JP2681631B2 - AC power control device - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to an AC power control device, and more particularly to an AC power control for controlling AC power supply to a plurality of loads by a proportional zero-cross method using a thyristor, a triac, or the like. Regarding the device. (Prior art and its problems) Conventionally, when controlling AC power supplied to a load, a thyristor is connected between the load and the AC power supply, and the timing of generation of a trigger pulse for ignition given to the thyristor gate. The method of controlling the AC power supplied to the load by changing is widely adopted. There are generally two methods for controlling the gate pulse,
One of them is the so-called phase which controls the electric power in the range of 0 to 100% by controlling the firing angle timing for the phase angle of 0 to 180 ° with the zero potential cross point (called zero cross point) of the AC power supply as the starting point. Control method (Fig. 1), the other one is a basic unit of two consecutive gate pulses to be fired at the Xerox point, and by this gate pulse unit, one cycle of sine wave power is used for a certain period T period. There is a system (specifically, FIGS. 2 and 3) that controls the load power depending on whether (n units) is given, and this is called a zero-cross control system. In the system of FIG. 2 in the zero-cross control system, the period during which the power is supplied during the T period (ON period) is n cycles, that is, n × 20 ms (50 Hz) or n × 16.6 ms (60 Hz),
The power is zero (off) during the remaining T-n × 20 ms or T-n × 16.6 ms. That is, the power is turned on and off during the T period. The system of FIG. 3 is a system in which the power-on timing is dispersed evenly during the T period, and the n-cycle ON period is dispersed during the T period. As a drawback of each of these methods, in the case of the phase control method, the ignition period is the rear cycle of the power cycle, which is equivalent to the current of the delayed phase, and as a result, the power factor is poor even with a pure resistance load. become. In addition, transient noise is generated at the time of ignition, which also causes an obstacle. On the other hand, in the case of the zero-cross method, since the control is an on / off type control as a result, a load variation is given to the power source, a voltage variation is likely to occur, and other devices are adversely affected. When a plurality of loads using these control methods are connected in parallel, inconveniences due to these drawbacks increase and sometimes become a social problem. As an example, in a diffusion furnace which is a semiconductor manufacturing apparatus, one heater is divided into 3 to 5
The temperature of the furnace is controlled by the thyristor power controller of the phase control system. Since factories using many such furnaces all use the same phase control method, the power factor of the entire plant is bad at 60-70%, and the loss due to the reduction in power efficiency is significant. Even in the zero-cross method, when the on-cycle is similarly superimposed, the power fluctuation also increases and the timing of the superimposition is irregular, which may cause a large fluctuation from time to time. . A concrete example is shown in FIG.
Shown in In the figure, the on-cycles overlap and the power fluctuations occur at this point. (Object of the Invention) The present invention, in an AC power control device using a thyristor or a triac, when controlling the supply power by the zero-cross method, it is possible to control the power of a plurality of loads simultaneously between control systems (called zones). An AC power control device that adjusts the timing so that it does not turn on and does not affect the control as a whole, while improving the overall power efficiency of the power supply as a whole. Is. (Structure and Operation of the Invention) The AC power control device of the present invention connects two thyristors between a plurality of (n = 1 to N) loads and an AC power supply, and connects the two thyristors to each of the two thyristors. A plurality of control systems for supplying power to the load by igniting the thyristor in units of one cycle of the AC power supply by giving each one of two consecutive gate pulses (firing pulse) are provided.
By controlling the pulse output timing that gives two consecutive gate pulses to the thyristors of the plurality of control systems, the power supply in units of one cycle of the AC power in the period T having the fixed period T as a cycle is performed. In a zero-cross control AC power control device including a microcomputer that changes the number of on-cycles, the microcomputer controls the number of pulse output timings that can be output during the period T.
FT, the operation output is set for each of the plurality of control systems, and the operation amount C (n) that should be in an on-cycle for firing the thyristor during the period T to supply power to the load is calculated, and For each pulse output timing during the period T, for each control system, the number of on-cycles (B × C (n) / F) that should be fired up to the timing count B of that timing.
Output expectation x at that timing obtained by the difference between T) and the number A (n) of on-cycles that have already been fired
(N) = (B × C (n) / FT) −A (n) is calculated, and the obtained output expectations of the respective control systems are compared with each other. The firing pulse output priority is determined, and the total number XT of the number of on-cycles (B × C (n) / FT) to be fired by the timing number B of each control system over the entire control system and the timing number B Total AT over all control systems with on-cycle number A (n) already fired at
When the AT is smaller than XT, the ignition system outputs the ignition pulses of the control system in the order of the higher priority order of the ignition pulse output to be an on-cycle, and when the AT is equal to or larger than XT, the control system is It is characterized in that the ignition pulse is controlled so as not to be output. (Example) The present invention will be described in detail below with reference to the drawings. The gist of the AC power control method in the device of the present invention is, as shown in the conventional example of FIG.
(A), (b), (c) three) load control systems (hereinafter referred to as zones), the on-cycles due to the zero-cross output pulses supplied to the thyristors overlap at the points of As shown in FIG. 5, the microcomputer controls the timing so as not to overlap each other. By doing so, in AC power control using a thyristor, the current was reduced to 60% to 90% in effective value (depending on the manipulated variable) compared to the case of phase control. FIG. 6 shows an example of an AC power control device to which the AC power control method of the present invention is applied. In the figure, reference numeral 1 is a microcomputer for executing a control algorithm which is a main part of the present invention. The control signal converted into a digital value by an AD converter or the like is taken into the microcomputer 1. In the microcomputer 1, proportional, integral, and derivative (PID) operations are performed by taking the difference from the target value, and the operation result becomes an operation output. This device adopts a zero-cross proportional control method in which the on-timing is dispersed, and the timing of the zero-cross pulse is applied to the microcomputer 1 by the zero-phase synchronization detection circuit 2 from the power supply, and the thyristor points of two consecutive thyristor points are synchronized with the timing. The arc pulse is determined by the microcomputer 1 and applied to the thyristors 5 to 5a via the program counters 3 to 3a and the pulse amplifiers 4 to 4a of the control system of the loads 6 to 6a. In the present invention, the timing of outputting two consecutive thyristor firing pulses to turn on one cycle of the AC power supply is called pulse output timing. The operation output is usually given at 0 to 100%, and now, for a certain period T (for example, T = 5 seconds, in a 50Hz power source,
250 cycles), with 100% of all on-cycles (ie, full power) and 0% of all off-cycles (ie, zero power) for that period T, and the number of on-cycles during the T period is proportional to Shall be controlled. That is, the operation output (%) is converted by the microcomputer 1 into the number of on-cycles (operation amount), and this is distributed on average during the T period. That is, the microcomputer 1 calculates the number of on-cycles during the T period in order to supply the electric power to the loads 6 to 6a in each zone, but the point of each thyristor is calculated by the algorithm described in the following operation section. Arc pulses are generated by the pulse amplifiers 4-4a so that the on-cycles of each zone do not overlap at the same time as much as possible. Naturally, if the total number of on-cycles to be fired during the T period of each zone is larger than the number of cycles of the T period (the number of pulse output timings that can output the firing pulse), overlapping occurs, but this also occurs. It is intended to disperse as averagely as possible. The timing of the on-cycle is determined by the ratio of the number of on-cycles already fired to the number of cycles (timing number) up to that point at each 20 ms interval during the T period. A method is adopted in which the ratio is closest to the ratio of the number of on-cycles to be fired to the number. Further, for a plurality of loads as in the present device, first of all, regarding which zone of each zone the thyristor should be outputted with an ignition pulse to be on-cycle,
For each pulse output timing during the period, calculate the output expectation expressed by the difference between the number of on-cycles to be ignited and the number of ignited on-cycles for each zone up to the other time points. The priority order of the ignition pulse output (on cycle) is determined in order from. Next, the total sum XT of the on-cycle numbers of all zones to be ignited by that timing is compared with the total sum AT of the number of ignited on-cycles of all the zones, so that it should be output at that timing. If AT <XT, it is determined that the firing pulse should be output to the zone, and if AT ≧ XT, it is determined that the firing pulse is not output to the zone. Then, the basic algorithm is to sequentially control the firing pulse output to the thyristors in each zone in accordance with the priority order. This is shown in the flowchart of FIG. The program of the flow of FIG. 7 is executed by the microcomputer 1 of FIG. 6 and is activated in synchronization with the interrupt timing of the zero-potential synchronization detection circuit 2 that detects a zero-cross point. In the algorithm of this flow, the reason why the on-timing of each zone does not overlap is that the ignition on-cycle of all zones (control system) is satisfied so that equation (3) always holds under the condition of FIG. Total number AT
To increase the point P to T while increasing the value of T. At this point, the sum CT of the manipulated variables (the number of on-cycles) of all zones to be output during the T period is evenly distributed during the T period. become. That is, according to FIG. 8, the following equation holds when the output pulses are distributed in a well-balanced manner. FT: B≈CT: AT (1) However, if the number of pulse output timings (= the number of cycles of the T period) that can be output during the FT: T period, for example, with a 50Hz commercial power supply, a 5 second period is the basic period T , FT = 250) B: Number of timings up to a certain time point (point P) CT: Manipulation amount of all zones during T period, that is, sum of manipulation amount of each zone (number to be on-cycle) C (n) AT: The number of on-cycles in all zones up to a certain time (point P), that is, the number of ignited on-cycles in each zone up to point P
Rewriting equation (1) gives the following equation. FT x AT ≒ B x CT (2) Here, since the AT in equation (3) is the total number of on-cycles in each zone over all zones, the on-cycles in each zone are output so that they do not overlap each other as much as possible. Further, the reason that the on-cycles of the specific zones are not biased to a part is that the output expectation of each zone is obtained for each pulse output timing and the on-cycles are set in descending order of the output expectation. In FIG. 7, the start is entered for each pulse output timing that can be output. The output expectation x (n) of each zone shown in step (35) is x (n) = (B × C
It is represented by (n) / FT) -A (n), and the larger x (n), the higher the output expectation. Further, in step 40, the processing loop is started from a zone (or channel) having a high priority. Next, the flowchart of FIG. 7 will be described. An interrupt is started at each pulse output timing that can be output, and it is determined whether the pulse output timing count B up to that point has reached the pulse output timing count FT of the period T (5). ), And if not yet reached, determine whether there is a change in the number of on-cycles (manipulation amount) C (n) that should be fired for all of the zones (n = 1 to N) (15), and change If there is, the on-cycle number (operation amount) C (n) to be fired is changed (20). After this processing loop ends (10) for all zones, (25)
If there is a change in any of the number of on-cycles (operation amount) C (n) that should be fired in each zone after shifting to, the total CT of the number of on-cycles (operation amount) C (n) that should be fired To clear the number of fired on-cycles AT in all zones.
If there is no change in C (n), the process shifts to (30), and the timing count B is increased by one. In (35), output expectation x for each zone (control system)
(N), that is, the difference between the number of on-cycles (B × C (n) / FT) to be ignited by the pulse output timing and the number of on-cycles A (n) ignited up to that point, That is, the rest of the number of on-cycles to be fired during the T period is calculated, and the firing pulse is output in the descending order of the rest, that is, in the descending order of the output expectancy, and the on-cycle priority is determined. After (40), the processing is performed in the given priority order. In (45), the total sum XT of the on-cycle numbers of all zones to be ignited by that timing is calculated, and in (50) the total sum AT of the number of ignited on-cycles of all zones and the total number of zones to be ignited. When the total number of on-cycles is compared with XT, if AT is smaller than XT, an ignition pulse is output to that zone at (65) to turn it on-cycle, and then return to (40) to have the next highest priority. Similar processing is performed for the zone. At (50), when AT is XT or more, the ignition pulse is not output to that zone and the process returns to (40). This is repeated until the processing is completed for all zones. (Effect of the Invention) As will be understood from the above description, the present invention has the following effects. (1) Compared with simple zero-cross AC power control, the current superposition of multiple loads is reduced, power consumption is leveled, and voltage fluctuations are reduced. (2) Phase control Compared with AC power, the effective value of the current is reduced and the power factor is improved.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a waveform diagram for explaining a gate trigger pulse and an AC control waveform in a phase control system, FIG. 2 is a waveform diagram for explaining on-off type zero-cross control, and FIG. FIG. 4 is a waveform diagram for explaining zero-cross control, FIG. 4 is a waveform diagram for explaining an example of weighting of zero-cross waveforms in conventional multiple loads, and FIG. 5 is a waveform diagram for explaining an operation of adjusting overlap of zero-cross output waveforms of the present invention. FIG. 6 is a block diagram showing a configuration example of the device of the present invention, FIG. 7 is a flowchart showing an operation example of the present invention by the N-zone time division distributed proportional zero-cross method, and FIG. 8 is an explanatory diagram of the operation principle of the present invention. 1 ... Arithmetic control microcomputer, 2 ... Zero phase synchronization detection circuit, 3, 3a ... Programmable counter, 4, 4a
...... Gate pulse amplifier, 5,5a …… AC control thyristor (or triac), 6,6a …… Load.

Claims (1)

(57) [Claims] Two thyristors are respectively connected between a plurality of (n = 1 to N) loads and an AC power supply, and each one of two consecutive gate pulses (firing pulse) is given to each of the two thyristors. A plurality of control systems for supplying power to the load by igniting the thyristor in units of one cycle of the AC power supply are provided, and pulse output timing for giving two consecutive gate pulses to the thyristors of the plurality of control systems In the AC power control device of the zero-cross control method, which is equipped with a microcomputer that changes the number of on-cycles of power supply in units of 1 cycle of AC power in the period T having a fixed period T as a cycle, The microcomputer determines the number of pulse output timings that can be output during the period T by FT.
The operation amount is set for each of the plurality of control systems, and the operation amount C (n) that should be in an on-cycle for igniting the thyristor to supply power to the load during the period T is calculated. For each pulse output timing in T, for each control system, the number of on-cycles (B × C (n) / F) to be fired up to the number of times B of the timing
Output expectation x at that timing obtained by the difference between T) and the number A (n) of on-cycles that have already been fired
(N) = (B × C (n) / FT) −A (n) is calculated, and the obtained output expectations of the respective control systems are compared with each other. The firing pulse output priority is determined, and the total number XT of the number of on-cycles (B × C (n) / FT) to be fired by the timing number B of each control system over the entire control system and the timing number B Is compared with the total sum AT over the entire control system of the number of on-cycles A (n) that has already been ignited, and while the AT is smaller than XT, the ignition pulses of the control system are output in descending order of priority of the ignition pulse output. And an on-cycle, and when the AT becomes equal to or larger than XT, the control system controls so as not to output an ignition pulse.