JPH0474958B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a load current switching method suitable for driving a DC motor using forward converters connected in antiparallel.

FIG. 1 shows a typical circuit example in which a DC motor is driven using forward converters connected in antiparallel. In this figure, 1 and 2 are forward converters each composed of a thyristor, and the armature 3 of the DC motor
are connected in antiparallel to each other. Further, a three-phase alternating current power supply AC is supplied to each of the forward converters 1 and 2. 4 is a field winding, which is connected to a variable DC power source 5.

By the way, as is well known, the rotational speed of a DC motor is controlled by controlling the armature current (hereinafter referred to as load current), and the direction of rotation is reversed by reversing the direction of the load current.

In the circuit shown in FIG. 1, when controlling the load current, a firing angle signal corresponding to the load current command value is supplied to the forward converter 1 or 2, and
When switching the direction of the load current, switch the operating forward converter. For example, if the forward converter 1 is in an operating state when the DC motor is rotating in the forward direction, when the DC motor is rotating in the reverse direction, the forward converter 1 is put into a non-operating state and then the forward converter 2 is put into an operating state.

Conventionally, the following two methods have been used to switch the load current direction.

First, in order to stop the operation of the forward converter for forward rotation, the firing angle supplied to the forward converter is maximized and the load current is guided to zero. Since the load current does not immediately become 0 due to the inductance component of the armature, after a pre-calculated predetermined time (the time when the load current becomes 0), the firing angle signal that was being supplied to the forward converter is changed. to sever. Then, supply the firing angle signal to the forward converter for reverse rotation,
Reverses the direction of load current.

It is almost the same as the method described above, but after maximizing the firing angle of the forward converter for forward rotation, the average value of the load current is detected, and when this value reaches 0, the firing angle of the forward converter for reverse rotation is Provides firing angle signal.

However, in the above-mentioned method, it takes a long time to switch the direction of the load current, and in order to maximize the firing angle at the time of switching, it takes time to return the firing angle to the desired value after switching. There was a drawback that it took a while. It is well known that when controlling the firing angle of a forward converter during operation in a decreasing direction, it cannot be rapidly decreased (generally by a maximum of about 30 degrees).

In view of the above, the conventional method also has the following drawbacks.

When controlling the rotational speed of a DC motor driven in a light load state to a constant speed, the command value of the load current fluctuates around 0, and the polarity is repeatedly reversed. In this case, in the conventional method described above, the switching time of the forward converter and the firing angle recovery time after switching are long;
Due to the poor followability of the polarity reversal of the load current command value, the constant speed control characteristics were extremely poor.

In view of the above-mentioned circumstances, this invention provides an anti-parallel connected forward converter which has extremely short switching time of the forward converter and firing angle recovery time after switching, and which has excellent constant speed control characteristics of a DC motor under light load. The present invention provides a load current switching method in which one of the forward converters connected in antiparallel is appropriately selected to supply current to the load.
At light load or no load, it is detected whether the load current value immediately before the ignition of the selected forward converter is 0 or not, and if it is 0, the next ignition is applied to the other forward converter. This is a load current switching method for an inverse-parallel connected forward converter characterized by switching the load current.

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 2 is a block diagram showing the configuration of an embodiment of the present invention. In this figure, parts corresponding to those in FIG. 1 are designated by the same reference numerals, and their explanation will be omitted.

In this figure, _S1 is a current value command signal, which is a signal supplied from another circuit not shown. This current value command signal S ₁ is supplied to the command signal converter 10 and also to the comparator 22 . The command signal converter 10 outputs the absolute value of the current value command signal S ₁ , and its output signal S ₂ (=|S ₁ |) is supplied to the deviation detection point 11 . Further, the command signal converter 10 is configured to set the output signal S ₂ to 0 when the signal S ₃ supplied from the exclusive NOR circuit 27 goes to "L" level. The output signal S ₁₁ of the load current detector 20 is supplied to the deviation detection point 11 as a subtraction signal. This load current detector 20 converts the signal _S10 corresponding to the load current Ia detected by the converter CT into a value equal to the load current Ia and outputs the signal S10. The amplifier 12 is the deviation detection point 11
The deviation (S ₂ −S ₁₁ ) detected at is amplified and supplied to the firing angle calculation section 13 . The firing angle calculating section 13 calculates the firing angles of the forward converters 1 and 2 based on the supplied signals, and calculates the firing angles so that the deviation (S ₂ -S ₁₁ ) becomes zero. The output signal of this firing angle calculation section 13 is supplied to a rate control section 14. The rate control section 14 is the firing angle calculation section 1
When the output signal No. 3 is a signal for decreasing the firing angle, if the decrease width is greater than a predetermined value (generally about 30 degrees), the decrease width at this time is divided.
For example, if the output signal of the firing angle calculation unit 13 decreases by 60° with respect to the previous firing angle, the amount of decrease
The firing angle signal of 30° is divided into two parts and output. Also,
When the output signal of the firing angle calculation unit 13 is a signal that increases the firing angle, and when the signal decreases the firing angle but the amount of decrease is small, the rate control unit 14 controls the output of the firing angle calculation unit 13. Output the signal as is. The output signal S ₄ of the rate control section 14 is supplied to the gate pulse generation section 15 and also supplied to the deviation detection point 25 as a subtraction signal.

Here, other functions of the firing angle calculation section 13 and rate control section 14 described above will be explained. A firing angle signal of 240° is supplied as an addition signal to the deviation detection point 25, and the deviation from the output signal _S4 of the rate control section 14 is detected here. If the signal S ₄ indicates the firing angle α ₁ , the deviation at the deviation detection point 25 will be (240°−α ₁ ). This deviation signal is then supplied to the firing angle calculation unit 13 via the amplifier 26. Then, the firing angle calculation unit 13 receives a pulse from the one-shot multi 28.
When P ₃ is supplied, a deviation signal (240°-α ₁ ) is taken in, and a signal corresponding to this signal, that is, a signal instructing the firing angle (240°-α ₁ ), is supplied to the rate control section 14. do. The rate control section 14 also receives pulses from the one-shot multi 28.
When P ₃ is supplied, the signal supplied from the firing angle calculating section 13 is directly supplied to the gate pulse generating section 15 . In this case, even if the output signal of the firing angle salt calculator 13 significantly reduces the firing angle,
Do not suppress the decline.

Next, 15 is a gate pulse generation section. This gate pulse generator 15 generates three pulses, namely a gate pulse G _P , a pre-ignition pulse P ₁ and a post-ignition pulse P ₂ based on the output signal S ₄ (a signal instructing the firing angle) of the rate control unit 14. They occur as a set. Here, the gate pulse G _P , the pre-ignition pulse P ₁ and the post-ignition pulse P ₂ are shown in FIGS. 3a to 3c.
Indicates the timing of occurrence. The gate pulse _GP is a pulse for firing the forward converters 1 and 2, and is a pulse corresponding to the firing angle indicated by the signal _S4 . The post-ignition pulse _P2 is supplied to the input terminal 23b of the AND gate 23, and the pre-ignition pulse _P1 is supplied to the G of the D-type flip-flop 1 (hereinafter abbreviated as _FF1 ).
The gate pulse G _P is supplied to the input terminals 16a and 17 of the AND gates 16 and 17.
supplied to a. The other input terminals 16b and 17b of the AND gates 16 and 17 are connected to the Q output terminal and output terminal of FF ₂ , respectively, and one of the AND gates 16 and 17 is configured to be open. . 18 and 19 are gate pulses respectively
This is a pulse amplifier that amplifies _GP to a predetermined level, and each output signal is supplied to the gates of forward converters 1 and 2, respectively. And the gate pulse G _P is FF ₂
Depending on the output state of the signal, the signal is supplied to the forward converter 1 via the AND gate 16→pulse amplifier 18 path, or the AND gate 17→pulse amplifier 19 path to the forward converter 2.

On the other hand, 21 and 22 are comparators, which output a "H" level signal when the input signal exceeds 0, and output a "L" level signal when the input signal is less than 0. . Comparator 21 has a current transformer
The output signal S ₁₀ of the CT is supplied, and the current value command signal S ₁ is supplied to the comparator 22 as described above. Note that the signal S ₁₀ is a signal having a value equal to the absolute value |Ia| of the load current Ia. The output signal _S12 of the comparator 21 is
It is supplied to the D input terminal of FF ₁ , and the output signal of FF ₁ is supplied to the input terminal 23a of the AND gate 23 as an open/close signal. The output signal of the AND gate 23 is then supplied to the G input terminal of _FF2 . The output signal S ₆ of the comparator 22 is connected to the D input terminal of FF ₂ and the input terminal 27 of the exclusive NOR 27.
supplied to a. This exclusive Noah 27
The Q output signal of FF ₂ is supplied to the other input terminal 27b of FF 2 . And exclusive Noah 27
The output signal is supplied to the one-shot multi 28 and also to the command signal converter 10 described above. The one-shot multi 28 receives an input signal,
In other words, when the output signal of the exclusive NOR 27 changes from "L" level to "H" level, 1
It outputs pulses.

Further, of the above-described configuration, the portion surrounded by the dashed line in FIG. 2 constitutes the load current switching section 30.

Next, the operation of this embodiment with the above-described configuration will be explained with reference to FIGS. 2 and 4, taking as an example the case where the polarity of the current value command signal _S1 is reversed from positive to negative. .

Further, a description of the operation of this embodiment when the power is turned on will be omitted for the sake of brevity for the following two reasons.

In this embodiment, the operation when the power is turned on is approximately the same as the operation when the polarity of the current command signal _S1 is reversed.

When the power is turned on, if the current value command signal S ₁ is positive, the AND gate 16 is opened and the forward converter 1 for forward rotation is driven, and similarly, if the current value command signal S ₁ is negative, It can be easily understood from the following operation description that the AND gate 17 is opened and the forward converter 2 for reverse rotation is driven.

Now, Fig. 4 a to j show the electric motor 3 shown in Fig. 2.
FIG. 4 is a diagram showing waveforms of various parts of the circuit when the current value command signal S 1 is linearly changed from positive to negative when the electric current value command signal S ₁ is driven with a light load.

First, the operation before time _t1 when the current value command signal _S1 crosses 0 will be explained. In this case, the AND gate 16 is open, the AND gate 17 is closed, and the gate pulse corresponding to the current value command signal _S1 is
G _P (see c in the figure) is supplied to the forward converter 1 for forward rotation via the AND gate 16 and the pulse amplifier 18, thereby causing the armature 3 to rotate forward. Also, at this time, the respective output signals S ₁₂ and S ₆ of the comparators 21 and 22
Since each input signal S ₁₀ and S ₁ is greater than or equal to 0,
Both are at the "H" level (see e and f in the same figure). When the signal _S12 is always at the "H" level, the state of _FF1 shown in FIG. 2 does not change even if the pre-ignition pulse _P1 is supplied, and the output signal is always at the "L" level ( (See Figure 4i). Therefore, the AND gate 23 is in a closed state, and the "L" level signal continues to be supplied to the G input terminal of FF ₂ . As a result, the state of FF ₂ does not change, and an "H" level signal continues to be output from the output terminal (see FIG. 4j). As a result, Exclusive Noah 27
An "H" level signal is always supplied to both input terminals 27a and 27b, and the output signal _S2 is as shown in Fig. 4g.
The "H" level is maintained as shown in FIG. As a result, the one shot multi 28 does not operate and the pulse
P ₃ is never output. Also, since the signal S3 is at the "H" level, _the output signal _S2 of the command signal converter 10 is a current value command signal as shown in FIG. 4a.
Equal to the absolute value of S ₁ .

Next, when the current value command signal S ₁ becomes 0 at time t ₁ , the output signal S ₆ of the comparator 22 becomes “L” level. As a result, the output signal _S3 of the exclusive NOR 27 becomes "L" level, and the output signal _S2 of the command signal converter 10 becomes 0 as shown in FIG. 4a. As a result, after time _t1 , the ignition calculating section 13 calculates the ignition angle such that the load current Ia becomes zero.

On the other hand, the load current Ia suddenly becomes 0 between time t ₂ and _{t 3} .
become. As is well known, this is a phenomenon called a continuous current state, and when the DC motor is driven under a light load and the current command signal S ₁ is around 0, the load current
This is a phenomenon in which I ₂ becomes 0 at the next ignition time.
Further, in this state, the load current immediately before the next ignition time always becomes 0. In this embodiment, as explained below, the load current continuation state is detected at time _t3 , and at the next ignition, the load current Ia
Switch the orientation.

When the load current Ia becomes 0 at time _t2 , the output signal _S12 of the comparator 21 becomes "L" level as shown in FIG. 4f. As a result, when the pre-ignition pulse P ₁ is supplied to the G input terminal of FF ₁ at time t ₃ , the output signal of FF ₁ becomes "H" level as shown in Figure 4 i, and the current is in an intermittent state. Detect.
When the output signal of FF ₁ becomes "H" level, the AND gate 23 becomes open. Then, when the gate pulse _GP is issued at time _t4 , since the output state of FF ₂ has not changed at this point, the gate pulse _GP is forward-converted for forward rotation via the AND gate 16 and the pulse amplifier 18. is supplied to vessel 1. Then, at time _t5 , when the post-ignition pulse _P2 is supplied to the G input terminal of _FF2 via the AND gate 23, since the signal _S6 is already at the "L" level, the output of _FF2 is The state is reversed and the output signal goes to "L" level (see FIG. 4j). As a result, the input terminal 27 of the exclusive Noah 27
Since "L" level signals are supplied to both a and 27b, the output signal _S3 of the exclusive noor 27 becomes "H" level, and the one shot multi 28 calculates the firing angle using the pulse _P3 . 13 and rate control section 14. When the firing angle calculation unit 13 is supplied with the pulse P3, the firing angle calculation unit ₁₃ detects the deviation detection point 2.
5 receives the deviation signal (240°-α ₁ ) supplied through the amplifier 26, and sends a signal instructing the firing angle (240°-α ₁ ) to the gate pulse generator 15 via the rate control unit 14. supply Furthermore, since the rate control section 14 is supplied with the pulse _P3 at this time, even if the output signal of the firing angle calculation section 13 significantly decreases the firing angle, the reduction width is not suppressed. Then, the gate pulse generator 1
5 outputs a gate pulse _GP corresponding to the deviation signal (240°-α ₁ ) at time t ₆ .

On the other hand, after time _t5 , the output state of FF ₂ does not change as can be seen from FIGS. 2 and 4, so at time _t3 , the AND gate 17 is in an open state.

Therefore, the gate pulse G _P at time t ₆ is supplied to the forward converter 2 via the AND gate 17 and the pulse amplifier 19, thereby switching the direction of the load current Ia and causing the armature 3 to rotate in the reverse direction.

In this way, in this embodiment, as can be seen from FIG. 4a, when the polarity of the current value command signal _S1 is reversed,
The direction of the load current Ia is switched simply by delaying the firing period.

On the other hand, when the signal S ₃ becomes "H" level at time t ₅ , the output signal S ₂ of the command signal converter 10 becomes equal to the absolute value of the current value command signal S ₁ again. As a result, the firing angle after time _t6 is based on signal _S2 (see FIG. 4a). This shows that this embodiment has extremely good followability for the current value command signal _S1 after switching the load current.

Here, the reason why the followability is good will be explained.

First, as shown in reference figure 1, the output voltage of the forward converter for forward rotation is vp, and the output voltage of the forward converter for reverse rotation is vN.
shall be. Since the motor rotates at a constant speed, a constant speed electromotive force (generated inside the motor) Ec is generated. Figure 5 shows when the load current Ia = 0.
The output waveforms of vp and vN are shown. Here, the portion shown as the conduction period is the output waveform of vp and vN, and the voltage values at the starting points A and B are equal to the speed electromotive force Ec. Therefore, the output currents ip and iN of each forward converter become zero. That is, the current does not suddenly flow immediately after switching, and speed pulsation is suppressed.

Then, each ignition αpo on the forward rotation side and the roll call angle pαNo on the reverse rotation side are determined by the following formula: αpo=-sin(Ec/Em)-2π/3 αNp=-sin(-Ec/Em)+2π/3 Calculated. Therefore, there is a relationship αpo + αNp = 4π/3 (=240°). Therefore, the roll call angle αNo on the reverse side when switching from normal rotation to reverse rotation is αNo=240°−αpo, and when switching from reverse rotation to normal rotation, αpo=240°−αNo. If it becomes smaller than the above value, V>>Ec V>>-Ec immediately after switching, and a large current suddenly flows and speed pulsation occurs. On the other hand, if the firing angle is larger than the above value, vp<Ec vN<-Ec immediately after switching, so it takes a long time until vp>Ec vN>-Ec is reached by subsequent firing, which is wasteful. Control characteristics deteriorate over time.

In light load and no-load control, the load current command value repeats polarity reversal, so it is necessary to shorten the switching time during polarity reversal as much as possible. However, the firing angle determination method in this example is as follows. , has special effects in such situations.

That is, the output voltage value immediately after switching of the forward converter becomes equal to the internal electromotive voltage value, and as a result, no current flows immediately after switching, and speed pulsation is prevented.

As can be seen from the above, this embodiment is extremely suitable for frequently switching the direction of the armature current of a DC motor driven with a light load.

Note that the pulse amplifier 18 in this embodiment,
Operations other than those of 19 and load current detector 20 may be performed using a microprocessor. As an example of a control method in this case, for example, the load current
There is a method of controlling Ia in synchronization with gate pulse _GP . In this method, the post-ignition pulse _P2 becomes the start signal for the next firing angle control calculation and load current switching. In addition, if the initial firing angle value (240°−α ₁ ) after switching is not required, use the pulse
P ₃ and the deviation detection point 25 are no longer necessary.

As explained above, according to the present invention, in a circuit in which one of the forward converters connected in antiparallel is appropriately selected to supply current to the load, when the load is light or there is no load, The system detects whether the load DC value immediately before the ignition of the forward converter is 0 or not, and if it is 0, the next ignition is switched to the other forward converter, so the current continues. It is possible to instantly detect when this occurs, and to quickly switch the forward converter. Therefore, the control characteristics of constant control of the rotational speed of the DC motor during light loads can be greatly improved.

In addition, by subtracting the firing angle immediately before switching from a predetermined value when switching and setting the next firing angle, speed pulsations that occur during switching can be suppressed, allowing control with extremely high followability. can be realized.

[Brief explanation of drawings]

FIG. 1 is a circuit diagram showing an example of a circuit when a DC motor is driven using forward converters connected in antiparallel,
FIG. 2 is a block diagram showing the configuration of an embodiment of the present invention, FIGS. 3 a to c are waveform diagrams showing the output waveforms of the gate pulse generator 15 shown in FIG. 2, and FIGS. FIG. 2 is a waveform diagram showing the waveforms of each part of the circuit, FIG. 5 is an equivalent circuit diagram for explaining the control principle of the same embodiment, and FIG. 6 is a waveform diagram for explaining the control principle of the same embodiment. It is. 30...Load current switching section.

Claims (1)

[Claims] 1. In a circuit in which one of forward converters connected in reverse parallel is selected to supply current to a DC motor, the selection is made during constant speed operation under light load or no load. The anti-parallel method is characterized in that it detects whether or not the load current value immediately before the ignition of the forward converter being turned on is 0, and if it is 0, the next ignition is switched to the other forward converter. Load current switching method for connection order converter. 2. The inverse parallel connection forward converter according to claim 1, characterized in that, in the switching, the firing angle immediately before the switching is subtracted from 240°, and the subtraction result is used as the next firing angle. Load current switching method.