JPS6016198B2 - Inverter control device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an apparatus for driving an AC motor by vector control using a current source inverter, and particularly to an inverter control apparatus for generating control signals to an inverter section and a commutation circuit.

As a method for driving AC motors using external inverters, a vector control method has been developed that gives AC motors torque control characteristics and high long-range response similar to those of DC motors. These points have been evaluated and are now being put into practical use.

The object of the present invention is a current source inverter, for example, a collective commutation type. This will be explained below based on the drawings. FIG. 1 shows an example of an inverter main circuit configuration to which the present invention is applied, where 1 is an AC power supply, 2 is a converter section, 3 is a DC reactor, 4 is an inverter section, 5 is an AC motor, and 6 is a commutator. It is a circuit.

That is, the converter part 2 includes thyristors 2a, 2b,
2c, 2d, 2e, and 2f, it converts one input of an AC power source into a DC voltage, and controls the DC voltage and, ultimately, the magnitude of the AC motor 5 current by adjusting the firing phase of the thyristor. The DC reactor 3 improves the characteristics of the AC motor 5 by suppressing the pulsating part of the output current of the converter section 2, and the inverter section 4 includes thyristors 4a, 4b, 4c,
4d, 4e, and 4f convert DC to AC, and control the frequency of the AC output coupled to the AC motor 5 by adjusting the firing interval of the thyristor. operates to perform forced commutation. Here, the commutation operation of the circuit configuration shown in FIG. There are six types of energization modes for the inverter portion 4, although a detailed explanation will be avoided because of the nature of the present invention.

Assuming that these modes are A, B, C, D, E, and F, the thyristors fired in each mode are indicated by symbols as shown in Table 1. Table 1 That is, in mode A, the positive side thyristor 4a and the negative side thyristor 4e are ignited, and in mode B, the negative side thyristor 4e is commutated to the thyristor 4f.

In such a commutation operation, the thyristor 6e is turned on at the time of positive side thyristor evening commutation, and the voltage of the capacitor 6b shown in the figure is reversed by the resonant circuit action with the commutating reactor 6d, and then the thyristor 6f is turned on. Ignition, capacitor 6b → thyristor 6f → any of diodes 6g, 6g', 6〆 → any of thyristors 4a, 4b, 4c →
A reverse bias is applied to the positive side thyristor in the loop of the diode 6a and the capacitor 6b to extinguish it and fire the positive side thyristor in a new mode.

Furthermore, when the negative side thyristor is commutated, the same operation is performed by firing the thyristor 6f' instead of the thyristor 6f described above. Now, in the circuit configuration shown in FIG. 1, the magnitude of the current of the AC motor 5 can be controlled by the firing phase of the converter section 2, and the frequency of the current can be controlled by the firing interval of the inverter section 4. However, in the case where the vector control method is adopted, it is necessary to control the phase as well as the magnitude and frequency of the current, and this point must be taken into consideration when controlling the thyristor of the inverter section 4. Here, in the case of a constant frequency command, the energization mode of the inverter section 4 is changed from mode A to normal rotation.
Mode B → Mode C → Mode D → Mode E → Mode F →
Mode A...or when reversing mode F→mode E→...mode A→mode F...
However, if the phase command changes during this time, the intervals will not be the same, and sometimes mode B
It may even be necessary to temporarily change →mode C in the opposite direction, such as mode B → iodine A.

This is now the period from mode A to mode F (0 to 2 m
), and if the frequency command is ,v*, and the phase command is 8*, then the phase is determined by the following formula:
Based on this result, the energization mode may be determined according to Table 2. = of, v*dt10*(o≦〈2m)……
．．・-[11 Table 2 Here, the phase command 8* is a function of the torque command T* and the main magnetic flux command ◇* of the AC motor, but in normal applications, the torque command T* changes rapidly and the rate of change is It is often fast and has a large pulsation component.

For example, when controlling the speed of the AC motor 5, the deviation between the speed setting and the speed detector is often calculated using a speed control amplifier and the output thereof is used as the torque command T*. However, due to large or medium changes in the speed setting or sudden changes, the torque command, and thus the phase command, changes rapidly from 0 to 0 and contains many pulsation components due to pulsations included in the speed detector output. If the energization mode is determined by equation [1] using such phase command 8*, the following inconvenience may occur.

'1} The duration of the same energization mode is shortened. 5 For example, immediately after commutation from mode A to mode B, mode change command B→C or mode change command B→A is issued, and the time in mode B is shortened. Become. In the commutation circuit 6 shown in FIG. 1, the polarity reversal time of the capacitor 6b due to the resonance circuit constants of the capacitor 6b and the commutation reactor 6d, the filling time of the capacitor 6b due to the main circuit current, and the time required for absorbing commutation energy. Although a certain amount of time is required for one commutation operation depending on the replenishment time from the capacitor 6c to the capacitor 6b, etc., the next commutation cannot be performed unless a predetermined period of time has elapsed after the commutation operation, that is, the mode change. The number of commutations will increase due to the pulsation of the '21 phase command 8*, which will cause commutation failure if performed abnormally.

Now, if there were no pulsations, the commutation from mode A to mode B would only take place once, but due to the presence of pulsation, the commutation would go back and forth between modes like A → BB → A, A → B, etc.
This increase in the number of times also leads to an increase in the capacity of various circuit components. '3} Even in the case of commutation to the same mode, it is necessary to distinguish between the commutated thyristors at the advance stage and the latter stage, since the thyristors are different.

When commutating to mode B, when changing from mode A, the commutation is from thyristor 4c to thyristor 4f, which is on the negative side, whereas when commutation is from mode C, commutation is from thyristor 4b to thyristor 4a, on the positive side. therefore,
Even in the same mode B, the thyristor 6f of the commutation circuit 6
, 6f' needs to be used properly. The present invention solves the above-mentioned problems and realizes a simple device suitable for vector control. Embodiments will be described in detail below with reference to drawings. FIG. 2 is a system diagram showing the main part configuration of an embodiment according to the present invention, and 7 indicates the magnitude of the current of the AC motor 5 from the torque command T*, the main magnetic field command *, and the motor rotational angular velocity M. A known vector calculation circuit calculates lv*, 8* of the frequency and phase commands 1, *, as described later. Converter control circuit that controls the point phase of the thyristor; 9 is a voltage frequency converter VF that converts the frequency command v* signal into a pulse train having a frequency that is an integral multiple of the frequency command; , 11 is an analog-digital code converter AD that converts the phase command 0* into a digital code, 12 is an adder that adds the output of the counting circuit 10 and the output of ADII, and 13 is an inverter section 4 that converts the output signal of the adder 12. 14 is a monostable circuit that provides pulses at both the rising and falling edges of the input signal;
15, 15', 15ro, 15''' are holding circuits; 16 is a delay circuit that keeps the output at a low level for a certain period of time after the signal input;
17 is a digital comparator, 18 is a commutation control circuit for creating a thyristor drive signal for the commutation circuit 6, 19 is a differential amplifier OR circuit, and 20 and 20' are AND circuits. It is known that the vector calculation circuit 7 performs the following calculations. 1,=K.・T*
/○*) ......[21IJ:K2・〇*
………(3}s=K3・(IT〉10)……{4}1.*=ノ(IT〉2)
Ten (one) 2......[51, V*D N+S
......[6}0*=nen-1(IT/1
0) ......[71 However, K,,K2,K3
is a motor constant, IT is a torque component current, 10 is a magnetic flux component current, and s is a slip angular frequency.

The operation of such a system will be explained using the numerical values shown in Table 1 as an example. Here, the vector calculation circuit 7 and the converter control circuit 8 have the functions described above, and are not intended to be used in the application of the present invention. Since there is no close relationship, I will not elaborate further. Now, VF9 generates a pulse train having a frequency that is 192 times the current frequency as shown in Table 1 according to the required inverter output frequency, and the counting circuit 10 counts this and its output is sequentially from zero to "191". It rises and returns to zero with the next pulse.

On the other hand, phase command 8* is converted into a digital code by ADII. Here, the phase command is 0. In principle, [(1 m
/2) Ku8*ku (汀/2)] with only bamboo in transition,
Since (0 to 191) of the output of the counting circuit 10 corresponds to two numbers, the ADI I output is set to be (0 to 95). Then, the adder 12 outputs the output of the counting circuit 10 and the ADI1
Add the outputs and get the 8-bit output signals Bo, B, B2, B
3, B4, B, &, B7, and a carry signal Co is generated. Here, these adder 12 outputs and the aforementioned energization mode,
It is determined that the ignition thyristors of the inverter section 4 correspond to each other as shown in Table 1.
A firing signal for the inverter section 4 is created by determining B and carry signal Co. For example, if the adder 12 output is between (32~), CwB7~B
o is 0, 0, 0, 1, XXXXXXX (x is 0 or 1), it is determined that the mode is B, and the ignition signals of the thyristors 4a and 4f are sent out. In this way, it is possible to determine the firing signal of the thyristor of the inverter part 4, and also whether the firing signal of the thyristor of the commutation circuit 6 changes from mode A to mode B or from mode C to mode B even in the same mode B.
The monostable circuit 14, the holding circuit 15, and the exclusive OR circuit 19 make the determination.

When the monostable circuit 14 generates a change in the signal B5 output from the adder 12, a narrow pulse is applied to the holding circuit 15 as a hold command, and the signal B4 output from the adder 12 is held when the signal B4 output from the adder 12 is green after the pulse. do. Therefore, when moving from mode A to mode B, as is clear from Table 1, the holding circuit 1
5 output becomes "0", and when the mode changes from mode C to mode B, the output becomes "1". Also, exclusive or circuit 1
9 is a signal ear, and since it outputs the exclusive OR of B5, when mode A→B, "When mode C→B", "
0". If this "1" is defined as the load side commutation of the inverter portion 4 and "0" is defined as the positive side commutation, correct commutation operation can be performed. Further, the output signal of the exclusive OR circuit 19 is applied to the commutation control circuit 18 through the holding circuit 15', and the commutation control circuit 18 is applied to the AND circuit 2.
When the commutation command of the 0' output is input, a firing signal for the thyristor of the commutation circuit 6 is sent out.

This holding circuit 15' holds the output of the conversion circuit 13 and the output of the exclusive OR circuit 19 using the output signal of the AND circuit 20'. Furthermore, digital comparator 17
compares the inverter section 4 firing signal of the input and output signals of the holding circuit 15', and when the two do not match, outputs "1", and when the output pulse B of the monostable circuit 14 is generated, this signal and The result of the AND is held in the holding circuit 15^. Also, when the above two match, the monostable circuit 1
Even if 4 outputs are generated, the output of the holding circuit 15r does not become "1", and if "1" is held, it is returned to "0". Furthermore, the holding circuit 15''' holds the "1" signal by the input pulse of the counting circuit 10.

Therefore, the holding circuits 15'', 15... are both reset by the output of the AND circuit 20', and the output is set to "0".
shall be. Here, the delay circuit 16 sets the output to "0" for a certain period of time after the input is applied to prevent the AND circuit 20' from becoming "1" again. In this way, the holding circuits 15'', 15''
' and the output of the delay circuit 16 are all "1", the output is given to the AND circuit 20', the holding circuit 15' holds the new mode firing signal, and the commutation control circuit 18 and inverter part 4
and generates a thyristor firing signal for the commutation circuit 6.
Due to the operation of the delay circuit 16 as described above, the phase command 0*
Even if suddenly changes, even if the conversion circuit 13 output requests a new energization mode before the previous commutation operation is completed, the AND circuit 20' output will not occur, and the commutation operation will not be performed and the commutation will fail. can be prevented.

Furthermore, even if a request to change the energization mode occurs frequently due to the pulsation of the phase command 8*, the mode cannot be changed due to the action of the holding circuit 15''' until the input to the counting circuit 10 occurs, and the number of commutations is wasted. Furthermore, the holding circuit 15'' also prohibits the commutation operation in the following cases,
Preventing the increase in trans-Muslims. That is, if there is now a mode conversion request B→A, but this is prohibited by the action of the holding circuit 15 or the delay circuit 16, a conversion request A→B is made again before the prohibition is lifted. If the prohibition is lifted after that, when a commutation operation is performed to mode B even though it is currently in mode B, this will cause an increase in the commutation circuit capacity even though it will not result in abnormal operation such as commutation failure. However, it is clearly desirable to prevent this. As described above, according to the present invention, it is possible to provide a device having a simple circuit configuration that can eliminate harmful or unnecessary operations during vector control execution and effectively generate a correct firing signal.

[Brief explanation of drawings]

FIG. 1 is a circuit diagram showing an example of an inverter main circuit structure to which the present invention is applied, and FIG. 2 is a system diagram showing the main part structure of an embodiment according to the present invention. 4... Inverter part, 6... Commutation circuit,
7... Vector calculation circuit, 8... Converter control circuit, 9... Voltage frequency converter (VF), 1
0...Counting circuit, 11...Analog-digital converter (AD), 12...Adder, 13...
... Conversion circuit, 14 ... Monostable circuit, 15,
15', 15^, 15'''...Holding circuit, 1
6...Delay circuit, 17...Digital comparator, 18...Commutation control circuit, lv*...
・Frequency command, 0*...phase command. Younger brother/Figure 2

Claims (1)

[Claims] 1. In a vector control type current source inverter that drives an AC motor, among the switching elements constituting the inverse conversion section, the elements connected to the positive DC bus are commutated at once, and the elements connected to the negative DC bus are also commutated. a counting circuit that includes a commutation circuit that performs batch commutation and counts pulse trains with a frequency that is an integer multiple of a motor current frequency command; and an analog-to-digital converter that converts a phase difference command between the motor current and the main magnetic flux into a digital code; an adder that adds the output of the counting circuit and the output of the analog-to-digital converter; a conversion circuit that creates a drive mode signal that is the basis of a drive signal for the switching element of the inverse conversion section according to the numerical value of the output of the adder;
a determination circuit that determines whether the commutation of the element connected to the positive side DC bus or that of the load side occurs when the drive mode signal changes;
At least three conditions exist: (1) the output of the conversion circuit is different from the drive signal of the current inverse conversion section switching element; (2) a pulse is input to the counting circuit; (3)
an AND circuit that takes a logical product of the fact that a certain period of time has passed since the drive mode signal changes, a holding circuit that changes the drive mode when the output of the AND circuit has an output, and an output of the AND circuit that has An inverter control device comprising: a commutation control circuit for creating a drive signal for the commutation circuit.