JPH0322889A - Inverter control system - Google Patents

Abstract

PURPOSE:To apply a correct periodic voltage vector to an induction motor by executing a simple logical operation with the current direction and switching direction examined, and by adding it to the time TPS of a switching signal as a correction term. CONSTITUTION:As an additional function a short-circuit prevention period correction section 19 of a switching period and a counter value 16' are provided to a CPU. The switching signal command in the transistor short-circuit prevention period of an inverter is determined in accordance with the switching condition immediately before the command and the polarity of motor current, while the time width TPS of the voltage vector is to be corrected by the transistor short-circuit prevention period of the inverter in compliance with this switching signal command. The error of voltage applied to a three-phase induc-motor(IM) 3 resulting from the short-circuit prevention period can thereby be eliminated and the torque pulsation and torque error reduced.

Description

Detailed Description of the Invention (Industrial Field of Application) The present invention provides a three-phase induction motor (3-phase induction motor) with a PWM inherter that is controlled digitally at high speed by the instantaneous space hector method using a microcomputer (hereinafter abbreviated as CPU). This relates to a second method for controlling the magnetic flux and torque of (hereinafter abbreviated as "group").

(Prior technology) In recent years, inverter control has been common as a control method for +M, but instantaneous space hector control has been attracting attention due to problems such as noise and transient response. It was also published in the paper ``Torque control method based on secondary magnetic flux control of induction motors and its characteristics'' published on pages 361-364 of the Proceedings of the 1986 National Conference of the Industrial Application Division of the Institute of Electrical Engineers of Japan, published by ing.

FIG. 2 is a block diagram of an example of an IM control system using the instantaneous space vector method, and the control system of instantaneous space vector control according to the prior art will be explained using this diagram.

A voltage supplied from a DC voltage source 1 having a value of Vdc is connected to the IM 3 via a three-phase inverter section (hereinafter abbreviated as INV) 2 made up of six generally known transistors. .

The CPU calculation unit 6 receives the current signal of the IM3 detected by the direct current transformer (hereinafter abbreviated as DCCT) 7, the output signal of the PG4 that generates a pulse with a frequency proportional to the rotational speed of the IM3, and an external signal. A torque command τ3 is inputted thereto, and a base signal calculated from these by a method described later is output to the base circuit 5.

The base circuit 5 turns on/off each transistor of the INV 2 in response to a base signal manually inputted from the CP[I calculation section 6, so that the I? Drive I3.

Furthermore, I? which is the output of DCCT 7? The current signal of 13 is
It is converted into a space vector value i by a conversion calculator (not shown).

Next, a calculation block diagram of the CPU calculation unit 6 is shown in FIG. 3 and will be described in more detail. In the figure, DCCT 7 and PG4 are shown in Figure 2, and are shown as (n-1) . (n) and (n+1) indicate the values at the (n-1)th and nth sampling times and the values at the (n+1)th sampling times in each sampling period T.

At the (n-1)th sampling time TSfn-1), the current i-,, of I)13 is read, and the instantaneous magnetic flux φ(,,-11) at that time is calculated by the magnetic flux calculation unit 8.
Calculate by Instantaneous magnetic flux φ. -1. Of course, space vector?
Le {direct.

Furthermore, the rotor position θlIfM-11 of the IM3 at this time is detected by the rotor position detection unit 9 using a pulse sent from the PG4, while the torque command τ input from the outside is detected by the rotor position detection unit 9.
0, the slip frequency command ωS'' (fi-11) obtained in the slip frequency calculation unit 10 is input to the magnetic flux command calculation unit 11, and the sampling time T, <.2 sampling cycles t! n+1)
Second sampling time Tsf. Calculate the magnetic flux command value φ1(,,.,,,, at Il1. Furthermore, the current command value 1'" at this sampling time Tsfn+l+.
, is calculated by the current command calculation 12 using this magnetic flux command value φ (nu).

Also, the integral value Δλ of the output voltage vector from sampling time Ts+n-+1 to 1゛■1. In order to correct the switching signal outputted by the counter valve 16, the period T2 during which it is outputted, and the transistor short-circuit prevention period T4, voltage vector integral calculation is performed from the current status code ■, which is the output of the current direction determination unit 18. The calculation is performed by the unit 17.

Command value φ (null and current j (R-11 + current command {ii!! 1 ”
,. ．． ,i,,,. 11””i1. A value Δλ, which is the electric sweat vector to be output at sampling time T1 multiplied by the sampling period T, is calculated so that I.

In the hector selection unit l4, the hector calculation unit 13 calculates ? Select the switching signal S■1 corresponding to the voltage vector V(r+1) whose direction is almost the same as the Δλ axis from among the output voltage vectors ■1 to ■6, and select the switching signal S■1 corresponding to the voltage vector The switching signal S1 corresponding to the zero voltage vector with the smaller number of transistors is filtered by iI, and the switching signal Sol(
. > is output to the counter valve l6. Here, the subscript X of the switching signal SX (Ill and S Xf.,l is!
Assume that the phases u, v, and w of NV 2 are respectively applied, and SX(nl and Sx(n+1) are 1 if the positive transistor of the phase is on and the negative transistor is off. Conversely, when the transistor on the positive side is off, it is 9, and when the transistor on the polar side is on, it is 0.
It shall be expressed as Incidentally, the symbol 1 in parentheses not only distinguishes whether the vector is a valid voltage vector or a zero voltage vector, but also indicates which sampling point it is by adding or subtracting the number.

In the switching period calculation section 15, the vector selection section 14
The period Tp during which INν2 outputs the voltage vector selected by
T-1Δs) i/V...
... Calculate from ■ and output to the force/5-input valve 16. Here, ■ is the absolute value of the voltage vectors ■1 to ■. In addition, in the case of T,>T, T. =T.

The counter valve 16 outputs the switching signal SxLM1 corresponding to the voltage hector selected by the hector selection unit 14 to the transistor base circuit 5 for a period Tp, and then outputs the switching signal SxLM1 corresponding to the voltage hector selected by the hector selection unit 14 to the base circuit 5 of the transistor for the remaining period (T-Tp). A switching signal S x (m) is output to the base circuit 5.

In this way, at every predetermined sampling period T, the instantaneous magnetic flux φ
The magnetic flux command φ1 after two sampling periods is calculated according to the torque command τffi-11. ,,φ. ．． Find the voltage vector Δλ (71/T) such that the value coincides with the magnetic flux command value φ" axis. Then, find the output voltage hector V1 to V6 of INν2 shown in Fig. 4 in the direction close to it. Select one and output it from iNV 2 for a period corresponding to Δλ, .}.
It controls 3.

(Problem to be solved by the invention) Magnetic flux command value φ where instantaneous magnetic flux φ is Ll5 to torque command τ2
3 without delay, find the value Δλ which is the voltage hector to be output multiplied by the sampling frequency NJJT, then find the voltage vector to be output and its period Tp, and set the counter valve 16. is the switching signal S1 corresponding to the voltage hector (,,) for the period Tp. , is output.

However, the transistor of INT2 has a short-circuit prevention period Td, and the period during which the voltage H is actually output to the I gate 3 may be different from T9. Furthermore, the zero voltage vector V0-. The voltage vector ■. 1, the normal voltage vector ■ or the previous voltage vector V for the shortening prevention period T. -1, different voltage vector 1
−L may be applied to +M3. Therefore, an incorrect voltage vector is applied to the bolt 3, and the instantaneous magnetic east φ does not follow the {R flux command value φ'', causing torque pulsation.

The present invention has been made to solve the above-mentioned problems.

(Means for solving the problem) The above-mentioned drawback is that the 11J1 outputting the voltage vector V(n+
Sinch due to short-circuit prevention period T in calculation of interval Tp? This is due to the fact that the delay in the switching is not taken into account, and that a voltage vector that should not be applied during the short-circuit prevention period T is applied to IM3.

FIG. 5 shows a circuit diagram for one phase of INν2, in which two transistors are connected between one terminal and one terminal of DC voltage source 1: transistor Tr1 on the positive side and transistor Trz on the negative side. are connected in series and configured to supply the current mi of this phase from the connection point e between them to lM3,
Each l transistor T, l and T. diodes D1 and D2 are connected in antiparallel to each other. In the figure, the direction of the arrow, that is, the direction from the connection point e toward IM3, is the positive direction of the current i.

When transistor T■ is turned off from a state where transistors T and ■ are on and transistor Tri is off (S■,, +-1), when current i>0 (represented by state code 1.=1), current i becomes Since the current flows through the diode D2, the potential at the connection point e immediately becomes the potential at one terminal.

However, when the current i<O (represented by the status code +.=0), the transistor T. Even if it turns off, is the current j still da? Ode D
．． Flow. Therefore, the potential at the connection point e remains the same as the potential at one terminal, and the transistor T is delayed by the short-circuit prevention period T.
, ■ are turned on, the potential of the connection point e becomes the potential of one terminal for the first time.

This is the switching delay due to the short-circuit prevention period T, and depends on the state of the transistor 1r1, that is, the state of the switching signal SX (nl or S1), and the direction of the current i, that is, the state code!.

Note that the subscript X of these symbols is 1); as described in j, IN
Each phase u, v, w of V 2 is fitted.

FIG. 6 shows sampling time T=t. 〉 and T g(
n. ,), the output switching signal of the counter valve 16 according to the conventional inverter control system and the corresponding output voltage vector of INV 2, and the output switching signal of the counter valve 16 according to the inverter control system of the present invention and its corresponding INI/ 2 output voltage vectors.

In the conventional imperter control system, the output switching signal of the count valve is changed from Sffi-1, to SX(I1+,
Also, when changing from S x (nl to S■1, INV
Due to the effect of the short-circuit prevention period Td mentioned above, the output of 2 is any voltage vector V'[h] during the short-circuit prevention period T4.
and V'(m), and the voltage vectors are not necessarily around them. Also, the normal voltage vector Vl++
) is outputted may also be shorter or longer than the predetermined period Tp.

However, in the inverter control method of the present invention, the sampling time Tl (switching signal S x'lfi according to the switching state immediately before n+ and the polarity of the motor current) is calculated by the method described later, and then the short circuit prevention is performed. By outputting from the counter valve during the period Td, the output voltage vector of INV 2 during this period can be set to either the voltage vector V+m-11 or VD+l before and after the period Td. When the output of INV2 changes from the voltage vector V'' to the zero voltage vector V Cm+, the number of transistors that change is only for one phase, U phase, ■ phase, or W phase, so the short circuit prevention period Td at this time is Since the output voltage vector of INV 2 is always either V(1 or v《1), a special switching signal S 11
'+III) is not required.

In addition, in the inverter control method of the present invention, the time width in which the counter valve outputs the normal switching signal SX (,,,, Corrected to width TPS, IN
V2 outputs the voltage vector V(+[.

Hereinafter, the method for selecting the output switching signal S x'(r+1) of the counter valve in the inverter control system according to the present invention and the corresponding normal switching signal S
A method for determining the output time width TPS of Fl) will be explained.

As mentioned above <I. is the state code of the current direction during switching, and the switching signal is SX (+++-11 to S
x (.), the signal AX(n) that determines whether the switching is delayed by the short-circuit prevention period T for each phase is expressed as A x (n+ = T x - d x C + e - 11
S x (?ll+T.・SX(re-1)・2S-8
Kui...■? It can be determined using a logical formula.

Here, ゜′・゜゛ means logical product, ゜゜+'' means logical sum, and ``1'' means negation. Also, A X (PI>=
1 means that the switching of the X phase is delayed by the short circuit prevention period Td, and when AXL■r=O, it means that the X phase operates as instructed without delay.

From each phase of this A■1, short circuit prevention period action state B (I
l+Bin)=Aufnl+AvCn)+Aw+n+”
...Determined by the logical formula of ``■.

B (+ul = O means that there is no effect of the short circuit prevention period T, and S X'+Ill = S x (++1T p s'
- T p T a ......■ ......■ V (+*-11 to voltage vector ■., output voltage vector V of INV2 during short circuit prevention period Td
'+l is V,. , becomes. Here, T and 3' are provisional values for determining the time width TPS for outputting the final switching signal S(I+1).

What if B (,1) = 1 in 2■? X'CFll = S X is-+)・S x
(PI) + IX・ (S■#- 11 + S X [
+11)...■TPs = Tp
・・・・・・■■、-． By replacing n with m and replacing -1 with n, the switching signal changes from Sx+n) to Sx(++
When changing to +1, short circuit prevention period operation state B (1111
In the case of B (-) = O, there is no influence of the short-circuit prevention period T, -, and the previous temporary value T
The time width TP3 for outputting the switching signal S from P; is TPS-TP3...■, and when B i+nl = 1, the short-circuit prevention period T
Since there is an influence of d, Tps-Trs Td ”...■ The above is summarized in Table 1 below.

(Function) As in the past, although there is actually a short-circuit prevention period T4 in the transistor drive of INV 2, if this is ignored and a switching signal directly corresponding to the voltage vector command is output, , when two or more phase transistors are switched, the switching may or may not be delayed during the short-circuit prevention period T4, and during the short-circuit prevention period Td, a voltage vector other than the predetermined voltage vector is output from INV2. There were times when the IM3 was set to 0.

In addition, when the switching signal corresponding to the calculated voltage vector is directly output to INν2 as per the calculated period T, INV 2 outputs the predetermined voltage vector to the short circuit prevention period Td during the predetermined period T. Therefore, an appropriate voltage vector cannot be applied to the IM3 for an appropriate amount of time. Therefore, the instantaneous magnetic flux command value φ
“The instantaneous magnetic flux φ has a large error with respect to
This caused torque pulsation and torque errors.

According to the inverter control method of the present invention, only when a delay in switching occurs due to the short-circuit prevention period T as described above, a special switching signal SX is generated during the short-circuit prevention period T.
', so that the previous voltage vector is always applied to IM3 during the short-circuit prevention period, and a new time is set so that the predetermined voltage vector is always applied to IM3 during the calculated period Tp. By calculating the width T6 and outputting a predetermined switching signal, the short circuit prevention period T
The error in the voltage applied to the IM3 due to d is eliminated, and torque pulsation and torque error can be reduced.

(Embodiment) FIG. 1 is a calculation block diagram of a CPυ calculation unit according to an embodiment of the present invention. The difference from FIG. 3 is that block 16 is 16'
, new functions have been added, and new 1 and 2 blocks i. 9. 20 is only added to 4', so a description of the same parts as in FIG. 3 will be omitted, and only the additional functions will be described.

The added block 19 is a short-circuit prevention period correction section for the switching period, which inputs the switching period T from the switching period calculation section 15 and generates a switching signal Sx corresponding to the voltage vector input from the vector selection section 14.
(From r+1 and the state code of the current input from the current direction determination unit 18, use the logical formulas ■ and ■ to determine the short-circuit prevention period action states B, and B, and refer to Table 1 to determine the short-circuit prevention period. Switching time width T p s corrected for the influence of
is output to the counter valve 16'.

The block 20 is a switching signal calculation unit during the short circuit prevention period, and the block 20 is a switching signal calculation unit for the short-circuit prevention period. From the switching signal S fi corresponding to the vector and the state code IX of the current input from the current direction determining unit l8, the short-circuit prevention interoperability state B (7) is determined by the logical formulas ■ and ■, and Table 1 is obtained. Refer to the switching signal S i' during the short circuit prevention period.
．． Calculate n by formula (■) as necessary, and calculate counter valve 1.
Output to 6'.

The counter valve 16' receives a switching signal 38'. . After outputting the switching signal Sx (n+) for the short-circuit prevention period T4, the switching signal Sx (n+) inputted from the vector selection unit 14 by the time width T, , which is inputted from the block 19, and then manually outputted from the vector selection unit 14. A switching signal S■.〉 corresponding to the zero voltage vector is output.

(Effects of the Invention) As explained in detail above, conventionally, the switching signal corresponding to the calculated IT pressure vector V(n+ is directly converted to IfJV 2 for the calculated switching period Tp)
Since the transistor of IN'll 2 actually has a short-circuit prevention period T4, the time width of the output voltage vector of INV 2 is calculated during the predetermined period Tp.
In addition, during the short circuit prevention period Td, the calculated predetermined voltage vector Vtn+
In some cases, INV 2 outputs a different voltage hector.

According to the inverter control method according to the present invention, by checking the current direction and the switching direction and performing a simple logical operation, it is possible to determine whether the short circuit prevention period shortens or lengthens the time width of the voltage vector. By using this as a correction term at time TP3 of the switching signal, it is possible to apply a voltage hector to IM3 for an accurate period.

In addition, a special switching signal S is provided during the short circuit prevention period T.
By newly providing x'fr+1, if there is a delay in switching due to the short-circuit prevention period, INV 2 can output the voltage hector before switching or zero voltage hector, and the predetermined voltage vector or zero voltage vector No other voltage hector is output.

In this way, torque pulsations and torque errors can be reduced.

[Brief explanation of the drawing]

FIG. 1 is a calculation block diagram of a CPU calculation unit according to an embodiment of the present invention, FIG. 2 is a block diagram of an example of an IP control system using the instantaneous space hector method, and FIG. FIG. 4 is a vector diagram showing the drop pressure vector l·le that can be output from the inharter, FIG. 5 is a circuit diagram for l phase of the inharter, and FIG. The figure is a diagram comparing the state of the output switching signal of the counter valve and the voltage vector actually output by the inverter before and after the sampling time for the conventional method and the inharter control method according to the present invention. 1... DC voltage source 2... 3-phase inverter section (INV) 3... 3-phase induction motor (old 4... Pulse generator (PG)) 5... Base circuit 7... DC Current transformer (DCCT) 9... Rotor position detection unit 11... Magnetic flux command calculation unit 13... Hector calculation unit 6... CPU calculation unit 8... Magnetic flux calculation unit IO... Slip frequency calculation Part l2...Current command calculation unit 14...Hector selection unit 15...Switching period calculation unit 16. 16'...Counter valve 17...Voltage Hector integral calculation unit 18...Current direction determination Part l9...Short circuit prevention period correction unit 20...Switching signal calculation unit 3rd for short circuit prevention period
Figure 6

Claims (1)

[Claims] 1. The on/off pattern of each transistor that makes up the 3-phase PWM inverter is determined by arithmetic processing by a microcomputer at each fixed sampling period, and the necessary voltage vector is supplied to the 3-phase induction motor for the required time width. , by rotating the magnetic flux generated inside the electric motor.
In the inverter control method for operating a phase induction motor,
A switching signal command for the inverter transistor short-circuit prevention period is determined according to the previous switching state and the polarity of the motor current, and the time width of the voltage vector is corrected by the inverter transistor short-circuit prevention period according to the switching signal command. An inverter control method characterized by: