FI82799C - Power regulator for lamp load connected to an AC network - Google Patents

Description

! 82799

Lamp load power regulator connected to the AC mains.

The power regulator for the lamp housing is connected to the power supply.

The invention relates to a power regulator for a lamp load, in particular incandescent lamps, connected to the AC mains, having a bi-directional switching element connected in series with the load, controlled in each half cycle to switch off only from the mains to the load but allow current to flow in the opposite direction. A second bidirectional switching element must be connected in parallel with the load, which is controlled in each half cycle to prevent the flow of current in the direction of the mains voltage, but to allow the flow of current in the opposite direction.

Such a power regulator is known from Applicant's U.S. Patent 4,456,855.

Here, as in other known power controllers based on the use of phase angle control, the problem is the harmonics generated in the supply network, which are caused by the high rise rate of the current. In demanding installations where effective attenuation of audio frequency mains interference is therefore necessary, it has been necessary to equip the thyristor and triac controllers with large inductive series chokes. Such additional attenuation is typically necessary, for example, in studios and theaters where audio amplifier equipment is used. However, additional chokes are physically large, heavy, and expensive, increase installation costs and power dissipation, and cause audible noise.

The object of the invention is to improve said type of power regulator so that the proportion of lower harmonics in the current taken by the regulator from the network and fed to the load can be substantially reduced.

2 82799 This object is achieved by the invention in that a capacitor is connected in parallel with said switching element, between the phase of the supply network and the load. The capacitor must be dimensioned large enough to achieve a small proportion of mains and load current harmonics.

In the following, the invention will be described in more detail with reference to the accompanying drawings, in which Figure 1 shows a block and circuit diagram of a power controller according to the invention.

Fig. 1A shows the timing of the control signals of the controller switches during normal control operation (switches S1 and S2 conduct).

Figure 2 shows a schematic circuit diagram of the power controller.

Figure 2A shows the timing of the controller switches when the control is at a minimum (S1 and S2 do not conduct).

Fig. 2B shows the timing of the controller switches when the control is halfway and Fig. 2C shows the timing of the controller switches when the control is at its maximum.

Figure 3 shows the waveforms of the power stage voltages when the control is at a minimum (S1 and S2 do not conduct).

Fig. 3A shows voltage waveforms when the control is halfway and Fig. 3B shows voltage waveforms when the control is close to the maximum.

Figure 4 shows graphically the harmonic pro-

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3,82799 centimeters of the fundamental wave and Figure 5 graphically shows the harmonics of the mains current as a percentage of the fundamental wave.

The main parts of the power regulator shown in Fig. 1 are: C1 is a capacitor with a high capacitance, which provides a low rate of change of the current taken from the network. The semiconductors V1, V2, V5 and V6 form a controlled bidirectional switching element for controlling the load current. The semiconductors V3, V4, V7 and V8 form a switch unit connected in parallel with the load, the load capacity of which needs to be substantially lower than that of the first-mentioned semiconductor switch element. K1 and K2 are controlled electromechanical switches (e.g. relays or contactors). Li is a rather low-inductance choke which, together with capacitors C4 and C5, forms the RF filter of the device and also helps in the overcurrent protection of the longitudinal switching element V1 / V2. Surge protection is implemented with components R1, C2, R2, C3 and F1 and F2, the latter of which are high-speed surge protectors (e.g. zinc oxide varistors). The control circuit Ai contains the necessary power supplies and the connections required for synchronization with the mains, and A2 takes care of the actual control of the device.

The operation of the power controller is as follows. The power control of a load connected between ^ - N takes place inversely compared to a conventional thyristor and / or triac controller, where current is applied to the load from a certain trigger moment until the end of the mains half-cycle, whereby the power switch is switched off. as a result of natural commutation. In this controller, on the other hand, V1 and V2 start conducting current at the zero point of the mains voltage and continue until a certain cut-off moment, after which the switch element v1 / V2 cuts off the current going to the load. If there were no capacitor C1, a power failure would occur rapidly, with a large amount of harmonics. Now, however, when the element V1 / V2 ceases to conduct, the load receives current through the large capacitor C1 4 82799 and the power failure occurs slowly and thus with little interference.

The device also has a so-called a transverse switching element V3 / V4, the purpose of which is to prevent a change in the direction of the load voltage following the switching off of the switching element V1 / V2 under the action of a capacitor C1 during each mains cycle, which would be very detrimental when the longitudinal element V1 / V2 tends to conduct at the next mains voltage zero. In this case, a large voltage difference between the network and the load would cause a dangerously large current peak through the element V1 / V2. In addition, with the transverse element V3 / V4 the so-called post-adjustment in a situation where the lamp voltage is desired to be minimum (V1 / V2 does not conduct). In this case, the current flowing through the capacitor C1 into the load may cause the low-wattage incandescent lamp to burn too brightly. With the help of the switching element V3 / V4, the load voltage can be set to zero if necessary.

The general timing of the control signals for the operation of the switching elements is shown in Figure 1A. The timing margins shown are necessary to prevent the possibility of a phase short circuit caused by switch delays. The timing of the operation of the switch elements in different control situations is shown in Figures 2A-2C. The waveforms essential for the operation of the power regulator (resistive or incandescent load 11a) are shown in Figures 3, 3a and 3b). In these figures, Uv is the mains supply voltage (phase voltage), Uj ^ is the load voltage and Uc is the voltage across the capacitor C1.

With an incandescent lamp load, cold filaments can be heated by a current conducted through a capacitor C1 before the switching element V1 / V2 is made conductive. Thus, a current spike through the switching element V1 / V2 is prevented.

When the controller is started, the switch K1 is controlled to be conductive after a random delay for a certain period of time from the moment the device was connected to the network. In this way, the switching current impulse caused by the controllers individually connected to the same network phase can be minimized. Another alternative is that the moment of switching on the switch K1 is determined by one controller of the controller group, the so-called a master that transmits that control information to other controllers via a digital serial bus.

Of the semiconductor switches, switch V1 or switch V2 is conductive throughout its mains half-cycle, in which case it does not normally conduct load current. Thus, the load voltage is prevented from exceeding the mains voltage, as also disclosed in Applicant's U.S. Patent 4,456,855.

Bipolar power darling transistors, MOSFET power transistors, gate-cut thyristors or IGT transistors can be used as switching elements V1 to V4 of the device. Figure 1 shows the implementation of a bidirectional switching element with a bipolar power darlington. The advantage of the bidirectional switching element implemented in this way is that the voltage of the load cannot in any case exceed the voltage of the network, because it is possible to provide an unobstructed path for the current from the load to the network. However, this possibility is not exploited in the timing diagrams of Figures 2B and 2C. In this case, for example, S1 should be on throughout the negative half cycle.

Central to the usability of the device is operation in the following special situations: - switching on the supply voltage, - short-circuiting or overloading the load - interrupting the supply voltage.

When switching on the voltage, the transverse switching element V3 / V4 should be guided continuously at all times before the main switch K1 is closed, in order to prevent the flash of light visible in the lamps during switching on. If C1 is completely discharged before the switch-on takes place, a large current impulse passes through the element V3 / V4. To avoid the resulting need for oversizing, the device has an electromechanical switch K2 6 82799 alongside element V3 / V4. The contacts of this are closed during the switching on of the voltages when the contact of the switch K1 closes. Switch K2 is only opened when the switching current impulse has passed and element V3 / V4 is controlled to be fully conductive. The main switch Kl is required in high-power devices due to electrical safety regulations.

Due to a possible short circuit in the load, circuit Ai must include protection logic to protect elements V1 / V2 and V3 / V4 from overcurrent. When using transistors, the protection circuit can be based on monitoring the saturation voltage of the transistors. This also has the advantage that in this case the switching on of the transistors is possible only at the zero point of the voltage and the operation becomes more reliable also in the event of possible malfunctions of the logic circuit A2. At the same time, excessive device lamp loads prevent the device from being used.

If it is desired to disconnect the device from the mains, the V1 / V2 element must take care of switching off the load current, after which the contacts of the switch K1 are opened. When the switch K1 opens, care must be taken to discharge the capacitor C1 from the element V1 / V2 so that a dangerously large amount of charge is not stored in this large capacitance.

Thus, the electromechanical switch K1 does not have to switch on or off the load current of the device, but this is taken care of by the switch element V1 / V2, thus reducing the electrical stress on the contacts of the switch K1.

Figures 4 and 5 show a comparison of mains and load current harmonics with a thyristor controller with an additional choke. The higher proportion of upper harmonics shown in Figure 5 is not a serious problem for the device according to the invention, as these higher frequencies can be physically attenuated by a reasonably small filtering circuit (components Li, C4, C5).

I! 7 82799

In the measurements shown in Figures 4 and 5, the load was 2.2 kW incandescent lamps, the ignition / cut-off angle was 90 ° and the current 10% / 90% rise / fall time was 850 / is. In this case, the weight of the additional choke required by the thyristor / triac controller is about 60 times the weight of the required capacitor and the cost is about 4 times. The external dimensions of the choke are 125 x 100 x 130 mm ^. The capacitor has a diameter of 40 mm and a height of 75 mm, respectively. This capacitor, unlike the above-mentioned choke, does not substantially increase the physical size of the control device and can be placed inside the device housing, which reduces electrical installation costs.

Claims (7)

8 82799 A power regulator for a lamp load, in particular incandescent lamps, connected to the AC mains, comprising: - a first two-way switching element (S1 / S2; V1 / V2) connected in series with the load, controlled in each half cycle to switch off only , and - a second bidirectional switching element (S3 / S4; V3 / V4) connected in parallel with the load, controlled in each half cycle to prevent current flow in the direction of the mains voltage but to allow current flow in the opposite direction, characterized in that said first switching element (S1 / S2; V1 / V2), a capacitor (C / Cl) is connected between the supply network phase and the load. Power regulator according to claim 1, characterized in that the current impulse through said second switching element (V3 / V4) is blocked by an electromechanical switching element (K2) when the switch (K1) connecting the device to the mains is closed. Power regulator according to claim 1 or 2, characterized in that with the incandescent lamp load, the cold filaments are heated by a current conducted through said capacitor (C1) before the first switching element (V1 / V2) is made conductive to prevent a current spike through said switching element. Power regulator according to one of Claims 1 to 3, characterized in that when the mains supply is interrupted, the first switching element (V1 / V2) takes care of discharging said large capacitor (C1) in order to ensure absolute safety. Power regulator according to any one of claims 1 to 4, characterized in that said first switching element (V1 / V2) switches off the load current, thus reducing the electrical stress on the contacts of the electromechanical switch (K1) connecting the device to the mains. Power controller according to one of Claims 1 to 5, characterized in that the switch (K1) connecting the device to the mains is switched on after a random delay in a certain time from the time the device was connected to the network in order to minimize the switching current caused by control units connected to the same network phase. . Power controller according to one of Claims 1 to 6, characterized in that the moment of switching on the switch (K1) connecting the device to the mains is determined by one device in the controller group, the so-called a master that transmits that control information to other devices via a digital serial communication bus. 10 82799 Paten.tk.rav