JPS626432B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention provides a direct digital control device for variable speed control of a DC motor or the like that is supplied with power via a power converter such as a thyristor by controlling the firing angle of the thyristor. (DDC), and more generally, detects the actual load current value of an inductive load supplied via a converter,
A DDC that calculates the firing control angle of the converter and controls the firing angle accordingly to control the load current.
In the device, highly accurate detection of the actual value of the load current,
This relates to a method that enables import.

FIG. 1 is a block diagram showing a DC Leonard DDC device as an example of a DDC device. In the figure, a DC motor M is supplied with power from a three-phase power source via a power converter 1. The DDC device is shown in this case as consisting of a speed regulator (ASR) 3, a current regulator (ACR) 4, a firing angle regulator (FAR) 5 and a pulse amplifier (PA) 6; Instead of being constructed from individual circuits, it can also be constructed from a microprocessor.

Explain the operation. The rotational speed of the electric motor M detected by the pulse generator PG is compared with the speed set by the speed setting device 2, and the error signal is subjected to, for example, PID calculation in the ASR 3, and detected by the output and current detector 7. The actual value of the supplied power current is compared with the actual value of the supplied current, and the error signal is subjected to, for example, a PID calculation in the ACR 4, and the output thereof is input to the FAR 5. As a result, a phase-controlled firing pulse is output from the FAR 5, amplified by the PA 6, and then applied to the converter 1 to control its conduction angle, and the rotational speed of the electric motor M is controlled by the speed setting device 2. Variable speed control is performed to achieve the set speed.

In this way, in a DDC device, it is necessary to detect and capture the actual value of the current supplied from the multiphase AC power supply. The present invention relates to a method for detecting and capturing the actual value of the current supplied with high precision.

Now, the conventional current actual value acquisition method in a DDC device is a method in which amplitude values are repeatedly detected by shifting the time from the alternating current waveform, and the average value is taken as the actual current value. Generally, when controlling the speed or torque of a motor fed by a three-phase pure bridge-connected thyristor converter, as explained with reference to Figure 1, the armature current is feedpacked and the current is adjusted. The phase of the conduction angle of each thyristor is controlled by the output. In this case, the firing pulse interval applied to the gate terminal of the thyristor is normally 60 degrees (electrical angle) and 60 degrees during acceleration.
less than the degree. When this phase control and current adjustment is performed by a DDC device using a microcomputer, a current adjustment calculation is executed to determine the next firing point after the firing pulse is generated. Therefore, it is necessary to detect the feed current value (armature current value) early after the ignition pulse is generated, and it is difficult in terms of time to repeatedly detect the current amplitude value and calculate the average value. Further, when the firing control angle of the thyristor changes, the ripple waveform of the current changes, causing an error in the current detection value.

This invention was made in order to solve the problems in the prior art as described above, and the purpose of this invention is to improve the current (speed) of DC motors, etc.
In a DDC device that performs control, the next current amplitude value detection point in an AC power supply waveform is set at an optimal position according to the control angle of a firing pulse generated for a power converter such as a thyristor converter, It is an object of the present invention to provide an acquisition method that can accurately detect and input the actual current value.

The main point of the configuration of the present invention is that, in a DDC device, the ignition control angle is determined in advance with respect to the time from the time when the ignition pulse is generated to the detection of the current amplitude value as the actual value of the supplied current in a polyphase AC waveform that is the supplied current. The determined optimal relationship is memorized, and detection time data obtained from the control angle of the ignition pulse outputted to the power converter in light of the relationship is outputted;
The point is that the acquisition phase of the amplitude value of the multiphase alternating current, which is the power supply current, is controlled depending on the data. In other words, if we detect and capture the instantaneous current value that changes sinusoidally when it reaches the average current value, it is possible to capture the current without error. The relationship between and the time from the time when the ignition pulse is generated to the time when the instantaneous current value reaches the current average value is determined in advance, and the time point at which the instantaneous current value is detected is determined according to the above relationship according to the ignition control angle. That's the point.

Next, the principle of this invention will be explained in more detail.
The relationship between the ignition control angle α and the electrical angle (ωt _c ) from the time when the ignition pulse is generated to the time when the instantaneous value of the current amplitude in the AC waveform reaches the current average value is generally expressed as follows, if the commutation overlap phenomenon is ignored: When the current is continuous, it is given by the following formula.

However, tan=ωL/R, where R is armature circuit resistance, L is armature circuit inductance, and ω is AC power supply angular frequency.

Figure 2 shows 0<cos<1, 0<α<π, 0<
It is a graph displaying the relationship between the ignition control angle α and the electrical angle ωt _c under the condition that ωt _c <π/6. In the same figure, ○A is for cos=0.2,
○B is the graph for the case of cosα=0.8. That is, if you have this graph, when the control angle α is given, the electrical angle ωt _c
is determined, thereby making it possible to detect and capture the current amplitude value at the time when the instantaneous value of the current amplitude in the AC waveform reaches the current average value.

Since it seems that the cause of the present invention has been clarified above, one embodiment of the present invention will now be described with reference to the drawings.

FIG. 3 is a book diagram showing an embodiment of the present invention. In the figure, a microcomputer 14
is a DDC device. An electric motor (not shown) is supplied with power from a three-phase AC power source via a thyristor conversion element 23. The microcomputer 14 detects and imports the current supplied to the motor from the three-phase AC power supply (motor armature current 25), and inputs the current to the setting device 24.
The setting speed input from the thyristor conversion element 23 and the actual value of the motor rotational speed (not shown) are input, and the firing control angle α is determined by calculation. It is controlled to maintain the set speed. Thus, the present invention relates to a method for detecting and capturing the armature current 25. The following will explain from this perspective.

First, the other symbols will be explained. Filter 1
1 is a circuit that removes the ripple component when detecting and taking in armature current, and a sample and hold circuit 12 samples and holds the output of the filter 11 when an instruction (interrupt signal) is received from the counter 21 and converts it into an A/D converter. The A/D converter 13, which is a circuit that outputs to the converter 13, is a converter that converts the analog input supplied from the sample hold circuit 12 into a digital value and inputs it to the computer 14, and is completed when the A/D conversion is completed. A signal is also provided to the computer 14. The phase angle adjuster 18 receives the firing angle control signal from the three-phase AC power supply 27 and the microcomputer 14, and outputs a firing pulse signal (in the case of three phases, six pulses with different phases are output). Output.
The ignition pulse signal is supplied to the thyristor conversion element 23 via the pulse amplifier 19, and is also supplied to the counter circuit 21 via the OR circuit 22. The signal conversion circuit 17 receives one phase of the three-phase AC power supply 27 (see FIG. 4c), sends a clear signal to the counter 16 at the first zero cross point t0 in the input waveform, and then sends a clear signal to the counter 16 at the first zero cross point _t0 in the input waveform. A latch signal is sent to the latch circuit 15 at the cross point _t1 . The counter 16 measures the clock 26 (having a sufficiently large repetition frequency compared to the power supply frequency), and inputs the measured value to the microcomputer 14 via the latch circuit 15. Counter circuit 2
1, the electrical angle ωt _c determined with reference to the graph in FIG. 2 is input to the microcomputer 14 via the latch circuit 20, and
1, an interrupt signal is connected to the microcomputer 14. The same clock signal 26 is applied to counter circuits 16 and 21. In addition to the program, the memory in the microcomputer ₁₄ stores the graph shown in FIG. Of course.

Note that the waveform of the motor armature current 25 in FIG. 3 is as shown in FIG.
It will be appreciated that the current amplitude A applied will also vary. It was an object of the present invention to detect when the current amplitude A shows an average value. In addition, in the explanation so far, the detection time t is the electrical angle ωt _c
It has been expressed and explained as. FIG. 4b shows the output waveform (for one phase) of the thyristor conversion element 23, and in this waveform diagram, α is the firing control angle. As previously explained, the graph in FIG. 2 shows the relationship between the ignition control angle α and the electrical angle ωt _c when the amplitude A takes the average value in FIG. 4a.

Returning to FIG. 3, the operation will be explained. The signal conversion circuit 17 changes the phase every cycle of the AC power supply 27.
Generates clear and latch signals that are 180 degrees apart. Counter circuit 1 counting clock 26
6 is reset every cycle by a clear signal, and the latch circuit 15 holds the measured value (for half a cycle of the AC power supply) of the clock 26 of the counter circuit 16 by the latch signal. The phase angle adjuster 18 receives the ignition control angle signal α from the microcomputer 14.
ignition pulse signals are generated from the three-phase AC power source 17, and these ignition pulse signals are transmitted to the pulse amplifier 19.
The signal is applied to the thyristor conversion element 23 via the OR circuit 22, and to the counter circuit 21 via the OR circuit 22. The latch circuit 20 holds current detection point data (optimal electrical angle ωt _c ) output from the microcomputer 4, and
reads the data from the latch circuit 20 and starts subtraction every time it receives a signal from the OR circuit 22.
When the count value reaches zero, an interrupt signal is sent to the microcomputer 4, and at the same time a hold command signal is sent to the sample hold circuit 12.

Upon receiving the interrupt signal, the microcomputer 4 interrupts the current process and executes the interrupt process in the following steps.

(1) From set value 24 to current (speed) set value and A/
Waiting for the completion of the conversion operation of the D converter 13, the actual current value (current amplitude value A in Fig. 4a) is fetched from the A/D converter 13, the firing control angle α is determined as a result of the current control calculation, and the phase is determined. It outputs to the angle adjuster 8 (up to this point, it is a normal DDC device function).

(2) Current detection point data ω corresponding to ignition control angle α
Read t _c from memory.

(3) Corrected with the measured value N ₁ of the number of clocks for half a cycle of the power supply taken in from the latch circuit 15 (for example, if the unit of current detection point data ωt _c is electrical angle (degree), the measured value (N ₁ ) is the number of clocks for 180 degrees of electrical angle in a half cycle, so the calculation (ωt _c ×N ₁ )/180 is performed to convert the data ωt _c into the number of clocks.), and the result is sent to the latch circuit 20. Output to.

After finishing the interrupt processing, the microcomputer 14 resumes the interrupted processing. If the program is configured so that the interrupt processing is completed by the time the next firing pulse occurs, the latch circuit 20 that the next firing pulse is generated and captured by the counter circuit 21
The data is always current detection point data corresponding to the ignition control angle α.

By repeating the above operations, the current detection point can be changed according to the ignition control angle α, and the optimum current amplitude value (for example, average value) can be detected and taken in.

As explained in the example, since the current is detected and taken in when the instantaneous current value reaches, for example, the average current value, the current control results in changes in the actual current value due to setting changes, disturbances, etc. There is an advantage that even if the arc control angle changes, an accurate value can always be detected as the actual current value with high precision.

In addition to what has been described above, the present invention is also applicable to cases where the phase adjuster is implemented by a microcomputer.

[Brief explanation of the drawing]

Figure 1 is a block diagram showing an ordinary DC Leonard DDC device, and Figure 2 shows the ignition control angle α and electrical angle ω.
₃ is a block diagram showing an embodiment of the present invention, and FIG. 4 is a waveform diagram showing signal waveforms at various parts in the circuit of FIG. 3. Explanation of symbols, 1...Converter, 2...Speed setter, 3...
Speed regulator, 4... Current regulator, 5... Firing angle regulator, 6... Pulse amplifier, 7... Current detector, 11...
Filter, 12...Sample hold circuit, 13...
A/D converter, 14...microcomputer, 1
5... Latch circuit, 16... Counter, 17... Signal conversion circuit, 18... Phase angle adjuster, 19... Pulse amplifier, 20... Latch circuit, 21... Counter, 22...
OR circuit, 23... Thyristor conversion element, 24... Setting device, 25... Armature current of motor, 26... Clock, 27... Three-phase AC power supply.

Claims (1)

[Scope of Claims] 1. The current of an inductive load such as an electric motor that is supplied with power through a converter is taken in at least the actual value of the current that is supplied to the load, and the firing control angle that the converter should take is determined by calculation. A method for capturing the actual value of the current supplied in a direct digital control device that controls the current by determining the current value,
A predetermined relationship of the ignition control angle to the time from the time when the ignition pulse of the converter is generated to the detection of the current amplitude value as the actual value of the power supply current in the waveform of the polyphase alternating current that is the power supply current is memorized. output the detection time data obtained in light of the above relationship from the control angle of the ignition pulse output towards the converter,
A method for acquiring an actual value of a current in a direct digital control device, characterized in that the phase of acquiring an AC amplitude value as an actual value of an actual current in a direct digital control device is controlled depending on the data. 2. In the acquisition method according to claim 1, the current amplitude value as the actual value of the power supply current in a direct digital control device is characterized in that the current amplitude value as the actual value of the power supply current is an average value of an AC waveform. Value import method.