JPS5849085A - Controlling circuit for current type 3-phase inverter - Google Patents

Abstract

PURPOSE:To improve the adaptability of a current type 3-phase inverter by deciding the phase difference alphaN to the varying time point at the load current after the variation and selecting the thyristor to be conducted, thereby reducing pulsating torque. CONSTITUTION:The phase difference alphaT from the start of the state of 1' of a load currentIL at the present time to the end of the state of 1' in the load currentIL after the variation is calculated by an alphaT arithmetic unit 16, while the phase difference theta from the start of the state of 1' of the loadIL at the present point to the varying time point c is compared by (alphaT-theta) arithmetic unit 18, thereby calculating (alphaT-theta). An arithmetic unit 20 selects the state of the load currentIL after the variation at the varying time point is selected by the magnituide relation to a certain period based on the output of the unit 18. Then, the phase difference alphaN from the start of the state to the varying time point is calculated, thereby selecting the thyristor to be conducted.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a control circuit for a current-type three-phase inverter, and is useful for PWM control of the current-type three-phase inverter.

Figure #11 is a circuit diagram showing a current type three-phase inverter together with its control circuit and three-phase induction motor. As shown in the figure, the current type three-phase inverter 1 has six thyristors Tls.
Mushrooms, 1. Te,, 〒@eT- and 6 condensers for commutation"'Ol m'! eosa o4e '藝、
0 and diode DI e D s DI s D4
e DI e D-), three-phase AC power II
(not shown) Kill! Sanwa bridge rectifier circuit 2
The rectified direct current is further reversely converted into alternating current, and load currents i, , 1b, io having mutual phases of xzfJIe are supplied to the three-phase induction motor 3. At this time, the ring counter 4 makes the voltage determined by the setting value of the speed setting device 5 correspond to the frequency of the signal converted by the voltage/frequency converter 6, and converts the voltage determined by the setting value of the speed setting device 5 to the frequency of the signal converted by the voltage/frequency converter 6.・When triggered sequentially, the load current 'a e 1b e L.'a e 1b e L. The speed of the three-phase induction motor 3 is controlled by controlling the frequency of the three-phase induction motor 3. As a result, the load current i, which is the output of current type three-phase inverter 1, , ! b# 1° is 12 as shown in Figure 2.
The result is a rectangular wave whose phase differs by G'. The output voltage control system of the three-phase bridge rectifier circuit 12 is composed of the operational amplifiers 8 and 9° gate position adjuster 10 and diodes 11 and 12 shown in FIG. However, in this technique, since the above-mentioned passing load currents ia, ib, 1° are rectangular waves, harmonic components (particularly low-order harmonics such as the third harmonic and the fifth harmonic) are included. This causes a pulsation component to be mixed into the torque of the three-phase induction motor 3. Therefore, the waveforms of the load currents 1&, 113, and 16 should be made as close as possible to sine waves to remove the pulsating components (a PW control method has been proposed. A PWM pattern generating section is provided, and the trigger timing of the thyristors 1 to 6 of the current type three-phase inverter 1 is controlled according to the trigger pulse which is the output signal of this pattern generating section.l! For example, as shown in Fig. 3, when the thyristor is turned on during a period of 6f (hereinafter referred to as the commutation period T) prior to the rise of the long pulse width period of the load current, The thyristors T1~?, are made conductive alternately, and the thyristor T! is made conductive in a commutation period of 6f after the rise of the long period of the pulse width of the load current -, and the thyristor is kept in good condition x*rsf:
(by conducting alternately), a plurality of short pulses are formed before and after a long pulse width period. The shaded areas in Figure 3 are each thyristor! l~!・indicates that it is in a conductive state. A similar operation is performed for the load current 1b,i. Thus the load current ia
1c has a waveform as shown in FIG. 4, and is not just a single rectangular wave, but is also close to a sine wave.

On the other hand, in the current-type three-phase inverter I, a vector control method has also been proposed in which the phases of the load currents 1a to 1c are controlled to obtain good coordination.

This is as follows. Figure 5(a), h>),
(c) shows the magnetic flux φ of the three-phase induction motor 3 and the load current construction L (
The load current 1a, ib#i. These are collectively referred to as (hereinafter referred to as). Of these, Fig. 5 (6) shows the magnetic flux Φ (
(See FIG. 5(a)). That is, the phase difference Φ0 of the magnetic flux when the load current is small is different from the phase difference φN of the magnetic flux Φ when the load current IL is large, and the relationship is ΦN>Φ0. If the set speed of the induction motor 3 is changed in that ζ,
For example, when the load current IL increases,
5(c) is changed to maintain the phase relationship shown in FIG. 5(c), but there is a problem in that the response characteristics in this case are poor.

This is because the change in load power construction from the state shown in FIG. 5 (lagoon) to the state shown in FIG. 5(a)K is gradual.

Therefore, in the vector control, the load current IL is adjusted as shown in Fig. 5 (b).
IK: The state shown is forcibly changed to the state shown in FIG. 5(a). The slippage is achieved by appropriately triggering thyristor states 1 to 3 of the current type three-phase inverter 1, ignoring the normal order.

However, an appropriate control method that combines the two methods on paper has not yet been proposed. This is because if there is a sudden change in load power construction, the conduction thyristor of the current-type three-phase inverter 1 must be changed and the current vector must be controlled to the optimal position, making control extremely complex. . For example, as shown in Fig. 5 m) and (c) K, for example, the load current IL is changed to 6 at the change point C shown by the two-dot chain line.
) is changed to the state shown in FIG. 5(c)K, and each shaded area is the commutation period T.
For example, in the case of the load current i & (see Figs. 1 and 4) in the state shown in Fig. 5 (6))), the thyristor T of the current type three-phase inverter 1 is conductive and On the middle side, either the thyristor 1 or the thyristor Ts is electrically conductive (see FIG. 3). Figure 5 (a)
), the thyristor T1 is made conductive on the welfare+ side and the thyristor T! is made conductive on the one side at the convenience time 0. Or one of the thyristors 〒4 must be made conductive C&! (See Figure 3). It is necessary to appropriately select the thyristors T1 to T to be made conductive in this manner so that the phase of the load current is optimized.

In view of the current situation, it is an object of the present invention to provide a control circuit for a current-type three-phase inverter that has both the advantages of the PWM control method and the vector control method, is economical, and has high performance. The present invention, which achieves the above object, is based on the following principle as its technical idea. Said Figure 5 et al.) ~ 5th
The description of the mode of change in the commutation period T based on FIG.

Figures 6(c) to 6() list all of these combinations.
j). That is, FIG. 6(6) is the current waveform of the load power application, and this changes to any one of FIG. 6(c) to FIG. 6(theta)). For this explanation, as shown in Fig. 186 (a), the commutation period T after the middle side of one load current (indicated by diagonal lines in the figure; the same applies hereinafter) is in the state of ■, and this commutation period T The state of the commutation period T'fr ■ before the load is applied to one side, the steady state period of one side following this, the commutation period after this one side. The state of t-■, the commutation period before the middle side that follows this, the state of ■, the period of the steady state of the middle side that follows this, the state of ■, which commutation period te and the period of the steady state. is also 6C. If we take the load current 1a as an example and refer to the aFI4t-th- to correspond to the conduction of Tillistaf 1 to T-, Table 1 is obtained.

Table 1 On the other hand, Figure 6 (a) and 6
When the state IIK changes as shown in FIG. Similarly, if we divide the change state into cases, when the state IIK shown in Figure 6 (top) and Figure 6) changes, the state IIK changes, and the state IIK changes as shown in Figure 6 (sha) and Figure 6). At times, the state is 0, when it changes to the state shown in Wg6&[mK, it changes to the state shown in ■, and when it changes to the state shown in Fig. 6k)K, it changes to the state shown in ■. A quantitative analysis of this results in the following. Now Figure 6-G16
As shown in Figure θ), - = the phase difference at the time of change ci from the beginning of the state of ■ of the current load current IL; Assuming the phase difference in the load current ILIC until the end of the state of ■, when 0°<(err-II)<61', if the state of When the state changes to ■, 6d'<(αT-#)<
When 121' changes to the state of ■, -12σ<
(-〒-#) □When the state changes to the state shown in Figure 6&)K (changes to the state shown in ■) and when it changes to the state shown in Figure 6 (j) 1DK change)#
iIt can be ignored for practical purposes. This is because when the conditions shown in ■ and ■ occur, the change in load power construction is very steep, and it can be assumed that such a steep change does not actually occur. . Therefore, Table 2 is created by putting these together.

Table 2 Thus, nine operations are determined depending on the state change of the load current In, but if we examine the more specific commutation process of the thyristor states 1 to te a, we will find the following. Load current after change 11. Conduction thyristor in 〒1～!・ is the phase difference between the predetermined PWM pattern and the start of the state to which the change point a belongs in the load current IL after Km conversion to the change point C as shown in FIGS. 6(c) to 6(j) lc. It is determined from .

For example, if we consider the case where the load current changes from the state shown in Figure 7 (-) to the state shown in Figure 7 (6) K, in this case the state of ■ is maintained, so there are 8 modes. but,
In the case of the thyristor T1~〒, which should be made conductive (Fig. 7, etc.), the thyristor TI in the case of AL changes from snow to thyristor risk, so the thyristor TI glass is immediately changed to It is necessary to perform commutation R and set the time in the next commutation type to -.This is done by calculating time #N and making it correspond to the PWM pattern.
It will be decided. Therefore, Table 3 summarizes the calculation formula for time for each mode.

Similar consideration to Table I3, that is, the combination of the load current installation state after the change with respect to the actual state of the load current II at change time 0 is summarized, and the mode of commutation correction at that time is summarized as follows.
Tables 4 to 6 summarize the changes from the state for each mode. 〇Table 4 Table 5 Table 6 Table 6 Note that #! In Tables 4 to 6, current conducting thyristor and #
Cyrisk Tl that is actually conducting at the time of i-sensei C.”
'rs, new conduction thyristor is load current IL after change
The thyristor that should be made conductive in order to create an OK state at the time of change of -〒, ~〒@, What is normal rotation in commutation correction? 8→! −→
Shifting to T1, and the conduction thyristor on the negative side! It is said that the order of transition is Spirit -> Te4 -> T6 -> 〒Feng, and "reversal" refers to the case that the above order is reversed.

Therefore, according to the magnitude relationship of a-1, j” e 8 #
Select one of the modes in B, and then select each mode.

Since the new conduction thyristor with respect to the current conduction thyristor in 8.8 is determined by the phase difference -, if the conduction pipes of the thyristors T1 to - are controlled accordingly, even during the commutation period T of load current construction. It is possible to forcibly change the phase to the changed phase.

A solid line example of the present invention based on this knowledge will be described in detail with reference to the drawings. As shown in Fig. 8, one example is a current type three-phase inverter (see Fig. 1).
The load current xL is calculated by inputting the excitation current IL and the excitation electric current into the load current calculation section 13, and the load current xL is further inputted into the phase difference detection section . The phase difference φ between the two is determined and sent to the town calculation section 15 and stored in the phase difference storage section 16. That is, when there is a command to change the load current applied to the three-phase induction motor 3 (see Figure 1) KFi, the phase difference mT between the current load current and the changed load current I is the magnetic flux. α in the calculation unit 15 through Φ! tL (ms) (see Figure 1 to tlXs (a)). On the other hand, the phase difference - is stored in the l storage section 17, and its output is (sd -').
It is sent to the calculation unit 18.

(αT-#) The arithmetic unit 18 also receives the nine phase difference aT calculated by the signal arithmetic unit 16.
By calculating the value of T#) and sending it to the mode determination section 19, the mode M can be determined depending on its magnitude relationship with respect to the commutation period TK.
, 8. It is determined which one of B. Here mode M,
8. B is identified/identified. On the other hand, aN calculation unit 20 (#T-#) calculation unit 18
The phase difference fit- is calculated based on the output signal of and sent to the PWM/:turn storage section 21. By this ζ'', the phase difference between the state start t] to which the change point 0 of the load current IL after change belongs and the change point Of is stored.The PWM pattern storage section 21 generates the load current II. A pattern is stored, which is converted into a time interval in the time!converter 22, and becomes the clock pulse OLK of the ring counter 23.The ring counter 23 uses its output signal to convert the current m.
Thyristors L to T of the three-phase inverter 1 are triggered as appropriate. At this time, the ring counter 23ti has a forward/reverse rotation terminal Form, and the input thereto causes, for example, a forward commutation from thyristor 1 to thyristor 7g and a reverse commutation from thyristor ts to thyristor TI. Flow is selected. The output of the PWM pattern storage section 21 is also input to the forward/reverse rotation terminal FOrH during the commutation period of the load current II! By alternately selecting normal rotation and reverse rotation, for example, thyristor Tl5Ts is alternately turned on. The commutation correction storage unit 24 stores each mode M, B,! Commutation correction information W shown in Tables 4 to 5 corresponding to I is stored. At the same time, the commutation correction storage section 24 stores the Kll conduction thyristor state based on the contents of the FWM pattern storage section 21.
The contents of the current conduction thyristor storage section 25 and the contents of the PWM pattern storage section 21 which store .

Thus, the mode determination unit 19 determines that the mode is 9, 8.
．． The commutation correction command corresponding to BK, that is, the number of commutations and either forward rotation or reverse rotation, is formed based on the contents of the current conduction thyristor storage section 25 and the PWM pattern storage section 21, and the ring counter 23 outputs the forward and backward pulses OLK and forward rotation. - Sent as a reverse selection pulse.

As specifically explained above in conjunction with the embodiments, according to the present invention, even during the commutation period of the load current, the load current can be forcibly shifted to the changed load current. This has the effect of having a small amount of noise, the features of vector control, and the effect of having good series response.

[Brief explanation of the drawing]

Figure 1 is a block diagram showing a current-type three-phase inverter together with its conventional control circuit and three-phase induction motor;
Figure 2 is a waveform diagram of the load current that is the output, Figure 3 is Fi
Ninth explanatory diagram explaining the conduction state 1M of the thyristor in PWM control method 2, Figure 4 is a waveform diagram showing the waveform of the load current corresponding to this, Figure 5 (a) is a waveform diagram showing the magnetic flux,
Figures 5(b) and 5(c) are waveform diagrams showing the load current corresponding to the fin, Figure 6-)/d is a state diagram showing the state of the load current, and Figure 6(6) is the current state. Waveform diagram showing load current,
Figure 6 (C) to Figure 6 (j) Waveform diagrams showing the load current after it change, Figure 7 Rime and Figure 7 6) show the state of the load current at the current moment and after the change. Waveform diagram, No. 8
The figure is a block diagram showing an embodiment of the present invention. In the figure, 1#i current type three-phase inverter, 3 is induction motor, machine is load current, ``?e''# is phase difference, T is commutation period, 0 is change time, Tlers # Tm s 74 aT number e Tm
is a thyristor. Patent Applicant Meidensha Co., Ltd. Attorney Mitsuishi Shibu (1 other person) Figure 1 Figure 2 c Figure 5 Figure 6

Claims (1)

[Claims] Another condition is a steady period having a short duration or b complex for a predetermined period from the beginning of the positive side of the load current for a three-phase induction motor, and then the above-mentioned for a predetermined period until the end of the positive side of the load current. A current-type three-phase inverter that flows a PWM-controlled load current that has another state that is a commutation period with a plurality of similar pulses, and has six types of states with a similar waveform on the negative side. In the control circuit,
The phase difference between the current load current and the load current to be changed according to the fluctuation command is detected, and the phase difference between the current load current and the load current to be changed according to the fluctuation command is detected, and this is used to determine the beginning of the state with the current load current to which the change point in time when the load current should be changed according to the fluctuation command belongs. While calculating the phase difference from the beginning of the certain state of the load current after the change to the end of the same state, the change is calculated from the beginning of the certain state of the current load current to which the slippage and the time of the change belong. The phase difference up to the point in time is compared with beginning of tb
A control circuit for a current type three-phase inverter, characterized in that a thyristor to be rendered conductive is selected based on a phase difference My flc from to a time point of change.