JPS6111069B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for digitally controlling a firing phase controlled power converter comprising a plurality of controllable electric valves.

With recent remarkable technological advances in microcomputers, various studies have been made to digitize control devices in the field of controlling this type of power converter.

In this case, it is always desirable from an economical point of view to realize the various functions that a control device should have using as few microcomputers as possible.

For example, in the case of a thyristor converter that is connected to an AC power source and supplies power to a DC load, the functions necessary for controlling the current thereof are represented by two functions: a current adjustment function and a firing angle adjustment function. At present, the only way to digitize these functions is to inherit the idea of the conventional analog system and simply digitize it in a very general way. For example, regarding the current regulation function, the current target value and current actual value are sampled at a predetermined fixed time interval, and each time arithmetic processing such as PI or PID is executed according to a predetermined algorithm. be. Regarding the firing angle adjustment function, the starting point for the counter operation for adjusting the firing angle is provided by a synchronization signal derived from the AC power supply voltage.

For example, in the case of a power converter consisting of three-phase bridge-connected thyristors, firing angle adjustment must be carried out for six thyristors. Although it is not that difficult to make these firing angle adjustments with a single microcomputer, if the method described above was adopted, the microcomputer would have to run at extremely high speeds. The current commercially available N-
It is difficult to satisfy this requirement with a MOS type microcomputer. Even if such dual use could be realized, in this case the performance of at least one of the two functions would have to be degraded to an unacceptable level.

SUMMARY OF THE INVENTION In view of the above, it is an object of the present invention to provide an adjustment function for a controlled variable, such as current, and a firing angle adjustment function for all controllable electric valves in a power converter, each with sufficient performance. The object of the present invention is to provide a digital control method that can be realized with a single microcomputer while ensuring the same.

This object, according to the invention, is to provide a method for digitally controlling the firing phase of a power converter consisting of a plurality of controllable electric valves, each time a firing signal for one of the controllable electric valves is generated. , the time until the next ignition signal should be generated using the generation point as the time reference, is determined in the steady state according to the calculation result for controlling the control amount using the target value and actual value of the control amount. It is determined by modifying the predetermined firing interval, and is selected to fire each time it is detected that the time determined according to the arithmetic processing result has elapsed from the time when the previous firing signal was generated. This is achieved by generating a firing signal for a controlled electric valve.

For example, in the case of a power converter consisting of six thyristors connected in a three-phase pure bridge, these thyristors are fired at time intervals corresponding to an electrical angle of 60 DEG in steady state conditions. In the present invention, the correction amount +Δm _o of the control amount adjustment calculation result is added to this predetermined firing interval, and a time corresponding to 60° + Δm _o has elapsed from this point based on the firing signal generation time point. When the arrival of the thyristor is detected, a firing signal for the respective selected thyristor is generated. In this case, if the previous firing angle was α, the next firing angle would be α+ _Δmo .

In contrast, in conventional control methods, the synchronous voltage is extracted for each individual thyristor from the AC power supply voltage of the power converter, and the reference point is the point at which the synchronous voltage passes the zero point (the point corresponding to the firing angle of zero). When the arrival of a time corresponding to the desired firing angle is detected, a firing signal for the corresponding thyristor is generated.

In the case of conventional control methods, a function is provided for each thyristor to detect when a time corresponding to the desired absolute firing angle has elapsed from a synchronization point corresponding to a zero firing angle (e.g. counter function) starts working. Since synchronization points at which these functions operate occur at 60° intervals, three sets of such functions must be able to operate in parallel at the same time in order to make the firing angle variable within the range of 0° to 180°.

In contrast, according to the control method of the present invention, the predetermined firing interval in a steady state is corrected by the relative correction amount Δm _o with respect to the previous firing angle, and Since the arrival of the time corresponding to the correction result is detected, it is sufficient that only one set of the above-mentioned functions can be operated at any time. Therefore, according to the present invention, when implementing a control method using a microcomputer, it is possible to simplify the hardware or reduce the processing responsibility of the processor.

Further, according to the control method according to the present invention, since the firing signal itself is the time reference for the generation point of the next firing signal, the control amount for correcting the predetermined firing interval in the steady state It is possible to synchronize the adjustment calculation process with the ignition signal without difficulty.
In particular, it is sufficient to perform such arithmetic processing only once between the time when an ignition is performed and the next ignition is performed, and it is wasteful to perform such arithmetic processing more than once. Through such synchronization, the control adjustment calculation process can be performed while guaranteeing that the control amount adjustment calculation process is executed at least once in the time space between two temporally adjacent firing signals. , it is possible to perform only a minimum of one controlled variable adjustment calculation process in that time space.

Conventionally, the control amount adjustment calculation process is not synchronized with the ignition signal and is executed at a short constant sampling period regardless of the ignition signal. If it is attempted to guarantee that the controlled variable adjustment calculation process is executed at least once in the time space between the ignition signals, a sampling period will inevitably occur in which the controlled variable adjustment calculation process is executed two or more times in vain. For this reason, conventional methods have required the microcomputer to do extra work, which has sometimes sacrificed other processing.

Hereinafter, the present invention will be explained in more detail with reference to embodiments shown in the drawings.

FIG. 1 shows an example of a hardware configuration for implementing the power converter control method according to the present invention. In this figure, reference numeral 1 denotes, for example, a three-phase pure bridge-connected thyristor converter, whose AC side is connected to a three-phase AC power source 3 via a power transformer 2. A load 4 is connected to the DC side of this converter. 5 is a microprocessor, which includes a CPU 51 and a memory 5.
2 and an input/output interface 5, and according to the present invention, it has a current adjustment function and a firing angle adjustment function. microprocessor 5
The current target value of the digital display to be input into is given by the current setter 6. Further, the actual current value is detected via the current transformer 7, converted into a digital quantity by the A/D converter 8, and input to the microprocessor. Furthermore, the synchronization signal to be guided to the microprocessor is transmitted through a synchronization signal step-down transformer 9 and a quantization circuit 10 connected to the AC power supply 3.
given by. Microprocessor 5 outputs a firing signal for pulse amplifier 11.

The pulse amplifier 11 then supplies a firing pulse to the corresponding thyristor in the thyristor converter 1 via the pulse transformer 12 in accordance with its firing signal.

FIG. 2 is a block diagram showing the control system of FIG. 1 in a simple form, with reference numeral 20 indicating a control section and 21 indicating a controlled object. C is the actual value of the controlled variable, which in the example of FIG. 1 is the actual current value. r is the target value of the controlled variable, and in the example of FIG. 1 is the current target value. Furthermore, m is a manipulated variable, which in the example of FIG. 1 can be considered to be a firing angle.

For the previous operation amount m _o-1 , this time it is Δ
Assume that only m _o should be corrected and it should be output as the current manipulated variable m _o . In other words, m _o = m _o-1 + Δm _o ...(1). It is assumed that m takes a positive value, and Δm _o can take either a positive or negative value. For example, in the case of the PID adjustment principle, the calculation formula for determining Δm _o is as follows.

Δm _o = Kp (C _{o -1 -} C _o ) + K _I (r _{o -} C _o ) + K _D (2C _{o -1} - C _o - C _{o -2} ) ...(2) However, the suffix for r and C n is the current sample value, n-1 is the previous sample value, n-2
represents the sample value from the previous time. Also, as is well known, in the above equation, Kp is a proportional constant, K _I is an integral constant, and K _D is a differential constant.

If the thyristor converter 1 has a three-phase pure bridge connection, firing signals are generated sequentially at intervals of 60° in a steady state. Therefore, the previous firing angle m _o-1
If the next firing angle m _o is to be corrected by △m _o to All that is required is to generate the next ignition signal.

In this case, which thyristor to generate a firing signal for firing is determined each time by firing phase determination processing based on the synchronization signal. Therefore, the microprocessor 5 has an angle of 60°+Δ
Within the time corresponding to the electrical angle of m _o , the above-mentioned
PID calculation processing and firing phase determination processing must be performed. The time required for the ignition phase determination process is almost negligible; however,
How much time it takes to process PID calculations may be an issue. However, the execution time of the program that implements PID calculation using the 8080A, which is currently the world standard 8-bit microcontroller, is approximately 0.5 msec, which is approximately 50 msec.
When the electrical angle is approximately 9° with Hz power supply and approximately 11° with 60Hz power supply, and Δm _o takes a negative value,
In general, the size of the angle does not exceed 20° (even if it does, it is easy to set appropriate limits). Considering these things collectively,
The time required for PID calculation processing is also not a particular problem.

FIG. 3 shows an example of a flowchart of processing operations performed by the microprocessor 5. The microprocessor 5 reads the current target value and the current actual value, and performs PID calculation processing (~). Next, from the PID calculation processing result Δm _o , calculate the count value X for the counting operation to detect the arrival of the next ignition point by using the formula shown in
(The meaning of Θ in this equation will be explained later.) Then, for example, store the value X in a counter register, and subtract the value () whose value becomes zero. Next, read the synchronization signal. Then, based on the synchronization signal (taking into consideration the range to which the current firing angle m _o commanded by the PID calculation result belongs), a firing phase determination process is performed to determine which thyristor should be fired next. Based on the result, a firing signal corresponding to the selected thyristor is output (). This firing signal supplies a firing pulse to the thyristor through the corresponding pulse amplifier 11 and pulse transformer 12. After the microprocessor outputs the ignition signal, it replaces the current manipulated variable m _o found in the memory location designated to accommodate the previous manipulated variable m _o-1 ( ), return to , read the target current value, read the actual current value,
Performs PID calculation processing. Thereafter, similar operations are repeated. Here, in addition to replacing the manipulated variables, it is also possible to shift the storage location of the current target value and current actual value as past values in preparation for the next calculation.

In particular, regarding the manipulated variable _mo , if a value _mo different from the result of PID calculation is executed due to firing angle restrictions, etc., _mo should be the executed value.

Regarding Θ in the formula for the count value If the counter operation is to be started immediately after the arc signal is generated, Θ=0° may be used. However, the time required for PID calculation to process ignition phase judgment etc. is a known value depending on the program, so
Set the value of Θ taking into account that time, and
Even if you perform a counter operation after calculation processing, perform ignition phase judgment processing after counting up, and then output an ignition signal, the ignition signal will be output from the previous ignition phase occurrence point. This method is preferable because the result is the same: the interval up to the point in time when the arc signal is generated is 60° + Δm _o .

When setting a limit on the firing angle range, the next firing angle m _o = m obtained by adding the firing angle correction amount Δm _o obtained in the PID calculation process to the previous firing angle m _o
When _o-1 +Δm _o exceeds the limit range, the next firing angle is forcibly kept at the minimum limit αmin value or maximum limit value αmax, and the correction amount Δm _o is determined again by calculating backward from that limit value. The counter value X may be determined based on this.

The firing phase determination is performed, for example, as follows. First, by reading the synchronization signal, it becomes clear in which phase range of the AC power supply voltage the current phase point is located. For example, in the case of a three-phase pure bridge-connected thyristor converter, 1 of the AC power supply voltage
The cycle is divided by the natural commutation point (point of zero firing angle) into six phase ranges each spaced by 60°.

Once such a phase range is known, the command value m _o of the firing angle of the thyristor to be fired next is
αmin~60°, 60°~120°, or 120°~
Depending on the range of αmax, it is possible to determine which thyristor should be fired next time.

The actual current value is not limited to being read once, but may be read a predetermined number of times at regular intervals, and the average value thereof may be used as the actual current value for PID calculation. In addition, PID calculation is not limited to one time,
This may be done a certain number of times if the microprocessor has room, but generally once is sufficient. It goes without saying that the synchronization signal reading and firing phase determination processing can be performed before the counter operation. Furthermore, the controlled amount is not limited to current, but may also be voltage, for example.
Further, the calculation is not limited to PID calculation, but may be PI calculation or P calculation. Further, for example, if the constant value Θ is taken into consideration, there is a possibility that the microprocessor can perform other processing.

Another process is, for example, arithmetic processing for speed adjustment for a thyristor Leonard device,
In this case, the current target value is formed within the microprocessor according to the result of the calculation process.

As described above, according to the control method of the present invention, the predetermined firing interval in a steady state is modified according to the calculation result for adjusting the control amount, and Next, find the time until the point when the ignition signal should be generated,
The system generates a firing signal for the controllable electric valve selected to fire each time it detects the arrival of the time exactly after the calculated time has elapsed, so it measures the elapsed time from the reference time. In addition, only one set of functions for monitoring the coincidence of the elapsed time and the time corresponding to the result of adjustment calculation processing is required. Therefore, when implementing the control method using a microcomputer, the hardware It is possible to simplify or reduce the processing responsibility of the processor. Furthermore, according to the control method according to the present invention,
Since the ignition signal itself is the time reference for the next ignition signal generation point, the execution of the control amount adjustment calculation process that corrects the predetermined ignition interval in a steady state is synchronized with the ignition signal. To be able to perform the control without difficulty, and in particular, to perform only one necessary minimum control amount adjustment calculation process between once ignition is performed and the next ignition is performed. I can do it.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing an example of a hardware configuration for implementing the control method according to the present invention, and FIG.
FIG. 3 is a simplified block diagram of the control system shown in FIG. 3, and FIG. 3 is a flowchart showing an embodiment of the control method according to the present invention. 1... Thyristor converter, 2... Power transformer,
3... AC power supply, 4... Load, 5... Microprocessor, 6... Current setting device, 7... Current transformer, 8
...A-D converter, 9...Step-down transformer for synchronous signal, 10...Quantization circuit, 11...Pulse amplifier, 12...Pulse transformer.

Claims (1)

[Claims] 1. In a method of digitally controlling the firing phase of a power converter consisting of a plurality of controllable electric valves, each time a firing signal for any controllable electric valve is generated, the next time is The predetermined firing interval in a steady state is corrected according to the calculation result for adjusting the controlled variable based on the target value and actual value of the controlled variable. When it is detected that the time determined according to the arithmetic processing result has elapsed from the time when the previous ignition signal was generated, the controllable electric valve selected to be ignited each time is A method for digitally controlling a power converter, characterized in that it generates an ignition signal.