. The load circuit 5 includes a series circuit of an inductance L and a capacitor Ca, and a DC cut capacitor cb and a load l)-Wit IvFIB a are connected between both ends of the capacitor Ca.
Stop sardine bound nine? ? ◆A load here! Assume that a discharge lamp such as a fluorescent lamp is used. On the other hand, the voltage across the impedance Z corresponding to the current flowing through the switching element SW2 is input to the zero-crossing detection circuit 7, where the zero-crossing point is detected, and the voltage across the impedance Z corresponding to the current flowing through the switching element SW7. The output voltage of the voltage control circuit 6 is controlled so that the inversion of SW2 substantially coincides with the zero-crossing point of the resonant current of the load circuit 5. That is, the voltage control circuit 6
uses the power supply E as an input, and changes the output voltage according to the output of the zero-cross detection circuit 7. The basic operation will be explained based on FIG. The left half of FIG. 2 shows the voltage control circuit 6 and the zero-cross detection circuit 7.
This shows the operation when the output frequency of the oscillation circuit 2 is increased in order to reduce the energy supplied to the load I without providing a , and as the load current increases, the load voltage decreases. In other words, the impedance changes depending on the supplied energy.6 Therefore, when the output frequency of the oscillation circuit 2 increases, the impedance of the load circuit 5 increases, and the energy supplied to the load l decreases. do. In addition, as shown in FIGS. 2(g) and (h), the current flowing through the switching elements SW, SW2 has a phase lag with respect to the resonant current of the load circuit 5, and the current flowing to the load l decreases. Since the zero-cross point of the common ri current of the load circuit 5 and the switching times of the switching elements sw, , sw2 are shifted, switching loss increases. The left half of FIG. 2 shows the operation when the voltage control circuit 6 and zero-cross detection circuit 7 are activated. As shown in FIG. 2(j), when the output voltage Vi of the voltage control circuit 6 is lowered, the energy supplied to the load circuit 5 is reduced, so that the impedance of the load 1 is increased. As a result, the resonant frequency of the load circuit 5 increases,
It becomes approximately equal to the output frequency of the oscillation circuit 2. thus,
This allows the switching timing of the switching elements sw, , sw to substantially coincide with the zero-crossing point of the resonant current of the load circuit 5. In short, when increasing the output frequency of the oscillation circuit 2 to decrease the load current, the output voltage of the voltage control circuit 6 is decreased, and when decreasing the output frequency of the oscillation circuit 2 to increase the load current, the voltage control circuit By increasing the output voltage of 6, it is possible to adjust the energy supplied to the load 1 while keeping the switching timing of the switching elements sw, , sw2 almost coincident with the zero-crossing point of the resonant current of the load circuit 5. It can be done. The specific circuit is shown in Fig. 3, and the switching elements SW, S
W2 uses a field effect transistor.1 The oscillation circuit 2 is a timer integrated circuit known as "r555" with peripheral components externally attached, and the output V of the oscillation circuit 2 has a 4 As shown in Fig. 4 (a), the output ■ of the 0 oscillation circuit 2, in which high and low binary voltages are obtained alternately at a constant period, is composed of a pair of current mirror circuits equipped with four transistors Q1 to Q. The signal is inputted to the drive circuit 41, which is a buffer, through the level shift circuit 3, and the switching element SW is on/off controlled by the output Vc+ of the drive circuit 4I. Further, the output V of the oscillation circuit 2 is input to the level shift circuit 3 and also to the drive circuit 4□ consisting of an inverting circuit.
Drive circuit obtained from 4. The switching element SW2 is controlled on/off by the output VC2, which is opposite to the output Vc+ of the switching element SW2. The voltage control circuit 6 is a step-up chopper circuit, in which a series circuit of a choke coil CH and a transistor T, which is a switching element, is inserted between both ends of a power supply E, and a diode D is inserted between the collector emitter of the transistor T1. Connect a series circuit with capacitor C5, and transistor T,
A control signal is input to the base of capacitor C.
The output voltage Vi is obtained between both ends of 1. The transistor T is controlled by the output of an on-period control circuit 8, which is constructed by externally attaching peripheral components to a timer integrated circuit known as r555J. The on-period control circuit 8 is configured to be able to change the on-period of the transistor T by changing the impedance of the series circuit of the resistor R1 and the transistor T. In addition, the impedance of the transistor T can be adjusted using the transistors T*, T4 and the resistors R4~
This is done through a circuit configured by R7. That is, in the reference state, transistor T is off, transistor T is on, and transistor T2 is almost completely on. As the on-period of the transistor T increases, the impedance of the transistor T2 decreases, the on-period of the transistor T1 becomes shorter, and the output voltage Vi of the voltage control circuit 6 becomes lower. Furthermore, if the off-period of the transistor T increases, the impedance of the transistor T2 increases, the on-period of the transistor T1 becomes longer, and the output voltage Vi of the voltage control circuit 6 becomes higher. Resistor R2, capacitor C2, Zener diode ZD,
is the drive circuit 4. The power supply circuit, resistor R1, capacitor C1, and Zener diode ZD3 are power supply circuits for other parts of the control circuit 1. The zero cross detection circuit 7 detects the resonant current of the load circuit 5 based on the voltage obtained by dividing the voltage across the load circuit 5 by resistors Ra and Rs, and the voltage across the impedance Z connected in series with the switching element SW2. Detect zero crossing point. The configuration and operation of the zero-cross detection circuit 7 will be explained below with reference to FIGS. 4 to 6. FIG. 4 shows the operation when the zero-crossing point of the resonant current of the load circuit 5 and the switching timing of the switching elements SW, SW2 coincide with each other. In this case, the 41st m (h
) is lower than the reference voltage of the comparator 11, and the output level vb of the comparator 11 shown in FIG. 4(i) becomes "L". Therefore, the voltage Va shown in FIG. 4(1) The output level Ve of the AND circuit 12 is "L", and the inverting circuit 13 shown in FIG.
The output level vf of becomes "H". Therefore, the transistor T is turned off and the transistor T4 is turned on, resulting in the above-mentioned reference state, and the output voltage Vi of the power supply control circuit 6
is currently being maintained. Next, if the output frequency of the oscillation circuit 2 is increased to reduce the energy supplied to the load l, then
), when the switching elements SW, , sW2 are switched, currents II, I2 flow through the switching elements SW, , SW2 in the opposite direction to the arrows in FIG. Therefore, as shown in FIG. 5(h), the voltage Va across the impedance Z also becomes the current I. It occurs in the same direction as I2. Further, a falling detection circuit is configured by the inverting circuit 14, the capacitor C9°, and the resistor R1°, and when the voltage across the load circuit 5 falls, as shown in FIG. 5(j), the inverting circuit Since the input voltage Vc of the circuit 14 also falls, the potential Vd at the connection point between the capacitor C3° and the resistor R1° increases over time as shown in FIG. 5(k). At this time, the output level vb of the comparator 11 also temporarily becomes "H", so the output level Vc of the AND circuit 12 temporarily becomes "H'" as shown in FIG. 5(1). , transistor T, turns on, reducing the impedance of transistor T,. On the other hand, when the potential at the connection point between the capacitor C1° and the resistor R1o rises and the input level of the AND circuit 12 is "H", the input terminal of the AND circuit 16 becomes "L" through the inverting circuit 15, and the interface Since it is locked, the output level of the AND circuit 17 is also kept at "L", and the output level Vf of the inverting circuit 13 is kept at "H". Therefore, the transistor T continues to be in the on state in the reference state. As described above, the output Vg of the on-period control circuit 8 shown in FIG. 5(n) reduces the on-period of the transistor T1, and the output voltage Vi of the voltage control circuit 6 shown in FIG. 5(o) increases. It goes down. As a result, the energy supplied to the load circuit 5 decreases, the impedance of the load l increases, and the resonant frequency rises, so that the switching elements sw, sw , the currents I, , I2 flowing through the switching elements SW+, S
The switching timing of W2 almost coincides with the zero-crossing point of the resonant current of the load circuit 5. Next, a case where the output frequency of the oscillation circuit 2 is reduced so as to increase the energy supplied to the negative 'Frl will be explained based on FIG. 6. In this case, the currents flowing through the switching elements SW, SW2. I2 becomes as shown in FIGS. 6(f) and 6(g), and when the switching elements sw, , sw2 are switched, a current flows in the direction shown by the arrow in FIG. 3. Therefore, the sixth
As shown in figure (h), the voltage V across the impedance Z
a also has a current of 1. , I2. When the input voltage Va to the comparator 11 becomes a liability, the comparator 1
1's output level vb becomes "H", and FIG. 6 (e
), during the period when the voltage v0 across the load circuit 5 is 0, the output level of the inverting circuit 18 is "H", and in the second half of this period, as shown in FIG. As shown, the potential Vd at the connection point between the capacitor C3° and the resistor RIo is 0, and the output level of the inverting circuit 15 is "H".
Therefore, the output level of the AND circuit 16 becomes "H", and therefore the output level of the AND circuit 17 becomes "H".
As a result, the output level Vf of the inverting circuit 13 shown in FIG. As shown in Figure (n), the on period of the transistor T1 becomes longer, and the output voltage Vi of the voltage control circuit 6 becomes higher. That is, as the energy supplied to the load l increases, the impedance of the load l decreases, the resonant frequency of the load circuit 5 decreases, and the currents I+ and I2 decrease as shown by broken lines in FIGS. 6(f) and (g). changes. As described above, if the output frequency of the oscillation circuit 2 is changed to adjust the energy supplied to the load circuit 5, the output voltage of the voltage control circuit 6 is changed, so that the switching elements S W + and S W 2 The switching timing is controlled so as to coincide with the zero-crossing point of the resonant current of the load circuit 5, and as a result, almost no switching loss occurs and noise generation is reduced. In the above embodiment, the switching element SW. Although a field effect transistor is used as SW2, a switching element such as a transistor or a thyristor with a diode connected in antiparallel may also be used.A step-up chopper circuit is used for the voltage control circuit 6. However, it may be of a step-down type, and is not limited to the form of the embodiment as long as the output voltage can be varied.

[Example 2] When the load is a discharge lamp such as a fluorescent lamp, the impedance is almost constant and low when the lamp is on, and the impedance becomes very high when the lamp is not lit, and the impedance does not change significantly. be. therefore,
In the non-lighting state, if the switching elements sw, , sw continue to be switched near the zero-crossing point of the resonant current of the load circuit 5, the series circuit of the inductance L and the capacitor Ca in the load circuit 5 will be severely damaged. A large current flows, which may lead to destruction of the switching elements sw, , sw. In order to solve this problem, in this embodiment, as shown in FIG. A detection stop circuit 9 for stopping adjustment of the output voltage of the voltage control circuit 6 is provided. That is, the detection stop circuit 9 stops the operation of the zero-cross detection circuit 7 during the time from when the discharge lamp serving as the load 1 is started until it is lit, and during the period when the discharge lamp, which is the load 1, is in an unlit state due to turning off or the like. by this,
When the load 1 has high impedance, it is possible to prevent current from flowing into the inductance L and the capacitor Ca of the load circuit 5 more than necessary. During the period when the zero cross detection circuit 7 is not operating, the output frequency of the oscillation circuit 2 may be any frequency as long as it is not the resonant frequency of the load circuit 5; If the resonance frequency is set higher than the resonance frequency of No. 5, stress on the switching elements SW + and SW 2 will be reduced. FIG. 8 shows a simple concrete configuration of the load state detection circuit 10 and the detection stop circuit 9. The state of the load l is detected by the voltage across the load l, and the voltage across the load l is detected by the resistor R+ +
+ RI 2 divides the voltage and applies it to the base of the switching transistor S, and transfers the voltage to the switching transistor S.
-t L-〒≧, 1-lot no/I-' -d-7
It is connected to both ends of the wire Z. Hence the load! When the discharge lamp is not lit, the voltage across the load l increases and the transistor S is turned on, and the detection voltage to the zero-cross detection circuit 7 becomes 0, so the zero-cross detection circuit 7 cannot be stopped. It can be done. When the load 1 is turned on, the transistor S is turned off, so the zero-cross detection circuit 7 operates normally.

[Embodiment 3] In this embodiment, as shown in FIG. 9, the switching elements sw, , sw2 are not controlled by the output of the oscillation circuit 2, but the inductance of the load circuit 5 is controlled by the feedback coil CH+. A series circuit is formed with an inductance La having a winding, and switching elements sw, , sw are connected by the output of the feedback winding. It has an automatic configuration that controls. Choke coil C
A switch SW is connected in parallel to H, and by opening and closing the switch SW, the energy supplied to the load I is adjusted. Kometsui prayer/, -71. ＼Pl
Switching loss can be reduced by performing the ψ calculation 1 and the opening.

[Embodiment 4] In this embodiment, as shown in FIG. 10, the switching element SW2 is on/off controlled by the oscillation circuit 2 as in the first embodiment, and the switching element SW+ is controlled by the load circuit. Even in the configuration in which control is performed by the output of the feedback winding provided across the inductance No. 5, the effect of reducing switching loss is the same as in the first embodiment.

[Embodiment 5] As shown in FIG. 11, this embodiment is an example in which the alternating current power supply AC is controlled at a stage before the rectification and smoothing circuit 11 that obtains the power supply E, and the effect is different from that of the embodiment. It is the same as 1. Although the basic configuration of the embodiment shown above is a half-bridge type inverter device, even a full-bridge type or single-stone type can be configured to switch the switching elements at the zero-crossing point of the resonant current of the load circuit. If it is something,
The technical idea of the present invention is applicable to any inverter device having any configuration. In addition, the power source E may be a rectified and smoothed AC power source, and the AC power source may only be rectified for input to the voltage control circuit 6 having the configuration shown in Embodiment 1. The impedance Z to be detected is also not limited to the position of the embodiment.

【Effect of the invention】

As described above, according to the configuration of claim 1, the load circuit is configured so that the resonance frequency changes depending on the supplied energy, and the zero-cross detection circuit detects the zero-cross point of the resonance current of the load circuit, and the zero-cross detection circuit detects the zero-cross point of the resonance current of the load circuit. A voltage control circuit is provided to control the output voltage of the DC power supply so that the switching timing of the switching element coincides with the zero crossing point based on the output of the circuit, so that the switching timing of the switching element matches the resonance of the load circuit. This almost coincides with the zero-crossing point of the current, reducing switching loss and noise. In addition, since the output voltage of the DC power supply is controlled, the circuit configuration does not become complicated even if the energy supplied to the load circuit is continuously changed, making it easy to implement. . According to the structure of claim 2, since a detection stop circuit is provided that stops the operation of the zero-cross detection circuit at least when the load circuit is not in a stable operating state, By keeping the output voltage of the DC power supply constant, it is possible to prevent excessive current from flowing through the switching element, thereby preventing damage to the switching element.

[Brief explanation of drawings]

1 is a circuit diagram showing a first embodiment of the present invention, FIG. 2 is an explanatory diagram of the same operation, and FIG. 3 is a circuit diagram showing a specific configuration of the same,
4 to 6 are explanatory diagrams of the same operation as above, FIG. 7 is a circuit diagram showing Embodiment 2 of the present invention, FIG. 8 is a specific circuit diagram of the main part of the same as above, and FIG. 9 is an embodiment of the present invention Circuit diagram showing 3, 10th
The figure shows the solid line OIA*Yuno turntable a 箪1-1SUI1+
FIG. 12 is a circuit diagram showing a conventional example, and FIGS. 13 to 15 are explanatory diagrams of the same operation. 5... Load circuit, 6... Voltage control circuit, 7... Zero cross detection circuit, 9... Detection stop circuit, E... Power supply, SW, SW2... Switching element, l...・
load.

Claims (2)

[Claims] (1) Equipped with a switching element that is controlled on and off,
In an inverter device that converts DC power to AC output and supplies AC output to a load circuit, the load circuit is configured so that the resonant frequency changes depending on the supplied energy, and the zero-crossing point of the resonant current of the load circuit is detected. and a voltage control circuit that controls the output voltage of the DC power supply so that the switching timing of the switching element coincides with the zero-crossing point based on the output of the zero-crossing detection circuit. Inverter device. (2) The inverter device according to claim 1, further comprising a detection stop circuit that stops the operation of the zero-cross detection circuit at least when the load circuit is not in a stable operating state.